Sliding Mode Contouring Control for Feed Drive Systems Using Nonlinear Sliding Surface

Abstract

Machining accuracy as well as consumed energy saving is an important issue in machining by multi-axis feed drive systems. Contour error, which is defined as the error component orthogonal to the desired contour curve, is a better indication of machining precision. This paper presents a novel sliding mode contouring controller with nonlinear sliding surface to improve the machining accuracy for biaxial feed drive systems and reduce the consumed energy. Unlike the conventional sliding mode control, the proposed nonlinear sliding surface depends on the output so that the damping ratio of the system changes from its initial low value to final high value as the output changes from its initial value to the set point. Hence, the proposed algorithm allows a closed-loop system to simultaneously achieve low overshoot and short settling time, resulting in small error and small energy consumption. Because contour error is more important than the tracking error with respect to each feed drive, the contour error component is included in the proposed sliding surface. Simulation result for a typical biaxial feed drive system with bounded disturbance has shown an improved performance of the proposed method in terms of a contouring error and robustness to disturbance.