GB2321450A

GB2321450A - Sheet feeding

Info

Publication number: GB2321450A
Application number: GB9801422A
Authority: GB
Inventors: Herbert Hermann
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1997-01-22
Filing date: 1998-01-22
Publication date: 1998-07-29
Anticipated expiration: 2018-01-22
Also published as: GB9801422D0; JPH10203669A; GB2321450B

Abstract

The uppermost sheet of a pile 1 is lifted by a pneumatic sucker 4, and pulled backwards a distance x so as to remove its leading edge from under a catch 8. Thereafter the sheet is advanced to feed rollers by a further sucker 10. The catch, may be domed (8', figures 6 - 8) and freely movable in a mounting (13'), eg as a piston (17) which directs air out of apertures (24) at the front edge of the sheet stack. Guide fingers (32) may direct the sheet to the feed rollers.

Description

2321450 SHEET FEEDERS This invention relates to sheet feeders and

particularly to sheet feeders for use in printing presses.

In particular, it relates to sheet feeders of the general type having a lifting table on which a pile of sheets to be processed may be placed and having one or more separating elements by means of which, in the rhythm of the sheet processing machine, the respectively uppermost sheet on the sheet pile and can be grasped, lifted, and then fed in the feed direction to further transport mechanisms.

This sort of known sheet feeder generally has in the uppermost front region of the sheet pile a sheet flap which, in the rhythm of the sheet processing machine, can be driven swivellably between its upright, upwardly directed position and a position inclined somewhat in the feed direction. In the vertical position, it should prevent sheets of the sheet pile shifting in the feed direction thus leading to a double sheet feed, while in the position inclined in the feed direction, the lifted uppermost sheet supported by blown air can be forwarded with its front end securely grasped to a further feeding device, for example pull-off rollers.

Such pull-off rollers can, however, only be arranged at least at a certain distance from the sheet pile front edge in order that the sheet flap can be swivelled freely and without hindrance into its position directed somewhat in the feed direction. This means that the path travelled by the sheet, for example whilst lifted by sliding suckers of the sheet feeder, until the sheet can be grasped by the pull-off rollers, is large. This relatively long movement path must be controlled in the rhythm of the sheet processing machine, for which purpose high accelerations and decelerations of the sliding sucker are necessary. Particularly in the case of the turnround in movement of the sliding sucker, its high inertial deceleration is a disadvantage because results in substantial stresses and strains on the materials of the sliding sucker and support structures which in turn leads to a tendency for the sliding sucker and support structures to suffer high levels of defects and failures.

The big acceleration of the sliding sucker following transfer of the lifted sheet from the sheet pile to the sliding sucker by temporary attachment to the rear region of the sheet when looked at in the feeding direction, leads to the problem that the front end of the sheet flutters. If this occurs, the sheet may not be taut or flat when the front end of the.sheet enters the pull off rollers. This can prove very problematical. In order to compensate for this disadvantage, the lifted sheet must be blown underneath with a relatively intensive stream of blown air in the feed direction. This intensive stream of blown air requires a corresponding blown air generator with a correspondingly high energy requirement.

It is accordingly the object of the invention to create a sheet feeder of the above noted type which, in simple fashion, guarantees secure feeding of the sheet to a further feeding device.

This problem is solved in accordance with the invention in that in the front region of the sheet feeder as seen in the feed direction, one or more catch hooks are arranged to lie on the front end region of the sheet pile and which extend by a certain distance in the direction counter to the feed direction across the top of the sheet pile, and that the separating element or elements, after grasping the uppermost sheet, exert a pulling movement on the grasped sheet counter to the feed direction and through at least the distance by which the catch hooks extend over the top of the sheet pile. This makes possible, among other things, leaving out a sheet flap and because of this construction, the further feed device such as, for example, pulling off rollers, can now be arranged closely adjacent the front side of the sheet pile, so that the distance of the sliding path which the front edge of the sheet has to traverse is substantially reduced. This reduces the accelerations and decelerations acting on the sliding sucker, which increases its service life and it requires a substantially smaller stream of blown air in order to blow under and support the lifted sheet.

In addition to all of this because of the short sliding path, the possibility is also provided of shortening the cycle or increasing the rhythm for the sheet processing machine while nevertheless still guaranteeing - 4 satisfactory sheet feeding.

The catch hooks which lie on the front end region of the sheet pile ensure, because of their pressure on the sheet pile the one hand, that the sheet located underneath the lifted separated sheet is securely held on to the sheet pile and accordingly a double sheet feed is prevented, and on the other hand by means of the component of the sheet separating movement in the direction counter to the sheet feed direction any hooking of the sheets which arises from a badly cut edge in the sheet pile is suppressed.

The separating elements can, in a preferred embodiment, is be separating suckers and the further transport elements can be sliding suckers.

To generate the pulling movement counter to the feed direction acting on the first sheet, the separating elements can be drivably movable linearly counter to the feed direction.

If the separating elements are drivable swivellably, in particular around a swivel axis arranged at a distance from its sheet grasping surface, then by the swivelling, both the pulling movement of the sheet and also an increase of the slot between the top of the sheet pile and the underside of the lifted sheet end into which air can be blown is achieved. Such an increase leads to an improved build-up of an air cushion under the lifted or uppermost sheet by subjecting the rear upper region of the sheet pile to a blast of air from directed blowers, and thereby an improved separation of the entire lifted or uppermost sheet from the sheet pile is achieved.

This is improved even further if the separating elements after grasping the lifted or uppermost sheet can be lifted away from the sheet pile.

The catch hooks can be guided vertically and freely movable in the vertical direction and can lie just with their own weight on the sheet pile.

In order to guarantee a satisfactory and unhindered separation of the uppermost sheet of the sheet pile from the catch hooks, the catch hooks can be drivable so that they can be lifted in the time or rhythm of the sheet processing machine during the separating process and/or the pulling movement from the front region of the sheet pile. In this connection, the catch hooks can be drivable liftably by pneumatic means.

In order to prevent any shifting of the uppermost sheet of the sheet pile in the sheet feed direction and thereby to prevent incorrect sheet feeding, in the feed direction, the front uppermost sheets of the sheet pile can lie against a stop on which the catch hooks are arranged.

If, in this connection, the stop has at its lower end a running in oblique surface which slopes away from the sheet pile, then, simultaneously on lifting the sheet pile, an alignment of the front edge of the uppermost sheet takes place. Achievement of the alignment of the front edges of the sheets at the top of the sheet pile is further enhanced if the stop can be resiliently made to lie against the front region of the sheet pile. The effect of such alignment is that it is thereby guaranteed that the catch hooks with their laying on part always 6 - securely project over a portion of the uppermost sheet and lie on it.

To achieve the resilient lying of the stop against the front region of the sheet pile, the stop can have one or more guide rod extending in the feed direction which are arranged to be slidably guided in a corresponding aperture(s) of a fixed constructional part, wherein between the stop and the fixed constructional part, a compression spring under pre-compression can be arranged.

In simple fashion without any sort of holding elements being required for the compression spring, the compression spring can be a helical spring surrounding the guide rod.

A free mobility of the catch hook is achieved if the catch hook is arranged in a fashion guided vertically movable on the stop. A simple embodiment ensuring free vertical movability of the catch hook consists of the catch hook having a guide rod attached to it and the guide rod extending from its vertically downwards and being guided in a corresponding guide aperture of the stop in vertically movable fashion.

In order to lift the catch hooks for separating the uppermost sheet from the pile, the guide rod can constitute a piston and the guide aperture a cylinder, wherein the cylinder can be subjected to compressed air in the rhythm of the sheet processing machine to lift the guide rod.

If the guide rod of the guide aperture has a circular cross-section and the pressing on part of the catch hook is constructed as a substantially rotationally symmetric pressing on plate, then the pressing on plate is freely movable not only vertically, but also about the longitudinal axis of the guide rod, which yet further increases the security of the application of the catch hook to the sheet pile under its own weight.

In order to lift freely the free end of the lifted sheet in the feed direction by blowing air underneath it, the catch hook can have an oblique surface which is constructed so that it rises from the end of the part of the laying on portion or pressing on plate of the catch hook which is directed against the feed direction, the oblique surface substantially rising from the plane of the uppermost sheet of the sheet pile in the feed direction.

Aeration of the front upper pile region and thereby avoidance of double sheet feeding is achieved in that in front of the upper front region of the sheet pile, one or several loosening blowers having blowing nozzles directed against the sheet pile are arranged. It is space-saving in constructional terms if the blowing nozzles are integrated constructionally in the catch hooks. In this case, the catch hooks are secured against turning around their longitudinal axes.

A feed of compressed air can take place in simple fashion simultaneously with the lifting of the catch hook if the guide rod has an axial bore debouching in the cylinder, from which, in the region near the pressing or laying on part of the catch hook, there extend one or more recesses directed substantially radially to the sheet pile and forming outwardly directed blowing nozzles.

Preferably, in this connection, several blowing nozzles are constructed along the longitudinal extent of the guide rod.

On the emergence of the blowing nozzles from the guide recess on lifting the separating hook or catch hook and guide assembly, the blowing nozzles are unblocked or opened and the compressed air in the cylinder can, via the axial bore and the blowing nozzles, impact on the upper region of the sheet pile.

In one embodiment, the further transport elements can comprise a first roller which can be rotatably driven around an axis extending transversely to the feed direction and a further roller mounted rotatably about an axis parallel to the axis of the first roller and arranged above the first roller, whereby the sheet fed from the sheet feeder can be gripped between the first and the further roller at its front end region and can be transported further.

A refinement of this embodiment of the further transport elements consists of a construction in which the first roller is formed by one or several feed rollers of small diameter which are arranged rotatably near the front edge of the sheet pile of the sheet feeder, one or more endless drive belts are guided about the feed roller(s), which drive belts extend somewhat in the feed direction from the feed rollers and pass round further feed rollers arranged at a distance from the first feed rollers.

By virtue of the refined embodiment, the apex region of the first and the further roller that grasps the sheet fed from the sheet feeder in the region adjacent the upper sheet pile front edge and thus the path to be retraced by the elements of the sheet feeder moving the sheet from the top of the sheet pile to a position in which the front edge of the sheet may be grasped is small. Since the fed sheets are pressed by the upper further roller on to the drive belts, the sheets are also securely grasped without distortion and transported further.

The small feed path to be travelled does not lead only to small loads on the elements of the lay-up table feeding the sheet, but also requires a substantially smaller blowing of air underneath the sheets which are lifted by the feeding elements from the sheet pile and accordingly as well as the energy saving for the sheet feeding elements, there is also a substantially reduced energy requirement for the compressed air requirements.

The smaller loading on the feeding elements also makes possible an increase in the cycle frequency and accordingly the capacity of the sheet feeder.

The drive belt or belts can be guided substantially in a triangular run extending about a third roller located in the region below the feed roller and feed drum. Preferably, in this connection, the third roller is a tensioning roller so that the drive belts can be maintained always at their optimum tension.

If the feed drum is a rotatably driven drum and feed rollers and tensioning rollers are freely rotatably mounted rollers, then all of the drive belts can be driven together in common by the feed drum.

An overlapped type sheet stream is thereby generated in simple fashion in that the further roller arranged above the feed rollers is a timing roller which can be lowered on to and lifted away from the feed rollers in the working rhythm of the sheet feeding device.

If the further roller has a substantially larger diameter than the feed rollers, then the security of correct grasping of the sheet is yet further increased. Since above the front region of the sheet pile there is space, the further roller can, without problems, project with a part of its diameter above the front region of the sheet pile.

Correct grasping and forwarding of the sheet can thereby be increased if two or more feed rollers are arranged at a distance to prompt one another and a drive belt is guided around each feed roller.

If, in this connection, the distance between two feed rollers is smaller than the smallest width of the sheet to be worked with, then without any necessity for a rebuild, all sheet sizes which are customarily worked with can be processed by the sheet feed device.

In a simple construction, the feed rollers can be rotatably mounted on a common axle.

In order to prevent any shifting of the uppermost sheet in the sheet pile in the feed direction, between the feed rollers and/or adjacently outer feed rollers, a drivable sheet flap can be arranged swivellably about a swivel axis in the rhythm of the sheet feeding device between a vertically upwardly directed position lying against the front edge of the sheet pile and a position inclined in the feed direction.

In order to feed the front edge of the lifted sheet on to without the upper side of the first roller or on to the feed drum with the avoidance the front corners of the sheets hanging down, between the catch hooks and/or the feed rollers of small diameter, one or more sheet guide devices can be arranged which extend substantially roughly from the front side of the sheet pile to the upper side of the first roller or the feed drum.

In a simple construction, in this connection, the sheet guide devices can have several guide fingers arranged at is a distance from one another and directed toward the first roller or to the feed drum.

If the guide fingers are directed inclined at an angle relative to the feed direction towards that lateral edge of the sheet feeder which is nearest the respective guide finger, then the sheet guided past the guide device receives stretching transverse to the sheet feed direction.

For optimal guidance of the sheet, the end of the sheet guide device adjacent the sheet pile is preferably arranged below the level of the uppermost sheet in the sheet pile and the other end directed in the feed direction is located at the apex side of the first roller or of the feed drum.

The invention is illustrated by way of example with reference to the accompanying drawings which show diagrammatically various aspects and details of sheet feeders in accordance with the invention. In the drawings Figure 1 is a side view of a sheet feeder diagrammatically and at the point of transfer of a sheet to pull off rollers.

Figure 2 is the sheet feeder according to Figure 1 after grasping and separation of the rear end of the uppermost sheet by means of separating suckers.

Figure 3 shows the sheet feeder according to Figure 1 with separating suckers raised and swivelled counter to the feed direction.

Figure 4 shows the sheet feeder according to Figure 1 in the transfer position for the uppermost sheet from the separating suckers to sliding suckers.

Figure 5 is a side view of a second embodiment of a stop with catch hooks.

Figure 6 is a side view of a third exemplary embodiment of a stop with catch hooks with a sheet feed device.

Figure 7 is a side view of a fourth exemplary embodiment of a stop with catch hooks with a sheet feed device in a first working position.

Figure 8 is a side view of the stop with catch hooks according to Figure 7 in a second working position.

Figure 9 is a view in the feed direction of a sheet feed device according to Figure 7 with a sheet guiding unit.

13 - Figure 10 is a side view of the sheet feeding unit according to Figure 9.

Figure 11 is a view in the feeding direction of a sheet feed device according to Figure 6 with a sheet guiding device.

Figure 12 is a side view of the sheet feeding device according to Figure 11.

The sheet feeder illustrated in the Figures has a lifting table which is not illustrated on which a pile of sheets 1 is set. The respectively uppermost sheet 2 of the sheet pile 1 is grasped at its rear end as seen in the feed direction 3 by a separating sucker 4 and lifted (Figure 1).

Thereafter, the separating sucker 4 is so swivelled around a swivel axis spaced at a distance from the sheet grasping surface 5 of the separating sucker 4 that its sheet grasping surface 5 moves somewhat counter to the feed direction 3 (Figure 2). This leads to the fact that the uppermost sheet 2 which has been lifted and grasped by the separating suckers 4 is pulled counter to the feed direction 3. By this pulling movement, the (in the feed direction 3) front edge 7 of the uppermost sheet 2 moves counter to the feed direction 3 through a path "x".

This path "x" is by an extent lly" larger than the extension of a laying on portion 9 of a vertically freely movable catch hook 8 in a direction counter to the feed direction 3, by means of which the catch hook 8 lies under its own weight on the, as seen in the feed direction 3 front, end of the sheet pile 1.

Thereby the uppermost sheet 2 is pulled out by the pulling movement effected by the separating suckers 4 from below the laying on portion 9 of the catch hooks 8 (Figure 3).

By the blowing underneath in the feed direction of the lifted first sheet 2 which has been put into effect in the interim using compressed air and by means of not illustrated blowers arranged behind the sheet pile 1, an air cushion is built up under the uppermost sheet 2 which separates the sheet 2 along its entire length securely from the sheet pile 1 and stretches the sheet 2 in the feed direction 3 (Figure 4).

Simultaneously the lifted sheet 2 is grasped by the sliding suckers 10 and the grasping by the separating suckers 4 is released.

While now the sliding suckers 10 transport the sheet 2 in the feed direction 3 until its front edge is fed into pull off rollers 11, the separating suckers 4 swivel back again into their vertical orientation and drop for grasping the next sheet again on to the sheet pile 1 (Figure 1).

After grasping the sheet 2 by the pull off rollers 11, the sliding suckers 10 free this sheet 2 and move counter to the feed direction 3 back into their starting position.

The catch hook 8 is constructed on its upper side with an incline 12 which is constructed counter to the feed direction 3 from the end opposite the feed direction 3 so that it rises substantially from the plane of the is uppermost sheet of the sheet pile 1 rising in the feed direction 3. Thereby, the uppermost sheet 2 on its feed towards the pull off rollers 11 cannot remain hanging caught on the catch hooks 8.

In the Figures 1 to 4, the catch hook 8 is constructed with a stop 13 extending downwardly vertically from the laying on part 9, against which the front upper region of the sheet pile 1 lies.

In order that on lifting the sheet pile 1 its sheets do not impact on the underside of the stop 13, this has a running in ramped oblique surface 14 which runs out at its lower edge away from the pile 1.

In the exemplary embodiment illustrated in Figure 5, the catch hook 8' likewise has a stop 131 with a running in oblique surface 14. The laying on part is, however, not connected rigidly with the stop 13', but constructed as a rotationally symmetric laying on plate 15, the underneath surface of which is flat and the face 16 of which turned away from the surface of the pile and which constitutes the incline is constructed rather in the fashion of a spherical cap or slice cut from the side of the sphere.

The laying on plate 15 has a central downwardly projecting guide rod 17 of circular cross-section which is guided both rotatably and slidably in a corresponding guide recess 18 constructed in the stop 131.

The stop 131 has a guide rod 19 directed in the feed direction 3 which, with its free end, is slidably guided in a corresponding aperture 20 of a fixed constructional part 21.

Between the stop 13' and the fixed constructional part 21 under compression there is arranged a helical spring 22 surrounding the guide rod 19 which always holds the stop 131 which is freely slidable in the feed direction 3 securely adjacent the upper front region of the sheet pile 1.

The stop 131 illustrated in Figures 6 to 12 with catch hook 8' corresponds substantially to the exemplary embodiment in Figure 5.

While, in Figure 5, the laying on plate 15 with its guide rod 17 is movable in the guide recess 18 of the stop 131 subject only to its own weight, in Figure 6 the guide recess 18 constitutes a cylinder which can be subjected to compressed air in the rhythm of the sheet processing machine and the guide rod 17 constitutes a piston secured against rotation about a longitudinal axis.

The guide rod 17 has an axial bore 23 which debouches in the guide recess 18 and from which, in the region next to the laying on plate 15, several apertures 24 radially directed outwardly towards the sheet pile 1 debouch. These apertures 24 constitute, in this connection, blowing nozzles and are constructed at distances from one another along the longitudinal extent of the guide rod 17.

As can be seen, in particular, in Figures 7 and 8, the apertures 24 in the lowered position (Figure 7) of the catch hook 81 are almost all closed by the guide recess 18, while in the moved out condition of the catch hook 8', they are freed and the compressed air which has lifted the catch hook 8' in the guide recess 18 can simultaneously go through the axial bore 23 to the apertures 24 and can emerge in the front upper region of the sheet pile 1 from the apertures 24 freeing up the sheets.

As further transport elements in the exemplary embodiments of Figures 6, 11 and 12, there are arranged drivably rotatable about an axis extending in a direction transverse to the feed direction 3 a first roller 25 and arranged above the first roller 25 and rotatably mounted about an axle parallel to the first roller 25 are further rollers 26 which corresponds to pull off rollers corresponding to Figure 1.

is The sheet 2 fed from the sheet feeder is graspable between the first roller 25 and the further roller 26 at its front edge 7 and can be transported further.

In the exemplary embodiments of Figures 7 to 10, the further transport elements consist of several feed rollers 27 of small diameter which are arranged rotatably about an axis in a direction transverse to the feed direction 3 near to the upper front edge of the sheet pile 1. In the feed direction 3 at a distance to the feed rollers 27, there is arranged a feed drum 28 drivable rotatably about an axle parallel to the rotational axis of the feed rollers 27. The upper apex of the feed rollers 27 and of the feed drum 28 are located substantially at the height of the laying on plate 15 of the lowered catch hook 81.

Above the feed rollers 27 there is arranged a further roller 26 corresponding to the further rollers 26 in Figures 6, 11 and 12.

- 18 At a distance below the feed rollers 27, there is freely rotatably arranged a third roller 29 with a rotational axis parallel to the rotational axes of feed rollers 27 and feed drum 28. With a triangular shaped run, drive belts 30 are guided around feed rollers 27, feed drum 28 and third roller 29.

The rollers 26 arranged above the feed rollers 27 have a substantially larger diameter than the feed rollers 27 and are constructed as cycling rollers which can be lowered and raised in the working cycle of the sheet processing machine on to and away from the feed rollers 27.

Thereby, in known fashion, the fed sheets 2 are formed into an exactly overlapped sheet stream.

In the exemplary embodiments of Figures 9 and 10, in each case a catch hook 81 and a feed roller 27 are arranged closely adjacent one another. Near the side turned away from the adjacently lying catch hooks 8' or the adjacently lying feed rollers 27 there extend transverse to the feed direction 3 sheet guide devices 31. In similar fashion in Figures 11 and 12, there extend to both sides by the catch hooks 8' sheet guiding devices 31.

These sheet guiding devices 31 are arranged with their one end next to the sheet pile 1 and below the uppermost sheet of the sheet pile 1 and have a plurality of adjacently arranged guide fingers 32 which, with their free ends 33 are directed with respect to the feed direction 3 inclined towards the side edge of the sheet feeder relative to which the respective guide fingers 32 are closer.

The free ends 33 of the guide fingers 32 directed in the feed direction 3 are located substantially at the apex side of the first roller 26 (Figures 11 and 12) or of the feed drum 28 (Figures 9 and 10).

Claims

1. Sheet feeder with a lifting table on which a pile of sheets may be supported and having one or more separating elements by means of which, in the rhythm of a sheet processing machine, the respective uppermost sheet of the sheet pile can be grasped, lifted, and then fed in the feed direction to further transport means, wherein arranged in the front region of the sheet feeder seen in the feed direction of the sheets are one or more catch hooks which lie on the front end region of the sheet pile and which extend by a given amount in the direction opposite the direction of sheet feeding above the sheet pile, and including means for causing the separating elements, after grasping the uppermost sheet, to exert on the sheet a pulling movement counter to the feed direction to an extent at least as great as the given amount by which the catch hooks extend over the sheet pile.

2. Sheet feeder according to Claim 1, wherein the separating element(s) are separating suckers.

3. Sheet feeder according to Claim 1, wherein the means for transporting the sheets further are sliding suckers.

4. Sheet feeder according to Claim 1 or 2, wherein the separating element(s) can be driven movably linearly counter to the feed direction.

5. Sheet feeder according to Claim 1 or 2, wherein the separating element(s) is arranged so that it can be driven swivellably about a swivel axis arranged at a distance from its sheet grasping surface.

6. Sheet feeder according to any one of the preceding Claims and including means for lifting the separating elements away from the sheet pile following engagement of the uppermost sheet.

7. Sheet feeder according to any one of the preceding Claims wherein the catch hooks are guided vertically and are freely movable.

8. Sheet feeder according to any Claim 7 and including means for lifting the catch hooks from the front region of the sheet pile in the rhythm of the sheet processing machine during the separating process and/or the pulling movement.

9. Sheet feeder according to Claim 8 and including pneumatically driven lifting means for the catch hooks.

10. Sheet feeder according to any one of the preceding Claims and including stop means arranged to lie against the upper front region of the sheet pile as seen in the feed direction, the catch hooks being arranged on the stop means.

11. Sheet feeder according to Claim 10, wherein the stop means has on its lower end a running-in surface extending obliquely away from the side of the sheet pile.

12. Sheet feeder according to Claim 10 or 11 and including means for resiliently biasing the stop means against the front region of the sheet pile.

13. Sheet feeder according to Claim 12, wherein the stop means includes one or more guide rods extending therefrom - 22 in the feed direction of the sheets to be processed, which guide rod(s) are arranged slidably guided in a corresponding aperture(s) of a fixed component of the feeder.

14. Sheet feeder according to Claim 13, wherein a compression spring under pre-compression is arranged between the stop means and the fixed component.

15. Sheet feeder according to Claim 14, wherein the' compression spring is a helical spring surrounding the guide rod.

16. Sheet feeder according to any one of Claims 10 to 15 wherein the catch hook(s) are arranged guided in a vertically movable fashion on the stop means.

17. Sheet feeder according to Claim 16, wherein the catch hook(s) have a guide rod extending from their support portion which is adapted to lie on the front end region of the sheet pile, the guide rods extending vertically downwards and being vertically movable in corresponding guide recess(es) in the stop means.

18. Sheet feeder according to Claim 17, wherein the guide rod constitutes a piston and the guide recess a cylinder and means are provided enabling the cylinder to be subjected to compressed air to lift the guide rod in the rhythm of the sheet processing machine.

19. Sheet feeder according to Claim 18, wherein the guide rod and guide recess have a circular cross-section and the part of the catch hook which lies on the sheet pile is constructed as a substantially rotationally symmetric hold down plate.

20. Sheet feeder according to any one of the preceding Claims wherein the catch hook(s) have an oblique surface which is constructed so that it rises in the feed direction substantially from the plane of the uppermost sheet in the sheet pile from the end of the hold down portion of the catch hook directed counter to the feed direction.

21. Sheet feeder according to Claim 20, wherein the hold down portion of the catch hook is constructed on its face remote from the surface of the pile substantially as a part spherical surface.

22. Sheet feeder according to any one of the preceding Claims and including loosening blowers having one or more blowing nozzles directed against the sheet pile arranged in front of the upper front region of the sheet pile.

23. Sheet feeder according to Claim 22, wherein the blower nozzles are formed integrally with the catch hooks and wherein means are provided to secure the catch hooks against turning around the longitudinal axis of their guide rods.

24. Sheet feeder according to Claims 18 and 23, wherein the guide rod has an axial bore opening out into the cylinder from which in a region close to the hold down portion of the catch hook apertures extend substantially radially which constitute one or more blowing nozzles directed outwardly towards the sheet pile.

25. Sheet feeder according to Claim 24 and including two or more blowing nozzles spaced apart from one another along the longitudinal extent of the guide rod.

26. Sheet feeder according to any one of the preceding Claims and wherein the further transport means comprises a rotatably drivable first roller having an axis extending in a direction transverse to the feed direction and a rotatably mounted further roller rotatable about an axis parallel to the axis of the first roller and arranged above the first roller, wherein the sheet fed from the pile can be grasped by its front edge between the first and further rollers and transported further.

27. Sheet feeder according to Claim 26, wherein the first roller is constituted by one or several feed rollers of small diameter which are rotatably arranged near the front edge of the sheet pile in the sheet feeder, and wherein one or more endless drive belts are guided about the feed roller(s), which belts extend somewhat in the feed direction from the feed rollers and pass round further feed rollers arranged at a distance from the first feed rollers.

28. Sheet feeder according to Claim 27, wherein a third roller or set of rollers is arranged in the region below and between the first and further feed roller(s) and the drive belts run in an essentially triangular shape around the three rollers or sets of rollers.

29. Sheet feeder according to Claim 28, wherein the third roller or set of rollers is constructed as a tensioning roller or set of rollers.

30. Sheet feeder according to any one Claims 26 to 29 1 1) and including means for driving the first feed roller or rollers and wherein the remaining rollers are mounted in freely rotatable fashion.

31. Sheet feeder according to any one of Claims 26 to 30 wherein the further roller or rollers arranged above the feed roller(s) are mounted vertically movably and the sheet feeder includes means for lifting and lowering the further roller(s) in the working rhythm of the sheet processing machine.

32. Sheet feeder according to any one of Claims 26 to 31 wherein the further roller(s) have a substantially larger diameter than the feed roller(s).

33. Sheet feeder according to any one of Claims 27 to 32 and including two or more feed rollers arranged at a distance from one another and a drive belt guided around each feed roller.

34. Sheet feeder according to Claim 33, wherein the distance between two feed rollers is smaller than the narrowest width of the sheets to be processed.

35. Sheet feeder according to Claim 33, wherein the feed rollers are rotatably mounted on a common axle.

36. Sheet feeder according to Claim 30 and including, located between the feed rollers and/or adjacent the outermost feed rollers, a sheet flap, means for driving the sheet flap swivellably about a swivel axis in time with the rhythm of the sheet processing machine between a vertically upwardly directed position in which it lies against the front edge of the sheet pile and a position inclined in the feed direction of the sheets.

37. Sheet feeder according to any one of the preceding Claims and including located between the catch hooks and/or the feed rollers of small diameter one or more sheet guide devices which extend substantially from the front side.of the sheet pile.towards the top surface of the first roller(s) or of the feed.roller(s).

38. Sheet feeder according to Claim 37, wherein the sheet guide devices have several guide fingers arranged at a distance from one another and directed towards the first roller(s) or towards the feed roller(s).

39. Sheet feeder according to Claim 38, wherein the guide fingers are directed at an angle with respect to the feed direction inclined towards that side edge of the sheet feeder relative to which the respective guide finger is closest.

40. Sheet feeder according to Claim 37, wherein the of the sheet guide devices nearest to the sheet pile are arranged below the level of the uppermost sheet of the sheet pile and that the other ends directed in the feed direction are located substantially at the height at the top of the first roller(s) or of the feed roller(s).

42. A sheet feeder substantially as described herein and with reference to Figures 1 to 4.

42. A sheet feeder substantially as described herein and with reference to Figure 5.

43. A sheet feeder substantially as described herein and 27 - with reference to Figures 6 to 8.

44. A sheet feeder substantially as described herein and with reference to Figures 9 to 12.