Programmable motor drive system for a polygon scanner

A scanning polygon in a ROS system is driven by a motor (20) whose speed is varied in response to desired changes in the resolution of the scan line being formed at a photosensitive surface. The motor of choice is a 2-phase AC hysteresis synchronous motor which is run by square wave input signals (48, 50) to the two motor windings which are 90 DEG out of phase. The motor input signals are at a power level which is variable (36) in response to changes (33) in the frequency of the square wave inputs. The power level variations are applied at the wave front transition so as to prevent the motor from jumping out of synchronism at these points, thus enabling smooth motor operation.