CA1147435A - Block position and speed transducer for a computer- controlled oil drilling rig - Google Patents

Abstract

ABSTRACT
Apparatus for indicating the position of a travelling block along a vertical axis within a computer-controlled oil drilling rig is characterized by a magnetically responsive element for generating a pulse when a metallic member, movable with the travelling block, passes in proximity thereto. A
counter is operatively associated with the magnetically responsive element to count the pulses therefrom. An electrical signal of a predetermined magnitude functionally related to the output of the counter is representative of the position of the travelling block.

Description

~7~35 sLocK POSITION AND SPEED TRANSDUCER FOR COMPUTER-CONTROLLED OIL
DRILLING RIG

This application is a division of Canadian patent application Serial No. 296,905 filed February 15, 1978.

BACKGROUND OF THE INVENTION

Field of the Invention This invention relates to a computer-controlled oil drilling rig, or derrick and in particular to a block position ~:
and speed transducer therefor.

Description of the Prior Art The physical structures utili~ed in the generation of a hydrocarbon producing well are known in the art. For e~ample, drawworks have been long utilized 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.
~elly and assigned to the assiqnee 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 functions performed by the mentioned structural systems requires the superintendence of many skilled derrick operators. 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 associated structures mesh so

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as to maintaill the task o~ ma~ing-up or breakinc3-out a drill string at a minimum from a time standpoint consistent with safety of the personnel and the bore.
It is therefore advantageous to provide each of those structural systems with an appropriate èlectronic control system and to utilize a pro~ra~ed general purpose, digital colnputer to superintend and sequence thc proper operation of the physical structures to most efficiently control derrick operations. It is appreciated that the lQ elimination of manual control increases the effi,ciency al~d lowers the cost of well drilling operations.
By way of particular examples, in the prior art, the lifting or hois-ting 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 auxiliary brake which absorbs the potential ener~y '~ of the string during lowering. The manual control oE these functions may be inefficient during foul weather or other-wise detrimental environments. It would be advantageous to provide an electronlc control system in cooyerative association with a programmed digital computer to control the lifting and lowering cycles, and specifically the velocity and position of the travelling block and elevatGr.
The loading on the travelling block and elevator, and specifically the increase in block loading when in the brea~-out cycle occasioned by friction in the bore as well as

3(i the decrease in block loading in the make-up cycle occasioned by an obstruction in the bore, present problems in the manual control of the derrick. It is therefore advantageous to ~L~47435 provide an electronic load sensing arrangcment to provide inputs to an electronic drawworks control to adjust the velocity and position of the travelling block in response thereto and to recogni~e 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 breakinc3 joints in a drill string. It is advantageous to provide an electronic network controlling the operations of the 1~ tongs, and to interconnect that control network with a programmed general purpose digital computer so as to repeatedly and efficiently operate the tongsto perfoLm its function. Of course, since various of the physical structures discussed are actuated by hydraulic or pneumatic operators, sui-table 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.

7L~35 SU~IMARY OF THE INVENTION

The invention to which th:is divisional application is directed pe~tains to an apparatus for indicating the position and velocity of a travelling block with respect to a vertical guide track within a computer-controlled oil drilling rig. The apparatus includes a friction wheel mounted on the travelling block and biased into contact with the guide track, displacement of the travelling block upwardly or downwardly with respect to the guide track rotating the friction wheel in a first or a second angular direction, respectively, at an angular velocity related to the velocity of the travelling block. A toothed wheel is mechanically coupled to the frictlon wheel for rotation~
therewith. A magnetically responsive element is operatively associated with the toothed wheel and is adapted to generate an electrical signal representative of the direction of motion of the toothed wheel and to generate a pulse each time a tooth on the toothed wheel passes in proximity thereto. A converter ;~ 2 0 `

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arrangement response to the frequency of the pulses output from the magnetically responsive element is provided for generating a current signal representative of the velocity of the travelling block and a counter arrangement counts upwardly or downwardly the pulses output from the magnetically responsive element in accordance with the electrical signal representative of the direction of motion of the travelling block. A further converter is responsive to the count output from the counter arrangement for generating a current signal representative of the position of the travelling block with respect to the guide track.

More particularly the invention herein relates to a block position and speed transducer for indicating the position of a travelling block along a vertical axis of a computer-controlled oil drilling rig. The transducer includes magnetically responsive means for generating an output pulse when a metallic member, as a tooth in a gear wheel, passes in proximity thereto. Counting means for counting the pulses from the magnetically responsive means are provided. Means associated with the counting means output a current signal, the magnitude and polarity of which are functionally related to the position and direction of movement of the travelling block.
Further, means for outputting a signal functionally related to -the number of pulses for a predetermined unit of time to indicate the velocity of the travelling block is included.

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7~35 BRIEF DESC~IPTION OF Tll~ DR~WINGS

The invention will be more fully understood from the following detailed description of a preferred en~bodiment thereof, taken in connection with the accompanying drawings, which form a part of -this application, and in which:
Fig~re 1 is a generalizeA block diagram illus-trati}lg the interactions between derrick structure 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 dra~orks 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 drawworks control system embodying the teachings of this invention, appearing with Figure l;
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 diaqram of the electronic-to-pneumatic interface associated with the drawworks brake actuator; :~
: Figures 8A and 8B are detailed schematic diagrams of the brake control subsystem shown in the block diagram Figure 3;

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7~35 Figures 9A and 9s are detailed schematic diagrams of ~he motor control subsystem shown in the block diagram Figure 3;
Figure 10 is a detailed schematic diagram of the velocity comparator shown in the block diagram Figure 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; and Figure 13 is a detailed schematic diagram of associated safety networks and override arrangements embodied,~by the invention.

~7435 DESCRIPTION OE PREFERRED EMBODIMENT

Throughout the following description, similar reference characters and reference numerals refer to similar elements in all Ei~ures of the drawings.
Referring first to Figure 1, a generali~ed 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 s~/stem 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 24.
The derrick also includes a power tongs structural system 28 and a tong control system 29 associated there-with. The tong systems generally provide the make-up or break-out o~ individual pipe stands into or out of a drill string. Command signals initiatin~ or ceasing the physical _ 9 _ ~7~35 actions oE structural elements of the ton~s structural system 28 are input thereto from the tongs control system as 29, as illustrated by a line 30. Feedback signals represen-tative of various physical parameters associated with each of the structural elements wi-thin the tongs structural system 28 are input to the tongs control sys-tem 29 as illustrated by a line 31.
Also provided is a racker structura] 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 line 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. 1,069,4~3, ~;
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 diagrammatically by a line 41 (to the drawworks control system 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 back various ; ;
signals to the computer 40, as illustrated by the lines 44, ::

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~7435 45, and 46, from the drawworks control system 21, tongs control system 29, and racker control system 35, respectively.
Further, the computer 40 receives direct data input of physical parameters, as illustrated as by a line 47.
The computer, in accordance with the programmed instructions, sequentially initiates the operations oE
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 tongs, are through 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.

: ' 1~47435 STRUCTURE

Referring to Figure 2, shown is an illustration oE
the oil drilling rig, or derrick 20 incorporating the basic rig features and having thereon the structural elements which are included in the structural systems outlined in connec-tion with Figure 1. These structural systems are in co-operativelassociation with their associated control systems to initiate and cease the operation 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 e~tending su`bstantially 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 derric~ and provides the rotational energy whereby a drill string, comprised of end-to-end connected drill pipe stands, ma~- 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 Figure 2, the upper end of the drill string, or more precisely, the upper end of the uppermost pipe stand con~ected within the drill string, is shown as protruding above the slips 55. Each upper end of the pipe ~;
stand has a distended joint 56 used in connection with the ~ ~
tong operation. The programmable general purpose digital ; ~ ;

computer 40 may be convenientIy housed in a structure 57 on ~ ;
the floor 53.

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The axis of the bore being ~enerated beneath the floor 53 of the derrick extends centrally ancl axi~llly thro~(Jh the derrick. A racker structural system, generally indicated bv the reference numeral 34, carries individual pipe s~ands between a storage location, or "set back", disposed at the side of the derrick and a location along the vertical axis thereof. It is along the vertical axis of the derrick 20 that the drill string is retracted 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 control systems has been disclosed and claimed in the above- ~-~
referenced copending Canadian Serial No. 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 b~ 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 elevator 75 is ~; ~ offset below the travelling block 68 by a predetermined ;
distance h. The elevator 75 includes a gripping arrange~
ment to grasp or release the distended~joints 56 of a pipe stand.
A block retractor arrangement~78 lS connected to the ~;
travelling block 68 and serves to retract the travelling - 13 ~
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1L~47435 block (~ith depending elcvator 75) away from the vertical.
axis of the derrick along which it usually depcnds. The retractor 78 includes a carriage 79 which is rectillnearly moveable through a wheeled arrangement along a substan--tially ~Jertically extending retractor guide track 80.
block position and speed transducer (B.P.S.T.) 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 1) and to the computer 40.
The block position transducer 83 also provides a feedback signal representative of the velocity at which the traYel-ling block 68 is moving along the track 80. Of course, i.t ~ay be readily appreciated that since the elevator 75 is vertically offset by the distance h from the travelling block !~
68, the position of the travelling block 68 along the track 80 also indica-tes the position of the elevator 75 with respect thereto, and vice versa. And, since the travellin~
~o 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 axis of the derrick ~0 may be : accurately monltored by the block position and speed trans-ducer 83. The structure and internal circuitry of the block position and speed transducer 83 is set forth in full herein.
For a purpose more fully disclosed herein, upper and lower limit switches 84 and 85 (Fig. 11) are provided on the :
carriage 81. An upper target 86 and a lower target 87 a~re provided at predetermined locations on:the retractor guide track 80.

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1~47~35 As is the usual practice in the art, the cabLe arran~ement 67 which supports the travelling bloc~ 68 and structures (including 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 in the drawworks structural system. More particularly, the fast line 90 is attached to a spool or drum 91 of the drawworks. The drum 91 is driven by an electric motor 92 of any suitable type as diagrammatically illustrated in Figure 2. For example, a motor manufactured by the Electromotive Division of 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 THYRIG manufactured 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 ener(3y whereby the travelling block 68 and the structures depending there-from may be moved with respect to the vertical axis of the derrick 20 from a first predetermined to a second pre-determined elevation. Therefore, control of the motor drive 93, and in turn, of the motor 92, effectively controls the velocity and acceleration of the travelling block f8 as it is lifted from a first to a second elevation. The drawworks includes a suitable clutch and gear arrangement therein.
~' ~7435 ~ drum tachometer 94 is physica~ly locatccl in adj.l-cency to the spool 9l. The output of the drum tachometer 94 is a feedback signal to the drawwor}:s control svstem 21 representative of the velocity of the drum 91 which si~Jnal is directly proportional to the velocity of the travelling block 68 and depending structures. Within the dead line 88 is provided a transducer 95 known as the dead 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 eable arrangement 67 at all times supports the travelling block 68 and its clepending structures. The unloaded, statie weight of these structures defines a "tare" weight of the structure supported by the cable arrangement 67. When the elevator 75 acquires a lo~d, 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, frietional or other forces may alter the load carried by the elevator 75. The D.L.F.S. 95 therefore provides an accurate feedback signal as to the ; instantaneous loading on the elevator 75 of the drawworks structure. As lS generally the ease with the other trans-dueers, other eonvenient physieal loeations therefor may be ;
used to measure the desired parameters. In addition, any ~ ~ ;
appropriate means for measuring the desired parameters may also be utilized, as is appreeiated by those skilled in the ~ ~
art. ~ ;
~lso included within the drawwork~s structural systcm ~30 is a brake. The drawworks brake includes a primary hrake the functiOn of which is to control the velocity and de-celeration of the drawworks travellincJ hlock (when unloaded) - 16 - ~

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1~7435 and to stop the motion thereof. An auxiliary brake is also provided within the drawworks structural system to sub-stantially absorb the potential energy associatecl with the lowering of a loaded travellinq b:Lock. In the particular embodiment of the invention shown in Figure 2, the primary brake is a drum brake 96, manually operable by a pivotable lever 97. A spring 9~ biases the drum brake 96 into 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 cylinder 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, it isknown 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. ~ 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 ~1 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.

~7~35 It is important to note that whate~er auxiliary brake configuration and act~lator therefor is utilized, the drawworks structure includes ~ brake which is controlled by the dra~orks control system 21 so that the desired velocity acceleration of the travelling block 68 is maintained as it moves from an upper to a lower final positlon. ~lso, the brake is operable to set and hold a liftecl or hoistecl loa-l in the upper position. If the operator deems it necessary to halt the movement of the physieal structures associated ., lo with the dra~orks, 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 dra~orks control system 21 by de-pressing a push-button switch loeated in the control panel 103a. The spring 98 may be manually overridden to release the brake.
The raeker strueture 34 is operable to carry a pipe stand from the vertieal centerline of the derrick to the set '0 baek. In a make-up cycle, the pipe stand to be added is stabbed into the already emplaeed and eonneeted stands which comprise the drill string. When joined to the drill string, the raeker strueture 34 relinquishes the load to the draw-works, whieh lowers the string into position. In a breakout eyele, the drawworks strueture 22 withdraws the drill string, and, as eaeh pipe stand therein is disconneeted from the string, the raeker strueture 34 aeeepts the load from the drawworks and moves the pipe stand to a storage loeation.
The aetual eonneetion and diseonnection of pipe stancls ~0 Erorn t:he drill string is aeeomplishecd by the power tongs strueture 28 uncler the eontrol of the tongs eontrol system 29. Very briefly, the tongs ineludes a baekup, which holds . ~

~7435 the lower pipe element defining the joint, while a second element of the tongs - the power driven tong - connects or disconnects a pipe stand to the upper pipe element thereto.
The tongs also includes a lift to move the associated backup-jaws structure at a predetermined speed to a pre-determined operating elevation with respect to the vertical axis of the derrick. The backup and the jaws usually circumferentially surround the dr:ill string as it advances in the bore. Put another way, the vertical 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 convenien~ 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 dra~works. 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 hich the tongs are moved from the storage position to standby position. The particular joint sensor 1025 embodied by the teachings of this invention is made clearer herein.
The details of the structure of the tongs, the joint sensor and the tongs control system (including an electro-hydraulic interface) is discussed in detail herein.

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- ' 7~35 OP~RATION

~ aving defined the elements of the various structural systems, the operating sequency thereof during a typical make-up or break-out cycle is presented, to graphically illustrate the physical interactions between the defined structures. Once this is done, a detailed description of each of the control systems initiating and ceasing the physical operations performed ~y the structuxal 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 string is lifted from the bore. With the upper end of the still-attached 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 elevator suspended therefrom is lowered under the control of the drat~works 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 the next-removed pipe stand. The drawworks program and racker program operate on a time-shared basis. The tongs are in a storage position.
The computer sends an actuating signal to the elevator load control subsystem which derives its input signals from the dead line force sensor. A momentary signal output ~rom the computer samples the weight of the unloaded : .

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travelling block and elevator. This tare weight is used, as discussed herein, to ascertain the instantaneous loading on the travelling block and elevator. The elevator then acc~pts the loading of the drill string, and an output feedback signal to that effect from the elevator load control subsystem is used to coordinate opening of the slips. The computer outpu-ts a momentary load sample signal before the velocity 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 deter-mining whether the instantaneous loading on the elevator has exceeded a permissible range of values as selected by an experienced drilling operator.
In response to an actuating signal from the computer, the drat~works 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 subsystem provides output signals to the drawworks motor drive to lift the drill string in a manner wh ch takes into account the position error (the difference between the actual position and command position of the drill string being lifted), a predetermined command 3~ velocity output by the computer, and -the dynamic loading.
During the major portion of the travel the load is hoisted at an uniform velocity equal to the command velocity. As ,:

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~7~35 the precletermined command position is approclche(l, the hoisting velocity is reduced in a manner proportional to the position error. Put another way, the drawworks motor control sybsystem responds to position and velocity feedback si~nals input to it from the block position and speed transducer and the drum tachometer, respectively, to move the travelling block and elevator to a predetermined command elevation at a predetermined command velocity output by the computer.
During the hoisting operation, signals from the elevator load control subsystem are taken into consideration in determining the magnitude of the output signal to the draw~Jorks 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. ~f 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.
~0 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 lifting, 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 system reverts to manu~l 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 also place the joint between thc pipe stand and t:he next lower pipe stand at an elevation for . - ~ , . , , ~474L~S
operation by the power tongs. When the ~loc~ velocity is sufficiently close to zero, a zero v~locity signal is returned to the computer. This sigllal, along with a block position feedback signal sufficiently close to the command position signal are necessary conditions before the actuating command to set the slips to retain the load-is out~ut from the comp-lter. Only with the slips set and supporting the full load of the dr.ill string will the elevator relin~luish the pipe stand to the racker structure. ~s mentioned, after ~o rackillg the previous stand, the racker is moved back toward the vertiGal centerline of derrick, so as to be in a position to accept the nex-t pipe stand. The elevator and block are retracted away from the vertical centerlin~ 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 ~Yere in the storage position above the floor of the derrick.
After the ele~ator had been hoisted above a potentially obstructing position the tongs were actuated and moved to a standby position. After the pipe stand has been finally positioned and the slips set, a jOillt sensor associated with the tongs controls a slower lifting move~ent 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 separated therefrom. The racXer then begins to store the now-separated pipe stand, while the tongs are moved to the storage position. The elevator then is brought into the clevation alon~ the central a~is of the derrick where it may engage the upper end of the still-attached pipe stand to be ' next-removed and the breakout process repeated.

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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. With 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 t slower, speed beyond the standby position wi-th 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 tlle joint. Thereafter, the tongs are lowered to the storage position. The elevator, at the upper elevation, is raised at a creep speed to acquire the drill string load. After the elevator load control subsystem dete~cts that the drill string load is acquired by the elevator, the slips are raiQed and the drill string is hoisted further to disengage~the slips from the drill string. At this time, the rackers, under control of the computer racker program, proceed to acquire the next pipe ;~ ;
stand and carry it toward the vertical centerline of the :: ~
~ 24 ~
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~ ~ ~7435 derrick to the racker standby position. From there t}le rac~ers proceed to the vertical centerline of the derric~.
In response to con~and velocity and col~land position sigllals output from the computer, and utilizing a position feedbac~ signal from the block positi~n and speed trans-ducer, and a v~locity feedback signal ~rom the dra~orks drum tachometer, the drawworks brake control subsystem supervises the lowering of the drill string to a predeter-mined ]ower elevation. The brake control subsystem outputs control signals to the drawworks brake actuator so as to maintain the block velocity near the comnland velocity for the major portion of the travel, and to position the bloc~
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 lo(~d is acquired but before the downward velocity ~hereof 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 loading on the elevator has exceecled . .
a permissible range of loading normally anticipated during a ~ lowering operation.

; During the lowering operation, the outputs to the bra~e actuator from the brake control subsystem take into account the signals relative to loading;from the elevatox ~- 25 ~

~7~3S
load control subsystem. If the actual loading is deviating from the initial s-tatic condition by more than the specified amount, the drat~works brake control slows the velocity ~o brin~ the loading back to acceptable limits. If the actual loadinq is deviating 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 shut down. Other inter-rupt conditions may occur if, during the lowering operation,an indication tha-t 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. ~ith 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.

, 3~
DR}~WWORI;S ~ONTROL SYSTr.M

The dra~works structural system 22 is the collection of the structural elements on the ~errick which perform all of the physical ac-ts associated with the lifting or lowerirl-7 of the drill string. These structural elements have been detailc?d in connection with Figure 2.
The physical actions performed by the drawworks structural system 22 are controlled by an arrangement k}Iown as the dra~orks control system, indicated by reference numeral 21 on the general block diagram Figure 1 and on the more detailed drawworks control system block diagram Figure 3. The computer is interfaced with the drawworks control system 21 through a plurality of input and output lines, each of which will be cliscussed herein. FurtiIer, the draw-works control system 21 i5 input with various feedback si~nals 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.
he drawworks control system 21 includes several interconnected subsystems, as follows: the drawworks brake control subsystem lO5; the drawworks motor control subsystem ]06; the drawworks elevator ]oad control subsystem 107; ~n(l the dra~orks velocity comparator subsystem 108. Further, ;: ~
logic 109 is connected within the drawworks control 21 in ~Q cooperative association wlth the brake control subsystem 105 and the motor control subsystem 106. -~

Feedback signals to the drawworks control system 21 are provided from the block position and speed transducer (s.P.S.T.) 83, which speci~ically provides position feedback signals to -the brake and motor control subsystems, 105 and 106 respectively. The block position and speed transducer ~3 also ~urnishes a velocity feedback signal to the velocity ~omparator 108. However, the primary velocity feedback 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. Any 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, spe_ifically 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 system 21 is connected to the motor drive 93 of the drawworks. For convenience of operation, various voltage-to-current (as the converter 274, for example) and current-to-voltage conversions are effected, with the electronic arrangements for effecting these conversions being detailed herein.
Input to the drawworks control system 21 are signals from various safety overrides present on the physical structure of the drawworks. For example, the STOP control ~74~5 button located on the driller's console is an element of an interlocking circuit. When the STOP button is depressed, it functions to d~nergize the A~TO/MANUAL bus. This bus is input to the motor control subsystem 106 by a line 111.
The line 111 connects to a relay coil 112 and a solenoid cGil 113 of a valve 114. Actuation of the STOP button causes the system to revert from automated to manual control.
g~,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.

- 2g - :~

~7435 DRA~ORKS BRAKE AND MOTOR CONTROL SUBSYSTEMS

The dra~orks brake and motor control subsystems 105 and 106 are now discussed. Both the brake control sub-system 105 and the motor control subsystem 106 receive a

4-20n~ 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 magnitude of the COM~AND 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 signals, also from the velocity comparator 108, are input to the brake control subsystem 105 and the motor control subsystem 106 on the lines 134B and 134M, respectively. The magnitude of the ACTUAL VELOCITY ~ ~:
signal is functionally related to the speed at which the ~ - ;
travelling block 68 is moving under the control of the motor :.

- 30 - ~

or brake. The origin of these signals will be discussed in connection with the description of the velocity comparator 108.
The brake control subsystem 105 and the motor control subsystem 106 each receive an ACTUAL LOAD vol-tage signal related to the actual load on the elevator 75 from the elevator load control subsystem 107 on lines 136B and 136M, respectively. Moreover, from the elevator load control subsystem 107, the brake control subsystem 105 receives an appropriately scaled INITIAL LOAD voltage signal on a line 138B while an appropriately scaled INITIAL LOAD voltage signal is input to the motor control subsystem 106 on a line 138M. The derivation of thesè load si~nals is discussed in connection with the elevator load control 107.
Although the interaction of the logic 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 control subsystem 105 and to the motor control subsystem 106 on lines 140B and 140M, respectively. A BRAKE
RUN signal on a line 142 is output from the logic 109 to the brake control subsys-tem 105. The logic ].09 receives MOTOR
MODE SELECT command on a line 144 from the computer channel B. The logic 109 receives a BRAKE SELECT command from the : channel C on a line 145. As mentioned earlier, the motor control subsystem 106 receives a signal from the override switch 103 on the line 104. As is more clearly shown herein, :
information concerning a manual override is transmitted from the motor control subsystem 106 to the brake control sub-system 105 on a line 147.
Computer channels H and I respectively output CREEP
and CREEP TO ` ENGAGE CLUTCH to the motor control subsystem 106 ~7~35 on lines 150 and lSl. Upon receipt of a CRE~P signal on the line 150, the motor control subsystem 106 outputs a signal CREEP FLIP-FLOP to the brake control subsystem 105 on a line 152.
The output signal from the brake control subsystcm 105 is carried by a line 158 to the brake actuator 99. ~he output signal from the motor control subsystem 106 is carried by a line 159 to the motor drive 93 (throuqh a converter 274). In the preferred embodiment of the inven-tion, both of these output signals are ~-20mA current signals.
In general, it may be stated 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 AUTO/MANUAL bus is con-nected to the dra~orks 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/~NUAL bus voltage de-energizes the coils 112 and 113.
The effect of 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 (Figure 7) from the cylinder 100.
The brake control subsystem 105 and the motor control subsystem 106 are basically similar to each other, at least insofar as to the basic operating principles. They can, there~ore, be discussed together to illustrate how each of the above-enumerated inputs interact to generate brake or .

~7~35 motor control output signals. They differ, of course, in the implementation thereof due to differences in technical requirements and functions to be performed. Preferred embodiments of each subsystem are discussed 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 COMMAND VELOCITY; the COMM~ND
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 instantaneously 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 ~0 a relatively static cvndition. 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, the analog signal representative of the actual position of the travelLing ~ `
block (ACTUAL POSITION~ is substracted at a differential :
ampliiier 200 from the analog signal representative of the ~redetermined final position selected by the computer (COMM~ND POSITION). The resulting difference, or position error signal Ep, taken from the output of the differen-tial - 33 ~

- .. , . . . , :

~7~5 amplifier at the node 201 is summed at a summing junction 202 with -the ACTUAL VELOCITY signal to define a position error plus velocity signal, Ep+ V. The COMMAND VELOCITY
signal is input to an amplifier 204 and a series diode, the combination of which acts as a limiter to limit the magni-tude of the position error signal Ep present at the node 201 ~ This effectively results in the magnitude of the COMMAND VELOCITY signal establishing a maximum velocity at which the travelling 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 208 is a total error signal ET, from which the output signal of the motor or bra~e control subsystem is derived.
The load factor signal VLF is derived from the ACTUAL
I.OAD 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 20 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 factor VLF. An adjustable portion of the load factor signal (adjustable through the potentiometer KL) is input to an implifier 214, the output of which is applied as the scaled load factor signal tKL)-(VLF) to the difference amplifier 208. The effect of the load factor signal VLF is to change the total error signal ET 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 movement has not exceeded the allowed range of devia-. .

7~35 tions from the initial static load) -the total error signal ET is then derived exclusivcly from thc position error plus velocity signal, Ep-~ V.
The total error signal ET, comprised of the above-mentioned input factors, is, in effect, used as an input to a closed-loop servo control system operative 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 ET, 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 veloci;-~y producing the zero total error signal ET.
As may be appreciated, the magnitudè of the total error signal ET determines the rate of change of velocity.
The greater the absolute magnitude 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. ~he smaller the absolute magnit~de of ET, the smaller is the rate of change of block velocity - either through decreased driving signals to the drawworks motor or increased application of the drawworks brake. To reiterate, however, the nature of the motor and brake control subsystems is such that the magnitude of the total error signal ET tends toward zero. As the magnitude of the output of the integrator-amplifier network 218 increases, the motor speeds up (if in motor mode) or the brake goes on (if in brake mode), ais explained in connection with Figures 5 and 6.

7~3~
The load factor VLF tends to change the total error ET so as to reduce the hoisting or lowering velocity. The effect of the load factor VLp is to limit the actual velocity of the travelling block to a value less than the programmed command velocity and a value necessary to maintain the instantaneous elevator load within the range of limits set by the factor ~N~
Having described the general operating principles behind the drawworks brake and motor control subsystems, ~o reference is invited to Figures 5 and 6, which are sirn-plified signal diagrams patterned upon the signal diagram of Fi~ure 4 and which are directed toward the brake control subsystem 105 and the motor control subsystem 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 ~ are, of course, utilized, and need not be summarized again. In Figure 5, i the position signals are input to the termlnals of the differential amplifier 200B, as shown. The position error signal (Ep)B is adjustable through a potentiometer (Kp)B
and amplified by an amplifier 230B havin~ a resistor 231B `~
at its output. At the node 201B, the readjusted portion of the position error signal (Kp)B (Ep)B from th~ output ~ ~of the amplifier 230B is connected to the summin~ junction ~ -202B through a resistor 232B. The ACTUAL VELOCITY signal is connected through a resistor 233B to the junction 202B.

- 36 ~

.. , . . ... .- ~ . . . .. . . .. . .

LgL7~35 The magnitude of the adjusted position error signa1 (Ep)B-(Kp)B at the node 201B is limited by the macJnitude of the CO~ND 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 magnitude of the position error exceeds the magnitude of the COMMAND VELOCITY signal, it is limited thereby and the COMMAND 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 computer. The composite position error plus velocity 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 summed at the amplifier 212B. The output of the amplifier 212B is the basic load factor signal (VLF)B
indicative of the magnitude ~y which the actual load differs from a predetermined fraction Kl of the initial static load. 'rhis load factor signal is connected through a diode 237B to the potentiometer (KL)B~ The ampli~ier 214B is connected to the potentiometer (KL)B, with the ~ ~
amplifier output being connected to the difference ~ -- 37 - ~
~:
:
- - - . : . .

3~
amplifier 208B. The voltage value input to the difference amplifier 208B is, of course, equal to zero or to the value (~L)B-(VLF)B. A zero output signal is present at the amplifier 214 output as long as the ACTUAL LOAD signal is greater than or equal to the absolute value of the pro-duct of INITIAL LOAD- (-Kl). However, if the ACTUAL LOAD
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 output 210B ofthe difference amplifier 208B iS applied to the integrator-amplifier network 218B. The magnitude of the ou-tput of the integrator-amplifier 218B on the line 220 determines the velocity at 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 ractor signal, if one is present, is to reduce the velocity of the block.
Thus, the block is limited in its velocity to the lower of the maximum COMMAND VELOCITY programmed into the computer (which limits the signal at the node 202B) or the velocity level required to maintain the elevator 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 signal (ET)B is split at anode 238B, with an adjustable portion thereof taken by a ,. ~

7~35 potentiometer (KFF)B and input to an amplifier 239B con-nected to a resistor 240B. This path improves the overall dynamic response of the network 218B to step-changes in the total error siynal. The other parallel branch includes a potentiometer (KINT)B which pres~ents an adjustable portion of the error signal (ET)B to an integrating amplifier 241B.
The output oE the integrating amplifier 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 output 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 includes 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 spring 98 moves the brake (Figure 2) toward the release position. The lever 97 is physically connected to the piston cylinder arrangement such that the introduction of a pressurized fluid into the ~0 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 ~7435 proportional to press~lre of the fluid in the cylind~r 100.
~s discussed immediately above, the output of the voltac~e-to-current converter 246B is a current signal the m.lgnitude of which determines the degree to which the brake is applied. The output line 158, (together with a common line) is connected to a current-to-pressure transducer 265. Of course, the output signal on the line 158 may be operated upon by any suitable signal conditioners, ramp or d~lay 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 265 outputs a three-to-fifteen p.s.i.
air signal on a line 266 connected- to a hiqh-volume three-to-one booster relay 267. The output of the booster relay 267 is applied through a line 268 to the brake air cylinder 100. The output of the relay 267 is limited by a regulator 269 disposed in a line 270 from the supply to the relay 67. Similarly, the output of the transducer 265 is held within predetermined limits by a regulator 271 disp3sed 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/MANUAL bus, the valve 114 discon-nects the booster 267 from the cylinder 100 and vents the cylinder 100 to atmosphere, thus applying full braking effort. In connection with the Figure 7, it is noted that the operator may manually override the brake control sub~
:30 system by applying a physically superior force on the lever 97 in opposition to the force of the fluid within the cylinder 100. An electrical override signal applied to the :~

~~40 line 104 by actuating of the switch 103 would be a preferred mean~.of overriding the brake (Fiqure 3). The effec~ of such an override signal on the motor and brake subsystems is discussed herein. Similarly, the brake may be released by manually applying a force to overcome the force of the spring 98.
Shown in Figure 6 is a simplified signal diagram for the motor control subsystem 106. The operation of the motor control subsystem 106 is very similar to that discussed in connection with the brake control subsystem 105. The position error signal (Ep)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 (Kp)M and amplified by the amplifier ~30MI 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 surnming junction 202M through a resistor 232M. The ACTUAL
VELOCITY signal is connected to the surnming junction 202M
20 through 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 a~nplifier 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 COMMAND ~; ;
~ -, VELOCITY signal. If the magnitude of the position error exceeds the magnitude of the COMMAND VELOCITY signal, it is ~ -limited thereby and the COMM~ND VELOCITY signal is sumrned at the summing junction 202M. The effect of the above~
described arrangement is to~effectively limit the maximum ' - . . .

~7435 velocity of the block while it is beill~ hoisted. This maximum velocity is programmable into the computer and ~ro-tects the bore from the detrimental effects of swabbing.
The appropriately limited (if necessary) composite position error plus velocity signal (Ep+ V~M is presented to the inverting input of the difference amplifier 208M.
To the non-inverting input of the difference amplifier 208M is applied a signal related to the load factor signal (VLF)M, derived from the load signals input to the motor control subsystem 106, including the ACTUAL LOAD and the INITIAL LOAD scaled by the appropriate factor ~-K2). 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 tVLF)M. It represents the dif-ference between the ACTUAL LOAD and the INITIAL LOAD
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 20 voltage applied to the diffPrence amplifier 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 LOAD signal scaled by a factor K2. Thus, the actual load may range as high as (INITIAL LOAD)- (K~) without causing a load factor output.
However, if the ACTUAL LOAD increases beyond the INITIAL
LOAD multiplied by a factor K2, an outpùt signal equal to the difference betwePn the ACTUAL LOAD and the scaled INITIAL
LOAD is applied to the potentiometer (KL)M. This load factor output is suitably scaled by the potentiometer (KL)M.

The total error signal ~ET)M is applied to the in~egrator-amplifier network 218M. The magnitude of the output of the integrator-amplifier network 218M on the line 220 determines the velocity at which the block is moved up-wardly. In general, the larger the signal 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 chan~e of veloci-ty. That is, the greater the total error signal (ET)M, the lar~er 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 limited by controlling the velocity at which the block is lifted. This prevents excessive damage to the bore during hoisting by excessive hydrostatic forces caused by excessive hoisting -~
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 (K~F)M and to the inverting input of the amplifier 244M. This path improves .
the overall dynamic response of the integrator-ampli~ier 218M to step-chcmges in the total error signal. The other parallel branch includes a potentiometer (KINT)M which takes an adjustable portion of the total error signal and inputs that signal to the integrating amplifier 241. The output o~ the integrating amplifier 241M is presented to the non-inverting input of the ampllfier 244M.
, , ~

_ 43 _ 7~35 The output 220M of the integrator-amplifier network 218M is applied to a voltage-to-current converter 246M
through a resistor 245M. A 4-20MA current siynal propor-tional to the voltage output of the integrator-amplifier network 21~M 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 motor control subsystem 106 is the solenoid relay 112, operable to interrupt the current flow from the converter 246M to the current-to-voltage converter 274. The output of the converter 274 is connected to thP 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 supplied by a reference amplifier network, including a feedback path 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 ~ain voltage follower. The output voltage signal taken at the emitter of the transistor 277 is connected to the motor drive 93 to drive the drawworks mo.tor 92 at a speed related to the output of the integrator-amplifier network 218M.
Detailed descriptions of the brake control subsystem 105, the motor control subsystem 106 and the logic 109 are now set forth.

.;~

, .,, . ~ : :

74~35 13R~KE CONTROL SUBSYSTEM SCII~MATIC

Referring -to Figure 8, the detailed description of the brake control subsystem 105 :is shown. The COMM~ND
POSITION signal is input on the :Line 115B (Figure 3) and connected through a resistor 284 to the inverting input of the differential amplifier 200B. The ACTUAL POSITION signal is input on the line 116B and is presented to the non-inverting input of the differential amplifier 200B through the resistor 285. The non-inverting input is connected through a resistor 286 to ground potential. Both the ACTU~L -~
and COM~ND 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 respPnse. 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 through a resistor 295 to the non-inverting input of the amplifier 230B. The inverting input of the amplifier 230 is connected through a resistor ; 296 to the wiper of~a potentiometer 297, the high end of which is tied to a negative potential through a resistor 3n 298. The purpose of the potentiometer 297 is to set a - 45 ~

, 7~35 minimum velocity. The output of the ampl:ifier 230B is fed back through a resistor 299 to the inverting input thereof.
This, in combination 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 204B through the diode 239B. The COMMAND VELOCITY signal is input from the line 132B to the non-inverting in~put of the amplifier 204B
through the resistor 300. The inverting input is con-nected to the output through the resistor 301 and ~he 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 ir.
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 is formed, as discussed, by the summation of the adjusted position error signal with a signal representative of the ACTUAL VELOCITY taken 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 signal is applied to the inverting input of a comparator 302 by a line 356, as discussed herein. The signal at the summing junction 202B is presented to the inverting input of the difference amplifier 208B. The non-inverting input is con-nected to ground through a resistor 303. As discussed, however, the non-inverting input of the difference amp- ~
lifier 208B is also presented with an adjusted portion of a ~`
load factor signal.

~ 7435 ACTU~L LOAD si~nals are input on the line 136B and 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 236~, 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 the in-verting input through a loop including the diode 305 and t~e resistor 306. The output of amplifier 212B is connected through the diode 237B to the potentiometer (KL) B. The cathode of the diode 237B is connected with the inverting input of the amplifier 212B through a resistor 307. The wiper of the potentiometer is connected through a resistor 308 to the non-inverting input of the amplifier 214B. The inverting input is connected to ground potential thro~gh 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 31OA.
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 paths. Once such path includes the potentiometer (KFF) B ~ the wiper of which is connected to the in~erting input of the amplifier 239B
through a resistor 312. The non-inverting input is tied to ;~
ground potential through a resistor 313. The output of the amplifier 239B is fed back through a resistor 314 to the inverting input thereof and is also connected to the node 243B through the resistor 242B. The second parallel path - ~7 -~;,'' :

~7~3~

includes the potentiometer (KINT)B, the wiper of which is connected through a resistor 315 to the inverting input of the inte~rating amplifier 241B. The non-inverting input of the amplifier 241B is tied to ground potential through a resistor 316. The offset of the integrating amplifier 241B
is set to zero by a potentiometer 317. The output of the integrating amplifier 241B is fed back through 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 applied to the inverting input of the amplifier 244B. The non-inverting input is tied to ground potential through a resistor 319. The out-put of the amplifier 244B is fed back to the inverting input through a resistor 320.
The output 220B of the integrator-amplifier network 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 collector of the transistor 324 is tied to a positive potential. The signal at the emitter 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 resistor 245B and the potentiometer 321 establish the conversion gain of the network 246B. The output of th~ brake control subsystem 105 is taken from the emitter bf the transistor 324 at the junction of the resistors 326 and 327 and is carried by the :

.~ - . . . .

output line 158. The emitter of the transistor 324 is connected to the ungrounded side of the resistor 323 through tile s~ries connection of the resistors 326 and 327 and a pc~tentiometer 328. This cornbination of resistors makes the output on the line 158 a constan-t current source.
The potentiome-ter 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 lQ anode of the zener diode 331. The anode of the diode 331 is also tied to a negative potential through the resistor 427s.
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 xesponse 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 1~7 to impose a suitable voltage on the inverting inputs of the amplifiers 239B and 241B so tha-t 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 loclic 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 are connec-ted at one side to a positive potential and at the other sides, through resistors 340 and 341, respectively, to the inverting inputs of the amplifiers 239B and 241B. When energi~ed, the positive pot:entials 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 signal from the difference amplifier 208B.

' ~`:
-- d~ 9 -- : ~

"

~7~35 Another override circuit of a sort is provided at 342. This network response to a MOTOR RUN signal from the logic 109 on the line 140B to release the brake despite the signal inpu-t to the amplifier 244B. The logic 109, in general, outputs a MOTOR RUN signal when in receip-t of a MOTOR MODE SELECT signals, as is discussed fully herein.
The line 140B is 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 ~mplifier 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 20mA output signal from the converter 246B to the ou'put 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 going 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 logic 109 is discussed her~in.
Various other components illustrated in Figure 8A, but not as yet discussed, are now set forth for future reference. The position error signal from the differential amplifier 200B on the line 293 is applied to the lnverting input of the position comparator 294. A signal derived from a final position potentiometer 351 ~onnected to a positive potential through a resistor 352 is applied through a resistor 350 to the non-inverting input of the comparator 294. The po-tenti~meter 351 sets a predetermined voltage signal so that when the position of the block is within a predetermined close distance of the command position, the comparator 294 output signal connected , ' ' .
through a resistor 353 and a diode 354 switches from a logic 0 to a logic 1.

This signal is carrie~ by a line 355 into the logic 109.
Similarly, a brake release comparator 302 derives its inverting input from the ACTUAL POSITION signal on the line 356. The non-inverting input is connected through a resistor 357 to a point between resistors 358 and 359 con-nected in serles between a positive potential and ground.
The comparator 302 is connected through a resistor 360 an(l a diode 361 and carried by a line 362 to the logic 10~.
This establishes a switching threshold voltage for the comparator 302, and thus a threshold velocity. During the motor mode, the ACTUAL VELOCITY is positive. Durinq 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 ~41B (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 and the resistor 366 and ground.
This network is provided so that when a signal is present on the line 152 the integrator gain is effectively in-creased so that the integ~ator-amplifier 218B responds more `~
rapidly to the small creep velocity signal.

~;

7~35 I.OGIC OPERATION

The logic 109 includes input lines 194 (MOTOR MOD~
SELECT) and 145 (BRAKE MOD~ S~LECT) from the computer channels 3 and C respectively (Figure 3). Output lines 140B (MOTOR RUN) and 142 (~RAKE RUN) from the logic 109 are connected within the brake control subsystem 105 as dis-cussed above. The output line 140M (MOTOR RUN) (Fic3ure 3) from tlle logic 109 i9 input to the motor control subsystem 106. The logic 109 includes cross-coupled NAND gates 370C
and 370D with inverter gates 370A and 370B. 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 gates 382, 384 and 386. The NOR
~ate 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 output of the NOR gate 384 is also input to the NOR gate 386. The other input to the NOR
~ate 386 is derived from the output of the NOR gate 382.
The output of the gate 386 is carried by the line 142 (BRAKE -~

RUN) to the brake control override 334 to assert the BRAKE
RUN function thereof.

'" ' , .

~L~47435 The logic 109 is respectively input on the lines 144 and 145 with MOTOR MODE SELECT or BRA~E MODE SELECI' signals 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 discussed above. The output line 140M (MOTOR RUN) (Figures 3 and 8A) from the logic 109 is input to -the motor control subsystem 106.
The tied inputs of the inverter gate 370A are con-nected to the line 145, BRAKE MODE SELECT, through a diode 371 and a capacitor 372. The inputs are normally high, due to their connection to a positive potential 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 logic 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 194 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 NOR gates 382, 384 and 386. The NOR gate 382 derives its inputs from the 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 384 derives one input from the output of the inverter gate 370B. The second inputs to the NOR gate 384 is derived from the velocity comparator 302 on the line ' -- 5 1 -- :

,.~.,. -.. - - - ' :

43~
362. 1'he output of the NOR ga-te 384 is the second input to the NOR GATE 386, and also is connected to the line 140B
(MOTOR RUN) leading from the logic 109 to the switch 343 in the override 342. The output of the NOR gate 386 is connected by the line 142 (BRAKE RUN) from the logic 109 to the override 334 to assert the BE~KE RUN function.
If the computer asserts the BRAKB MODE S~I.ECT line 145 (i.e., the block is travelling downward) and if this is the only asserted signal (as checked by the EXCLUSIVE OR) the motor control subsystem 106 is disena~led on the line 140M and the NOR gates 382, 384 and 386 operate to switch 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 BRAKE 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 SEI,ECT 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 terminal of the NAND gate 370C are at logic 1 condition~ Both terminals of the inverter gate 370A and the A terminal of the NAND
gate 37 OD are in the logic 0 condition.
The output of the inverter gate 370A is therefore a logic 1, placing this condition (logic 1) at the A input of the NAND gate 370C. The output of the inverter gate 370B
is a logic 0, placing this condition at the B input of the -- 54 ~

3~
NAND gate 370D. Thus, the output of the NAND clate 370C is at logic 0 and the output of the NAND gate 370D is at logic 1. These are the conditions at the A input of the NOR gate 372 ~logic 0 from the output of the NAND gate 370C) and at the A input of the NOR gate 374 (logic 1 from the output of the N~ND gate 370D). Note tllat the logic 1 at the output of the NAND gate 370D is carried by the line 140M to the motor control subsystlem 106 enabling the motor override ne-twork 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 input leading 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 384 and the B input of the NOR
gate 386 are both at logic 0 as long as a BRAKE MODE SELECT
condition is present 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 is at a logic 0 at all times that a BRAKE MODE SELECT is asserted on the line 145. The B input to the NOR gate 382 is derived from the output of the final 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 of the NOR gate 382 is at a logic 0. Thus, the output of the NOR gate 382 is a logic 1. The logic 1 input condition to the A input of the NOR gate 386 results in the situation that as long as the block is greater than ~7~3S
the threshold distance (set by the potentiometer 351) from the final, command position, the line 142 (BRAKE RUN) is at logic 0, allowing the normal control subsystem functions derived from the magnitude of the total error signal (ET)B
to be controlling the velocity of the block.
However, as the block approaches the final position, the output of the comparator 294 switches and provides a logic 1 output on the line 355 connected to the B terminal of the NOR gate 382. This results in the output thereof, and the A input to the NOR gate 386, switching to a logic 0.
As a result, the output of the NOR gate 386 goes to a logic 1, and BRAKE RUN output line 142 is energized. With a logic 1 at the output of the NOR gate 386 and on the line 142, the switches 337 and 338 are turned on. With such an occurrence full braking is applied since the positive inputs to the amplifiers 239B and 241B overriding the normal brake control subsystem, and setting the brake when the position error has reached an acceptably low value.
If the computer asserts the MOTOR MODE SELECT line (i.e., the block is hoisted upwardly) and if this 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 b~ 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 signal on the line 144, `~
the A and B ter~inals to the inverter gate 170A are at a logic 1 condition. Likewise, the A input of the NAND gate 370D. The A and B inputs to the inverter gate 370B, and the B input to the NAND gate 370C, are at a logic 0 condition. Thus, the output of the inverter gate 370A, ~L47~35 and the A input to the MAND gate 370C, are at a logic 0 condition. Accordingly, the output of the NAND gate 370C
and the A input to the NOR gate 382 are in a logic l condition. The output of the inverter gate 370B, and the B input of the NAND gate 37OD are in a logic l condition.
Accordingly, the output of the NAND gate 370D and the A
output to the NOR gate 383 are in a logic 0 condition. The output of the NAND gate 37OD 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 O.
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 l. 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 ~0 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 302, the output thereof on the line 362 connected to B input of the NOR gate 3E34 is a logic l. 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 B input of the NOR
gate 386 is also a logic 0, resulting in a logic l output therefrom. Accordingly, the line 140B (MOTOR RUN) is not asserted (due to logic 0 at the output of the NOR gate 384) while the BRAKE RUN function at the output of the NOR gate - 57 - ~

-.

74~3S
386 on the line 142 is asserted. The result is when the motor mode is selected (the override being disenabled), the bra~e is asserted as long as the velocity is below the defined threshold.
When the block is li~ted at a velocity exceeding 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 r 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.
Fur-ther, 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 BRAKE 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 back to a logic 1, changing the B input to the NOR gate 384, and switching 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 line 142 (BRAKE 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 7~35 within a predeterminecl distance oE the command position, to assert a motor override and top the hoisting motion.

MOTOR CONTROL SUBSYSTEM SC~IEMATIC

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 COM~ND 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 POSImION signal is input on the line 116M and is ~;
presented to the non-inverting input of the differential amplifier ~OOM 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 P~SITION
signals are current signals and are converted to an appro-priate voltage for application to the differential amplifier 200~1 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 xesistor, in combination with the resistor 402, establishes the amplifier gain. The position , error signal output is taken by a line 410 to the non~inver-ting input of a position comparator 412. The in-vertin~ input of the position comparator 412 is furnished with a signal derived from a potentlometer 414 connected to a negative pot~ntial through a resistor 415. The wiper o~
the potentiometer is connected through a~resistor 416 to the inverting input. The position comparator 4l2 outputs a signal through a diode 417 to a line 418 when the position error signal at the output of the dif~erential amplifier 200~1 is less than the voltage level as set by the poten-tiometer 419. 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 potentiometer (Kp)M.
An adjustable portion as set by (Kp)M of the position error signal is applied through a resistor 421 to the non-inverting input of the amplifier 230M. The inverting input of the amplifier 230M is connected through 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 amplifi~r 204M
and the diode 234M has been discussed earlier in con-nection with the simplified signal diagrams of the draw `
~orks motor control.
I'he 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 VELOCITY ta~en from the input line 134~1 through the resistor 233M. The velocity signal may be derived from the drum tachometer 94 or, .~

~74~5 alternativel~, from the 1~lock position transducer 83. '1'he ~CT~1AL vrLocITY signal is applied to the invertin~ terminal of a comparator 430, as is discussed herein. The siqnal at the summing junction 202M is applied to the invertinq in~)ut of the difference amplifier 208M. The non-invertinc3 input is connected to grollnd potential through a resistor 431.
As discussed, however, an adjusted portion of a load factor signal is also applied to the non-invertin~ input.
An ACTU~L LOAD si~nal is applied on the line 136M
and the appropriately scaled INITIAL LOAD-(-K2) si~nal is input on the line 138M. These load signals are summed at the inverting 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 2]2M is fed ::
back to the inverting input through a loop including the :~
aiode 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
establish the amplifier gain. The output of the amplifi.er ;~
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 ~otentiometer (KL)M is connected through the resistor 437 to the non-inverting input of the amplifier ~1'lM. The lnverting input of the amplifier 214M is con-nected to ground potential through a resistor 438. The output of the amplifier 214M is fed back to the invcrting input through a resistor 439 and is also tied to the non~
3n inverti.nc; terminal of the difference ampllfier 208M.
The output of the difference ampl.ifier 208M is con-nected to the integrator-amplifier network 218M (Figure 9B).

,, - 61 ~

~74;~5 This output is also fed back to the inverting input through the resistor 440. The integrator-ampli~ier network 21~ takes the OUtpllt of the difference ampli~ier 208M from the node 238M along two parallel paths. One path includes the potentiometer (KFF)M, the wiper of which is connectecl to the inverting input of the diff~rential amplifier 244M
through a resistor 441. The second parallel ~ath includes the potentiometer (KINI~)M, the wiper of which is connccted through a resistor 442 to the inverting input of the integrating amplifier 241M. The non-inverting 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 44fi 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 integrator-amplifier network 218M is connected through the resistor 245M to the voltaye-to-current converter 246M. The converter 246M is sub-stantially identical to the inverter described earlier in connection with the brake control subsystem 105 except for '' ~ "
- 62 - ~ ~
~' ~

.47~35 the ma~nitude of the reference voltage applied to the amplifier 453. T}le resistor 245M is connected to ~ poten-tiometer 451 and a resistor 452 throu~h which it is also connected to the inverting input of an amplifier 453. The non-invertiny input of the amplifier 453 is ticd to groun-~
through a resistor 454. The output of the amplifier dri~Je~
a transistor 455 of the NPN type, the collector of which i5 connected to a positive potential. The emitter of the transistor 455 is fed back through a feedback resistive network 456 to the inver-ting input. The emitter 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. The output line 159 has a relay contact operated by the coil 112 therein.
An initial voltage condition is applied -to the in-~rerting 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 networ~ is to supply a reference voltaye so a~s to obtain a 4m~ current output under a æero signal input condition.
The motor control subsystem 106 is connected (Figure 9B~ to the computer output channel I through the line 151.
rrhis line is connected through a diode 470 to the inputs o~
a NAND gate 471 having both the inputs tied to a positive po-tential through a resistor 472. ~ switch 473 is tied to a positive potential on one side, and on the other throu~h a resistor 474 to the non-inverting input of the comparator 453 within the voltage-to-current converter 246M. Upon receipt of a CREEP TO ENGAGE CLUTCH command signal from the - 63 - ;
.~:

-computer on the line 151 (line 151 goes to logic 0), a predetermined current signal is output to the motor dri~e 93 on the line 159 to move the motor 92 very slowly to permit the clutch to engage for further hoisting operations.
The motor control subsystem 106 has a CREEP control network 480 tFigure 9A) connected therein. The network includes the inverting amplifier 430. The ACTUAL 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 4~2. 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, respectively. 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 H) from the computer on the line 150. The output of the flip-flop network 500 conne~ted to the input of a switch 503. The output of the amplifier 208M is connected to a resistor 504A and a diode 504B in series. The switch 503 is connected between the junc~
tio~ ~ the resistor 504A and the diode 504~ and the non-inverting input of the integrating amplifier 241M. The ;

7~3~
output of the flip-flop network 500 is also connectcd through the line 152 to the switch 365 in the brake control subsystem 105 (Figure 8~).
The purpose of a CREEP command is to slowly raise the travelling block so as to acquire the drill string load with the elevator as discussed in connection with the operation section earlier.
Upon receipt of the CREEP COMMAND a signal at the set input from the line 150 causes an output from the flip-flop network 500 to switch to logic 1. This closes the switch 503. This effectively increases the gain of the integrating amplifier 241M. At the same time, the output on the line 152 from the flip-flop ne-twork 500 closes the switch 365 in the brake control subsystem 105 to increase the gain of the integrating amplifier 241s ~Figure 8). Thus, the CR~E~
command signal, in conjunc-tion 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 acquirinq or releasing the load. When the velocity e~ceeds a creep threshold velocity determined by the combination of resistors 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 motor control subsystem 106 is dis-enabled the logic 109, the line 140M has a loqic high slgnal thereon. The line 140M is connected to a diode 511, the output line from the diode 511 being indicated as MOTOR OFF
line 512. The primary override path includes a zener diod 513 connected through a resistor 514 to ~he base of an NPN

.
:, , ~

.
~: : ' -~
:

131 ~7435 transistor 515. The emitter of the transistor 515 is con-nected to a negative potential. The emitter of the tran-sistor 515 is tied to the anode of the zener diode 513 by a resistor 516. The collector of the transistor 515 is con-nected through a resistor 517 to a diode 518. The primary override is connected to the inverting input of the inte-grating anplifier 241M. The second path of the override 510 includes a switch 524 connected between the junction of resistors 525 and 526 and ground. The resistor 525 is tied to a positive potential. The non-inverting input of the amplifier 527 is tied to ground through resistor 528. The output of the amplifier 527 is applied through a diode 529 to the inverting input of the voltage-to-current converter 2~6M. 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-Lide 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 o~ ;
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, groundiDg~the junction of the resistors 525 and 526. This holds the input to the voltage-, :
to-current at zero. This precaution is taken since there may still be a signal at the output of the amplifier~244 ; even though the integrating amplifier 241M is overridden. ;
The MOTOR OFF line 512 can be energized in ways other than by receipt of a computer command via the logic 109.

: .;
~: .

In order to shut the motor off when the ~)osltion o~
the block comes within a predetermined close tolerance to the command position, an output signal from the position com-~arator 412 on the line 418 operates the override 510 in a manner exactly as discussed.
Further, when the operator asserts the override on the line 104, a signal is applied to an optical coupler 536 (Figure 9A) acting as a switch. When energized the switch 536 connects a positive potential 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 concluctive, placing a high signal 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 detailed schematic diagram of the velocity comparator 108.

" ,.

VELOCITY COMPARATO~

Shown in Figure 10 is a detailed schematic dia~3ram of the velocity comparator 108 utilized in the drawworks control system 21. As seen from the block diagram Figure 3, the velocity comparator 108 is input from the computer channel G on the line 165 with a 4~20mA signal representative of the CO~ND VELOCITY, the velocity at which it is desired to move the travelling 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 conver-ted 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 capacitar 574 and is applied to the non-inverting input of an amplifier 575. ~he output of the amplifier 575 is fed back to the inverting input throu~h 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 from the drum tachometer 94 is representative of the ACTUAL VELOCITY at which the travelling block 68 (Figure 2) is moving. The ; polarity of the voltage 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 th~e vertical axis of the - 68 ~

: ~:':

derrick 20. An upward direction of travel, of course, implies that the motor mode is being asserted. A negative 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 VELOCITY signal is filtered to remove com-mutatinq spikes by a single-pole, low-pass filter network 580 which is comprised of a resistor 581 and a capacitor 582. Diodes 583 and 584, respectively connected to positive and negative potentials, limit the signal to an amplifier 586. The filtered ACTUAL VELOCITY signal is presented through a resistor 585 to the inverting input of the ad-justable gain amplifier 586. t The non-inverting 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 is 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 applied 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 ground potential through a resistor 592. The output of the amplifier 590 is fed back to the inverting input thereof through a resistor 593. The output is also connected by a line 594 to -the output line 134, which is the ACTUAL VELOCITY signal lnput to the brake control subsystem 105 and the motor control subsystem 106 on the lines 134B and 134M, respec~ively. With the circuit ~ ~
configuration described, the magnitude of the voltage signal ~ -' 74~;
on the line 134 repres~nts the actual velocity o~ the bloc~, with a positive polarity indicating upward movement at a negative polarity indicating downward motion.
The output of the amplifier 586 is taken by a line 597 to a wrong direction indicating network 598. The network 598 includes comparators 599 and 600, and transistors 601 and 602 connected in a lo~ic OR configuration. The in-verting input of the comparator 5~9 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 switching 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 positive potential source through the resistors 605 and 606. The inverting input of the comparator 600 is connected to a potential 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 junction of the base of the tran-sistor 601 and the resistor 613 is tied to ground potential through a resistor 614. ~, One or the other of the comparators 599 or 600 is disenabled, dependent upon whether a signal is present on the line 615 or 616,, The line 615 is connected to a line 167 tied -to the MOTOR MODE SELECT line 144 from the computer.
The line 616 i5 connected to a line 168 tied to the BRAK

- - : . . ~

MODE SELECT line 145 from the computer. A diode 617 is connected in the line 615 to the junction 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 throu~h the resistors 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 connec-ted to the com-puter input channel E. The network 598 operates to give a WRONG DIRECTION OF MOTION signal on the line 169 if the motion of the block exceeds the nominal setting 0.5 feet/
second in the wrong direction. If this occurs, either transistor 602 or 601 ceases to conduct. A WRONG DIRECTION
OF MOTION signal 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 direction is sensed. If, for example, the ~ -~
motor control subsystem is controlling a hoisting motion, the MOTOR MODE SELECT line 144 is low and the BRAKE MODE
SELECT line 145 is high so that the output of the comparator 599 is enabled and the outp~t of the comparator 600 is not enabled. During hoisting the ACTUAL VELOCITY signal polarity at the non-inverting input of the comparator 600 ~ ~7~35 is negative so that the transistor 601 would tend to be turned off, but the comparator output 600 is disconnected since the diode 612 is back-biased. In this condition, the transistor 601 is maintained in conduction by the signal applied through the diode 618. However, if the ACTUAL
VELOCITY signal at the inverting input of the comparator 699 should become positive with a magnitude greater than ap-proximately 0.5 volt, indicating a "wrong" direction of travel, neither the diode 609 nor the diode 617 conducts, so that the transistor 602 becomes non-conductive, signaling an interrupt condition on the line 169 to the computer. The "wrong" 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 Oll the other. The output of the comparator 625 is fed back to the non-inverting terminal thereof through a loop including resistors 630 and 631, and a capacitor 632. This positive feedback loop provides hysteresis so that the comparator 625 ~`
will provide pc~sitive signal action with signals close to the switching polnt.- The non-inverting lnput of the com-parator 626 is also connected to the output of the ampli-fier 59~ throucJh a resistor 63~. The inverting input lS ~ ' i2 ~

79~5 connected through a resistor 635 to a switching point voltage set by the "up" potentiometer 636 which is connectod to ground on one side and to a positive potential through a resistor 637. The output of the comparator 626 is fed bac~ to the non-inverting terminal thereof through a loop including a resistor 638 and a capacitor 639. This positive feedbac~ loop insures that the comparator 626 will provide a positive switching action at input signals near threshold.
The outputs of the comparators 625 and 626 are con-nected, through diodes 640 and 641, respectively, and 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 ground. 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 through a resistor 647. The 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 potentiometers 628 and 636, respectively, such that a predetermined small velocity in ~ ;
either the downward or upward direction is recognized AS a zero velocity condition and a signal to that effect is applied on the :Line 170 to the computer. Zero velocity on the line 170, indicated by the transistor 648 being switched on, is only one of the two necessary conditions for the computer to recognize that the block is at its programmed destination.

~ - 73 -:: :
. , . ~ . . ~ :

As will be set forth in detail herein, the block position and speed transducer 83 outputs a 0-10mA velocity signal on a line 171 to the velocity comparator 108. This unipolar current signal on the line 171 is applied to a maximum velocity network 653. The current signal is con-verted to a voltage signal by the action of a resistor 654 tied to ground potential. The voltage signal is applied to the non-inverting input of a voltage follower amplifier 655 through a resistor 656, with a capacitor 657 tied to ground potential. An adjustable maximum velocity signal derived 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-sistors 664 and 665, respectively, and are summed at the inverting input of an amplifier 667 effectively 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 ~0 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 VELOCITY
signal on the line 172 is connected to the computer input channel F.
The maximum velocity threshold set by the potentio-meter 659 is normally greater than the actual velocity signal 3n to the follower 6S5, so that the output of the comparator 667 is at positive saturatlon, holding the transistor 674 in conduction. How~ver, if the BLOC~ VELOCITY from the B.P.S.T.

:: ~
7~ _ ~

~7~35 83 exceeds the threshold however, the transistor 674 is cutoff. The indication that the maximum velocity is ex-ceeded is thus output to the computer on the llnes 675 and 172. Note that on both the lines 621 and 675, a normal condition is indicated by current flow. When an abnormal condition is sensed, that current signal drops to zero.
Diodes 677 and 678 are, respectively, tied between the lines 621 and 675 and a positive potential.

t :

.

BLOCK POSITION ~ND SP~ED TR~NSDUCE~

Referring to Figure 11, a detailed schematlc ~iagram of the block position and speed transducer (B.P.S.T.) 83 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 signal is input to the brake control subsystem 105 and the motor control subsystem 106 on the lines 116B and 116M, respectively. Also, as discussed in connection with Figure 10, the B.P.S.T. 83 puts a 0-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 ~ith 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 includes a zero velocity magnetic pickup 635, such as that manufactured by Airpax and sold under Model No. 4-000~. The pickup 695 outputs a square wave pulse each time a tooth of the wheel 693 passes 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 - . .

~7435 direction in which the teeth of the wheel 69~ are ~)assing.
This sigllal is hereafter referred to as the "B" sigllal. It is quickly appreciated that a predetermined yiven number of output pulses from the pickup calibrated and used to repre-sent displacement of the block a predetermined rectilinear distance along the track 80. Similarly, the frequency of the pulses is proportional to the speed at which the carriage ?8 moves. The "A" and "B" signals of the pickup 695 are connected to a signal le~el 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 699. 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 voltage proportional to the frequency of the square wave input signal. Potentiometers may, of course, be provided to adjust the zero and full scale out-pu~t. 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 the inverting amplifier 700 is applied to a voltage-to-current converter ;
701. The converter 701 is similar in circuit details to the voltage-to-current converter 246B shown in Figure $B.
The converter functions to provide a O-lOmA output propor-tional to the O to -10 volt input signal. A suitable trimming resistor may be provided to adjust the output ~7435 current to a predetermined value, for example, IOmA 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 698 and, accordingly, to the speed of the carriage 78 and the travelling block 68 associated therewith. As before, the current signal is preferred due to the high noise .;mmunity offered thereby.
Further, the constant current source characteristic ma~es 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 ~rom th`e 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, carrying the "B" signal representative of the direction of motion of the wheel 693 are both input to a cascaded array of counters, 706A, 706B, and 706C, such as those manufactured by 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 directional signal ~ 78 -~7~35 input on the line 70~ ~letermines whether th~ count is to ~c ad~ed or subtracted (i.e., countup or countdown) from the initial value. In the Figure, the array of counters 706 provides a total count of 4096.
The parallel outputs Q(N) of t}~e counters 706 are applied to a digital-to-analog converter 710, such as that manufactured by Hybrid Systems Corporation and sold under the model number DAC 380-12. The output of the converter 710 is a current proportional to the magnitude of the count received. Potentiometers 711 and 712 are, respectively, provided to adjust the zero and full scaIe current levels.
These potentiometers may be set, for example, so that a 4mA
signal corresponds to a zero count and a 20mA current corresponds to a register count of 4095. The output current, is, therefore, proportional to the elevation of the travelling biock. The output current signal, sharing the same attributes as discussed above, is applied to the output line 116 to the computer (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. ls an incremental position sensing 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 8~
and 85 are located on the carriage 78 which are actuated by metal targets 86 and 87. This arrangement provides un- ~;
ambiguous reset points near the upper and lower ends of the retractor guide 80. Each reset switch output is applied 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 ' - 79 - ~

~7~35 720. The output of the network 720 ~unctions to ~aintain one or the other or 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 reset bus 722 each have a diode-resistor network wire thereto which forms a pattern to the preset inputs ;r (N) of the counters 706 representing a predetermined count for the physical elevation of each target. The output of the anti-bounce networks are fed through a NAND gate 723 to the preset inputs of the counters 706. Thus, the counters 706 are preset to a predetermined count each time a sensor passes its respective target.
NAND gates 724A, 724B and 724C are connected as a Schmitt trigger network. The output of the trigger network pro~ides 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 resets 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 time 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 ~eset to zero following power-up, one spurious count combined with a down signal from the magnetic pickup could cause the counters 706 to register a full count of 4095. To prevent this situation, the reset pulse described above is also applied to a NAND gate 727 functioning as an inverter. It5 output functions to switch the lower reset: bus 722 to logic 1 through the diode 728.
During a predetermined additional time interval, set by :' ~.... . - ~ .

the capacitor 730 and resistor 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 count is entered following each power-up. In this example, a count of 48 is entered, although any value can be preset by appropriate rearrangement of the logic.

~' ' , ' ~ ~.

743~i ELEVATOR I.OAD CO~TROL

As alluded to above, during both the make-up and break-out cycles it is necessary and desirable to ~onitor the load being carried by the elevator 75 (Figure 2).
~cc~rdingly, as discussed in connection with the brak~ control subsystem 105 and the motor control subsystem ]06, feedback signals from the elevator 102d control subsystem 107 are utilized in the determination by the motor or brake controls of the speed at ~Ihich the drill string is lifted (by the motor) during break-out cycle or the speed at which the string is permitted to ~all (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, 0, 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 actual elevator load is output to bol:h 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, ~' - 82 ~
, ~7~3S
respectively. The derivation of these signals is discussed herein.
The elevator load control subsystem 107 derives its operating input from the deaclline force sensor (D.L.F.S.) 95 on the line 110 (Figure 3). The signal from the D.L.F.S. 95 may be conditioned, if desired. As is the case with all signals derived from relatively distance transducers, the signal from the D.L.F.S. is a 4-20m~ current signal, chosen for the reasons outlined above.
Rererring now to Figure 12 r which is a detailed schematic diagram of the elevator load control subsystem 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 elevator 75 (Figure 2) at any given instant is conne~ted by a line 747 to a sample-and-hold network 748. The network 748 includes a buffer amplifier 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 .. . :

to ground potential through a resistor 753 while a Zener diode 754 is interposed between the junction of the re-sistor 751 and the switch 752. The output of the switch 752 is connected to the gate of a field effect transistor 755 with the gate also being connected to ground po-tential 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 SA~IPLE ZERO LOAD line 175 leading from computer channel N.
The NA~D 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 charged 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 "SAMPLE ZERO LOAD" signal is activated when the elevator and block are not in motion and at an appropriate point in the cycle when the elevator has not acquired any load. The signal presented at the inverting 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 long-term drifts existinc~ ln the load measuring networks.
At the diEferential amplifier 742, the zero signal is sub-tracted from a signal representative of the instantaneous elevator load input on the line 741 so that the instantaneous signal representative of the actual loading on the elevator at the output line 766 from the clifferential amplifier 742 is presented to the output line 136 ACTUAL LOAD.
The output from the field effect transistor 755 on the line 759 is fed back through a line 767 to the inverting ln input of the amplifier 749.
A substantially identical sample-and-hold network 770 is connected to the output of the comparator 7~2 through the line 771. The non-inverting input of a buffer amplifier 772 is connected to the slgnal on the line 771. The output of the amplifier 772 is connecte~ throu~h 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 ~- -ground 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 779 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 Eed back to the inverting input of the amplifier 772 by a line 783. The output of the transistor 780 is also con-nected through series resistors 784 and 785 to ground potential. A llne 786 is connected at the junction of the transistors 78~ and 785 for a purpose to be discussed herein. The output of the sample-and hold network 770 is .
connected by a line 787 to a switch 788.

~7~3~i The switch 775 is connected to a NAND gate 790, the tied inpu-ts of which are connected through a diode 791 to the line SA*lPLE LOAD on the line 176 leading from the out-put channel 0 of the computer. ~he inputs to the NAN~ ga-te 790 are connected to a positive E)otential through a resistor 792. With the receipt of a signal from the 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 output switches to a logic 1 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 at 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 line 787 represents the "dead weight" of the drill string load. This is the INITIAL LOAD 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 at its input by a line 796 to the non-inverting input of a buffer amplifier 797.
The switch 788 is controlled by a transistor 798 of the NPN
type, the base of which is connected through a resistor 799 and the diode 800 to the line 177. The LO~D CONTROL ON
signal from the computer output channel P is applied on the line 177. The signal end of th~ resistor 799 is connected .:

.~ : . ~ .. . ..... .. .

`----~474~5 to a positive potential through a resistor 802. The col-lector of the transistor 798 is connected to a positive potential through 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 799 is also connected by a line 804 to the control lead of a second switch 805. The switch 805 connects the output of the amplifier 742 through a line 806 to the non-inverting input of the buffer amplifier 797. Except during the CRE~P
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 LOAD on the line 787 ~
to the input of the amplifier 797. At the same time, the ~-bilateral switch 805 is turned off. The INITIAI, LOA
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 buffer amplifier 816. The non-ihverting input of the buffer amplifier is connected through a resistor 817 to ground potential. The output of the amplifier 816 is fed back through its inverting input through a resistor 818. The settin~ selected by a skilled driller and dialed ~;
into the level colltroller 812 is an adjustable fraction K
between 0 and 0.9 of the INITIAL LOAD. This level is in~
verted by the amplifier 816 and applied on the output line 819 to a connection with the line 138B input to the brake control subsystem 105. ~ -- -, . ,: . . , ~

~7435 The physical effect of choosin~ the factor Kl may be seen by a consideration of the lowering operation. During lowering, the actual load on the elevator will be less than or equal to tlle initial INITIAL LOAD value due to frictional forces on the moving pipe. Ther~efore, it is reasonable to anticipate that some deviation of the actual load on the elevator below that of the INITIAL 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 inverting 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 inverting input of a comparator 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 829. 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 output taken at the emitter of a transistor 834. The base of the transistor 834 is connected to the LO~D CONTROL ON line with the collector thereof being tied to a positive potential. Thus, ~ ;
during those periods of time when the LOAD CONTROL ON is -asserted by the computer, the transistor 834 is not con~
ducting and the output of the comparator 824 is enabled.

:''' - \ -~ ~7435 The resistors 8Zland 822 establish an under-limit switching threshold for the comparator 824 for a given Kl selected.
When the value of the actual load falls below the preset fraction of the scaled INITIAL L~AD at the inverting input of the comparator 824, the comparator switches so that t~e transistor 829 switches off. This constitutes an alarm signal indicating that the elevator load is under pre-determined limit and actuates an interrupt system, halting the program 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. A diode 845 is connected between the junction of the diode 83g and the resistor 840. This maintains the transistor 841 in conduction when the transistor 834 is in conduction (i.e., when the LOAD CONTROL ON signal is not asserted). Thus, the ;
function of the LOAD OVER LIMIT interrupt is inhibited.
During a hoisting operation, the actual load may be increased over t:he INITIAL LOAD value through the effect of 89 ;~ ;

43~
friction between the pipe and th~ bore. Therefore, durin-~
a hois ing operation, the INITIAL LOAD is scaled by an appropriate factor K2 selected from the level controller 813. The setting of the selector switch establishes the gain of the amplifier 849. This appropriately scaled 1OA(1 is present~d by the line 834 to the output line 138M carried to the motor control subsystem 105. As long as the ~CTUAL
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. However, 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 sig~al 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 1 and the tran-2Q 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 load acquired network 850. The signal is applied to a high-pass 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 through a resistor 857. The non-inverting ~
- 9 0 - ~ . , : .

input of the comparator 856 is conducted by a line 858 through a resistor 8~9 from the output of a buffer amplifier 860. The non-inverting input of the amplifier 860 is taken from the line 786. The output of the amplifier 860 is applied through a diode 861 and is fed back to the inverting input thereof through a resistor 862. The output of the amplifier 860 taken through the diode 861 is applied through resistor 863 to an amplifier 864. The non-inverting 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 866. 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 amplifier 854 and the line 85S 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 reference signal equal to approxi-~ ~ ;
mately 1/3 the value of the INITIAL LOAD signal as estab~
lished by the resistors 784 and 785. The reference sigl~al to the comparator 868 is inverted by the amplirier 864 to maintain the proper signal sense. The~reference signals are -- 91 -- . ~
,:

:~4743S
necessary so that the comparators can accommodate a wide range of hook loads. It adjusts the switching point of the comparators 856 and 868 to a level consistent with the drlll strin~ ]oad 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 string make-up the per cent change in weight is ne~ligible. 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 877 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 ievel drops to zero.
. .

~ ~ ~7435 ASSOCIATED S~FETY SYSTEMS

~ eferring to Figure 13, a schematic diagram of an automatic sequence disenable and interrupt logic circuit 900 is shown. The purpose of this circuitry is to permit an e~perienced driller on the derrick to manually correct some physical problem on the ri~ which is causinc3 the automate~
sequence to "hang-up" (a temporary halt to the computer pro~ram sequencing) and to perform that action without risk of physical injury. Since it is possible that correction of the structural disorder will enable the automated sequence to continue, and perhaps imperil the operator, it is im-perative from a personnel safety stand point that the automatic 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 1 signal to the A input of NOR ~ate 903C. When a "hang-up" exists in the drawworks program, indicating tha-t the elements controlled by the drat~.~orks elements (Figure 2) are in a motionless condition, the line 904 from the computer goes to logic 0. Similarly the line 905 from the computer goes toa logic 0 condition each time a "hang-up" exists in the racker control program.
Thus, all of the structural elements controlled by that program (numeral 34, Figure 2) are also static or motion-less. A "hanq-up" therefore occurs only when an appropriate feedbac~ signal is absent due to a malfunction or at a point where one program is awaiting a function which occurs in tlle ~ ~-other program to be completed.

: ~ ' The NOR ~ates 903A, 903B, 903C and 903D are con-nected as shown so that when the three signals (from the switch 901, and on the lines 904 and 905) are logic 0, a transistor 906 of the NPN type ceases conduction. This con-stitutes an output siynal carried by the line 907 which causes the AUTO/MANUAL bus to be de-energized. This in-hibits all control function and the entire system reverts to a manual mode, and all sequencing is halted. This con-dition remains until the ~UTO MODE switch is returned to the NORMAL position. Thus, after actuating the AUTO MODE
switch to the DISABLE position, the operator can safely correct a malfunction without the danger of the system immediately continuing on in the automatic sequence. Then the repair has been effected, the switch 901 can be re-turned to the NORMAL position and the automatic cycle is resumed. Thus, a fault in the structural system (or any other operator correctable malfunction) can therefore be corrected without disrupting the computer program, 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 912 is conducting and current in a line 914 is a normal condition. When any of the monitored power sources fail, i.e., +15 VDC, -15 VDC, -24 VDC (tong supply) and 26 V, 400 ~Iz. AC, the transistor 911 conducts whi.ch biases the optical coupler 912 to an off or non-conducting state. Therefore, an output current signal to the line 914 is interrupted. This constitutes an ~, _ 9~
~ :.

.... ,...... , ~ . , .. : ................ . ~ ~ .
., ~147435 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 receives lnput signals on the lines 921 and 922 from the high drum clutch and the low drum clutch feedback switches. The drawwor~s control utilizes two clutches in the particular embodiment shown.
One or the other of the clutehes may be damaged by simul-taneous engagement of both. The EXCLUSIVE OR gate accepts only one or the other of the eluteh signals, but not both.
This effectlvely prevents simultaneous engagement of the elutchesO The output of the gate 920 drives a transistor 923 of the NPN type when, eondueting supplies a CLUTCH
EWGAGED feedbaek signal to the eomputer on the line 924.

:

. . : . : ~ ,, :

Claims (6)

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

1. Apparatus for indicating the position and velocity of a travelling block with respect to a vertical guide track within a computer-controlled oil drilling rig comprising:
a friction wheel mounted on the travelling block and biased into contact with the guide track, displacement of the travelling block upwardly or downwardly with respect to the guide track rotating the friction wheel in a first or a second angular direction, respectively, at an angular velocity related to the velocity of the travelling block;
a toothed wheel mechanically coupled to the friction wheel for rotation therewith;
a magnetically responsive element operatively associated with the toothed wheel and adapted to generate an electrical signal representative of the direction of motion of the toothed wheel and to generate a pulse each time a tooth on the toothed wheel passes in proximity thereto;
a converter arrangement responsive to the frequency of the pulses output from the magnetically responsive element for generating a current signal representative of the velocity of the travelling block;
a counter arrangement for counting upwardly or downwardly the pulses output from the magnetically responsive element in accordance with the electrical signal representative of the direction of motion of the travelling block; and, a converter responsive to the count output from the counter arrangement for generating a current signal representative of the position of the travelling block with respect to the guide track.

2. Apparatus according to Claim 1 wherein the current signal representative of the position of the traveling block with respect to the guide track is supplied as a signal to a general purpose digital computer operating in accordance with a program to automatically sequence the operation of the drilling rig.

3. Apparatus according to Claim 1 further comprising means for setting a predetermined count into the counter arrangement when the traveling block passes into proximity to an upper and to a lower metal target associated with the guide track, the means comprising:
a first diode-resistor network connected to the counter arrangement and forming a count pattern representative of the position of the upper target with respect to the guide track;
a second diode-resistor network connected to the counter arrangement and forming a count pattern representative of the position of the lower target with respect to the guide track;
a first, upper, switch mounted to the traveling block and operative when the traveling block passes in proximity to the upper metal target to load into the counter arrangement the count pattern representative of the position of the upper target; and a second, lower, switch mounted to the traveling block and operative when the traveling block passes in proximity to the lower metal target to load into the counter arrangement the count pattern representative of the position of the lower target.

4. Apparatus according to Claim 3 wherein the counter arrangement includes three cascaded counter elements, each counter being connected to selected portions of the second diode-resistor network, further comprising a trigger arrangement associated with one of the counter elements to reset that counter element to the count pattern formed by that portion of the resistor-diode arrangement to which the counter element is associated a predetermined time interval after the power-up of the apparatus.

5. Apparatus according to Claim 1 further comprising a trigger arrangement associated with the counter arrangement to reset the counter arrangement to a predetermin-ed count a predetermined time after the occurrence of an event.

6. Apparatus according to Claim 5 wherein the predetermined count is zero and wherein the event is the power-up of the apparatus.