Sheet transport device

Abstract

The invention relates to a sheet transport device, preferably for arrangement on the sheet-delivery side of a printing machine, including at least two rollers that are axis-parallel with respect to each other and form between them a transport gap for the sheets for a reversible deformation and stiffening of the sheets respectively transported between them. The rollers are such that a sheet which exceeds a specific intrinsic stiffness is able to move the rollers apart against the applied force in order to avoid said sheet's deformation and/or in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, a rounded transition has been implemented in at least one section.

1 . Sheet transport device, preferably for arrangement on the sheet-delivery side of a printing machine, specifically an electrophotographically operating printing machine, comprising: 
 at least two rollers that are axis-parallel with respect to each other and form between them a transport gap for the sheets, the relative distance between said rollers being variable in that the rollers and/or zones of the rollers can be crossed or staggered relative to each other for a reversible deformation and stiffening of sheets respectively transported between them, and a force being applied toward a magnification or increase of said crossing of the rollers and/or the roller zones, and the deformation of the sheet being pre-specified, characterized in that the rollers are arranged and configured and the application of force is set or selected in such a manner that a sheet which exceeds a specific intrinsic stiffness is able to move the rollers apart against the applied force in order to avoid said sheet's deformation.    
   
   
       2 . Device as in  claim 1 , characterized in that the application of force is set or selected relative to a weight per unit area of the sheet.  
   
   
       3 . Device as in  claim 2 , characterized in that the application of force relative is set or selected relative to the force applied to a sheet having a weight per unit area, which is greater than or approximately equal to approximately 220 grams per square meter.  
   
   
       4 . Device as in  claim 2 , characterized in that the application of force is set or selected in such a manner that a sheet having a weight per unit area of greater than or approximately equal to 100 grams per square meter is deformed to its maximum.  
   
   
       5 . Device as in  claim 2 , characterized in that one of the rollers is driven by a shaft, while the other roller, follows on its axle said other roller.  
   
   
       6 . Device as in  claim 5 , characterized in that the follow-roller is subject to the application of pressure in the direction toward the driven roller.  
   
   
       7 . Device as in  claim 2 , characterized in that the applied force can be set in such a manner that, taking into consideration the inherent weight of the roller to which the force is applied, said applied force corresponds to a weight of approximately 400 grams.  
   
   
       8 . Device as in  claim 2 , characterized in that the two rollers have profiles that are in engagement with each other in the transport gap, whereby the profile of a first roller has a reduced diameter in a central region, while the profile of a second roller has an enlarged diameter in an approximately corresponding region such that the profile engagement can serve for stiffening a respective sheet transported through the transport gap.  
   
   
       9 . Device as in  claim 8 , characterized in that, in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, a rounded transition is implemented in at least one section.  
   
   
       10 . Device as in  claim 8 , characterized in that the rollers are configured symmetrically with respect to a respective diameter extreme.  
   
   
       11 . Sheet transport device, preferably for arrangement on the sheet-delivery side of a printing machine, specifically an electrophotographically operating printing machine, comprising: 
 at least two rollers that are axis-parallel with respect to each other and form between them a transport gap for the sheets, said two rollers having profiles that are in engagement with each other in the transport gap, whereby the profile of a first roller has a reduced diameter in a central region, while the profile of a second roller has an enlarged diameter in an approximately corresponding region such that the profile engagement can serve for stiffening a respective sheet transported through the transport gap, characterized in that, in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, a rounded transition has been implemented in at least one section.    
   
   
       12 . Device as in  claim 11 , characterized in that, in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, a rounded transition is provided at least in respectively one section on both sides of the diameter maximum.  
   
   
       13 . Device as in  claim 12 , characterized in that the rollers are configured symmetrical with respect to a respective diameter extreme.  
   
   
       14 . Device as in  claim 13 , characterized in that the second roller is essentially slightly barrel-shaped.  
   
   
       15 . Device as in  claim 13 , characterized in that the first roller has approximately the shape of a dumbbell.  
   
   
       16 . Device as in  claim 13 , characterized in that, between the axis-parallel rollers a force acts in engagement direction, said force being set or selected in such a manner that a thin sheet is deformed to stiffen it in such a manner that it follows the profile of the second roller.