Process and apparatus for characterizing and controlling a synchronous

Abstract

A process for characterizing the motion of a synchronous motor in microstep mode to achieve desired precise velocity motion at the final output. The motor velocity is directly proportional to the frequency of the microstep excitation pulses which control the rate of change of sine/cosine motor currents. The motor is initially operated at normalized frequency by means of a digital memory which controls a microstep clock pulse rate. Velocity and position errors at discrete locations are then determined and frequency correction terms are inserted into the memory at a predetermined time before the correction is to take effect on the motor. Also disclosed is apparatus for controlling the operation of the motor with the thus created characterization enhanced memory. The operating apparatus includes means to devise sine and cosine signals which always remain in synchronism and through which the signals from the memory are applied to the quadrature windings of the motor. The rate at which the sine-cosine waves are incremented is determined by the preprogrammed digital memory so that the resultant rotational velocity is controlled. Additionally, when the motor operates in an optical system, the preprogrammed memory corrects not only for motor motion errors but also for non-linearities or image plane distortions resulting from optical distortions in the lens system by modifying the scan speed in the manner previously mentioned. Additional aspects of the invention includes a feedback arrangement comprising the motor windings to correct for resistance variations and temperature changes, and a capacitor across each of the windings to reduce the effects mechanical resonance.