Sheet deskewing with automatically variable differential NIP force sheet driving rollers

Abstract

A system of deskewing sheets moving in a process direction in a sheet path, such for a printer, by variably differentially driving the sheet in transversely spaced apart sheet driving nips formed by sheet driving rollers and mating idler rollers in response to sheet skew sensing. A variable differential nip force is applied via the respective idlers sufficient to provide a differential sheet driving velocity of a sheet in the respective sheet driving nips. The idler rollers may be mounted on a common shaft which is pivoted by a pivoting system to provide sufficiently different nip forces on the two driving rollers for a sufficient time to deskew the sheet. The sheet driving rollers may be commonly driven on a single fixed shaft by a single drive system.

1 . In a printing system with a paper path for feeding print media sheets in a process direction, said paper path having a sheet deskewing system, wherein said sheet deskewing system has a sheet skew detection system and at least two sheet deskewing nips transversely spaced apart across said paper path for variably differentially driving a print media sheet in said sheet deskewing nips to provide partial rotation of a print media sheet in said nips for sheet deskewing in response to said sheet skew detection system while said sheet is moving in said process direction; wherein said at least two deskewing nips are formed by first and second sheet driving rollers and mating first and second mating idler rollers; and wherein a variable differential nip force system provides a variable differential nip force in said nips to provide differential sheet feeding in said process direction in said nips with differential movement of said first and second idlers towards and away from sheet driving rollers in response to said sheet skew detection system to provide said partial rotation of said print media sheet in said nips for said sheet deskewing in response to said sheet skew detection system.  
   
   
       2 . The printing system of  claim 1 , wherein said first and second mating idler rollers are mounted on a pivotal member, and wherein said variable differential nip force system comprises a tilting drive system for tilting said pivotal member in response to said sheet skew detection system.  
   
   
       3 . The printing system of  claim 1 , wherein said variable differential nip force system automatically reduces the nip force in one of said sheet deskewing nips relative to said other sheet deskewing nip sufficiently to allow a sheet therein to slip relative to said other sheet deskewing nip.  
   
   
       4 . The printing system of  claim 1 , wherein said first and second sheet driving rollers are elastomeric and radially deformable, to provide a variable differential radial deformation of at least one of said radially deformable sheet driving rollers and wherein said variable differential nip force system automatically increases the nip force in one of said sheet deskewing nips relative to said other sheet deskewing nip to provide said variable differential driving of said sheet in said sheet deskewing nips.  
   
   
       5 . The printing system of  claim 1 , wherein said first and second sheet driving rollers are elastomeric and radially deformable and have nominal radius mounted on a common drive shaft, and wherein said first and second idler rollers are non-elastomeric rollers on a common idler roller mounting shaft, and wherein said common idler roller mounting shaft is pivotal about a pivot axis between said first and second idler rollers, and wherein said variable nip force system forcibly pivots said common idler roller mounting shaft about said pivot axis in response to said sheet skew detection system to provide a variable radial deformation of a nominal radius of at least one of said radially deformable sheet driving rollers to provide said variable differential driving of said print media sheet in said sheet deskewing nips to provide said partial rotation of said print media sheet in said nips for said sheet deskewing in response to said sheet skew detection system.  
   
   
       6 . The printing system of  claim 1 , wherein said first and second idler rollers are non-elastomeric rollers rotatably mounted on a pivotal common idler roller mounting shaft which is pivotal intermediately of said nips, and wherein said variable nip force system forcibly pivots said common idler roller mounting shaft.  
   
   
       7 . The printing system of  claim 1 , wherein a spring system maintains a nominal nip force in said sheet deskewing nips.  
   
   
       8 . A method of deskewing sheets moving in a process direction in a sheet path with a sheet deskewing system, comprising: 
 variably differentially driving a sheet moving in said process direction for sheet deskewing by partially rotating that sheet by variably differentially driving that sheet with at least two transversely spaced apart sheet deskewing nips, wherein said sheet deskewing nips are formed by first and second sheet driving rollers and mating first and second idler rollers,    by applying a variable differential nip force to said first and second idlers in response to sheet skew detection sufficient to provide said variable differential driving of said sheet in said sheet deskewing nips sufficient to provide said partial rotation of said sheet in said nips for said sheet deskewing.    
   
   
       9 . The method of deskewing sheets of  claim 8 , wherein said first and second idler rollers are automatically variably differentially driven towards and away from said first and second sheet driving rollers to change their respective nip forces, and said first and second sheet driving rollers are commonly driven by a common drive system on a single fixed drive shaft.  
   
   
       10 . The method of deskewing sheets of  claim 8 , wherein said first and second idler rollers are commonly rotatably mounted on a pivotal mounting member which is automatically variably pivoted to oppositely move said first and second idler rollers towards and away from said first and second sheet driving rollers to change their respective nip forces.  
   
   
       11 . The method of deskewing sheets of  claim 8 , wherein said first and second sheet driving rollers are elastomeric and radially deformable.  
   
   
       12 . The method of deskewing sheets of  claim 8 , wherein said first and second idler rollers are non-elastomeric rollers on a common idler roller mounting shaft, and wherein said common idler roller mounting shaft is pivotal about a pivot axis between said first and second idler rollers, and wherein said applying of said variable differential nip force to said first and second idlers is in response to sheet skew detection by forcibly pivoting said common idler roller mounting shaft about said pivot axis in response to said sheet skew detection to provide said variable differential driving of said sheet.  
   
   
       13 . The method of deskewing sheets of  claim 8 , wherein said first and second idler rollers are rotatably mounted on a common idler roller mounting member pivotable about a pivot axis intermediate of said first and second sheet driving rollers, wherein said variable differential nip force is provided by forcibly pivoting said mounting member about said pivot axis from adjacent to one end thereof.