Variable speed photographic paper feed system

Abstract

A paper feed system for a photographic printer which includes a motor driven takeup spool which pulls paper from a supply reel across a paper deck to the takeup spool. An encoder is turned by the paper, and provides encoder pulses which indicate incremental rotation of the encoder, and thus incremental movement of the paper. Prior to each paper feed cycle, a slow-down count is subtracted from a total feed length count to provide a high speed count. The motor is initially operated at high speed until the encoder has produced pulses equal to the high speed count. The motor is then switched to the low speed for the remaining portion of the paper feed corresponding to the slow-down count. During each paper feed cycle, the encoder pulses during the high speed portion of the paper feed are monitored to provide an indication of the average velocity of the paper during the high speed feed. The slow-down count for each paper feed cycle is a function of the average velocity from the previous paper feed cycle. As the takeup roll fills (i.e. its diameter increases), the paper velocity increases, and the slow-down count is increased to allow the paper the necessary time to equilibrate at the low speed prior to stopping the motor.