A hybrid digital and analog controller for DC and brushless servomotors

Abstract

A hybrid digital and analog controller for DC and brushless servomotors is described. Given a serial pulse train whose pulse count and frequency specify the target position and the velocity of the motor under control, respectively, the digital position loop compares it in real time with the actual position indexed by the incremental encoder, to drive the motor to the specified position. When the motor reaches the specified position, the position control is automatically switched to the analog position loop. Operating as a proportional-derivative regulator in the steady state, the analog position loop eliminates the instability that would otherwise be caused by the response delay of the digital loop. Each block necessary for implementing the hybrid controller is integrated into a monolithic or hybrid IC form for easy assembly. The resultant controller is compact and can be widely applied to robots, numerical control machinery, and measurement instruments.<>