Abstract:
Sheets are conveyed through a rotary press with linear travel grippers. The novel conveying apparatus prevents collisions between the grippers and printing unit cylinders. The grippers are fixed to circulating links to convey a sheet through a nip between two cylinders that interact during printing. The links and the cylinders are coupled to drives that can be activated separately. In each case a collision disk is mounted on a shaft journal of at least one cylinder. A slip clutch is provided between the collision disk and the cylinder. A braking element is coupled to the grippers which, in the event of non-synchronous running with the cylinder, runs onto the collision disk and prevents the collision disk from moving.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an apparatus for conveying sheets through a rotary press, having grippers fixed to circulating links in order to convey a sheet through a nip between two cylinders that interact during printing. The links and the cylinders are coupled to drives that can be activated separately. 
     Sheet-fed rotary presses are known wherein the sheets are conveyed through the machine held by grippers. The grippers are located on gripper bars, which are moved through the machine by a chain mechanism or by linear motors. This type of sheet conveyance makes it possible to convey the sheets virtually on a straight line. The grippers are moved synchronously with the printing unit cylinders. In the case of a linear press for offset printing, channels are provided on the impression cylinder and/or the transfer cylinder, wherein channels the gripper bars with the grippers dip during conveyance. If a fault occurs in the drive of the grippers and/or the printing unit cylinders, there is then the risk of the grippers colliding with the printing unit cylinders. In the case of machines wherein sheets are conveyed in grippers both at the leading edge and at the trailing edge, the drives for the leading edge grippers and trailing edge grippers can be controlled separately as a function of the sheet length. If the drives for the leading edge and trailing edge grippers come out of synchronism, then there is also the risk of the gripper bars colliding with one another. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide an apparatus for conveying sheets through a rotary printing machine which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for an apparatus for conveying sheets through a rotary press with improved collision prevention between grippers and printing unit cylinders. 
     With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for conveying sheets through a rotary press, the rotary press having shaft journal-mounted cylinders that interact during printing, comprising:
         grippers fixed to circulating links for conveying a sheet through a nip between the cylinders;   separately activated drives for driving said links and the cylinders, respectively;   a collision disk mounted on a shaft journal of at least one of the cylinders;   a slipping clutch disposed between said collision disk and the respective cylinder; and   a braking element coupled to said grippers, said braking element being disposed to, in an event of non-synchronous running with the respective cylinder, run onto said collision disk and prevent a movement of said collision disk.       

     According to the invention, a collision disk with a slipping clutch is arranged on a shaft journal of a cylinder. For the case wherein synchronism between the grippers and the cylinders is lost, a braking element revolving with the grippers is provided, which runs onto the collision disk and stops the collision disk moving. In the process, a limiting force on the slipping clutch is overcome, so that the cylinder continues to rotate. 
     It is possible to stop the sheet conveyance when the braking element runs onto the collision disk. The fact that it has run on can be registered by sensors, the sensor signals being processed by a control device which is connected to the drives for the printing unit cylinders and the grippers. 
     Furthermore, a centering disk having a radial centering groove can additionally be provided on a shaft journal of the cylinder or an adjacent cylinder so as to rotate with it. During synchronous running with the cylinders, a pin coupled to the grippers dips into the centering groove. 
     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 Apparatus for Conveying Sheets through a Rotary 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. 
     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 DRAWINGS 
         FIG. 1  is a schematic illustration of a linear press; 
         FIG. 2  is a diagram showing a collision between a gripper bar and the surface of an impression cylinder; 
         FIG. 3  is a diagram showing a collision between a gripper bar and the edge of a channel of an impression cylinder; 
         FIG. 4  is a partial cross section through a printing unit of the linear press according to  FIG. 1 ; 
         FIG. 5  is a section through the linear press taken along the line V-V in  FIG. 4 ; and 
         FIG. 6  is an elevational view of an elastomeric damper on a gripper bar. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a schematic drawing of a sheet-fed offset press with a straight sheet run through four printing units  1 - 4 . Each printing unit  1 - 4  contains an impression cylinder  5 , a transfer cylinder  6 , a printing form cylinder  7 , inking rolls  8 ,  9  and an ink metering device  10 . To convey sheets  11 , grippers which hold a sheet  11  at the leading edge and at the trailing edge are provided on gripper bars  12 ,  13 . The gripper bars  12 ,  13  circulate on a path  14  which runs in a straight line between the printing units  1 - 4 . The gripper bars  12  for the leading edges and the gripper bars  13  for the trailing edges of a sheet  11  are driven by linear motors. The cylinders  5 - 7  and rolls  8 ,  9  of the printing units are coupled to a gear train, to which at least one drive motor is assigned. The drive motor or motors for the printing units  1 - 4  and the linear motors are connected to a control and regulating device, which ensures that the cylinders  5 - 7  and gripper bars  12 ,  13  are driven synchronously. During synchronous driving, the gripper bars  12 ,  13  dip into channels  15 ,  16  which are in each case formed on the impression cylinder  5  and on the transfer cylinder  6 . The sheets  11  are separated from a stack  18  by a suction head  17  and fed to the grippers of the gripper bars  12 ,  13 . The printed sheets  11  are allowed to fall out of the grippers over a stack  19 . 
       FIGS. 2 and 3  illustrate faults wherein the gripper bars  12 ,  13  are not running synchronously with the impression cylinder  5  and the transfer cylinder  6 . In  FIG. 2 , the gripper bar  12  located below the path  14  for the leading edge of a sheet collides with the surface of the impression cylinder  5 . In the case according to  FIG. 3 , there is only a slight deviation in the synchronous running. The gripper bar  12  collides with the trailing edge of the channel  15  of the impression cylinder  5 . 
     In  FIGS. 4-5 , details of a printing unit  1 - 4  are illustrated in section. The impression cylinder  5  and the transfer cylinder  6  are held at their journals  20 ,  21  in bearings  22 ,  23  of a side wall  24  of the sheet-fed press. A passive part  25  of a linear motor is incorporated in the side wall  24  in accordance with the path  14 . The passive part  25  simultaneously forms a guide for an active part  26  of the linear motor, which is coupled via a driver  27  to a gripper bar  13  for a trailing edge of a sheet  11 . Given synchronous running of the active part  26  or the gripper bar  13  and the cylinders  5 ,  6 , the gripper bar  13  dips centrally into the channel  16 , as shown in more detail in  FIG. 5 . 
       FIG. 6  shows an enlarged section corresponding to the central portion of  FIG. 5 . In the conveying direction  28  of the sheets  11 , there are rubber buffers  29 ,  30  having a damping action on both sides of the gripper bar  13 . 
     On the journal  21 , a collision disk  32  is held in a bearing  31 . At the end, the collision disk  32  has a drilled hole  33  to accommodate a ball  34  of a ball detent inhibitor. The ball  34  is pressed into the drilled hole  33  with the force of a spring  35 , it being possible for the ball  33  to be displaced in the axial direction of the transfer cylinder  6  in a drilled hole  36  at the end, and the spring  35  being supported in the drilled hole  36  on the transfer cylinder  6 . When the ball  33  is seated in the drilled hole  33 , a cutout  37  in the collision disk  32  corresponding to the shape of the channel  16  is aligned with the profile of the channel  16 . 
     Furthermore, on the journal  21  there is a centering disk  38  fixed so as to rotate with it. The centering disk  38  has a centering groove  39 , wherein a pin  40  engages, which is fixed laterally to the gripper bar  13 . Given synchronous running of gripper bar  13  and transfer cylinder  6 , the pin  40  runs along in the centering groove  39  without contact. 
     Furthermore, there is a collision disk  42  which can rotate on a bearing  41  and a centering disk  43  which is fixed on the journal  20  of the cylinder  5  so as to rotate with it. Between the collision disk  42  and the end of the impression cylinder  5  there is a further ball detent inhibitor  44 . The centering disk  43  has a centering groove  45 . The centering disk  43  having the centering groove  45  and the collision disk  42  having the ball detent inhibitor  44  interact with centering pins and rubber buffers on the gripper bars  12  for the leading edge of the sheets  11 . 
     The rubber buffers  29 ,  30  on the gripper bars  12 ,  13  offer effective protection for the case wherein the gripper bars  12 ,  13  do not run synchronously with the impression cylinder  5  or with the transfer cylinder  6 . If the gripper bars  12 ,  13  have a differential speed in relation to each other, then the gripper bars  12 ,  13  collide with the equal-height rubber buffers  29 ,  30 , so that the energy of movement is converted into heat in the rubber buffers  29 ,  30 . 
     In the event of slight asynchronism between a gripper bar  12 ,  13  and a cylinder  5 ,  6 , the respective pin  40  is centered in the respective centering groove  39 ,  45  and the gripper bar  12 ,  13  is moved through the channel  15 ,  16  without any collision. 
     In the event of slight asynchronism, a gripper bar  12 ,  13  would collide with the surface of the cylinder  5 ,  6 . Since, on the gripper bars  12 ,  13 , the rubber buffers  29 ,  30  are located at the height of the respective collision disk  32 ,  42  in the axial direction of the cylinders  5 ,  6 , the rubber buffers  29  run onto the circumferential surface of the relevant collision disk  32 ,  42 . As a result, a braking moment acts on the relevant collision disk  32 ,  42 . The collision disk  32 ,  42  comes to a standstill, while the relevant cylinder  5 ,  6  continues to rotate. The ball detent inhibitors  33 - 36 ,  44  act as a slipping clutch in this case, the force of the spring  45  determining the disengagement moment. Stopping a collision disk  32 ,  42  prevents the respective gripper bar  12 ,  13  being pulled into the press nip between impression cylinder  5  and transfer cylinder  6 . 
     If a slipping clutch is disengaged, at the same time a signal can be generated, which acts on the drive controller of the linear motors and of the printing units  1 - 4  such that the sheet-fed press comes to a standstill. 
     In order to avoid a collision between the gripper bars  12 ,  13  and the cylinders  5 ,  6 , there is also the possibility of arranging a barrier, such as a stop finger, upstream of the press nip. In the event of a fault in synchronism, the stop finger is moved in front of the press nip as a stop and prevents a gripper bar  12 ,  13  moving into the press nip. It is a precondition that the gripper bars  12 ,  13  are synchronized positively as they run through between the cylinders  5 ,  6 , for example by means of centering disks  38 ,  43  and centering pins  40  described above. 
     This application claims the priority, under 35 U.S.C. § 119, of German patent application No. 10 2004 052 657.5, filed Oct. 29, 2004; the entire disclosure of the prior application is herewith incorporated by reference.