Method and apparatus for conveying sheets onto a stack

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.

1 . A method for conveying sheets onto a stack, which comprises the steps of: 
 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.    
     
     
         2 . The method according to  claim 1 , which further comprises stopping the conveyance after the signal has been output.  
     
     
         3 . The method according to  claim 1 , which further comprises controlling a movement of the stop such that a sheet falls freely down onto the stack if the sheet lies over the stop.  
     
     
         4 . The method according to  claim 3 , which further comprises moving the stop away from the stack with an acceleration that overcomes an inertia of the sheet.  
     
     
         5 . The method according to  claim 1 , which further comprises actuationg a sheet slide such way that a sheet falls freely down onto the stack if the sheet lies over the stop.  
     
     
         6 . The method according to  claim 1 , which further comprises aligning the sheets coming after the output of the signal, during a conveyance of the sheets, by varying a speed of a sheet differently in regions transverse with respect to a conveying direction.  
     
     
         7 . The method according to  claim 6 , which further comprises causing braking forces to act on the sheet by setting a pneumatic brake on both sides with a different braking action at a distance from a sheet axis of symmetry lying in the conveying direction.  
     
     
         8 . The method according to  claim 7 , which further comprises setting a braking action in dependence on a printing image.  
     
     
         9 . The method according to  claim 1 , which further comprises: 
 providing a detector emitting measuring signals in a region of the stop adjacent to the stop surface; and    monitoring the position of the side edge by a measurement of a signal propagation time of the measuring signals propagating between the detector and a respective sheet.    
     
     
         10 . The method according to  claim 9 , which further comprises sending out the measuring signals toward an underside of the sheet located behind the stop surface.  
     
     
         11 . An apparatus for conveying sheets onto a stack, the apparatus comprising: 
 a device for moving the sheets forward one after another over the stack;    at least one stop with a stop surface for a side edge of the sheet, said stop being moved to and fro for aligning the sheets;    at least one detector for determining a position of the side edge in relation to the stop surface; and    a control device connected to said at least one detector, said control device causing a positioning and/or aligning of the sheets as necessary.    
     
     
         12 . The apparatus according to  claim 11 , wherein: 
 said stop has an edge located at a top; and    said detector is aimed at a region in an environment beside the sheet edge.    
     
     
         13 . The apparatus according to  claim 11 , wherein during conveyance of a sheet by grippers disposed on a gripper bar, said detector has an ultrasonic distance sensor with a registration region lying outside a path of the gripper bar.  
     
     
         14 . The apparatus according to  claim 11 , wherein said stop together with said detector can be positioned in a conveying direction of the sheet in accordance with a sheet length.  
     
     
         15 . The apparatus according to  claim 11 , further comprising a pneumatic actuator connected to said control device, said pneumatic actuator provided for accelerating said stop transversely with respect to the conveying direction.