CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2007 013 805.0, filed Mar. 22, 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 gripper bar for the transport of sheets in a sheet-processing machine, in particular in the delivery of a printing press, the gripper bar being arranged on driven chains. 
         [0003]    A device of this type is described in the commonly assigned German patent DE 195 27 439 C2 and its counterpart U.S. Pat. No. 5,758,576. There, the gripper bar is attached to two chains guided in parallel in side frames, in each case by way of a rigid pin connection to a chain link. The two pins of a chain link are thereby designed to be so long that the gripper bar can be fixed thereto. In the event of high loadings of the gripper bar, the chain links tend to slip on an inner edge. This leads to premature abrasion of the chain as a result of increased wear. 
       BRIEF SUMMARY OF THE INVENTION 
       [0004]    It is accordingly an object of the invention to provide a device for transporting sheets by way of a chain-driven gripper bar which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides for an attachment of the gripper bar to the transport chains which eliminates the above disadvantages. 
         [0005]    With the foregoing and other objects in view there is provided, in accordance with the invention, a sheet transport device, comprising: 
         [0006]    a gripper bar; 
         [0007]    transport chains for driving said gripper bar, said transport chains having a plurality of alternately arranged inner and outer links, and chain pins connecting said inner and outer links to one another; 
         [0008]    wherein said gripper bar is mounted to two different chain links of a respective said transport chain; and 
         [0009]    wherein a bearing point is disposed between two chain pins of a common said chain link. 
         [0010]    It is a great advantage of the invention that the gripper bar is arranged on the transport chains in an articulated manner. In this way, the chains rest on their chain tracks virtually without any torques, since only normal forces still act. 
         [0011]    In order to achieve good support on the chain tracks of the transport chains, which are preferably implemented as roller chains, two bearing points are provided on the adjacent inner links and adjacent outer links, respectively, at least one outer or inner link being arranged between two inner or outer links. As a result of this measure, the forces applied by the gripper bar are distributed uniformly to a plurality of chain links and thus to a plurality of chain rollers on each side, for instance to four chain rollers per transport chain. 
         [0012]    In accordance with an added feature of the invention, the bearings between the gripper bar and the transport chain are formed by spherical ball and socket bearings. Preferably, one spherical ball and socket bearing is formed as a fixed bearing and rigidly connected to a respective inner link or outer link. Additionally, one spherical ball and socket bearing may be formed as a loose bearing configured to be movable in a sheet transport direction in a groove formed in a respective inner link or outer link. 
         [0013]    As mentioned above, the transport chains are preferably formed with chain rollers. These are preferably disposed in each case at a connecting point between a respective said inner link and outer link. In a preferred embodiment of the invention, there is provided a rail forming a lower guide rollingly supporting said chain rollers, and an upper guide for said chain rollers. 
         [0014]    In accordance with a preferred feature of the invention, each gripper bar is mounted to said transport chains by way of a fixed bearing, a loose bearing with one degree of freedom, and two loose bearings each having two degrees of freedom. 
         [0015]    In accordance with a concomitant feature of the invention, the transport device is a chain-driven gripper bar in a delivery of a printing press. 
         [0016]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0017]    Although the invention is illustrated and described herein as embodied in a device for the transport of sheets by means of a chain-driven gripper bar, 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. 
         [0018]    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 
         [0019]      FIG. 1  is a schematic, sectional side view of a rotary press; 
           [0020]      FIG. 2  is a plan view of a gripper bar in the delivery of a sheet-processing machine; 
           [0021]      FIG. 3  is a perspective view of an attachment of the gripper bar to a roller chain; 
           [0022]      FIG. 4  is a perspective view of the gripper bar guidance in the sheet transport direction; and 
           [0023]      FIG. 5  is a schematic illustration showing a section through the bearing plane. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is seen a sheet-processing machine, represented here by a printing press  1 . The machine has a feeder  2 , at least one printing unit  3  and  4  and a delivery  6 . Sheets  7  are removed from a sheet stack  8  and, separated or overlapping, are fed over a feed table  9  to the printing units  3  and  4 . The printing units each contain, in a known way, a plate cylinder  11 ,  12 . The plate cylinders  11  and  12  each have a device  13 ,  14  for fixing flexible printing plates. Furthermore, each plate cylinder  11 ,  12  is assigned a device  16 ,  17  for fully automatic or semiautomatic printing plate exchange. 
         [0025]    The sheet stack  8  rests on a stack board  10  that can be raised under control. The sheets  7  are removed from the top of the sheet stack  8  by means of what is known as a suction head  18  which, inter alia, has a number of lifting and dragging suckers  19 ,  21  for separating the sheets  7 . Furthermore, blowing devices  22  for loosening the upper sheet layers and sensing elements  23  for stack tracking are provided. In order to align the sheet stack  8 , in particular the upper sheets  7  of the sheet stack  8 , a number of side and rear stops  24  are provided. 
         [0026]    The sheets are transported though the machine by way of a number of sheet-carrying cylinders equipped with gripper devices, e.g. a feed cylinder  26 , a first impression cylinder  31 , a transfer drum  27 , a storage drum  28 , a turner drum  29  and a second impression cylinder  41 , from which the sheets are transferred to a gripper bar  32  of a chain delivery system  33 . 
         [0027]    The chain delivery system  33  has two transport chains  36  arranged in parallel, which are preferably formed as roller chains. These are guided in guides  37  in the side frame  38  of the delivery  6  and deflected over two chain wheels  39 ,  42 , of which at least one is driven. 
         [0028]    The transport chains  36  carry a relatively large number of gripper bars  32  spaced apart from one another in the sheet transport direction. The transport chains  36  each have a large number of chain links, outer links  43  and inner links  44  alternating. 
         [0029]    In order to fix the gripper bars  32  to the transport chains  36 , provision is made, for example according to  FIG. 3 , for these to be arranged on two chain links spaced apart from each other, e.g.  43 - 43  or  44 - 44 . As a result of this measure, the gripper bar  32  is carried by four rollers  46 ,  47 ,  48 ,  49  of the chain links  43 ,  44 . 
         [0030]    The fixing or bearing points  51 ,  52  of the gripper bar  32  are in each case arranged between two chain pins  45  which in each case connect an inner link  44  and an outer link  43  to each other. Rollers  46 ;  47 ,  48 ;  49  are preferably arranged on the chain pins  45 . 
         [0031]    Of course, these fixing or bearing points  51 ,  52  of the gripper bar  32  can also be provided between two rollers, e.g.  47 ,  48 , of outer links  43 . 
         [0032]    If the gripper bar  32  is to be carried by three rollers, the bearing points  51 ,  52  on an inner link  44  and a directly adjacent outer link  43  must in each case be arranged between the chain pins  45 . 
         [0033]    The fixing or bearing points  51 ,  52  of the gripper bar  32  are formed as ball and socket bearings. 
         [0034]    In the exemplary embodiment according to  FIG. 3 , the ball and socket bearing  52  is a spherical ball and socket bearing and is arranged such that it can be displaced in a groove  53  in the chain link  43  or  44  and thus serves as a loose bearing. The ball and socket bearing  51  is likewise formed as a spherical ball and socket bearing and serves as a fixed bearing. 
         [0035]      FIG. 5  shows the mounting of the gripper bar  32  on both sides on the transport chains  36 . 
         [0036]    In addition to the degrees of freedom of a spherical ball and socket bearing, the fixed bearing  51  has no further degrees of freedom. The adjacent loose bearing  52  additionally has two degrees of freedom in the axial direction and in the transport direction. A loose bearing  57  arranged opposite the fixed bearing  51  on the opposite side has an additional degree of freedom in the axial direction. An adjacent loose bearing  58  has two additional degrees of freedom in the axial direction and in the transport direction. By means of this special mounting, the result is a torque-free bearing point of the gripper bar  32  in the chains  36 .
In a device for the transport of sheets in a sheet-processing machine, preferably a printing press, provision is made to transport the sheets on chain-guided gripper bars. The gripper bars are fixed respectively to two chain links arranged indirectly beside each other. The forces acting on the gripper bars are more evenly distributed.