US3101013A - Indexing apparatus for marking devices and the like - Google Patents

Description

Aug. 20, 1963 1, s. AYERS ETAL 3,101,013

INDRXING APPARATUS RoR MARKING DEVICES AND TRE LIRE Filed Oct. 26, 1959 3 Sheets-Sl'lee'tl 1 INVENToRs John S. Ayers 8 Alvin M.Brown BY I M, Mami 'DI t ATTORNEYS Aug. 20, 1 963 Y J. s. AYERs ETAI. 3,101,013

` INDEXNGV APPARATUS FOR MARKING DEVICES AND THE LIKE Filed Oct. 26, 1959 3 Sheets-Sheet 2 INVENTORS John S. Ayers 8 By Alvin M. Brown ATTORNEYS Aug. 20, 1963 J. s. AYERs ETAL 3,101,013

INDEXING APPARATUS FOR MARKING DEvIcEs AND THE LIKE 5 Sheets-Sheet 3 Filed OCT.. 26, 1959 JON mvENToRs: John S. Ayers Alvin Brown M y MM ATTORNEYS:

United States Patent O 3,1l1,lll3 INDEXING APPARATUS FOR MARKING DEVICES AND THE LIKE John S. Ayers, Scott Township, Allegheny County, and Alvin M. Brown, Penn Township, Allegheny County, Pa., assiguors to las. H. Matthews & Co., Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 26, 1959, Ser. No. 848,740

5 Claims. (Cl. 74-S18) This invention istor an indexing apparatus for selectively adjust-ing ia movable element to a predetermined setting from a remote location. The invention, while being applicable to various operations, is particularly useful for operating relatively heavy movable parts whose position must be accurately adjusted. The invention is especially useful for rotating marking dies for marking steel billets and slabs with data that is usually marked on such products to identify the billet or slab as to theheat number, date and perhaps coded information as to its composition, or like markings.

IIn billet marking machines disclosed in certain prior applications in which -We are co-inventors; namely, Serial No. 737,041 tiled May 22, 1958, now Patent No. 3,0201,- 834, granted IFebruary 13, 19612, Serial No. 765,513, tiled October y6, 1958, now Patent No. 3,002,918, there is disclosed a marking device having a marking head comprised of ia plurality of gear wheels in side-by-side relation, each being independently rotatable and each having an impression forming marking character -on the outer ends of the gear teeth thereof. Mechanism is provided for advancing the marking head into contact with the edge of the slab or billet and when Contact has been made, the marking head is struck ia heavy blow, whereupon the characters on those gear teeth of the marking head which contact the billet make an impression in the billet. The marking head is then retracted and in the retracted position each gear die is engaged by a separate indexing gear. The `selective rotation of the indexing gears may then be effected to rotate the gear dies tov bring diierent characters into marking position. The indexing gears are -rotated in step-by-step increments through pawls which are reciprocated by pneumatic cylinders, each reciprocation of a pawl rotating the indexing gear one tooth, and such rotation is in turn transmitted to the gear die.

It is necessary that the indexing be effected from a consol or panel remote from the marking head and that it be rapidly but accurately effected. The gear dies must be heavy to withstand the impact, and the entire system must be fool-proof and secure against error due to jarring, failure of ia pawl to effectively ratchet, or error due to some bounce or inertia ecect that occurs when heavy parts such as are here 4involved are moved rapidly or stopped or their direction of movement suddenly reversed.

In a copending yapplication Serial No. 765,513 tiled October 6, 1958 in which we are co-applicants, the indexing is effected through electric circuits responsive to the reciprocation of the pawl thatrotates the indexing gears and which include stepping relays that are energized through such limit switches. While this system is normally satisfactory, it is subject to possible error since it really counts the reciprocations of an operating pawl and not the actual rotation of the indexing gear. Bouncing or jarring or inertia may result in a movement of `a pawl with no corresponding movement or improper movement of au indexing Wheel. Should this happen, the stepping relay would reach the intended setting ahead of `or out of phase with the actual turning of the gear die to the selected character, so that `an erroneous marking might be made, and the operator at the consol would be unaware of it because he must assume that the indexing mech- 3,101,013 Patented Aug. 20, l 963 ICC ' indexing the several dies must be conned in a relatively 'indexing gear to properly rotate cannot occur.

small space.

An `object of the present invention is to provide an indexing system which is responsive tothe movement of the indexing gears directly as distinguished from movement of fthe pawls, whereby any error due to failure of an Since the indexing gears lare meshed with the marking gears, the marking gears must correspondingly move with each increment of movement of the indexing gears, and error cannot occur.

A further object of our invention is to provide an indexing mechanism that will not `be disturbed by the jarring of the machine or possible bounce lot' any of the parts. i

A further object of our invention is to provide an indexing system which will continue to operate until the gear die has moved to its selected position and provide an indication at the control panel or consol only when the selected character is in marking position.

A -further important object of our invention is to eliminate stepping relays from the selector circuit and provide switch means operated by the movement of the indexing gears to operate the pawls until the selected character is in marking position, simplification of the circuits being also accomplished by elimination of stepping relays.

These and other objects and advantages are secured by our invention as will more fully appear from the detailed description thereof in conjunction with the accompanying drawings, in which:

FIG. 1 is a more or yless schematic view of the indexing gears and operating mechanism thereforV with a portion lof the circuits for controlling the same;

FIG.'2 is an elevation on Aa larger scale showing the indexing gear and the'` contact Wheel operated thereby;

FIG. 3 is a transverse section through one of the con- .tact Wheels in the plane iof line III-III of FIG. `2; and

FIG. 4 is a schematic simplified circuit diagram for the system; `and i FIG. 5 is a yfragmentary View showing an alternate torni of contactor for use in the indexing head, the view being partly in vertical transverse section and partly in elevation.

In the drawings we have shown a single indexing gear and associated parts and control circuit therefor, `and it is to be understood that this is substantially duplicated (except for the rectifier and transformer) for each marking die or other-member to be indexed.,

Referring iirst to FIG. lof the drawings, we have shown the marking head in dotted lines, -and it is designated generally as 2. Itis shown in :the retracted position land i-t moves toward the right as viewed in FIG. l to engage a face of the billet or slab to be marked. A single gear idie is indicated at 3 and the end faces of the teeth have character imprinting 'dies thereon, one character on each tooth. Typically these characters may comprise the numerals 0 to 9, or a succession of letters of the alphabet. The tooth in position 3a of the gear :die 3` is the one which is selected rto mark. The construction and operation of the marking head and the Courel-ated movement of the indexing head is more fully described in `appl-ication Serial No. 7 37,041 and brief reference is made thereto only to enable 4the `objects and purposes of the present invention 'to be more fully understood.

The indexing head I4 in the billet marker `above refer-red tois mounted 'on a vertically movable support 4a by which the indexing head is moved into and fout of engagement with the gear dies of the marking head. The

Vmovement of the indexing gear is transmitted to the gear die 3 to rotate'it one increment. 'Fixed in the indexing p head is apivoted holding pawl 11 that holds the indexing gear against free rotation and prevents any over-travel. it is normally held in gear llocking position by a ieaf spring 1-2 and is tripped by tan abutment 13 fon the slide As explained above, and as more ful-ly described in the copending applications above last referred to, we have here shownbut one indexing gear and operating rod 6,

Y but the complete machine embodies a head in which there would be several of these gears and operating bars in side-by-side relation and the single shaft 9 would carry all of the indexing gears.

y The rod ty has an lopenating yextension 14 that passes through la cylinder 15, the rod having a piston 16 aixed thereto inside fthe cylinder. The cylinder has a port at each end in which is entered .a pipe, the pipe at one end being designated 16a and at the other end 1Gb. These pipes lead to a slide valve 17 of va well known type in which there is a reciprocating valve element 18. The valve body has exhaust ports '19 :and two spaced lair inlet ports leading from Van air supply pipe 2d. The arrangement is such that when the valve '17 admits air from pipe 2()` to one end tot the cylinder 15 the other end of the cylinder is vented to atmosphere. The valve is shown in the drawings in a position rwhere piston 16 has completed its stroke tothe lett'tand the operation is about to reverse. This is the normal or rest position of the parts. The valve is magnetically operated in yone direction and then the other, and this is indicated in the drawings where the ends of the slideV valve project beyond the valve housing and constitute armatures 17a and 17b for solenoids 17e` and 17d respectively. These solenoids are energized through micro-switches 21 tand 22 that are arranged to` be engaged by abutments 21a fand v2lb respectively on the pis-1 ton rod 14 so positioned that the micro-switches will be tripped at Vthe opposite limits of travel of the piston 16.`

'Y The switches 21 and 22 eachhave one poile connected to a current supply line 23. The other pole of switch 21 is connected through wire 24 with :solenoid 17`c and the other pole of switch 22 is connected through wire 25 with solenoid 17d. The other terminals of the solenoids are Y connected to a return conductor indicated by the ground vof the valve 17 to be shifted to the right as viewed in this diagram. When this shift is made, the left-hand port 19' Y will be closed `and air can enter from pipe 2t) and iiow through pipe 16h to the left :end of cylinder 15. This will drive piston 16 to the right, moving the pawl 7 on rod 6 to the right of gear 10. As piston 16 reaches the righthand limit of travel, abutment 2lb engages switch 22 to close it, energizing solenoid 17d to shift the slide valve to the opposite limit of its travel, so that the left port 19 is vented to atmosphere and yair tlows from pipe 2d into pipe 16a and the opposite end of the cylinder 15 to drive piston 16 to the left. As the rod 6 moves to the left, pawl 7 rotates the index gear wheel 1d through one increment. As the piston returns again to the left-hand l limit of traveL-switch 21 is tripped and the cycle is repeated, and this operation will continue asv ilong as wire 23 remains energized. The present invention is'primaniiy concerned with the opening and closing of the circuit to the wire `23 and associated circuits. A magnetic single pole double throw switcher relay is shown at 26`in HG. l,

and when this switch is in the position in which the switch is there shown, Vthe Wire 23 is connected with a source of energizing current. The relay has a coil 26a and an armature 26h .and its biased to normally assume the position shown in FIG. l when the coil 26a is not energized.

According to the present invention, the rotation of the indexing gear wheel 10 in combination with a selector switch at the operators consol controls the operation of the switch 26. As here shown, there is ia multiple contact switch 27 in the form of -a second gear wheel supported on a shaft 28 on theindexing head ywith the teeth of this gear wheel meshing with the teeth of the gear wheel it?. It might have wide pitched teeth, like the gear die 3, but is here shown yas having two teeth operating as a single tooth between two teeth of the indexing gear wheel 1d. Gear wheel 27, as best shown in FIGS. 2 and 3, is a ber gear orwheel made of insulating material. On one face is ,a conducting disk or plate 29 `of metal. There `is Ia spiral series of contact posts on this plate which pass through the face of the switch, the ends of which are exposed on the opposite surface of the switch 27. Each pin is arcuately and radially separated from the others and they `are all designated with t .e letter P in FIG. l2.

wiper 32 vfor each'pin P. They are so positioned that they bear vagainst the :surface of the Agear wheel 27 on a line corresponding to radius R in FIG. 2, and each wiper is wide enough to contact only one of the pins P. Thus, as

' the gear wheel 27 is rotated, rst one pin P andl then the -next will in turn =be carried into contact with one of the wipers 32. There is a separate wire 33 leading from each of these wipers 32 through a rnultiple conduct-orecable, designated as 34, to a selector switch 35 that may be located in a consol or control panel remote Vtrom the marker. This is usually nearby, but comfortably removed from the machine.

At the selector switch the cable branches out into a number of wires 36 corresponding to the number of wires 33 and Wipers'32, and each of these wires terminates at a switch contact 37. There is an adjustable switch arm 38 manually adjustable to selectively engage any one contact 37, so that when the switch arm 3S is on a selected contact, a circuit may be completed from the selected contactto a corresponding '-wiper 32, and 'when the gear 10 moves to the right position, the circuit will tbe closed through the pin P for that wiper to the disk 29 and brush 30.

Referring now toFIG. 4, the manual selector switch 35 is indicated in the upper left corner of the figure, and the multiple contact switch on the gear 27 is indicated below it. Itis here ydiagrammatically indicated for clarity of illustration as a switch having a numlber lof contacts `arranged in an arc rather than being shown according to its actual construction, but each contact 32 corresponds to a contact 32V of FIG. 2.

. The selector system with the multiple contact switches is preferably operated at low voltage, wherefore current from supply linesd and 41 is passed through the primary of a stepadown transformer 43. The secondary of this transformer is .designated 44, and one side of the secondary is connected to a .Wire 45 leading'to one side of a relay coil 26a of switch or relay 26. The other side of the relay coil is connected through wire 46 with manual selector switch Varm 38. The contacts 37 of this selector switch lead through wires 36 and cable 34 to Wires 33 leading to the several brushes 32. The circuit from wipers 32 is through one of the pins P and disk 29 (indicated as a swinging switch arm 29 in FIG. 4), brush 30 through wire 46 to the other side of the secondary 44 of the transformer 43. Thus it may ybe seen that only when the circuit may be completed through the selected Contact on the selector switch 35 and the corresponding pin P on the gear-actuated multiple contact switch 27 will the electromagnet 26a of the control switch or relay 26 be operated. i

Wire 40 connects to both contacts 26o and 26d of the relay switch 26. Contact 26e of the relay switch connects to Wire 23 leading to the two micro-switches 21 and 22 as above described, and through one or the other valveoperat-ing solenoids 17d-17e to ground or return current :supply line 41. There is a switch 47 in line 40, diagrammatically indicated in FIGS. l and 4 that is closed when the indexing head 4 moves down into the operating position to closedposition, and which is biased to open when the indexing head is raised.

When the condition arises that the circuit is closed through the manual selector switch 35 and the gearoperated switch, relay magnet 26a is energized, lifting the armature of the relay to open the circuit from contacts 26e and 26e :of switch 26 and close a circuit across con-` tacts 26d and 261. Current then flows from line 40 through contacts 26d and a signal lamp 49 to ground. A branch circuit 50 leads through relay Winding 51 to ground. The energizing of relay `e1 closes switch 51a. This switch is in series with like switches Ifor each of the other indexing wheels of the indexing head, for which reason the balance of the circuit is indicated in dotted lines. If there are, for example, nine indexing wheels, a switch corresponding to 50`51a for each wheel would have to close, whereupon a circuit would then be complete through a main indicator lamp 52. Also the circuit would then be established through this series of switches and line 53 to the stamp-operating switch 54, so that when the operator pushed the switch54 down, current would flow through this switch to those electro-pneumatic devices that move the marking head 2 toward the object to be marked and eitect the marking operation as more fully described in the last two applications above mentioned. The operation may now be completely followed. The operator sets selector switch arm 38 to the character which he wants next to -be brought into marking position. When the indexing head 4 moves down to operating engagement with the marking head 2, switch 47 is closed, so that current flows through line 40, contacts 26c--26e of switch 26 to micro-switch 21, which at that time is closed. This initiates the reciprocation of piston 16 to move the rod 6 and turn the indexing gear 10, and thereby turn marking die 3. Rotation of the indexing wheel 10 also rotates contact gear wheel 27. The reeiprocation of the piston 16 continues automatically upon the closing of switch 47 until a circuit is completed through the selected contact of switch 35 and the corresponding contact of switch 27 to energize relay Winding 26a to open the circuit between contacts 26C and 26e to stop rfurther reciprocation of the pawl 7. It will be seen that until switch 47 is closed by the supp-ort 4a lowering to a position where indexing gear 10 meshes with ygear die 3, no :operation of the indexing gear can be effected. It is therefore possible for the operator to pres-select the position of the switch arm 38 when the support 4a is raised, with no operation of the indexing gear taking place. Since the complete machine embodies several marking dies and, therefore, several selector switches 35, it is an advantage that the manual selector switches can be adjusted at the operators consol while the marking cycleis being carried out, and thus be set in advance of the return of the marking head to its retracted position when the support 4a is next lowered.

For the further utility of the device, and to reassure the operator that the proper number has been set and enable the operator to make correction if he has set his selector dial at the wrong setting, the system may include a second switch 60 operating with a gear Wheel 27, as

indicated by the diagram in FIG. 4. This switch has contacts 61 corresponding in character sequence to the ones above it in the diagram. Each contact 61 has a wire 62 leading therefrom to a cable 63, the Awires of which lead to the several contacts of a so-called nixie lamp `64, which is a -glow tube having a number of characters therein, a selected one of which will glow when its circuit is energized, such lamps being well known in the art. The common terminal of the nixie lamp is connected to one o utput 65 of rectifier 66 The other output terminal of the rectifier is connected through line 67 with the moving Contact 66 of the switch 66. The lamp operates on 200 volts, direct current. The input terminals of the rectitier are connected across lines 68 leading to the output terminals of the voltage step-up transformer `69. The primary of this transformer is connected through Wire 70 across the current supply lines 4t? and 41.

The circuit described causes the selected character on the nixie light to glow when the indexing wheel 10 has moved to the chosen position, which will be at the same time lamp 49 is lighted, giving the operator two signals that the particular wheel is at the pre-selected position. It will be apparent to those skilled in the art that while two switches operating in unison are shown in the diagram, the etfect of two switches may be secured electrically through the use of blocking circuits or relays separating the alternating and direct current circuits, and that the simplified wiring digram of FIG. 4 is more or less symbolic or schematic.

In the particular system shown, the marking Wheel or gear dies is separate from the indexing gear Wheel, but in sorne instances, as for example with rubber stamps used for making boxes, the indexing wheel might itself be a type of marking wheel, or the Wheel switch 27 might be a marking wheel, or one wheel could combine all of the functions of the three wheels here shown.

However, the system here shown is especially adapted for a billet or slab marker where the gear dies are heavy, the setting of the dies fast, and bouncing or jarring is likely to occur. lf the pawl 7 fails to catch on the indexing gear, the mechanism must continue to operate until it does, or ior such length of time that the operator knows that there is a failure of the indexing wheel to turn, and shut the machine down for repair or adjustment. Since all operations of the contact gear `27, the marking wheel 2 and the indexing wheel 10 occur when the gears are in mesh, movement of any gear will reliect correspondingly on the others.

In FIG. 5 we have shown an alternative form of contactor on the indexing head. In this View, the gear 27 corresponding to -gear 27 in FIG. 2 is made of conducting material, andinstead of having a succession of contact pins P as in FIG. 2, it carries a single brush, 27a. Alongside the gear 27 there is a lixed arm or plate 31 in the location of part 31 of FIG. 2, but in this case it has a circular series of equally spaced contacts 32 thereon arranged to be engaged in succession by the brush 27a as the gear 27 rotates. A wire 33' corresponding to wires 33"f FIG. 2 leads from each contact 32' while a brush 30 connected to wire 46 is the counterpart of brush 30 in FIG. 2, in that a circuit may be completed through brush 3G to ,gear 27 to brush `27a and from this brush through a contact 32 on fixed support 31 to Wire 33'. Except -for the rotating multiple contact switch construction, the circuits for FIG. 5 would be the same as above described.

It will be understood that while we have shown one embodiment of our invention, various changes and modiiications may be made in the construction and arrangement of partsrwithin the contemplation of ourl invention.

We claim:

l. An indexing apparatus comprising an indexing gear, a pawl `mechanism movable between two positions engaging the indexing gear in one direction of movement only to rotate the gear incrementally, a uid motor including a reciprocating piston and a rod, the red extending beyond the meter and connected to the pawl mechanism for imparting rectilinear motionk thereto, a fluid slide valve having a reciprocating slide element therein, armatures connected to the slide element for movement therewith and extending beyond the valve at opposite ends of the slide element,pconduits how-connecting the fluid slide valve with the motor for introducing fluid from the Valve to operate the motor piston selectively from one pesitionto another whereby the motor piston rod is reciprocatecl, solenoid coils connected in parallel and coupled magnetically te each of the armatures, a source of current connected to each of the solenoid coils, a switch connected in series lwith each of the solenoid coils and the source of current, beth switches being normally open and positioned for tripping alternately by travel of the pawl mechanism such that the coils are energized alternately to move the slide element'of the valve `for controlled movement of the motor piston by dluid ported from the valve selectively onrboth sides of the piston, a relay with a contacter connected in series between the current source and the switches and with a coil for operating the coni taeter to close the circuit from the source to the switches in Vone kposition and te open the circuit in another position, a manually adjustable switch with `a plurality of contacts and a contacter selectively movable to any one of the contacts, :a rotary switch with a contacter operatively connected te the indexing gear for rotation and includingT a plurality of contacts corresponding to the contacts ofthe selector switch, the corresponding contacts Vof the rotary switch and the selector switch beingA electrically connected, the electrical source being connected serially to both the contacter of the selector switch and the'centactor of the rotary switch whereby a closed circuit is 4formed joining the source to the selector switch contacter and eneof its contacts to a corresponding centact of the rotary switch and its contacter back to the source, and the relay coil being in series connection with the source and the selector switch contacter wherebythe coil is energized when corresponding contacts of the selector switch and the rotary switch are contacted by the `contactors of such switches te move the relay contacter te the other position to open the circuit from the source to the switches connected to the solenoid coils for stepping the action of the valve and motor and the rotation of the indexing gear. l

2. An indexing apparatus as defined in claim 1 includ- Vinga1 suppent movable from a iirst position to a vsecondV position; the rndexinggear being mounted for rotation on S switch being open when the support is moved to the irst position whereat the indexing gear and the gear die are disengaged.

3. An indexing apparatus as in claim 1 wherein the s rotary switch contacts are pins in radially spaced arrangement on a wheel and a series of brushes are lixed in the path oftravel of thepins with one brush positioned for wiping contact with each pin, each of the brushes being electrically connected to a contact `of the selector switch,

and the source of current being connectedto each et the dicating circuit including an indicating device is cennected to the relaygcontactor when it is moved vrte the other position, the contacter electrically connecting the indicating circuit with the source of current when the relay is in such other position which is effected when the relay coil is energized by completion of a circuit from the source through a selector contact and corresponding contact of the rotary switch.

5. An indexing Vapparatus as in claim 1 wher-ein a further rotary switch is provided with a contacter mechanically connected to the 'rotary switch for movement in unison therewith and having a series yof contacts corresponding in number fte those yof the rotary switch and similarly contacted by its contacter, the source of current being connected to the further switch contacter, and indi* eating means serially connected between the contacts'of the further rotary switch and source of curnent for visual display of the particular one `of the further rotary switch contacts made by its contacter which is indicative of the particular one of the contacts of the rotary switch made by its contacter.

References Cited in the iile of this patent UNITED STATES PATENTS 1,637,606 Deurent Aug. 2, 1927 2,085,442 Newell June 29, 1937 '2,192,251 Y Whittaker Mar. 5, 1940 2,305,326 :Swallow Dec. 15, 1942 2,346,238 Schmidt et al. Apr. 11, 1944 2,350,454 Goebel Iune`6, 1944 2,398,178 Ellison lApr. 9, 1946 f 2,630,181 Solum Mar. 3, 1953 2,665,589 Rusher Ian. 12, 1954 2,848,677 Stockwell Aug. 19, 1958 2,880,652 Welte Apr. 7, 1959 2,901,615 Deven Dorf Aug. 25, 1959 2,905,029 Gustafson Sept. 22, 1959 2,926,535 Heselwood' Mar. 1, 1960

Claims (1)

1. AN INDEXING APPARATUS COMPRISING AN INDEXING GEAR, A PAWL MECHANISM MOVABLE BETWEEN TWO POSITIONS ENGAGING THE INDEXING GEAR IN ONE DIRECTION OF MOVEMENT ONLY TO ROTATE THE GEAR INCREMENTALLY, A FLUID MOTOR INCLUDING A RECIPROCATING PISTON AND A ROD, THE ROD EXTENDING BEYOND THE MOTOR AND CONNECTED TO THE PAWL MECHANISM FOR IMPARTING RECTILINEAR MOTION THERETO, A FLUID SLIDE VALVE HAVING A RECIPROCATING SLIDE ELEMENT THEREIN, ARMATURES CONNECTED TO THE SLIDE ELEMENT FOR MOVEMENT THEREWITH AND EXTENDING BEYOND THE VALVE AT OPPOSITE ENDS OF THE SLIDE ELEMENT, CONDUITS FLOW-CONNECTING THE FLUID SLIDE VALVE WITH THE MOTOR FOR INTRODUCING FLUID FROM THE VALVE TO OPERATE THE MOTOR PISTON SELECTIVELY FROM ONE POSITION TO ANOTHER WHEREBY THE MOTOR PISTON ROD IS RECIPROCATED, SOLENOID COILS CONNECTED IN PARALLEL AND COUPLED MAGNETICALLY TO EACH OF THE ARMATURES, A SOURCE OF CURRENT CONNECTED TO EACH OF THE SOLENOID COILS, A SWITCH CONNECTED IN SERIES WITH EACH OF THE SOLENOID COILS AND THE SOURCE OF CURRENT, BOTH SWITCHES BEING NORMALLY OPEN AND POSITIONED FOR TRIPPING ALTERNATELY BY TRAVEL OF THE PAWL MECHANISM SUCH THAT THE COILS ARE ENERGIZED ALTERNATELY TO MOVE THE SLIDE ELEMENT OF THE VALVE FOR CONTROLLED MOVEMENT OF THE MOTOR PISTON BY FLUID PORTED FROM THE VALVE SELECTIVELY ON BOTH SIDES OF THE PISTON, A RELAY WITH A CONTACTOR CONNECTED IN SERIES BETWEEN THE CURRENT SOURCE AND THE SWITCHES AND WITH A COIL FOR OPERATING THE CON-

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