Abstract:
A method and an apparatus convey sheets onto a stack which reduces the risk of damaging a sheet or the conveying elements. The sheets are conveyed over the stack one after another and aligned on the side edge by moving a surface of at least one stop. A position of the side edge of the respective sheet in relation to the stop surface is monitored, and a signal is output if the side edge lies behind the stop surface. The apparatus contains a detector for detecting the position of the side edge in relation to the stop surface.

Description:
BACKGROUND OF THE INVENTION  
     Field of the Invention  
       [0001]     The invention relates to a method for conveying sheets onto a stack, in which the sheets are conveyed over the stack one after another and aligned on a side edge by moving a surface of at least one stop. The invention further relates to an apparatus for implementing the method.  
         [0002]     Published, non-prosecuted German patent application DE 43 28 445 A1, corresponding to U.S. Pat. No. 5,582,400, discloses an apparatus for conveying sheets onto a stack in which, in the region of a deliverer of a sheet-fed press, there are various sensors registering a fluttering movement of a sheet. The sensor signals are evaluated in a fuzzy controller. In the event of undesired fluttering, blowing or vacuum actuators are actuated, which settles the run of the sheet. The sheets are deposited onto the stack by being allowed to fall.  
         [0003]     During manual setting of blowing or vacuum actuators, it is possible for sheets to arrive from the conveying path provided and to be deposited on straight joggers, which can be moved to and fro laterally on the stack for correct stack formation. The deposition on the straight joggers can lead to an accumulation of a plurality of sheets, so there is a risk of collision with gripper bars running past, which hold the sheet during the conveyance.  
       SUMMARY OF THE INVENTION  
       [0004]     It is accordingly an object of the invention to provide a method and an apparatus for conveying sheets onto a stack which overcomes the above-mentioned disadvantages of the prior art methods and devices of this general type, which reduce the risk of damage to a sheet or to the conveying elements.  
         [0005]     With the foregoing and other objects in view there is provided, in accordance with the invention, a method for conveying sheets onto a stack. The method includes conveying the sheets over the stack one after another and aligned on a side edge by moving a stop surface of at least one stop, monitoring a position of the side edge of the sheets in relation to the stop surface, and outputting a signal if the side edge lies behind the stop surface.  
         [0006]     According to the invention, at least one detector, in particular an ultrasonic distance sensor, is used to monitor whether a sheet is deposited on lateral sheet stops. If a sheet projects in the horizontal direction over a vertical stop surface of a stop, then a signal is generated in a control device, by using which the conveyance of sheets is adjusted or actuating elements for the position or alignment of the sheet are controlled in such a way that the projecting sheet falls onto the stack and sheets arriving later are no longer deposited on the stop.  
         [0007]     For the sheets, a permissible path region can be defined in which each sheet should be located during proper conveyance. The action of leaving the path region is detected by the detector. If sheets are conveyed one after another by grippers on gripper bars then, according to a first variant, the action of leaving the path region can be detected by a check being made as to whether, during a conveying cycle, no gripper bar is detected, since the gripper bar is concealed by a sheet lying wrongly in the registration direction of the detector. In a second variant, the detector is aimed directly at the sheet lying wrongly.  
         [0008]     If straight joggers moving to and fro at the side of the stack are provided as a sheet stop, then if a sheet lies wrongly on the straight joggers, the straight jogger can be accelerated in the lateral direction in a manner deviating from its periodic movement sequence, so that, as a result of inertia, the sheet slides off the straight jogger and falls onto the stack. The unusual lateral movement of the straight jogger provides the sheet with sufficient clearance for the sheet to fall freely.  
         [0009]     In the event of a sheet lying wrongly on a straight jogger, a slide, a blowing or vacuum device or another conveying device can also be actuated, so that the sheet is guided back into the permissible path region.  
         [0010]     In presses, sheet brakes are used in the delivery region in order to reduce the speed of the sheets. If the detector has detected a sheet over a straight jogger, the sheet brake can be controlled in such a way that the braking action with respect to the sheet axis of symmetry is different transversely with respect to the sheet running direction. As a result, there is a position change in the following sheets, in particular a slight rotation of the sheets into the permissible path region.  
         [0011]     Other features which are considered as characteristic for the invention are set forth in the appended claims.  
         [0012]     Although the invention is illustrated and described herein as embodied in a method and an apparatus for conveying sheets onto a stack, 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.  
         [0013]     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  
       [0014]      FIG. 1  is a diagrammatic, side view of a press having an apparatus for conveying sheets onto a stack according to the invention;  
         [0015]      FIG. 2  is a diagrammatic, plan view of the stack;  
         [0016]      FIG. 3  is diagrammatic, plan view of the stack with a sheet lying on a straight jogger board;  
         [0017]      FIG. 4  is a diagrammatic, front view of the stack with the sheet according to  FIG. 3 ; and  
         [0018]      FIG. 5 a  diagrammatic, plan view relating to unusual movement of a straight jogger.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a printing unit  2  operating in an offset process and having an impression cylinder  2 . 1 . The latter guides a respective sheet in a processing direction indicated by a direction of rotation arrow  5  through a press nip between the impression cylinder  2 . 1  and a blanket cylinder  2 . 2  interacting therewith, and in the present example subsequently transfers it to a gripper row of a single-turn transfer drum  2 . 3 , opening a gripper row disposed on the impression cylinder  2 . 1  and provided for gripping a sheet  3  at a gripping edge at the leading end of the sheet  3 . A corresponding transfer of the sheet  3  is then carried out from the single-turn transfer drum  2 . 3  to a further transfer drum  2 . 4 , a half-turn transfer drum in the present example, which transfers the sheet  3  to a chain conveyor  4  of the deliverer  1 . The chain conveyor  4  includes 2 endless conveyer chains  6 , of which a respective one circulates along a closed chain path in the vicinity of a respective side wall of the chain deliverer  1  during operation. A respective conveyor chain  6  in each case runs around one of two synchronously driven drive chain wheels  7 , whose axes are aligned with each other and, in the present example, is guided in each case over a deflection chain wheel  8  which is located downstream of the drive chain wheel  7  with respect to the processing direction, so that a respective one of the conveyor chains  6  passes through a closed chain path. Between the two conveyor chains  6  there extend gripper systems  9  carried by the latter and having grippers, which move through gaps between the grippers disposed on the transfer drum  2 . 4  and in the process pick up a respective sheet  3  by gripping the aforementioned gripping edge at the leading end of the sheet  3  directly before the opening of the grippers disposed on the transfer drum  2 . 4 , transport the sheet over a sheet guide device  10  to a braking station  11  and open after the sheet  3  has been transferred to the braking station  11 . In the braking station  11 , the sheets are braked to a deposition speed that is reduced with respect to the processing speed and, after reaching the speed, are finally released, so that a respectively now decelerated sheet  3  finally strikes leading edge stops  12  and, being aligned with the latter and with trailing edge stops  13  opposite these, together with preceding and/or following sheets  3 , forms a stack  14 , which can be lowered by a lifting mechanism to the extent to which the stack  14  grows. Of the lifting mechanism, only a platform  15  carrying the stack  14  and lifting chains  16  carrying the platform and indicated dash-dotted are reproduced in  FIG. 1 . Along their paths between the drive chain wheels  7  on the one hand and the deflection chain wheels  8  on the other hand, the conveyor chains  6  are guided by chain guide rails which determine the chain paths of the chain runs. In the present example, the sheets  3  are transported by the lower chain run in  FIG. 1 . The section of the chain path through which the latter runs is followed by a sheet guide surface  17  facing the latter and formed on the sheet guide device  10 . Between the surface and a sheet  3  respectively guided over it, a supporting air cushion is preferably formed during operation. To this end, the sheet guide device  10  is equipped with blow air nozzles opening into the sheet guide surface  17 , of which only one is reproduced in  FIG. 1  as representative of them all, and in a symbolic illustration in the form of a connecting piece  18 . In order to prevent mutual adhesion of the printed sheets in the stack  14 , a dryer  19  and a powdering apparatus  20  are provided on the path of the sheets  3  from the drive chain wheels  7  to the braking station  11 . In order to avoid excessive heating of the sheet guide surface  17  by the dryer, a coolant circuit is integrated into the sheet guide device  10 , this being indicated symbolically in  FIG. 1  by an inlet connecting piece  21  and an outlet connecting piece  22  on a coolant trough  23  assigned to the sheet guide surface  17 . Illustration of the aforementioned chain guide rails has been omitted from  FIG. 1 . However, the path of the same in the present example can be seen from that of the chain runs.  
         [0020]     In order to align the sheets  3  on the stack  14 , lateral straight joggers  24  are provided.  
         [0021]      FIG. 2  shows a plan view of the stack  14  during proper stack formation. The braking station  11  contains five suction belt modules  26 . 1 - 26 . 5  transversely with respect to the sheet running direction  25 . Each suction belt module  26 . 1 - 26 . 5  applies a braking force F 1  to the sheet  3 . The suction belt modules  26 . 1 - 26 . 5  are located symmetrically with respect to the sheet axis of symmetry in the sheet running direction  25 . The side edges  27 . 1 ,  27 . 2  of the sheet  3  lie parallel to the sheet running direction  25 . The straight joggers  24  in each case contain a stop plate  28 . 1 ,  28 . 2 , a longitudinal guide  29 . 1 ,  29 . 2  and a linear drive  30 . 1 ,  30 . 2 . During proper sheet conveyance, the sheet  3  is located centrally with respect to the stop plates  28 . 1 ,  28 . 2 . Provided at the sides of the stop plates  28 . 1 ,  28 . 2  are ultrasonic distance sensors  31 . 1 ,  31 . 2 , which in each case emit a measuring beam  32 . 1 ,  32 . 2  in the vertical direction on the underside of the sheet. The ultrasonic distance sensors  31 . 1 ,  31 . 2  and the linear drives  30 . 1 ,  30 . 2 , are connected to a control device  33 .  
         [0022]      FIGS. 3 and 4  show a situation in which a sheet  3  has been deposited on the stop plate  28 . 2 . As can be seen in more detail in  FIG. 4 , the measuring beam  32 . 2  strikes the underside of the sheet  3  lying over the stop plate  28 . 2 . In accordance with the propagation time principle, the ultrasonic sensor  31 . 2  outputs a signal that the sheet  3  is lying obliquely over the stop plate  28 . 2 . A registration depth  34  of the ultrasonic distance sensor  31 . 2  is dimensioned such that no signal is generated during the passage of a gripper bar of the gripper system  9 . The signal is evaluated in the control device  33  together with signals from a rotary encoder  35 . In order to correct the skewed position of the sheet  3  above the stack  14 , actuating signals are generated in the control device  33  which change the braking forces of the suction belt modules  26 . 1  and  26 . 2 . As shown in  FIG. 3 , the braking forces F 3 , F 2  of the suction belt modules  26 . 1 ,  26 . 2  are increased slightly as compared with the braking forces F 1  on the suction belt modules  26 . 3  to  26 . 5 , until the sheet  3  is again guided straight and centrally over the stack  14 . During the setting of the braking forces F 1 , F 2 , F 3 , the weight distribution of the sheet  3  specific to the printing image can be taken into account.  
         [0023]     Additionally or alternatively, as shown in more detail in  FIG. 5 , the straight jogger  24 . 2  can be activated in order to move the sheet  3  down from the stop plate  28 . 2  onto the stack  14 . If the ultrasonic distance sensor  31 . 2  supplies the signal that a sheet  3  is lying on the stop plate  28 . 2 , then, by the control device  33 , the linear drive  30 . 2  is activated in such a way that the stop plate  28 . 2  for intercepting the sheet  3  is moved away from the side surface of the stack. As a result of the acceleration of the stop plate  28 . 2  and the inertia of the sheet  3 , the sheet  3  falls down from the stop plate  28 . 2  onto the surface of the stack  14 . As illustrated in  FIG. 4 , the stop plates  28 . 1 ,  28 . 2  are provided with inclines  36 . 1 ,  36 . 2 , so that the falling sheet  3  falls approximately centrally onto the stack  14 . After the sheet  3  has fallen down from the stop plate  28 . 2 , the stop plate  28 . 2  is displaced in the direction of the side surface of the stack again. The stroke of the lateral intercepting movement of the stop plate  28 . 2  can be set as a function of the extent of the overlap of the sheet  3  over the stop plate  28 . 2 . For this purpose, use can be made of a detector which, in addition to the presence of a sheet  3 , also supplies the overlap. In trouble-free operation of the sheet conveyance, the stop plates  28 . 1 ,  28 . 2  carry out a periodic reciprocating movement for the purpose of straight jogging of the sheets  3  deposited on the stack  14 . This reciprocating movement has a substantially lower amplitude than the stroke of the intercepting movement of the stop plate  28 . 2 .  
         [0024]     This application claims the priority, under 35 U.S.C. §119, of German application DE 10 2005 047 177.3, filed Sep. 30, 2005; the prior application is herewith incorporated by reference in its entirety.