Linear motor digital servo control

Abstract

A linear motor which mounts and drives a hammer bank shuttle assembly in reciprocating fashion within a dot matrix line printer is controlled by a digital servo. The digital servo includes an encoder for generating a pulse each time the shuttle assembly passes one of a succession of different positions along a linear path of movement therefor together with apparatus for measuring the time intervals between successive pulses, comparing the time intervals with a reference value, generating error signals in accordance with the difference and applying the error signals to vary the durations of driving pulses applied to the linear motor. Whenever the shuttle assembly reaches either of opposite end positions along the path of linear movement, the digital servo provides to the linear motor a turnaround signal of predetermined value which drives the linear motor through rebounding from an elastomeric stop member independent of the actual speed of the shuttle assembly and in a manner which is designed to compensate for friction losses during the rebounding. Following each rebounding of the linear motor from an elastomeric stop member the speed of the shuttle assembly is measured, stored and subsequently applied to adjust the value of the turnaround signal applied to the linear motor during the immediately following rebounding of the linear motor from the same elastomeric stop member.