Abstract:
A transfer drum between printing units in a sheet-fed printing press includes gripper systems which can be switched to a desired mode of operation by simple measures and ensure stable and reliable transport of a sheet between printing units when in a respective operating position. A drum body has journals for supporting the drum body in side walls and two gripper systems provided on the drum body. The gripper systems are radially extendable into an operating position depending on a selected mode of operation for printing on only one side or for printing on both sides of the sheet. The gripper systems are disposed diametrically opposite each other relative to an axis of rotation of the drum body and are attached to a support disposed in the drum body to move in radial direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2007 022 131.4, filed May 11, 2007; 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 transfer drum between printing units of a sheet-fed printing press. The transfer drum includes a drum body having journals for supporting the drum body for rotation in side walls. Two gripper systems are provided on the drum body so as to be extendable in radial direction into an operating position, depending on a selection of a mode of operation for printing on only one side of a sheet or of a mode of operation for printing on both sides of a sheet. 
         [0003]    German Published, Non-Prosecuted Patent Application DE 41 18 584 A1 discloses a transfer drum of a sheet-fed printing press. The transfer drum includes two gripper systems of different types, which may be activated depending on whether the press is in the straight-printing mode or in the perfecting mode, i.e. whether one or both sides of the sheets are to be printed. In order to set a desired mode of operation, gear mechanisms including a plurality of gearing elements, for example gearwheels, levers, joints, stops, and a clutch, are provided. The main element of the gear mechanism is an adjustment disk that can be adjusted into two rotary positions about the axis of rotation of the transfer drum. The gripper systems are coupled to the rotation of the adjustment disk. In the respective stop position, the grippers of the gripper system assume a specific radial position and cooperate with or are uncoupled from control cams. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    It is accordingly an object of the invention to provide a transfer drum between printing units of a sheet-fed printing press, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which has gripper systems that are adjustable to a desired mode of operation by simple measures and ensure stable and reliable conveying of sheets between printing units when in an operating position. 
         [0005]    With the foregoing and other objects in view there is provided, in accordance with the invention, a transfer drum to be disposed between printing units of a sheet-fed printing press. The transfer drum comprises a drum body having an axis of rotation and journals for supporting the drum body for rotation in side walls. Two gripper systems are disposed on the drum body for extension in radial direction into an operating position, depending on a selection of a mode of operation for printing on only one side of a sheet or of a mode of operation for printing on both sides of a sheet. A support is disposed in the drum body for radial adjustment to support the gripper systems diametrically relative to the axis of rotation of the drum body. 
         [0006]    In accordance with the invention, two gripper systems of different construction are disposed on a support in such a way as to be diametrically opposite each other with respect to the axis of rotation of a transfer drum. The support is movable in the radial direction between two operating positions. 
         [0007]    A transfer drum for reversing a sheet between two printing units may include a gripper system that is constructed as what is referred to as a straight-printing gripper system, including gripper fingers and gripper pads that are stationary with respect to the support, and another gripper system constructed as what is referred to as a perfecting gripper system, including pivotable pliers-type grippers. A displacement of the support causes one of the gripper systems to be moved into an operating position in which a transfer of a sheet from a revolving element upstream of the transfer drum or to a downstream revolving element is possible. The gripper system that is not being used in the specific case is located radially below the revolving contour of the gripper system that is in the operating position. When it is moved into the operating position, a gripper system is coupled to a gear mechanism for controlling the grippers. If the controlling gear mechanism is a cam mechanism, in the operating position, a cam follower is brought into engagement with a control cam. 
         [0008]    In a sheet-fed printing press that includes a transfer drum, a storage drum, and a reversing drum for reversing a sheet between two impression cylinders, the gripper systems are disposed diametrically opposite each other on the reversing drum. Depending on the mode of operation, i.e. printing on only one side of the sheet or printing on both sides of the sheet, the phases of the reversing drum, the upstream storage drum, and the downstream impression cylinder must be matched. In order to adjust the phases, two gearwheels may be provided on a journal of the reversing drum, with one gearwheel meshing with driving gear of the storage drum and the other meshing with driving gear of the impression cylinder. The gearwheels are separately couplable to the journal of the reversing drum. 
         [0009]    In order to adjust the phase, the reversing drum is locked in its angular position, for example through the use of a locking lever. Then, the coupling of the gearwheel that meshes with the gearwheel of the impression cylinder is released. Then, the angular position of the impression cylinder is adjusted relative to the angular position of the reversing drum in such a way that the desired gripper system of the reversing drum cooperates with a gripper system of the impression cylinder. Afterwards, the gearwheel that meshes with the driving gear of the impression cylinder is firmly recoupled to the journal of the reversing drum. Subsequently, the second coupling between the gearwheel meshing with the driving gear of the storage drum and the journal is released. Then, the angular position of the storage drum relative to the angular position of the reversing drum is adjusted in such a way that the desired gripper system of the reversing drum cooperates with a gripper system of the storage drum. Finally, the second clutch is activated to fix the gearwheel meshing with the driving gear of the storage drum against rotation relative to the journal. Both phase adjustments may take place simultaneously. If the pliers-type gripper system has been moved into the operating position for printing on both sides and needs to be adapted to a new sheet length, only the clutch of the gearwheel that meshes with the driving gear of the storage drum is released, and the angular position of the storage drum is adjusted to the new sheet length. Hydraulically operated clutches that can be switched separately can be used to couple the gearwheel to the journal of the reversing drum and to uncouple it therefrom. Alternatively, the clutches may be operated jointly. In this case, the impression cylinder needs to be locked for an adjustment to the sheet length to be carried out. 
         [0010]    The gripper system that is not being used can be covered by a guard that may simultaneously act as a sheet-guiding element during conveying of a sheet. The sheet-guiding element may additionally be equipped with blowers and/or suction devices. 
         [0011]    In the respective operating position, the support rests against stops and is locked against radial displacement. 
         [0012]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0013]    Although the invention is illustrated and described herein as embodied in a transfer drum between printing units of a sheet-fed 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. 
         [0014]    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 
         [0015]      FIG. 1  is a side-elevational view of a reversing drum with a gripper system support in a first operating position; 
           [0016]      FIG. 2  is a side-elevational view of a reversing drum with a gripper system support in a second operating position; 
           [0017]      FIG. 3  is a sectional view along an axis of rotation of a reversing drum having two gripper systems; 
           [0018]      FIG. 4  is a partly-sectional view of a drive for drums in a reversing device; 
           [0019]      FIG. 5  is a side-elevational view of an actuating cylinder for a support of two gripper systems; and 
           [0020]      FIG. 6  is a fragmentary, side-elevational view of a clamping device for a support of two gripper systems. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a transfer or reversing drum  1  of a reversing device in a sheet-fed printing press. Journals  2  support the reversing drum  1  for rotation about an axis  3  in side walls of the sheet-fed printing press. A support  5  for two gripper systems  6 ,  7  is disposed in a drum body  4  of the reversing drum  1  so as to be movable in the radial direction  8  in a linear guide  9 . 
         [0022]    The gripper system  6  is formed of a plurality of gripper fingers  10  attached to a gripper shaft  11 . The gripper shaft  11  is supported for rotation in bearing blocks  12 . The gripper shaft  11  is parallel to the axis  3 . The bearing blocks  12  are screwed to the support  5 . A gripper pad  13  that is firmly connected to the support  5  is associated with each gripper finger. The gripper fingers  10  are actuated by a cam mechanism, which includes a roller lever  14  connected to the gripper shaft  11 , a cam follower  15 , a control cam  16  and a stop  17  for the roller lever  14 . The support  5  is located in a first radial position, which defines an operating position of the gripper system  6 . In this operating position, the gripper pads  13  are located on a radius R 1 . Thus, to print on only one side of sheets  18 , the gripper system  6  can take over a leading edge  19  of the sheets  18  from an upstream storage drum and transfer it to a downstream impression cylinder. 
         [0023]    The gripper system  7  is formed of a plurality of first and second gripper fingers  20 ,  21 , which cooperate in pairs. The gripper fingers  20 ,  21  are attached to a gripper shaft  22  and a gripper tube  23 . The gripper shaft  22  and the gripper tube  23  are disposed to be coaxial with respect to each other and are supported for rotation in bearing blocks  24  parallel to the axis  3 . The bearing blocks  24  are screwed to the support  5  in such a way that the gripper systems  6 ,  7  oppose each other on the support  5 . With the aid of cam mechanisms, the gripper fingers  20 ,  21  carry out opening and closing movements and a pivoting movement about a joint axis  25  of the gripper shaft  22  and the gripper tube  23 . For this purpose, gears meshing with toothed segments  26 ,  27  are attached to the gripper shaft  22  and the gripper tube  23 . The toothed segments  26 ,  27  are supported on the support  5  to pivot about an axis  28 . Roller levers  29 ,  30  are connected to the toothed segments  26 ,  27 . The roller levers  29 ,  30  support cam followers  31 ,  32  associated with control cams  33 ,  34 . The control cam  33  is used for opening and closing the gripper fingers  20 ,  21 . The control cam  34  causes the gripper fingers  20 ,  21  to pivot about the axis  25 . When the gripper system  6  has been moved to the operating position, the cam followers  31 ,  32  are disengaged from the cams  33 ,  34 , and the roller levers  29 ,  30  rest against stops  35 ,  36  on the support  5 . In the operating position of the gripper system  6 , an opening  37  above the gripper system  7  is covered by a cover  38 , which may be slid over the opening  37  through the use of an actuating cylinder  39 . 
         [0024]      FIG. 2  illustrates the support  5  in the second operating position in which the gripper system  6  is retracted and the gripper system  7  is extended in the radial direction. The gripper system  7  revolves on a radius R 2 . Consequently, to print on the respective second side of a respective sheet  18 , the trailing edge of a sheet  18  can be taken over from an upstream storage drum and transferred to a downstream impression cylinder. In the second operating position, the cover  38  is slid back to clear the opening  37 . A further actuating cylinder  41  has moved a cover  42  to close an opening  40  over the gripper system  6 . In the second operating position, the cam rollers  31 ,  32  are engaged with the cams  33 ,  34 , the levers  29 ,  30  are disengaged from the stops  35 ,  36 , the cam follower  15  is disengaged from the cam  16 , and the lever  14  rests against the stop  17 . 
         [0025]      FIG. 3  is a sectional view of the reversing drum  1 , taken along the axis  3 . The journal  2  is formed on the drum body  4  for supporting the drum body  4  in a side wall  43  of the sheet-fed printing press. In the direction of the axis  3 , the support  5  extends across the entire width of the sheet  18 . The support  5  is in the operating position shown in  FIG. 2  for printing on both sides of the sheet  18 . The roller lever  29  is fixed against rotation on a shaft  44 , which is supported for rotation in bearings  45  in a bore  46  of the support  5 . An axis of rotation  47  of the shaft  44  is parallel to the axis  3 . The toothed segment  26  is fixed to the shaft  44 . The toothed segment  26  meshes with a gear  48 , which is fixed against rotation on the gripper shaft  22 . The control cams  16 ,  33  are formed on the side wall  43 . The cam follower  31  runs on the cam  33 , whereas the cam follower  15  is disengaged from the cam  16  during printing on both sides of the sheets  18 . 
         [0026]      FIG. 4  is a diagram of a drive of a storage drum  49 , of the reversing drum  1  and of an impression cylinder  50 . The storage drum  49 , the reversing drum  1  and the impression cylinder  50  have respective journals  51 ,  2 ,  52  and bearings  53 ,  54 ,  55  for supporting them in the side wall  43 . Gears  56 ,  57  are fixed against rotation on the journals  51 ,  52 . Two gears  58 ,  59  are disposed on the journal  2 . The two gears  58 ,  59  are connectible to the journal  2  so that they rotate therewith, and are disconnectible from the journal  2 , through the use of a clutch  60 ,  61  operated by a pressure fluid. In a coupled state of the clutch  60 ,  61 , the gears  58 ,  59  and the journal  2  form an interference fit assembly. In an uncoupled state, oil in lines  62 ,  63  and in grooves  64 ,  65  formed in the surface of the journal  2  is pressurized to release the interference fit, i.e. to cause the gears  58 ,  59  to be freely rotatable on the journal  2 . In the uncoupled state, the angular positions of the storage drum  49  and of all other drums and cylinders connected thereto, and of the impression cylinder  50  and of all drums and cylinders connected thereto, can be adjusted relative to the reversing drum  1 . Thus, during printing on only one side of the sheets  18 , the gripper system  6  cooperates with the gripper systems of the storage drum  49  and of the impression cylinder  50 , and during printing on both sides of the sheets  18 , the grippers of the gripper system  7  have the desired angular position relative to the gripper systems of the storage drum  49  and the impression cylinder  5 . 
         [0027]      FIG. 5  illustrates one way of moving the support  5  and the gripper systems  6 ,  7  into the respective operating position. A coupling link  66  is provided on the support  5 . The coupling link  51  is connected to an actuating cylinder  67  attached to the drum body  4 . When the actuating cylinder  67  is actuated, the support  5  can be displaced in the linear guide  9  into the operating position, which is illustrated in dashed lines. 
         [0028]      FIG. 6  shows a clamping device for the support  5  in an operating position. The actuating cylinder  67  has moved the support  5  against a stop  68 . The support  5  has a shoulder  69  on which ends of ratchet levers  70 ,  71  are placed. The levers  70 ,  71  are supported on the drum body  4  for rotation about bolts  72 ,  73 . Toothed segments  74 ,  75  meshing with gears  76 ,  77  are fixed to the respective other ends of the levers  70 ,  71 . A torque exerting a force on the lever  70 ,  71  through the toothed segment  74 ,  75  is applied to the gears  76 ,  77 . The levers  70 ,  71  secure the support  5  in the radial direction. In order to secure the tangential position of the support  5 , clamping levers  78 ,  79  are provided and are supported for rotation on the drum body  4  through the use of bolts  72 ,  80 . Toothed segments  81 ,  82  meshing with gears  83 ,  84  are provided on one end of the levers  70 ,  71 . Torques are applied to the gears  83 ,  84  in order to clamp the support in the tangential direction. A force acts through the toothed segments  81 ,  82  on the levers  78 ,  79  so that the respective other end of the lever presses the support  5  in the tangential direction against the guide path of the linear guide  9 . The lever  78  is used to clamp the support  5  in the illustrated operating position. The lever  79  is used when the support  5  is moved in the illustrated second operating position. 
         [0029]    An identical locking or clamping device of the support  5  is provided on the side having the gripper system  6 .