Variable structure control of AC servomotors for performance improvement in CNC applications

A variable structure controller is developed for AC servomotors used in computer-numerical-controlled (CNC) milling machines. The controller designed is implemented as an outer loop controller to a factory designed motor servo-pack system. The variable structure controller is designed for a fast response when the speed tracking error is large, and for small oscillations when the speed tracking error is small. The controller designed is installed on a CNC milling machine using a PC, and milling experiments were performed. The results show improved performance over the factory-designed controller.