US3822060A

US3822060A - Apparatus and method for feeding sheets from the bottom of a stack

Info

Publication number: US3822060A
Application number: US00326003A
Authority: US
Inventors: A Gates
Original assignee: NRG Manufacturing Ltd
Current assignee: NRG Manufacturing Ltd
Priority date: 1972-01-24
Filing date: 1973-01-23
Publication date: 1974-07-02
Anticipated expiration: 1991-07-02
Also published as: DE2303392B2; IT978386B; AU5136073A; DE2303392C3; CA980823A; DE2303392A1; FR2169627A5; BE794420A; AU472464B2; JPS5211821B2; JPS4886254A; GB1381851A

Abstract

A sheet feeding method and apparatus wherein sheets are fed from the bottom of a stack by being buckled downwardly while retained at the leading edge by a trip bar. The leading edge is then released and urged forwards, preferably towards a guide and forwarding rollers. Operation of sheet forwarding means and the trip bar is by means of a reciprocable operating plate, and a control arrangement moves the plate when a lever is moved. The control arrangement can also control forwarding rollers, grippers on a machine cylinder and movement of a collector tray.

Description

United States Patent 1191 Gates 1 i 1 July 2, 1974 [54] APPARATUS AND METHOD FOR FEEDING 2,720,135 13/1322 gulilixgonket a] 27 )2? 1 0 3,273,8 4 l a ra ni .1 2. I SHEETS FROM THE B0 M OF A STACK 3,28l,l43 l0/l966 Mommsen et al. 271/23 X Inventor: Albert George Ronald Gates, 3,379,433 4/1968 Gates 271/19 x England FORElGN PATENTS OR APPLICATIONS V Assigneel Geslemel Limited, London, England 659,210 10/1951 Great Britain 271/23 22 F] d: 23, 1973 1 1 1e Jan Primary Examiner-Evon C. Blunk PP N05 326,003 Assistant Examiner-Bruce H. Stoner, Jr.

Attorney, Agent, or Firm-Fleit, Gipple & Jacobson [30] Foreign Application Priority Data 57 ABSTRAQT Jan. 24, 1972 Great Britain; 3265/72 A sheet feedlng method and apparatus wherein sheets 52 US. Cl 271/23, 221/43 271/165 are fed from the bottom of a Stack by being buckled 51 lm. c1 e651] 3/30 downwardly While retained at the leading edge y a 58 Field 61 Search 271/23 21 16, 20, 19, trip The leading edge is released and urged 271/4 53 82 121 165 1 221/43 forwards, preferably towards a guide and forwarding rollers. Operation of sheet forwarding means and the {56] References Cited trip bar is by means of a reciprocable operating plate, and a control arrangement moves the plate when 21 UNITED STATES PATENTS lever is moved. The control arrangement can also con- 655,668 3/1900 Bl lglam et al. 271/23 tro] forwarding rollers, grippelrs on a machine cylinder and movement of a collector tray. 20201925 11 /1935 Young: 271/23 x 21 Claims, 5 Drawing Figures APPARATUS AND METHOD FOR FEEDING SHEETS FROM THE BOTTOM OF A STACK This invention relates to a method of and apparatus for sheet feeding, particularly, but not exclusively, the feeding of sheets such as lithographic plates or masters. The invention also relates to printing machines provided with such sheet feeding apparatus.

It is an object of the invention to provide an improved method and apparatus for feeding sheets.

According to one aspect of the present invention there is provided a method of feeding sheets from a stack including the steps of urging the bottom sheet of the stack against a trip bar which holds the leading edge of the sheet so that the sheet buckles downwardly, and then releasing the leading edge of the sheet from the trip bar so that the sheet unbuckles and the leading edge is driven forwards.

Preferably, the buckle is flattened to assist the forward motion of the leading edge of the sheet on release from the trip bar.

According to a second aspect of the invention there is provided apparatus for feeding sheets from a stack such apparatus including a sheet stack support, a trip bar adjacent one end of the support and positioned to engage an edge of the bottom sheet of a stack when positioned on the support, means to forward the bottom sheet of the stack against the trip bar so that the sheet is buckled downwardly, through an aperture in the support and means to move the trip bar to a releasing position wherein, in use, it releases the leading edge of the buckled bottom sheet. l

The means to forward the bottom sheet is preferably one or more feed wheels operating on the lower surface of the bottom sheet.

There may, suitably, be a buckle flattening member adapted to act on the buckled bottom sheet to flatten the sheet when released by the trip bar.

The forwarding means suitably project through the or another aperture in the sheet support adjacent the trip bar, and the bottommost sheet will buckle downwards through the aperture and be fed therethrough when the trip bar is actuated to release the edge of the sheet. Also, it is advantageous to provide a temporary support member to support the forward end of the stack of sheets when the trip bar is in the buckle releasing position, as otherwise the stack of sheets will tend to sag downwards through the aperture. This member may be a buckle flattening member which acts on the buckle to flatten the sheet as mentioned above. It is also appropriate to provide a feed weight assembly which urges the stack of sheets downwardly with a predetermined force, depending on the friction between the feed wheels and the sheets and the friction between the sheets, against the feed wheels to ensure proper engagement of these with the bottommost sheet. This assembly may be adapted to' cause a degree of prebuckling of the bottommost andother sheets, to ensure that sheets buckle rather than crumple when forwarded. There may also, suitably, be provided an upward sheet guide to guide the front edge of the sheet to further forwarding means, such as feed rollers, when the buckle is released.

The feeding of the sheets is suitably controlled by a single operating plate whichreciprocates adjacent the stack support. In a preferred form, the movement of the operating plate controls therotation of the forwarding means, suitablyfeed wheels, and the releasing and vided to flatten the buckled and forwarded sheet and to support the stack, its movement towards the stack can also be controlled by the operating plate.

The operating plate may suitably be controlled by a control and timing arrangement which may be fitted to the shaft of a cylinder such as the plate cylinder of a printing machine. In a suitable form the arrangement causes one cycle of movement of the operating plate, during which one sheet, plate or master is fed, each time a control lever is actuated in a particular way. The arrangement may include, for this: purpose, a continuously oscillating cam follower moving in an arcuate cam track in a connecting member, the track having at one end an extension, in which the follower is engaged if the connecting member is rotated from a disengaging position. When the follower is engaged in the extension the connecting member is reciprocated with a movement which is transmitted to the operating plate to feed a sheet. The connecting member may be allowed to rotate from its disengaging position for engagement under gravity by removing a support on actuation of the control lever.

The apparatus of the invention may also include feed rollers for forwarding sheets fed from the feeding device towards, for instance, a plate cylinder of a printing machine.

If such feed rollers are provided, their operation can be controlled by the above mentioned control and timing arrangement. For this function; the arrangement can include a rotatable pin plate connected to at least one of the rollers and having gear teeth engaged bya gear track on an oscillatable member. The oscillatable member may have a cam follower engageable with a cam which is adapted to fit on the cylinder shaft of a printing machine and which is rotated during the cycle of movement of the operating plate. A clutch mechanism can be included in the control arrangement for thepurpose, and may suitably comprise two clutch plates normally separated by a lever. The lever may be moved to a position to allow engagement of the clutch plates and rotation of the cam on movement of the actuating lever, returning to its separating position after one revolution of the shaft.

The control arrangement can also include devices to control a plate gripper on a plate cylinder.

Generally, grippers on plate cylinders include a pivoted gripping member which can be controlled to open and close by a cam follower. The control arrangement can include a cam to engage the cam follower when feeding or ejection of plates is required. In one suitable form the cam can be axially adjustable to engage the cam follower when the control lever is actuated. In a particularly suitable form the cam is a double cam to provide alternative modes of opening of the grippers according to the axial position of the cam, thus providing one mode of opening of the grippers to receive and grip a fed plate, and another mode to release a plate for ejection after printing. A wedge and pin device can be used to cause the required axial movement.

The apparatus of the invention can also include a plate ejector and collector mechanism including a piv- The control arrangement can be adapted to control the ejector and collector mechanism by the provision of cams to pivot the tray on actuation of the control lever. Suitably the cams are fixed to move with the control lever, and cause movement of the tray when the control lever is moved to an eject position, in which a suitable mode of opening of the grippers is also caused to take place.

The invention also provides a printing machine including such apparatus.

The provision of an automatic plate loader and ejector in a printing machine means that the machine can be used more efficiently in applications wherein a small number of copies areprinted from each of a large number of plates or masters.

Bottom sheet feeding is advantageous in the feeding of plates or masters because the forwarding means will contact the bottom of the plate rather than the top, which reduces the chances of marking of the printing surfaces by smudging, abrasion or the deposition of dirt or ink. Such marks can be reproduced in final copies. In addition, with bottom feeding, plates are fed in the order in which they are placed on the stack. This makes the addition of plates to a stack while printing takes place a much simpler matter than it is if top feeding is employed.

In order that the invention may be more clearly understood, the following description of a single embodiment of plate feeder and ejector according to the invention is given merely by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a side view of the timing and control arrangement of the embodiment;

FIG. 2a is a side view of the sheet feed mechanism;

FIG. 2b is a side view of part of the mechanism of FIG. 2a not shown in that Figure;

FIG. 3a is a side view of the sheet ejector and collector mechanism; and

FIG. 3b is a plan view of part of the ejector mechamsm.

The sheet feeder of the invention is shown in IG. 2a,

and, generally, comprises a fixed feed tray 30 with a reciprocable operating plate 36 adjacent one side thereof. Movement of the operating plate causes rotation of a feed wheel 31, to buckle plates downwards against a trip bar 33 which is then operated to release the buckle whereby the plates are forwarded under trip bar 33 to feed rollers 42,43 which guide the plates towards the plate cylinder shown at the right of the figure. The plate cylinder has a plate gripper 46.

Reciprocation of the operating plate is caused by movement of a drive pin 23 shown in FIG. 2a and this drive pin can also be seen in FIG. 1. The control and timing arrangement shown in FIG. 1 provides a longitudinal reciprocal motion of the drive pin 23, together with rotary motion to the lower of the feed rollers 43 via a pin plate 44 which is shown in both figures, an intermittent movement for the ejection of plates from the grip of the grippers 46 and an intermittent gripping movement for retaining forwarded plates by the grippers 46.

More specifically, as shown in FIG. 2a, there is a fixed tray 30 for a stack of plates (not shown) which at its left end as shown (in FIG. 2b) has a back weight 34 to rest upon the topmost plate, and a feed weight assembly 35 which is pivoted in an upright slot adjacent the back of the tray andwill make planar contact with the topmost plate of the stack. The tray 30 has an aperture at its right end as shown and bottom feeding can occur through this aperture.

Feeding is caused by reciprocal movement of the operating plate 36, to which is pivoted a sprung lever, 37,

having an upwardly extending finger 37A at its free end. Mounted below the tray is feed wheel 31, and a lever 38 connected to the shaft of this feed wheel has a follower 38A at its free end which engages in a cam track e in the operating plate. The cam track e has a first portion parallel to the line of movement of plate 36, followed by a first, upward curve, then a second parallel portion and a second, downward curve. Mounted at the right end of the aperture in the stack tray 30 is a trip bar 33 which comprises a rotatable rod having a rearwardly extending flange which, in the position shown, is co-planar with the tray 30. Fixed on the trip bar is a rotatable plate 39 which carries two studs 40. The lower stud can be engaged by the upwardly extending finger 37A on the sprung lever 37 as it moves to the right while the upper stud can be engaged by an abutment h on the operating plate at a later stage in the rightward movement thereof. In addition a stud 40A limits rotation of the plate 39 in both directions, the plate having radial abutments to engage this stud. Two mounting brackets 41 are connected to a side frame (not shown) of a printing machine and support the feed tray and feed apparatus. A latch 81 is pivoted to one of the brackets and is spring urged into engagement with the plate 39 on the trip bar and tends to hold this plate in the rotational position shown or in the position wherein its other radial abutment contacts stud 40A. Below the trip bar is an upward guide 82 which leads towards the nip between upper and lower feed rollers 42 and 43, while (also shown in FIG. 1) at 44 is a pin plate drive for the lower feed roller 43. The upper roller 42 is mounted in a support pivotable in the brackets 41. Pivoted to a fixed point is a support plate 32 with an associated lever 32A which projects downwardly into the path of movement of an abutment f on the operating plate 36.

In operation of the plate feeder the operating plate is moved longitudinally with a reciprocal motion by the drive pin 23 as will be described later. In addition, when feeding takes place, the lower roller 43 is rotated at appropriate moments and the clamp 46 on the plate cylinder is opened and closed appropriately.

The operation of the feeder will now be described.

As shown in FIG. 2a the feed mechanism is in a position where it is ready to feed the lowermost plate of a stack (not shown) on the tray 30, the front of the stack being in abutment with a guide 83 and above the flange on the trip bar 33. Feeding commences on movement of the operating plate 36 to the right as shown and, when this occurs, although the tray 30 remains fixed the bottommost plate of the stack is urged against the trip bar 33 by rotation of the feed wheel 31, and buckles downwards. The wheel 31 is rotated by reason of the follower 38A moving in the cam track e in an upward direction as shown in the first, upward, curve to rotate the wheel clockwise, and make lever 38 vertical and the buckle develops to the right of the feed wheel. As the operating plate 36 is moved to the right so the sprung lever 37 is moved in this direction and after a certain time it contacts the lower stud 40 on the rotatable plate 39 on the trip bar. Continued movement of the operating plate 36 and the sprung lever 37 to the right causes rotation of the rotatable plate 39, and therefore of the trip bar, so that the lowermost plate is released from the trip bar and the buckle is released. Rotation of the rotatable plate causes pivoting of sprung latch 81. After a given rotation, the sprung latch will be urged into contact with the straight edge on plate 39, to keep it in a releasing position. Release of the buckle tends to drive the forward edge of the plate against the guide 82, and the plate is also at this time flattened by upward movement of the support plate 32, which is caused by the abutment f contacting the lever 32a causing this to rotate in an anticlockwise direction. Further rotational movement of the feed wheel 31 is then caused by the follower 38A following the second downward curve in track e which is now to the right of the axis of the feed wheel 31 and the front edge of the forwarded plate is driven between the feed rollers 42, 43 and forwarded by these towards the plate cylinder. At approximately the same time the abutment h on the operating plate contacts the upper stud 40 on the plate 39, causing the plate to rotate clockwise back to its original position, with the trip bar flange again under the front edge of the stack. The stack thereafter remains supported by support plate 32, and, at its front edge by the flange on the trip bar, while the gripper 46 on the plate cylinder is opened and closed to clamp the plate.

Once the plate has been forwarded the operating plate 36 remains in its position advanced to the right until a further plate is to be forwarded, whereupon the operating plate 36 is moved back towards the position shown in FIG. 2a, the sprung lever 37 being pivoted by lower stud 40 to pass underneath that stud, and in addition the lever 32A is released so that the support plate 32 moves downwardly away from the bottom of the stack which is supported thereafter at its front end by the flange on the trip bar 33. V

The lever 38 on the shaft of the feed wheel 31 can be provided with a free-wheel device so that wheel 31 does not rotate as the follower 38A returns along cam track e to the position shown. Alternatively, wheel 31 can be moved out of engagement with the stack at that FIG. 1 shows a side view of the control and timing arrangement needed to drive the feed mechanism of F IG.

2a and also to control the ejector mechanism of FIG. 3. As far as FIG. 2a is concerned it will be recalled that the motions imparted to the feed mechanism are a longitudinal reciprocal motion of the drive pin 23 and a rotary motion to pin plate 44, which is attached to the lower of the secondary feed rollers 43.

The control and timing arrangement of FIG. 1 is centered around a plate cylinder drive shaft 1. Clutch plates 2 and 3 are mounted on this shaft, the outer plate 2 being fixed thereto and the inner plate 3 being rotatable with respect to the shaft. Fixed to the inner clutch plate 3 is an operating cam 4. A clutch lever 6 in the position shown separates the clutch plates and thus prevents rotation of the operating cam 4. If this lever 6 is rotated out of position the clutch plates engage and the cam 4 is rotated with the plate cylinder. The lever 6 is pivoted at a control shaft 7 to which there is also fixed an operating arm 16 connected to an operating handle, 15.

frame of the machine (which is not shown) and which has, at its upper end, a follower 11 which describes an arcuate reciprocal motion as the eccentric cam 5 rotates. The follower 11 is movable in a cam track a in a cam plate 21 the track a being generally arcuate, and having at its right end an upward extension a2 below the control shaft'7. The follower 11 will only engage in this upward extension a2 if the cam plate 21 is allowed to rotate from its illustrated position in a clockwise direction. The cam plate 21 is held in position by a stud 20 fixed on one end of a lever 18 which is itself pivoted about a fixed point and can be contacted by a link 17 pivoted to the operating arm 16. Movement of the operating handle 15' in an anticlockwise direction as shown will cause link 17 to press the lever 18 downwards thus allowing the cam plate 21 to rotate clockwise, so that when the follower 11 on the lever 9 is next at its extreme righthand position it will engage in the upward extension a2 of the cam track a. As the follower next reciprocates, the entire cam plate including the drive pin 23 will also reciprocate, and it will be seen with reference to FIG. 2a that this will cause operation of the operating plate 36 and thus the feeding of a plate to the plate cylinder. Although the eccentric cam 5 can continuously rotate with the printing cylinder, the operating cam 4 only rotates when the clutch lever 6 is removed from between the clutch plates 2 and 3. The lever 6 is removed by a stud 22 on the cam plate 21, when engaged and reciprocated, striking a stud b on the lever 6 and causing it to pivot to the left as shown. Thus the clutch will only be engaged when cam plate 21 is engaged and moved. On such pivoting the clutch plates 2 and 3 are drawn together and the lever 6 maintained out of position for one revolution of the printing cylinder by reason of the stud b being engaged by a hook g in a latch 24, which is pivoted about a fixed point. During the revolution of the printing cylinder, a stud c on the operating cam 4 follows the inside of a curved edge d on the latch 24, moving it upwardly as shown to release the stud b on the lever 6 which then moves back to separate the clutch plates under the action of a spring 6A.

During the time that the operating cam 4 is rotating, it causes rotary reciprocal movement of an arm 13 pivoted about a fixed point and having a follower 12 contacting the cam 4. At its outer end the arm 13 has a gear track which engages a gear wheel coaxial with the pin plate 44. Thus the feed rollers 42, 43 of FIG. 2a only operate, according to the profile of operating cam 4 when the clutch plates 2 and 3 are engaged.

The control and timing arrangement of FIG. 1 also controls the ejector mechanism shown in FIGS. 30 and 3b. This mechanism comprises a collector tray which is spring mounted and pivotable at 53 and has two locating pins 54 at either side, which can be con tacted by two cams (not shown) mounted on the con-:

' trol shaft 7 shown in FIG. 1. These cams can raise Fixed on the shaft 1 of the plate cylinder is an eccen v tric cam 5 which rotates in a fork 9 pivoted on the side and lower the collecting tray 50 according to the rotational position of the control shaft 7. Atthe left end of the tray as shown is a shaft bearing one or more rotatable take off rollers 52. A number of stripper fingers During feeding and ejection of plates to and from the plate cylinder it is necessary to open and close the grippers 46 at appropriate times. This is done by respective parts of a double cam 55 which is mounted inside a machine frame and is axially movable so that one or other or neither of its parts may be followed by a follower 57 on the arm of the gripper 46 which is pivoted on the cylinder. The cam is moved axially by means of a spring stud 59 which is best seen in FIG. 3b and which is urged into contact with the cam 4 or with a ramp 58 having an inclined edge and attached to the operating cam 4, and which is also shown in FIG. 1. If the spring stud 59 contacts the cam 4 itself, then the cam 55 is not pushed out and is not contacted by the follower 57. If the spring stud 59 contacts the inclined edge of the ramp, then the cam 55 is partly pushed out, and the follower 57 will contact and follow the outer cam part 55A as it rotates with the plate cylinder. Finallyif the spring stud 59 contacts the thickest part of the ramp 58, then cam 55 will be pushed out to allow the inner part 553 to be contacted by the follower 57 as it rotates. Cam part 55B is used during plate feeding, and part 55A during plate ejection. The spring stud 59 is bushed in the side frame 56 of the machine which is shown in the FIG. 3b.

During feeding of a plate, the spring stud 59 contacts the thickest part of the ramp 58 shortly after the cam 4 starts to rotate, which will occur at approximately the same time as the operating plate 36 starts its feeding movement to the right as shown in FIG. 2A. The stud thus moves the inner cam part 558 to a position wherein it is engaged by the follower 57 as the plate cylinder rotates, to open the grippers to receive the leading edge of the forwarded plate. When the cam 4 does not rotate stud 59 contacts the cam 4 itself so that the follower 57 does not contact the cam 55, and the grippers are not opened while the plate cylinder rotates.

The operation of the sheet ejector is caused by movement of the operating handle of FIG. 1 in a clockwise direction as shown. This cause rotation of a lever in a clockwise direction until its free end contacts a stud c on the operating cam 4 and causes that cam to rotate through a small arc in a clockwise direction. While this occurs'the front edge of the collecting tray 50 is lowered by the cams on the control shaft 7, so that the stripping fingers 51 are moved in between fingers on the gripper 46. The small clockwise rotation of the cam 4 is sufficient'to move the ramp 58 from the position in which it is shown in FIGS. 1 and SE to a position wherein the sprung pin 59 contacts the inclined part of the ramp 58. This causes the double cam 55 to move so that its outer part 55A is followed by the follower 57 during rotation of the cylinder which causes appropriate gripper opening. This procedure is followed when the required number of copies has been printed with a given master and can be followed by movement of the operating handle to the left as shown, so as to start the cycle of feeding a fresh plate to the cylinder.

1 claim:

1. A method of feeding sheets from a stack including the steps urging the bottom sheet of the stack against a trip bar which holds the leading edge of the sheet so that the sheet buckles downwardly and then releasing the leading edge of the sheet from the trip bar and pressing the buckle fiat to cause the sheet to unbuckle and the leading edge to be driven forwards past the trip bar.

2. Apparatus for feeding sheets from a stack, such apparatus comprising a sheet stack support, an aperture in said support, a trip bar positioned to engage an edge of a bottom sheet of a stack when positioned on the support, means to forward the bottom sheet of the stack against the trip bar so that the sheet is buckled downwardly, through said aperture, means to move the trip bar to a releasing position wherein, in use, it releases the leading edge of the buckled bottom sheet; and a buckle flattening member adapted to act on the bottom sheet when buckled to flatten the sheet when its leading edge is released by said trip bar.

3. Apparatus as claimed in claim 2 wherein said means to forward the bottom sheet comprise at least one feed wheel positioned to operate on the bottom sheet when the stack is positioned on said support.

4. Apparatus as claimed in claim 2 and further comprising a feed weight positioned to engage the top of a stack of sheets when positioned on said support so as to urge the stack downwardly.

5. Apparatus as claimed in claim 4, wherein said feed weight is located above said aperture in said sheet support to bear downwardly on all the sheets of the stack.

6. Apparatus as claimed in claim 2 and further comprising an upward sheet guide located adjacent said sheet stack support to guide the leading edge of a sheet upwardly on release from said trip bar.

7. Apparatus as claimed in claim 2 and further comprising feed rollers located adjacent said support to engage the leading edge of a sheet when released from said trip bar.

8. Apparatus as claimed in claim 2, and further comprising an operating plate reciprocable adjacent said stack support and operatively connected to said forwarding means, said trip bar and said buckle flattening member to control the sheet feeding operation of said forwarding means, movement of said trip bar to and from its releasing position, and buckle-flattening movement of said buckle-flattening member.

9. Apparatus as claimed in claim 8 wherein said forwarding means comprise feed wheels and further comprising an axle for said feed wheels, a lever on said axle, a follower on said lever, and a cam track in said operating plate, said follower engaging in said cam track.

10. Apparatus as claimed in claim 8 wherein said trip bar is pivotable and further comprising a control plate fixed to said trip bar and projections on said control plate, said projections being engageable by said operating plate to rotate said trip bar to and from said releasing position.

11. Apparatus as claimed in claim 8 and further comprising a control and timing arrangement, and a control lever to said arrangement, said arrangement being connected to said operating plate and adapted to cause one cycle of reciprocal movement of said plate each time said control lever is moved in a given direction.

12. Apparatus as claimed in claim 11 and further comprising, in said arrangement, a continuously oscillatable cam follower, a rotatable connecting member connected to said operating plate, a cam track in said connecting member, said follower engaging in said track, and an extension to said track in which said follower is engageable when said connecting member is rotated to an engaging position.

connecting member in a disengaging position and a second position in which it allows said connecting member to rotate under gravity to its engaging position.

14. Apparatus as claimed in claim 11 and further comprising feed rollers located adjacent said sheet stack support, a gear connected to one of the rollers and an oscillatable toothed track engaging said gear.

15. Apparatus as claimed in claim 14 and further comprising a clutch engageable on actuation of said control lever, a cam rotatable when said clutch is engaged, and a follower for said cam on said toothed track.

16. A printing machine comprising a cylinder, and apparatus arranged to feed sheets from a stack towards said cylinder, such apparatus comprising a sheet stack support, an aperture in said support, a trip bar positioned to engage an edge of a bottom sheet of a stack when positioned on the support, means to forward the bottom sheet of the stack against the trip bar so that the sheet is buckled downwardly, through said aperture, means to move the trip bar to a releasing position wherein, in use, it releases the leading edge of the buckled bottom sheet, and a buckle-flattening member adapted to act on the bottom sheet when buckled to flatten the sheet when its leading edge is released by said trip bar.

17. A printing machine as claimed in claim 16 and further comprising an operating plate reciprocable ad- 5 jacent said stack support and adapted to control at least the operation of said forwarding means and movement of said trip bar to and from its releasing position.

18. A machine as claimed in claim 17 wherein said cylinder is a plate cylinder and further comprising grippers on said plate cylinder, a cam follower connected to said grippers, and a gripper cam, said grippers being pivotable to an open position when said follower engages said gripper cam, and said gripper cam being axially movable to a position wherein it is engageable by said cam follower.

19. A machine as claimed in claim 18 wherein said cam is a double cam to provide alternative modes of opening of said grippers according to its axial position.

20. A machine as claimed in claim 19 and further comprising an axially adjustable stud and a movable ramp to engage and adjust said stud, said stud abutting said gripper cam to impart axial movement thereto.

21. A machine as claimed in claim 18 and further comprising a pivoted collector tray adjacent said cylinder and stripper fingers on said tray.

Claims

1. A method of feeding sheets from a stack including the steps urging the bottom sheet of the stack against a trip bar which holds the leading edge of the sheet so that the sheet buckles downwardly and then releasing the leading edge of the sheet from the trip bar and pressing the buckle flat to cause the sheet to unbuckle and the leading edge to be driven forwards past the trip bar.

13. Apparatus as claimed in claim 12 and further comprising a movable support movable by said control lever between a first position in which it maintains said connecting member in a disengaging position and a second position in which it allows said connecting member to rotate under gravity to its engaging position.

17. A printing machine as claimed in claim 16 and further comprising an operating plate reciprocable adjacent said stack support and adapted to control at least the operation of said forwarding means and movement of said trip bar to and from its releasing position.