US3616979A

US3616979A - Hydraulic stepping mechanism for forms feeding

Info

Publication number: US3616979A
Application number: US887474A
Authority: US
Inventors: Stanley C Titcomb
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1969-12-23
Filing date: 1969-12-23
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: FR2072197A5; GB1280445A; DE2059918A1

Abstract

A two-position stepping valve automatically releases a first detent of a form feed drive shaft to allow a fluid motor to accelerate the shaft under control of a fluid commutator, and simultaneously drives a second detent toward shaft latching position to latch the same after a short angular rotation of the same. Fluid controlled deceleration of the shaft into full latched position follows under control of the shaft driven fluid commutator.

Description

United States Patent Inventor Stanley C. Tltcomb Endwell, N.Y.

Appl. No. 887,474

Filed Dec. 23, 1969 Patented Nov. 2, 1971 Assignee International Business Machines Corporation Armonk, NY.

HYDRAULIC STEPPING MECHANISM FOR FORMS FEEDING 12 Claims, 2 Drawing Figs.

U.S. Cl. 226/157, 91/40 Int. Cl B65h 17/22 Field of Search 91/39, 40,

[56] liteierences Cited UNITED STATES PATENTS 2,880,838 4/1959 Panissidi 226/9 2,938,501 5/1960 Titcomb 91/39X Primary Examiner-Richard A. Schacher Altorney--Sughrue, Rothwell, Mion, Zinn & MacPeak PATENTED 2 I97! V REL HYDRAULIC STEPPING MECHANISM FOR FORMS FEEDING BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a fluid control system for a fluid motor which provides for intermittent and continuous movement and, more particularly, to such a fluid motor drive system for controlling the form feeding carriage drive for an accounting machine or the like.

Cross Reference to Related Applications This invention relates to US. Pat. No. 2,880,838, patented Apr. 7, 1959 and assigned to the common assignee.

2. Description of the Prior Art For the feeding of forms or paper in strip or web form for high-speed printers, such as those used forming components of accounting machines, it is necessary to selectively advance the paper or forms for line-spacing and ejecting the same. Due to the high-printing speeds required for such machines, the mechanical clutching devices or other mechanical drives are incapable of properly driving the paper due to their design limitations without excessive wear and failures requiring excessive shutdown time to repair the same.

The referred to patent provides a completely fluid controlled drive system for indexing the paper drive shaft by selectively bypassing the output of a continuously driven fluid pump around the fluid motor which rotates the paper feed drive shaft. The back pressure from the fluid motor is employed to maintain a fluid operated shaft locking detent against a shaft ratchet wheel to lock the shaft against movement until released to allow indexing to the next line position.

The fluid motor and its fluid control system for a carriage drive system is illustrated in FIG. 1. Referring to the prior art system of this figure, a motor or the like drives a gear pump 12 through a shaft 14 in a continuous manner. Thus, hydraulic fluid 18 which partially fills reservoir 20 drains into conduit 22 feeding the gear pump 12 and causing the discharge of hydraulic fluid under high pressure from discharge pump conduit 24. Conduit 24 is connected directly to inlet conduit 26 of fluid operated motor 28 constituting, for instance, a gear motor, whose output drive shaft is directly connected as indicated by dotted lines to accounting machine platen drive shaft 30. The hydraulic fluid passing through the gear motor 28 is discharged into conduit 32 where it enters chamber 34 of valve casing 36. Bypass conduit 38 is fluid connected to valve chamber 40. Within bore 42 of valve casing 36, there is positioned a control valve 44 having spaced

lands

46, 48, and 50,

lands

46 and 48 defining chamber 40, and lands 48 and 50 defining chamber 34. A single valve actuating magnet 52 receives solenoid armature 54 which is mechanically coupled to valve 44 by a shaft 56. An apertured wall 58 allows the shaft 56 to extend therethrough but confines a compression spring 60 between casing wall 58 and land 46 such that the spring tends to position valve 44 to the right while energization of the solenoid coil 52 causes the valve to move to the left against the bias of the spring. The right-hand valve chamber 34 is directly coupled to a second chamber 62, within which is mounted a piston 64 secured to an outwardly projecting stem 68 forming a retractable detent or pawl. The detent 68 is adapted to shift axially to engage the appropriate teeth 70 of ratchet wheel 72 which in turn is fixedly coupled to the platen shaft 30. Thus, detent 68 locks the platen shaft in position.

Under the conditions shown, the control valve is urged to the right by means of compression spring 60. Fluid under pressure is discharged from the pump 12 into conduit 24 and passes via bypass conduit 38 into chamber 40 and is thus bypassed around the motor 14 to drain through return line 74 to reservoir 20. Since chamber 34 is cut off from exhaust port 76 leading to return 74, the back pressure at the outlet side of motor 28 maintains an equally high pressure in the detent piston chamber 62 urging the same to the right and in detent or latch position with respect to tooth 70 of ratchet wheel 72. This holds the platen shaft 30 stationary.

During both line-spacing and eject conditions, the control valve 44 is shifted to the left by energizing coil 52 allowing the outlet side of motor 28 to drain into return conduit 74 through chamber 34 and exhaust port 76. At this time, the pressure drops in the piston chamber 62 and the coil spring 78 shifts the detent 68 out of engagement with its engaged rachet tooth 70. Thus, at all phases of operation, when the motor 28 is being actuated, the low pressure prevailing on the outlet side of the motor maintains the detent 68 retracted and of course permits the motor connected platen shaft 30 to rotate. At the end of the line-space or eject pulses, the coil 52 is deenergized and the valve returns to its normal motor outlet cutoff position. This action thereby prevents further discharge through the motor and allows bypassing of the entire output from the pump to the left-hand chamber 40. As cutoff occurs, a slight continued rotation of the motor quickly provides an increasing back pressure which in turn acts on the detent piston to overcome the force of detent spring 78 and shifts the detent 68 outwardly and into engagement with a tooth on ratchet wheel 72. In this case, while the drive motor 10 is continuously energized, electrical pulses through the solenoid coil 52 insure selected line space rotation of platen shaft 30 or eject feed over a considerable number of lines, all controlled electronically by a pulse feeding means (not shown) to coil 52. However, the type of drive system illustrated in FIG. 1 is both insensitive to temperature variations and because of the single solenoid coil 52, rapid recycling of the electrically operated control valve is prevented.

SUMMARY OF THE INVENTION The present invention is directed to an improved hydraulic mechanism for indexing paper in a high-speed printer which provides significantly higher stepping speeds, has reduced temperature sensitivity, eliminates the need of adjustments of the system components, reduces appreciably the effect of ter minal velocity of the moving parts, and eliminates critical valve transfer timing. The hydraulic stepping mechanism of the present invention divides the acceleration and deceleration into two separate drives.

A fluid operated motor receives a continuous source of fluid under pressure from the output of a continuously driven fluid pump. The platen shaft is driven directly by the motor and a bypass circuit includes means for normally bypassing the source of fluid pressure around the motor. The bypass circuit includes an acceleration valve and a fluid commutator operatively coupled to the platen shaft allowing selective application of a portion of the fluid to the motor for intermittent advancing of the same. First and second fluid controlled detent means alternately latch the shaft against movement and a stepping valve shifts the accelerator valve to intermittently advance the shaft by momentarily closing the bypass circuit until the shaft driven commutator advances sufficiently to reopen the same. The stepping valve simultaneously releases the latched detent means prior to motor movement and drives the unlatched detent means towards latching position. Each detent means includes a ratchet wheel fixed to the platen shaft and a pivotable detent arm pivotable into and out of the path of the ratchet wheel teeth by opposed hydraulic actuator pistons. These are alternatively moved by a two-position stepping valve, so as to release one detent and move the other towards latch position with respect to associated, angularly offset ratchet wheels. A spring biased skip latch is provided for each detent means and is normally spring biased into latch position to hold the detent out of the path of the ratchet wheel teeth. A solenoid associated with the skip latch is energized simultaneously with the solenoid driving the two-position stepping valve to momentarily release the detent to allow line spacing. Alternate stationary commutator slots are fluid coupled to respective detent means and. responsive to cyclic movement of the movable commutator slot for cyclic line spacing. Individual electromagnets hold the bidirectionally moving stepping valve in either of two extreme operative positions. Each electromagnet is energized simultaneously with an associated ratchet skip latch solenoid for respective detent means. While the detent ratchet wheels are angularly offset for single line spacing, they may be manually shifted to in line position for double line spacing. Line skipping, other than double line spacing, is accomplished by latching up both detents to allow the motor to slew until a predetermined number of spaces has passed. Hydraulic pistons carried by the detent arms dampen detent latching for controlled deceleration of the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic, sectional view of a prior art fluid motor indexing system for a carriage of an accounting machine;

FIG. 2 is a diagrammatic partial sectional and perspective view of the improved fluid carriage motor indexing system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 2 of the drawing, as mentioned previously, the indexing system of the present invention divides the acceleration and deceleration into two separate drives. The acceleration function is achieved by a constant input flow hydraulic system similar to that of FIG. 1. ln this respect, the reservoir 120 carries hydraulic fluid 118 which is supplied to the hydraulic gear type pump 112 through an inlet conduit 122, the pump discharging liquid under pressure through outlet pump conduit 124 which is coupled directly to inlet conduit 126 of the hydraulic gear type motor 128. Motor 128 is mechanically coupled to platen drive shaft 130, preferably by direct mechanical connection as indicated by the dotted connection line. Outlet conduit 132 from the drive motor 128 returns hydraulic liquid to reservoir 120. Unlike the prior art system, instead of a single detent means, plural detent means 156 and 158 are employed for the drive shaft 130. in this respect, a first detent ratchet wheel 172 is coupled to the shaft 130 and adjacent thereto, and preferably angularly offset therefrom, is a second ratchet wheel 172'. Further, mechanically coupled to the same drive shaft 130 is a fluid commutator 200 consisting of an outer stationary cylindrical commutator element 202 and an inner rotatable cylindrical commutator element 204.

Control of the flow hydraulic liquid under pressure to the drive motor 128 is achieved by the commutator 200 and acceleration valve 144. In this respect, the bypass conduit 138, which is coupled intermediate of the hydraulic pump 112 and the hydraulic motor 128, and specifically between the output conduit 124 of the pump and the inlet conduit 126 to the motor, allows hydraulic fluid to enter acceleration valve chamber 140 defined by bore 142 within accelerator valve casing 136. The acceleration valve 144 carries a pair of spaced

lands

146 and 148, the valve casing being further provided with leftand right-hand outlet passages 150 and 152. The right-hand outlet passage 152 is coupled to circumferentially spaced commutator slots A, C, E, G, l, and K of stationary commutator element 202 through manifold 160 while the left-hand acceleration valve outlet passage 150 is coupled to alternate commutator slots 13, D, F, H, .l and and L by means of manifold 168. With the outer commutator element 202 stationary and the inner commutator element rotating by being mechanically coupled to platen carriage drive shaft 130, the hydraulic fluid is returned to the sump or reservoir 120 via return line 176 whose end remote from reservoir 120 is sealably connected to the rotating inner commutator element 204. Commutator element 204 carries a central bore or passage 178 and a single radial passage or slot 180, which aligns itself cyclically with the spaced outer, stationary commutator slots A through L in that order. Cylinder 202 is fixed, with cylinder 204 rotating therein about a common axis. Where there are only l2 stationary slots shown for 12 consecutive lines of spacing of the web 182 carried by the platen to be printed thereon, this embodiment is illustrative only of one example of the present invention. A greater or lesser number of stationary commutator slots may be employed. The acceleration valve is bidirectional in movement within bore 140, between extreme positions defined by leftand right-hand

adjustable stops

184 and 186, respectively.

Bidirectional shifting of the accelerator valve is controlled by stepping valve 186 which comprises a valve casing 188 carrying a longitudinal bore 190 provided in turn with

enlarged counterbores

192, 194, and 196. The stepping valve 186 comprises a valve shaft 198 carrying three spaced

lands

206, 208, and 210, all being sealably received with bore 190. The stepping valve 198 is solenoid operated, that is, the valve 198 is moved between extreme positions by leftand right-hand solenoid coils 212 and 214 respectively, operatively associated with valve shaft 198.

Lands

206 and 208 define stepping valve chamber 216 while

lands

208 and 210 define valve chamber 218. A gear type hydraulic pump 220 is provided with an inlet conduit 222 for removing hydraulic liquid 118 from reservoir 120. Pressure relief valve 219 and conduit 221 bypass excess fluid from pump 220 maintaining a substantially constant fluid pressure and causing pressurized hydraulic fluid to be discharged therefrom and passed into conduit 224 for delivery to valve inlet passage 226. With the valve in the extreme lefi-hand position shown, high-pressure hydraulic fluid enters counterbore 194 and passes via chamber 218 to right-hand stepping valve outlet passage 228. It enters left-hand chamber 164 of the acceleration valve 144 through accelerator valve control passage 230 driving the acceleration valve to the extreme right-hand position defined by left-hand stop 186 (as shown).

Alternatively, when solenoid coil 214 is energized, the stepping valve 198 moves from its extreme left-hand position shown to the right-hand position thereby blocking ofi' fluid outlet passage 228 from inlet passage 226, and allowing fluid to flow into left-hand outlet passage 232 since intermediate land 208 moves to the right causing chamber 216 to feed liquid therebetween. The chamber 218 existing between

lands

208 and 210 allows hydraulic fluid to leave chamber 164 behind left-hand land 146 of the acceleration valve and pass through passages 230 of the acceleration valve and passage 228 of the stepping valve to return to the sump via sump or discharge passage 234. Meanwhile, high-pressure hydraulic fluid is now directed from passage 232 of the stepping valve to passage 236 of the acceleration valve, entering chamber 166 and acting on the rear face of right-hand land 148 of acceleration valve 144 to move it off the right-hand stop 186 and causing the left-hand land 146 to impinge against left-hand adjustable stop 184. A sump or return passage 238 is provided for the stepping valve to return hydraulic fluid to the reservoir 120 from chamber 166 during movement of the acceleration valve from left to right.

An important aspect of the present invention resides in the employment of the multiple detent means 156 and 158. In this respect, detent wheel 172, carried by the shaft 130, is operatively associated with a T-shaped detent arm or pawl 168. The detent arm 168 is supported for pivotable movement about an axis defined by a hollow shaft 240 having one end fluid blocked and the other fluid coupled to a conduit 242. A solid bar 244 extends to the right of hollow shaft 240 while the lefthand bar 246 of the detent arm 168 is bored and counterbored to receive a reciprocating damping piston or plunger 248, the head end of which 250 is carried by the counterbore. The counterbore is fluid coupled to the hollow shaft 240 and the wall of the counterbore carries a series of orifices 252 through which may pass hydraulic fluid emanating from line 242. The detent arm 168 is further provided with an upstanding latch arm 254 which cooperates with skip latch 256.

In this respect, the skip latch 256 comprises a spring biased pivotable detent latch 258 terminating at its outer end in a sloped contact surface 260, and carries a detent notch 262 which acts to receive and hold the end of detent latch arm 254. The detent latch 258 is biased towards latching position by a coil spring 264 which is positioned between the pivotable latch 258 and a fixed stop 266. A skip latch solenoid coil 274 is provided such that when it is energized, it moves the detent latch 258 against the bias of coil spring 264, since the detent latch 258 acts as the armature for the solenoid to release detent latch arm. The right-hand bar 2440f the detent 168 has, abutting on either side thereof,

hydraulic actuator pistons

276 and 278, respectively. In this respect, fixed

casings

280 and 282 define hydraulic cylinders for the

pistons

276 and 278, which are supplied with hydraulic fluid through

lines

284 and 286 respectively. In similar fashion, ratchet wheel 172 is associated with a detent arm 16$ of identical construction to that of detent arm 168. In this case, damping piston 248' receives hydraulic fluid under pressure via hydraulic line 288 while

hydraulic actuator pistons

276 and 278 are operated in response to fluid under pressure being delivered to respective actuator cylinders 280' and 282' through

lines

290 and 292, respectively. Further skip latch solenoid 274' controls the position of detent latch 258' by selective energization of the same, to pivot the latch 258 upwardly against the bias of coil spring 264'. The

lines

284 and 292 are respectively coupled to outlet passage 228 of the stepping valve 198 while, actuator piston

fluid passages

286 and 290 are fluid coupled to outlet passage 232 of the same stepping valve. Further, hydraulic fluid under pressure is continuously delivered to the damping pistons 248 and 248' of

respective detent arms

168 and 168 via line 300 and lines 240 and Zflh, respectively. It is noted that teeth or detent notches of ratchet wheels 172 are angularly offset with respect to the detent notches of ratchet wheel 172' and further that the slot A, for instance, of the commutator element 202 is associated with detent notch A of ratchet wheels 172 and the next adjacent slot B of commutator element 202 is associated with detent notch B on wheel 172, etc.

With this in mind, operation of the improved hydraulically controlled and driven indexing mechanism of the present invention will be described.

In similar fashion to the prior art indexing system of FIG. 1, rapid acceleration is achieved from an asynchronous electrical input signal which, in this case, is applied simultaneously to one of the

solenoids

212 or 214 of the stepping valve 198 and one of the solenoids 274 and 27 1' of the skip latches associated therewith. After a given displacement, the constant flow system is shunted by means of the commutator 200 and the control is passed to one of the piston type fluid dampers, that is either

damper piston

248 or 248 of respective pivotable detent

arms

168 and 168. This type of system is insensitive to temperature variation and a constant pressure source is provided to power the deceleration system, as evidenced, to eliminate the rapid recycling of electrically operated valves. A dual system is employed involving

solenoid groups

212 and 274, and 2M and 274'. This allows one initiating valve transfer to complete a single index.

In the position shown, the constant flow from the acceleration pump 112 bypasses the drive motor 128 tending to rotate platen drive shaft 130, the hydraulic fluid under pressure passing through conduit 138 into chamber 140 of the acceleration valve and through outlet passage 152 and slots A and 180 of the commutator, and then to the reservoir 120 via passage 176. The back pressure generated by this flow urges the acceleration motor 128 and the detent ratchet wheel 172 against the end of detent arm 168 which rests within the detent notch A of wheel 172. This is the idle condition maintained during printing. The constant pressure system is holding the detent arm 168 in this position. Detent arm 168' is in an ineffective position and is latched in this position by skip latch 256' under the bias of spring 26 1'. The constant application of fluid pressure from pump 220 further maintains the acceleration valve 144 shifted into the extreme right-hand position and is also providing refill oil for the damping piston 248 in detent arm 168 through line 300. The energization of the electromagnet 212 holds the stepping valve 1% in the extreme left-hand position shown.

A single line index is accomplished by transferring the stepping valve 1% from its Iefbhand position shown to the alternate location wherein the hydraulic fluid at inlet 226 will pass to stepping valve outlet passage 232 rather than passage 228. This will cause a flow of high-pressure fluid to detent actuator pistons 2'78 and 276' and allow liquid to discharge from behind detent actuator pistons 276 and 278' returning to sump via stepping valve passages 22% and 234. As a result, the detent arm 168' comes in line with stop or notch B of ratchet wheel I72 and detent arm 16h moves to an ineffective position sliding over the curved surface 260 at the end of detent latch 258 to fall behind detent latch notch 2052 whereby it is latched in ineffective position. In energizing the stepping coil 214, the skip latch coil 274 associated with detent latch 258 is simultaneously energized to release detent arm 168 to enable it to be moved hydraulically into in-line position with the next succeeding detent ratchet wheel notch B.

Simultaneously, the acceleration valve 1 M transfers to direct the pump flow from pump 112 into the blocked channel created by commutator slot B. The spring of the oil and the mass of the load causes the drive motor 123 to accelerate rapidly, rotating the drive shaft and of course the rotating commutator element 204 counterclockwise. When the motor has traveled one-half ofthe 30 required for a single space, the rotating commutator slot moving with the motor advances to slot B on the commutator stationary element 202. This frees the input to the accelerator motor 128 which coasts forward under its own inertia. The damping piston 248 on detent arm 168 is of course extended such that the outer end of the same makes initial contact with the detent notch B on ratchet wheel 172', this engagement occuring at the one-half single space travel of the platen drive shaft 130. The inertia of the load forces the oil out of the series of orifices 252' and thereby decelerates the load to 10 percent of its terminal value. The remaining velocity is lost in the impact of the detent wheel against the detent arm 168. The bypass back pressure from pump 1112 holds the motor 128 and the load against the stop 168. The next index is accomplished in a similar manner by transferring the stepping valve from its right-hand position to the left-hand or original position shown. Each subsequent transfer of the stepping vaive results in a one line index of platen 162 and paper 182.

Double line spacing is accomplished in the same manner as single line spacing but necessarily after the detent ratchet wheel 172' is manually shifted to be in line with detent wheel 172 (by means not shown). Single single line space is accomplished by decelerating from full speed, no difficulties occur in double line spacing. As mentioned previously, paired

coils

212 and 274 are simultaneously energized as are coils 212 and 2741 for single or double line spacing. However, skip is accomplished by latching up the two detent latches 258 and 258' by continued energization of both coils 274 and 294. This allows the motor to slew until a predetermined number of spaces has passed. Electronic logic circuits (not shown) position the stepping valve correctly so that the correct detent will engage, that is, if an even number of spaces are to be passed. the stepping valve is in the correction position, and if an odd position of spaces are to be passed, the stepping valve must be transferred. The correct timing for rel-ease of the skip latches 256 and 256 is also under control of the electronic logic. Further, the stopping from a single velocity for all conditions eliminates the need for cumbersome hydraulic adjustment inherently present in the prior art apparatus.

What is claimed is:

1. In a fluid drive system for a fluid driven paper feed carriage, the combination of a fluid motor, a carriage drive shaft driven by said motor, a substantially constant supply of fluid under pressure, a bypass circuit for normally bypassing said supply around said motor, said bypass circuit including an acceleration valve and a fluid commutator, said fluid commutator being operatively coupled to said shaft for movement therewith, and a stepping valve for shifting said accelerator valve to initiate intermittent advancing of said motor by momentarily closing said bypass circuit until said shaft driven commutator advances sufficiently to reopen the same.

2. The fluid drive system as claimed in claim 1 further comprising: first and second detent means for alternately latching said shaft against movement and means responsive to movement of the stepping valve for simultaneously releasing the latched detent means prior to motor movement and driving said unlatched detent means toward latching position.

3. The fluid drive system as claimed in claim 2 wherein: said fluid commutator comprises a rotary commutator element operatively coupled to said shaft and carrying a single commutator slot for returning fluid pressure to said source of fluid pressure, and said stationary commutator element carries a plurality of slots fluid coupled to alternately blocked outlet passages of said acceleration valve, and said system further includes: means for moving said acceleration valve bidirectionally, and means for fluid coupling said acceleration valve within said bypass circuit between the input side of said fluid motor and said stationary commutator element such that, under bidirectional movement of said acceleration valve, alternate slots of said commutator are fluid coupled to the same outlet of said acceleration valve.

4. The fluid drive system as claimed in claim 3 wherein: each detent means comprises a ratchet wheel fixed to said shaft for rotation therewith and a fluid actuated detent arm movable into the path of said rotating ratchet wheel, said stepping valve is bidirectionally movable individual solenoids move said stepping valve in opposite directions to extreme positions, said detent arms are oppositely driven by fluid operated pistons, and said pistons are fluid coupled to said stepping valve such that by energizing one of said solenoids, one of said detent arms is moved to inoperative position while the other is moved into ratchet wheel engaging position.

5. The fluid drive system as claimed in claim 4 further comprising: a skip latch for each detent arm, said skip latch being normally spring biased into engagement with said detent arm to prevent movement of said detent arm into ratchet wheel engaging position, and a solenoid for each skip latch for simultaneous energization with an associated solenoid for said stepping valve for moving said detent latch against the bias and away from said detent arm to release the detent arm for movement into ratchet wheel engaging position under control of said opposed hydraulic pistons.

6. The fluid drive system as claimed in claim 5 wherein said detent arm carries a damping piston slidable therein with the outer end extending therefrom for initial engagement with said ratchet wheel, means exerting continuous hydraulic pressure on said detent damper piston for maintaining said piston in an extended position and orifices carried by said detent arm and selectively cut off by movement of said damping piston into retracted position, whereby retraction of said damping piston reduces the number of orifices discharging high-pressure fluid to rapidly decelerate said rotating shaft into latched position.

7. In a fluid control system for a fluid driven paper feed carriage, the combination of a rotatable platen to be advanced in line-space and eject modes, a fluid operated motor provided with an inlet and outlet and connected to said platen to rotate the same, a pump for delivering fluid under pressure to the inlet of said motor, a bypass circuit for bypassing fluid under pressure around said motor, said bypass circuit including an acceleration valve having an inlet fluid connected to the inlet side of said motor and first and second outlets, said acceleration valve being bidirectionally movable to couple said valve inlet selectively to one of said valve outlets, a fluid commutator operatively coupled to said platen for rotation therewith, said commutator including stationary and movable slot means, one of said slot means including at least two slots and fluid connected to respective first and second outlets of said acceleration valve, said other slot means comprising a single slot, and means for shifting said acceleration valve bidirectionally to fluid connect the inlet of said acceleration valve alternately to said first and second acceleration valve outlets to initiate intermittent advancement of said motor by momentarily closing said bypass circuit until said said platen driven commutator advances sufficiently to reopen the same.

8. The fluid control system as claimed in claim 7 further comprising: a bidirectionally moving stepping valve operatively coupled to said acceleration valve for controlling the position of said acceleration valve, and individual solenoids for shifting said stepping valve between two operative positions.

9. The fluid control system as claimed in claim 8 further comprising: first and second fluid operated detent means for limiting movement of said platen during line-space operation, and means operatively associating each detent means to respective slots of said commutator, and means including said stepping valve for simultaneously releasing one of said detent means and moving said other toward detent position.

10. The system as claimed in claim 9 wherein each detent means comprises: a ratchet wheel rotatable with said platen, a pivotable detent arm including a first portion movable into the path of said ratchet wheel, a second portion extending at some angle thereto, a pair of hydraulic pistons positioned on said opposite sides of said second portion for pivoting said detent arm respectively into release and detent positions, a third portion extending at some angle to said first and second portions, a spring biased skip latch biased into latching position with respect to said arm third portion to normally maintain said detent arm in inoperative position, and a solenoid for selectively overcoming said bias to unlatch said third portion during skip latch solenoid energization.

11. The fluid control system as claimed in claim 10 wherein said ratchet wheels are angularly offset by a distance corresponding to a one-half single space rotation of said platen.

12. The fluid control system as claimed in claim 11 wherein said first detent arm portion includes a longitudinal bore and a counterbore internally thereof, a damping piston slidably received within said counterbore and having a portion extending through said bore and outwardly beyond the end of said first detent arm portion, fluid under pressure carried within said bore and behind said damping piston and a series of axially spaced holes carried by said portion rearwardly of said piston such that upon initial contact of said damping piston extension with said ratchet wheel, said platen is decelerated as the piston sequentially closes off said holes during retraction within said counterbore.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 979 Dated Q 1971 Inventor(s) Stanley omb It is certified that error appears in the above-identified patent and that said Letters Patent are hereby correctedas shown below:

Column 4, line 65, after "head end" and before "of which", insert 250 and after "of which" and before "is carried,"delete [250].

Column 7, line 28, between "movable" and "individual", insert Signed and sealed this 16th day of May 1972.

(SEAL) A l; best:

EDWARD M.FLETCIihIR,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents RM ($59) USCOMM-DC scene-P09 U S EDVEFNMENT PRINTING OFFICE l9. 0-365-33