Print head velocity control system using analog and digital feedback

Claim 2

Print head velocity control system for maintaining a constant velocity of a print head as it moves across a record medium, characterized in that it comprises : motor means (36) having a rotatable shaft, said shaft rotating at a velocity related to the magnitude of a control signal applied to said motor means, said shaft means being coupled to said print head such that said print head moves as said shaft rotates; emitter means (40) coupled to said shaft for providing pulses (40a, 40b) representing increments of movement of said shaft; processor means (28) for providing a reference voltage, said processor means responding to said emitter means pulses to vary said reference voltage as the time between emitter pulses varies; frequency-to-voltage converter means (33) responsive to said emitter means pulses for providing a voltage related to the velocity of rotation of said shaft; and means (35, 37) for generating said control signal in response to the difference between said reference voltage and said voltage from said frequency-to -voltage converter means.

Claim 3

System in accordance with claim 1 in which said processor means includes: a microcomputer which receives said emitter means pulses; and a digital-to-analog converter connected to the output of said microcomputer for generating said reference voltage. 3. System in accordance with claim 3 including a ramp generator connected to said digital-to-analog converter for generating a voltage representing the desired velocity profile of said shaft means. 4. System in accordance with claim 3 in which said digital-to-analog converter supplies signals to said ramp generator which define the maximum positive and negative limits of said ramp generator output voltage. 5. System in accordance with claim 3 or 4 including summing means for comparing the output voltage of said ramp generator with the output of said frequency-to-voltage converter means to generate said control signal. 6. System in accordance with claim 5 including current feedback means connected to said summing means, said current feedback means being responsive to the current in said motor means for limiting the magnitude of said control signal which can be applied to said motor means. 7. System in accordance with claim 5 or 6 including pulse width modulator means connected to the output of said summing means, the output of said pulse width modulator means being supplied as said control signal to said motor means.