Combined Design of Adaptive Sliding Mode Control and Disturbance Observer with Friction Compensation for a Feed Drive System

Mechanical friction and disturbance are the key issues in precision control of mechanical systems especially in computer numerical controlled (CNC) feed drives. The friction does not only deteriorate the motion accuracy but also increases consumed energy of machining process. Feed drives have diverse applications and operate for a long time over the world, and therefore energy saving is highly expected. This paper proposes a combined design of adaptive sliding mode control and disturbance observer with a nonlinear static friction compensation to improve the motion accuracy and save consumed energy of a biaxial feed drive system. The friction compensator is designed based on a nonlinear friction model. Contour error, which is defined as the shortest distance between the actual position and the reference trajectory, is more important on the machining accuracy than the tracking error in each axis, and therefore contouring controllers are designed by feeding back contour errors. The disturbance observer and friction compensator are integrated into sliding mode contouring control and adaptive sliding mode contouring control. In order to verify the effectiveness of the combined design, comparative experiment was carried out with a biaxial feed drive system. The proposed approach effectively improved the contouring performance and achieved a significant reduction of the consumed energy.