US3542360A

US3542360A - Sheet-feeding apparatus

Info

Publication number: US3542360A
Application number: US727770A
Authority: US
Inventors: Carl M Carey
Original assignee: Harris Intertype Corp
Current assignee: Harris Graphics Corp
Priority date: 1968-05-09
Filing date: 1968-05-09
Publication date: 1970-11-24
Anticipated expiration: 1987-11-24
Also published as: FR1593932A; JPS4831325B1; DE1923625B2; DE1923625A1; DE1923625C3; GB1210989A

Description

United States Patent [54] SHEET-FEEDING APPARATUS 17 Claims, 6 Drawing Figs.

[52] 0.8. CI. 271/54, 271/58 [51] Int. Cl B65h 5/04 [50] Field ofSearch 271/54. 14,

Primary ExaminerRichard E. Aegerter Attorney-Yount, Flynn & Tarolli ABSTRACT: The present sheet feeding apparatus has transfer belts for rapidly transferring a sheet onto the press cylinder after the sheet has been registered against front stops in the feeding apparatus and while the sheet is held on the belts by vacuum. Each transfer belt has a sheet-engaging portion which extends between rear and front idler rolls, and the bell extends down around these idler rolls for attachment ofits opposite ends to a rotatable drive pulley at a single location. The transfer belt is wrapped around the drive pulley for substantially less than 360, and the transfer of a sheet onto the press cylinder is effected by turning the drive pulley through substantially less than 360.

Patented Nov.'24,1970 3,542,360

AIR i DRMS'CAM 1 3/05 au/oe! MOVEMENT! l VACUUM 1 INVENTOR. CARL M. CAREY Pa tented Nov. 24, 1970 Sheet .4 TTOR/VEYS Patented Nov. 24, 1970 Shet 3 of '5 INVENTOR. CARL M. CARL-Y 1' r My? (ac/M ATTO/PNIFYS Patented Nov. 24, 1970 I 3,542,360

Sheet L of 5 I N VENTOR.

CARL M CAREY Patented Nov. 24, 1970

sheet

6 or 5 INVENTOR. CARL M. CARE Y TTORNEYS' 1 SHEET-FEEDING APPARATUS This invention relates to-a sheet feeding apparatus having an improved transfer mechanism fortransferring the sheet to a sheet handling machine, such as a rotary printing press, after the sheet has been registered against front stops in the feeding apparatus.

In US. Pat. No. 3,309,078 to E. D. Nash, there is disclosed and claimed a sheet feeding apparatus for-use with a rotary sheet-fed printing press. In that apparatus the sheets are advanced successively in underlapped relationship by a conveyor against front stops, which register the leading edge of the lead sheet, after which the front stops are retracted and the lead sheet is rapidly transferred by transfer belts onto the press cylinder while the conveyor continues to advance the following sheets. The sheet being transferred is held against the transfer belts by vacuum. The transfer belts in that upparatus are driven by it drive arrangement which, while effective for its intended purpose, is somewhat complex and expensive.

The present invention is directed to a transfer mechanism in a sheet-feeding apparatus which is simpler and less expensive than that of the aforementioned patent, which facilitates the installation and the continuing proper operation of the transfer belts, and which provides more room for other operating parts of the sheet-feeding apparatus.

Accordingly, it is a principal object of this invention to provide a sheet-feeding apparatus having a novel and improved transfer mechanism of greater simplicity for transferring the sheets successively into a sheet-handling machine, such as a rotary sheet-fed printing press.

Another object of this invention is to provide a sheet-feeding apparatus having a novel transfer mechanism therein which enables the transfer belts to be more readily installed with the desired initial. tightness settings and to retain these tightness settings more effectively.

Another object of this invention is to provide a sheet-feeding apparatus having a novel transfer mechanism therein which requires fewer parts and fewer manufacturing tolerances, which iseasier to install, which is more reliable in operation, and which takes up less space at critical areas in the apparatus than the transfer mechanisms used previously in similar sheet-feeding apparatus.

Further objects and advantages of this inventionwill be apparent from the following description of two presentlypreferred embodiments, which are illustrated in the accompanying drawings in which:

FIG. 1 is a top perspective view, with parts broken away for clarity, showing a sheet-feeding apparatus having a first embodiment of the present transfer mechanism therein;

FIG. 2 is an enlarged fragmentary view, partly in side elevation and partly in section, showing this first embodiment of the present transfer mechanism just before it transfers the lead sheet onto the cylinder of a printing press;

FIG. 3 is a view similar to FIG. 2 and showing the position of the parts after the sheet has been partially transferred onto the press cylinder;

FIG. 4 is a side elevational view of the drive mechanism for the drive pulley in the transfer mechanism of FIGS. 1-3;

FIG. 5 is a timing chart showing the timing of certain operations in the sheet-feeding apparatus of FIG 1; and

FIG. 6 is a view similar to FIG. 2 and showing a second embodiment of the present transfer mechanism in the sheet-feeding apparatus.

Referring to FIG. 1, the sheet-feeding apparatus in which the present invention is embodied includes a conveyor of known design for advancing sheets of paper or the like individually in succession from a stack or pile 10. The conveyor includes a plurality of laterally-spaced endless feed tapes 11, here shown as six in number, which advance the sheets from left to right in FIG. 1. The sheets are picked up individually from the pile 10 by conventional suckers (not shown) and transferred onto the feed tapes l1 beneath overlying pull-in wheels 12. The feed tapes 11 are continuously driven across a tape table 13, which is inclined downward to the right at a slight angle. The sheets are held down against the feed tapes 11 by a plurality of rollers 14, which bear down on the sheets with sufficient force tomaintain each sheet in frictional engagement with the feed tapes. Preferably, the sheets are underlapped, with the trailing end of a preceding sheet overlying the leading end of the immediately following sheet as they are advanced by this conveyor.

The feed tapes 11 discharge the successive sheets onto a register plate 15 which extends downward to the right from the front ends of the feed tapes at the same angle of inclination as the tape table 13. A plurality of laterally-spaced front stops are provided for engaging and registering the leading edge of each sheet as it passes over the register plate 15 and before it transferred onto the cylinder E6 of the printing press by the transfer mechanism ofthe present invention.

As shown in FIG. I. each of these front stops is constituted by 0 depending lip 17 on the lower end of a respective lever arm 18, which is clamped to a rocker shaft 19 extending laterally across the register plate 15 at a location above the latter. In the particular embodiment shown there are six such front stops at different positions laterally across the register plate 15, although itwill be understood that a greater or smaller number may be provided, as desired.

At one point in each cycle of operation of this sheet-feeding apparatus, shaft 19 is turned counterclockwise in FIG. 1 to lift the front stops 17 up out of the path of movement of the oncoming sheet. At another point in each cycle of operation, shaft 19 is turned clockwise to lower the stops down into the path of the oncoming sheet.

The register plate 15 .has openings 20 for receiving the respective front stops 17 when the respective lever arms 18 are in their lowered positions, as shown in FIGS. 1 and 2. In these positions, the front stops are in the path of the front or leading edge of the sheet S which is moving across the register plate 15 from left to right. The front stops 17 are in precise alinement with each other laterally across the register plate 15 so that, when engaged by the leading edge of the oncoming sheet, they aline this edge in precise parallelism with the axis of rotation of the press cylinder 16 onto which the sheet is to be fed.

When shaft 19 is turned to raise the lever arms l8 (FIG. 3), the front stops 17 move up out of the path of the sheet which had just been registered'against these front stops, permitting this sheet to be transferred onto the press cylinder by the transfer mechanism of the present invention, to be described.

The sheet-feeding equipment also includes a side register mechanism 21 (FIG. 1) of known design. This side register mechanism operates automatically to position each sheet at the correct position laterally before it is transferred onto the press cylinder 16. This side registration of the sheet takes place after its leading edge has been front registered by the front stops 17.

A plurality of laterally-spaced retaining fingers 22, only two of which appear in FIG. 1, overlie the sheet as it passes over the register plate 15. These retaining fingers are attached to a rocker shaft 23 extending laterally above .the tape table 13. This rocker shaft is turnedat predetermined times during each cycle of operation to raise and lower the retaining fingers 22, as explained hereinafter.

The press cylinder 16 is rotatable at the front end of the register plate 15 of the sheet-feeding apparatus. This cylinder carries a plurality of gage pins or stop pins 24 for engagement by the leading edge of the sheet which is then being trans ferred onto the cylinder 16. These stop pins 24 are in precise alinement with each other across the cylinder 16 along a line extending parallel to the cylinders rotational axis and parallel to the front stops 17.

The press cylinder 16 also has a plurality of grippers 25 of known design which are all mounted on a cross-shape 26 carried by the cylinder.

Just before the advancing sheet moves against the front stops 17, it passes over a plurality of transfer belts 27 in the present transfer mechanism. These belts are located at respective laterally-spaced, rectangular openings 28 in the register plate 15. Each of the transfer belts 27 hasits opposite ends secured to a respective rotatable drive pulley 29, which is turned back and forth in opposite directions in timed relationship with the advance of each sheet againstthe front stops l7 and with the rotation of the press cylinder 16, as explained hereinafter.

Each transfer belt 27 passes up from one side of the drive pulley 29 over a rear guide in the form of an idler roller 30, which is located near the rear edge of the respective opening 28 in the register plate 15. From this rear idler roller 30 the transfer belt passes across the opening 28 in the register plate to a front guide in the form of an idler roller 31, which is located near the front edge of the opening 28. The transfer belt passes down around this front idler roller 31 and over the opposite side of the drive pulley 29 to its point of attachment to the drive pulley.

Between its rear guide roller 30 and the front guide roller 31 each transfer belt 27 passes over a respective vacuum table 32, which is located at the respective opening 28 in the register plate 15. As shown in FIGS. 2 and 3, this vacuum table has a recess 33 at the top across which the respective transfer belt 27 passes. This recess 33 in each vacuum table is com nected through a timing valve 34 alternately to a pressurized air source or to vacuum. The portion of the transfer belt 27 which passes over this recess 33 has a plurality of openings which enable either the air pressure or the vacuum in recess 33 to be applied to the underside of a sheet S which then overlies this portion ofthe belt.

Valve 34 has a stator and a cooperating rotor which provides passages for connecting the vacuum table recess 33 to a pressurized source or to vacuum, depending upon the rotational position of the rotor. The valve rotor is driven from the press drive in timed relationship with the rotation of the press cylinder 16 and in timed relationship with the operation of the sheet-feeding apparatus.

FIG. 2 shows the position of the drive pulley 29 and the transfer belt 27 just after the sheet S has moved into registration with the front stops 17 and hasbeen side registered by the side registration mechanism 21. The drive pulley 29 is in its extreme counterclockwise position at this time. Shortly before the stop pins 24 on the press cylinder 16 have moved up past the front edge of the register plate 15, shaft 23 is turned to force the retaining fingers 22 which it carries down against the sheet S to press it down against the transfer belt 27. Then the timing valve 34 applies a vacuum to the vacuum table recess 33, causing the sheet S to be held against the transfer belt by vacuum.

Following this, shaft 23 is turned counterclockwise in FIG. 1 to retract the retaining lingers 22 upwardly away from the sheet, so as to provide an appreciable clearance for the sheet. Next, the front stops 17 are retracted upward away from the leading edge of the sheet, and then the drive pulley 29 is rapidly turned clockwise from the FIG. 2 position to the FIG. 3 position by a drive mechanism to be described. This forward rotation of the drive pulleys causes the transfer belts 27 to move from left to right between the

guide rollers

30 and 31, carrying with them the sheet S because of the vacuum which is continued to be applied to the underside of the sheet through the openings in the transfer belts.

This forward movement of the transfer belts 27 is at a velocity substantially greater than the speed at which the drive tapes 11 are advancing the following sheets onto the register plate 15 and greater than the peripheral velocity of the press cylinder 16. Consequently the sheet S which is advanced by the belts 27 has its leading edge forced into engagement with the stop pins 24 on the rotating press cylinder 16, after which the grippers grip it securely against the press cylinder in the usual manner. The stop pins 24 register the leading edge of the transferred sheet on the press cylinder. As shown in FIG. 3, the retaining fingers 22 are retracted far enough up away from this sheet to avoid marking the sheet if it bows upwardly after its leading edge first engages the stop pins 24 on the press cylinder 16 and while its trailing end continues to be advanced by the belts 27 'at a speed greater than the peripheral velocity of the press cylinder.

After the grippers 25 on the press cylinder 16 have gripped the sheet, the timing valve 34 now connects the recesses 33 in the vacuum tables 32 to a pressurized air source and at the same time it disconnects the vacuum, so that the trailing end of the sheet S is released from the transfer belts 27.

After the trailing edge of this sheet has moved past the front stops 17, the rocker shaft 19 is turned clockwise in FIG. 1 to lower the front stops 17 into the respective openings 20 in the register plate 15, so as to be positioned for engagement by the leading edge of the next sheet 8-1 in the series which is being moved forward continuously by the feed tapes 51. At the same time, the shaft 23 is turned clockwise in FIG. l to lower the retaining fingers 22 to a sheet-guiding intermediate position for retaining the oncoming sheet 5-1 on the register plate 15 without, however, exerting any significant pressure on this sheet as long as it engages the register plate.

While the oncoming sheet 8-1 is moving across the register plate 15 and over the transfer belts 27 at the openings 28 in the register plate, air pressure is applied to each vacuum table recess 33 to provide athin film of air for keeping the underside of the sheet separated from the corresponding transfer belt 27. At this time, the transfer belts are being retracted from right to left between the front guide roller 3?. and the rear guide roller 30 by the rotation of the drive pulleys 29 counterclockwise from the FIG. 3 position. The drive pulleys reach their extreme counterclockwise position, shown in FIG. 2, before the leading edge of the oncoming sheet S-l. has reached the front stops 17.

Significant practical advantages accrue from the use of the single drive pulley 29 for each transfer belts 27 in the present transfer mechanism. As shown in FIGS. 2 and 3, the opposite ends of the transfer belt are attached to the drive pulley at the same circumferential location thereon. The drive pulley has a longitudinal groove or recess 35, which extends along its complete axial length, as shown in FIG. 1. The drive pulley has several longitudinally-spaced screw-threaded openings 36 which extend radially inward from the groove 35 for receiving the screw-threaded shank of a respective clamping bolt 37. The end of this shank is received in a corresponding key 38 in the shaft 39 to which the drive pulley 29 is attached.

The opposite ends of the transfer belt 27 extend into this pulley groove 35 from opposite sides, and these ends of the belt are superimposed over one another as indicated at 27a and 27b in FIG. 2. These overlapped belt ends have openings for passing the shanks of the bolts 37. A plurality of shims 40 are engaged between these belt ends and the bottom of the pulley groove 35. A clamping plate 41 extends along the complete axial length of the groove 35, as shown in FIG. 1, directly overlying the overlapped belt ends 27a, 27b and beneath the heads on the bolts 37.

With this arrangement, the clamping bolts 37 clamp both ends of the transfer belt 27 to the drive pulley 2.9 at the same circumferential location on the latter (where the groove 35 is located). These bolts 37 also perform the function of releasably attaching the pulley 29 to its shaft 39. The tension on the transfer belt 27 may be readily adjusted by inserting more or fewer shims 40 in the groove 35. Preferably, the clamping bolts 37, clamping plate 41 and shims 40 are all of metal for a more reliable clamping action to prevent a change in the belt tension over a period of operation of the transfer mechanism.

The length of the belt wraparound on the drive pulley (i.e., the belt length around the pulley between its two points of tangency to the opposite sides of the pulley) is greater than the distance of the belt movement required to advance the sheet from the position where its leading edge is at the front stops 17 to the position where it is clamped to the press cylinder. In the embodiment shown in FIGS. 2 and 3, this complete forward stroke of the transfer belt 27 requires a rotation of its drive pulley 29 through only about l50 from the FIG. 2 position, in

which the point of attachment of both ends of the belt is below the point of tangency of the front side of the belt to the pulley, to the FIG. 3 position, in which this point of attachment is below the point of tangency of the back side of the belt to the pulley. Consequently, in all operating positions of the drive pulley, whether at rest in either extreme position or in motion between these positions, the transfer belt has enough wraparound on the pulley between the clamp 37, 41 and either point of tangency that the belt tightness is maintained and proper tracking of the belt on the pulley is assured.

Preferably, the diameter of the drive pulley 29 is greater than the distance between the spacing between the rear and

front guide rollers

30 and 31, as shown in FIGS. 2 and 3.

FIG. 4 illustrates the cam-operated drive mechanism for turning the pulley shaft 39 back and forth to advance and retract the transfer belts 27, as described. Pulley shaft 39 carries a gear 42 which is driving by a larger gear 43 mounted on a shaft 44 extending parallel to the drive pulley shaft 39. Shaft 44 also carries a smaller gear 45 which meshes with an arcuate rack 46 on the upper end of an upwardly-extending leg 47 ofa bellcrank lever L. This lever is pivotally supported on a pivot 48 at its lower end, and it has another leg 49 which carries a cam follower roller 50 on its free end. The leg 47 of the lever carries a cam follower roller 51 about midway between the lever pivot 48 and the arcuate rack 46.

Roller 50 is engaged by a first drive cam 52 attached to a rotary shaft 53, which is driven in timed relationship with the rotation of the press cylinder 16 and with the remainder of the sheet-feeding apparatus. Roller 51 is engaged by a second drive cam 54, which is also attached to shaft 53.

In the operation of this drive mechanism, as the shaft 53 rotates clockwise in FIG. 4, the rise on its first cam 52 will engage the roller 50 to pivot the bellcrank lever clockwise to impart a clockwise rotation to the drive pulley 29 through rack 46, gear 45, shaft 44, gear 43, gear 42 and the pulley shaft 39. This will cause the drive pulley to turn from the FIG. 2 position to the FIG. 3 position to advance the transfer belt through its sheet-transferring forward stroke.

Continued clockwise rotation of the shaft 53 moves the rise on its second cam 54 across the roller 51 to return the bellcrank lever L counterclockwise, so as to cause the drive pulley 29 to return from the FIG. 3 position to the FIG. 2 position, thereby retracting the transfer belt 27 to its starting position preparatory to receiving the next sheet in the series.

This simplified drive mechanism for the transfer belts is made possible by the use of a single drive pulley for each belt, to which both ends of the belt are fastened, as described. Also, the location of the drive pulleys 29 down away from the register plate 15 leaves more room there for the side register device 21.

Referring to FIG. ,5, the timing of the different operations of this sheet-feeding apparatus takes place as follows, with reference to the rotation of the press cylinder 16, whose 0 position is where the stop pins 24 are alined with the register plate 15.

The front stops 17 begin to move down at about 200 and they are in their sheet-registering position at about 240. The leading edge of the lead sheet reaches the front stops at about 250.

The side register device 21 accomplishes the side registration ofthe sheet during the interval from about 280 to 330.

The retraction of the front stops begins at 320 and is completed at 330.

The vacuum is applied to the transfer belts 27 at 320, and the transfer belts begin their forward stroke at 330, at which time the first cam 52 in the FIG. 4 drive mechanism begins to rock the bellcrank lever L clockwise.

This forward stroke of the transfer belts 27 continues until about 30", but the release of the vacuum on the transfer belts begins at and is completed by to permit the sheet to be readily transferred onto the press cylinder. The air pressure is applied to the vacuum table recesses 33 at the same time that the vacuum is released.

transfer mechanism for use in a sheet-feeding apparatus of the type shown in FIG. 1. The FIG. 6 mechanism has the ad- I vantage of using a smaller drive pulley for a given stroke of the transfer belt.

Corresponding elements of the FIG. 6 mechanism are given the same reference numerals as those of FIG. 1. but with a prime" suffix added, and the detailed description of these ele ments will not be repeated. lt is to be understood that the remainder of the sheet-feeding apparatus in which the FIG, 6 mechanism is embodied may be essentially the same as described with reference to FIG. 1, except as noted hereinafter, and that the drive mechanism for the drive pulley in FIG. 6 may be basically similar to that shown in FIG. 5.

In FIG. 6 the front side of the transfer belt 27' extends down from the front guide roller 31 across a deflection roller which is offset rearwardly. This deflection roller 60 changes the point of tangency which the front side of the belt 27 would otherwise have with the drive pulley 29, thereby increasing the wraparound ofthe belt on the pulley and enabling a smaller diameter pulley and a larger angular rotation of the pulley to be used for a given forward stroke of the transfer belt.

In the embodiment shown, the deflection roller 60 is mounted on a cross-shaft 61 which also supports a series of laterally-spaced, upwardly-extending levers 18 which provide the front stops 17.

If desired, however, the deflection roller 60 may be springbiased to exert a predetermined tension of the transfer belt 27', so that the attachment of the ends of the belt to the drive pulley would be less critical in that respect. Also, it will be understood that a similar deflection roller might be provided at the back side of the transfer belt in place of, or in addition to, the deflection roller 60 shown at the front side of the transfer belt.

While two presently-preferred embodiments of this invention have been described in detail with reference to the accompanying drawings, it is to be understood that various modifications and adaptations which differ from the disclosed embodiments may be adopted without departing from the scope of the present invention, as defined in the appended claims.

Iclaim:

1. In a sheet-feeding apparatus having a conveyor for advancing sheets in succession along a predetermined path toward a cylinder which operates on each of the sheets in turn, front stop means located along said path and movable between a sheet-registering position for engagement by the leading edge of a sheet to thereby front register the sheet relative to said cylinder, and a position retracted away from the path of the sheets, side guide means located adjacent to said path for engaging a side edge of a sheet to thereby side register the sheet relative to said cylinder, and a transfer belt having a sheet-engaging portion thereof which extends along said path behind the sheet-registering position of said front stop means and which is movable forward to advance a sheet beyond said front stop means when the latter is retracted, the improvement whichcomprises:

a drive arrangement for the transfer belt comprising guides for said sheet-engaging portion of the transfer belt, a single rotatable drive pulley for said transfer belt, said transfer belt extending around said guides to respective points of tangency with the opposite sides of said drive pulley and having its opposite ends secured to said drive pulley between said points of tangency, and means for turning said drive pulley back and forth in timed relation with the advance of successive sheets against said front stop means to move the transfer belt forward 7 through a stroke of predetermined length to advance the leading sheet beyond said front stop means when the latter is retracted while maintaining the front and side register of the leading sheet relative to said cylinder and thereafter to return the transfer belt rearwardly for receiving the next sheet, said predetermined stroke length being less than the distance on the drive pulley around which the transfer belt extends between said points of tangency.

2. Apparatus according to claim 1, wherein the transfer belt in all positions thereof from its forward position to its return position has an appreciable wraparound on the drive pulley in both directions from its attachment to the drive pulley to its points oftangency to the opposite sides of the drive pulley.

3. Apparatus according to claim 2, and further comprising means for fastening the opposite ends of the transfer belt to :the drive pulley at the same circumferential location on the latter.

4. Apparatus according to claim 2, wherein said means for turning the drive pulley turns the latter back and forth through an angular rotation of substantially less than 360 in either direction.

5. Apparatus according to claim 4, wherein the transfer belt is wrapped around the drive pulley for a greater length than the length of said sheet-engaging portion of the belt between said rear and front guides.

6. Apparatus according to claim 5, wherein said drive pulley has a diameter greater than the spacing between said guides.

7. In a sheet-feeding apparatus having a conveyor for advancing successive sheets along a predetermined path toward a cylinder which operates on each of the sheets in turn, a register plate for receiving the sheets from the conveyor, front stop means at said register plate movable between a sheetregistering position for engagement by the leading edge of a sheet on said register plate to thereby front register the sheet relative to said cylinder and a retracted position away from said sheet, side guide means located adjacent to one side of said register plate for engaging a side edge of a sheet to thereby side register the sheet relative to said cylinder, said register plate having an opening therein. behind said front stops, a perforated transfer belt having a sheet-engaging portion at said opening in the register plate, and means for selectively applying a vacuum or air pressure through the transfer belt to the underside of the sheet overlying said portion of the transfer belt, the improvement which comprises:

a drive arrangement for the transfer belt comprising spacedapart rear and front guides disposed below the register plate at said opening therein and supporting said sheet-engaging portion of the transfer belt, a single rotatable drive pulley for the transfer belt spaced below the register plate, said transfer belt extending down around said guides to respective points of tangency with the opposite sides of said drive pulley and having its opposite ends secured to said drive pulley between said points of tangency, and means for turning said drive pulley back and forth in timed relation with the advance of succes sive sheets against said front stop means to move the transfer belt forward through a stroke of predetermined length when vacuum is applied to the underside of the sheet which overlies said sheet-engaging portion of the transfer belt to advance said sheet beyond said front stop means when the latter is retracted while maintaining the front and side register ofthe sheet relative to said cylinder and thereafter, while air pressure is applied through the transfer belt, to return the transfer belt rearwardly for receiving the next sheet, said predetermined stroke length being less than the distance on the drive pun t 4 which the transfer belt extends between said points of tangency, each point of tangency of the transfer belt to the drive pulley being substantially above the attachment of the belt to the pulley in all rotational positions of the pulley from the forward to the return positions of the belt, whereby to provide an appreciable wraparound of the belt on both sides of the pulley above its attachment to the pulley.

8. Apparatus according to claim 7. and further Comprising means for fastening the opposite ends of the transfer belt to the drive pulley at the same circumferential location on the latter.

9. Apparatus according to claim 8, wherein said drive pulley has a longitudinal groove therein receiving the opposite ends of the transfer belt in overlapped relationship. a ciarnping bar received in said groove and overlying the overlapped ends of the transfer belt, and bolt means clamping said bar to the drive pulley.

10. Apparatus according to claim 9, and further comprising shim means in said groove for determining the tension of the transfer belt.

11. Apparatus according to claim 9, and further comprising a rotatable shaft supporting said drive pulley, and wherein said bolt means also fastens said drive pulley to said shaft.

12. Apparatus according to claim 8, wherein the length of the transfer belt wrapped around the drive pulley is greater than the length of its sheet-engaging portion between said rear and front guides.

13. Apparatus according to claim 8, wherein the diameter of the drive pulley is greater than the length of said sheetengaging portion of the transfer belt between said rear and front guides.

14. Apparatus according to claim 7, wherein the transfer belt extends straight from each guide to the respective side of the drive pulley.

15. Apparatus according to claim '7, and further comprising a deflection roller offsetting the transfer belt inwardly between one of said guides and the corresponding side of the drive pulley to increase the wraparound of the belt on the pulley.

16 Apparatus according to claim 1 wherein said means for turning said drive pulley back and forth includes first cam means for effecting forward movement of said transfer belt and second cam means for effecting rearward movement of said transfer belt to thereby provide positive forward and reverse movement of said transfer belt.

17. Apparatus according to claim 7 wherein said means for turning said drive pulley back and forth includes a gear train, first cam means for effecting operation of said gear train in a first direction to thereby drive said transfer belt in the forward direction; and second cam means for effecting operation of said gear train in a second direction to thereby drive said transfer belt in the reverse direction.