Motor speed control system

Abstract

A motor speed control system comprising a digital control circuit for working out and storing digital control signals in response to digital speed detection signals representing detected actual motor speeds and to digital speed command signals representing commanded nominal motor speeds, and further comprising an analog control circuit for controlling power supply to the motor in accordance with analog control signals corresponding to the digital control signals and with analog speed detection signals representing the detected actual motor speed. The digital control circuit receives the digital speed detection and command signals and produces, in a predetermined cycle, the digital control signal which is prepared based on a difference between the detected actual speed and the commanded speed of the motor, without being affected by ambient conditions of the system and drifts of control elements of the circuit during service. The analog control circuit regulates the power supply to the motor in quick response to the difference or deviation of the actual motor speed from the desired nominal speed during the predetermined cycle. The digital and analog control circuits cooperate to control the running speed of the motor with high levels of accuracy and response capability.