IDLER ROLL DESIGNED TO PREVENT SHEET SKEW
Original Publication Date: 1993-Oct-31
Included in the Prior Art Database: 2004-Apr-06
Xerox Disclosure Journal
Disclosed is an idler roll designed to prevent sheet skew in a sheet transport system for use in electrophotographic printing and copying machines. Skewing of sheets is a common problem when transporting sheet media with pinch roll systems containing elastomer covered drive rolls. This is due to the effective velocity of an elastomer covered drive roll being non-uniform along its axis. The normal design of an idler roll, that is, the roll loaded against the drive roll, calls for a roll surface that is smooth, thus having a low coefficient of friction. An improved idler roll design comprises fabricating the idler roll with a rough material thereby increasing the rolls coefficient of friction. A further aspect of the improved idler roll design in the case where more than one roll is used is to mount a multiplicity of drive rolls on a single drive access so that all idler rolls rotate at the same angular velocity. In a normal pinch roll drive system, if the idler roll engagement force is different from one end of the roll to the other it is likely that the velocities will also be different. This situation will lead to sheet skew. Elastomer roll systems will try to compensate or self-adjust so that the velocities at all points are in equilibrium. In the case of parallel roll system, the adjustment takes place through the distribution of drive force along the roll axis. Higher drive forces will be transmitted from the elastomer roll to the idler roll in the areas that travel at a higher velocity than will be transmitted in areas that travel at a lower or slower velocity. This situation leads to velocity adjustments for the reasons described herein. If enough torque can be transmitted through the nip formed between the rolls, the elastomer roll will drive itself to a velocity equilibrium condition at all points along its axis. If the idler roll surface has a low coefficient of friction, the amount of velocity adjustment that can occur is limited.