US2225006A - Sheet feeding - Google Patents

Description

Dec. A17, 1940.

M. S. GUDGER ET AL 4 SHEET FEEDING 5 Sheets--Sheet l Filed June 29, `19159 @Mcrm Dec. 17, 1940. M s, G'UDGER ETAL. 2,225,006

SHEET FEEDING 5 sheets-sheet 2 Illl lllllHHIIIIIIIIIIIIIIIIIIII Filed June 29, 1939 abbot/mm3 Dec. 17, 1940. 2,225,006

M. S. GUDGER ETAL SHEET FEEDING y Filed June 29, 1939 5 Sheets-Sheet 3 l lll/11,1111

Dec. 17, 1940. M,v GUDGER ETAL 2,225,006

SHEET FEED'ING Filed June 29, 1939 5 Sheets-Sheet 4 Dec. 17, 1940.

M. S. GUDGER E l'AL SHEET FEEDING Filed Jim@ 2e, 1959 5 sheets-sheet 5 2mm M @www APatented Dec. 17, 1940 A e UNITED srAf'rEs PATENT OFFICE Q f Morris S.4 Gudger, New York, N. Y., and Frederick W. Seybold, Elizabeth, N. J., assignors to Amcrican Type Founders, Inc., Elizabeth, N. J., a corporation of New Jersey Application June 29,'1939, Serial No. 281,989 l 16 Claims. (Cl. 271-27) This invention relates to sheet feeding 'and' venting the feeding of multiple sheets, or sheets more particularly to methods and apparatus for of greater thickness than those for which the separating and forwarding sheets of ymetal or machine is set; and certain embodiments of these other stiil material to various types of processing features form the subject matter of the copend- 5 machines, such as, for example, slittersishears.VN ing applications, Serial No. 278,942, filed June 13, punch presses, printing orlithographing presses, A1939, by M. SGudger, and Serial No. 281,990,

or the like. filed June 29, 1939, jointly by M. S. Gudger and The general object of the invention is topro- F. W. Seybold. i vide a novel and improved process and machine Otherobjects and features of noveltywill be l0 for emciently separating sheets-more especially apparent `from the following speciiication when i0 metal sheets-from a pile as received from the read ini connection with the accompanying drawmill on from prior processing operations, `and forings, in which one embodimentl of my invention warding them in timed relation with the operis illustrated by Way of example. ation of the machine to which they are to'be fed 1 In the drawings: l for further treatment. 'f Figure 1 is a view in rearelevation of a ma.- l5

Another object of the invention is to provide chine embodying the principles of the invention; a machine of the class described which is generportions lthereof being broken away and other ally automatic in operation, and equipped to reportions being shown in vertical section for the lieve the operator of the necessity of performing Sake of clearness of illustration; a number of manual operations. Figure 2 is an enlarged view in vertical longg A further object is to provide la device of this gitudinal section of the upper part of the device description which is conveniently arranged, comshown in Figure 1; pact in construction, and which utilizes a mini- Figure 3 is a fragmentary vertical longitudinal mum amount of floor space. sectional view of a portion of Figure f2, showing In its preferred embodiment, the invention one of the forwarding elements in sheet deliv- 25 contemplates the provision of a main supporting ering position; Y frame which houses most of the operating mech- Figure 4 is a view in vertical section of one of anism and serves also to supportthe pile carrying the suction slippers; platforms from which the sheets are fed. Means Figure 5 is a view in side elevation of the cenare provided within the confines of the frame trai plate of the rotary valve mechanism for con- :lov

for successively separating the top sheets from trolling the actuation of the grippers; the pile at their rear edges,'liitlng and moving l Figure 6 is a transverse sectional view taken them forwardly by engagement therewith .at on line 6-7-6 of Figure 5; and also showing other points adjacent their front edges. and finally portions of the valve assembly; transferring them to the machine. The efilcient Figure 'l is a sectional view of the inner sta- 35 separation of theA sheets is especially important tionary valve plate taken Orl 1iI1e1+1 cf Figure 5; in handling metallic sheets, such as tin plate or Figures 8 and 9 are elevational views of the the like, dueto the presence of oil or other adtwo rotary valve bodies forming parts of the valve hesive materials which may have lremained' on assembly illustrated in'Figures 5 and 6; both ng- 40 the sheets after previous coating .or processing ures representing the valve bodies as seen fromo operations, or due to rough or bent edges on the the left in Figure 6. sheets themselves. Figures 10 to 13 inclusive are somewhat dia- The separating and forwarding functions are grammatic views in side. elevation of the sucperformed by novel pneumatic gripping devices, tion STDDBIS ShOWing Ithem in the Successive comprising telescoping elements which are adaptpositions Which they occupy during the feeding 45 ed to be extended and retracted by means of the cycle; and same source of vacuum that is used to activate Figure 14 dS a diagram 0n Which are charted the suction cups on the lower ends of these dethe relative positions and'conditions of the sucvices. Novel timed valve 4mechanism is provided tio'n grippers and their control valves, throughfor actuating thegppers in the proper sequence out the cycle of operation of the machine.` 50 to effect the separating and feeding processes. As most clearly shown in Figure 1 of the draw- The sheet feeder illustrated and described ings, the novel sheet feeding machine comprises herein may also be provided with novel manually a supporting frame which includes the preferand automatically controlled pile elevating mechd ably unitary upper casting I0 and the four supanism, and novel detector-caliper devices for preporting legs I I of substantially channel shape. f

' bers 36.

` The feeding mechanism proper is conveniently disposed within the confines of the frame casting I0, and the piles of sheets are raised to a point within the range of operation of the feeders by means of pile elevating mechanism which includes Athe cross frames |2 which support the platforms I4 upon which the sheets S are disposed. The transversely extending fr-ames I2 are preferably arranged in pairs and are each provided with hooks I5 which are adapted to engage lugs I6 carried by the four sets of endless chains I8 which are guided around the sprockets I9 supported upon suitable bearing shafts, the lower ones 20 of which extend between adjacent legsy upon either side of the machine, and the upper ones 22 are provided with bearings in the frame casting I0. 'I'he upper chain shafts are provided intermediate their lengths with Worm wheels 23 which are adapted to be driven by the worms 24 carried upon 'the elevator drive shaft 25 which may either be manually rotated by means of the wheel 26 or driven by the motor 21 through the gearing generally indicated by the reference numeral 30. Feeler mechanism for gauging the height' of the pile and `controlling the pipe ele- Vator is indicated generally at 3|. These features will not be described in detail in 'the present specication since they form no essential part lof the' present invention, -and are more fully disclosed in the oopending application Serial No. 281,990.

The sheets from the pile S are forwarded to the feed roll 32 and its cooperating drop roll 33 from whence they are transferred by' suitable conveying means to the processing machine being fed. The separating of the top sheets T from the pile S and the forwarding of these sheets successively to the rolls 32 and 33 is accomplishedrby means of the front suction gripper members 35 and the rear suction gripper mem- The rearwardly disposed grippers are not movable during operation of the 'feeder in a forward and rearward direction, but are conned to an approximately vertical movement for separating the top sheet from the remainder of the pile. These grippers are supported upon the transverse rod 38, each end of which is adjustably secured at selected points along the side bars 39 as by means of the clamps 40, the side bars 39 being secured to the frame |0 as at 4|.

The rear suction separating grippers 36 are adjustably supported at selected points along the transverse rod 38 by means of the brackets 42. It will thus be seen that the rear grippers may be positioned at desired points adjacent the side and rear edges of the piles of sheets of various dimensions. I

During the separation, the rear corners of the top sheet are bent or curved upwardly and inwardly and also slightly upwardly and forwardly, in order to facilitate the separation of the top sheet from the underlying ones. For vthis purpose, the rear suction grippers 36 are pivotally adjustable with respect to the brackets 42 in a transverse plane about the pins 43 and the grippers may be tightened in adjusted positions appropriate tothe size, thickness and material of the sheets, by means of the nuts 4 4. 'I'he brackets 42 are also adjustable angularly in a longitudinal plane about the transverse shaft 38 and may be clamped in the desired positions by means of the nuts 44'.

The forward suction gripper members 35 are mounted by means of the brackets 45 upon,the oscillating shaft 46. These brackets 45 may be .and rear gripper members.

`cams 50 and 5| carried upon the cam shaft 52.

The cams 50 and 5| are so shaped that they will oscillate the shaft 48 to effect the swinging of the grippers 35 through a feeding cycle which will be described in detail hereinafter.

The operation of the feeding grippers and also of other parts of the machine, including the normal upward feed of the pile of sheets toward the grippers, may be eiected in synchronism with the processing machine or other device to which the sheets` are ultimately fed. A shaft 55 is mounted in bearings at one side of the upper frame casting I0 and through the bevel gears 56 is made to drive the transverse shaft 51, Ithis shaft having a sprocket 58 secured upon its outer end. v An endless chain 59 connects the sprocket 58 lwith a sprocket 60 on the shaft 6| of the feed roll 32. Another sprocket 62 on this same shaft is connected by means of the chain 63 with a sprocket 64 carried by the cam shaft 52. All of this gearing is conveniently disposed upon the outside of the frame I0 and may be of course covered by a suitable guard for safety purposes.

Each of the suction gripper membersv comprises a cylinder 15 within which is adapted to reciprocate a piston 16. The piston is hollow and is fitted around the tubular rod 11 upon the lower end of which is attached a suction cup element 18 as by means of the collar 19. The piston 16 is rigidly secured to the rod 11 between the nut 80 and the `shoulder 8|. The rod 11 passes through the tubular boss 82 formed at the lower end of the cylinder. The upper end of the cylinder is closed by means of a screw cap or head 85, and communication with the upper and lower endsv of the cylinder upon either side of the piston 16 is obtained by means of the nipples l the cycle of operation of the feeder is accomv plished by the introduction of varying pneumatic pressures into the cylinder upon the respective sides of the piston reciprocating therein.

' For developing the pneumatic power for operating the grippers, there` is provided the pump 95 which is connected by means of the sprocket gearing 96 to the transmission 30 driven by the electric motor 21. The vacuum pump 95 is connected with the vacuum tank |00 by means of the piping .|'0I and a flexible tube |02 connects this vacuum system with the rotary valve mem-` ber |05 which is supported from the underside of the upper portion of the frame casting |0 as at |06. Sections of flexible tubing |01 connect the casing of the valve assembly I 05 with the rear suction grippers 36 and the tubing |08 connects the forward ,grippers 35 with the valve l member. v

Before the details of construction of the rotary valve |05 are set forth, it will be well to describe the'cycles of operation of the forward In this connection,

particular reference is made to Figures 2,3, 4,

transverse and longitudinal directions. For purposes of comparison of the timing of the operation of the various elements, the diagram in Figure 14 has been prepared; the point at which the front or swinging grippers start their forward movement having been adopted as the zero point of the 360 cycles of movement shown upon the charts. From 0 to 120 the front grippers fare being swung from their rearward position to their extreme forward position as shown in Figure 10 of the drawings. During this portion of the cycle the rear grippers 30 are idle, and from 0 to 110 the atmosphere ports of the lower chamber of the stationary grippers 30 are open. Between 110 and 120, and while the top sheet T is still moving under control of the forward cylinders 35, but now out of range of the separating cylinders 30, the atmosphere port of the lower chambers of these latter grippers closes. Immediately following the closing of the atmosphere port the vacuum port opens, thereby effecting the lowering of the suction cup 10 of these grippers to the next underlying sheet of the pile, as indicated in broken lines in Figure 11 of the drawings. From 130 to 140, and while the vacuum is effective in the lower chamber, the vacuum line to the upper chamber of the rear grlppers opens while the atmosphere port is still closed (as indicated in chart IV), thus effecting the pneumatic seal of the suction head 'I0 against the sheet. By this time the previous sheet has passed between the feed rolls 32 and 33 and the forward grippers are dwelling at their forward limit of movement. At 140 the vacuum port for the lower chamber of the stationary grippers starts to close, and after it has closed at 150. the atmosphere port opens gradually, as indicated by the curved portion a of the atmosphere valve line. The resulting unbalance of pressure above and below the piston retracts the gripper and moves the rear end of the sheet upwardly, slowly at first, and then more rapidly so that the acceleration is maintained at a point below that at which the suction seal with the sheet would be liable to break. During this lifting movement to the position shown in full lines in Figure 1l, when the grippers 30 are inclined' as in the preferred operation, the sheet is buckled somewhat as indicated by the dotted line b in Figure 1, this serving to more effectively separate the top sheet from the underlying ones. Suitable blast or winding devices may be provided for blowing air beneath the top sheet to aid in the separation and forwarding operations.

When the sheet is seized between the drop rolls 33 and the feed rolls 32. the atmosphere port of the upper chamber of the forward moving grippers opens, as shown at 130, in chart 1I, releasing the sheet from the suckers. The moving grippers remain in their forward position from 120 to 160 due to the appropriate shaping of the cams 00 and 0| which control the swinging of these members. These grippers move rearwardly from 160 to 280, and during moet of this time the rear end of the sheet has been held by the vacuum existing in the upper chamber of the stationary grippers. mosphere port of the lower chamber of the moving grippers closes and the vacuum port opens,

end a sprocket' |20 At 300 the atas shown in chart III. causing the piston to move downwardly until the suction cup contacts the forward portion of the top sheet T, as shown in dotted lines in Figure 13 'of the drawings. At this time the vacuum port opens to the top chamb er and then at 340 the atmosphere port of the lower chamber opens and the forward grippers retract and lift the forward end of the sheet as shown in Figure 13. Then at 320 the atmosphere port of the upper chamber of the rear separating grippers 30l opens (see chart IV) and the rear end of the sheet is released. This occurs between the positions illustratedin Figures 13 and 10 of the drawings. From 340 to 360 the front end of the sheet is rising to the position shown in Figure. 13, ready to lbe forwarded to the feed rollers as in Figure 10.

The rotary valve member |00 is illustrated in detail in Figures to 9, inclusive, of the drawings and comprises the stationary central plate ||0 to which the end casing plates and ||2 are secured adjacent their margins. Bearing sleeves ||3 are provided centrally of these plates for the valve operating shaft opening at one end of the valve assembly is sealed by the coverl |0 which is secured by means of the bolts l|1. The shaft is packed at the other end of the valve housing as by means of the annular plate or gland ||0 secured by means of the bolts'lll. The shaft passes freely through the central opening |20 lin the plate ||0 and the space |20 is placed in communication with the supply of lubricant by means of the tube |2I and the bore |22. Keyed to the shaft ||0 as at |23 and |20 are the rotary valve elements |20 and |20 which fit snugly against the opposite faces of thev central plate ||0 for rotation with respect thereto. The valve actuating shaft ||0 is supported at its end remote from the valve casing in the bracket |20 and carries which is driven'by means of the chain |30 from the sprocket |3| on the end of the cam shaft 02.

The stationary plate ||0 of the valve assembly is provided with annular grooves |35 and |30 in its opposite faces and both of these grooves are connected by the transverse bore |30 with the radial passageway |30 which leads into the hollow internally threaded boss |00 which is adapted to be connected by means ofthe tube |02 with the vacuum tank |00. By this means both of the grooves or channels |30 and |30 are Ill. The bearing upon its outer in continuous communication with thesource of Y vacuum. A radial passageway |02 provides communication between the short transverse passageway |03 which opens into lthe left-hand face of the plate I|0, as viewed in'Flgure 6, and the internally threaded boss |00 which communicates through one of the tubes |00 with the upper chambers of the forward gripper cylinders. The lower end of the chambers of the front cylinders are connected to the hollow boss |01, which is in communication with the opening |00 in the same face of the plate ||0 but further from the center thereof than the openingv |03. The lower chambers of the rear gripper cylinders are similarly connected through the hollow threaded boss |00 with the opening |00 in the left-hand face of the plate ||0 outwardly of the groove |30. The upper ends of the rear cylinders are placed in communication through certain of the tubes |01 with by means of the radial passageway |03 with the short transverse passage |00 which opens upon the left-hand face of the plate ||0, as viewed in Figure 6, at a point inwardly of the groove |35.

, and at the samevdistance from the center as the opening |43 in the opposite'i'ace of the plate.

In Figure-8 ofthe drawings, there is illustrated the rotary valve member |26 as seen from theleft in Figure 6. This member is arranged to rotate in the direction of the arrow and during this rotation the vacuum cavity |60 which has a relatively narrow portion |6| which continually.

overlies the vacuum groove |36, and a wider extension |62 which is intermittently brought into registry with the opening |43 leading to the upper end of the front cylinders. 'Ihe cavity portion |62 has a shallower'extension |63 for the purpose of somewhat restricting the vacuum during a certain portion of the time. Another vacuum cavity |65 is provided in the rotary member |26 and this cavityhas a narrow portion |66 continually in communication with the groove Y |36 and a somewhat wider portion |61 which is regularly brought into communication with the opening |46 as clearly shown in Figure 6 of the drawings. It will be notedthat the rotary valve disc or plate |26 is of a generally smaller diameter than the interior chamber of thevalve and is provided with an extension |16 which tapers off at one side as at |-1| to nally merge with the main circular Iperiphery of the plate. This extension is adapted to cover the opening |48 leading to the lower end of the front cylinders at certain times to prevent communication with the atmosphere, with which the interiors of the chambers are continually in communication by means of the openings |13 and |14 in the respective cover plates and |I2. When these openings |46 are not covered by the extensions |10 of the member |26, the lower ends o1 the front cylinders are in communication with the atmosphere, or may be subjected to a slight super-atmospheric pressure in' certain cases. The

tapered portion |1| of the extension |10 provides for a gradual' admission of atmospheric pressure to these connections. An opening |15 is drilled through the plate |16 in order to admit atmospheric pressure to the opening |43 leading to the upper end of the front cylinders at the proper point during the cycle.

- The rotary valve' plate |25 shown inFigure 9 of the drawings is adapted to move in the direction of the arrow and is illustrated in this iigureasseeniromtheleitinllgure. This plate is provided with a vacuum cavity |11 having a smaller extension |16 in communication with the vacuum groove |35 and' a longer extension |60 which is adapted to register with the opening |54 leading to the upper end or o provided for admitting atmospheric pressure at the proper/time to the opening |54 of the upper end offthe rear cylinders.

It will thus be seen that these rotary valve members are so designed that the respective vacuum and atmospheric pressurecavities and openings'are in registry with the corresponding ducts communicating with the upper and 'which extends through the member |92 and' is spring connected with the hand lever |64 piv-v oted to the bracket |95.

spring |96 to open the valve. A

It is understood vthat various changes and alterations may be made in the embodiments illustrated and described herein without departing from the scope of the invention as dened in the following claims. Y f.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In a sheet ieeder'of the class described', a suction gripper comprising, in combination, a cylinder, a piston adapted to reciprocate within said cylinder, said piston dividing -the interior` of said cylinder into upper and'lower chambers, a rod secured to and extending from the piston through one end of said cylinder, a suction cup on the outer end of said rod, said rod and piston being provided with a bore communicating with the upper cylinder chamber, and separate means for individually placing the .upper and lower chambers of said cylinder in communication with sources of vacuum and pressure, the evacuating of the upper chamber serving both to effeet the gripping of the sheet and then the lifting of the rod and attached sheet when the cup is sealed.

2. Ina sheet feeder of the class described, a suction gripper comprising, in combination, a cylinder, a piston adapted to reciprocate within said cylinder, said piston dividing the interior -of said cylinder into upper and lower chambers,

a rod secured to and extending from the piston through one en'd o! said cylinder, a suction cup on the outer end of said rod, said rod and piston being provided with a boze communicating with the upper cylinder chamber, and openings communicating respectively with the upper and lower chambers of said cylinder, a .source of vacuum, conduits connecting said source Iof vacuum with said openings, valve means disposed in said conduits for individually' controlling the communication oi' said openings with said source ot vacuum, and means for intermittently actuating said valve means during the operation of the feeder.

3. In a sheet feeder=of the class described, a suction gripper comprising, in combination, a cylinder. a piston adapted to reciprocate within said cylinder, said piston dividing the interior of said cylinder into upper and lower chambers. a rod secured to and extending i'rom'the Apiston .through one end of said cylinder, a suc,

tion cup on the outer end oi' said rod, said rod and piston being provided with a bore communieating with the uppery -cylinderchamber, and openings in said `upper and lower chambers of the cylinder for communication with sources ot iluid pressure or vacuum.' a tension spring con- The hand lever is moved tothe right against the pressure of the l zoA necting the upper end o! said cylinder with the reciprocating piston and rod assembly and tending to urge the latter upwardly witloiin the cyl inder.

4. In a. sheet ieederof the class described, a

suction gripper comprising, in combination,v a cylinder, a piston adapted to reciprocate within said cylinder, said piston dividing theinteriorof said cylinderinto upper and lower chambers, a rod secured to and extending fronr` the .piston through one end of .said cylinder, a suction cup on the outer end of said rod, said rod and piston being providedy with a bore communicating with the upper cylinder chamber, and openings in said upper and lower chambers of the cylinder for,y communication with sources of fluid pressure or vacuum, a tension coil spring connected atits upper end with the upperhead of said cylinder,

, a rod secured to and`extending from the piston through one end of'saidcylinder, a suction vcup on the outer end of said rod, said-rod and piston being provided with a bore communicating with the upper cylinder chamber, a tension coil spring connected at its upper end with the upper head of the cylinder, extending through said bore and secured at its -lower `,end to the rod at a point adjacent said suction cup, and separate means for individually placing the openings in the upper and lower chambers of said cylinder in communication with sources of vacuum and pressure.

6. In a sheet feeder of the class described, in`

combination, pivoted suction grippers for seizing the forward portion of a sheet, lifting and forwarding the sheet from a pile, a source of vacuum, a rotary multiple valve assembly for intermittently placing said grippers in communication with said source of vacuum, a rotary lshaft upon which the rotary valve member is secured,

a cam shaft, a cam on said shaft for oscillating.

said suction grippers, a sprocket chain between said cam shaftv and said valve shaft, whereby said valve is'operated in synchrcnism with the operation of said grippers, additional grippers for seizing and lifting the rear portions of said sheets, and means for placing said last named grippers in communication with said valve for synchronous operation. u

'1. In a sheet feeding device of the class described, a rotary valve assembly for controlling the intermittent communication of fluid fpres sure to the suction grippers, said assembly comprising a central substantially cylindrical plate,

a pair of hollow casings secured to each lateral face of each plate to. provide valve chambers adjacent thereto, an annular groove formed in each face of said plate, radial passageways in said plate, certain of said passageways communicating with said grooves and others opening through the faces of said plate at points spaced from said grooves, valve plates disposed within said chamber for Vrotation in contact with saidl lateral faces, a shaft upon which said valve plates are secured, means for rotating said shaft, said valve plates being provided with recesses adapted to place certain of said openings in said central plate in communication with said respective grooves, and means formed on said plates for gradually placing certain of said openings in communication with said chambers. y

8. A sheet feeding device of the class' described comprising a front suction gripper and a rear prising a cylinder, a piston adapted to reciprocate therein and to divide said cylinder into upper and lower chambers, a rod connected to said piston and extending through one end of said cylinder and having a suction cup secured to the projecting end thereof, a source of vacuum, a rotary valve assembly for controlling the intermittent communication of vacuum and atmos- 1 pheric air to the respective chambers of the suctibn grippers, said valve assembly comprising a central substantially cylindrical plate, a pair of casings secured to each lateral face of said plate to provide valve chambers vadjacent thereto, an annular groove in each of said faces, a .radial passageway in said central plate communicating l with said source of vacuum and with both of said grooves, other radial passageways in said central plate communicating respectively with the upper and lower ends of said front and rear sucltion gripper cylinders, the passageways which communicate with the forward grippers opening at radially spaced points on one of said lateral faces and the passageways'which communicate with said rear grippers opening at radially spaced points on the other of said faces, rotary valve plates disposed within said valve chambers for rotation in contact with the respective lateral faces of said central plate, said valve plates being provided with recesses adapted to intermittentl`y and sequentially place said openings in communication with said grooves, whereby the upper and lower chambers of said forward and rear grippers are placed in communication with the source of vacuum in the proper sequence to effect the vintermittent extension and retraction of said gripper elements. l A

9. Asheet feeding device of the class described comprising a front suction gripper and a rear suction gripper adapted to perform' sequential separating and feeding operations upon successive sheets of a pile, each of the grippers comprising a cylinder, a piston adapted to reciprocate therein and to divide said cylinder into upper and lower chambers, a rod connected to said piston and extending through one end of said cylinder andhavlng a suction cup secured .to the project-f ing end thereof, a source of vacuum, a rotary valve assembly for controlling the intermittent communication of vacuum and atmospheric air to the respective chambers of the suction grip-- per cylinders, the .passageways which communicate withV the forward grippers opening at radially spaced points -on one of said lateral faces `and the passageways which communicate with said rear grippers opening at radially spaced points on the other of said faces, rotary valve plates disposed within said valve chambers for rotation in .contact with the respective lateral faces of said central plate, said valve plates being provided with recesses adapted to intermittently and sequentially place said openings in communication with said grooves,v whereby the upper and lower chambers of said forward and rear grippers are placed in communication with the source of vacuum in the proper sequence to effect the intermittent extension and retraction of said gripper elements, openings in said rotary plates for effecting communication between said first named openings and the interior of said valve chambers, and means for placing said chambers in communication with a source of pressure.

10. In a sheet feeding device of the class described, a rotary valve assembly for controlling I the intermittent communication of fluid pressure to the suction grippers, said assembly comprising a plate having a smooth face, a casing secured to said plate to provide a valve chamber adjacent said face, passageways in said plate opening through said face, a valve plate disposed within said chamber for rotation in contact with said face, a shaft upon which said valve plate is secured, means for rotating said shaft, said valve plate being provided with recesses adapted to place certain of said openings in communication with each other, and an opening vin said valve plate communicating with the atmosphere.

11. In a sheet feeding device of the class described, a rotary valve assembly'for controlling the intermittent communication of fluid pressure to the suction grippers, said assembly comprising a plate having a smooth face, a casing secured to said plate to provide a valve chamber adjacent .said face, passageways in said plate opening 'through said face, a valve plate disposed within said chamber for rotation in contact with said face, means for rotating said valve plate, said valve plate being provided with recesses adapted to place certain of said openings in communication with' each other, and a cut-away portion on the rim of said rotary plate for intermittently placing certain of said openings in communication with said chamber.

12. In a sheet feeding device of the class described, a rotary valve assembly for controlling the intermittent communication of uid pressure to the suction grippers, said assembly comprising a plate having a smooth face, a casing secured to said plate to provide a valve chamber adjacent said face, passageways in said plate opening through said face, means for placing certain of said passageways in communication with a source of vacuum and others with said suction grippers, a valve plate disposed within said chamber for rotation in contact with said face, means for rotating said valve plate, said valve plate being provided With recesses adapted to place certain of said openings in communication with each other, a spirally tapered cut-away portion on the rim of said rotary plate for gradually placing certain of said openings in communication with the interior of said chamber during each revolution of said valve plate, and an opening in said casing communicating with a source of pressure.

13. In a sheet feeder of the class described, in combination, suction grippersfor separating and forwarding the sheets from a pile, a vacuum pump and a vacuum tank communicating therewith, conduits connecting said vacuum tank with said grippers and intermittently operated valves in said conduits, and a manually operable relief valve in said tank.

14. In a sheet feeder of the class described, in combination, suction grippers for separating and forwarding the sheets from a pile, a vacuum pump and a vacuum tank communicating therewith, conduits connecting said vacuum tank with said grippers and intermittently operated valves in said conduits, a spring pressed inwardly Opening relief valve in the wall of said tank, and a hand lever for operating said valve against the pressure of said spring. Y

15. In a sheet feeder of the class described, a suction gripper comprising, in combination, a cylinder, a piston adapted to reciprocate within said cylinder, said piston dividing the interior of said cylinder into upper and lower chambers, a rod secured to and extending from the piston through one end of said cylinder, a suction cup on the outer end of said rod, said rod and piston being provided with a bore communicating with the upper cylinder chamber, spring means biasing said piston, said rod, and its attached cup toward their upward positions, and separate means for individually placing the openings in the upper and lower chambers of said cylinder in communication with sources of vacuum and pressure.

16. A sheet feeding device of the class described comprising a front suction gripper and a rear suction gripper adapted to perform sequential separating and feeding operations uponsuccessive sheets of a pile, each of the grippers comprising a cylinder, a piston adapted to reciprocate therein and to divide said cylinder into upper and lower chambers, a rod connected to said piston and extending through one end of said cylinder Aand having a suction cup secured to the projecting end thereof, a source of vacuum, means for giving said front gripper a sheet feeding and return movement, control means for individually and sequentially placing the lower chambers of the gripper cylinders in communication with i said source of vacuum to move the grippers downwardly toward a` sheet, and placing said upper chambers and the suction cups in communication with said source of vacuum for gripping and immediately raising said cups and attached sheets

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