Sheet feeding or delivering – Feeding – By means to convey sheet
Reexamination Certificate
1999-02-03
2001-07-03
Jillions, John M. (Department: 3653)
Sheet feeding or delivering
Feeding
By means to convey sheet
C101S410000
Reexamination Certificate
active
06254089
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a suction gripper for transferring the trailing edge of a sheet in a turning device of a sheet-fed rotary printing machine.
Published, Non-Prosecuted German Patent Application DE 38 29 626 A discloses a sheet-fed rotary printing machine having a turning device in which, during perfecting operation, a suction gripper is pivoted out of a periphery of a cylinder disposed downstream of a back-pressure cylinder toward the circumferential surface of the back-pressure cylinder. There, it grips the trailing edge of the sheet to be turned and, before passing the gripper center line in between the two cylinders, guides the trailing edge into the periphery of the downstream cylinder. Because of the rigid and stiff configuration of the suction gripper and of the fixedly predefined pivoting path, during the processing of printed materials of different thicknesses, the result is sharply varying pressure forces with which the suction head of the suction gripper is pressed against the paper and, respectively, the circumferential surface of the back-pressure cylinder when picking up the sheet trailing edge by suction. Thus, in the case of very thin papers, such as bible paper, there is the risk that the suction head of the suction gripper will not touch the surface of the sheet at all. This can result in relatively large fluctuations in the location of the trailing edge of the sheet in relation to the suction gripper, and lead to register errors when transferring the sheet trailing edge to subsequent gripper devices. However, during the processing of thick printed materials, high mechanical forces are exerted on the trailing edge of the sheet, on the suction gripper as such and on the gear mechanism actuating the suction gripper. As a result of which pressure points may form on the sheet and the suction gripper or the gear mechanism is subjected to high mechanical stress and hence to high wear.
Published, Non-Prosecuted German Patent Application DE 41 06 703 A1 discloses a swinging sucker system, which can be pivoted about a first rocker shaft and, in perfecting operation, grips the trailing edge of a sheet to be transferred in the region of a gripper center line between upstream and downstream sheet-conveying cylinders. In order to adapt to different printed material thicknesses, the swinging sucker system is mounted on a rocker, which can be pivoted by an eccentric about a second rocker shaft. In order to limit the maximum adjustment travel of the eccentric and hence the maximum printed material thickness to be printed, the rocker is provided with a stop. The stop, in the case of maximum sheet thicknesses to be processed, rests on an associated stop on the cylinder body of the downstream sheet-conveying cylinder. Also disposed between the rocker and the cylinder body is a compression spring which, in order to produce a counterforce when the eccentric is rotated in the direction of the maximum printed material thickness, exerts a counterforce on the rocker. Apart from the fact that the device described is mechanically complicated to produce and contains numerous moving parts, it does not permit any automatic adaptation to different printed material thicknesses.
German Democratic Republic Patent No. 142 953 discloses a sucker in a turning device of a sheet-fed rotary printing machine, which has a suction head which is produced from flexible material and automatically adapts to printed materials of different thicknesses. Because of the flexible configuration of the suction head, in the event of the sheet being tautened before the transfer to a downstream gripper device, positional displacements of the sheet occur, which rule out the in-register transfer of the sheet trailing edge. Furthermore, the suction head made of flexible material that is described in the document has the disadvantage that its elastic properties can change sharply over the course of time and that, in the case of processing very thick sheets, for example those with a thickness in the region of 1 mm, very high forces nevertheless act on the sucker as such. These forces being brought about by the fact that it is not just the thin-walled lip of the sucker but the entire rubber body of the same that is compressed. This contradicts the requirement to configure the rubber lip to be as thin-walled as possible in the case of processing very thin sheets, in order to rule out the local sucking in and tearing of the paper in the region of the suction heads. The flexible suction heads described therefore constitute only a compromise.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a suction gripper for transferring the trailing edge of a sheet in a turning device of a sheet-fed rotary printing machine which overcomes the above-mentioned disadvantages of the prior art devices of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, in combination with a sheet-fed rotary printing machine having an upstream sheet-conveying cylinder and a turning device, a suction gripper for transferring a trailing edge of a sheet guided on the upstream sheet-conveying cylinder to the turning device having a downstream sheet-conveying cylinder with a circumferential surface, the suction gripper including: a holding arm to be extended out of the circumferential surface of the downstream sheet-conveying cylinder; a spring; and a suction head movably connected to the holding arm via the spring.
The invention achieves the object of providing a suction gripper for transferring the trailing edge of a sheet to be turned in a turning device of a sheet-fed rotary printing machine which permits automatic adaptation to the widest possible range of printed material thicknesses. In addition, the invention ensures extremely precise transfer of the sheet trailing edge to downstream gripper devices. Furthermore, it is an object of the present invention to provide a suction gripper which has a comparatively low weight, which has only a comparatively small number of mechanically moving parts and which needs virtually no maintenance and adjustment work.
In accordance with an added feature of the invention, there is a stop for limiting a movement of the suction head in a direction of a circumferential surface of the upstream sheet-conveying cylinder.
In accordance with an additional feature of the invention, the spring is a leaf spring having a first end connected to the holding arm and a second end connected to the suction head.
In accordance with another feature of the invention, the leaf spring has a threaded hole formed therein close to the suction head, and the stop is supported on the holding arm and has an adjusting screw to be screwed into the threaded hole of the leaf spring.
In accordance with a further added invention, the holding arm has a guide formed thereon, the suction head is accommodated in the guide and the guide permits a movement of the suction head in a direction running substantially perpendicular to the holding arm.
In accordance with a further additional feature of the invention, the spring is at least one compression spring accommodated in the guide and has a first end supported on the holding arm and a second end supported on the suction head.
In accordance with another added feature of the invention, the holding arm has an opening formed therein, the stop has a nut and a pin element with a threaded section springing out of the suction head and the threaded section extending through the opening formed in the holding arm, and the nut element is screwed onto the threaded section.
In accordance with an added feature of the invention, the holding arm has a greater stiffness in a sheet transport direction than in a direction towards a circumferential surface of the upstream sheet-conveying cylinder.
In accordance with an additional feature of the invention, the holding arm has a greater stiffness in a direction transverse to a sheet transport direction than in a direction towards
Becker Willi
Fricke Andreas
Greenberg Laurence A.
Heidelberger Druckmaschinen Aktiengesellschaft
Jillions John M.
Lerner Herbert L.
Stemer Werner H.
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