CA1136733A - Computor-controlled oil drilling rig having drawworks motor and brake control arrangement - Google Patents

Abstract

COMPUTER-CONTROLLED OIL DRILLING RIG
HAVING DRAWWORKS MOTOR AND BRAKE CONTROL ARRANGEMENT

ABSTRACT OF THE INVENTION

An oil drilling rig includes a racker, a power tongs, a drawworks having a motor and a brake, and a general purpose programmable digital computer associated with each to sequentially initiate the operation thereof.
Closed-loop control systems for the drawworks motor and drawworks brake are included to provide control signals to a motor drive and to a brake actuator.

Description

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COMP~TER-CONTROLLED OIL DRILLING P~IG
HAVING DRAWWORKS MOTOR AND BRAKE COI~TROL ~RR~NGF,MI:Nl' B~CKGROUND OF THE INV~N'r ON

Field of the Invent on This invention relates to a computer-control]ed oil drilling rig, or derrick.

Description of the Prior Ar_ The physical structures utilized in the generation of a hydrocarbon producing well are known in the art. For example, drawworks have been long u-tilized in oil drilling rigs, or derricks, to raise or lower pipe stands and drill string into and out of the bore. Tongs are well known for making and breaking joints between pipe stands and the drill string. United States Patent 3,881,375, issued to Robert R.
Kelly and assigned to the assignee of the present invention, generally relates to a tongs. Racker arrangements for moving pipe stands from a storage location on a "set back"
to an operating location within the derrick are also well-known. United States Patent 3,501,017, issued to Noal E.
Johnson et al. and United States Patent 3,561,811, issued to John W. Turner, Jr., both relate generally to well pipe rackers and are both assigned to the assignee of the present invention.
Usually, each of the broad ~unctions pereormed by the mentioned structural systems requires the sup~rintendence of many skilled derrick op~rators. Further, the work is often inefficiently performed, adding to the overall cost of the well. Yet further, even if the work is periodically efficient, it is difficult to maintain peak operating levels whereby each operation of the assoclated structures mesh so ~13~33 as to maintain the task of making-up or breaking-out a (~rill string at a minimum from a time stan~point consistent with safety of the personnel and the bore.
It is therefore advantageous to provide each of those structural systems with an appropriate electronic control system and to utilize a proyrammed yeneral purpose digital computer to superintend and sequence the proper operation of the physical structures to most efficiently control derrick operations. It is appreciated that the elimination of manual control increases the efficiency and lowers the cost of well drilling operations.
By way of particular examples, in the prior art, the lifting or hoisting of the -travelling block and elevator is done by the manual control of the electric motor drive on the derrick. The lowering motion of the travelling block is normally manually controlled by a drum brake. The lowering motion of a loaded travelling block (having a drill string thereon) is done by the manual control of the drum brake and using an au~iliary brake which absorbs the potential energy of the string during lowering. The manual control of these functions may be inefficient during foul weather or other-wise detrimental environments. It would be advantageous to provide an electronic control system in cooperative association with a programmed digital computer to control the lifting and lowering c~cles, and specific~ the velocity and position of the travelling hlock and elevatox.
The loading on the traveJ.ling block and elevator, and specifically the increaC;e :in block loading when in the break-out cycle occasioned by friction in the bor~ as well as the decrease in block loadiny in the make up cycle occasioned by an obstruction in the bore, pr~sent problems in the manual control of the derrick. It is therefore advantag~ous to ~~

provide an electronic load sensing arrangement to provide inputs to an electronic dra~Jworks control to adjust the velocity and position of -the travelling block in response thereto and to recognize potential dangerous loading con-ditions on the block.
The tongs are, as is known in the art, a hydrauli-cally powered arrangement capable of making and break:ing joints in a drill string. It is advantageous to provide an electronic network controlling the operations of the tongs, and to interconnect that control ne-twork with a programmed general purpose digital computer so as to repeatedly and efficiently operate the tongsto perform its function. Of course, since various of the physical structures discussed are actuated by hydraulic or pneumatic operators, suitable electro-hydraulic or electro-pneumatic interfaces must be provided. It is also advantageous to provide a sensor arrangement to locate the backup and power driven tong in vertical symmetry with respect to a horizontal plane passing through the tool joint.

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SUMMARY OF TIIE INVENTION
___ _ This invention relates to an oil drilling rig including a racker means for carrying a pipe stand between a storage locatlon and the vertical axis of the rig, tongs to make or break the joints between the pipe stand and a drill string, and a drawworks, including a motor and a brake, for liftiny and lowering a predetermined length of drill string after a joint is made or broken by the tongs.
A general purpose programmable digital computer is as-sociated with each of the racker, tongs and drawworks forsequentially initiating the operation of each. Closed-loop control systems provide control signals for the draw-works motor and brake.
~ ore particularly in one broad aspect, the invention comprehends a closed-loop control system for controlling a drawworks mechanism for moving a predetermined length of drill string to a predetermined position within an oil derrick at a predetexmined velocity. The system includes a block arrangement connected to the drawworks mechanism and adaptable to support the upper end of a drill string during lifting thereof, and means for outputting a position signal functionally related to the elevation of the block arrange-ment with respect to a vertical axis extending through the derrick. The system also includes means for outputting a velocity signal functiona:Lly related to the velocity of the block arrangement, and means for outputting a load ~ignal functionally related to the magnitllde by which the weight supported by the block arrangement deviates from a pr~-determined portion of the weight supported by thc block arrangement when it is in a substantially static condition.

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Means are provided for genera-ting an error si,gnal funtional-ly related to the clifference hetween the position siynal and a signal representative of the predetermined position to the difference between -the velocity signal and a siynal representative of the predetermi,ned velocity, and to the load signal. Means responsive to the error signal operate the mechanism in a manner so as to chanye the error signa:L
in a direction such as to reduce the block veloci,ty other- !
wise prevailing.
10Another aspect of the invention pertains to an oil drilling rig having a travelling block vertically upwardly and vertically downwardly movable and havi,ng transducer means for generating an electrical signal representative of the actual direction of motion of the travelling block and an electrical signal representative of the actual block velocity. The improvement comprises first means for comparing the signal representative of the actual velocity of the block with a signal representative of a predetermined maximum velocity and for outputting a first alarm signal indicative of the actual velocity being greater than the predetermined maximum velocity, and second means for com-paring the signal representative of the actual direction of motion of the block with a signal representative of a pre-determined direction of motion and for outputting a second alarm signal if the actual direction of the block, deviates from the predetermined d,irection, _ r~ _ 1~3tj733 BRIEF DF,SC~tIPTION OF '1'111~ D~W~MG~

The invention will be more fully understood from th~ following detailed description of a preferred embodiment thereof, taken in connection with the accompanyinCJ (Irawinys, which form a part of this application, and in which Figure 1 is a generalized block diagrarn illus-trating the interactions between derrick s-tructure and control systems therefor and a digital computer in accor-dance with the teachings of this invention;
Figure 2 is an illustration of the structural elements included on an oil derrick, drilling rig, or and the various structural systems disposed thereon;
: Figure 3 is a more detailed block diagram of the drawworks control system embodying the teachings of this invention;
Figure 4 is a simplified signal diagram illustrating the principles of operation of the motor and brake control subsystems of a drau~lorks control system embodying the teachings of this invention, appearing with Figure 1, Figures 5 and 6 are more detailed signal diagrams based upon the signal diagram of Figure 4 and specifically relating to a brake control subsystem and to a motor control subsystem, respectively, each embodying the teachings of this invention;
Figure 7 is a schematic diagram of the electronlc-to-pneumatic interface as.sociated wi-th the drawworks brake actuator;
Figures gA and 8B are d~tailed schernatic diagrams of the brake control subsy~tem shown in the block d:iacJram Figure 3;

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Figures 9A and 9~ are detailed schernatic diagrams of the motor control subsys-tem shown in the ~lock diagram Figure 3;
Figure 10 is a detailed schematic diayram of the velocity comparator shown in the block diayram Fi.cJure 3;
Figure 11 is a detailed schematic diagram of the travelling block position and speed transducer shown in the block diagram Figure 3;
Figures 12A and 12B are detailed schematic diagrams of the elevator load control subsystem shown in the block diagram Figure 3;
Figure 13 is a detailed schematic diagram of associated safety networks and override arrangements embodied by the invention;
Figure 14 is a highly stylized pictorial represen-tation, similar to Figure 2, of a power tong assembly illustrating conventional tong elements and elements associated therewith according to this invention;
Figure 14A is a detailed schematic diagram of an electro-hydraulic interface embodying the teachings of this invention and disposed in a power tong assembly in accordance with Figure 14;
Figure 15 is a block diagram similar to Figure 3 indicating the interconnection between a programmable general purpose digital computer and the tong control assembly according to this invent.ion;
Figure 16 is a detailed schematic diagrclm of an automatic tong control syst~m embodying the teachings of this invention, and is made up of E'igures 16~, 16B, 16C and 16D arranged as shown in a portion of F'iyure 16C;

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Figures 17~ and 17B are timirlg diagrams for the automatic tongs control system shown in Figure 16 in the make-up and break-out cycles, respectively;
Figures 18~ and 18B, are, respectively detalled elevational and top views of a joint sensor for a power tongs assembly in accordance with the teachings of this invention; and, Figure 19 is a definitional diac~ram of two commonly used drill pipe configurations illustrating the structures thereof to assist in the description of the joint sensor shown in Figures 18A and 18B, appearing with Figure 15.

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,, - ~3 -~3~33 ~ESCRIPTION OF PREFERRED EM~IMENT

Throughout the following description, simil~r reference characters and reference numerals refer to similar elements in all E'igures of the drawings.
Referring first to Figure 1, a c~eneralize~ block diagram of a computer controlled oil drilling rig, or derrick embodying the teachings of this invention is il-lustrated. Generally speaking, the derrick includes three broad structural systems each performing a particular set of functions relating to the drilling of an oil well, and a control system related to each structural system to control the physical actions performed thereby.
The derrick 20 (Figure 2) includes a drawworks structural system 22 having a drawworks control system 21 associated therewith. The drawworks systems generally pro-vide the hoisting (or lifting) and lowering functions associated with the generation of a well bore. Command signals output from the drawworks control system 21 are input to the structural system 22, as diagrammatically illustrated by a line 23, and initiate or cease the physical actions of elements within the structural system 22. Feed-back signals representative of various physical parameters associated with each of the structural elements within -the drawworks structural system 22 are input to the control system 21, as illustrated by a line 2~.
The derrick also includes a power tongs structural system 28 and a tong control s~stem 29 associated ~here-with. The tong systems generally provide the makc-up or break-out of individual pipe stands into or out o~ a drill string. Command signals initiatlng or ceasinc3 the physical 9 _ ~ , .

~3~733 actions of structural elemerlts of the tong~ structural system 28 are inpu-t thereto from the tongs control system as 29, as illustxatecl by a line 30. Eeedback signals represen-tative of varlous physical parameters associated with each of the structural elements within the tongs structural system 28 are input to the tongs control system 29 as illustrated by a line 31.
Also provided is a racker structural system 34 which, in general, provides the structure necessary for carrying individual pipe stands from a storage location to a location along the vertical axis of the derrick for make-up or from the location along the vertical axis of the derrick to the storage location during break~out. The storage location is known in the art as the "set back". A racker control system 35 is provided, with control signals being output therefrom to the structural system 34, as illus-trated by a llne 36. Feedback signals from the structural system 34 are input to the racker control system 35, as illustrated by a line 37. The racker structural system 34 ~ and control system 35 have been disclosed and claimed in the copending application of Loren B. Sheldon, James R. Tomashek, Robert R. Kelly, and James S. Thale, Cdn. Ser. No. 243,613, filed January 15, 1976, now Canadian Patent No. 1,069,493, granted January 8, 1980, and assigned to the assignee of the present invention.
A general purpose programmable digital computer 40 is interfaced with each of the above-mentioned control systems, as illustrated dlagrammatically by a line 4l (to the drawworks control systern 21), a line 42 (to the power tong control system 29) and a line 43 (to the racker control system 35). Each of the control systems feed hack various signals to the computer 40, as il]ustrated by the lines 44, 1~6t733 45, and 46, from the drawworks control systeln 21, tongs control system 29, and racker control system 35, respectivel~.
Further, the computer 40 receives direct data inpu-t of physical parameters, as illustrated as by a line 47.
The computer, in accordance with -the progral~ned instructions, sequenti.ally initiates the operations of various of the structural systems to perform various physical functions within the derrick. To economize operating time and maximize efficiency, control of -the systems may be on a time shared basis, as with control of the drawworks and racker systems. Any interactions between the systems, as between drawworks and ton.gs, are throuyh the computer 40. A
respective listing of the program for the digital computer 40 is appended to applicant's U.S. patent No. 4,128,888 granted December 5, 1978.

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ST RI~ICTU RE

Referrlng ~o Figure 2, shown is an i~lustration of the oil drilling rig, or derrick 20 incorporatinq ~he ~asic rig features and having thereon the structural elements which are included in the structural systems outllned in connec-tion with Figure l. These structural systems are in co-operative association with their associated control systems to initiate and cease the opera-tion of the physical functions performed by the structural systems. The derrick 20 is illustrated in simplified form, with various structural supports, sway bars, and other similar members being omitted for clarity.
The basic derrick structure 20 includes corner posts 51 and 52 extending substantially upwardly from suitable base members. The base members are supported on a drilling floor 53, the drilling floor 53 being mounted on the surface of the earth, on an off-shore drilling platform or on a drill ship. A rotary table is provided in the floor 53 of the derrick and provides the rotational energy whereby a drill string, comprised of end-to-end connected drill pipe stands, may be advanced toward a hydrocarbon producing formation.
Slips 55 are shown on the floor 53. When engaged, the slips 55 support the full weight of the drill string depending therebeneath. In E'igure 2, the upper end of the drill stringr or more precisely, the upp~r end of the uppermost pipe stand connected within the drilL string, is shown as ; protruding above the slips 55. E~lch wpper encl of the pipe stand has a distended joint 56 us~d in connection with the tong operation. The programmable general purpose digital computer 40 may be conveniently housed in a structure 57 on the floor 53.

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The axis of the hore being yenera-ted beneath the floor 53 of the derrick e~tends centrally and axially through the derrick. A racker structural system, generally ind,icated by the reference numeral 34, carries individual pipe stands between a storage location, or "set back", disposed at the side of the derrick and a location along the vertlcal axis thereof. It is along the vertical axis of the derrick 20 that the drill string is re-tracted from or lowered into the bore being generated. The racker structure 34 includes a lifting head 58, an upper arm 59 with a latch thereon, carriages 60 and 61 for the head 58 and for the arm 59, respectively, and a racker board 62 for receiving and sup-porting individual pipe stands. The racker structure and cbntrol systems has been disclosed and claimed in the above-referenced copending Canadian Serial ~lo. 243,613.
The corner posts 51 and 52 are interconnected with and supported by transverse supports at various elevations along the derrick 20. The derrick 20 is capped by a water table 65 which supports the usual crown block 66. Suspended from the crown block 66 by a cable arrangement 67, or reaving, are elements of the drawworks structural system, including a travelling block 68. The travelling block 68 supports a hook structure 70 by interengaged bales 71.
Elevator links 72 are suspended from ears 73 on the hook structure 70. The links 72 have an elevator 75 swingably attached at the lower ends thereof. The elcvator 75 is offset below the travelling block 68 by a predeterrnined - distance h. The elevator 75 inc'ludes a grippirlg arrange-ment to grasp or release the di~tended joints 56 of a pipe stand.
A block retractor arrangement 78 is connec,ted to the travelling block 68 and serves to retract the travelli,ng -block (with depending elevator 75) away from the vertical axis of the derrick along which it usually depends. The retractor 78 includes a carriage 7g which is rectilinearly moveable through a wheeled arrangement along a substan-tially vertically extending retractor guide track 80. A
block position and speed transducer (B.P.S.q'.) 83 is mounted on the retractor carriage 79 and produces output feedback signals representative of the actual physical position of the travelling block 68 along the track 80. These feedback signals, as will be seen, are provided both to the draw-works control system 21 (Figure l) and to the computer 40.
The block position transducer 83 also provides a feedback signal representative of the velocity at which the travel-ling block 68 is moving along the track 80. Of course, it may be readily appreciated that since the elevator 75 ls vertically offset by -the distance h from the travelling block 68, the position of the travelling block 68 along the track 80 also indicates the position of the elevator 75 with respect thereto, and vice versa. And, since the travelling block 68 and the elevator 75 are generally extended to move along the vertical axis of the derrick, the position (elevation), and velocity of the travelling block 68 with respect to the vertical a~is of the derrick 20 may be accurately monitored by the block position and speed trans-~` ducer 83. The structure and i.nternal circuitry o~ the b].ock position and speed tran~ducer 83 is ~c~t forth in full herein.
For a purpose more full~ d.isclosed hcrein, uppcr ancl lower limit switches 84 and 85 (Fig. 11) arc providcd on t:hc carriage 81. An upper target 86 and a lower target 87 are provided at predetermined .locations on the retractor guidetrack 80.

~1~ti733 As is the usu,~l practice in the art, the cable arrangement 67 whlch supports the travelling block 68 and structures (inc]uding the elevator 75) depending therefrom are reaved about the block 66. One end 88 of the cable arrangement 67, known as the "dead line" in the art, is anchored to the derrick 20 as illustrated at 89. The second end 90 of the cable arrangement 67, known as the "fast line"
is connected to other elements included i,n the dra~orks structural system. More particularly, the fast line 90 is attached to a spool or drum 91 o~ the drawworks. The arum 91 is driven by an electric motor 92 of any suitable type as diagrammatically illustrated in Figure 2. For e~ample, a motor manu,factured by the Electromotive Division ~f General Motors, sold under Model No. D79GB and rated at 800 horse-power for drilling is a typical motor for a drawworks structural system. Determination of a motor lies well within the skill of the art. The motor 92 is provided with a motor drive 93, such as a THYRIGTM manufactùred by Baylor Company, although any other motor drive arrangement may be used. The motor 92 may be wound in any predetermined con-figuration to meet the needs of a particular rig. It is noted, however, that the motor 92 imparts the energy whereby the travelling block 68 and the structures depending there- ~-from may be moved with respect to the ver-tical axis of the derrick 20 from a first predetermined to ~ second pre-determined elevation. Therefore, con~rol of the motor drive 93, and in turn, of the motor 92, effectively controls the velocity and acceleration of the travelling bLock 68 as it is lifted from a first to a second elevation. 'rhe drawworks include~ a suitable clutch and gear arrangement therein.

~ , ~31~t~33 A drum tachometer 94 is physicall~ located in ad-ja-cency to the spool 91. The output of the drum tachometer 94 is a feedback signal to the drawworks control system ~l representative of the velocity of the drwrl 91 which signal is directly proportional to the velocity of the travelling block 68 and depenciing structures. Within the dead line 88 i~ provided a transducer 95 known as the dcad line force sensor (D.L.F.S.). The transducer 95 provides a feedback signal to the drawworks control system 21 related to the physical loading of the structures supported by the cable arrangement 67. Of course, the cable arrangement 67 at a]l times supports the travelling block 68 and its depending structures. The unloaded, static weight of these structures defines a "tare" weight of the structure supported hy the cable arrangement 67. When the elevator 75 acquires a load, the D.L.F.S. 95 appropriately reacts. Similarly when the elevator load is properly relinquished, the sensor 95 responds accordingly. Yet further, during movement of a loaded travelling block 68, frictional or other forces may alter the load carried by the elevator 75. The D.L.E`.S. 95 therefore provides an accurate feedback signal as to the instantaneous loading on the elevator 75 of the drawworks structure. As is generally the case with the other trans-ducers, other convenient physical locations therefor may be used to measure the desired parameters. In addit:ion, any appropriate means for measuring the desircd parameters may also be utilized, as is appreciated by those skilled in the art.
Also included within the drawworks ~tructural system is a brake. The drawworks brake includes a prirnary brake the function of which is to control the velocity and de-celeration of the drawworks travellinc3 block (when unloadeci) ~ f, _ ."~

~13~'733 and to stop the motion thereof. ~n auxiliary brak,e i.5 also provided within the drawworks structural syst~m to sub-stan~ially absorb the potential energy associated with the lowering of a loaded travelling block. In the parti,cular embodiment o~ the invention shown in Figure 2, the primary brake is a drum brake g~, manually operable by a pivotable lever 97. A spring 98 biases the drum brake 96 i,nto its fully asserted position. The lever 97 may be connected to a brake actuator assembly generally indicated by the numeral 99. As seen also in Figure 7, the brake actuator assembly 99 includes a cylinder 100 having a piston 101 therein. The piston 101 is coupled to the lever 97. The brake actuator 99 also includes an electronic-to-pneumatic interface 102 (Figure 7) such that the cylinde~ 100 may be coupled to a suitable supply of pressurized air or any other fluid such that introduction of the fluid into the cylinder 100 moves the piston 101 therein which moves the lever 97 so as to modulate the force on the brake.
As mentioned above, itisknown to those skilled in the art that the secondary brake is provided to absorb the energy when the loaded travelling block is moved downwardly from an upper to a lower elevation. A manually controlled hydromatic brake may be used as an auxiliary brake. How-ever, an electric brake, such as an ELMAGCOTM brake sold by Baylor Company could typically be used. The brake control subsystem of the drawworks control system 21 can be readily interfaced with an auxiliary brake by those havin~,~ skill in the art so as to provide the desired velocity and decelera-tion control. Final positions are ultimately controlled by the drum brake 96.

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~L3tii733 It is important to note that whatever au~iliary brake configuration and actuator there~or i5 util:i~ed, -the drawworks structure includes a brake which is controlled ~y the dra~orks control systern 21 so that the desired velocity acceleration of the travelling block 68 is maintained as it moves from an upper to a lower final position. Also, the brake is operable to set and hold a lif-ted or hoisted load in the upper position. If the operator deems it necessary to halt the movement of the physical structures associated with the drawworks, the operator may at any time override the electrical signal output from the drawworks control system by actuating a switch 103 mounted on the lever 97.
The operator may also, at any time, override the electrical signal output from the drawworks control system 21 by de-pressing a push-button switch located in the control panel 103a. The spring 98 may be manually overridden to release the brake.
The racker structure 34 is operable to carry a pipe stand from the vertical centerline of the derrick to the set back. In a make-up cycle, the pipe stand to be added is stabbed into the already emplaced and connected stands which comprise the drill string. When joined to the drill string, the racker structure 34 relinquishes the load to the draw-works, which lowers the string into position. In a breakout cycle, the drawworks structure 22 withdraws the drill string, and, as each pipe stand therein is disconnected frorn the string, the racker structure 34 accepts the load from the drawworks and moves the pipe P,tand to a storagc location.
; The actual connection and disconnection of pipe stands frorn the drill string is accomplishe(l by the power tongs structure 28 under the control of the tongs controL system 29. Very brie~ly, the tongs includes a backup, which holds ~L3ti733 the lower pipe element ~efining the joint, while a second element of the tongs - the power driven tong - connects or disconnects a pipe stand to the upper pipe element theret,o.
The tongs also inclucles a lift to move the assocl~ted backup--jaws structure at a predetermined speed to a pre-determined operating elevation with respect to th~ vertical axis of the derrick. The backup and the jaws usually circumferentially surround the drill string as it advances in the bore. Put another way, the ver-tical axis of the derrick usually extends through the openings in the backup and jaws of the tongs -to facilitate gripping and dis-connection or connection operations. Until needed, the tongs are stored in a lowermost storage position. When it is convenient to do so, the tongs are lifted to a standby position which is proximate to the elevation at which the distended joint 56 of the drill string is raised by the drawworks. To sense the distended joint 56, a joint sensor 1025 is provided to contact the exterior of the drill string as the tongs are moved from the standby to the operating position. The movement from the standby to the operating position is at a slower speed, of course, than the speed at which the tongs are moved from the storage position to standby position. The particular joint sensor 1025 ernbodied by the teachings of this invention is made clearer herein.
The details of the structure of thc tongs, thc -joint sensor and the tongs control sy,stem (including an electro-hydraulic interface) is discuss~d in detail herein.

~3~ 3 OPE'RA'I'ION

Having defined the elernents of the various structural systems, the operating sequency thereof duriny a typical make-up or hreak-out cycle is presented, to graphically illustrate the physical interactions between the defined structures. Once this is done, a detailed descrip-tion of each of the control systems initiating and ceasincJ the physical operations performed by the structural systems is set forth.
In the break-out cycle, the objective is to dis-assemble the drill string into its constituent pipe stands as -the drill s-trlng is lifted from the bore. With the upper end of the still-a-ttached pipe stand to be next-removed held by the slips at a predetermined elevation along the vertical axis of the derrick, the travelling block with the e]evator suspended therefrom is lowered under the control of the drawworks portion of the computer program and under the influence of the drawworks brake control subsystem which stops and sets the brake at an elevation so as to permit the elevator to accept the pipe stand. During this period the racker is placing the last-removed pipe stand in a storage location on the set back, and will eventually be moved under control of racker portion of the computer program to a position to accept thc next-removed pipe stand. The drawworks progratn and racker procJratn operatc on a time-shared basis. The tongs ar~ in a StOraCJ~ pOS.itiOIl.
The computex ~ends an actuating ~ic,~naJ, to the `; elevator load control subsystem which clerives it~ input signals from the dead line force sensor. A momentary si~nal output from the computer samples the weight of the unloaded ~ 2() -, ,`~! ', i ~L3~73~

travelling block and elevator. This tare weight is used, as discussed herein, to ascert~in the instantaneous loading orl the travelling block and elevator. The elevator then accepts the loading of the drill string, and an ou-tput feedbac~. signal to that effect from the elevator load con-trol subsystem is used to coordinate opening of the slips. The computer outputs a momentary load sample signal before the veloclty of the loaded elevator is increased. This static or initial load signal is used, as discussed herein, when modified by a predetermined fractional multiplier, as a basis for de-ter-mining whether the instantaneous loading on the elevator has exceeded a permissib]e range of values as selected by an experienced drilling operator.
In response to an actuating signal from the computer, the drawworks motor control subsystem provides a throttle signal to the drawworks motor drive to hoist the drill string to a predetermined elevation. It may be necessary to move the block slightly, or creep to engage the drawworks clutch. The drill string is hoisted under the control of the drawworks motor control subsystem. A logic network operates to release the brake whenever the hoisting velocity ~ exceeds a preset threshold value and tends to apply the ; brake at hoisting speeds below this threshold velocity (the drum brake being a self-energizing brake).
The motor control subsy~tem provides output signals to the drawworks motor drive to lift the drill string in a manner which takes into account the position error (the difference between the actual position and command position of the drill string being lifted), a predetermined command velocity output by the computer, and the dynamic loading.
During the ma~or portion of the travel the load is hoisted at an uniform velocity equal to the command velocit~. As ~L3~i~33 the predetermined commarld position i5 approached, the hoisting velocity is reduced in a manner proportional to ~he position error. Put another way, the drawworks motor control sybsystem responds to position and velocity feedb~ck signals input to it from -the block position and speed transducer and the drum tachometer, respectively, to rnove the travelling block and elevator to a predetermined command elevation at a predetermined command velocity output by the computer.
During the hoisting opera-tion, signals ~rom the elevator load control subsystem are taken into considera-tion in determining the magnitude of the output signal to the drawworks motor. For if the actual loading on the elevator exceeds the predetermined value by which actual load may deviate from the static loading, the motor is slowed to bring the loading into the acceptable limits. Of course, if the deviation goes beyond a threshold above even the scaled initial value range, indicating that the string is caught in the bore, the automated control shuts the system down and the system reverts to manual control.
` 20 As the block is hoisted and approaches the final position, the motor is stopped and the brake is set. The brake is applied when the lifting velocity drops below the predetermined threshold mentioned. The motor is stopped when the position reaches within some predetermined close distance to the command elevation. During liting, if the block is indicated as moving in the wrong direction of travel or at a greater than commanded velocity, the automated sequence is halted and the systcm reverts t:o manual con~rol.
The block final elevation is selected such that the height at which the upper end of the pipe stand to be removed finally stops will a:Lso place the joint bctween the pipe stand and the next lower pipe stand at an elevation for

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. ~, operation by the power -tongs. When the block velocity is sufficiently close to zero, a zero velocity si~Jnal is returned to the computer. This signal, alony with a block position feedback signal sufficiently close to the command position signal are necessary conditions before the actuating cor~mand to set the slips to retain the load is output frorn the computer. Only with the sliE)s set and supporting the full load of the drill string will the e]evator relin~uish the pipe stand to the racker structure. As mentioned, after racking the previous stand, the racker is moved back toward the vertical centerline of derrick, so as to be in a position to accept the next pipe stand. The elevator and block are retracted away from the vertical centerline of the derrick and drop under the control of the drawworks brake to be in position to repeat the lifting sequence.
When the lifting movement started, the power tongs were in the storage position above the Eloor of the derrick.
After the ele~ator had been hoisted above a potentially obstructing position the tongs were actuated and moved to a standby posi-tion. After the pipe stand has been finally positioned and the slips set, a joint sensor associated with the tongs controls a slower lifting movement to bring the tongs into operating position. When the tongs are positioned properly with respect to the joint, the motion thereof is halted, and the joint sensor retracted. The tong backup then engages the drill string, the tong jaws engage the pipe stand to be removed, and the pipe stand is scparated therefrom, The racker then begin.s to store the now-separated pipe stand, while the tongs are moved to the storage position. The elevator then is brought into the elevation along the central axis of the derrick where it may engage the upper end of the still-attached pipe stand to be ., . ~
, - 23 7~3 next-removed and the breakout process repeated.

* * *

In the make-up cycle, the objective is to assemble the drill string from its constituent pipe stands and to lower the string into the bore. ~ith the upper end of the last-connected pipe stand supported at a predetermined elevation by the slips, the drawworks motor control subsystem lifts the block and elevator along the vertical axis of the derrick to a position at which it will receive a pipe stand from the racker.
The tongs are moved upwardly from the storage to the standby position at a first, normal, speed. The tongs -~`` continue to move upwardly at a second, slower, speed beyond the standby position with the joint sensor extended. When the joint is sensed, upward motion is halted with the tongs at the operating elevation and the backup is closed. A pipe stabber is extended to guide the lower end of the pipe stand being made up into the threaded connection at the distended upper end of the drill string. When the pipe is stabbed, the tongs proceed to make up the joint. Thereafter, the ` 20 tongs are lowered to the storage position. The elevator, at the upper elevation, is raised a-t a creep speed to acquire the drill string load. After the elevator load control subsystem detects that the drill striny load is ~cquired by the elevator, the s].ips are rai~ed and the drill string is hoisted further to di~engage the 51ips from the ~rill string. ~t this time, the rackers, un~er control of the computer racker program, proceed to acquire the next pipe stand and carry it toward the vertical centerline of the - 2~ -i, ~L3L3~733 derrick to the racker standby position. E;'rom there the rackers proceed to the vertical centerline of -the derrick.
In response to cornmand velocity and corr~and position siynals output from the compu-ter, and utilizing a posltion feedback s-ignal from the block position and speed trans-ducer, and a velocity feedback siynal from the dra~70rks drum tachometer, -the drawworks brake control suhs~stem supervises the lowering of the drill string to a predeter-mined lower elevation. The brake control subsystem outputs control signals to the drawworks brake actuator so as to maintain the block velocity near the command velocity for the major portion of the travel, and -to position the block as close as possible to the command position during the final position of the travel.
The elevator load control is activated by -the computer and is responsive to a momentary signal to sample the loading of the block and elevator in the unloaded condition. This signal is used to discern whether or not the elevator is supporting any of the drill string load.
Also in response to a signal output from the computer, the loading on the elevator is sampled and held after the load is acquired but before the downward velocity thereof is appreciable. This initial static loading signal is used, when appropriately modified by a predetermined factional multiplier, as the basis for determination as to whether or not the instantaneous loadiny on the elevator ha~ e~ceeded a permissible range of loading normally anticipated duriny a lowering operation.
During the lowering operation, thc outputs to the brake actuator from the brake control subsystem take into account the signals relative to loading from the e]evator !~
~ V~. .

3L~3ti733 load control subsystem. If the actual 1Oading is deviatiny from the initial static condition by more than the specified amount, the drawworks brake control slows the velocity to bring the loading back to acceptable limits. If the actual loading is devlating by more than a predetermined threshold below the scaled static value (indicating that the bore is obstructed and the drill string unable to penetrate), then ; the automated control sequence is terminated, reverted to manual control, and the system is shu-t down. Other inter-rupt conditions may occur if, during the lowering operativn, an indication that excessive speed has been reached, or that the block is moving in a wrong direction of travel.
As the block reaches the command position, the dif-ferences in the actual position and velocity from the com-mand position and velocity are such that -the brake is set.
That is, when the block and elevator come within a pre-determined distance of the command position, the brake is set. Zero position error and zero velocity are necessary conditions which must be met before the computer sets the slips. With the slips set, and the weight of the drill string supported thereby, the elevator surrenders the load, and the block and elevator lifted to the upper most position to accept the next-to-be lowered pipe stand. The process is then repeated.

7~

DR7~WORKS CONTROL SYST~M
, _ The drawworks structural system 22 is the collection of the structural elements on the derrick which perform all of the physical acts associated with the lifting or lowering of the drill string. These structural elements have been detailed in connection with Figure 2.
The physical actions performed by the drawworks structural system 22 are controlled by an arrangement known as the drawworks con-trol system, indicated by reference numeral 21 on the general block diagram Figure 1 and on the more detailed drawworks control system block dia~ram Figure

3. The computer is interfaced with the dra~lworks control system 21 through a plurali.ty of input and output lines, each of which will be discussed herein. Further, the draw-works control system 21 is input with various feedback signals representative of physical quantities associated with the structural system, such as velocity, position, direction, etc. Through the use of the computer commands and the feedback signals, the drawworks control system 21 outputs signals initiating or ceasing the functions performed by certain structural elements. All inputs and outputs of the drawworks control 21 to and from the physical structures with which it is associated will be detailed herein.
The drawworks control system 21 includes several interconnected subsystems, as ~ollows: the draw~orks brake control subsystem 105; the drawworks motor control subsystem 106; the drawworks elevator load control subsystem 107; and the drawworks velocity comparator subsystem 10~. F'urther, logic 109 is connected within the drawworks control 21 in cooperative association with the brake control subsystem 105 and the motor control subsystem 106.

Feedback signals to the drawworks control system 21 are provided from the block posi-tion and speed transd~cer (B.P.S.T.) 83, which specifically provides positior. feedh,~c~
signals to the brake and motor control subsystems, 105 and ]06 respectlvely. ~'he block position and speed transducer 83 also furnishes a velocity feedback signal to the velocity comparator 108. However, the primary velocity feeclhack signal to the drawworks control 21 is the signal from the drawworks drum tachometer 94 provided to the velocity com-parator 108. The deadline force sensor (D.L.F.S.) 95 pro-vides feedback current signal of 4-20mA to the drawworks control system 21, particularly to the elevator load control subsystem 107 on a line 110. ~ny of these feedback signals may be conditioned, recorded or otherwise operated upon prior to their input to the control system 21.
One output from the drawworks control system 21, specifically from the brake control subsystem 105, is con-nected to the brake actuator 99 which is connected to the brake. The brake actuator 99 includes the electronic-to-pneumatic interface 102 (discussed in detail herein) which converts electrical output signals from the brake control subsystem 105 into pneumatic signals compatible with draw-works brake cylinder 100. Another output from the draw-works control s~stem 21 is connected to the motor drive 93 of the drawworks. For convenience of operation, various voltage-to-current (as the convertcr 27~, for example) and current-to-voltage conversions are effected, with the electronic arrangements for eff~cting th~se conv~rsions being detailed herein.
Input to the dra~works control system 21 are signals from various safety overrides present on thc physical structure of the drawworks. For exarnE~le, the S'l'OP control ~-. - 2~3 -, .

-~3~733 button located on the driller's console is an element of an interlocking circuit. When the STOP button is depressed, it functions to ~nergize the AUTO/MA~IUAL bus. This bus is input to the mo-tor control subsystem 106 by a line 111.
The line 111 connects to a relay coil 112 and a solenoid coil 113 of a valve 114. Actuation of thè STOP button causes the system to revert from automated to manual control.

B~de-energizing the relay 112 the throttle signal from the motor control subsystem 106 is disconnected from the motor drive 93, stopping the motor 92. By d~-energizing the coil 113 of the valve 114, the actuator pneumatic signal to the cylinder 100 is disconnected and the cylinder 100 is vented to the atmosphere, thus applying a full braking signal.
The electronic arrangement of each of the recited drawworks control subsystems, the operation of each, and the interactions between them are now discussed.

ti73~
DRP.WWORKS BRAK~: AND MOTOR CONTROL SUBSYSTEMS
. .

The drawworks brake and motor control subsyc;tems 105 and 106 are now discussed. ~oth the brake control sub-system 105 and the motor control subsystem 106 receive a

4-20mA analog signal COMMAND POSITION output from channel A
of the computer 40. The COMMAND POSITION signal is carried by lines 115B and 115M as inputs to the brake control sub-system 105 and motor control subsystem 106, respectively.
The magnltude of the COMMAND POSITION signal is related to the elevation to which it is desired the travelling block 68 to be raised or lowered by the motor 92 or brake under the control of the motor or brake control subsystems. ACTUAL
POSITION voltage signals are received from the block position transducer 83 by the brake control subsystem 105 and the motor control subsystem 106, respectively, on lines 116B and 116M. The derivation of the position signal is discussed in connection with the block position transducer 83.
Both the brake control subsystem 105 and the motor control subsystem 106 receive a 0-10v COMMAND VELOCITY
signal from the velocity comparator 108 on lines 132B and 132M, respectively. The magnitude of the COMMAND VELOCITY
signal is related to the velocity to which it is desired to lift the travelling block 68 to the desired elevation.
ACTUAL VELOCITY voltage signal.s, also from the velocity comparator 108, are input to the brake control subsystem 105 and the motor control subsyst~m 106 on the line~ 134B and 134M, respectively. The magnitudc of the ACTUAIJ VELOCITY
signal is functionally related to the speed at which the travelling block 68 is moving under the control of the motor ,.,~

3~
or brake. The or.ic3in of thcsc s:iclna:Ls will be dis~sse~ ir, connection with the desc:ripti-)n o~ the vel,oci,ty corrl~,arator 108.
The brake control subsystem 1.05 arld the motor control subsystem 106 each receive an ACTUAT, LOAD voltage signal.
related to the actual load on the el.evator 75 from the elevator load control subsystem 107 on l,ines 136B and 136M, respectively. Moreover, from the elevator 1oad control subsystem 107, the brake control subsystem 105 receives ~n appropriately sealed INITIAL LOAD voltage slgnal on a line 138B while an appropriately scaled INITI~L LOAD voltage signal is input to the motor eontrol subsystem 106 on a line 138M. The derivation of these load signals is di~cussed in eonnection with the elevator load control 107.
Although the interaetion of the logie 109, the brake control subsystem 105 and the motor control subsystem 106 is set forth in detail herein, for present purposes it should be noted that the logic 109 outputs MOTOR RUN voltage signals to the brake eontrol subsystem 105 and to the motor eontrol subsystem 106 on lines 140B and 140M, respeetively. A BRAKE
RUN signal on a line 142 is output from the logie 109 to the brake eontrol subsystem 105. The logie 109 reeeives MOTOR
MODE SELECT eornmand on a line 144 from the computer channel B. The logic 109 receives a BRAKE SELECT eommand from the ehannel C on a line 145. As mentioned earlier, the motor control subsystem 106 r~eeives ~ sic3r)~1 f,'rorn th~ ove~rr,ide switeh 103 on the line 104. As is rnore el~arly shown herein, information concerning a manual override ,is tr~nsmitted Erorn the motor eontrol subsystem 106 to the brake eontrol sub-system 105 on a line 147.
Computer ehannels H and I respectively output CREEP
and CREEP TO ENGAGE CLUTCII to the motor control subsystem 106 - 31 ~
~, ~3~33 on lines 150 and :L51. U~on receipt oE a CREEP si(~nal on the line 150, the motor control subsyst~m 106 output~ a signal CREEP FLIP-FLOP to the brake control subsystern 105 on a line ]52.
The output signal from the brake control subsystem 105 is carried by a line 158 to the brake actuator 99. The output signal from the motor control subsystem 106 is carried by a line 159 to the motor drive 93 (throuyh a converter 274). In the preferred embodiment of the inverl-tion, both of these output signals are 4-20mA current signals.
In general, it may be sta-ted that current signals are pre-ferred for carrying information over the longer of the con-duction paths used in the preferred embodiment. Current signals provide high noise immunity over long cable runs through electrically noisy environments.
As alluded to earlier, the AUT0/l~ANUAL bus is con-nected to the drawworks control system 21, and in parti-cular, to the motor control subsystem 106 by the line 104.
The effect of this signal, as discussed in detail herein, is to isolate the motor and brake control output signals from their associated controlled apparatus. The loss of AUTO/MANUAL bus voltage de-energizes the coils 112 and 113.
The effect o-E de-energizing the coil 112 is to interrupt the motor control output line 159. In the case of the coil 113, de-energization thereof opens a brake solenoid valve 114 to disconnect the brake pneumatic system (I'igurc 7) from the cylinder 100.
The brake control subsystem ].05 and the motor control subsystem 106 are basically similar to each other, at least insofar as to the basic operating pxinciples. They can, therefore, be discussed -together to illustrate how each of the above-enumerated inputs interact to generate brake or ~ r~
~: ;i ,~

~L~3~3~
motor control output signals. They di~er, of cour~e, in the implementation thereof dlle to clifference~ in technlcal requirements and functions to be perormed. Preferred embodiments of each subsystem are discussecl herein.
Referring to the simplified block diagram shown in Figure 4, the six enumerated inputs utilized in generating an output control signal from either the brake or motor control subsystems are: the CO~M~ND VELOCITY; the COM~AND
POSITION; the ACTUAL VELOCITY; the ACTUAL POSITION; the ACTUAL LOAD; and, the initial load signal multiplied by a predetermined constant. (This last-mentioned signal is symbolized hereinafter by INITIAL LOAD-(KN), where N = 1 or 2). In both the motor and the brake control subsystems, -the first two listed signals are provided by the computer using certain input rig data, operating conditions, etc. The next-three listed signals are ins-tantaneously provided by outputs from the transducers. The last mentioned input signal is an appropriately scaled representation of the initial load on the elevator taken while the elevator is in a relatively static condition. The scaling factor is selected by an experienced driller to define an acceptable range within which the instantaneous actual load may deviate from the static load during displacement of the travelling block. It is noted that the scaling factor K is different for each subsystem.
In operation, as seen in Figure 4, thc-- analoc3 s:iynal representative of the actual position of the travelling hlock (ACTUAL POSITION) i5 substracted at a clifEerential amplifier 200 from the analog signal re~resentative of the predetermined final position selec-tecl by the compu-ter (COMMAND E'OSITION). The resulting cllffcrence, or po~itior error signal Ep, -taken from the output oE the cliffercrl~ial :s --~L~3~733 amplifier at the node 201 ls summed at a summing jllnction 202 with the ~CTUAL VELOCITY signal to define a ~ositior error plus velocity signal, ~ ~ v. The COMMAMD VELOCIr~'~
signal is input to an amplifier 20~ and a series diode, the combination of which acts as a limiter to limit the magrli-tude of the position error signal E present at the node 201. This effectively results in the rnaynitude of the COMMAND VELOCITY signal establishing a maximum velocity at which the trave]ling block is displaced from a first to a second predetermined position. The position error plus velocity signal, Ep-~ V, together with a signal related to a load factor VLF, are input to a difference amplifier 208.
At the output 210 oF the difference amplifier 20~ is a total error signal ET, from which the output signal of the motor or brake control subsystem is derived.
The load factor signal VL~ is derived from the ACTU~L
LOAD and the INITIAL LOAD~(KN) signals. These signals are summed algebraically to input to an amplifier 212. If the ACTUAL LOAD signal deviates from the initial static elevator load by a fraction greater than the appropriately selected scaling constant KN, an output is emitted from the ; amplifier 212 related to the difference. This output is the load error, or load fac-tor VLF. An adjustable portion of the load factor signal (adjustable through the potentiometer KL) is input to an amplifier 214, the output of which is applied as the scaled load factor sigrlal (KL)~(VLI~) to the difference amplifier 20~. The effect of the load Eactor signal VLF is to change the total error sicJnal I~T in a direction such as to reduce the drawworks velocity otherwise prevailing. Of course, if the load factor signal VLF is zero (indicating that the actual load on the elevator during the movemen-t has not e~.ceeded the allowed range oE dcvia-- 3~ -~:3~733 tions from the lnitial static load) the total error siynal ET is then derived exclusively from the p~s:ition error plus velocity signal, Ep+ V, The total error signal ET, comprised o~ the above-mentioned input factors, is, in effect, used as an input to a closed-loop servo con-trol system opcrative to drive the controlled elements, either the drawworks motor or drawworks brake, in a manner so as to change the total error signal in a direction such as to reduce the drawworks velocity other-wise prevailing. In accordance with this invention, the totalerror signal ET is applied as the input to an integrator-amplifier network 218. When the total error signal ~T' reaches zero, the output 220 of the integrator-amplifier net-work 218 is constant and uniform drawworks velocity is main-tained. The output 220 of the integrator-amplifier network 218 operates to maintain the drawworks motor or brake at the velocity producing the zero total error signal ET.
As may be appreciated, the magnitude of the total error signal ET determines the rate of change of velocity.
The greater the absolute rnagnitude of ET, the greater is the rate of change of block velocity - effected either by increased driving signals to the drawworks motor or de-creased application of the drawworks brake. The smaller the absolute magnitude of ET, the smaller is the rate of change of block velocity - either through decreased driviny signals ko the drawwork.s motor or increased application o~ the drawworks brake. To reiterate, however, the nature o~ the motor and brake control subsystems is such that the magnitude of the total error signal F~T tends toward zcro. As the magnitude of the output of the integrator-amplifier network 218 increases, the motor speeds l~p (i~ in Motor modc) or the brake goes on (i~ in brake mode), as explained in conncction with Figures 5 and 6.

i733 The load fac-tor VIF tends to change the tot~l error ET so as to reduce the hoisting or lowering velocity. The effect of the load fac~or vLp is to llmit the actual velocity of the travelling block to a value less than the prograrnmed command velocity and a value necessary to maintain the instantaneous elevator ]oad within the range of limits set by the fac-tor KN.
Having described the general operating principles behind the drawworks brake and motor control subsystems, reference is invited to Figures 5 and 6, which are sim-pliEied signal diagrams patterned upon the signal diagram of Figure 4 and which are directed toward the brake control subsystem 105 and the motor control subsys-tem 106, respectively. Figures 5 and 6 elaborate more fully upon an operative embodiment of both the brake and motor control subsystems. In the Figures, the prevailing polarity at the designated circuit points are indicated by reference symbols comprising circled positive or circled negative signs.
In both Figure 5 (brake) and Figure 6 (motor), those inputs recited in connection with Figure 4 are, of course, utilized, and need not be summarized again. In Figure 5, the position signals are input to the terminals of the differential amplifier 200B, as shown. The position error signal (Ep)B is adjustable throuc3h a potentiometer (Xp)B
and amplified by an amplifier 230~ having a rcC;istor ~3]~
at its output. ~t the node 201B, the readjustcd portion of the position error signal (Kp)~(L~,p)~ ~rom the output of the amplifier 230B i5 connecte~ to thc summing junction 202B through a resistor 232B. The ~CTUAL VELOCITY signal is connected through a resistor 233B to the junction 202B.

b73~

The magnitude of the adjust;ed position error sign~l (Ep)B(Kp~B at the node 201B is limited by khe magnitude of the CO~AND VELOCITY signal taken through the amplifier 204B and the diode 234B. In effect, the magnitude of the voltage at the node 201B is equal to the output of the amplifier 200B (adjusted by ~Kp)B) as long as the adjusted position error is less than the magnitude of the COMMAND
VELOCITY. If the magni~ude of the position error exceeds the magnitude of the COMM~.ND VELOCITY signal, it is limited thereby and the COMM~ND VELOCITY signal is summed at the junction 202B. In this manner a maximum velocity for the lowering motion of the block is programmed by the comput~r. The composite position error plus velocit~
signal (Ep~ V)B (appropriately limited by the COMMAND
VELOCITY if necessary) is applied to the inverting input of the difference amplifier 208B.
The non-inverting input to the difference amplifier 208B is presented with a signal related to the load factor signal (VLF)B derived from the load signals input to the brake control subsystem 105. Note that the INITIAL LOAD
signal input is scaled by a factor (-Kl), chosen by a skilled well operator for reasons discussed in connection with the elevator load control subsystem 107. The load signals are connected through resistors 235B and 236B and algebraically sumrned at the ampl:ifier 212B. Thc output of the amplifier 212B is the ba~ic load factor signal (VL~,,)B
indicative of the magnitude by which the actual load differs from a predetermined fractiorl Kl oE the :initial static load. This load factor signa:l .is connected through a diode 237B to the potentiometer (K~)B~ Tile alnpli[i.er 214B is connected to the potcntiometer (KL)B, with the amplifier output being connected to the difference .~

amplifier 208B. q'he voltage value input to the difference amplifier 208B is, of course, e~ual to ~ero or to the value (KL)B-(VLF)B. A zero output signal is present at the amplifier 214 outpu-t as long as the ACTUAL LOAD signal is greater than or equal to the absolute value of the pro-duct of INITIAL LOAD (-K]). I-~owevcr, if the ACTU~L L~n signal is less than the absolute value of the quantity defined, an output signal equal to the magnitude~ by which the ACTUAL LOAD is exceeded is applied to the potentio-meter (KL)B. This is the basic load factor signal (VLF)B

applied for scaling by the potentiometer (KL)B.
The total error signal (ET)B at the OUtpllt 210B of the difference amplifier 208B is applied to the inteyrator-amplifier network 218B. The magnitude of the output of the integrator-amplifier 218B on the line 220 determines the velocity a-t which the block is moved downwardly. In general, the larger the signal on the line 220, the smaller is the block velocity. The net braking effort is pro-portional to the output signal from the integrator-amplifier 218B. That is, the smaller the signal on the line 220, the less the brake is applied, and the faster -the block moves downwardly. The effect of a load factor signal, if one is present, is to reduce the velocity of the block.
Thus, the block is ].imited in its velocity to the lower of the maximum COMM~ND VELOCITY programrne~l into the cornputer (which limits the signal at the node 202l3) or thc velocity level required to maintain the ~lcvator load at the pre-determined factor Kl of the initial value.

In the drawworks brake control subsystem the inte-grator-amplifier network 218B comprises two parallel con-duction paths. The total error sigrlal (¢T)B is split at anode 238B, with an adjustable portion thereof taken hy a ~L~3t~33 potentiometer (KFF)~ and :input ~o an amplifier 239B con-nected to a resistor 240B. This path improves the overall dynamic response of -th~ network 2] 8B to s-tep-changes in the total error signal. The other parallel branch includes a potentiometer (KINT)B which presents an adjusta~le portion of the error signal (ET)B to an integratiny amplifier 2~
The output of the integrating arnpli~ier 241B is connected to a resistor 242B and summed at a junction 243B. The signal at the junction 243B is input -to an amplifier 244B.
The brake control subsystem output signal at 220B is carried by a resistor 245B to a voltage-to-current con-verter 246B. This network converts the signal outpu-t to a current for reasons discussed. A negative reference voltage is applied to the current-to-voltage converter 246B
through a resistor 247B. The reference voltage is summed with the brake signal on the line 220B. The difference signal (since the polarities are opposite) is converted to a 20-4mA current signal and is presented on the line 158 to the brake actuator 99, which inc]udes an electronic-to-pneumatic interface 102 described in full detail hereafter.
Connected within the brake actuator 99 is the brake solenoid valve 114 (Figure 3).
The electronic-to-pneumatic interface 102 associated with the brake actuator 99 is illustrated schematically in Figure 7. As discussed previously, movement of the actuator lever 97 against the bias of the s,pring 98 move~ the brakc (Figure 2) toward the release position. q'he lever 97 is physically connected to the piston cylinder arrangement such that the introduction of a pressurized fluid into the cylinder 100 moves the piston 101 and the lever 97 attached thereto so as to disengage the brake. It is apparent that the force applied to the brake lever 97 by the piston 101 is ~ 39 -F

proportional to pressure of the flui.d in the cylinder 100.
As discussed immediately above, the Outpllt of the voltaye-to-curren~ converter 246s is a current signal the rrla~Jnitude of which determines the degree to which the brake is applied. The output line 158, (together with a comrnon line) is connected -to a current--to-pressure transducer 265. Of course, the output signal on the line 158 ma~ be opera-ted upon by any suitable signal conditioners, ramp or clelay circuits or the like, in a manner known to those skilled in the art.
Dependent upon the magnitude of -the input current signal, the transducer ~65 outputs a three-to fifteen p.s.i.
air signal on a line 266 connected to a high-volume -three-to-one booster relay 267. The output of the booster relay 267 is applied through a line 26g to the brake air cylinder 100. The output of the relay 267 is llmited by a regulator 269 disposed in a line 270 from the supply to the relay 267. Similarly, the output of the transducer 265 is held within predetermined limits by a regulator 271 disposed within a line 272 connecting the downstream side of the regulator 2&9 to the transducer 265.
Disposed downstream of the booster relay 267 in the line 268 is the brake solenoid valve 114. In the event of an interrupt, or any other condition resulting in the de-energization of the AUTO/MA~IUAL bus, the valve 114 discon-nects the booster 267 from the cylinder 100 and vents the cylinder 100 to atmosphere, thus applying full braklny effort. In connection with the Figure 7, it is noted that the operator may manually override the brake control sub-system by applying a physically superior force on the lever97 in opposition to the force of the fluid within the cylinder 100. An electrical override signal applicd to the .~

line 104 by actuating of the switch 103 would be a ~referred mearl~>of overriding the brake (Figure 3). The efect of such an override signal on the ~oto~ ~nd br~e suhs~stern~ is discussed herein. Similarly, the brake may be re]eased by manually applying a force to overcome the force of the spring 98.
Shown in Figure 6 is a simplified signal diayram for the motor control subsystem 106. The opera-tion of the motor control subsystem 106 is very similar to that discussed in connectlon with the brake control subsystem 105. The position error signal (E )M at the output of the differen-tial amplifier 200M (derived from the difference between the COMMAND POSTION and ACTUAL POSITION signals) is adjustable through a potentiometer (Xp)M and amplified by the amplifier 230M having a resistor 231M tied to the output thereof. The adjusted portion of the position error signal (Kp)M-(Ep)M
at the output of the amplifier 230M is connected to the summing junction 202M through a resistor 232M. The ACTUAL
VELOCITY signal is connected to the summing junction 202M
~hrough a resistor 233M.
The magnitude of the adjusted position error signal (Ep)M at the node 201M is limited by the magnitude of the COMMAND VELOCITY signal taken through the amplifier 204M
and the diode 234M. The magnitude of the voltage at the node 201M is equal to the output of the differential amp-lifier 200M (adjusted by ~Kp)M~ as long as the adjusted position error is less than the magnitude of the COMM~ND
VELOCITY slgnal. If the magnitude of the position error exceeds the maynitude of the COMMAND Vr~LOCITY si(Jnal, it is limited thereby and the COMMAND VEI.OCITY signal is summed at the summing junction 202M. The e~fect of the above-described arrangement is to effectivel~ limit the maximum ~., 7~

velocity of the block while it is be:inc3 hoist~d, ~rhis maximum velocity is proyra~nable into the ccjmputer and pro-tects the bore from -the detrimental effects of swahbinc~.
The appropriately limited (if necessary) compo.site posit,ion error plus velocity signal (Ep+ V)M is presented to the inverting input of the di.Efcrence amp1.ifier 208M.
To the non-invertiny input of -the difference amplifier 208M is applied a sic~nal related to the load factor signal (VLF)M, derived from the load signals input to the motor control subsystem 106, including the ACT~AL LOAD and the INITIAL LOAD scaled by the appropriate factor (-K~). The load signals are algebraically summed at -the input of the amplifier 212M. The output of the amplifier 212M is the basic load factor signal (VLF) M. It represents the dif-ference between the ACTUAL LOAD and the INITIAL IIOAD
multiplied by a factor (K2). The load factor signal is connected through a diode 237M to the potentiometer (KL)M~
The output of the potentiometer ( KL) M is applied through the amplifier 214M to the difference amplifier 208M. The voltage applied to the difference amp].ifier 208M is equal either to zero or the adjusted load factor (KL)M- (VLF) M~
A zero signal is present at the output of the amplifier 214M as long as the ACTUAL LOAD signal is less than or equal to the absolute value of the INITIAL I.OAD signal scaled by a factor K2. Thus, the actual load may range as high as (INITIAL LOAD) ~(K2) without causiny a ,1,oad factor output.
However, if the ACTUAL LOAD increases beyond the INITIAL
LOAD multiplied by a factor K2, an output sic3nal equal to the difference between the ACTUAL LOAD and the ~caled INITIAL
30 LOAD is applied to the potentiometer (KL)M. This load fac~or output is suitably scaled by the potentiometer (KL)M~

-- ~2 --~L~3~ ~3~

The total error signal (~T)M is applied to the integrator-amplifier network 21~M~ Th~ m~gnitud~ of the output of the integrator-amplifier net~or~. 218M on the line 220 determines the velocity at which the block is moved up-wardly. In general, the larger the siynal on the line 220, the greater is the block velocity and the larger the total error signal (ET)M, the greater is the rate of change of velocity. That is, the greater the total error signal (ET)M~ the larger the driving current input to the motor, and the faster the block moves upwardly. The load factor signal, if present, changes the total error signal so as to reduce the velocity of the block. The maximum lifting velocity attainable is that predetermined by the computer program. The dynamic loading on the block is limitecl by controlling the veloclty at which -the block is lifted. This prevents excessive damage to the bore during hoisting by excessive hydrostatic forces caused by excessive hois-ting velocity.
As in the brake control subsystem, the integrator-amplifier network 218M in the motor control subsystem 106 includes first and second parallel paths. The total error signal (ET)M is split at the node 238M, with an adjustable portion thereof taken by a potentiometer (KFF)M and to the inverting input of the amplifier 244M. This path improves the overall dynamic response of the integrator-amplifier 218M to step-changes in the total ~rror sic3nal. Thc other parallel branch includes a potentiorneter (KINrr)M which takes an adjustable portion of the total error s.igncll and inputs that signal to the integrating amplifier 241. The output of the lntegrating amplifier 241M is presented to the non-inverting input of the amplifier 244M.

'`lf~
~.

7~

The output 220M of the inteclrator-amplifier network 21~M i5 applie~ to a voltage-to-current converter 246M
through a resistor 245M. A ~-20MA current signal propor-tional to the voltage output of the integrator-alrlplifier network 218M is connected by the line 159 to the motor drive 93, which drive 93 includes a suitable current-to-voltage converter 274 discussed herein. Within the nlotor control subsys-tem 106 is the solenoid relay 112, operable to interrupt the current flow from the converter 245M to the current-to-voltage converter 274. The output of the converter 274 is connected to the motor drive 93.
Within current-to-voltage converter 274, the current signal output on the output line 159 of the motor control subsystem 106 is applied to a resistor 275 connected at its opposite end to a negative potential. The negative poten-tial may be supplled by a reference amplifier network, including a feedback pa-th around a transistor, in a manner known to those skilled in the art. The voltage present across the resistor 275 is applied to the non-inverting input of an amplifier 276 driving a transistor 277 to define a unity gain voltage follower. The output voltage signal taken at the emitter of the transistor 277 is co~nected to the motor drive 93 to drive the drawworks motor 92 at a speed related to the output of the integrator-amplifier network 218M.
Detailed descriptions of the brake control subsystem 105, the motor cont,rol subsy.ste~n 106 and the logic 109 are now set forth.

a, a, --,,~.

BRAKr. CONTROL StJBSY~TFM SC~ MATIC

Referring to Figure 8, the detailed description of the brake control subsystem 105 is shown. rI'he COMMAND
POSITION signal is input on the line ll~B (Figure 3) ~nd connected through a resistor 28~ to the invertin~3 input of the differential amplifier 200s. The ACTUAL POSII'ION signal is input on the line 116B and is presented to the non-inverting input of the differential amplifier 200B through the ~esistor 285. The non-inverting input is connected through a resistor 286 to ground potential. Both the ACTUAL
and COMMAND POSITION signals are current signals. They are each converted to an appropriate voltage for application to the differential amplifier 200B by the resistor arrangement of 287, 288, 289 and 290 connected, as shown, in pairs between the position input signals and a negative potential.
The output of the differential amplifier 200B is fed back to the inverting input through a resistor 291. This resistor, in combination with the resistor 284, determines the amplifier gain. A capacitor 292 reduces the amplifier'~
high-frequency response. The output is also taken by a line 293 to the non-inverting input of a final position com-parator 294, discussed in more detail herein. The output of the differential amplifier 200B is connected to the potentiometer (Kp)B. An adjustable portion of the position error signal is presented throu~h a re~ tox 295 to the non-inverting input of the amplifier 230B. Th(~ inverting input of the amplifier 230 ir~ connected through a reC;istor 296 to the wiper of a potenti.ometex 297, th~ high end of which is tied to a negative potential through a resistor 298. The purpose of the potentiometer 297 is to set a - ~5 ~

..

~l~3~'7~

minimum velocity. rL~he outpu-t of the amplifier 230B is fed back through a resistor 299 to the inverting input thereof.
This, in comblnation with the resistor 296, determines the amplifier gain. The output of the amplifier 230B is tied through the resistor 231B to the node 201B which is also connected to the output of the amplifier 204s through the diode 239B. The COMMAN~ VELOCITY signal is input from the line 132B -to the non-inverting input of the amplifier 204B
through the resistor 300. The inverting input is con-nected to the output through the resistor 301 and the diode234B. This effectively fixes the amplifier gain at unity.
Since the output is taken at the junction of the resistor and the diode, the effects of diode voltage drop are eliminated. The limiting effect of the diode 234B in combination with the amplifier 204B on the potential at the node 201B has been previously discussed.
The signal at node 201B is connected to the summing junction 202B through the resistor 232B. At the summing junction the composite position error plus velocity signal 20 is formed, as discussed, by the summation of the adjusted position error signal with a signal representative of the ACTUAL VELOCITY ta~en from the input line 134B through the resistor 233B. The velocity signal may be derived from the drum tachometer 94, or, alternatively, from the block position transducer 83. The ACTUAL VELOCITY siynal is applied to the inverting input of a comparator 302 by a line 356, as discussed hcrein. ~rhc signal at the summinCJ
junction 202B iS presented to the inverting input oE the difference amplifier 208B, The non-inverting input is con-nected to ground through a resistor 303. ~S discussed,however, the non-inverting input of the difference amp-lifier 208B is also presented with an adjusted portion of a load factor signal.

;r~ 3~

ACTUAL LOAD signals are input on the line 136B arld the appropriately scaled (INITIAL LOAD) (Kl) signal is input on the line 138B. These are summed at the inverting input of the amplifier 212B through the resistors 235B and 236B, respectively. The non-inverting input of the amplifier 212B
is connected to ground potential through a resistor 304.
The output of the amplifier 212B is fed back to thel in-verting input through a loop including the diode 305 ancl the resistor 306. The output of amplifier 212B i6 connected through the diode 237B to the potentiometer (KL)B. The cathode of the diode 237B is connected with the inverting input o~ the amplifier 212B through a resistor 307. The wiper of the potentiometer is connected through a resistor 308 to the non-inverting input oE the amplifier 214B. The inverting input is connected -to ground potential through a resistor 309. The output of the amplifier 214B is fed back to the inverting input thereof through the resistor 310 and is also connected to the non-inverting input of the differ-ence amplifier 208B through a resistor 310A.
The output of the difference amplifier 208B is con-nected to the integrator-amplifier network 218B. The out-put is also fed back to the inverting input through the resistor 311. The integrator-amplifier network 218B takes the output of the difference amplifier 208B from the node 238B (Figure 8B) along parallel conduction path~. Once such path includes the potentiomcter (KE,F)B, the wiper of which is connected to the inverting input of the ampliEier 239B
through a resistor 312. The non-inverting input i~ tied to ground potential through a resistor 313. The output of the amplifier 239B is fed back through a resi.stor 3L~ to the inverting input thereof and is also connected to the node 243s through the resistor 242B. The second parallel path ~ , ti7~3 includes the potentiometer (KINT)B, the wiper of which :is connected through a resistor 315 to the :inverting input of the integrating amplifier 241B. The non-invertin~ input of the amplifier 241B is -tied to ground potential throu~h a resis~or 316. The offset of the integrating amplifier 241B
is set to zero by a potentiometer 317. I'he output of the integrating amplifier 241B iS fed back throuyh a capacitive network 318 to the inverting input thereof. The output is also connected to -the node 243B through the resistor 240B.
The signals at the node 243B are appliecl to the inverting input of the amplifier 244B. The non inverting input is tied to ground poten-tial through a resistor 319. The out-put of the amplifier 244B is fed back -to the inverting inp~t through a resistor 320.
The output 220B of the integrator-amplifier net~ork 218B iS connected through a potentiometer 321 and the re-sistor 245B to the inverting input of an amplifier 322.
This input signal is summed with a reference signal de-veloped across the zener diode 331 and is applied through the combination of resistors 329 and 333 and a potentiometer 330. The network including amplifiers 322 and 324 forms a voltage-to-current converter. The output of the amplifier 322 drives the NPN-type transistor 324 connected as an emitter follower. The col]ector of the transistor 324 is tied to a positive potential. The signal at the emi.tter of the transistor 324 is fed back to the inverting input of the amplifier 322 through a resistor network 325. These re-sistors, in combination with the r~sistor 245B and the potentiometer 321 establish the conversion gain of the network 246B. The output of the brake control subsystem 105 is -taken from the emitter of the trarlsistor 324 at the junction of the resistors 326 and 327 an~l is carried by the - ~3 -output line 158. ~rhe emitter of the transistor 324 is connected to the ungrounded side of the resistor 323 through the series connection of the rcsistors 326 and 327 and a potentiometer 328. This combination of resistors makes the output on the line 158 a constant current source.
The potentiometer is adjusted to make the output current independent of load resistance.
The inverting input of the amplifier 322 is connected through the resistor 329 and the potentiometer 330 to the anode of the zener diode 331. The anode of the diode 331 is also tied to a negative potential through the resistor 427B.
The resistor 333 shunts the resistor 329. This network acts to set an initial signal output in the line 158.
A brake control override 334 is operative in response to a BRAKE RUN signal from the logic 109 on the line 142 or in response to an override signal from the motor control subsystem 106 on the line 147 to impose a suitable voltage on the inverting inputs of the amplifiers 239B and 241B so that the brake is asserted regardless of the total error signal present at the output of the difference amplifier 208B. The line 142 BRAKE RUN from the logic 109 is con-nected through a diode 335 and a node 336 to switches 337 and 338. The override line 147 from the motor control subsystem 106 is connected to the node 336 through a diode 339. Both of the switches arè connected at one sidc to ~
positive potent:ial and at the other ~idcs, throucJh resistors 340 and 341, respectively, to the invertinc3 inputs of the amplifiers 239B and 241B. When encrgiæed, the po.sitive potentials are presented to the amplifiers such that the brake is imposed - i.e. the brake is applied - regardless of the magnitude of the total error output siyn~l from the difference amplifier 208B.

_ ~9 _ ~3~733 Another override circuit of ~ sort is pro~ided at 342. This network respvnse ~o a MOTO~ ~UN signal from the logic 109 on the line 140s to release the brake despite the signal input to -the amplifier 244s. The logic 10'3, in general, outputs a MOTOR RUN signal when in receipt of a MOTOR MODE SE1ECT signals, as is discussed fully hercin.
The line 140B ls connected to a switch 343. The switch 343 is connected at one side to a positive potential and at the other side through a resistor 344 to the inverting input of the amplifier 244B. When -the switch 343 is energized, the positive potential is applied to the inverting input of the amplifier 244B. This has the effect of maintaining the output of -the amplifier 244B at zero volts. A ~0mA output signal from the converter 246B to the output line 158 due to the reference signal input is effective to fully release the brake. The zener diode 345 prevents the output of the amplifier from yoing negative and limits the positive output of the amplifier 244B to the zener voltage. The application of the MOTOR RUN output on the line 140B from the loyic 109 is discussed herein.
Various other components illustrated in Figure 8A, but not as yet discussed, are now set forth for future reference. The positlon error signal from the differential amplifier 200s on the line 293 is applicd to the inverting input of the position comparator 294. A signal derived from a final position potentiometer 351 aonnecte(l to a positive potential through a resistor 352 is appliccl through a resistor 350 to the non-invertirl~ input o~ the comparator 294. The potentiometer 351 sets a predetcrm:ined voltage siynal so that when the position of the ~Jlock is within a precletermined close distancc o~ thc con~mclnd position, the cornparator ~sa output signal conn~cted through a resistor 353 and a diode 354 switches from a logic 0 to a loyic 1, This signal is carried by a line 355 into the logic 10g.
Similarly, a brake rel~ase cornparator 302 derive~
its inverting inpu-t from the ACTUAL POSITION signal on the line 356. The non-inverting input is connected ~hrough a resistor 357 to a point be-tween resistors 358 and 359 con-nected in series between a positive potential and ~roun~.
The comparator 302 is connected throuyh a resistor 360 and a diode 361 and carried by a line 362 to the logic 109.
This establishes a switching threshold vol~age for the comparator 302, and thus a threshold velocity. Durinq the motor mode, the ACTUAL VELOCITY is positive. During the motor mode, when the velocity exceeds the threshold velocity, the comparator switches so that the line 362 switches from a logic 1 to a logic 0. The function of this network is to "release" the brake above some threshold velocity. Note that the line 355 and the line 362 have been omitted from Figure 3 for clarity.
The CREEP FLIP-FLOP line 152 output from the motor control subsystem 106 (Figure 3) is input to the brake control subsystem 105 and to a switch 365 thereof. The switch 365 is connected between the inverting inputs of the integrating amplifier 241B (Figure 8B) and the difference amplifier 208B output, and in series with a resistor 366 (Figure 8A). A junction diode 368 is connected between the junction of the switch 365 an~ the rcsis~or 366 an(l ~round.
This network is providcd so that when a skJrllll is prcsent on the line 152 the inteyrator gain is e~fectivcly in-creased so that the integrator-amplifier 2]8B responds more rapidly to the srnall creep velocity sl~3nal.

:' ~ ,i -~3~

LOGIC O~'E~ATION
__ The logic 109 includes input lines 144 (Mo~r SELECT) and 145 (BR~KE MODE SEI.ECT) from the computer channels B and C respectively (Figure 3). Output lines 140B (MOTOR RUN) and 142 (BR~KE RUN) from the lo~ic lOg are connected within the brake control subsystem l05 as dis~
cussed above. The output line 140M (MOTOR RUN) (~'igure 3) from the logic 109 is input to the motor control subsystem 106. The logic 109 includes cross-coupled NAN~ gates 370C
and 370D with inverter gates 370A and 370s. These are connected to form an EXCLUSIVE OR function. The purpose of that portion of the logic 109 is to ascertain that only one signal-either MOTOR MODE SELECT from channel B of the computer of BRAKE MODE SELECT from channel C - is effective at one time. If both are asserted, for any reason, neither is effective due to the EXCLUSIVE OR gating described. The logic also includes NOR yates 382, 384 and 386. The NOR
gate 382 is input with one output of the NAND gate 370C and at the other with the line 355 from the final position comparator 294. The NOR gate 384 is input at one terminal with the output of the NAND gate 370D and at the other with the line 362 from the velocity comparator 302. The output of the NOR gate 384 is carried from the logic 109 on the line 140B (MOTOR RUN) to the switch 343 to assert the MOTOR
RUN function thereof. The OlltpUt of the NOR yate 384 is also input to the NOR gate 386. The other input to the NOR
gate 386 is derived from the output of the NOR gate 382.
The output of the gate 386 is carried by the line 142 (B~KE
RUN) to the brake control override 334 to assert the BRAKE

RUN function thereof.

,~ , .

~3~733 The loyic 109 i.s respectively input on th~ lines 1~4 and 145 with MOTOR MOI)~ SELECl~ or B~.hKE MODE SELECT si~na].s from channels B and C of the computer 40 (Figure 3).
Output lines 140B and 142 from the logic 109 carry MOTOR
RUN (line 140B) and BRAKE RUN (line 142) to the overrides 342 and 334 connected within the brake control subsystem 105, as discussecl above. The output line 140M (MOTOR RUN) (Figures 3 and 8A) from the logic 109 i.s .input to the mc>-tor control subsystem 106.
The tied inputs of the inverter yate 370A are con-nected to the line 145, BRAKE MODE SEL~CT, through a diode 371 and a capacitor 372. The inputs are normally high, due to their connection to a positive potenti.al connected through a resistor 373. The tied inputs of the inverter gate 370B are connected to the line 144, MOTOR MODE SELECT, through a diode 374 and a capacitor 375. These inputs are normally high due to the positive potential connected through the resistor 376. This portion of the l.ogic 109 functions to accept only one signal-either MOTOR MODE SELECT
from channel B or BRAKE MODE SELECT from channel C - from the computer at one time. If, for any reason, the lines 144 and 145 are both asserted (logic 0), the EXCLUSIVE OR
functions to make neither signal effective. Note the output of the NAND gate 370D is connected to the motor control sub-system 106 on the line 140M.
As noted, the logic 109 also includes ~OR c3ates 382, 384 and 386. Thc NOR ~ate 382 derivcs its :inputs fr(>m thc output of the NAND gate 370C and from the final position comparator 294 on the line 355. The output of the NOR gate 372 is one input to the NOR gate 386.
The NOR GATE 3~4 derives onc input from the output of the inverter gate 370B. The second inputs to the NOR gate 384 iS derived from the veloc:ity comparator 302 on the line ~ 53 ~

,~

362. The output of the NOR gate 384 is the second :input to the NOR GATE 386, and also i5 connected to the line 140B
(MOTCR RUN) leading from -the loyic 109 to the switch 3A~
in the override 342. The output of the NOR gate 386 is connected by the line 142 (BR~K~ ~UN) from the logic 109 to the override 334 to assert the BRAKE RUN function.
If the computer asserts the B~KE MODI;: SEL,E:C'r line 145 (i.e., the block is travelliny downward) and if this is the only asserted signal (as checked by -the EXCI,USIVE OR) the motor control subsystem 106 is disenabled on the line 140M and the NOR gates 382, 384 and 386 operate to swi-tch the line 142 to logic 0, thus not asserting the BRAKE RUN
function (on the line 142). During the greater part of the downward journey of the block, the brake control subsystem , 105 operates on the basis of the total error to modulate the brake and control the block velocity within the command limits. As the block approaches the final position, an output from the final position comparator interacts with the logic 109 to assert the BP~AKE RUN function (on the line 142) and sets the brake to stop the block.
Therefore, with a BRAKE MODE SELECT input on the line 145, and MOTOR MODE SEL~CT on the line 144 not asserted, for the greater part of the downward movement of the block the following conditions would prevail: The A and B
terminals of the inverter gate 370B and the B terrninal of the NAND gate 370C are at loyic 1 condition. Both terminclls ;~ of the inverter gate 370A and the ~ terminaL oE the NAND
gate 370D are in the logic 0 condition.
The output o~ the invert~r gLIte 370~ i9 therefore a logic 1, placing this condition (logic 1) at the ~ input of the NAND gate 370C. The output of the inverter gate 370B

is a loyic 0, placing this condition at the n input oE the ~3t~33 NAND gate 370D. Thus, the output of the NAN~ gate 370C is at logic 0 ancl the output of the NAND c3~te 370~ is at logic 1. These are the conditions at the A input o~ the NOR ga~e 372 (logic 0 from the output of the NAND gate 370C) and at the A input of the ~OR gate 374 (logic ] from the output of the NAND gate 370D). Note that the logic 1 at the output of the NAND gate 370D is carried by the line 140M to the mo-tor control subsystem 106 enabling the motor override network therein.
With regard to the NOR gate 384, -the presence of a logic 1 at the A input thereof insures that the output thereof is a logic 0, despite the signal presented at the B inpu-t lèading from the velocity comparator 302 on the line 362. Thus, in the brake mode, the velocity comparator 302 is not effective in releasing the brake. Thus, the output from the NOR gate 38~ and the B input of the NOP~
gate 386 are both at logic 0 as long as a BRAKE MODE SELECT
conditlon is presen-t on the line 145. Accordingly, the output line 140B from the logic 384 to the override 342 is a logic 0. That is, the MOTOR RUN function is not asserted.
Note that the output of the velocity comparator is not effective in a BRAKE MODE SELECT condition.
" With regard to NOR gate 832, the A input thereof i5 at a logic 0 at all times that a BRAKR MODE SELECT is asserted on the line 145. The B input to the NOR gate 382 is derived from the output of the ~inal position comparator 294 on the line 355. Therefore, during the greater portion of the downward travel of the block, the output on the 355 to the B input o~ the NOR gate 382 is at a logic 0. Thus, the output of the NOR gate 382 is a logic 1. rrhe logic 1 input condition to the A input of the NOR c3ate 386 results in the situation that as long as the block is c3reater than ~L~3~iJ33 the threshol~ di,stance (se-t by the potentiometer 35L) from the final, command position, the line 142 ~B~KE RUN) i5 at logic 0, allowing the normal control subsystern functi,ons derived from the magnitude of the tota], error signal (E,T)~
to be controlling the velocity of -the block.
Ilowever, as the block approaches the final position, the output of the comparator 294 switches and provides a logic l output on the line 355 connected to the s terminal of the NOR gate 382. This results in the output thereof, and the A input to the NOR gate 386, switching to a ]ogic 0.
As a result, the output of the NOR gate 386 goes to a loc3ic 1, and BRAKE RUN output lirle 142 is energized. With a logic l at the output of the NOR gate 386 and on the line 142, the switches 337 and 338 are turned on. Wi-th such an occurrence full braking is applied since the positive inputs -to the amplifiers 239B and 241B overriding the normal hrake control subsystemt and setting the brake when the position error has reached an acceptably low value.
If the computer asserts the ~OTOR MODE SELECT line (i.e., the block is hoisted upwardly~ and if ~his is the only asserted signal (as checked by the EXCLUSIVE OR) the motor control subsystem is enabled on the line 140M (MOTOR
RUN). However, the brake is kept asserted by the logic 109 even though the computer has asserted the motor mode, until the block reaches a predetermined threshold velocity. This ` is implemented as set forth herein.
With the MOTOR MODE SELECT sic3nal on the linc 144, the A and B terminals to the inverter gatc 370A are at a logic 1 condition. I,ikewise, the ~ input of thc3 NAND gate 370D. The A and B inputs to the invcrtcr gate 370B, and the B input to the ~JAND gate 370C, are at a logic 0 condition. Thus, the output of the i.nverter c3ate 370A, , - 56 --and the A input to the N~ND gat~ 370C, a~e at a ]oglc 0 condition. Accordingly, the outpu-t of the NAND gate 370C
and the A input to the NOR gate 382 are in a loqic 1 condition. The output of the inverter ga-te 37OB, and the B input of the NAND gate 37OD are in a loyic 1 condition.
Accordingly, the output of the NAND gate 370D and the A
output to the NOR gate 383 are in a logic 0 con~ition. The output of the NAND gate 370D is conducted to the motor control subsystem 106 on the line 140M. The motor is, in effect, enabled because the MOTOR RUN line 140B is at logic 0.
With respect to the NOR gate 382, as long as a MOTOR
MODE SELECT condition is asserted on the line 144, the A
input is a logic 1. The output of the NOR gate 382, there-fore, is at all times a logic 0, regardless of the signal present on the line 355 from the final position comparator 294. Thus, the position comparator in the brake control subsystem 105 is not effective during a MOTOR MODE SELECT
condition. The A input to the NOR gate 386 is at all times a logic 0.
With respect to the A input of the NOR gate 384, it is at all times a logic 0. However, as long as the velocity at which the motor lifts the block is less than the velocity represented at the inverting input of the comparator 30~, the output thereof on the line 362 connected to B input of the NOR gate 384 is a logic 1. Therefore, the output of the NOR gate 384 is a logic 0 as long as the velocity of the block is below the threshold. The E3 input of the NOR

gate 386 is also a logic 0, resultiny in a logic 1 output therefrom. Accordingly, the line 140B (MOrrOR RUN) is not asserted (due to logic 0 at the output of the NOR qate 384) while the BRAKE RUN function at the output of the NOR gate - 57 ~
t l 386 on the line 142 is asserted. The resu]t is when the motor mode is selected (the overric~ beiny clisenah]ed) th~
brake is asserted as lony as the velocity is below -the de~ined threshold.
When -the block is lifted a-t a velocity ~Y~ceediny the threshold the output of the velocity comparator 302 switches, placing a logic 0 at the B input of the NOR gate 384~ The output thereof shifts to logic 1, asserting the MOTOR RUN function on the line 140B. The switch 343 is turned on overriding the signals presented to the in-verting inputs of the amplifier 244B. Thus when the velocity exceeds the predetermined threshold velocity the override 342 is enabled in the manner described to prevent unnecessary wear on the brake as the block is raised.
Further the B input to the NOR gate 386 is also switched to the logic 1 state thereby placing a logic 0 at the out-put thereon disenabling the BR~KE RUN function on the line 142.
Of course during this period of the block travel the velocity is controlled by the time integral of the total error (ET)M as discussed. As the block nears its final position, the total error (ET)M tends to go positive thus decreasing the velocity of the block. As the velocity of the block falls below the threshold set by the velocity comparator 302 the output thereof switches bac~ to a I.ogic 1 changing the B input to the NOR gate 384 and switchinc3 the output of the NOR gate 384 to a logic 0. This dis-enables the MOTOR RUN line, and switches the output of the NOR gate 386 to a logic, enabling the l:ine 142 (B~KE RUN) to set the brake. As will be seen herein, within the motor control subsystem 106, a position comparator, similar to that discussed above is operable when the block approaches

- 5~ -;i733 within a predetermined distance of the commarld position, : to assert a motor overrid~ and top the holsting mo-tion.

. MOTOR CONTROL SUBSYSTEM SCHEMATIC
__, Referring now to Figure 9, a detailed description of the motor control subsystem 106 is set forth. The basic ; features of the motor control subsystem 106 are similar to those of the brake control subsystem 105, as seen in earlier discussions.
The COMMAND POSITION signal is input on the line 115M (Figure 3) and connected through a resistor 402 to the inverting input of the differential amplifier 200. The ACTUAL POSITION signal is input on the line 116M and is presented to the non-inverting input of the differential amplifier 200M through the resistor 403. The non-inverting input is connected through a resistor 404 to ground poten-tial. Both the ACTUAL POSITION and the COMMAND POSITION
signals are current signals and are converted to an appro-priate voltage for application to the differential amplifier 200M by the resistor arrangement 405, 406, 407 and 408, connected in pairs between the input signals lines 115M and 116M and a negative potential. The output of the differ-. ential amplifier 200M iS fed back through a resistor 409 to the inverting input. This resistor, in combination with -the resistor 402, establishes the ampli~ier gain. The position error signal output is taken by a line 410 to the non-inverting input of a poRition comparator 412. The in- :
verting input of the position comparator 412 ig furnished with a signal derived from a potentic~meter 414 connected to a negative potential through a resistor 415. The wiper of the potentiometer is connected through a resistor 416 to ` F - 59 -3;:~
the invertin~ input. 'I'he E)ositior1 cornp~lrator 4l2 outl~utC; a signal through a diode ~17 to a line ~lg ~hen the position error siynal at the outpu-t of the differential arnplifier 200M is less than the voltage level as set ~y the poten-tiometer 414. As seen herein, this condition overrides the motor control to shut off the motor.
The output of the differential amplifier 200M is connected through a resistor 420 to the potentiome-ter (Kp)M.
An adjustable portion as set by (K )M of the position errox signal is applied throuyh a resistor 421 to the non-inverting input of the amplifier 230M. The inverting input of the amplifier 230M is connected throuyh a re-sistor 422 to the wiper of a potentiometer 423 tied to a positive potential through a resistor 424. The purpose of the potentiometer is to set a minimum velocity signal. The output of the amplifier 230M is fed back through a resistor 425 to the inverting input thereof. The output of the amplifier 230M is tied through the resistor 231M to the node 201M to which is also connected the output of the amplifier 204M through the diode 234M. The limiting effect at the node 201M of the combination of the amplifier 204M
and the diode 234M has been discussed earlier in con-nection with the simplified signal diagrams of the draw-works motor control.
The signal at the node 201M is connected to the summing junction 202M through the resistor 232M. At the summing junction 202M the composite position error plus velocity signal, (Ep~v)M, is formed, as discussed, by the summation of the adjusted position error signal with the signal representative of the ACTUAL V~I.OCITY taken from the input line 134M through the resistor 233M. The velocity signal may be derived from the drum tachometer 94 or, -- ~0 ~

i7~3 alternatively, frorn the hlock position transducer ~3. The ACTUAL VELOCITY signal is applied to the invertiny terminal of a comparator 430, as is discussed herein, The signal at the sumrning junction 202M is applied to the inverting input of the difference amplifier 208M. The non inverting input is connected to ground potential through a resistor 431.
As discussed, however, an adjusted portion of a load factor signal is also applied to the non-invertiny input, An ACTUAL LOAD signal is applied on the line 136M
and the appropriately scaled INITIAL LOAD- (-K2) signal is input on the line 138M. These load signals are surnmed at the invertlng input of the comparator 212M through the resistor 235M and 236M, respectively. The non-inverting input of the amplifier 212M is connected to ground through a resistor 433. The output of the amplifier 212M is fed back to the inverting input through a loop including the diode 434 and the resistor 435 as well as the loop in-cluding a resistor 436 and a diode 437. These components in combination with the input resistors 235M and 236M
20 establish the amplifier gain. The output of the amplifier 212M is connected to the potentiometer (KL)M~ The output is taken from the junction of the resistor 436 and diode 437 to remove the effects of diode 437 voltage drop. The wiper of the pQtentiometer (KL)M is connected through the resistor 437 to the non-inverting input of the amplifier 214M. The invertiny input of the arnplifier 214M is con-nected to ground potential through a resistor 438. The output of the amplifier 214M is fed back to the invertiny input through a resistor 439 and is al~o tied to the non-30 inverting terminal of the difference amplifier 208M.

The output of the difference amplifier 208M is con-nected to the integrator-amplifier network 218M (Figure 9B).

`i`'r- - hl. ~
..~.

~L~3~73~
This output is ~lso fed back to the inverting inpllt through -the resistor 440. ~he inte-~rator-amplifier network 218M takes the output of the clifference amplifier 208M from the node 238M along two parallel paths. Onc path inc:Ludes the potentiometer (KFF)M, the wiper of which is connected to the inverting input of the differential amplifier 244M
through a resistor 441. rrhe second parallel pa-th includes the potentiometer (KINT)~, the wiper of which is connected through a resistor 442 to the inverting input of the integrating amplifier 241M. The non-invertinc~ input is tied to ground potential through the resistor 444. A
potentiometer 445 sets the zero point of the integrating amplifier 241M. The output of the integrating amplifier 241M is fed back through a capacitive network 446 to the inverting input thereof. The output of the integrating amplifier 241M is connected through a resistor 447 to the non-inverting terminal of the amplifier 244M. The non-inverting terminal is also tied to ground potential through a resistor 448. The circuit details of the motor control subsystem differs from that of the brake control subsystem in that the parallel paths within the integrator-amplifier network 218M are not summed at a node 243B.
Instead, the output of the integrating amplifier is com-bined differentially with the potentiometer output in the amplifier 244M. The output of the amplifier 244M is fed back through a parallel path including the resistors 449 and the diode 450.
The output 220M of the inteyrator-amplifier network 218M is connected through the resistor 245M to the voltaye-to-current converter 246M. The convertcr 246M is sub-stantially identical to the inverter described earlier in connection with the brake control subsystem 105 except for .j,,, ~,L, .

~L~3~;~7~3 the magnitude of the reference vol-tage appLied to the amplifier 453. The resistor 245M is connected to a poten~
tiometer 451 and a resistor 45~ through which it is ~lso connected to the inverting input of an amplifier 453. ~he non-inverting input of the amplifier 453 is tied to ground through a resistor 454. I~he output of the amplifier drives a transistor 455 of the NPN type, the collector of whlch is connected to a positive potential. The emi-tter of the transistor 455 is fed back through a feedback resistive network 456 to the inverting input. The emi-tter is con-nected to the high side of the resistor 454 through a series connection of resistors 457 and 458 and a potentio-meter 459. The output of the motor control subsystem is taken at the junction of the resistors 457 and 458. I'he output line 159 has a relay contact operated b~ the coil 112 therein.
An initial voltage condition is applied to the in-verting input of the comparator 453 and includes a resistor 461 and potentiometer 462 in series with a negative poten-tial. A resistor 463 shunts the resistor 461. The purpose of this network is to supply a reference voltage so as to obtain a 4mA current output under a zero signal input condition.
The motor control subs~stem 106 is connected (Figure 9B) to the computer output channe] I through the line lSl.
This line is connected throu~h a diocle 470 to th~ inputC; of a NAND gate ~71 having ~oth the inputs tied to a positive potential through a resistor 472. A s~7itch 473 is tied to a positiv~ potential on one side, and on the other through a resistor 474 to the non-inverting input of tile comparator 453 within the voltage-to-current converter 246M. ~pon receipt of a CREE,P TO ENGAGE CLU'rC~I command signal from the ~9 ~3~73~

computer on the line 151 lline 151 ~oes to loc3ic 0), a predetermined current signal is output to the motor drive 93 on the line 159 to move the motor 92 vert~ slowl~ to permit the clutch to engage for further hoisting operations.
The motor control subsystem 106 has a CREEP control network 480 (Figure 9A) connected therein. The network includes the inverting amplifier 430. The ~CTUAL VELOCITY
signal on the line 134M is applied to the non-inverting input through the resistor 481. The inverting input of the comparator 430 is tied to the ground potential through a resistor 482. The output of the comparator is fed back to the inverting and non~inverting inputs through the paths including the diode 483 and resistor 484, and the diode 485 and the resistor 486, r~spectively. The output of the amplifier 430 is connected through a resistor 487 to the inverting input of a creep comparator 490. The non-inverting input of the comparator 490 is connected through a resistor 491 to a voltage divider network including re-sistors 492 and 493 connected between a positive and ground potential.
The output of the creep comparator 490 is connected through a resistor 495 to the reset input of a creep flip-flop network 500. A diode 496 with a capacitor shunt 497 is connected between the reset input and ground. The set input of the flip-flop network 500 is connected through a diode 502 to the CREEP signal (channel ~1) from the computer on the line 150. The output o the fllp-flop network 500 connected to the input of a switch 503. The output of the `~ amplifier 208M i5 connected to a resiqtor 504A and a diode 504B in series. The switch 503 is connected between the junc-tiO~I o the resistor 504A and the diode 504B and the non-inverting input of the integrating amulifier 241M. The - 64 ~

~13~33 output of the Elip-flop network 500 is also connected through the line 152 ~o ~he s~itch 365 in the brak.e control subsystem 105 (Figure 8~).
The purpose of a CRE~P command is to slowly raise the travelling block so as to acquire the drill string load wi~h the elevator as discussed in conncction with th~ operation section earlier.
Upon recelpt of the CREE,P COMM~ND a signal a-t the set input from the line 150 causes an output from -the f:Lip-flop network 500 to switch to loyic 1. This closes the switch 503. This effectively increases the gain of the in-tegrating amplifier 241M. At the SaJne time, the output on the line 152 from the flip-flop network 500 closes the switch 365 in the brake control subsystem 105 to increase the gain of the integrating amplifier 241B (Figure 8~. Thus, the CREEP
command signal, in conjunction with other signals, is used to slowly raise or lower the elevator to acquire or to release a load, as the case may be. Higher velocities are programmed after acquiring or releasing the load. When the ~` 20 velocity exceeds a creep threshold velocity determined by -the combination of rçsistors 492 and 493, the comparator 490 switches to logic 0 to reset the flip-flop network 500 to the normal condition.
A motor control override network 510 (Figure 9B) in-cludes a primary and secondary override path connected to the MOTOR RUN line 140M. The line 140M is output from the ~ logic 109 and when the mo-tor control subsystem 106 is dis-; enabled the logic 109, the line 140M has a logic high signal `` thereon. The line 140M is connected to a diode 51l, the output line from the diode 511 bein~ indicatcd as MOTOR OFF
line 512. The primary override path includes a zener diode 513 connected through a resistor 514 to the base of an NPN

~5L 3~i~33 transistor 515. The emitter of -the transistor 515 is con-nected to a neg~tive potential. The ernitter o the tran-sistor 515 is tie~ to the anode of the ~ener diode 513 by a resistor 516. The collector of the transis-tor 515 is con-nected through a resistor 517 to a diode 518. The primary override is connected to the invertinc3 input o~ the inte-grating amplifier 241M. The second path of the override 510 includes a switch 524 connected between the junc~tion of resistors 525 and 526 and ground. The resistor 525 is tied to a posi-tive potential. The non-inverting input o~ the amplifier 527 is tied to ground through resistor 52~. The output o~ the amplifier 527 is applied through a diode 529 to the inverting input of the voltage-to-current converter 246M. The output is also fed back through the inverting input to a resistor 530.
When an appropriate signal (a logic 1) is received from the logic 109 on the line 140M, -the motor control over-ride 510 is actuated to effectively turn off the motor, regardless of the output of the amplifier 244M. When the signal on the line 140M is applied to the diode 511 the out-put is a signal on the MOTOR OFF line 512 which renders the transistor 515 conductive, effectively setting the output of the integrating amplifier 241 to zero. The secondary path, when in receipt of the MOTOR OFF signal on the line 512, renders the switch 524 conductive, groundiny the junction o~ the resistors 525 and 526. This holds the lnput to the vo]tage-to-current at zero. This precaution i3 taken since there may still be a sic~nal at the output of the ampli~ier 24~
even though the inteyrating ampLifier 24lM is overridden.
The MOTOR OF'F line 512 càn be energized in ways other than by receipt of a computer command via the logi( 109.

.

~:~3~733 In order -to shu-t the motor o~f when -the position of the block comes within a predetermined close tolerance to the command position, an output signal from the positiorl com-parator 412 on the line 418 operates the override 510 in a manner e~actly as discussed.
Further, when the operator asserts the override on the line 104, a signa] is applied to an optical coupler 536 (Figure 9A) acting as a switch. When energized the switch 536 connects a positive potentia~ to the line 512 through a diode 537. A resistor 538 ties the line 512 -to ground.
Upon receipt of a manual override signal, the switch 536 is conductive, placing a high siynal on the line 512 to turn the motor off by -the override 510 in a manner discussed above. At the same time, the line 147 (OVERRIDE) is at logic 1 due to its connnection to the switch 536, thereby asserting the override network 334 (Figure 8).
Having completely discussed the brake control sub-system 105, the motor control subsystem 106, and the logic :~ .
109, attention is directed to Figure 10, which is a ~et~iled 2u schematic diagram of the velocity comparator 108.

.~; ' ,~
: ~`

, .

L3~i7~3 VELOCITY COMPARATOP~

Shown in Figure 10 is a detailed schema-tic diagram of the velocity comparator 108 utilized in the drawworks control system 21. As seen from the block diayram Figure 3, the velocity comparator 108 is input from the computer channel G on the line 165 wi-th a 4-20mA signal representative of the COMMAND VELOCITY, the veloci-ty at which it is desired to move the travell.ing block 68 from a first to a second elevation within the rig or derrick 20(Figure 2). With reference to Figure 10, the current input signal is taken on a line 570 and converted to a voltage by the action of the resistor 571 connected between the line 570 and a negative potential. The resulting voltage signal is filtered by a filter 572 comprising a resistor 573 and a capacitor 574 and is applied to the non-invertiny input of an amplifier 575. The output of the amplifier 575 is fed back to the inverting input through a resistor 576, and is also con-nected to the output line 132 which carries the 0-10 volt COMMAND VELOCITY signal to the brake control subsystem 105 and the motor control subsystem 106, on the lines 132B and 132M respectively.
The velocity comparator 108 is also input, on the line 166 with a bi-polar voltage signal derived from the drum tachometer 94. The magnitude of the signal frorn the drurn tachometer 94 is representati.ve of the ~CTU~r, VFi,LOC:r'['Y at which the travelling block 68 (Figure 2) is moviny. The polarity of the voltaye signal on the line 166 is repre-sentative of the direction of travel of the travelLing block 68. Consequently, a positive polarity indicates an upward direction of travel with respect to the vertical axis of the ~.~3~733 derrick 20. An upward direction of travel, of course, implies that the motor mode is being ~sserted. A n~gative polarity of the signal on the line 166 indicates downward motion of -the travelling block. 68 with respect to the derrick axis, and implies the brake mode is being asserted by the computer.
The ACTUAL VEI,OCITY signal is f.iltered to remove com-mutating spikes by a sing:Le-pole, low--pass filter network 580 which is comprised of a resistor 581 and a capacitor 582. Diodes 533 and 584, respectively connected to positive and negative potentials, limit the signal to an amplifier 586. The filtered ACTUAL V~I,OCITY sic~nal is presented through a resistor 585 to the invertiny input of the ad-~ustable gain amplifier 586. The non-invertiny input of the amplifier 586 is connected to ground potential through a resistor 587. Connected in a feedback loop from the output of the amplifier 586 to the input thereof i5 an adjustable resistor 588. The gain of the amplifier 586 depends upon the setting of the resistor 588. The output may be adjusted to represent some nominal velocity, for example, 1 volt per foot per second.
The output of the amplifier 586 is appliecl to the - inverting input of a unity gain inverter amplifier 590 `~ through a resistor 591. The non-inverting input of the ` amplifier 590 is connected to yround potential through a res.istor 592. The output of the amplifier 590 is fed back to the inverting input thereof throw~,~h a re~sistor 593. The output is also connected by a line 594 to the output line 134, which is the AC'rUAL VEI.OCI'rY si~3nal, input to the brake control subsystem 105 and the motor control subsystem 106 on the lines 134B and 134M, respectivcly. With the circuit configuration described, the macJni.tu(le of the volt~ge signal .~

~L13~3~
on the line 134 represents the actual velocity of the bloc~., with a positlve polarity indicatiny llpward movemen-t at a negative polarity indicat:ing downward rrlotion.
The output of the amplifier ~86 i5 ta~en by a line 597 to a wrong dlrection indicatin~ network 59~ The network ; 598 includes comparators 5g9 and 600, and transistorci 601 and 602 connected in a logic OR configuration. The in-verting input of the comparator 599 and the non-inverting input of the comparator 600 are connected with the output of the amplifier 586 through resistors 603 and 604, respec-tively. The swi.tching points of the comparators are fixed at a nominal, predetermined threshold level, for example, a level corresponding to the velocity of about .5 foot/second.
The non-inverting input of the comparator 599 is connected to a positive voltage from a pos:itive potential source through the resistors 605 and 606. The inverting inpu-t of the comparator 600 is connected to a po-tential source through the resistors 607 and 608.
The output from the comparator 599 is connected through a diode 609 and a resistor 610 to the base of the NPN transistor 602. The junction of the transistor 602 and the resistor 610 is connected to ground potential through a resistor 611. The output of the comparator 600 is connected through a diode 612 and a resistor 613 to the base of the NPN transistor 601. The ~unction of the base of the tran-sistor 601 and the resistor 613 is tied to c3round potential through a resistor 614.
One or the other of the cornparators 599 or 600 is disenabled, dependent upon whether a si.gnal is present on the line 615 or 616~ The line 615 is connected to a line 167 tied to the MOTOR MODE SELECT li.ne 144 from the computer.
The line 616 is connected to a line 16~ tied to thc BR~KR

F

~67~3 MODE SELECT llne 145 from the computer. A diode 617 is connected in the line 615 to the junc~ion between the diode 609 and the resistor 610. A diode 618 is connected in the line 616 to the junction between the diode 612 and the resistor 613. The diodes 617 and 618 are normally forward biased, due to the connection of the anode of each diode 617 and 618 to a positive potential through the reslstors 619 and 620, respectively.
The output of the wrong direction network 598 is taken from the collector of the transistor 602 by a line 621.
The line 621 is connected to a line 169 connected to the com-puter input channel E. The network 598 operates to give a WRONG DIRECTION OF MOTION signal on the llne 169 if the motion of the block exceeds the nominal setting 0.5 fee-t/
second in the wrong direction. If this occurs, either transistor 602 or 601 ceases to conduct. A WRONG DIRECTION
OF MOTION slgnal is an interrupt condition, which disables all systems and halts the program. As with all other interrupt conditions, the entire system reverts to manual control and all automatic operation is halted.
The enabling signals on the lines 167 and 168 from the computer to the motor and brake control are applied, through the lines 615 and 616, respectively, to the com-parator outputs through the diodes 617 and 618. These signals enable the appropriate comparator so that only the "correct" wrong direct.ion is s~n~;ed. If, for exL~mple, the motor control sub.system is controllinc3 a hoistin~3 motion, the MOTOR MODE SELECT line 144 is low and the ~AKI. MODE
SELECT line 145 is high so that the output of thc comparator 599 is enabled and the output of the comparator 600 is no-t enabled. During hoistiny the ACTUAL V~LOCITY si~3nal polarity at the non-inverting input of the comparator 600 `s ~ -is nec3ative so that the transistor 601 would tend to be turned off, but the comparator output 600 is disconnected since the dio~e 612 is back-biase~. In this condition, the transistor 601 is maintained in conductlon ~y the siynal applied through the diocle 618. ~lowever, if the ~CTUAL
VELOCITY signal at the invcrtiny input of the comparator 699 should become pos:itive with a magnitude greater than ap-proximately 0.5 volt, indicating a "wrong" direction of travel, neither the diode 609 nor the diode 617 c~nducts, so that the transistor 602 becomes non-conductive, signaling an interrupt condition on the line 169 -to the computer. The "wron~" direction during a braking motion operates in a similar manner.
The output of the amplifier 590 is also connected to a zero velocity detector network 624. The network 624 in-cludes comparators 625 and 626 connected as zero velocity detectors. Since the output of the drum tachometer 94 is a bipolar signal, two comparators 625 and 626 are required, one effective for each direction. The inverting input of the comparator 625 is connected to the output of the ampli-fier 590 through a resistor 627. The non-inverting input is connected to a switching point voltage set by the "down"
potentiometer 628, connected to ground on one side and to a negative potential through a resistor 629 on the other. The output of the comparator 625 is fed back to the non-inverting terminal thereof through a 1oop including resistors 630 and 63:l, and a capaei-tor 632. This positive feedbaek loop provides h~steresis so that the comparator 625 will provide positive signal aet:ion with ~,iynals c1ose to the switehing point. The non invertiny input of the com-parator 626 is also connected to the output of the ampli-fier 590 through a res:istor 634. The invertiny input is ~3tj~33 connecte~d through a resistor ~,35 to a swltching point voltage set by the "up" potentiometer 636 which is connected to ground on one side and to a posit:ive potential throu(~h a resistor 637. I~he output of the comparator 626 is fed back to the non-inverting terminal thereof throuyh a loop including a resistor 638 and a capacitor 63'~. ~.[~his positive feedback loop insures that the compara-tor 626 will provide a .~ positive switching action at input siynals near threshold.
The outputs of the comparators 625 and 626 are con-nected, through diodes 640 and 641, respectively, ancl a through network including the resistor 642 and capacitor 649 to the base of an NPN-type transistor 645. The emitter of the transistor 645 is connected to yround. The cathodes of the diodes 640 and 641 are connected to ground through a resistor 646. The collector of the transistor 645 is tied to a positive potential throuyh a resistor 647. l'he col-lector of the transistor 645 is connected to the base of an NPN transistor 648. The emitter of the transistor 648 is tied to ground, with the collector thereof being tied to an output line 649. A diode 650 is connected between the line 649 and a positive potential. The output line 649 is con-nected to a line 170, ZERO VELOCITY, (Figure 3) to the computer channel D. The switching points of the comparators : 625 and 626 are set by the potentiometer~ 628 and 636, respectively, such that a predeterm:irlt3cl c;rnal:l velot:ity in either the downward or upward direttiorl is recocJrli7.cd a~ a zero velocit~ condit.i.on and a s:i.gncll. to that effcct ic;
applied on thc line 170 to the comr)llter. %ero vck~cit~ on the line 170, ind.icated hy the transi~tor 648 bt;~i.ncJ switched on, is only one o~ the two necessar~ conditions for the computer to recognize that the block i~ at its programmed destination.

~F

7~3 As will be set forth in detai.:L herein, th~ block position and speed tLansducer 83 outputs a 0-l0mA velocity signal on a line 171 to the velocity cornparator 1~ his unipolar current signal on the li.ne 171 is appliecl to a maximum velocity network 653. The current siynal is con-verted to a voltage signal by the action of a resistor 654 tied to ground potential. The voltage siynal is applied to the non-inverting input of a voltagc follower amplifier 655 through a resistor 656, with a capacitor 657 tied to yround potential. An adjustable maximum velocity signal clerived from a potentiometer 659 connected to a negative potential through a resistor 660 is applied to the non-inverting input of a voltage follower 662. The opposed polarity outputs of the voltage followers 655 and 662 are applied through re-sis-tors 664 and 665, respectively, and are sumrne~ at the inverting input of an amplifier 667 effectivel~ operating as a comparator. The non-inverting input is tied -to ground through a resistor 668. The output of the comparator is fed back to the non-inverting input thereof through parallel feedback paths including a resistor 669 and a capacitor 670.
The output of the comparator 667 is tied through a diode 671 and resistor 672 to the base of an NPN transistor 674. The emitter of the transistor 674 is tied to ground, while the output thereof is tied to a line 675. The line 675 is connected to an output line 172. This M~XIMUM V~L,OCITY
signal on the line 172 :is connected to the computcr in~ut channel F.
The maximum velocity threshold ~et by the l~otentio~
meter 659 is normal.ly yrea-ter than thc actucll velocity signal to the follower 655, so that the output of the cornparator 667 is at positive sa-turation, hold:iny the transistor 674 in conduction. However, if the Bl.OCK VrJI,OCI'rY ~rom the B.P.S.T.

- 7~ -t'~3 83 exceeds the thresholcl however, the trans:istor 57~ is cutof~. The indica-tion that the mclximurll velocity is e~.-ceeded is thus output to the cornputer or. the line.s 675 and 172. No-te that on both the lines 621 and 675, a normal ; condition is lndicated by current flow. When an abnormal condition is sensed, that curren-t signal drops to ~ero.
Diodes 677 and 678 are, respectively, tied between the lines 621 and 675 and a positive potential.

-,~t-! i 7~3 BLOCK POSITION AND SPF,ED TR ISDUCr,R

Referring to Figure 11, a detailed schematic ~i,agram of the block position and speed transducer (B~P~SoT~ ) ~33 is shown. As mentioned, the B.P.S.T. 83 outputs a position feedback signal to the computer input channel J on the line 116. Further, a position ~ignal is input to the brake control subsystem 105 and the motor control subsystern 106 on the lines 116B and 116M, respectively. Also, as discussed in connection with Figure 10, the B.P.S.T. 83 puts a O-lOmA
BLOCK VELOCITY signal on the line 171 to the velocity com-parator 108.
The B.P.S.T. 83 associated with the block 68 and is mounted on the carriage of -the block retractor 78 for travel therewith along the guide track 80. The travelling block 68, of course, moves with the carriage 78. The mounting details are illustrated diagrammatically with any suitable means of mounting being within the contemplation of this invention.
A friction wheel 690, manufactured of any suitable material, as urethane, is contacted against the retractor guide track 80. A spring 691 biases the wheel 690 into contact with the track 80. Displacement of the carriage 78 causes rotation of the wheel 690 and a shaft 692 suitably coupled thereto.
At the opposite end of the shaft 692 is coupled a toothed wheel 693 which is driven by movement of the wheel 690.
The B,P.S.T. 83 include~ a zero vel,oclty mcl(Jnetic pickup 695, such as that manufactured by Airpax and sold under Model No. 4-0002. The pickup 695 outputs a s~uare wave pulse each time a tooth of the wheel 693 pas~e~, in proximity to the pickup 695. This signaL is hereafter referred to as the "A" signal. The pickup also outputs a signal, either a logic 1 or a logic 0, indicative of the - 7h -lF

direction in which the te~th of thc wheel 6g3 ar~ passin~.
This signal is hereafter referred to as the "T3" sign~ t is quickly appreciated that a predetermined (Jiven num~er of output pulses from the pickup calibratecl and used to reure-sent displacement of the block a predetermined rec-ti]inear distance along the track 80. Similarly, the frequency of the pulses is proportional to the speeci at which the carriage 78 moves. The "A" and "B" siynals of the pickup 6g5 ar~
; connected to a signal level translator 697. A suitable translator 697 is that manufactured by Motorola and sold under Model No. MC 666. The function of the translator 697 is to translate the magnitudes ofthe "A" and "B" signals to a level compatible with the electronic components which follow. The "A" signal is also transmitted by a line 698 to the input of a frequency-to-voltage converter 6~9. Any suitable converter 699 may be utilized, such as that manu-factured by Teledyne Filbrick and sold under Model No. 4702.
The frequency-to-voltage converter 699 serves to pro-vide an average output voltaye proportional to the frequency of the square wave input signal. Potentiometers may, of course, be provided to adjust the zero and full scale out-put. For example, a nominal sensitivity of 1.0 volt/foot/
second with a full scale of 10 volts, or any other pre-determined setting may be utilized. The output from the converter 699 is applied to a unity gain inverting amplifier 700 (shown schematically). The output of thc irlvertlng amplifier 700 is applied to a voltac3e-to-current converter 701. The converter 701 is similar in circuit d~t~ils to the voltage-to-current converter 246B shown in F'igure 8B.
The converter functions to provide a O-lOr~ output propor-tional to the O to -10 volt input signal. ~ suitable trimming resistor ma~ be provided to adjust the output ~1 ~f~1')q current to a predetermined value, for exam~le, lOmA when the input voltage is 10 volts. Resistors or potentiometers may also be provided to make -the current output independent of load resistance. A O-lOmA output current signal on the line 171 is functionally related to the frequency of the square wave input on -the line 6g8 and, accordingly, to the speed of the carriage 78 and the travelLing b]ock 68 associated therewith. As before, the current signal is preferred due to the high noise immunity offered thereby.
Further, the constant current source characteristic ~akes the cable resistance and/or cable length uncritical. Thus, long cable runs through electrically noisy environments using economical unshielded cable are possible. The output from the voltage-to-current converter 701 is connected by the line 171, discussed above, to the velocity comparator 108. Although the velocity feedback signals are received at the velocity comparator 108 from the drum tachometer 94, it is noted that redundancy is provided by the velocity signal output from the B.P.S.T. 83. The velocity signal from the B.P.S.T. 83 provides excess velocity information should the drum tachometer 94 develop a malfunction.
As noted, the "A" and "B" output signals from the pickup 695 are output from the level translator 697. A
line 703 carrying the "A" signal (also input to the con-verter 699), and a line 704, carrylny the "B" sic3nal representative of the direction of motion of the wheel 693 are both input to a cascaded array of counters, 706~, 706B, and 706C, such as those manufactured ~y Motorola and sold under model number MC14516CP. The counters register the number of pulses received on the line 703 during the motion of the block. Thus, the totaL count is the measure of the vertical distance traversed. The direc~ional sicJnal . s<

~36733 input on the line 704 de-termines whether -the courlt is -to be added or subtracted (i e., countup or countdowr,) frorn the initial value. In the Figure, -the array of counters 706 provides a total count of 4096.
The parallel outputs Q(N) of the counters 706 are applied to a digital-to-analog converter 710, such as that manufactured by llybrid Sys-tems Corporation and scld under the model number DAC 380-12. The outpu-t of the converter 710 is a current propor-tional to the magnitude of the count received. Potentiometers 711 and 712 are, respectively, provided to adjust the zero and full scale current levels.
These potentiometers may be set, for example, so that a 4rnA
sic~nal corresponds to a zero count and a 20mA current corresponds to a regis-ter count of 4095. The output current, is, therefore, proportional to the elevation of the travelling block. The output current si.gnal, sharing the same attributes as discussed above, is applied to the output line 116 to the cornputer (on input channel J) and to the brake and motor control subsystems 105 and 106, respectively on the lines 116B and 116M.
Since the B.P.S.T. is an incremental position sensiny system, a reset is employed to establish a definite and repeatable correlation between the count registered and the physical position of the block 68. As noted earlier in connection with Figure 2, two proximity switch sensors 84 and 85 are located on the carria(3e 78 whi.ch are ~Ictlllted by metal targets 86 and 87. This arranyemfrlt provides un-ambiguous reset points near the upper and lower ends of the retractor yuide 80. Each resct switch output is a~)plied to an anti-bounce network 715 and 716, each utilizing two cross-coupled NOR gates 718 and 719. The output of each of the networks 715 and 716 is applied to a bistable network - 7~3 -720. The output of the network 720 func-tlons to rnaintain one or the other of reset buses 721 or 722 high (i.e., at logic 1), depending upon which reset switch 715 or 716 is actuated.
The upper reset bus 721 and the lower res~t bus 722 each have a diode-resistor network wire thereto which forms a pattern to the preset inputs J(M) of the countcrs 706 representiny a predetermined count for the physical elevation of each target. The output of the anti-bounce networks are fed through a WAND gate 723 to the preset inputs of the counters 706. Thus, the counters 706 are preset to a predetermined count each time a sen~or passes its respective target.
NAND gates 724A, 724s ancl 724C are connected as a Schrnitt trigger network. The outpu-t of the trigger network provides a reset pulse to the reset inputs of each counter 706 through a capacitor 725 and a diode 726. The output of the trigger network reset.s the counters 706 at a fixed time delay after the system power is applied. This time delay is set by the resistor 728 and the capacitor 725.
Any predetermined tirne delay may be used. As a result, the counters 706 are automatically set to zero count each time the system is powered-up.
However, there remains the possibility that after -the counters 706 are reset to zero fo]lowing power-up, one spurious count combined with a down sicJnal from thc rnagne~tic pickup could cause the counters 706 to re~ister a full count of 4095. To preverlt this s;tuation, thc ~c.qct pulse described above is al50 applied to a N~ND gate 727 functioning as an inverter. Its output functions to switch the lower reset bus 722 to logic 1 through the diode 728.
During a predetermined additional time interval, set by , -- ~0 --F

~ G733 .
:~ . the capacitor 730 and resi.s-tor 731, the preset pin of the middle counter 706B is enabled through an inverter 732 and a diode 733. The result is that a preset coun-t is entered following each power-up. In this example, a count of 4~
is entered, although any value can be preset by appropriate rearrangement of the logic.

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EL~VATOR LO~D CONTROI.

As alluded to above, during both the make-up and break-out cycles it is necessary and desirable to monitor the load being carried by the elevator 75 (Figure 2).
Accordingly, as discussed in connection with the brake control subsys-tem 105 and -the motor control suhsystem 106, feedback signals from the elevator load control subsystem 107 are utilized in the determinati,on by the motor or brake controls of the speed at which the drill string is lifted (by the motor) during break-out cycle or the speed at which the string is permitted to fall (by the brake) during make-up cycle. The necessity and advantage of considering the elevator loading is apparent. If -the drill string is encumbered as it is lifted out of or lowered into the bore, the loading on the elevator departs from a predetermined preset minimum (during lowering) or a predetermined preset maximum (during hoisting). In either case damage to bore may occur if the velocity of the block is not limited.
As seen in Figure 3, the basic drawworks control block diagram, it is noted that the elevator load control subsystem receives output signals from computer channels N, O, and P on lines 175, 176 and 177, respectively. Feedback signals to the computer channels K, L, and M are carried from the elevator load control subsystem are carried on lines 178, 179 and 180, respectively. It is also noted that a feedback signal representative of the ackual elevator load '~ is output to both the brake control subsystem 105 and the motor control subsystems 106 through the lines 136B and 136M, respectively, while appropriately scaled initial load feedback signals are respectively output to the brake and motor control subsystems through the lines 138B and 138M, - ~2 -3~733 respectlvely. The clerivation of the~e signal~ i 5 ~i~cussed herein.
The elevator load control subsystem 107 derlvec3 its operating input from the deadline force sensor (~.L,.F.S.) 95 on the line 110 (Figure 3). The signa] from the D.L,.F.S. 95 may be conditioned, if des.ired. As is the case with all signals derived from relatively distance transducers, the signal from the D.L.F.S. is a 4-20mA current signal, chosen for the reasons outlined above.
Referring now to Figure 12, which is a detailed schematic diagram of the elevator load control subsys-tem 107, the 4-20mA signal is taken from the input line 110 and converted to a voltage signal by the action of resistor 735 connected to a negative potential. This is a configuration similar to that used throughout the invention to convert a current to a voltage signal. The voltage signal is filtered by a filtering network 737 including a resistor 738 and a capacitor 739. The filtered voltage signal is taken through : a buffer amplifier 740 and carried by a line 741 to the non-inverting input of a comparator 742 through a resistor 743.
The non-inverting input of the comparator 742 is tied to ground potential through a resistor 744. A potentiometer 745 connected to a positive potential adjusts the zero point of the comparator 742.
The output of the amplifier 740 representative of the loading on the elevatc)r 75 (Fi~ur~ 2~ at any given instant is connected by a line 747 to a sample-and-hoLd network 748~ The network 748 includes a buer ampli~ier 749 connected to its non-inverting input to the line 747.
The output of the amplifier 749 is taken through a diode 750 and a resistor 751 to a bilateral switch 752.
The junction of the diode 750 and the resistor 751 is tied F

to groun~ poten-tial through a resistor 753 while a Zener diode 754 is interpos~d between the junction of the re~
sistor 751 and the switch 752. The Outp-lt of the switch 752 is connected to the gate of a field effect transistor 755 with the gate also being connected to ground potential through a capacitor 756. The drain of the transistor 755 is connected to a positive potential. The source is con-nected to a negative potential through a resistor 757. The output of the sample-and-hold network 748 is taken by a line 759 at the source of the transistor 755 and applied through a resistor 760 to the inverting input of the differential amplifier 742. The output of the differential amplifier 742 is fed back to its inverting input through a resistor 761. The switch 752 is connected through a NAND 763, both inputs thereof being tied through a diode 764 to the line SAMPLE ZERO LOAD line 175 leadiny from computer channel N.
The NAND gate 763 inputs are connected to a positive potential through a resistor 765.
When the switch 752 is closed momentarily by an enabling signal on the line 175 from channel N of the com-puter, the capacitor 756 is charyed to a level corresponding to the elevator load signal at the output of the amplifier 740. The signal level at the output of the transistor 755 ; on the line 759 remains at the level existing when the switch 752 is gated off until the next gate signal is applied. The computer is programmed such that channel N
the "SAMPI.E ZERO LOAD" signal is activate~ when the elevator and block are not in motion and at an appropriat~ point in the cycle when the elevator has not acquired any load. The signal presented at the invertiny input of the comparator 742 may then be thought of as consisting of the tare weight of the elevator and block plus any offsets and accumulated - ~4 -~3~733 long-term drifts existing in the load measurinc3 net~orks.
A-t the differential amplifier 742, ~he æero sign~l is sub-tracted from a si~nal representative of the instantaneouselevator load input on the line 741 so that the instantaneouc, sic3nal representative of the actual loading on th~ ele~ator at the output line 766 from the differential amplifier 742 is presented to the output line 136 ~CTU~L L~A~, The output from the field effect transistor 755 on the line 759 is fed bac~ through a line 767 to the inver-ting input of the amplifier 749.
A substantially identical sample-and-hold network 770 is connected to the output of the comparator 742 through the line 771. The non inverting input of a buffer amplifier 772 is connected to the signal on the line 771, The output of the amplifier 772 is connected through a diode 773 and a resistor 774 to a bilateral switch 775. The junction be-tween the diode 773 and the resistor 774 is connected -to ~round potential through a resistor 776. The junction between the resistor 774 and the switch 775 is connected to ground potential through a zener diode 777. The output of the switch 775 is connected to a capacitor 77~ and to the gate of a field effect transistor 780. The drain of the transistor 780 is connected to a positive potential while the source thereof is connected to a negative potential through a resistor 781. The output of the network 770 is taken from the source of the transistor 780. This output is also fed back to the invertin-~ input of the amp].ifier 772 b~
a line 783. The output of the transistor 780 is also con-nected throuc3h series resi~tors 78~ and 785 to c3round potential. A line 786 is connected at the junct:ion of the transistors 784 and 785 for a purpose to be discussed herein. The output of the sample-and-hold network 77~ is connected by a line 787 to a switch 788.

~1 ~13~73~
The switch 775 i~ connect~d to c- N~r~lD gat~ 7~0, -the tied inputs of which are connected through a dio~e 7~1 to the line SAMPLE LOAD on the line 176 leading frortl the out-put channel 0 of the computer. The inputs to -the N~ND g~te 790 are connected to a positive potentia], through a resistor 792. With the receipt of a siqnal from t~lc com~
puter channel 0 on the line 176 the positive signal present on the input of the NAND gate 790 connected as an inverter switches to a logic 0. The outpu-t switches to a logic 1 10 which gates on the switch 775. With the switch 775 gated on, the capacitor 779 charges to a signal level such that the output of the transistor 780 on a line 787 is equal to the signal level existing a-t the amplifier 742 output of the line 771. This signal level at the line 787 remains at the level existing when the switch 775 is gated off until the next gating signal is applied. The signal from the computer on the line 176 is activated at a point in the cycle when the elevator has acquired a load but is not yet in motion. Thus, the output of the transistor 780 on the 20 line 787 represents the "dead weight" of the drill string ]oad. This is the INITIAL l,OAD and is the base value of the drill string load used for comparison with the ACTUAL
LOAD by the brake control subsystem 105 and the motor control subsystem 106, as discussed in connection with the de-scription of those subsystems.
The switch 788 is connected ~t its input hy a line 796 to the non~inver-tiny input of a buffer ampli.fi.cr 797.
The switch 788 is controlled by a transistor 798 of the MPN
type, the base of which is connected through a r~sistor 799 30 and the diode 800 to the line 177. The LOAD CONTROI. ON
signal from the computer output channel P is applicd on the line 177. The signal end of the resistor 799 is connccted - ~36 -.~1 ~L~L3~733 to a positive potential through a resistor 802. 'rhe col-lector of the transistor 798 is connected -to a posltive potential throuc~h a resistor 803. The collector of the transistor 798 is also connected to the control lead of the bilateral switch 788. The signal end of the resistor 79g is also connected by a line 80~ to the control lead oE a secon~ switch 805. The switch 805 connects the output of the amplifier 742 through a line 806 to the non-inverting input of the bu~fer amplifier 797. Except during the CREEP
mode, the LOAD CONTROL ON signal is asserted whenever the drill string is being raised or lowered. When this signal is asserted, the switch 788 is gated on and this switches the signal representing the INITIAL LO~D on the line 787 to the input o~ -the amplifier 797. ~t the same time, the bilateral switch 805 is turned off. The INITIAL LOAD
signal at the output of the amplifier 797 is applied through parallel paths including resistors 810 and 811 to level control circuits 812 and 813, respectively.
Each of the level selectors comprises a bank of re-sistors such that, depending upon the setting of the selector switch, a predetermined fraction of the INITIAL
LOAD is applied through a resistor 815 to the inverting input of a bu~fer amplifier 816. The non-inverting input of the buffer amplifier is connected through a resistor 817 to ground potential. The output of the arnpl~fier 8l6 is fed back through its invertlng inpu~ through a resistor 818. The setting selected by a skilled clriller and dialed into the level cont~oller 812 is an adjustable fraction K
between 0 and 0.9 of the INITI~L L.OAD. This level is in-verted by the ampli~ier 8]6 and applied on the output line819 to a connection with the line 138B input to the brake control subsystem 105.

:F ~7 _ ~L~IL3~33 The physical effect of choosincJ th~ fact~r K] m~y b~
seen by a consideration of the lowering operation. During lowering, the actual load on the elevator will be leqs than or ~qual to the initial INITIAL LOAD value due to frictional forces on the moving pipe. Therefore, it is reasonable to anticipate that some deviation of the actual load on the elevator below that of -the INITI~L LOAD may be encountered during a normal lowering operation. The magnitude of the allowable deviation is defined by the magnitude of the constant Kl selectable by the level controller 812~
A portion of the signal at the invertiny input of the amplifier 816, the magnitude of that portion being defined by the ratio of the resistors 821 to 822 ~ is applied by a line 823 to the invertiny input of a comparakor 824~ The non-inverting input of the comparator 824 is connected through a resistor 825 to the actual load value carried thereto by a line 826~ The output of the comparator 824 is connected through a diode 827 and a resistor 828 connected to the base of an NPN transistor 829n A suitable base resistor 830 is provided. The output of the transistor 829 ~
which is normally conducting, taken at the collector thereof, is connected by a line 831 to the output line 178 leading from the elevator load control subsystem 107 to the computer input channel K. This is the LOAD UNDER LIMIT interrupt signal. The junction of the diode 827 and the transistor 828 is connected through a diode 833 to the out~ut taken at the emitter of a transistor 834. Thc base of th~ transistor 834 is connected to the LOAD CONTROL ON line with the collector thereof beiny tied to a positive poten~ial. Thus, during those periods of time when the LO~I) CONT~OL ON is asserted by the computer, the transistor 834 is not con-ducting and the output of the comparator 824 is enabled.

~ 88 ~

~3~733 The resistors 8Zland 822 establish an under-limit swi-tching threshold for the comparator 824 for a c3iven K1 selected.
When the value of the actual load falls below the preset fraction of the scaled INITIAL LOAD at the inverting input of the comparator 824, the comparator switches so that the transistor 829 switches off. This constitutes an alarm signal indica-ting that the elevator load is under prc-determined limit and actuates an in-terrupt system, halting the prograrn and applying full braking effort as discussed above. The interrupt causes the entire system to revert from an automatic to manual mode.
The level selector 813 operates in a similar manner.
The signal at the output of the level controller 813 is applied through a resistor 835 to the inverting input of a comparator 836. The actual load signal carried by the line 826 through a resistor 837 is summed at the inverting input of the a~plifier to produce a polarity inversion.
The non-inverting input is connected to ground potential through a resistor 838 so that the comparator switching threshold is zero potential. The output of the comparator 836 is connected through a diode 839 and a resistor 840 to the base of an NPN transistor 841 having a base resistor 842. The collector output of the transistor 841 is con-nected to line 844 and the line 179 to the computer input channel L. This is the LOAD UNDER LIMIT signal. ~ diode 845 is connected between the junction of the diode 839 and the resistor 840. This maintains the transistor 8~1 in conduction when the transistor 834 is in conductlon (i.e., when the LOAD CONTROL ON signal is not asserted). Thus, the function of the LOAD OVER LIMIT interxupt is inhibited.
During a hoisting operation, the actual loa~ may be increased over the INITIAI. LO~D value through th~ e~fect of _ ~9 _ ,..--.

~L~3~33 friction between the pipe and the ~ore. Therefore, duriny a hoisting oper~tion, the INITI~L LOAD is sc~led by ~n appropriate factor K~ selected from the level controller 813. The setting of the selector switch establishes the gain of the amplifier 849. This appropriately scaled load is presented by the line 834 to the output line 138~ carried to the motor control subsystem 105. ~s long as the ACTUAL
LOAD signal stays within the range of values defined by the constant K2, as described above, the motor control sub-system 106 is permitted to control the hoisting velocity without being affected by the load factor. ~lowever, as in the case of the lowering motion, if the actual loading on the elevator exceeds some preset fraction (set by the ratio of the resistors 835 to 837), an interrupt signal is output on the line 179 indicating that the elevator LOAD UNDER
LIMIT has been exceeded, interrupting the program and causing the entire system to revert from automatic to manual control. Note that when the LOAD CONTROL ON signal is not asserted, the line 177 is at logic l and the tran-sistor 798 conducts and the switch 788 is gated off. At the same time, the switch 805 is gated on. The ACTUAL LOAD
value is continuously applied to the load level selector rather than the INITIAL LOAD value. This effectively inhibits the function of the load control subsystem.
The actual load value at the output of the amplifier 742 is also applied by the line 771 to a Ic~ad acquired network 850. The signal is applied to a hiqh-p~ss filter network comprising a capacitor 852 and a resistor 853 con-nected to ground potential. The filter is tied to the non-inverting input of a buffer amplifier 854, the output of which is connected by a line 855 to the inverting input of a comparator 856 throuqh a resistox 857. The non-invertinq , -;;
.

input of the comparator 856 is conducted by a line 858 through a resis-tor 859 from the output of a buffer amp],ifier 860. The non-inverting input of the amplifier 8h0 i,s ta~en from the line 786. The output of -the amplifier 860 is applied through a diode 861 and is ~ed back to the invertin input thereof through a resistor 862. The Ollt,pUt of the amplifier 860 taken through the diode 861 is applied through resistor 863 to an amplifier 864. The non-invertiny input of the amplifier 864 is connected to ground potential through a resistor 865 while the output thereof is fed back to the inverting input through a resistor 366. The output of the amplifier 864 is connected to the inverting input of a comparator 868 through a resistor 869. The non-inverting input of the comparator 868 is taken through a resistor 870 from the line 855.
The output of the comparator 856 is connected through a diode 875 and a resistor 876 to the set pin of a cross-coupled NAND 877A and 877B connected as a flip-flop circuit. The output of the comparator 868 is taken through a diode 878 and a resistor 879 to the reset input of the flip-flop 877. The output of the flip-flop is taken through a resistor 880 connected to the base of an NPN
transistor 881. The collector output of the transistor 881 connected by a line 882 to the output line 180 from the elevator load control subsystem 107 to the computer on the input channel N.
The output of the ampli,fier ~5~ and the linc 855 is the LOAD ACQUIRED signal. It is fed to the two comparators 856 and 868. The other signal being applied to the com-parators is, as shown, a refererlce signal e~ua] to approxi-mately 1/3 the value of the I~ITI~rJ LOAD si~3nal a5 estab--lished by the resistors 784 and 785. The reference, siyrlal to the comparator 863 is inverted by the ampliEier ~64 to maintain the proper signal ~ense. Thc rcference sic3nals are F - 91 - ' ,. . . .

necessary so that the comparators can accommodate a wide range of hook loads. It adjusts the switchiny point of the comparators 856 and 868 to a level consis-tent with the drill string load during the previous cycle. The change in weight over a sequence cycle to cycle is equivalent to one stand of pipe and so for a -typical drill s-tring make-wp the per cent change in weight is negliyible. The output of the comparators 856 and 868 drive the flip-flop 877. Prior to load acquisition, the normal steady state outputs of the comparators 856 and 868 are at a logic 1 due to the reference signals applied. The load acquired flip-flop is at a logic 0. The capacitively coupled load acquired signal momentarily switches the comparator 856, so its output switches to logic 0. This sets the flip-flop ~77 so its output switches and remains at logic 1. Later, a negative going load released signal momentarily swithces the com-parator 868 so that its output pulse resets the flip-flop and the flip-flop output switches to logic 0. The tran-sistor 881 conducts during the interval that the elevator 75 is supporting the drill string load. Thus, during the time that load is acquired by the elevator, a current signal on the line 180 is applied to the computer channel N. When the load has been released, the signal current level drops to zero.

73~
ASSOCIATr,D SAF~TY SYSTE,MS

Referring to Figure 13, a schernatie diagram of an automatie sequence disenable an~ interrupt logic circuit 900 is shown. The purpose of this circuitry is to permit an experieneed driller on the derrlck to manually correct some physical problem on the rig which is causing the automated sequenee to "hang-up" (a temporary halt to the computer program sequeneing) and to perform that action without risk o~ physieal injury. Sinee it is possible that eorreetion of the structural disorder will enable the automated sequenee to eontinue, and pexhaps imperil the operator, it is im-perative from a personnel safety stand point that the automatie disenable be provided.
The driller's control console is provided with an AUTO MODE switch 901 which in the NORMAL position applies a positive voltage signal to a two-pole low-pass filter and diode limiter 902 to apply a logic l siynal to the A input of NOR gate 903C. When a "hang-up" exists in the draw~70rks program, indicating that the elements eontrolled by the drawworks elements (Figure 2) are in a motionless conditlon, the line 904 from the eomputer goes to logic 0. Similarly the line 905 from the eomputer goes toa logie 0 condition eaeh time a "hang-up" exists in the racker eontrol program.
Thus, all of the struetural elements eontrolled by that program (numeral 3~, Figure 2) are also statie or rnotion-less. A "hang up" therefore oeeurs only ~/hen an appropriate feedbaek signal, is absent due to a malfunetion or at a point where one program is awaitiny a funetion whieh oecurs in the other program to be eompleted.

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The NOR gates 903A, 903B, 903C and 903D are con-nected as shown so that when the three sicJnals (fro~l the switch 901, and on the lines g04 and 905) are logic ~)~ a transistor 906 of the NPN type ceases conduction. This con-stitutes an output signal carried by the line 907 which causes the AUTO/MANUAL bus to be de-energized. This ln-hibits all control function and the entire system reverts to a manual mode, and all sequencing is halted. This con-dition remains until the AUTO MODE switch is returned to the NORMAL position. Thus, after actua-ting the AUTO MODE
switch to the DISABLE position, the operator can safely correct a malfunction without the danger of the system imrnediately continuing on in the automatic sequence. Then the repair has been e~fected, the switch 901 can be re-turned to the NORMAL position and the automatic cycle is resumed. Thus, a fault in the structura] system (or any other operator correctable malfunction) can therefore be corrected without disrupting the computer proyram, and thereby avoid the complicated start-up and reloading pro~
cedures.
A power-fail sensing system may also be provided.
The circuit includes the transistors 910, 911 respectively, of the NPN and PNP types, and the optical coupler 912. This circuitry monitors the power supplies utilized in the in-vention. The transistor 911 is normally biased off and is non-conducting while the optical coupler 91~ is conducting and current in a line 914 is a norrnal condition. When any of the monitored power sources fail, i.e., ~15 VDC, -15 VDC, -24 VDC (tong supply) and 26 V, 400 Tlz. AC, the transistor 911 conducts which biases the optical coupler 912 to an off or non-conductiny state. Therefore, an output current siynal to the line 91~ is interrupted. This constitutes an _ 9~ _ - ```` ~ 13f~;733 interrupt signal to the computer on the line 914. Of course, loss of +24 VDC control power to the coupler 912 accomplishes the same result.
The EXCLUSIVE OR gate 920 receive5 input signals on the lines 921 and 922 from the high drum clutch and the low drum clutch feedback switches. The drawworks control utilizes two clutches in the particular embodiment shown.
One or the other of the clutches may be damaged by simul-taneous engagement of both. The EXCLUSIVE OR yate accepts !
~ only one or the other of the clutch signals, but not both.

This effectively prevents simultaneous engagement of the : ~ ., clutches. The output of the gate 920 drives a transistor 923 of the NPN type when, conducting supplies a CLUTCH

: ENGAGED feedback signal to the computer on the line 924.
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POWER TONGS STRIlCl'URE

Although the power tongs structural systern 28 is no-t previously described in detail in connection with Figure 2, power tongs for making and breaking join-ts be-tween a pipe stand and a drill string are well-known in the art.
For example, United States Patent 3,881,375, issued to Robert R. Kelley and assigned to the Assignee o~ the present invention, discloses the basic structure of a power tongs assembly. In Figure 14, shown is a highly stylized pictorial representation of a power tongs assembly 1000.
Figure 14 illustrates the main structural elements common to all power tongs assemblies and also diagramrnaticall~
illustrates additional s-tructural elements provided in accordance with this invention.
The tongs assembly 1000 is located adjacent to the slips 55 (Figure 2) provided on the floor 53 of the derrick 20. As is typical and well-known to the art, the tongs 1000 are mounted on a vertical column 1001, itsel~ mounted on bearing 1002 to permit the tongs 1000 to swing into and out of alignment with the bore being generated. A collar 1003 is mounted, as by rollers 1004, for movement along the vertical column 1001. A tongs supporting yoke 1005 is mounted to the collar 1003 and projects horizontally there-from. The yoke 1005 supports a cradle 1006 in which a backup tong 1007 and a power driven tong 100~ are disposed.
The backup tong 1007 is adapted to hold one (usually th~
lower) section o~ the pipe secti.ons de~ining the joint to be made-up or broken-out ayainst rotation while the driven tong engages the other section to rotate the same in a pre-determined direction. The direction o~ rotation dependsupon whether the joint is being madc-up or broken~out.

~L~IL3~33 Also mounted on the column 1001 in ~ny suit~ble relationship thereto (shown .in Figure 14 as bein~ in co-operative association with the collar 1003) is a stabber 1009. As is well-known to those skilled in the art, the stabber 1009 may or may not be provided in a conveJltional tongs assembly, but if it is so provided, the stabber 1009 is operative to assist in locating or "stabbiny" the ne~.t pipe stand to be added to the drill striny during a make-up cycle. Since the structures discussed are conventional, i.t is understood that any suitable configuration of elements e~hibiting these functions and operating to effect the make-up or break-out of a joint in the drill string may be con-trolled by a control system 29 embodying the teachings of this invention.
As is also conventional in the art, a tongs lifting arrangement 1010 is provided. The arrangement 1010 com-prises means for lifting the tongs from a lower, or storage, position to an upper, or standby, position and, past the standby position to a still-further upward operating posi-tion. Any suitable means may be utilized, as illustratedby the piston-cylinder arrangement associated with a chain drive. Fluid, such as pressurized hydraulic oil, for controlling the lifting and lowering motion of the tongs is conducted from a fluid supply to the piston-cylinder arrange-ment 1010 on a fluid line 1011. The speed at which the tongs is raised from the storaye to thc stand~y pos:itions and from the standby to the operating positions is regulated by the fluid i.n a line 1012 having a restrictor :lO13 therein.
Includ~d within the backup tong 1007 .is means 1014, such as a piston-cyLinder arrangement, for opening and closing the backup tong 1007. Fluid, such as pressurized hydraulic oils for operating the piston-cylinder arrangement t733 1014 is conducted thereto on a line 1015. ~irnilarly, means 1017, such as a -tonys motor, are provided in operative association with -the driven tong 1008 for openin~J and closing the jaws of the power driven to~g and for rotatiny ; the power driven tong 1008 in a predetermined direction to effect the make-up or break-out of the joint. Fluid for operating the tonys motor 1017 i9 carried on a line 101~ to a cylinder 1019 related thereto. Means 1020, such as a piston-cylinder arrangement, is associated with the stabber 1009 for controlling the extension thereof. Fluid, such as pressurized air, utilized to energize the piston-cylinder 1020 is conducted thereto on a line 1021. Each of these aboye means for lifting the tongs at a predetermined lift speed, for opening and closing the backup tong, for closing the ton~ motor jaws and rotating the same, and for extending the stabber, are conventional in the art and any arrangement to accomplish the recited functions may be made compatible with the control system 29 embodying the teachings of this invention.
The tongs 1000 also include a joint sensor arrange-ment 1025 embodying the teachings of this invention. Al-though the joint sensor 1025 is described in complete detail in connection with Figures 18A and 18B, it generally com-prises a sensor arrangement having a pivotally mounted roller arm with limit switch associated therewith such that deflection of the arm b~ a predetermined portion of a drill pipe (as, for example, the box end taper~ actua~es the limit switch. When the limit switch is actuated, it is `~ then known that a predetexmined location on the drill pipe has been reached by the roller. Further, due to the standardization of drill pipes for oil drillin~ work, it is also known that another ~eature of the pipe, such as the :"
~ - 98 -r733 joint itself/ is then a predetermined known distance Erorn the location on the pipe which eneryized the limit switch.
The joint sensor 1025 includes means 1026, such as a piston-cylinder arrangement, for extending the sensor to contact the pipe. Fluid (such as pressurized air) to actu~te the extension means 1026 is carried by a line 1027.
In a conventional arrangement, a rnanually operated valve 1030 is ~isposed in association with the fluid line 1011 (LIFT) to regulate the flow of fluid therein. The valve 1030 is usuall~ operable in two directions to energize the lift means 1010 for upward or downward movement of the tongs along the vertical column 1001~ A manual valve 1031 is associated with the fluid line 1012 (LIFT SPEED) and is manually operable to adjust the speed at which the tongs are raised. Usually, the speed is variable from a first, normal, speed exhibited during movement of -the tongs from the storage to the standby positions, to a second, slower, speed exhi~ited during movement of the tongs from the standby to the operating positions during which time the sensor is extended to sense the joint.
A manually operated valve 1032 is associated with the hydraulic line 1015 (BACKUP) to regulate the flow of hy-draulic fluid therein to the backup 1007. Manual actuation of the valve 1032 controls the opening or closing of the backup tong 1007, as is appreciated by those skilled in the art. A valve 1033 is associated with the fluid line 1018 (TONG) connected -to the tongs motor l01~ to control th~
opening and closing of the power driven tong 100~ and the rotation thereo~. The valve 1033 is similar to the valve 1030 and is a two-direction manual valve ~Ihich in one posi-tion operates the tongs motor 1017 to make up a drill string while in the other position operates thQ tongs motor 1017 to break out a joint in the drill string.

_ 99 ~
~ ~.

~ t7~

If a stab~er 1020 is utilized, a manual valve m~ be provlded therefor operative to control passage of fluid in the lines 1021 (STABBER) to extend or r~tract the stabber.
Further, it would be appreciated by those skilled in the art if a joint sensor 1025 embodying the teachings of this invention is utilized in a manual tongs assembl~, the ex-tension of the joint sensor may be manually effected throuyh the provision of an appropriate manual valve regulating the flow of fluid (such as pressurized air) on the lines 1027 (SENSOR) to control the extension and retraction thereof.
Since, in the conventional arrangement above-described (with the exception of the joint sensor 1025), the control of the tongs structure is effected by the manual manipulation of valves in the fluid lines, it would be advantageous to provide an automated electronic control system, such as the tongs control system 29 (Figures 1 and 16), to electronically operate the tongs structure. Such a control system is provided by this invention. However, since the outputs of the control system 29 are electrical control signals, and since the above-discussed conventional tongs assembly utilizes fluid energized operators, it is necessary to provide an electro-hydraulic interface (E.II.I.) module intermediate between the tongs control system 29 and the tongs structure 28 controlled thereby. This module is illustrated diagrammatically in Figure 14 and discussed in complete detail in connection with Fi.~ure 1~, rJach inter-` face module is generally indicated by rcference numeral `~ 102~ and is provided to disenahle the manuall~ operatcd valve with which it is associat~d and to ~ubstitute therefor . 30 an electrically responsive valve adaptable to be controlled - by the electrical output signa]s from the tonys control system 29.

~i'' ' ~

~3~33 In general, the interface module 1028 includes an electrically operated solenoid valve connected in ~aral.lel relationship with the manually operated valve ancl in the same cooperative relationship with the flu,icl line throuc3h which the structure of the tongs communicates with the source of fluid therefor. F~urther, each interface moclllle includes means for selectively enabling the electrically operated valve and si.multaneously disenablinc3 the manual valve. The select means can convenic-,~ntly be an electrically or manually operable switch arrangement, or any other suit-able arrangement. Thus, dependent upon the operative mode (automatic or manual) selected, either the electrically operated valve or the manually operated valve will be determinative as to the passage of hydraulic fluid in the lines with which it is associated.
As seen in Figure 14, four interface modules 1028A, 1028B, 1028C and 1028D are provided so as to make the above-described conventional system responsive to the electrical signal outputs from the tongs control system 29. (Of course, if a conventional system utilized other manually operated valves, an interface module could be provided to make the function provided by that manually-operated valve eletrically controllable). The interface module 1028A
(LIFT) is associated with the fluid line 1011 and controls movement oE the tongs 1000 in a verticall~ upward and vertically downward direct:ion. Since the manual.].~ operat~d valve 1030 wi,th which the inter~aee 1028~ i~ associ,ate(l i~
a four-way valve, the e:lectrieally responsive valve eon-nected in parallel relationship ko the valve 1030 w:ithin the interface 1028A is similarly a four-way valve. There-fore, electrical. lines 1035 (~IFT ~P) and 1036 (~.IF'r DOWN) are input to the interface moclu].e 1028~ ~om the toncJ~

- :101. --r ~
~ `

control system 29. The presence of a siynal on the appropriate line 1035 (LIFT UP) or 1036 ~LIFT ~OWN) from the tongs control system 29 initiates, respectiv~ly, an upward lifting movement of the tongs 1000 and a downward movement thereof.
The interface module 1028B is associated with the manually operated valve 1031 and includcs a valv~ conrlected in parallel relationship thereto which is responsive to an electrical signal on an electrical line 1037 (LIFT SPEED) to control the rate at which upw~rd speed of the tongs 1000 is effected. The interface module 102gC includes a valve connected in parallel relationship with the manually oper-ated valve 1032, the interface valve being responsive to a signal on an electrical line 103~ (BACKUP) from the tongs control system 29. Energization of the line 1038 with the manual valve 1032 disenabled actuates the electrically responsive valve within the interface module 1028C to effect the closing of the backup tong 1007. Interface module 1023D includes an electrically responsive valve ~0 connected in parall~l relationship with the manually operated valve 1033 and is actuable to control to the tongs motor 1017 to make-up or break-out a joint. Since the manually operated valve 1033 is operable in two-directions, the electrically responsive valve within the interface module 1028D is responsive to signals from the tongs control system 29 on electrical lines 10~9 (TONG MAK~) or 10~0 (TONG BREAK) -to respectively initiate motion o~ t~le tongs motor 1017 to drive the driven tonc3 100~ to make-uI) or - break-out the joint. It is understood that if othcr manual control valves were provided in a particular manually operated tongs assembly, suitable interfaces emboclying the teachings of this invention may be provicled to automate F

~3~733 the functions performed thereb~ and make control thereof possible by the use of the tongs control s~stern 29 e~bodying the teachings of this in-vention.
A four-way single solenoid, spriny offset electrical-ly responsive valve 1041 responds to an electrical signal on a line 1042 (EXTEND STABBER) from the tongs control system 29 to control the passaye of fluid in the line 1021 to actuate the piston-cylinder arrangement 1020 to extend or retract the stabber 1009. A four-way, single solenoid, spring offset electrically responsive valve 1043 (similar to the valve 1041) responds to an electrical signal from the tongs control system 29 on a line 1044 (EXTEND SENSOR) to actuate the piston-cylinder arrangement or other suitable extension means 1026 disposed within the joint sensor 1025.
It is, of course, understood that if either of these last two functions were provided by a manually operated control valve in a particular manually operated tonys assembly, a suitable interface module would be provided to disenable the manually operated valve and selectively enable the elec-trically responsive valve to permit automated control of thetongs assembly by a control system embodying the teachings of this invention.
In order to provide automated control of the tong structure 28, suitable feedback signal generating means, commonly limit switches, are disposed at predetermined locations within the structure o~ th~ tonys. ~n u~)per llmit switch 10~5 is dispo~ed so as to output a siyncll on a line 1046 (TONGS IN STANDBY OR ABOV~) to the tonys control system 29 representative of the fact that the tongs have been raised on the column 1001 to at least the~ standby position.
A lower limit switch 1047 is mounted within the tonys struc-ture 28 and outputs a feedback signal on thc line lO48 ~3~733 (TONGS IN STORAGE) to the tonys control system 2g repre-sentative of the fact that the toncJs are in a storage position along the vertical column 1001.
Suitable means, as a pressure sensing switch 1049 disposed on the backup tong 1007 outputs a feedback signal on a line 1050 (BACKUP CLOSED) to the tongs control system 29 representative of the fact that the backup tong is in the closed and locked condition. Similarly, a limit switch or other suitable detector 1051 outputs an electrical signal on a line 1052 (BACKUF OP~N) to the tongs control system 29 representative of the fact that the backup tong 1007 is open. Suitable means, such as a limit switch 1053, outputs a signal on a line 1054 (STABBER NOT EXTENDED) to the tongs control system 29 representative of the fact that the stabber 1009 is in the extended or not extended position.
Feedback signal generating means, such as a switch or pressure transducer 1055, disposed on the tongs makeup cylinder 1019 associated with the tongs motor 1017, outputs ~ a signal to the tongs control system 29 on a line 1056 `` (TORQUED UP) indicative of a fully torqued condition of the tongs motor 1017 and representative of the fact that during a make-up cycle the joint has been adequately made-up.
The joint sensor 1025 embodying the teachings of this invention includes feedback signal generating means such as limit switch 1057 outputting a siynal on a line 1058 (JOINT SENSOR RETRACTED) to thc tonc~s control system 29 representative of the fact that the joint s~nsor is in the retracted position. When a joint i~ sen~ed, a feedback signal from the limit switch 1059 associated with the detector in the joint sensor 1025 outputs a signal on a line 1060 (~OINT SENSED) to the ton~s control system 29 representative o the fact that the joint has been sensed.

- 10'1 -t7 l~

~ full discussion of the manner in which ~he above-listed feedback signals are utilized ~y the tongs control system 29 to energize appropriate ones of the output lines to the electrically responsive valves locate~ within the interface modules 1028 is discussed fully in connection with the tongs control system 29, herein.
Referriny now to Figure l~A, a detailed schematic diagram of each of the interface modu]es 1028A through 1028D is shown. Each of the interface modules 1028 in-cludes an electrically responsive solenoid valve adap-ted to control the flow of hydraulic fluid from a supply, or source, thereof to the respective user apparatus with which the interface module is associated. Whether the manually operated valve (and, therefore, the electrically responsive valve disposed within each interface) is a pilot valve (in the sense of initiating the operation of a larger valve) or is a control valve (in the sense of interdicting the flow of hydraulic fluid) i.s a design consideration dependent upon the particularities of a yiven tongs system. The electro-hydraulic interface module is an adjunct to the tongs control system 29 and is adapted to disenable the manually operated valve and replace it with an electrically responsive valve which performs the same function as per-formed by the manually opera-ted valve. Thus, if the manually operated valve were a pilot valve, -the electrical-ly responsive valve in the interface woul~ assuln~ a pilot valve function. Alternativ~ly, if the manllally operatecl valve were a control valv~, the electrically operated valve in the module would assume a control valve ~unction. The electrically operated valve is connoctod in a parallel flow path to the manually operated valve. Further, each interface module 1028A throuyh 1028D includes means, such as a select valve switch, dispose~ in series with the electrically responsive valve and ~lith -the manually operate~
valve to simul-tane~ ly ~isenable one of the va1ves and enable the other of -the valves. The select valve s~Ji-tches may be manually or electrically operate~, and are illus-trated as electrically operated in connection with Figure 14A.
The se]ect valves or switches are all energized by the same source, namely the AUTO/MANUAL BUS from the tongs control system 29. The manual valves are enabled whenever the AUTO/MANUAL BUS is de-eneryized and the electrically responsive valves are disenabled. The electrically respon-sive valves enabled when the AUTO/r~ANUAL BUS is energized to simultaneously energize all select valves.
~s seen in the schematic diagram of the interface module 1028A, the four-way manually operated valve 1030 with which the module is associated is also illustrated. An electrically responsive four-way solenoid valve 1065, con-nected in parallel relationship with the manually operated valve 1030, has solenoid coils 1066A and 1066B associated therewith. Connected in series with the electrically re-sponsive valve 1065 is an AUTO-MANUAL SELECT valve switch 1067, while connected in series to the manually operated valve 1030 is an AUTO-MANUAL SELECT valve switch 1068.
Actuation of all of the select valve switches simultaneous-ly enables either the electrically responsive or manually operated valves and simultaneou~ly disQnables the o~her.
The solenoid coil 1066A is connected to the electrical line 1035 (LIFT UP) ~rom the tonys control systcm 29 while the solenoid coil 1066B is connected to the electriccll line 1036 (LIFT DOWN) from the tonys control system 29. The presence of a siynal on the line 1035 (L~F'T UP) energizes F

~-3~3~

the coil 1066A and lifts the tongs frorn the storacJe to th~
standby position. Analogously, the presence oE a si~Jnal on the line 1036 (LIFT DOWN) energizes the coil la66~ and lowers the tongs from the standby to the storage position.
The interface module 1028B is associated with the manually operated valve 1031. An electrically responsive solenoid valve 1069 is connected in a parallel hydraulic path to the manually operated valve 1031. The valve 1069 has a solenoid coil 1070 associated therewith. AUTO/MANUAL
SELECT valve switches 1071 and 1072 are, respectively, connected irl series with the electrically responsive sole-noid valve 1069 and the manually operated valve 1031 for purposes analogous to those discussed in connection with the select valve switches 1067 and 106g. The solenoid coil 1070 of the electrically responsive valve 1069 is connected to the electrical line 1037 (LIFT SPI~ED) output from the tongs control system 29. If the select valve switches 1071 and 1072 are disposed so as to simultaneously disenable the manually operated valve 1031 and enable the electrically 20 responsive valve 1069, the presence of a signal on the line 1037 (LIFT SPEED) actuates the valve 1069 to regulate the speed at which the tongs are lifted from a first to a second elevation.
The interface module 1028C operates exactly as the structure described in connection with the module 1028B.
An electrically responsive valve 107~ havlng a solenoid coil 1075 attached there-to is connected i.n a parallel hydraul~
path to the manually opcrated valve 1032. ~U~O/M~Nt)~l, SEI,ECT valve switches 1076 ancl 1077 are respectively con-nected in series with thc electrically responsive valve 107and the manually c~perated valve 1032. The solenoid 1075 is connected to the electrical line 1038 (BACKUP) from the tongs contro] system 2g. If the select valve s~,Jltches 1076 and 1077 are disposed so as to disenable the manual].y operated val~e 1032 and to simultaneously enable the elec-trically responsive valve 1074, the presence of a sicJnal on the line 1038 (BACKUP) from the tongs control system 2g actuates the valve 1074 to close the ~ackup tong 1007.
The interface module 1028D is similar in con-figuration to that discussed in connection with the inter-face module 1028A. That is to say, a four-way electrically responsive solenoid valve 1078 having first and second solenoid coils 1079A and 1079B associated therewith is connected in a parallel hydraulic path -to the four-way manually operated valve 1033. AUTO/MANUAL SELECT valve switches 1073A and 1073B are respectively connec-ted in series to the electrically responsive valve 1078 and the manually operated valve 1033. The solenoid 1079A is con-nected to the line 1039 (TONG MAKE) from the tongs control system 29 whi].e the solenoid 1079B is connected to the line 1040 (TONG BREAK) output therefrom. If the select valve switches 1073A and 1073B were disposed so as to simul-taneously disenable the manually operated valve 1033 and enable the electrically responsive valve 1078, the presence of a signal on the line 1039 (TONG MAKE) actuates the ; electrically responsive valve 1078 to enable the tongs motor 1017 to make-up a joint of a drill string. The presence of a siynal on the line 1040 (I'ONG ~RE~K) ~rom the tongs control system 29 actuates the solerloid l()79B and energizes the tongs motor 1017 to break-out a drill string joint.
Since each of the four interface modules 1028 have substantially the same internal hydraulic circuitry and utilize substantially sirnilar type valvcs, the same supply - 10~3 ~
F

l~L3~jr~ 133 manifold may be utili~ed to reduce cost and provide a symmetrical electro-hydraulic interface assembly, The inter-face modules may be mounted on a common base and connecte~
to common pressure and tank manifolds. A pressur~-reducing valve and accumulator may, ofcourse, be included to supply a constant pressure. Suitable hydraulic line tubiny may be used to connect the valve manifolds and pressure-reducing valve to the common manifolds and to the input and output header plates of the electro-hydraulic interface.
The tongs control system 29 cannot equal the cycle times possible with the manual controls operated by experi-enced man. However, it does not make common mistakes such as forgetting to close the backup before rotating -the tong, which sometimes happens with a man at the controls, or positioning the tong too-high or too-low on the tool joint.
The cycle times of the tongs control system 29 are fast-enough, however, since the tongs sequence is coordinated with the racker and drawworks sequences. The -tongs cycle does not cause a delay in the overall program sequence.

POWER TONGS CONTROL SYSTEM
-Figure 16 is a detailed schematic diagram of a tonys control system 29 embodyiny the teachings of this in-vention. However, before embarking upon a detailed dis-cussion of the circuitry of the tongs control system 2g, reference is directed to Figure 15 whlc,h illustrates the interconnections between the tongs control system 29 with the computer 40. The interconnections between the tongs control system 29 and the tongs structural system 28 have been discussed in connection with Figure 14, but are re-produced on Figure 15 for clarity. As seen from Fiyure 15, the computer 40 outputs signals to the tongs control system 29 on a line 1080 (SELECT SEQUENCE), which signal represents a commandfrom the computer 40 for the tongs control system 29 to execute either a make-up or a break-out cycle. The line 1081 (RAISE TONGS) carries a signal from the computer to the tongs control system 29 initiatiny the raising of the tongs along the vertical column 1001 (Figure 14) from the storage to the standby position. A line 1082 (START
SEQUENCE) carries a command sign~l from the computer 40 to the tongs control system 29 initiating the start of the selected sequence.
Upon the receipt of the START SEQUENCE signal on the line 1082, the circuitry of the tongs control system 29 initiates operation of the tony's physical structure to perform the operations necessary to either mak~-up or break-out a drill string. These command siynals from the tonys control system 29 have been detailed in connection with Figure 14. Some of the command signals, as discussed, must be interfaced through the electro-to-hydraulic interface ii73~

shown in Figure l~A. The tong control system 29 is inpllt with various feedback signals represen-tative of the physical occurrence of certain actions within the tongs structure.
These ~eedback signals from the means provided on the tongs structure have been detailed in connection with Figure 14.
The tongs control system 29 outputs signals hack to the compu-ter. On the line 10~ (ST~BB~R EXTENDED), an out-put signal is carried to the computer 40 indicating that the stabber (1009, Figure 14) has been extendecl. This signal is meaningful only during the make-up sequence and provides information necessary to continue the pipe racker program.
A line 1085 (BACKUP OPEN) carries information to the com-puter 40 representative of the ~act that the backup tong 1007 is open. Finally, the tonc3s control system 29 outputs a signal on a line 1086 (SEQUE~ICE COMPLETE) representative of the fact that the selected cycle is complete and that the tongs have been returned to the storac3e position.
Referring now to Figure 16, a detailed schematic diagram of the tongs eontrol system 29 is illustrated. The ~0 operation thereof may be more full~ understood by reference to Figure 17A and 17B which are, respectively, timing diagrams for the tongs control system 29 shown in Figure 16 in the make-up and break-out cyeles.
In the overall computer controlled oil drilling rig embodying the teachings of this invention, the computer eoordinates and sequenees the operation of the tonc3s, draw-works and racker~ rrhe operating philosophy i~ to utllize a time-~laredarrangement between the drawworks and racker eontrol programs, with a rninimum o interaetion between the eomputer and the tongs. Basieally, the eomputer initiates the seleeted tonc~s aetivity at the appropriate place in the cycle, with the activity beinc3 eontrolled by the tonc3s . , ~3~;jt733 control system. Necessary signals ~rom the tongs control to the computer to enable i-t to sequence the draw~Jorks and racker are provided. When the tongs activity is completed a signal to this effect is sent to the computer.
It may also be noted that the control s~stern shown in Figure 16 is able to be utilized in connection wi-th any power tongs structure due to the similarity of the operatiny elements. As discussed, all power tonys require a lift and lift speed controls, back-up tong controls, power driven tong controls, as well as initiation signals to a stabber (if one is provided) and an initiation signal for operation of a joint sensor. Thus, the control system disclosed herein is adaptable and useful with any power tongs.
Although the initiating signals to the control system originate from a digital computer, it is understood that the initiating instructions may be provided to the control system 29 through a push-button control box, thus making the control "manual" (in the sense that the sequenciny signals to the tongs control originate from a human operator as opposed to a digital computer) but still "automatic" (in the sense that valves regulating the flow of pressurized fluid to the tongs structure are operated by the electrical signal outputs of the tongs control system).
All of the feedback signals from the tongs structure 28 are applied to the tongs control 29 through fllter elements 1090 as shown in Figures 16~ and 16C. Each ele-ment 1090 contains a two-pole, low-pass filter to remove transients. It also contains a diode limiter to limit the magnitude of the input signal to a level compatible with the succeeding logic components.

7~

In a make up cycle, the signal frorn ~he computer on the line 1081 (RAISE TOMGS) provides a loyic signal to raise the tongs to the stanclby position. rrhe RAIS~ TONGS sic~nal on the line 1081 is filtered and limited, as discussed above, and applied to a delay circuit 1093 including a multivibrator A, inverters B and C, and a NOR yate D, Tht-7 delay circuit 1093 provides a predetermined dela~ so tha-t the duration of an incoming signal on the line 1081 mu~t last at least the predetermined delay interval (for example, 0.3 seconds) before it is passed into the control logic. The delay 1093 provides additional protec~ion against line transients causing a false signal.
The output of the delay circuit 1093, and specifical-ly the output of the NOR gate D, clocks a LIFT UP flip-flop 1094. When clocked, the Q output of the LIFT UP flip-flop 1094 goes to a logic 1 and that signal, i5 amplified by an amplifier 1095 and applied to a transistor 1096 causing it to conduct, The output signal on the line 1035 (LIFT UP) is applied to the E.H.I. 1028A to raise the tongs in an upward direction from the storage towarcl the standby position. The output of the delay network 1093 also resets the BACKUP
CLOSED MEMORY flip-flop and the JOINT SENSED MEMORY flip-flop, as illustrated by the reference characters Z-Z.
At the standby position, a feedback signal on the line 1046 (from the upper limit switch 1045 (Figure 14)) generates a LIET SPEED ~ignal on the line 1037 to shift the speecl of the upward motion of the tongs to slow. The output signal on the line 1037 (I,IFT SPE~D) is derived throuc3h an inverter 1097, a NOR gate lO98, an ampli,fier 1099 and a transistor 1100. The NOR yate 1098 derives its other input from the Q output of the LIFT UP flip-flop 1094. The same signal from the output of the inverter 1097 clocks a JOINT

73~

SENSOR flip-flop 1102. The clock signal is derived from a NOR gate 1103 which deriv~s its inpu~s from th~ output of the network 1092 and the output of the inverter 10g7, both of which are at logic 0 at this time. The data input to the flip-flop 1102 is derived from -the output o~ a NOR gate 1104. The input~ to the gate 1104 (both of which are at logic 0 at this time) are derived from the output of the inverter 1097 and from th~ Q output of the LIFT UP flip flop 1094. The Q output of the flip-flop 1102 is applied through an inverter 1105 and a transistor 1106 to the line 1044 (EXTEND SENSOR) to extend the joint sensor 1025 (Figure 14).
The sensor 1025 is extended only when the tongs are being lifted and only when the tongs are above the standby position.
The slow upward motion of the tongs continue~ until ; a JOINT SENSED feedback signal is received from the joint sensor 1025 on the feedback line 1060.
The JOINT SENSED feedback signal on the line 1060 generates several responses within the tongs control network 29. The signal on the line 1060, after appropriate fil-tering and limiting, resets the LIFT UP flip-flop 1094 through an amplifier 1108 to thereby stop the upward motion of the tongs. A JOINT SENSED signal also resets the JOINT
SENSOR flip-flop 1102, again derived through the amplifier 1108, to retract the joint sensor 1025. Thirdly, the JOINT
SENSED signal on the line 1060 sets a JOINT S~MSED flip-flop memory 1110 as illustrated by refcrence charactc~s W-W.
Finally, the JOINT SRNSED signal on the line 1060 causes the stabber 1109 (Figwre 14) to extend by clocking a STABBER
flip flop 1112 which applies a signal through an inverter 1114 and a transistor 1115 to the line 1042 (EXTEND STABBER).

~L~3t~/733 The STABBER flip-flop :is clocked throuc~h a NOR ~Jate 1117.
The NOR gate 1117 derives it.s inputs from the output of t~e amplifier 1108 and from -the Q output of the Schmitt tr:igger network 1092.
The receipt of a JOINT SENSOR RETR~CTED signal on the line 1058 from the limit switch 1057 (Figure 14) clocks a BACKUP flip-flop 1119. The output of the BACKUP flip-flop 1119 generates a siynal on the output line ]038 (s~cK~p) through an inverter 1120 and a transistor 1121 to close the backup tong 1007. A feedbacX signal STABBER EXTENDED from the switch 1053 is ou-tput on the line 1084 to the computer 40.
At this point in the sequence there is a pause until a signal is received on the line 1082 (START SEQUENCE) from the computer (Figure 15) commanding that the joint mak.e-up sequence be started. This signal is conducted through a delay circuit 1124 comprising a multivibrator E, inverters F and G and a NOR gate H. The delay network 1112 acts to impose a predetermined delay (for example, 0.3 seconds) such that the interval of any incoming signal on the 1082 must be at least 0.3 seconds in duration before it is passed.
The output of the delay network 1124, and specifically the NOR gate H, resets the STABBER flip-flop 1112, retracting the STABBER 1109 (Figure 14). The output signal from the delay circuit 1124 provides one input to an AND gate 1126 through an inverter 1127 and a NOR gate 1128. The NOR gate 1128 derives its inputs from the inverter 1127 and ~rom the Q output of the bistable network 1092. The second input to an AND gate 1126 is derived from a feedback signal from the switch 1053 on the line 1054 indicatiny that the stabber is not extended.

rl~ ' J
:,"

~L~L3~t733 The output of the ~ND g~te l:L~6 :is applied t~ a NOR
gate 1130 which derives its other input from an inve-rter 1131. The inputs to the lnverter 1131 are derive~ from a feedback signal on the line 1058 (BACKUP CLOSE~) fror[l the limit switch 1049 (Figure 14). The input on the line 1058 : (BACKUP CLOSED) is applied to a delay circuit 1133 for reasons similar to those cliscussed above. The delay circuit 1133 includes a multivibrator I, an i.nverter J, and a NOR
: gate K. The output of the delay network 1133 is app]ied to the inverter 1131 and also sets a B~CKUP CLOSED MEMORY flip-flop 1134.
The output of the NOR gate 1130 sets a MAKE-UP flip-flop 1135. The Q output of the MAKE-UP flip-flop 1135 enables the appropriate one (1137A) of -the NAND gates 1137A
and 1137B through a ~iode 1138. The second input to the NAND gate 1137A is derived from the Q output of the bistable network 1092 as illustrated by the reference characters U-U.
The second input to the NAND gate 1137B is derived from the Q output of the network 1092 as illustrated by the reference characters V-V.
The output of the enabled NAND gate 1137A is applied to the line 1039 (TONG MAKE) through a diode 1139, an in-verter 1140, and a transistor 1141. This causes the jaws of the power driven tong to close and to rotate clockwise to make-up the joint. The output of the NAND gate 1137B, which is not enabled during the make-up mode, is applied to the line 1040 (TONG BREAK) through a diode 1143, an inverter 1144 and a transistor 1145. The tong.s motor 1017 is rotated until a TORQUED UP signal on the line 1056 is recei.v~d from the feedback means 1055 on the makeup cylin(ler (illustr~ted as a switch in Figure 16A). The signal on the line 1056 (TORQUED UP) resets the MAKE-UP flip-flop 1135, as ,.

illustrated by the reference characters P-P, ~Jhich stops the tongs motor rotation~ As the ~ output from the MAKE-UP
flip-flop 1135 goes low, a pulse is applied through a capacitor 1147 and an inverter 1148 to initiate a timer 1150 (tl) comprising NOR gate 1151A and an inverter 1151B. 'I'he output of the timer 1150 provides an adjustable delay tl (see timing diagram, Figure 17A), the period of which is set by a potentiometer 115OA.
When the time tl runs out, a pulse through a capacitor 1152 initiates a second timer 1154 comprising NO~
gates 1155A and an inverter 1155B. This timer 1154 (set by a potentiometer 1154A) provides an adjustable time t3 during which the electrically controlled solenoid valve 1077 con-nected by the line 1040 (TONG BREAK) in the interface module 1028A (Figure 14A) is energized through a resistor 1196 and a NAND gate 1157, a diode 1158, the inverter 1144 and the transistor 1145. This signal on the line 1040 reverses the tongs motor 1017 so that it rotates clockwise to open the jaws of the power driven tong 1008. The second input to the NAND gate 1157 is derived from the Q output of the Schmitt trigger network 1092 as illustrated by reference characters U-U. When time t3 runs out, the signal on the line 1040 terminates, de-energizing the transistor 1017. At the same time, a pulse is applied through an inverter 1160, a capac-itor 1161 and a diode 1162 to reset the BACKUP flip-flop 1119 which causes the hackup tong 1007 to opcn.
A signa:l on the line 1052 (BACKU~' OPEN) Prom t:he switch 1051 (Figure 14) clocks a LIFT DOWN flip-flo~) 1164.
The Q output (a logic 1) of the LIFT DOWN fl:ip-flop 1164 is applied to the line 1036 (LIFT DOWN) through an amplifier 1165 and a transistor 1166 to lower the tongs, In addition, the signal on the line 1052 (BACKUP OPEN) is AND-ed with two ., .

~3~3~
other slgnals through diodes 1168, 1169 and 1170. The BACKUP OPEN siynal is applied on the output line 1~85 through the amplifier 1172 an~ transistor 1173 only if the JOINT SENSED MEMORY flip-flop 1110 and the BACKUP CLOSE~
MEMORY flip-flop 1134 have both been previously set. There-fore, the BACKUP OPEN signal is output on the line 1085 to the computer is inh.ibited un].ess the tongs have been cycled - through the major phases of their operational sequence.
` As the tongs approach the storage position, the 10lower limit switch 1047 (Fiyure 14) outputs a signa]. on the line 1048 to the tongs control system 29. This signal is applied through an amplifier 1175 and a diode ].176 to reset the LIFT DOWN flip-flop 1164.
Resetting of the LIFT DOWN flip-flop 1164 stops the tongs lowering motion. A signal from the ].ower switch 1047 is also applied to the line 1086 (SFQUENCE COMPLETE) in-dicating that the tongs sequence is completed (Figure 15).
It signified to the computer that the tongs are clear of any potentially obstructing position with the elevator to permit the elevator 75 (Figure 2) to be lowered to the desired elevation.
A delay network 1178 (Figure 16C) consisting of a resistor 1179, a diode 1180, a capacitor 1181 and an in-verter 1182 function to reset all flip-flops as illustrated by reference characters R-R when system power is applied.
It insures that all logic components are preset to thc proper state at the beginning of the se~uencc.

* * *

The timing diagram for a break-out cycle is shown in Figure 17B. During a break-out cycle, a logic 1 signal on 3- l l 8 the line 1080 (SELECT SEQUENCE) from the computer 40 trans-fers the loglc circuits to the proper configuration.
Namely, the Q output of the Schmitt trigyer ne-twork 1092 is in a logic 0 condition while the Q output thereof is in a logic l condition. A RAISE TONGS signal on the line 1081 sets the LIFT UP flip-flop 109~ raising the tongs, as pre-viously discussed. The lifting motion of the tongs is halted by a feedback signal from the upper limit switch 1045 (Figure 14) on the line 1046 which is inverted by the inverter 1097, and coupled through a capacitor 118~ and a NOR gate 1185 to reset the LIFT UP flip-flop 1094. A
pause in the tong sequence follows with the tongs remaining in the standby position.
When the tool joint is hoisted into position, a break-out signal is applied on the line 1082 (START SEQUENCE) through the delay network 1124. The output of the delay network 1124 clocks the JOINT SENSOR flip-flop 1102 through inverter 1127 and a NOR gate 1187 to extend the joint sensor 1025. The other input to the NOR gate 1187 is derived from the Q output of the bistable network 1092. The output of the delay network 1124 also clocks the L~FT UP flip-flop 1094, again through the inverter 1127 and NOR gate 1187.
The Q output of the LIFT UP flip flop 1094 is NOR-ed at the gate 1098 with the signal from the upper limit switch 1045 on the line 1056 as inverted by the inverter 1097. The ou-tput of the NOR yate 1098 i,s a~)~lied through thc ampLi~ler 1099 and applied to the transistor 1100 switch~ to a con-- ductive state. The output signal on the linc 1037 (LIF'i' SPEED) switches the tongs lifting motion to a spced slow enough to detect the joint. The joint sensor is extended when the JOINT SENSOR flip-flop 1102 is clocked by a signal fxom the output of the NOR gate 1103. The NOR gate 1103 F -]19-73~S
derives i~s inputs from the output of -the inverter 1097 and the Q output of the bistable network 1092.
As the tonys reach the desired elevation, a JOIN~' SENSED feedback signal on the line 1060 from the joint sensor 1025 is received. The JOINT SENSED signal resets the LIFT UP flip-flop 1094 throuyh the amplifier 1108 to stop the lift motion of the tongs. The JOINT SENSED feedback signal also sets the JOINT SENSED MEMORY flip-flop 1110 as illustrated by the reference characters W-W. The JOINT
SENSED feedback signal also resets the JOINT S~NSOR flip-flop 1102 through the amplifier 1108 to retract the joint sensor 1025. The retraction of the joint sensor 1025 gen-erates a feedback signal on the line 1058 to clock the BACKUP flip-flop 1l19.
A signal from the feedback switch 1049 on the line 1058 (BACKUP CLOSED) is applied to the delay network 1133 to prevent any initial transients as the backup starts to close from appearing as a true signal. The output of the delay network 1133 sets the BACKUP CIJOSED MEMORY flip-flop 1134.
The output of the delay network 1133 is also applied to a NAND gate 1188. The second input to the NAND gate 1188 is derived from the Q output of the Schmitt trigger network 1092 as illustrated by the reference characters V-V. The output of the NAND gate 1188 is coupled through a capacitor 1189 to a timer 1190. The duration of the output of the timer 1190 is an adjustable time delay t5 (Fic3ure 17E~) set by a potentiometer 1190A. The output of ~he timcr 1190 is connected through a diode 1191 and swltches tho proporly enabled NAND gate. In this case th~ enabled gate, 1137B, derives its second input from tho Q output of the bistable network 1092 as illustrated by reference characters V-V.

, .

73~

A signal is applie~ to the line 1040 (T~NG BREAK) through the diode 11~3, the inverter 1144 and the transistor 114~ to the tongs motor 1017 to break-out -th~ joint by counterclock-wise rotation.
When the timer 1190 times out, the tongs motor 1017 is de-energized and a pulse is coupled through the capacitor 11~7 and the inverter 1148 to start the tl timer lL50.
During the break-out cycle the transistors 1192 and 1193 are conducting so that the potentiometer 1150A which normall~

sets the duration of tl is ~ypassed. A long delay is unnecessary in the break-out mode. When the tl timer 1150 times out, a pulse is coupled by a capacitor 1152 -to ini-tiate the t3 timer 1154. The output of the t3 timer 1154 is applied to a NAND gate 1195 through a resistor 1196. This input to the NAND gate 1195 is also coupled frorn the output of the inverter 1097 through a diode 1197 and an inverter 1198. The second input of the NAND gate is connected to the Q output of the Schmitt trigger network 1092 as illustrated by reference characters V-V.
When the output of the t3 timer 1154 is applied to the NAND gate 1195, its output switche.s to logic 1 and this is applied through a diode 1199 and the amplifier 1140 to the line 1039 (TONG BREAK). This energizes the tongs motor 1017 (Figure 14) for the time period t3 in a clockwise direction so as to open the jaws of the power driven tong 1008.
When the t3 timer 1154 is timed out, a pulse i~

coupled through the in~erter 1160, the capacitor 1161 and the diode 1162 to xeset the B~KUP flip-flop 1119. This opens the jaws of the backup tong 1007. A siynal on the line 1052 (BACKUP OPEN) ~rom the switch 1051 clocks the LIFT DOWN flip-flop 116~ to return the tongs to the storage F

73~

position. This signal (B~CKUP OPL,N~ is applied through the diode 1170 to the amplifier 1172 along with enabling slgnals, through the diodes 1168 and 1169 to switch the txansistor 1173 on. This output signal on the line 1085 (~CKUP OPEN) is applied to the computer only if the previously discussed preconditions have been me-t. This signal to the computer 40 signifies tha-t the pipe stand is ready to be rnoved to its storage position.
When the tongs reach the storage position the switch 1047 outputs a signal on the line 1048 (TONGS IN STORAG~) to reset the LIFT DOWN flip-flop 1164 halting the motion and a signal on the line 1086 (SEQUENCE COMPLETE) is output to the computer indicating that the tongs sequence is complete.
The diodes 1201 and 1202 prevent the BACKUP flip-flop 1119 from being clocked while the tong lift is in motion.
- Conversely, the sAcKup OPEN signal on the line 1052 is applied as an enabling signal to the data input of the LIFI' UP flip-flop 1094 as illustrated by reference characters Q-Q
and the data input of the LIFT DOWN flip-flop 1164. Neither flip-flop may be clocked unless the backup is open. This prevents tong lift motion unless the backup is open.

ti7~

JOIN'I' SENSOR

Referring to Figures l~A and l~B, respectively shown are side ele~ational and top views of a join~ sensor generally indicated by reference numeral 1~25 embodying the teachings of this invention. The joint sensor 1025 is attached beneath the backup tony 1007 of a power tonys assembly (Figure 14) and is operative to accurately position the backup tong 1007 and a driven tong 1008 in a symmetrical relationship with the tool joint being made-up or broken-out by the tongs 1000 under the control of a tongs control system 29. Since the gripping space for the ton~s dies is limited, and since considerable force must be applied to these dies, it is necessary to locate the backup tong 1007 and the driven tong 1008 as nearly as possible in vertical symmetry above and below a horizontal plane extending through the tool joint.
The joint sensor 1025 includes a sensor arrangement 1204 which comprises an arm 1206 having a roller 1208 there-on, the roller being contactable with a drill pipe and the arm being pivotally moveable with respect thereto from a first, normal, position to a second, deflected, position.
The detector arrangement 1204 also comprises means 1210, including the limit switch 1059, associated with the arm 1206 for generating an electrical signal on the output line 1060 (JOINT SENS~D) when the arm 1206 i~ pi~otall~ deflected a predetermined angular distance from the normal positlon by being brought into contact with a dist~nded location on the pipe. The arm 1206 is biased into the norrnal position by an internal spring assembly (not shown). The means 1210 may be any suitable commercially available assembly, such as that sold by Mirco under model number BZL~-2-R~I.

i~

In Figures 18A and l8s~ the joint se~sor arran~e-ment 1204 o~ the sensor 1025 is mounted on a carriage l~:L2 disposed for movement within a suitable housing 1214. The housing 1214 is connectable by any suitable attachrnent arrangement 1216 to the underside of the backup tong 1007.
; Disposed within the housing 1214 is a piston-cylinder arrangement 1026. The piston-cylinder arrangement is in fluid communication with a line 1027 illustrated diagram-matically in Figure 18A, the line 1027 carrying a fluid (such as pressurized air) (Fig. 14) which when provided extends the joint sensor from a first, horizontally re~
tracted, position to a second, horizontally extended, position. Included within the piston-cylinder 1026 is the limit switch 1057 which outputs an electrical signal on the line 1058 (JOINT SE~SOR RETRACT~D) to the tongs control system 29 when the sensor 1204 is in the horizontally re-tracted position. The cylinder 1026 may provide a stroke greater than is necessary to extend the sensor 1204 to contact the pipe whose joint is to be sensed to provide an additional ability to follow any longitudinal misalignments of the pipe or irregularities in its surface, as with pipes exhibiting an external upset (Figure 19). The pressure of the pressurized air in the line 1027 is'sufficient to hold the extended sensor 1204 in position against the pipe. It is most advantageous to use a compressible fluid, as pressurized air, so that the pressurized air in the piston-cylinder 1026 acts as a spriny to allow movement of the sensor 1204 after it is extended.
The carriaye 1212 has horizontal roller element 121 engageable with guide rails 1220 mounted within tlle housing 1214. The horizontal rollers 121~ are provided to facilitate the horizontal movement of the sensor 1204 and carriage 1212 - 12~ -F

ti;'733 therefor in response to actuation of the piston-cylinder 1026.
In one embodiment of thè invention, the c~rriage 1212 is provided with a palr of guide rollers 1222A and 1~22r~.
As shown in Figure l8s, the axes of rotation of e~ch of the guide rollers 1222 define a predetermined angle 1224 of approximately 120 degrees therebetween. The anyularity between the guide rollers 1222 assists in centering the sensor 1204 laterally with respect to the pipe. Centering springs 1226A and 1226B are also provided between the guide rails 1220 an~ the housing 1214 to permit the guide rollers 1222 to align the sensor 1204 with the pipe even though the pipe may not be centered within the tongs. In an alternate embodiment of this invention, the guide roller 1222 and the detector roller 1208 may each be of a predetermined lateral dimension and in a parallel relationship so as to be able to contact the pipe regardless of the centered orientation thereof with respect to the tongs. In such a structural embodiment, the carriage 1212 is moved horizontally from the retracted to the extended position by the piston-cylinder 1026 and lateral centering of the sensor 1204 on the pipe is not required.
In operation, the sensor roller 1208 moves with the tongs slowly upwardly until the arm 1206 is pivotally de-flected from its normally outwardly biased position against the surface of the pipe by a di~tended surface feature on the pipe. With reference to Fiyure 19, it is ther~ sho~n that dependent upon the pipe utili~ed, any one of a pre-determined number of distended portion~ on the pipe may be used to actuate the sensor arrangement embodyiny the teachings of this invention. The location on the box end taper (Figure 19) having a predetermincd diameter of approximately 5.70 inches when using 5.00 inch drill pipe, is such a - :L2ti ~

,. .~

-:~L3b~3 convenien-t location on -the pipe. When the predetermined location on the pipe is encountered by the sensor roller 1208 and the arm 1206 is plvotally deflected from the normal position, the switch 1059 emits an e]ectrical signal on the line 1060 that the joint has been sensed. When the pre-determined location on the pipe is encountered, the distance 1230 from that location to the joint is a known va]ue. ~5 discussed in connection with the tongs control system 29 in Figure 16, the lift is s~opped, the sensor is retracted, and the backup tong 1007 is locked.
Due to the standardization of drill pipes in the oil drilling industry, detection of a predetermined location, such as a predetermined diameter on the box end taper, insures that any other surface feature on the pipe, such as the joint itself, is then a predetermined known distance 1230 from the location which generated the deflection signal. Thus, it is insured that the tongs are in the operating position, that the backup tong and the driven tong are vertically symmetrical with respect to a hori-zontal plane through the pipe joint and that the joint maybe made-up or broken-out by the tongs.
With reference to Figure 19, shown are views of standard drill pipe stands havin~ the commonly named portions thereof indicated as shown. Each end of each pipe stand illustrated has a distended joint portion indicated on Figure 2 at reference numeral 56. One end of the stands includes a threaded male member while the opposite end thereof is an internally threaded female mem~Jer. Normally, the pipe stand is inserted into the drill strin~ such that the male end of each stand is in~erted into the bore before the female end thereof. The male end of the next-to-be engaged stand is then connected by a power tongs to the female member o~ the last-inr;ert~d starld protru~ing ~rom the bore.
Below the tool joint outer dlameter, a ~aper porti,on known as the box end taper and the pin end taper, res-pectively, are provided on the female and male ends of the stands. Depending upon whether an internal or external upset is provided, further tapering of the drill pipe stand may occur. The basic difference hetween an internal and external upset pipe stand is illustrated in Figure 19.
Basically, an internally upset pipe presents a constant outer diameter between each of the end tapers while an externally upset pipe exhibits an upset taper on the ex terior of the pipe stand. In order to accommodate either internally or externally pipe stands, the ~oint sensor 1025 embodying the teachings of this invention is operative to emit a signal when the roller 1208 and arm 1206 thereof comes into abutting contact with and is deflected by a pre-determined location on the box end taper. Of course, any predetermined location on the end taper sections, either on the internally or externally upset pipe stand, may be de-tected by a joint sensor 1025 embodying the teachings of this invention.
Having described a preferred embodiment of the invention, those skilled in -the art may appreciate that modifications may be imparted thereto yet remain within the scope thereof as defined by the appended claims.

F

Claims (33)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A closed-loop control system for controlling a drawworks mechanism for moving a predetermined length of drill string to a predetermined position within an oil derrick at a predetermined velocity comprising:
a block arrangement connected to the drawworks mechanism and adaptable to support the upper end of a drill string during lifting thereof;
means for outputting a position signal functionally related to the elevation of the block arrangement with res-pect to a vertical axis extending through the derrick;
means for outputting a velocity signal functionally related to the velocity of the block arrangement;
means for outputting a load signal functionally related to the magnitude by which the weight supported by the block arrangement deviates from a predetermined portion of the weight supported by the block arrangement when it is in a substantially static condition;
means for generating an error signal functionally related to the difference between the position signal and a signal representative of the predetermined position to the difference between the velocity signal and a signal representative of the predetermined velocity, and to the load signal; and, means responsive to the error signal for operating the mechanism in a manner so as to change the error signal in a direction such as to reduce the block velocity other-wise prevailing.

2. A closed-loop control system for controlling a drawworks motor for lifting a predetermined length of drill string to a predetermined position within an oil derrick at a predetermined velocity comprising:
a block arrangement connected to the drawworks motor and adaptable to support the upper end of a drill string during lifting thereof;
means for outputting a position signal functionally related to the elevation of the block arrangement with respect to a vertical axis extending through the derrick;
means for outputting a velocity signal functionally related to the velocity of the block arrangement;
means for outputting a load signal functionally related to the magnitude by which the weight supported by the block arrangement deviates from a predetermined portion of the weight supported by the block arrangement when it is in a substantially static condition;
means for generating an error signal functionally related to the difference between the position signal and a signal representative of the predetermined position to the difference between the velocity signal and a signal re-presentative of the predetermined velocity, and to the load signal; and, means responsive to the error signal for driving the motor in a manner so as to change the error signal in a direction such as to reduce the block velocity otherwise prevailing.

3. A closed-loop control system for controlling a drawworks brake for lowering a predetermined length of drill string to a predetermined position within an oil derrick at a predetermined velocity comprising:

a block arrangement connected to the drawworks brake and adaptable to support the upper end of a drill string during lowering thereof;
means for outputting a position signal functionally related to the elevation of the block arrangement with respect to a vertical axis extending through the derrick;
means for outputting a position signal functionally related to the velocity of the block. arrangement;
means for outputting a load signal functionally related to the magnitude by which the weight supported by the block arrangement deviates from a predetermined portion of the weight supported by the block arrangement when it is in a substantially static condition;
means for generating an error signal functionally related to the difference between the position signal and a signal representative of the predetermined position to the difference between the velocity signal and a signal representative of the predetermined velocity, and to the load signal; and, means responsive to the error signal for applying the brake in a manner so as to change the error signal in a direction such as to reduce the block velocity otherwise prevailing.

4. An automated oil drilling rig comprising:
a drawworks for lifting and lowering a predeter-mined length of drill string, the drawworks including a lifting motor, a lowering brake, and an elevator arrange-ment including a travelling block;
means (105, 106) for controlling the drawworks motor to lift and the drawworks brake to lower a length of drill string to a predetermined height at a predetermined velocity in response to electrical signals representative of a command position and a command velocity input thereto from a programmable general purpose digital computer operating under control of a program and in response to electrical signals representative of the actual block velocity, actual block position, actual elevator loading and a predetermined scaled portion of the initial elevator loading;
position indicating means (83) for generating an electrical signal functionally related to the actual position of the travelling block moving under the control of the drawworks motor and brake;
tachometer means (94) for generating electrical signals functionally related to the actual speed and actual direction of motion of the travelling block moving under the control of the drawworks motor and brake;
sensor means (95) for generating an electrical signal functionally related to the instantaneous actual net loading on the elevator;
elevator load control means (107) associated with the sensor means and responsive to a general purpose pro-grammable digital computer operating under control of a program for generating an electrical signal representative of a predetermined scaled portion of the acceptable loading on the elevator during lifting and lowering thereof; and, a general purpose programmable digital computer (40) operatively associated with the drawworks control means and the elevator control means and operable under control of a program to output electrical signals represen-tative of command position and command velocity to the drawworks motor and brake control means.

5. The automated oil drilling rig of claim 4 further comprising:
velocity comparison means (108) associated with the tachometer means for comparing the electrical signals representative of the actual speed and actual direction of motion of the block with electrical signals representative of a predetermined maximum velocity and a predetermined direction of motion input thereto from the programmable general purpose digital computer operating under control of a program and for generating alarm signals if either the actual speed or actual direction of motion of the block differs from the predetermined speed or predetermined direction of motion.

6. The automated oil drilling rig of claim 4 further comprising:
logic means (109) associated with the drawworks motor and brake control means and responsive to the pro-grammable general purpose digital computer for disenabling the motor control means during lowering of the travelling block from an upper to a lower height within the drilling rig under the control of the brake control means.

7. The automated oil drilling rig of claim 4 further comprising:
logic means (109) associated with the drawworks motor and brake control means and responsive to the pro-grammable general purpose digital computer for enabling the brake control means and the motor control means during a predetermined initial portion of a lifting motion of the travelling block from a first, lower, height to a second, upper, height and during a predetermined final portion of the lifting motion when the block is within a predetermined close distance of the upper height and for disenabling the brake control means during the portion of the lifting motion intermediate the initial and final portions while the travelling block is lifted under control of the motor control means.

8. The automated oil drilling rig of claim 4 wherein the motor control means comprises a closed-loop control arrangement including:
means (214M) for generating a load signal func-tionally related to the magnitude by which the actual elevator loading deviates from the predetermined scaled portion of the initial elevator loading;
means (210M) for generating an error signal func-tionally related to the difference between the command position signal and the actual block position signal, to the difference between the actual block velocity signal and the command velocity signal, and to the load signal;
and, means (218M) responsive to the error signal for driving the motor in a manner so as to change the error signal in a direction such as to reduce the block velocity otherwise prevailing.

9. The automated oil drilling rig of claim 4 wherein the drawworks brake control means comprises a closed-loop control arrangement including:
means (214B) for generating a load signal function-ally related to the magnitude by which the actual load supported by the elevator deviates from the predetermined scaled portion of the initial elevator loading;

means (208B) for generating an error signal func-tionally related to the difference between the actual block position and the command position, to the difference between the actual block velocity and the command velocity, and to the load signal; and, means (218B) responsive to the error signal for applying the brake in a manner so as to change the error signal in a direction such as to reduce the block velocity otherwise prevailing.

10. The automated oil drilling rig of claim 5 wherein the tachometer means outputs a bipolar electrical signal the magnitude of which is functionally related to the actual velocity of the block and the polarity of which is representative of the actual direction of motion thereof and wherein the velocity comparison means comprises:
a zero velocity network (624) for generating an electrical signal to the general purpose programmable digital computer when the magnitude of the electrical signal respresentative of the actual block velocity falls within a predetermined range of values close to zero velocity; and, a direction indicating network (598) for outputting an electrical signal to the general purpose programmable digital computer when the electrical signal representative of the actual direction of motion of the block differs from a predetermined electrical signal representative of a desired direction of motion.

11. The automated oil drilling rig of claim 10 wherein the direction indicating network (598) comprises:
a first comparator element (599) and a second comparator element (600) each associated with the bipolar electrical signal from the tachometer means and each operative to compare the bipolar electrical signal with a predetermined reference signal and to generate an electrical alarm signal to the general purpose programmable digital computer if the bipolar electrical signal deviates from the reference signals by a predetermined magnitude;
means (617, 618) responsive to the general purpose programmable digital computer for enabling a selected one of the first or second comparator elements.

12. The automated oil drilling rig of claim 10 wherein the zero velocity network (624) comprises:
a first comparator element (625) and a second com-parator element (626) connected to the bipolar electrical signal from the tachometer means at the inverting and non-inverting inputs, respectively;
first potentiometer means (628) for generating a reference electrical signal representative of a pre-determined range of velocities close to zero velocity connected to the first comparator element at the non-inverting input thereof the first comparator element operative to output an electrical signal to the general purpose programmable digital computer whenever the down-ward velocity of the block falls within the predetermined range of velocities close to zero velocity; and, second potentiometer means (636) for generating a reference electrical signal representative of a predeter-mined range of velocities close to zero velocity connected to the second comparator element at the inverting input thereof, the second comparator element operative to output an electrical signal to the general purpose programmable digital computer whenever the upward velocity of the block falls within a predetermined range of velocities close to zero velocity.

13. The automated drilling rig of claim 4 wherein the position indicating means (83) comprises:
magnetically responsive means (695) for generating a pulse when a metallic member associated with the travelling block passes in proximity thereto;
means (706) for counting the number of pulses out-put from the magnetically responsive means; and, means (710) associated with the counting means for outputting a signal with a predetermined magnitude functionally related to the output of the counting means and representative of the actual position of the travelling block.

14. The automated oil drilling rig of claim 13 further comprising means for resetting the counting means to a predetermined value when the travelling block passes a predetermined elevation within the drilling rig.

15. The automated oil drilling rig of claim 13 further comprising means (699) functionally related to the output of the counting means during a predetermined unit of time for generating an electrical signal representative of the velocity of the travelling block.

16. The automated oil drilling rig of claim 13 further comprising means responsive to the direction of motion of the travelling block for outputting a pre-determined logic signal representative thereof, the counting means being responsive to the predetermined logic signal to change the count in a direction in accordance therewith.

17. The automated oil drilling rig according to claim 13 further comprising means operatively associated with the output of the counting means for generating a current signal the magnitude of which is representative of the position of the travelling block along a vertical axis through the drilling rig.

18. The automated oil drilling rig of claim 17 wherein the means associated with the output of the counting means comprises a digital-to-analog converter.

19. The automated oil drilling rig according to claim 13 further comprising:
magnetically responsive means for generating a series of pulses of a frequency functionally related to the velocity at which a metallic member associated with the travelling block passes in proximity thereto; and, means responsive to the series of pulses and to the frequency thereof for outputting a voltage signal the magnitude of which is representative of the velocity of the travelling block.

20. The automated oil drilling rig of claim 19 wherein the means associated with the output of the magnetically responsive means comprises a frequency-to-voltage converter.

21. The automated oil drilling rig according to claim 14 wherein the resetting means comprises:
first means (721) associated with the counting means for forming a first predetermined voltage pattern represen-tative of a count corresponding to a first, upper, height along the vertical axis through the drilling rig; and, first switch means (715) responsive to the proximity of a first, upper, target disposed at the first location along the vertical axis and associated with the counting means for presetting in the counting means the count corres-ponding to the first, upper, height.

22. The automated oil drilling rig according to claim 21 wherein the resetting means further comprises:
second means (722) associated with the counting means for forming a second predetermined voltage pattern represen-tative of a count corresponding to a second, lower, height along the vertical axis; and, second switch means (716) responsive to the proximity of a second, lower, target disposed at the second height along the vertical axis and associated with the counting means for presetting in the counting means the count corres-ponding to the second, lower, height.

23. The automated oil drilling rig of claim 13 further comprising:
means associated with the counting means for re-setting the counting means to a predetermined count a predetermined delay time after the occurrence of an event;
and, means for controlling the magnitude of the delay time.

24. The automated oil drilling rig of claim 5 wherein the position indicating means (83) also generates an electrical signal functionally related to the actual velocity of the travelling block and wherein the velocity comparison means (108) includes means (653) responsive to the actual velocity signal generated by the position indicating means for comparing that velocity signal with a predetermined maximum velocity reference signal and for generating an output electrical signal to the general purpose programmable digital computer representative of the actual velocity signal from the means (83) exceeding the maximum velocity reference signal.

25. The automated oil drilling rig of claim 4 wherein the elevator load control means (106) comprises:
first means (748) responsive to an electrical signal output from the general purpose programmable digital computer operating under the control of a program for sampling the signal output from the sensor means (95) at a predetermined time prior to the elevator acquiring a load thereon and for generating the electrical signal functionally related to the instantaneous actual net loading on the elevator.

26. The automated oil drilling rig of claim 25 further comprising:
second means (770) responsive to an electrical signal output by the general purpose programmable digital computer operating under the control of a program for sampling the instantaneous actual net loading on the elevator at a predetermined time after the elevator acquires a load and prior to motion of the elevator under the control of the motor or brake control means to generate an electrical signal functionally related to the initial static loading on the elevator.

27. The automated oil drilling rig of claim 26 further comprising:
means (812,813) associated with the second sampling means for generating an electrical signal functionally related to a predetermined selectable portion of the initial static load signal to generate the electrical signal representative of the predetermined scaled portion of the initial elevator loading.

28. The automated oil drilling rig according to claim 27 wherein the means (812) includes a series-connected array of resistors adapted to scale the initial load by a factor greater than one, the predetermined scaled portion of the initial elevator load being applied to the motor control means (106).

29. The automated oil drilling rig of claim 27 wherein the means (813) includes a series-connected array of resistors adapted to scale the initial load by a factor between zero and one and wherein the predetermined scaled portion of the initial load is applied to the brake control means (105).

30. The automated oil drilling rig of claim 28 further comprising means (824) for comparing the scaled output with an electrical reference signal representative of an appropriate range of load limits imposable on the elevator during a lowering operation of the drill string and for outputting an electrical alarm signal to the general purpose programmable digital computer if the scaled signal deviates below the reference signal.

31. The automated oil drilling rig of claim 29 comprising means (836) for comparing the scaled output with an electrical reference signal representative of an appropriate range of load limits imposable on the elevator during a lifting operation of the drill string and for outputting an electrical alarm signal to the general purpose programmable digital computer if the scaled signal deviates above the reference signal.

32. The automated oil drilling rig of claim 4 wherein the elevator load control means (107) includes means for generating an electrical signal to the general purpose programmable digital computer representative of the acquisition of a load by the elevator.

33. The automated oil drilling rig of claim 32 further comprising means (850) associated with the actual instantaneous net load on the elevator for generating an electrical signal to the general purpose programmable digital computer representative of the acquisition of a load by the elevator.