Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2006 044 062.5, filed Oct. 20, 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 method and a device for switching between a single-sided or straight printing mode and a perfecting or recto/verso printing mode in a sheet-processing machine. The invention also relates to a reversing drum having the device. 
     When the mode of operation of a sheet-processing machine is changed from single-sided or straight printing to perfecting or recto/verso printing, pivoting movements and opening times of cam-controlled grippers in the machine must be adjusted appropriately. For that purpose, either cam followers are displaced or shifted on the control cams or the control cams are displaced or shifted below cam rollers. A further possibility is to stop or turn off the gripper movements by a partial blocking or locking. 
     German Patent DE 39 11 609 C1, corresponding to U.S. Pat. No. 5,076,164, discloses, for example, a reversing or turning device wherein a carriage carrying the cam followers is displaced when the mode of operation changes from straight printing or single-sided printing, to perfecting or recto-verso or double-sided printing. Due to that measure, the cam followers are brought into contact with a respectively adjacent control cam. 
     Due to the increasing circumferential speeds of the paper-guiding cylinders, the demand for printing presses processing or producing at ever increasing speeds results in greater centrifugal forces at the cam followers. Consequently, greater contact pressures are required to prevent the cam followers from losing contact with the control cams. When the operating mode is changed, the greater contact pressures cause greater frictional forces when the cam followers or control cams are displaced. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a method and a device for switching between a single-sided or straight printing mode and a perfecting or recto/verso printing mode in a sheet-processing machine and a reversing drum having the device, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which convert gripper control at the reversing drum with very low forces. 
     With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for converting a gripper system of a reversing drum between straight or one-sided printing mode and perfecting or recto-verso printing mode. The method comprises controlling pivoting and opening movements of grippers of the gripper system by a control cam, initially locking a cam follower in a position wherein it is disengaged from the control cam, subsequently locking a further cam follower in a position wherein it is disengaged from a further control cam, and subsequently converting the gripper system. 
     In accordance with another mode of the invention, the method further includes rotating the reversing drum so as to attain the disengaged positions. 
     In accordance with a further mode of the invention, the method further includes, for the purpose of attaining the disengaged positions, providing actuators for actively pivoting the cam followers until a corresponding spacing from the respective control cams is reached. 
     With the objects of the invention in view, there is also provided a device for locking a respective cam follower in a position wherein the cam follower is disengaged from a control cam cooperating with the cam follower. The device comprises a locking element for each cam follower, and an axially displaceable adjustment unit of a reversing drum. The locking element is disposed on the adjustment unit, and an actuator brings the locking element from a rest position into a locking position. 
     In accordance with a further feature of the locking device, the locking element is disposed so that it is movable into a space between a stop and an abutment of the adjustment unit of the reversing drum. 
     In accordance with an added feature of the invention, the locking device further includes a toothed segment carrying the cam follower. The toothed segment has a journal whereon the stop is disposed. 
     In accordance with an additional feature of the invention, the locking device further includes a toothed segment having a support roller. The locking element is formed as a guide and is disposed so as to be brought into operative contact with the support roller. 
     With the objects of the invention in view, there is additionally provided a device for locking a respective cam follower in a position wherein the cam follower is disengaged from a control cam cooperating with the cam follower. The device comprises a toothed segment having a support roller, a locking element to be disposed in a stationary position, and a motor spindle transmission unit for moving the locking element against the support roller. 
     With the objects of the invention in view, there is furthermore provided a reversing drum, comprising the device according to the invention. The reversing drum is part of a sheet-processing printing press. 
     A particular advantage of the invention is that a necessary conversion of a reversing drum from straight or single-sided printing to perfecting or recto-verso printing requires only very low forces. The useful life of the control cams and the cam followers may be increased due to this measure. 
     The reduction of these frictional forces is advantageously achieved by disengaging the cam followers, which are pressed against the control cams by spring forces, before the conversion is initiated. 
     Another particular advantage is the provision of actuators that are fixed to the cylinder, the actuators being, for example, pneumatic cylinders for indirectly locking the cam follower in a disengaged position. Compressed air for the pneumatic cylinders may be supplied through a rotary feedthrough. 
     In accordance with a further advantageous embodiment of the invention, a pivotal toothed segment that supports the cam follower is directly locked by a pivot lever. 
     In accordance with a concomitant advantageous embodiment of the invention, a device that is disposed to be stationary, namely a motor spindle transmission unit, pivots the toothed segment into a position wherein the cam follower is disengaged from the control cam. 
     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 method and a device for switching between a single-sided or straight printing mode and a perfecting or recto/verso printing mode in a sheet-processing machine and a reversing drum having the device, 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 THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a diagrammatic, longitudinal-sectional view of a sheet-fed rotary printing press constructed in accordance with the invention; 
         FIG. 2  is an enlarged, fragmentary, longitudinal-sectional view of a sheet reversing drum of the printing press; 
         FIG. 3  is an enlarged, fragmentary, longitudinal-sectional view of a portion III of  FIG. 2 , further illustrating a locking mechanism of the sheet reversing drum; 
         FIG. 4  is a cross-sectional view taken along a line IV-IV of  FIG. 3  in the direction of the arrows; 
         FIG. 5  is an enlarged, side-elevational view of the reversing drum showing cam followers thereof in disengaged position; 
         FIG. 6  is an enlarged, side-elevational view of another exemplary embodiment of the reversing drum with a locking element in a stationary configuration; and 
         FIG. 7  is a further enlarged, fragmentary, partly longitudinal-sectional view of another exemplary embodiment with a locking element acting on a toothed segment of the reversing drum. 
     
    
    
     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 a sheet-processing machine, for example a printing press  1 , which includes a feeder  2 , at least one printing unit  3 ,  4  and a delivery  6 . Sheets  7  are withdrawn from a sheet pile  8  and are fed as individual sheets or in a shingled stream to the printing units  3  and  4  over a feed table  9 . Each of the printing units  3  and  4  includes a plate cylinder  11 ,  12 , as known in the art. Each of the plate cylinders  11  and  12  includes a device for affixing flexible printing plates. In addition, a device  16 ,  17  provided for semi-automatic or fully automatic plate changing is associated with each of the cylinders  11  and  12 . 
     The sheet pile  8  rests on a pile plate  10  which can be lifted in a controlled manner. The sheets  7  are removed from the top of the sheet pile  8  by a so-called suction head  18 , which has, among others, a number of lifting and dragging suction cups  19 ,  21  for separating the sheets  7 . Moreover, blower devices  22  for loosening the upper layers of sheets, as well as sensing elements  23  for initiating the lifting of the sheet pile  8 , are provided. A number of lateral and trailing-edge stops  24  are provided for aligning the sheet pile  8 , in particular the upper sheets  7  in the sheet pile  8 . 
     A three-drum reversing device  26 , which includes a transfer drum  27 , a storage drum  28  and a reversing drum  29 , is provided between two impression cylinders  31  and  41 . The reversing drum  29  has a so-called tongs-type gripper system  32  for reversing the sheets in the perfecting mode, i.e. in a printing mode wherein both sides of the sheets are printed in one pass, as opposed to a straight or single-sided printing mode wherein only one side of the sheets is being printed. The remaining sheet-guiding cylinders include two respective gripper systems for transporting the sheets. 
     As is shown in  FIG. 2 , the tongs-type gripper system  32  is made up of at least one rigid gripper  33  and a spring-mounted gripper  34 . In the straight or single-sided printing mode, the rigid gripper  33  forms a gripper pad, and the spring-mounted gripper  34  forms a gripper finger. In the perfecting or recto-verso printing mode, the grippers  33  and  34  are pivotable about a common axis  36 . The grippers  33  are seated on a gripper shaft  37  that is coaxially surrounded by a gripper tube  38 . The grippers  34  are seated on the gripper tube  38 . The entire gripper system  32  is pivotably mounted on the reversing drum  29 . 
     A drive pinion  40  having teeth in engagement with a toothed segment  42 , is seated at one end of the gripper tube  38 . The toothed segment  42  has a journal  43  by which it is pivotably mounted on the reversing drum  29 . A cam follower  44  is rotatably mounted on the toothed segment  42  opposite to but offset from the shaft  43 . In the straight or single-sided printing mode, this cam follower  44  is in operative contact with a first control cam  46 . For the perfecting or recto-verso printing mode, the cam follower  44  is disposed so as to be capable of being brought into contact with a second control cam  47 . The control cam  47  and a control cam  57  control the pivoting movement of the gripper system  32  in the reversing mode. The control cam  46  and a control cam  56  control the gripper system  32  in the straight-printing mode. 
     A pinion  51  having teeth with which it is in engagement with a further toothed segment  52 , is provided on an end of the gripper shaft  37  on a side opposite to that at which the pinion  40  is located. The toothed segment  52  is pivotably supported by a journal  53  on the reversing drum  29 . A cam follower  54  rotatably supported on the toothed segment  52  is in operative connection with a control cam  56 . The control cam  57  for the reversing mode is provided parallel and adjacent thereto. The journals or shafts  43 ,  53  are connected by a pre-tensioned torsion spring  58 . Due to this configuration, the cam followers  44  and  54  are continually pressed against the control cams  46 ,  47  and  56 ,  57  associated therewith. 
       FIG. 3  shows, in an enlarged view, the torsion spring  58  disposed between the journals  43  and  53  of the respective pivotable toothed segments  42  and  52  shown in  FIG. 2 . Each of the journals  43  and  53  has at least one respective stop  61  and  62  which, together with the respective journal  43 ,  53 , reciprocatingly pivots, during operation, about an axis  63  of the torsion spring  58 . 
     A locking element, for example, in the form of a respective wedge  64 ,  66 , is provided for every stop  61 ,  62 . The respective wedge  64 ,  66  is disposed so as to be extensible into and retractable out of a gap or space a formed between the respective stop  61 ,  62  and a respective adjustable abutment  69 ,  71  disposed on the reversing drum  29 , as is seen in  FIG. 4 . A respective actuator, for example a respective pneumatic cylinder  67 ,  68 , is provided for thus extending and retracting the wedge  64 ,  66 . 
     Prior to a conversion of the reversing drum  29 , for example from the single-sided or straight-printing mode to the perfecting or recto-verso printing mode, and a concurrent disengagement of the cam followers  44 ,  54  from the control cams  46 ,  56  and engagement with the control cams  47 ,  57 , the cam followers  44 ,  54  are locked in a position wherein they are disengaged from the control cams  46 ,  56 . As a first step to achieve this aim, the reversing drum  29  is stopped in a first position wherein one of the two cam followers, for example the cam follower  44 , has been displaced further than in the converting position. At the same time, the respective associated toothed segment and the stop on the journal have been displaced, so that the space and distance a between the stop  61  and the abutment  69  has been set. Then the pneumatic cylinder  67  operates to insert the wedge  64  into this space a. In a further step, the reversing drum  29  is rotated backwards or forwards to such an extent that the second cam follower  54  is disengaged from the control cam  46 . In a manner corresponding to that of the first cam follower, the second cam follower  54  is locked in this position by pushing the wedge  66  into the space a between the stop  62  and the abutment  71 . Then, the reversing drum  29  is rotated into the converting position. In this position, both cam followers  44  and  54  have now been disengaged from the cams  46  and  56 , as shown in  FIG. 5 . 
     Once both cam followers  44  and  54  have been disengaged from their control cams, an axially displaceable adjustment unit, e.g., a carriage  50 , that carries the cam followers  44  and  54 , is displaced in the axial direction until the cam followers  44  and  54  are located in the region of the parallel control cams  47  and  57  for the perfecting or recto-verso mode. As the reversing drum  29  is rotated into appropriate positions, the cam followers  44  and  54  are reengaged with the respective control cams  46  and  56 . Due to this measure, the journals can be rotated and thus the space a between the stops and abutments is increased, so that the wedges  64 ,  66  can be pulled out almost without friction. The conversion operation is thus completed. 
     In a second exemplary embodiment shown in  FIG. 6 , a respective remotely-adjustable actuator  72 , for example in the form of a motor spindle transmission  73 , is supported on the side frame so as to be stationary. The actuator  72  includes a locking element  75  with a support surface  74 , which acts on a support roller  76  that is disposed on the toothed segment  42 ,  52  so as to be capable of rotating. As a result, the toothed segments  42 ,  52 , together with the cam followers  44 ,  54  disposed thereon, are disengageable from the associated control cam  46 ,  56  independently of the cylinder position. In the axial direction of the reversing drum  29 , the support surface  74  is wide enough for the support roller  76  to roll on the support surface  74  during the conversion from straight or single-sided printing to perfecting or recto-verso printing, and vice versa. 
     In a third exemplary embodiment shown in  FIG. 7 , the toothed segment  42 ,  52  carrying the cam follower  44 ,  54  is locked in a position wherein the respective cam follower  44 ,  54  is disengaged from the respective associated control cam. For this purpose, an actuator, for example in the form of a pneumatic cylinder  76 , is provided on the reversing drum  29 . The pneumatic cylinder  76  pivots a lever  78  provided with a roller guide  77  from a “rest position” into a “locking position.” In the locking position, the lever  78  is in operative connection with a rotatable support roller  79  disposed on the toothed segment  52 . During a conversion from straight or single-sided printing to perfecting or recto-verso printing, the support roller  79  can roll on the roller guide  77 .

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