Method and apparatus for registering images on the front and the back of a single sheet of paper

摘要

A sensing and a control system are disclosed for eliminating registration error during duplex printing in a multi-pass xerographic printing system. The system registers a common physical edge of a sheet using multiple pairs of sensors. During the first pass or simplex pass, a first set of sensors detect the leading edge of a sheet of paper, and during the second pass or duplex pass, a second set of sensors detect the trailing edge of a sheet of paper. The control system regulates the rate at which a sheet should be driven to be in timed registration with a developed image on a photoreceptor at a transfer station. Variations in sheet size due to sheet cut tolerances are eliminated by the sensing and the control system since any offset is directed towards a common physical edge when developed front and back images on a photoreceptor are registered with a sheet of paper.