Sheet transport and registration apparatus

Claim 1

An electrophotographic printing machine of the type having a document handling apparatus for advancing individual document sheets from a stack to an exposure station and for returning the document sheets to the stack in repeated cycles, a processor for forming copies of the documents, and a copy sheet attaching station with each copy sheet being aligned during the movement thereof to the sheet attaching station, wherein the improvement includes: a registration edge; a pair of idler rollers spaced from one another to define a gap therebetween; a drive roller spaced from said pair of idler rollers and having a portion thereof interposed between said pair of idler rollers in the gap with the copy sheet passing through the gap having one surface thereof contacting said pair of idler rollers and the other surface thereof contacting said drive roller so to bend the copy sheet in the gap, said drive roller and said pair of idler rollers having their respective longitudinal axes substantially parallel to one another and extending in a direction transverse to said registration edge; and means for resiliently urging said pair of idler rollers into contact with the copy sheet sheet, said drive roller and said pair of idler rollers moving the copy sheet along a path having a forward direction of movement and a lateral direction of movement substantially normal to the forward direction with the lateral movement of the copy sheet causing the side edge of the copy sheet to engage said registration edge so as to be aligned thereat, said drive roller and said pair of idler rollers applying a moving force having a magnitude proportional to the thickness of the copy sheet so that the moving force varies as a function of the thickness of the copy sheet being moved with the copy sheet slipping laterally when engaging said registration edge to prevent buckling thereof.