Patent Publication Number: US-7594658-B2

Title: Device for conveying a sheet through a typographic machine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2006 054 825.6, filed Nov. 21, 2006; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a device for conveying a sheet through a typographic or printing technology machine. The device includes a rotatable cylinder having at least one gap in which grippers for holding the leading, front margin of the sheet are disposed and having at least one carrying element that forms a cylinder-jacket-shaped sheet support surface. A chain conveyor has grippers that are fastened to endless chains placed over rotatable sprockets and are provided for holding and taking over a leading margin of the sheet from the cylinder and for holding the trailing, rear margin of the sheet. Coaxially revolving support elements for the sheet are disposed between the sprockets associated with the cylinder and are in rolling contact with the sheet resting on the support surface. Coaxially revolving auxiliary grippers provided for holding the trailing margin of the sheet are disposed between the sprockets associated with the cylinder. An actuating device opens and closes the grippers and a drive is provided for the cylinder and the sprockets. 
     German Published, Non-Prosecuted Patent Application DE 100 14 417 A1, corresponding to U.S. Pat. No. 6,578,846, describes a device for transporting a sheet in a rotary printing press. In the device described therein, a sheet is transferred from a cylinder to a chain gripper system. Grippers hold the leading and trailing edges of the sheet in the chain gripper system. The trailing-edge grippers take over the sheet in the outlet wedge between the support surfaces revolving with sprockets and the cylinder jacket surface. The sheet is held by suction grippers that likewise revolve with the sprockets, until the sheet is transferred to the trailing-edge grippers. Gripper seats of the trailing-edge grippers are located above a path that is described by the sheet held on the jacket surface of the cylinder. Appropriate cutouts are provided in the jacket surface of the cylinder to allow the trailing-edge grippers to pass the jacket surface of the cylinder without collision. That complicates the manufacturing process of the cylinders. 
     In a device described in German Published, Non-Prosecuted Patent Application DE 103 58 171 A1, corresponding to U.S. Pat. No. 7,234,395, two revolving chain gripper systems are provided for conveying a sheet at its leading and trailing edges from an impression cylinder to a stack. The chain gripper systems carry gripper bars with a plurality of grippers for the leading and trailing edges. A distance between the gripper bars for the trailing edge and the gripper bars for the leading edge is adjustable to accommodate different sheet lengths. During sheet transfer, the leading-edge grippers dip into a respective gap of the impression cylinder. As the trailing-edge grippers pass the closed jacket surface of the impression cylinder, the trailing-edge grippers are open to such an extent that they do not collide with the jacket surface. A cam gearing and a lever gearing are provided to open the trailing-edge grippers. High torques are transmitted to achieve an opening angle of approximately 90 degrees. The high torques cause a high degree of wear at the gearing elements and thus limit the useful life and component strength of the gear mechanisms. 
     BRIEF SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a device for conveying a sheet through a typographic machine, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and in which a sheet is transferred from a cylinder to a trailing-edge gripper system with increased reliability. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, a device for conveying a sheet through a typographic machine. The device comprises a rotatable cylinder having at least one gap formed therein, grippers disposed in the at least one gap for holding the leading, front margin of the sheet, and at least one carrying element forming a cylinder-jacket-shaped sheet support surface having a revolution contour. A chain conveyor has rotatable sprockets, endless chains placed over the rotatable sprockets, and grippers fastened to the endless chains for holding and taking over the leading margin of the sheet from the cylinder and for holding the trailing, rear margin of the sheet. Coaxially revolving support elements for the sheet are disposed between the sprockets associated with the cylinder and are in rolling contact with the sheet resting on the support surface. Coaxially revolving auxiliary grippers are disposed between the sprockets associated with the cylinder, for holding the trailing margin of the sheet. An actuating device is provided for opening and closing the grippers. A drive is provided for the cylinder and the sprockets. The grippers for the trailing margin are guided in a closed state along a path outside the revolution contour of the support surface, while passing the cylinder. The grippers for the trailing margin are guided in an opened state along the path to a radial level of the trailing margin held in the auxiliary grippers, after passing the cylinder. 
     Therefore, in accordance with the invention, trailing-edge grippers disposed on a chain gripper system are in a closed state when they are guided past a cylinder having at least one closed or continuous cylinder-jacket-shaped sheet support surface. As the trailing-edge grippers pass the cylinder, the trailing-edge grippers are guided on a path that is outside the revolution contour of the sheet support surface, so that a collision between the trailing-edge grippers and cylinder components that form the sheet support surface is avoided. Once the trailing-edge grippers have passed the cylinder, they are opened and moved radially outward so that a trailing sheet margin temporarily held by auxiliary grippers is captured by the trailing-edge grippers. After closing, the trailing-edge grippers substantially follow the path of the leading-edge grippers. The trailing-edge grippers only open as far as necessary for the trailing sheet margin to be inserted. The torques required for opening and closing the trailing-edge grippers are low so that only a low degree of wear occurs at the components of the gear mechanisms for opening and closing. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a device for conveying a sheet through a typographic machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic, longitudinal-sectional view of a delivery of a printing press including chain gripper systems; and 
         FIGS. 2-5  are fragmentary, side-elevational views of different phases of a transfer of a sheet at a trailing sheet margin. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen the last printing unit  1  of a sheet-fed printing press with a downstream delivery  2 . The printing unit  1  includes a sheet transport drum  3 , an impression cylinder  4 , a transfer cylinder  5  and a plate cylinder  6 . Rollers of an inking unit  7  and of a dampening unit  8  are associated with the plate cylinder  6 . The delivery  2  includes chain gripper systems with leading-edge gripper systems  9 . 1  to  9 . 7  and trailing-edge gripper systems  10 . 1  to  10 . 7 , which are mounted on gripper bars. The gripper bars are connected by endless chains guided over sprockets  11 ,  12  and chain paths  13 . At the end of lower strands or runs of the chain paths  13 , as viewed in a conveying direction  14 , there is a stack table  15  that carries a stack  16 . The stack table  16  can be lowered through the use of a chain transmission  17  in a manner corresponding to the progress of the production. 
     The sheet transport drum  3  conveys sheets  18  from the previous printing unit to the impression cylinder  4 . The sheets  18  are held on the impression cylinder  4  in grippers  19 . 1 ,  19 . 2  and guided through a printing nip  20  formed between the transfer cylinder  5  and the impression cylinder  4 . The dampening unit  8  and the inking unit  7  are used to ink a printing plate  21  provided on the plate cylinder  6  in accordance with an image to be printed. The transfer cylinder  5  has a rubber-elastic cover  22 , which transfers the printing ink to the sheet  18  in the printing nip  21 . In the delivery  2 , the leading edges of the sheets  18  are gripped by the leading-edge gripper systems  9  while the trailing margins of the sheets  18  are held by the trailing-edge gripper systems  10 . The gripper systems  9 ,  10  open just before the stack  16  to release a sheet  18  onto the stack  16 . A leading-edge stop  23  limits the movement of the released sheet  18  in the conveying direction  14 . 
     The diameter of the impression cylinder  4  is twice the diameter of the plate cylinder  6 . The impression cylinder  4  has two channels or gaps  24 ,  25  in which the leading-edge gripper systems  19 . 1 ,  19 . 2  are disposed on gripper bars. The gaps  24 ,  25  divide the cylinder-jacket-shaped surface of the impression cylinder  4  into two sheet support surfaces  26 ,  27 . The length of the sheet support surfaces  26 ,  27  in the circumferential direction  28  of the impression cylinder  4  corresponds to the maximum length of a sheet  18  to be conveyed. The impression cylinder  4  and the sprockets  11  are driven in synchronism in the directions of the arrows  28 ,  29 . A pitch diameter d 1  of the sprockets  11  of the chain gripper system for the leading-edge gripper systems  9 . 1 - 9 . 7  and a diameter d 2  of a revolution contour of the sheet support surfaces  26 ,  27 , are approximately equal. A connecting line between axes  31 ,  32  of the impression cylinder  4  and the sprockets  11  forms a line of transfer  33 . 
     When a sheet  18  is transferred from a gripper system  19 . 1 ,  19 . 2  to a gripper system  9 . 1 - 9 . 7 , the gripper closing lines in the revolution contour  30  are parallel with the axes  31 ,  32  and perpendicular to the line of transfer  33 . As the leading-edge gripper systems  9 . 1 - 9 . 7  take over the leading margin of the sheet  18 , they dip into the respective gap  24 ,  25 . 
     The transfer of a trailing margin of a sheet  18  to a gripper system  10 . 1 - 10 . 7  will be explained below with reference to  FIGS. 2-5 : The chains of the trailing-edge gripper systems  10 . 1 - 10 . 7  wrap around a sprocket that has a diameter d 3 &lt;d 1  coaxial with the axis  32 . A gripper bar  34  with a gripper finger  35  and a gripper pad  36  of the trailing-edge gripper system  10 . 1 - 10 . 7  is shown. The gripper finger  35  is disposed on a gripper shaft and is pivotable about an axis  37 . The gripper bar  34  is mounted in joints  38 ,  39  on the chains of the trailing-edge gripper system  10 . 1 - 10 . 7 . Auxiliary suction grippers  40  and lateral-edge support elements  41  revolve around the axis  32  in synchronism with the sprockets  11 . 
     In  FIG. 2 , the auxiliary suction grippers  40  and the gripper bar  34  are located just before the line of transfer  33  as viewed in the revolving direction  29 . The auxiliary suction grippers  40  revolve on the diameter d 1 . In the rotational position shown in  FIG. 2 , the leading sheet margin is held in a leading-edge gripper system  9 . 1 - 9 . 7 , while the trailing sheet margin of the sheet  18  is located in the line of transfer  33 . In this rotational position, the auxiliary suction grippers  40  are activated to hold the trailing sheet margin. The grippers of the trailing-edge gripper bar  34  are in a closed state wherein the gripper fingers  35  rest on the gripper pads  36 . The revolution contour of the gripper fingers  35  is below the diameter d 1 . As the gripper bar  34  moves onward, the closed gripper fingers  35  are guided past the respective sheet support surface  26 ,  27  of the impression cylinder  4 . A stationary cam body  44  defines a guide path  46  for a radial movement of the grinner bar  34 . A cam roller  45  is connected to the grinner bar  34  and is in rolling contact with the stationary cam body  44 . 
     As is shown in  FIG. 3 , the gripper fingers  35  open in the region of the angle of rotation that is beyond the line of transfer  33 . As they open, the gripper fingers  35  are moved radially outward and pivoted backward as viewed in the circumferential direction  29 . Gripper tips  42  are downstream of the trailing edge of the sheet as viewed in the circumferential direction  29 . 
     As the gripper bar  34  moves onward, it is moved in a chain guide on a path  43  that guides the gripper pads  36  and gripper fingers  35  radially outward as is shown in  FIG. 4 . The gripper pads  36  reach the radial level of the auxiliary suction grippers  40 , and the gripper tips  42  of the gripper fingers  35  move in above the trailing margin of the sheet  18 . 
     As the gripper bar  34  moves onward into the rotational position shown in  FIG. 5 , the gripper fingers  35  close and the auxiliary suction grippers  40  are deactivated. From then on, the trailing sheet margin of the sheet  18  is held between the gripper tips  42  and the gripper pads  36  and is conveyed above the stack  16 .