Effective Torque Ripple Compensation in Feed Drive Systems Based on the Adaptive Sliding-Mode Controller

Rotary or linear permanent magnet servo motor systems are widely used in mechatronics applications. When used in direct-drive configuration without any mechanical transmission, one of the bottlenecks in achieving precision positioning is the rejection of torque ripples, which are in the form of high-frequency harmonic disturbances varying with the operating condition of the servos. When attached to mechanical transmission, ripple disturbances occur due to misalignments, repetitive contact, or the process forces itself. In this paper, a robust adaptive sliding-mode control is proposed to reject harmonic disturbances in servo systems and attain accurate positioning. The overall sliding-mode control law is derived from the Lyapunov function without the switching condition allowing convenient implementation in a PID-like form. Effectiveness of the controller is demonstrated experimentally, where the ripple forces that occur due to mechanical contact in spur and worm-gear feed drive servo systems are compensated successfully.