Wide range, high accuracy, electronically programmed speed control system

Abstract

The disclosed system utilizes digital electronic programming to establish the rotational or translational speed of a motor driven member. The desired speed can be selected by manipulating a set of digital switches. A stable oscillator is employed to generate a high frequency signal which is processed by frequency dividers to produce a modulaton frequency signal. The modulation frequency is supplied to an optical encoder having a rotary shaft adapted to be connected to a rotary member, the speed of which is to be controlled. The encoder is constructed and arranged to produce a phase variable output signal at the modulation frequency, the phase of such output signal being variable as a function of the shaft angle. The high frequency signal is also processed by digital circuits under the control of the digital selector switches to produce a variable reference frequency signal having a frequency corresponding to the modulation frequency plus or minus a number which is established by the setting of the selector switches. The speed control system includes means for comparing the frequency of the phase variable signal with the frequency of the reference signal. This comparison circuit controls a motor operating circuit which increases or decreases the speed of the drive motor for the rotary member, until the phase variable signal has the same frequency and phase as the reference signal. The digital generation of the reference frequency signal insures that its frequency is established and maintained with an extremely high degree of accuracy.