Abstract:
In an apparatus for correcting a position of a sheet which is transported in the grip of grippers on a feed drum of a sheet processing machine, in particular a sheetfed rotary printing press, provision is made for a gripper device of the drum to be mounted in independently rotatable arranged supports and for it to be possible for each support to be driven by a step-up gear mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2009 050 752.3, filed Oct. 27, 2009; the prior application is herewith incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an apparatus for correcting the position of sheets which are transported in the grip of grippers on a cylinder or a drum of a sheet processing machine. 
     An apparatus of the generic type is disclosed by published, non-prosecuted German patent application DE 10 2006 061 431 A1. This document shows a cylinder of a sheet processing machine having a gripper device for fixing a sheet front edge. The gripper device is connected to the cylinder by resiliently deformable flexible webs, so that the gripper device can be set obliquely with respect to the cylinder, which permits the correction of an oblique position of the fixed sheet. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide an apparatus for correcting the position of sheets which overcome the above-mentioned disadvantages of the prior art devices of this general type, which corrects the position of a sheet beyond the possibility of oblique position correction, and also permits a correction of the position of the sheet in the circumferential direction. 
     With the foregoing and other objects in view there is provided, in accordance with the invention an apparatus for correcting a position of a sheet transported in a sheet processing machine. The apparatus contains a step-up gear mechanism, a drum having supports being rotatably mounted independently of one another and in each case being driven by the step-up gear mechanism, and a gripper device for fixing the sheet being mounted in the supports. The gripper device transports the sheet. 
     The substantial advantage of the invention is to be seen in the arrangement of a gear mechanism or a gear mechanism on each side of the cylinder or of the drum for the activation of the gripper device. The gear mechanism makes it possible for a sheet which is transported on a cylinder or a drum in the grip of grippers to be aligned, as it is transported, both in the transport direction and also with respect to its oblique position such that it can be transferred very accurately to the next gripper system in a defined intended position. The actual transport movement of the cylinder is coupled via mechanical components (e.g. gears) to the main drive of the sheet processing machine. As a result, the rotational oscillations of the overall machine are also transmitted to the cylinder. Only the movement with which the deviation of the sheet edge from the intended position is corrected is introduced by direct drives via a gear mechanism. Furthermore, it is possible with this apparatus to align the sheet with respect to its lateral position transversely to the sheet running direction. 
     In a particularly advantageous refinement, the gear mechanisms are formed as step-up gear mechanisms, in particular planet gear mechanisms. 
     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 an apparatus for correcting the position of sheets, 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 an illustration of a sheetfed rotary press in section according to the invention; 
         FIG. 2  is a diagrammatic, sectional view of a sheet transport drum having an adjustable gripper device for correcting a sheet position; and 
         FIG. 3  is a diagrammatic, side view of the sheet transport drum. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a machine for processing sheets  7 , e.g. a printing press  1 , that has a feeder  2 , at least one printing unit  3  and  4  and a deliverer  6 . The sheets  7  are removed from a sheet stack  8  and, separated or overlapping, are fed over a feed table  9  to the printing units  2  and  4 . The latter each contain a plate cylinder  11 ,  12  in a known manner. The plate cylinders  11  and  12  each have an apparatus  13 ,  14  for fixing flexible printing plates. Furthermore, each plate cylinder  11 ,  12  is assigned an apparatus  16 ,  17  for semiautomatic or fully automatic printing plate changer. 
     The sheet stack  8  lies on a stack plate  10  which can be raised under control. The sheets  7  are removed from the upper side of the sheet stack  8  by 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  are provided for loosening the upper sheet layers, as are sensing elements  23  for stack tracking. 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. 
     Alignment of the sheets  7  before the first processing station, for example the printing unit  3 , is carried out on a first cylinder or drum, for example a feed drum  26 . A transfer of the sheet  7  from the feed table  9  to the feed cylinder  26  is carried out in the exemplary embodiment according to  FIG. 1  by what is known as an oscillating pre-gripper  27 . The transfer of the sheet  7  can, however, also be carried out in another way, e.g. by a linearly driven gripper device. 
     As shown in  FIGS. 2 and 3 , the feed drum  26  contains a rotatably mounted base body  28  and a gripper bar  29  coupled thereto. By use of a coupling joint  31  arranged approximately centrally, the gripper bar  29  is arranged such that it can be pivoted with respect to the base body  28  in and counter to the sheet transport direction—in a circumferential direction of the drum. The gripper bar  29  bears a number of grippers  30  arranged beside one another at intervals for holding a sheet during a transport phase by the feed drum  26 . 
     The gripper bar  29  is mounted on both sides by sliding ball joints  32  in rotatably mounted supports, for example planet gear supports  33 , and in the region of an axis of rotation  25  of the feed drum  26  on ends of drive shafts  36 . 
     The supports  33  in each case have a drive gear  34 , what is known as a planet gear, and are in each case rotatably mounted on drive shafts  36  (sun gear shaft). The drive shafts  36  in each case have a drive gear  37  (sun gear), which meshes with a planet gear  34 . Furthermore, the planet gears  34  mesh with internal gears  39  which are rotatably mounted in side frames  38  of the sheet processing machine  1  and which in each case can be driven at the cycle rate of the sheet processing machine  1  by drive gears  41 , for example by meshing with a non-illustrated gear train belonging to the machine  1 . 
     The sun gear shafts  36  are in each case arranged such that they can be driven by an actuating motor  42 . 
     A further actuating motor  43  is connected to the base body  28  by a rod  44 . Here, the rod  44  is arranged in an axial bore  46  in the sun gear shaft  36 . Via the rods  44 , the actuating motor  43  produces a lateral deflection of the base body  28  and therefore a lateral displacement of the gripper bar  29  coupled thereto. 
     If, by sensors  47 , an erroneous position of a sheet is determined, the actuating motors  42 ,  43  are fed with corrective values, for example by a machine control system, which leads to an activation of the actuating motors  42 ,  43 . 
     In the event of an erroneous position of a sheet in relation to the circumferential alignment thereof (in or counter to the sheet transport direction), the actuating motors  42  are activated synchronously. By this measure, the planet gears  34  meshing with the sun gears  37  are driven more quickly or more slowly with respect to the drive gear  41 , so that, depending on the direction of rotation of the actuating motors  42 , the gripper bar  27  has superimposed on it a speed which leads to a lead or lag of the gripper bar  29  with respect to the gear train of the machine  1  and thus with respect to the following cylinder, for example printing cylinder  45 . 
     An activation of the further actuating motor  43  for the lateral position correction, carried out following an intended value-actual value comparison, leads to a lateral displacement of the base body  28  and thus to the lateral displacement of the gripper bar  29  and of the sheet  7  held by the grippers  30  of the gripper bar  29 . 
     In the event of an oblique position of the sheet, in order to correct the oblique position either the actuating motor  42  is driven in or counter to the direction of rotation of the drum  26  or the two actuating motors  42  are driven in the opposite direction of rotation.