Printing – Rolling contact machines – Rotary
Reexamination Certificate
2002-07-30
2004-05-25
Eickholt, Eugene H. (Department: 2854)
Printing
Rolling contact machines
Rotary
C101S483000, C101S409000, C101S183000, C271S276000, C271S277000
Reexamination Certificate
active
06739252
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method and apparatus for reversing sheet material in sheet-processing machines, such as sheet-fed printing presses, having a plurality of printing units disposed one behind another.
German Patent DE 26 33 183 C, corresponding to U.S. Pat. No. 4,165,689 to Giuiuzza, relates to an apparatus for reversing sheets in a multicolor rotary offset printing press. Such a press includes at least two printing units each having a plate cylinder, a transfer cylinder, and an impression cylinder, which are coupled together in terms of drive through circulating transmission elements. A reversing device associated with the transfer elements is provided, which includes a reversing cylinder having a gripper.
The gripper is driven and disposed such that the sheets that have already been printed on one side are gripped after they have passed a transfer cylinder and the sheets have been removed completely from a transfer device resting on the cylinder. The sheets printed on one side are gripped by a reversal mechanism, which acts at the trailing edge of the sheets, which, until this point, have still been held at the leading edge by the gripper of the reversing cylinder. As a result, these sheets are fed to the gripper of the transfer device again with the direction of advance reversed by a separate apparatus that can be configured as a swing gripper or as a table to which vacuum is applied.
German Published, Non-Prosecuted Patent Application DE 39 03 093 A1 discloses a sheet-reversing apparatus. According to such a solution of a sheet-reversing apparatus for in-line rotary printing presses, the impression cylinders of successive printing units are connected by at least one transfer drum. A storage drum is disposed downstream of a transfer drum, parallel to the recto printing sheet guidance. The sheet-reversing apparatus can be uncoupled from the rectoprint sheet guide cylinders during recto printing operation. Provided on a sheet-reversing apparatus is a format adjustment, which can be adjusted independently of the cylinders carrying sheets in recto printing.
German Published, Non-Prosecuted Patent Application DE 198 33 903 A1, corresponding to U.S. Pat. No. 6,401,610 to Becker et al., relates to a method for the transfer of a sheet trailing edge from an upstream cylinder of a sheet-fed rotary printing press. According to such a method for the transfer of the sheet trailing edge from a cylinder and its transfer to a gripper system of a reversing drum, a suction gripper is guided initially along the periphery of the cylinder until the suction gripper has securely gripped the sheet trailing edge. The trailing edge is then guided tangentially to the cylinder cover of the upstream cylinder into the periphery of the reversing drum, the sheet being tautened and end-compressed along a tangent to the cylinder. The sheet is then transferred under no tension to the gripper system of the reversing drum. A gear device used for such a purpose includes three drive systems that are coupled to one another and are controlled through stationary cams.
In single-drum reversing systems, in which the impression cylinder located upstream of the reversing drum acts as a storage drum in a perfecting mode (also referred to as a recto/verso mode or reversing mode), the storage length is not sufficient for a large-format sheet. Attempts have been made to peel the sheet material off the impression cylinder, according to a solution disclosed by German Published, Non-Prosecuted Patent Application DE 44 24 968, but problems have occurred with regard to in-register transfer of the sheet trailing edge. By placing pressure elements, attempts have been made to press onto the sheet, but this, in turn, entails problems with regard to smearing in the case of those sheets that do not have any print-free areas.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and apparatus for reversing sheet material in sheet-processing machines that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that turns large-format sheet material in register when the overall space is limited.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for reversing sheet material having edges in a sheet-processing machine having at least two printing units, including the steps of providing a gripper system on a reversing drum associated with at least one of the printing units, providing an impression cylinder operable as a storage drum in a recto/verso mode, the storage drum having a recto printing side and an impression-cylinder-side gripper system, the storage drum and the reversing drum defining a transfer centerline therebetween, and gripping, in the recto/verso mode, one of the edges of the sheet material at an angle before the transfer centerline with a holding and lifting system disposed parallel to the recto printing side of the storage drum before an edge of the sheet material fixed to the storage drum is released by the impression-cylinder-side gripper system.
With the objects of the invention in view, there is also provided a method for reversing sheet material having edges in a sheet-processing machine having at least two printing units, including the steps of providing a gripper system on a reversing drum associated with at least one of the printing units, providing an impression cylinder operable as a storage drum in a recto/verso mode, the storage drum having a recto printing side and an impression-cylinder-side gripper system, the storage drum and the reversing drum defining a transfer centerline therebetween, gripping a given edge of the sheet material with the impression-cylinder-side gripper system, and gripping, in the recto/verso mode, a given edge of the sheet material at an angle before the transfer centerline with a holding and lifting system disposed parallel to the recto printing side of the storage drum before the given edge is released by the impression-cylinder-side gripper system.
The advantages of the solution according to the invention can primarily be seen in the fact that, as a result of the early gripping of the sheet material at one edge before it passes the transfer centerline, early opening of the holding systems of the storage drum that grip the sheet material can be brought about. Such a configuration ensures that sheet material needing a large storage length can assume a substantially extended position underneath the storage drum. This prevents the sheet material from being able to run into the pocket area between storage drum and the transfer cylinder upstream of the latter and being damaged.
The holding and lifting system disposed outside the reversing drum tensions the sheet before it is turned and transfers the sheet to the gripper system of the reversing drum. The configuration ensures that the sheet material is transferred in register to the reversing drum so that both sides of the sheet material can be printed with the same quality. The in-register gripping of the sheet trailing edge of the sheet material is ensured by the fact that, at the time that it is gripped, a frictional or positive connection between the holding and lifting system and the outer surface of the impression cylinder serving as a storage drum is produced.
In a development of the idea on which the invention is based, the trailing edge of the sheet material is attracted by suction to the circumference of the storage drum before reaching the transfer centerline and is tensioned in the circumferential direction. Gripping the sheet trailing edge of the sheet material in the tensioned state of the sheet material ensures its in-register gripping and transfer to the reversing drum downstream of the storage drum. In accordance with the method proposed by the invention, the edge of the sheet material fixed to the circumference of the storage drum is released before it reaches a pocket between the storage drum and a transfer
Frankenberger Eckart
Helmstädter Karl-Heinz
Hiltwein Hans-Peter
Stephan Günter
Eickholt Eugene H.
Heidelberger Druckmaschinen AG
Mayback Gregory L.
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