A hybrid digital and analog controller for DC and brushless servomotors

A hybrid digital and analog controller for DC and brushless servomotors has been developed. Given a serial pulse train whose pulse count and frequency specify, respectively, the target position and the velocity of the motor under control, the digital positioning loop compares the target position in real time with the actual position, indexed by the incremental encoder, to derive the motor to the specified position. When the motor reaches the specified position, the position control is automatically switched to the analog positioning loop. Operating as a proportional-derivative (PD) regulator in the static state, the analog positioning loop eliminates the instability which would otherwise be caused by the response delay of the digital loop. Each block necessary to implement 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, NC (numerical control) machinery, and measuring instruments