Abstract:
A gripper control gearing has a reduced complexity for providing adjustments. Stops are provided on a reversing drum for a slide that supports cam rollers. Pinions with a helical toothing are arranged on a gripper shaft and on a gripper tube. Such a simplified arrangement allows for easier adjustments of the gripper system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2011 102 444.5, filed May 24, 2011; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a device for conveying a sheet through a printing press. 
         [0003]    Published, non-prosecuted German patent application DE 10 2005 045 287 A1, corresponding to U.S. Pat. No. 7,412,925, discloses a perfecting press in which a reversing device including a reversing drum and a storage drum is provided between two printing units. The reversing drum includes pincer-type grippers with gripper fingers disposed on a gripper shaft and on a coaxial gripper tube. The gripper fingers are pivotable independently of each other about the axis of the gripper shaft and of the coaxial gripper tube, respectively, in order to open and close to take over a sheet from the storage drum and to transfer the sheet to a downstream impression cylinder. To initiate the opening or closing of the gripper fingers and the pivoting of the gripper fingers, a respective pinion is provided on the end of the gripper shaft and of the gripper tube. A toothed segment engages in the pinion. The respective toothed segment is pivotably mounted to a slide. A cam roller supported on a track of a control cam that is fixed to a frame is provided on each toothed segment. Separate control cams are provided for the straight-printing mode and for the perfecting mode. To switch between modes of operation, the slide is displaced in the axial direction of the reversing drum to cause the respective cam roller to be supported on the track of a desired control cam. When the slide is displaced, the toothed segments remain in engagement with the pinions, which have a straight toothing. The displacement of the slide is predetermined by the geometry of an eccentric that is used to make the adjustment by hand. 
         [0004]    To ensure that the gripper fingers assume a desired pivoting position for receiving or transferring a sheet, the control cams and the stops of the gripper fingers are adjustable. A rotation of a control cam about the axis of rotation of the reversing drum causes a phase shift of the angular position of the reversing drum for opening or closing the gripper fingers. Stop screws of the gripper fingers are adjusted to adapt the gripper opening width so that the angular range in which the gripper fingers are closed is adjustable. In addition, the phasing of the gripper shaft or gripper tube can be adjusted based on the tooth distribution of the pinion in order to adjust the height of the gripper surface of the gripper fingers relative to the sheet during a takeover or transfer. 
         [0005]    A disadvantage of the known designs of a reversing drum that has the adjustment options described above is that the angular positions and gripper heights are not adjustable independently of each other in the two modes of operation. Gripper height errors and angular position errors that are due to manufacturing tolerances of the components or due to a deformation of the components can be corrected in the straight printing mode; yet this causes the angular positions and gripper heights to change in the perfecting mode, too. It is possible to average the aforementioned errors in both modes of operation. 
         [0006]    A disadvantage of correcting the gripper height by offsetting the position of the pinion on the gripper shaft or gripper tube is that it involves changing and readjusting the angular position of the gripper fingers. 
         [0007]    Due to the fact that an adjustment of the gripper in one mode has an influence on the gripper adjustment in the other mode and that an adjustment of the angular position has an influence on the gripper height and vice versa, any adjustment is complex and time consuming. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the invention is to develop a device for conveying a sheet through a printing press that provides ways to reduce the complexity involved in an adjustment to a gripper control gearing of a reversing drum and to reduce deviations of the movement of gripper fingers from a desired movement. 
         [0009]    With the foregoing and other objects in view there is provided, in accordance with the invention a device for conveying a sheet through a printing press. The device contains a transfer drum having a drum body, a gripper system disposed on the transfer drum and includes gripper fingers that cooperate in pairs, and a gear train for moving the gripper system. The gear train has at least one pinion with a helical toothing. A slide is displaceable on the drum body in a axial direction of the transfer drum into two stop positions. Elements for controlling a movement of the gripper fingers are provided. The elements are disposed on the slide to switch between a straight-printing mode and a perfecting mode. At least one stop is adjustable to determine the stop positions of the slide. 
         [0010]    In accordance with the invention, adjustable stops for a slide displaceable in the axial direction of a reversing drum are provided on the reversing drum. The slide supports at least one roller lever including cam rollers interacting with control cams for moving grippers of a pincer-type gripper system. A toothed segment engaging in a pinion with a helical toothing is provided on the roller lever. 
         [0011]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0012]    Although the invention is illustrated and described herein as embodied in a device for conveying a sheet through a printing press, 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. 
         [0013]    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 THE SEVERAL VIEWS OF THE DRAWING 
         [0014]      FIG. 1  is a diagrammatic, side view of a reversing device in a sheet-fed printing press, including a storage drum and a reversing drum illustrated in the straight printing mode according to the invention; 
           [0015]      FIG. 2  is a detailed, side view of a pincer-type gripper system; 
           [0016]      FIG. 3  is a side view of the reversing drum shown in  FIG. 1  in a perfecting mode; 
           [0017]      FIG. 4  is a front view of the reversing drum; 
           [0018]      FIG. 5  is a side view of a sheet transfer between the storage drum and the reversing drum in the straight-printing mode; 
           [0019]      FIG. 6  is a side view of a sheet transfer between the storage drum and the reversing drum in the perfecting mode; 
           [0020]      FIG. 7  is a side view of a sheet transfer between the reversing drum and the impression cylinder in the straight-printing mode and in the perfecting mode; 
           [0021]      FIG. 8  is a side view of a gripper height adjustment in the straight-printing mode; 
           [0022]      FIG. 9  is a side view of a gripper height adjustment in the perfecting mode; 
           [0023]      FIG. 10  is a front view of the reversing drum with a divided slide; and 
           [0024]      FIG. 11  is a table indicating the various adjustment options. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a storage drum  1 , a reversing drum  2 , and an impression cylinder  3  in a sheet-fed printing press in a straight-printing mode. The storage drum  1  has two segments  5 ,  6  adjusted to accommodate the length of a sheet  4  and having lateral surfaces  7 ,  8  shaped like a cylinder shell, and two gaps  9 ,  10 . Mechanical gripper systems  11 ,  12  for holding leading edges of sheets and suction gripper systems  13 ,  14  for holding trailing edges of sheets are located in the gaps  9 ,  10 . The reversing drum  2  is provided with a pincer-type gripper system  15 . As shown in  FIG. 2 , gripper fingers  16 ,  17  of the pincer-type gripper system  15  are fixed to a gripper tube  18  and to a coaxial gripper shaft  19 , respectively. A further mechanical gripper system  21  for gripping the leading edge of a sheet  4  is provided in a gap  20  formed in the impression cylinder  3 . 
         [0026]    The storage drum  1 , the reversing drum  2 , and the impression cylinder  3  are supported in side walls of the printing press and are driven in the direction indicated by arrows  22  in synchronism with each other. While being conveyed by the storage drum  1 , a sheet  4  rests on a revolving contour  23  that has an effective diameter D 1 , which is twice the effective diameter D 2  during transport by the reversing drum  2  or the impression cylinder  3 . In the rotational positions of the storage drum  1  and of the reversing drum  2  shown in  FIG. 1 , a sheet  4  is transferred from the grippers of gripper system  11  into the pincer grippers  16 ,  17  of the pincer-type gripper system  15 . Subsequently, the pincer grippers  16 ,  17  carry out a pivoting movement about a common axis  24  of gripper tube  18  and gripper shaft  19 . The dashed lines in  FIG. 1  illustrate the pivoting and opening positions of the pincer grippers  16 ,  17  for various rotational positions of the reversing drum  2 . 
         [0027]    As shown in more detail in  FIG. 2 , the pincer grippers  16 ,  17  are open against the force of a spring  25  in order to receive the sheet  4 . The spring is supported between a first protrusion  26  formed on a gripper housing  27  that supports a pincer gripper  16 , and a second protrusion  28  formed on the gripper tube  18 . The opening width of the pincer grippers  16 ,  17  is determined by a stop  29  on the gripper shaft  19  and an adjustable stop screw  30  provided on the gripper tube  18 . 
         [0028]    In  FIG. 3 , the storage drum  1 , the reversing drum  2 , and the impression cylinder  3  are shown in a perfecting mode. In the illustrated rotational position of the reversing drum  2 , the pincer grippers  16 ,  17  take over a trailing edge of a sheet  4  from the suction elements of a suction gripper system  13 . As the reversing drum  2  continues to rotate, the movement of the sheet  4  is reversed and the edge that was the trailing edge on the storage drum  1  becomes the leading edge. The reversed sheet  4  is transferred to the grippers of the gripper system  21  of the impression cylinder  3  to be printed. 
         [0029]      FIG. 4  is a front view of the reversing drum. The reversing drum consists of a drum body  31  with axial journals  32 ,  33  received in bearings  34 ,  35  provided in side walls  36 ,  37 . Vertical bearings  38 . 1  to  38 . 6  are provided on the drum body  31  for supporting the gripper tube  18  and the gripper shaft  19  supported in the gripper tube  18 , respectively. A respective pinion  39 ,  40  with helical toothing is located on a respective end of the gripper tube  18  and the gripper shaft  19 . On the drum body  31  side facing away from the gripper tube  18  and the gripper shaft  19 , a slide  41  displaceable in the direction of the axis of rotation  42  of the reversing drum  2  is provided. Toothed segments  43 ,  44  are pivotably supported on both sides of the slide  41 . The pivot axes  45 ,  46  of the toothed segments  43 ,  44  are parallel to an axis of rotation  42 . The teeth of the toothed segments  43 ,  44  engage in the pinions  39 ,  40 . Cam rollers  47 ,  48  are arranged on the toothed segments  43 ,  44  so as to be supported on tracks formed on cams  49 ,  50  and  51 ,  52 , respectively, which are fixed to a frame. 
         [0030]    The slide  41  has two stop surfaces  53 ,  54 , which interact with two adjustable stop screws  55 ,  56  provided on the drum body  31 . Depending on whether the slide  41  is pushed against stop screw  55  or stop screw  56 , the respective cam roller  47 ,  48  rests on the track of cams  49 ,  50  for the straight-printing mode or of cams  51 ,  52  for the perfecting mode. 
         [0031]    An adjustment of the stop screws  55 ,  56  limits the displacement path of the slide  41  in the direction of axis  42 . When the slide  41  is moved, the teeth of the toothed segments  43 ,  44  are continuously in engagement with the pinions  39 ,  40 . Due to the helical toothing of the pinions  39 ,  40 , the gripper tube  18  and the gripper shaft  19  pivot as the slide  41  is displaced. The pivoting of the gripper tube  18  and of the gripper shaft  19  upon a changeover between modes is compensated by an appropriate design of the cams  49  and  52  to ensure that the desired gripper movement is implemented both in the straight-printing mode and in the perfecting mode. Using the stop screws  55 ,  56 , it is possible to adjust the gripper heights h independently for both modes of operation by adjusting the end positions of the slide  41 . 
         [0032]    Stop screw  55  limits the end position of the slide  41  in the straight-printing mode. As shown in more detail in  FIG. 5 , the stop screw  55  can be used to adjust gripper height h schl,SD , which is required for a defined rotational position Ø schl,SD , to take a sheet  4  from the grippers of the gripper system  11 ,  12  of the storage drum  1 . This gripper height h schl , so is determined by the spacing between the sheet support surfaces  57  of gripper pads  58  of a the gripper system  11 ,  12  and the gripping surfaces  59  of gripper fingers  17 . The angle Ø schl , so for the rotational position of the reversing drum  2  is given as the angle through which the gripper shaft  19  is rotated about axis  42  relative to a horizontal plane  60 . 
         [0033]    The stop screw  56  limits the end position of the slide  41  in the perfecting mode. As shown in  FIG. 6 , the stop screw  56  is used to adjust the gripper height h schl,WD  at the moment of transfer of a sheet  4  from suction elements  61  of a suction gripper system  13 ,  14 . At the moment of transfer of the sheet  4 , the reversing drum  2  is in a rotational position Ø schl,WD . The gripper height h schl, WD  is determined by the spacing between the suction surfaces  62  of the suction elements  61  and the gripping surface  59  of the gripper fingers  17 . 
         [0034]    As shown in  FIG. 7 , both in the straight-printing mode and in the perfecting mode, at the moment of transfer of a sheet  4  to the grippers of the gripper system  21  of the impression cylinder  3  the reversing drum  2  reaches a rotational position Ø oeff,SD=Øoeff,WD . In this rotational position, the gripper height in the straight-printing mode is h oeff,SD  and the gripper height in the perfecting mode is h oeff, WD , with h oeff,SD  h oeff, WD . 
         [0035]      FIGS. 8 and 9  illustrate adjustments of the gripper height in the straight printing mode and in the perfecting mode by the stop screws  55  and  56 . When the3 stop screw  55  is adjusted in a direction −A or +A for a straight-printing operation, the gripper fingers  16 ,  17  rotate about axis  24  through an angular range Δα due to the helical toothing of the pinions  39 ,  40 . As long as there is no adjustment of the stop screw  56 , the gripper movement in the perfecting mode remains unaffected. 
         [0036]    As shown in  FIG. 9 , by an adjustment of the stop screw  56 , the gripper fingers  16 ,  17  can be adjusted in terms of their height over an angular range Δβ for a perfecting operation without affecting the adjustment for the straight-printing mode. 
         [0037]    In any case, an adjustment of the stop screws  55 ,  56  to correct gripper height errors does not have any influence on the opening and closing angle of the gripper fingers  16 ,  17 . 
         [0038]      FIG. 10  illustrates an exemplary embodiment including a divided slide  41 . 1 ,  41 . 2  of the reversing drum  2  configured as shown in  FIG. 4 . The illustrated embodiment provides improved ways of adjusting the closing and opening angles of the gripper fingers  16 ,  17  in addition to an adjustment of the gripper height independently of the mode of operation. As described with reference to  FIG. 4 , the pinions  39 ,  40  have a helical toothing. Thus during a changeover between modes, an axial displacement of the slide parts  41 . 1 ,  41 . 2  with the toothed segments  43 ,  44  supported thereon causes the gripper shaft  19  and the gripper tube  18  to rotate. The toothed segment  43  that is supported on slide part  41 . 1  is used to drive the gripper shaft  19 . The toothed segment  44  that is supported on slide part  41 . 2  drives the gripper tube  18 . The slide parts  41 . 1 ,  41 . 2  are coupled by a spring element  63 . The end positions of slide  41 . 1  are defined by adjustable stop screws  55 ,  64 . Adjustable end screws  56 ,  65  limit the displacement path of the slide part  41 . 2  in the axial direction  42 . Different settings of the stop screws  55 ,  64  and  56 ,  65 , respectively, result in different displacement paths of the slide parts  41 . 1 ,  41 . 2 . These different displacement paths are compensated by the spring element  63 . If the slide part  41 . 1  is connected to an actuating drive for axial displacement, the adjustment paths and stop positions are designed in such a way that slide part  41 . 2  always contacts stop screw  65  when the slide part  41 . 1  is in the straight-printing position against stop screw  55 . If slide part  41 . 1  is in the perfecting position against stop screw  64 , slide part  41 . 2  is in contact with stop screw  56 . Stop screws  64 ,  65  interact with stop surfaces  66 ,  67  provided on the drum body  31 . 
         [0039]    As indicated by the table of  FIG. 11 , the gripper heights h of the gripper fingers  16 ,  17  and the angular ranges Ø oeff-Ø   schl  with closed gripper fingers  16 ,  17  can be adjusted by adjusting the stop screws  55 ,  56 ,  64 ,  65 . As becomes apparent from the table, the stop screws  55 ,  65  need to be adjusted by the same amount and in the same axial direction to adjust the gripper heights in the straight-printing mode. To adjust the gripper heights in the perfecting mode, it is necessary to adjust the stop screws  56 ,  64  by the same amount and in the same axial direction. If only the stop screw  56  is adjusted, the angular range with the closed gripper fingers  16 ,  17  can be adjusted in the perfecting mode. If only the stop screw  65  is adjusted, the adjustment only has an effect on the angular range with closed gripper fingers  16 ,  17  in the straight-printing mode. The stop positions of the slide parts  41 . 1 ,  41 . 2 , which are indicated by letters A to D in  FIGS. 10 and 11 , are defined by stop screws  55 ,  56 ,  64 ,  65 . 
         [0040]    Due to the helical toothing of the pinions  39 ,  40 , an adjustment of the stop screw  55  results in an adjustment of the gripper shaft  19  about axis  24  in the straight printing mode without any influence on the rotational position of the gripper tube  18  about axis  24 . An adjustment of stop C causes an adjustment of the gripper shaft  19  in the perfecting mode without any influence on the gripper tube  18 . When the stop screw  65  is adjusted, the gripper tube  18  is adjusted in the straight-printing mode without any influence on gripper shaft  19 . When the stop position B with the stop screw  56  is modified, the rotational position of the gripper tube  18  about axis  24  is adjusted in the perfecting mode without any influence on the gripper shaft  19 .