US2781136A - Material handling apparatus - Google Patents

Description

b- Z w57 F. J. SE1-1N Erm.

lvmirxsRIAI. HANDLING APPARATUS s Smets-sheet 1 Filed DeC. 27, 1955.

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iNVENToR Feb. E2, 1957 F. J. SE1-1N ETAL QSE MATERIAL HANDLING APPARATUS Filed Deo. 27,'1955 s sheets-sheet 2 Jz/PPA y Feb. 12%, w57

F. J. SEHN Ei' AL MATERIAL HANDLING APPARATUS Filed Dec. 27, 1955 3 Sheets-Sheet INVENTORS' feAA/c/s J 55s/,v

nited States Patent 1 2,781,136 MATERIAL HANDLNG APPARATUS Francis 3. Selm, Detroit, and Maurice M. Clemons, Birmingham, Mich., assignors to Press Automation Systems incorporated, Detroit, Mich., a corporation of Michigan Application December 27, 1955, Serial No. 555,413 7 Claims. (Ci. 214-1) The present invention relates to a material handling apparatus for a press or the like machine, and more particularly to an apparatus for the handling of sheet metal and the like into or out of a press or a similar production machine.

In the interest of efficient and economical handling of materials to and from various production machines, and also for increased employee safety, various types of material handling apparatus have been provided. This is particularly true in the handling of sheet metal to and from a production press or similar machine. The present invention provides an improved material handling apparatus which is adapted for such use.

One of the primary advantages of the present apparatus resides in its adaption lto and convenient mounting upon or adjacent to a press or the like. The entire handling apparatus of the present invention may be readily suspended from a single supporting element, such as a bar or rod, the bar or rod either being positioned upon the press to project therefrom or being positioned adjacent the press.

Another advantage of the material handling apparatus of this invention is that the apparatus is automatically operable through a predetermined cycle to insert or remove material from the production machine. In addition, the device may be manually operated, if such is desired. The control apparatus for the device of this invention is quite simple in its construction and operation, preferably utilizing a pair of pneuma-tic cylinders which are operated in predetermined sequence by the subjection of the pneumatic actuating mechanisms to loads of diterent magnitudes, thus limiting the need for expensive, complicated, and troublesome pneumatic control mechanism. In fact, the apparatus of the present invention requires only a single actuating valve movable to two positions to alternately advance and retract the mechanism, and a very simple electrical control circuit which serves the sole function of actuating the single control valve.

Other advantages of the apparatus of the present invention include the use of fabricated sheet metal parts for the .supporting structure and the frame of the apparatus, and the utilization of a simple double rack and single pinion change-speed drive ,for actuating the apparatus toward and away from the press or other production machine, thus greatly increasing the material handling efficiency and the production speed of the machine.

it is, therefore, an important object of the present invention to provide an improved material handling apparatus for the insertion or removal of sheet metal from a press or similar production machine,

Another important object of the present invention is the provision of a material handling apparatus for a production machine which is suspended from a single supporting element forming a part of or placed in juxtaposition -to the production machine.

Another important object is the provision of an automatically or manually operative material handling apparatus which is provided with a simplified, inexpensive, and trouble-free actuating mechanism.

A further important object is to provide an improved material handling apparatus wherein a pair of fluid pressure cylinders are operated sequentially by virtue of the load imposed upon the cylinder-actuated parts and under the control of a single actuating valve. i

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Still another important object is the provision of an automatically operative material handling apparatus in which a fluid pressure control valve is actuated by an electric circuit including a part actuated by a press or the like and through which a holding circuit fora valve is energized, the holding circuit being interrupted upon the completion of movement of the fluid pressure actuated portion or" the apparatus, thereby actuating the valve to ei`- ect return movement of the apparatus.

it is yet another important object of this invention to provide an improved material handling apparatus wherein a double rack and single pinion change-speed drive is utilized to increase the effective stroke and the operating speed of a lluid pressure cylinder which ysupplies the source of power oir the apparatus.

Another and further important object -to the present invention will become apparent from a study of the drawings which are described in detail hereinafter and from the appended claims.

As shown in the drawings:

Fig. l is a side elevation of a material handling apparatos of the present invention particularly adapted for the retraction of nished parts from a press or the like;

Fig. 2 is a fragmentary View similar to Fig. 1 illustrating the workpiece-engaging portions of the apparatus in an adjusted position; Y

Fig. 3 is an enlarged end elevational View of the apparatus shown in Fig. l;

Fig. 4 is a diagrammatic View of a typical control circuit utilizable for either manual or automatic control of the apparatus;

Fig. 5 is a schematic representation of the pneumatic actuating mechanism controlled by the circuit of Fig. 5;

Fig. 6 is an enlarged sectional View, with parts Shown in elevation, taken along the planes 6 6 of Fig. l;

Fig. 7 is an enlarged sectional view, with parts shown in elevation, taken along the planes 7-7 of Fig. l; and

Figs. 8, 9 and l0 are schematic views illustrating different modes of adapting the apparatus to press.

On the drawings:

in Fig. l, reference numeral 15 referred generally to a material handling apparatus of the present invention.

The apparatus 15 includes a longitudinally extending sheet metal main frame indicated generally at 16 and comprising a vertically extending side plate 17 joining upper and lower laterally extending legs 18 and 19 terminating -in vertically extending flanges 20 and 21, respectively. The upper lateral leg 18 is secured, as bywelding at 22, to a centrally located, upstanding attachment block 23 which is generally rectangular in shape and which has a cylindrical aperture 242V adapted to receive therethrough a iixed mounting element 25 (Fig. 3). The block 23 forms a split clamp Vand a plurality of clamping screws 27 are utilized to secure the block 23 upon the mounting element 25 in secure assembly. The mounting block 2.3 is preferably located at the center of gravity of the assembly 15 (when the assembly is in the position shown in Fig. l) and this, together with the clamping screws Z7, retain the mounting frame 16 aga-inst tilting movement.

Secured to the under surface of `the leg 18 to depend therefrom are a plurality of longitudinally spaced hangers 2S which are centrally apertured to receive therethrough a fixed slide shaft 3d (Figs. l, 6 and 7). This shaft 30 support a longitudinally movable frame element indicated generally at 3l and of the. same general shape as the xed frame 15. M ore particularly, the movable frame 31 includes a side plate 32, upper and lower laterally extendling legs 33 and 34 respectively, and terminal vertically extending lianges 35 and 36. The upper surface of the leg 33`carries a slide block 37 apertured, as at 38, to tre- 3 ceive therethrough a bearing bushingj39 surrounding the slid-e shaft 30. Y

VIt will besappreciated that provision of thebearing 39 and the block 37, in combination with the shaft Sii, makes possible longitudinal relative sliding movement between the fixed frame i6 and the sliding yframe 31. This relative longitudinal movement is guidedby an elongated guide block dii'depending from' the Vlower lateral leg 19 of the frame element 16 and contacted Vby a pair of rollers 41 carried Ybythe lower leg 34 of the sliding'v frame 31 and laterally spaced to receive the guide block di? therebetween. The rollers 4l are secured to the sliding,V frame necessarily cause'longitudinal displacement of the pinion 76. This pinion '76, being meshed with the ixed rack 77,

Y will' be forced to rotate, and rotation ofthe pinion will effect a Vcorresponding longitudinal displacement of the upper rack 3 which is movable with the slide frmel relativeY to the fixed frame 16, such movement of the slide frame'being guided bythe shaft 3i) and the gui/de block i Because ofthe pinion and rack arrangement, the

.371 by support blocks 42' underlying Ythe sliding frame andseeured theretorby suitable means, as by nuts 43..

Y YThe rollers 4l, in combination with the guide block 4G,

not onlyV guide the frame for longitudinal movement, but

prevent relative oscillating movement between the fixed frame 16 and the sliding frame 31 about the shaft 30.

The lower leg 34 of -thelsliding frame 3l has secured thereto, as Yby screws 44, an additional mounting block Y' Y45 which is'provided with a central rectangular opening 46 through which a return cut-o5 cam 4.7 projects. This cam 47 also projects between the roller mounting blocks 42, as best shown in Figsg and6. The return cut-off cam 47 is provided at one end with a cam face 48 for a purpose to be hereinafter more fully described, and a set screw VV49,VV manually operable through a handle 49a, is carried by the blocl; 45 to accommodate longitudinal adjustrnent of the cut-oh cam 47 for a purpose Vto be herein'- after more fully described, Q ilu advance of the block 45, the lower leg 34 of the movable frame element 31 has secured thereto, as by welding,

afsupport block Sxedly attached, by nuts and bolts Si. Y

Y Yor the like, toa second depending support block 32 (i3-lgs.

land 3). The second support'block 52 is provided with Ya xed'depending ange 53 which is attached, as by'a screw 54, to a' shaft block 55 having an aperture 56 through which extends an additional slide'shaft 57.

The fixed slide shaft 57 isrsur'rounded by a tubular supporting collar 58V movable :along the shaft 'toward an end stop-59, the' slide collar 58 carrying l'with it a'lower forwardly'projecting, gripper frame 69 having pivoted thereto, as by pivot 61, a vertically movable gripping arm 62, which terminates at its rear end in an upstanding cam projection 63 Vand having at its Yforward end Va gripper Y Y iinger 64 which is'cooperable with a dependingtixed grip-V Y per'projection 65 (Figs. l and 2) for grasping a sheet" 'i I metal/press part therebetween. The slide shaft vstop 59 is Y provided with a depending' stop portion 66 which is coi operable withjthe rear "carni projection 63 on Vthe gripper arm 62 to move the gripping finger upwardly toward and intogclosely'spaced relationship Vto the gripperV proiectionV 65 when the element 60 is moved Yforwardiy with the slide SSon the shaft/57. The forward or finger end of themarrn 1 6 2 is heavier than the rear or cam lendk63 so that the arm i'sover-balancedV to its neutraler non-actuated 'released A laterally projectie Vstop position illustrated in Fig. 1. pin 67 is carried by the plate 6- to prevent undesired pivoting movement ofthe arm'beyond its released position. Y

To efect relative Vlongitudinal movement4 between the mounting frame Mend/the slide frame 3i, a fluid pressure from the lower-leg 19 of the fixed frarne i6, fas upon a' A V,bracket 71" andY a pivot`pin 72. The cylinder Vactuating rod'73 *(Fig., 6) Ais provided witha'rt'erminal Yclcvis 74 (Fig.

i Q 1)Vcarryi'ng'an axle pin'75 'upon which is disposed a pinion 76. l Y .A Y

'Y Thispinion 76, as best shown'in TEig. 3, meshes with a4V Vfirst yor iixed rack '77( carried byY the lower legi? of the fixedfrarne 16, andV simultaneously meshes withV an upperY movable rack 'which is carried by the upper leg 33 of I upper rack 78, and the movable frame 3l w'ilibe displaced through la distance equal to twice the displacement'VV lt will be of the cylinder piston and actuating rod 73'. appreciated that this gear speed increase will effect rapid 'longitudinal displacement of the Vmovable framel and those' parts attached thereto and will increase the electiv stroke of tbe actuating rod 73. Y Y

A second actuating cylinder 80 is provided to actuate Y' the gripping mechanism.V This cylinder 80 is supported in ixed position upon the slide shaft 57 through a mounting block Si, andthe actuating rod 32 of the cylinder Sii is connected to the gripper block 6% by suitable means, as by pin .$53. Gbviously, actuation of the cylinder 80 will ex#V tend the actuating rod 82 thereof to project the gripping element 69 forwardly to its position illustrated in Fig. '2V

of the drawings, wherein thecam portion 63 of the gripper 62 will abut the stop 66, and the linger 64 will be moved upwardly into itsgripping position for cooperation with the iixed gripping projection 65.

Fluid pressure for actuating the cylinders 7d and lit)V is provided through a pair of conduits 85 and S6(Fig. 3) whichcomrnunicate with a conduit box S7 disposed upon the upper leg i3 of the xed frame 16, and from the con-` duitV box S7 through conduits 88 and 39 to a second conduit box 96 mounted upon the upstanding leg 32 of the movable frame 3i through a protective shield 93..' A sec,-

ond shield 92 is carried by the upper leg 18ct the iixedV frame i6. kFrom the second conduit box 9d, conduits 93 andf: lead to the cylinder Si).

The supply of actuating fluid to the cylinders 76 and is best illustrated in the greatly simplified schematic sketch of Fig. 5, wherein it is seen that fluid is supplied from an air supply 95'through a pressure Vline 96 anda regulator valve 9S to a control'valve 1th?, actuatedV as iereinafter explained and effective to introduce iuid under A ressure to ,the opposite ends of the cylinders 7i) and Sil Vthrough a pair of uid transmission lines 85 and S6. The

lines 35 and S6 branch, as at 85a and 35h, and arand 36b,tosupply fluid to the cylinders 701 Yand Su. Each or" 'Y the cylinders and Si) is the double ,acting type, and iluid ,Y introduced through the branch conduitsa' and 85h will serve to YactuateV theactuating rods 73;'ar1dV 82 vof Vthecylinders in one direction, while fluid introduced throughthe branchV lines S6fzand 36h 'will serve to energize the cylinactuated cylinder, preferablynpneurnatic, indicated gener.- K allyj'at70 is utilized. One end of the cylinder is supportedV tion as illustrated in Fig-l. Y

' Y lf the valve 109 Werenow actuated'to interconnect the line 96 and the line 36, lluid will be; introduced simultaneouslyrinto the conduits 86a-andr86bfto subject both of lthe cylinders '70 andV 89 to uid pressure.

ders 7d and Sd. so 'as to move'tne actuating rods 73 and,

32, respectively, thereof, in the opposite direction.Y

. When thepneumatic system is in the condition lolf Fig, 5, and thepistons occupy'their relative positions as shown Y therein,'the machin-e is zat rest, both of the actuating rods v are retracted, the movable frame 3l isnt its furthest left Aposition'at whichVV it is telescoped within the fixed frame Vi6, and the 'actuating rod 82 is ,telescoped Withinits cylinder S9 Vso that the gripping arm 62 is in its released posi-V V However, due to the resistance of the much heavier movable frame to i movement, and because Vof the gear'rsp'eedadvantage of the slide frame 3.1L vIt will be appreciated thatV actuation ofthe cylinder70 will yrnoye the actuating rod 73 Ythereof f Y longitudinally ofjiae ered name 16.' ,such meyemenr win 2,781,1asj

nger into cooperative relation with the gripper stop 65. This movement completes the cycle of operation of the cylinder 80, and continued movement of the actuating rod will be impossible.

The resultant increased pressure within the cylinder 70 will cause actuation of the actuating rod 73 toward the right, that is to extend the actuating rod and the pinion 76 toward the right, causing actuation of the slidable frame 73 toward the right or from its telescoped position, thus retracting the movable frame and the gripping finger carried thereby from the press or other production machine. The workpiece, thus will be drawn from the press toward the right. When the actuating rod 73 approaches its furthest extended position, the condition of the valve 100 is reversed connecting the pressure line 96 to conduit 85 and consequently to conduits 85a and 85h. The first result will be that the cylinder 80 will receive fluid under pressure at its lefthand end, retracting the actuating rod 82 into the cylinder to move the gripping tinger toward the right away from the stop 66, the overbalanced gripping arm will necessarily release the workpiece. Upon the completion of movement of the actuating rod S2, pressure will build up in the line 55:1 and will actuate the actuating rod 73 in a leftward direction, thus returning the slide frame 31 to its retracted position illustrated in Fig. l. The machine thus returns to its inactive position of Fig. l and the cycle of operation has been completed.

The means for actuating the valve 100 to cause this cycle of operation are schematically illustrated in the wiring diagram of Fig. 4, wherein current of the desired voltage and from a convenient source enters the circuit through lead lines 101 and 102. A manual olf-0n switch 103 is provided in the lead line 100 and branch leads 104 and 105 connect the lead line 101 to the opposite sides of a dual action selector switch 106. When the switch 106 is in its auto position, indicating automatic operation, the switch connects the line 105 to a line 107 which leads to a press switch S which is closed, to the position shown in Fig. 4, whenever the press operation has ceased and the press is open. When the press is operating, or in its closed position, the switch 108 is open.

From the switch 108, a line 109 leads to a normally closed limit switch 110 which is connected through a circuit relay 111 to the other lead line 102. The circuit relay 111 is effective to operate contacts 112 connected to the lead line 101 through conductor 113 and through the coil windings 114 of a solenoid having a coil 115, to the other lead line 102. The solenoid core 115 actuates the valve 100, when the windings 114 are energized, and

the solenoid core 115 moves the valve 100 to its position to interconnect the iluid lines $6 and S6, as hereinbefore described. When the solenoid windings 114 are deenergized, the valve 100 is moved to its position preferably under spring load to interconnect the pressure line 96 and the iuid flow line 85. Thus, when the circuit of Fig. 4V is set for automatic operation, as illustrated in Fig. 4, and the press is open so as to close the switch 108, the solenoid windings 114 will be energized, the valve 100 will Ybe moved to its position to actuate the apparatus to retract a workpiece from the press.

Further, it will be noted that the relay 111 and the contacts 112 in elect form a holding circuit to retain the solenoid energized even though the switch 10S may be opened by the return of the press to its actuated or closed position. This holding circuit is completed from the lead line 101 through a conductor 117 and additional relay contacts 116 which, through a conductor 118, by-passes the press switch 108 to retain current ow through the relay 111 and the limit switch 110. However, upon opening of the limit switch 110, the relay 111 is deenergized, the contacts 112 will be opened, the solenoid windings 114 will be de-energized and the solenoid core 115 will return to position valve 100 in such a manner as to interconnect the lines 96 and 85.

This limit switch 110 is carried by the fixed frame 16 and is indicated generally at in Fig. 1. The limit switch 110 has an actuating arm 110:1 which is adapted to be abutted by the return cut-oli cam 48 when the carriage or movable frame member 31 approaches its fully extended position. The opening of the switch 110 will de-energize the solenoid windings 114 as hereinbefore described, and the press material handling apparatus will be Vreturned to its position in Fig. 1, as hereinbefore described.

For manual operation, the switch 106 is merely actuated to close the circuit between branch line 104, and conductor 120 which passes through a push-button switch 121 and a conductor 122 to the limit switch 110 and the relay 111 as hereinbefore described. Thus, the manual operation merely by-passes the press switch 108, and the same cycle will be performed as hereinbefore described, with the exception that the cycle will be manually initiated.

It will thus be appreciated that the present invention provides a new and novel material handling apparatus for a press or a similar production machine. Although the specific embodiment of the invention illustrated in the drawings shows an apparatus for removing workpieces from a press, it would be appreciated that the same principles may be applied and the same structure utilized for the feeding of parts to a press or similar machine.

The extreme simplicity of the control mechanism for the device of the present invention will be readily evident. The utilization of a simple hydraulic control valve, and the extremely simple control circuit which is provided for the control of this valve result in an inexpensive, extremely simple, practically foolproof construction.

The advantages of suspending the entire apparatus from a single overhead support will be readily appreciated by those skilled in the art, and these advantages are specically illustrated in Figs. 8, 9, and l0. In Fig. 8, the device is suspended independently of a press P by supporting the support element 25 upon a pair of uprights or stanchions 125 displaced to either side of a conveyor C and, if desired, forming a part of the conveyor supporting structure. In Fig. 9, the device is illustrated as being supported upon an arm 126 extending laterally from the press P and carrying the support member 25 in such manner as to dispose the device 15 over the conveyor belt C. In Fig. 10, the device 15 is supported upon an overhead arm 127 depending from an upward portion of the press P and eiective to dispose the device over the conveyor belt C. In each of the Figs. 8-10, inclusive, the device is shown schematically with the gripping mechanism extending into the press in position to retract a workpiece therefrom. Retraction of the gripping mechanism and the release thereof will deposit the workpiece upon the conveyor belt C for removal from the press location.

Another important advantage resides in the use of the stamped slides 16 and 31. The relatively light slidesV reduce the inertia factor so that there is no substantial inertia load imposed upon the pneumatic actuating system either in starting or stopping relative movment at either end of the stroke. This low inertia factor will be particularly appreciated by those skilled in the art and familiar with the grave inertia problems involved in the actuation and use of the prior art devices using massive and heavy cast or fabricated structural elements.

While a preferred embodiment ot' my invention has been disclosed and described above in detail, it will be understood that numerous modicationsmight be resorted to without departing from the scope of my invention as defined in the following claims.

We claim:

l. A handling apparatus for sheet material or the like comprising a xed frame, a movable frame carried by said ixed frame for relative translatory movement, a carrier frame carried by said movable frame for relative translatory movement and having means for engaging a'workpiece, change-speed gearing means interconnecting said', fixed Yframe and said movable frame, first uid pres- Vsure operated actuating means for energizing saidV gearing means to effect relative movement between said movable rame and said'fixed frame, second iiuid pressure operated actuating means for effecting relative movement between said carrier frame and said movable frame, and

actuatingl meansfor effecting relative teiescopic movement of said elements in either direction, work piece engaging; meansV guided by one of said elements for reciprocatory mcvementrrelative thereto, second actuating means for effecting relative movement of said engaging means and saidrone element, and control means for said actuating means including a control valve and valve operating means responsive to relative movement of Vsaid eie-v rnents inY one direction to move the valve soY that the dieringeiiective loads on Vthe actuating means will cause j actuation ofsaid second actuating means and then of said Y Vtrol means for sequentially operating said first and second actuating means, said rst actuating means being subjected to -an effective working load substantially greater than that to Vwhich the second actuating means is Ybecause of the presence of said overspeed gearing,V whereby upon Ythesubjection or both actuating means to the same pressure, the second actuating means'initially moves the gripping means toward the press and the first actuating means then relatively retracts the elements from the press.

4, A handling apparatus for sheet material or the like comprising a fixed frame, a movable frame carried by said fixed frame for relative translatory movement, a carrier frame'carried by said movable franefor relative transla- Ytoryrnovement and having/means for engaging -a work piece,ioverspeed gearing'interco'nnectinU said fixed trameY and said movable frame, iirst fluid pressure operated actu` working plane of the press, and reciprocation of said'engaging means withrrespect to said` other element effecting selective engagement and release of a Work piece by said means, and separately energizable actuating means for eiecting movement of said other of said elements and said engagingmeans respectively, said actuating meansrmcluding an overspeed 'gear set having a reaction member on said one element, anl output member Yon said other ele- Vment, ,and an input member interposed between the reaction member and the output member vfor engagement.

' Y therewith, iirst duid pressure means for operatingsa'id input member, second fiuid pressure means for reciprocating said Vengaging means, and a control valve for vent- 4ing pressure Viiuid to said iirst and second iluid pressure means,Y said second iiuid pressureV means being iirst actu'- ated dueto the interposing of said overspeed gear'set between said first iiuid pressure means and said other element.

`6. A handlingapparatus for sheet material or the likev comprising a fixed frame, a movable frame carried by the.

tory movement and, having means'for engaging a work piece, overspeed gearing including a reaction gear on said iixed frame, an output gear on said movable frame, and an input gear interposed between the reaction and the output gears, first fluid pressure operated actuating means for energizingl said input gear to effect relative Vmovement between Said movable frame and said xed frame VatV arnechanical disadvantage because of said overspeed gearing, second fluid pressure operated actuating means for effecti ing relative movement between said carrier frame and sai-d movable frame, and control means for said iirst and second actuating means including Ya source of fluid pressure and a valve interposed between the source and both of said actuating means, said second actuating means being first actuated due to said overspeed gearing to eiiect relative movement between the carrier frame and the movable frames, and the iirst actuating means being actuated only after the relative carrier frame and movable frame movementis complete. ,Y Y K 7. YAn apparatus for; handling a workpiece for` a press or the like comprising a pair of relatively telescopically movable elements, Work piece engaging means guided by oneV of Ysaid elements/for relativeV translatory movement, first telescopic pistonV and cylinder means, an Yoverdrive gear set actuated by the firstpistonsand,cylinder means and including an output gear on one of said elements, a

V ,reactionV gear Von Vthe other element, and an input gear ating means for energizing -said gearing means to etie'ct j relative movement between said movable trame and saidYA fixed irar'nerat the mechanical disadvantage ofsai-dV over?V Y speed gearing,V second uid pressure operated actuating means for'efiecting reia'tive movement between said carrier frame and said movable frame, 'and a control valve for simultaneously introducing fiud from a source of iiuid .pressure into both of said actuating means, saidV second actuating means being iirst actuated because of'the'lighter V Y rocable with respect to the one element and the press in Y a planeV substantially parallelsto the working plane of Ythe press, workV piece engaging means carried byrsaid otherV *Y creto and i for movement therewith in substantialiythe working, plane element ferire iprocatory'movement relative t ofthe press, reciproca-.tion ot'sai-d engaging'meansV with i Y saidptlier element bodily displacingV a work piece in the I driven by saidV iirst piston and cylinder means, a second teiescopic pistonV and cylinder' meansV connected between Y said one element andsaidlengaging means', and control,

Ymeans Vincluding `a control valve movable to a pair of positions and interposed between a source'ofluid'pressure and both of said piston Yandcylindervmeans,V and valvek movable only after completion of movement ofthe 'sec-V Y ond piston and cylinder'means when the valveisfmoved Y to either of its positions;

References Citedlin the nleof'this patentY l Y,

v UNITED STATES PATENTS'.

Y394,42) 'W'llman Y Di.Y 111J 1888 412,85l Kennedy et al. 'OC. Yl5, 15879Vv Y479,883 VStainesY Y 1892*V VSGP/,(118 Y Keily A Y y 1905 f 1,550,997V Lacke Aug.'25, 1925 x 2,324,817 Blaley 'Y y v k1943 s 2,609,775 saam 'sept;9, 19522 2,725,154 Hendricks .Nev. 29, v1;"55

Sahlin Y Y sept. is, `Y1956' s

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