Transfer loop synchronization in recirculating color printers

Abstract

A method and apparatus for synchronizing a transfer loop in a recirculating color printer includes two spaced pairs of pulleys having a conveyor belt positioned thereabout for conveying sheets to a transfer zone for image transfer and an external pair of idler pulleys. A gripper bar on the conveyor belt advances the sheet. A photoconductive drum includes a portion in the transfer zone. A corona generating device is located in the transfer zone to charge the sheet so that it will attract an image from the photoconductive drum. A motion control servo provides ground-referenced control of motion of the conveyor belt as the gripper bar is delivered to the transfer zone. In the transfer zone, control is shifted to a phase detector which maintains constant the initially sensed phase between idler pulleys and a photoconductive drum coaxial therewith. When the gripper bar has exited the transfer zone, control of the conveyer belts reverts to a ground based system and the velocity is maintained the same as it was with the gripper bar in the transfer zone. After the trailing portion of the sheet exits the transfer zone, a length compensation cycle begins which adjusts gripper bar position in accordance with length differences between the conveyor belt and photoconductive drum.