Sliding mode contouring control design using nonlinear sliding surface for three-dimensional machining

Abstract

Machining accuracy as well as consumed energy saving are important issues in machining by multi-axis feed drive systems. The contour error, which is defined as the error component orthogonal to the desired contour curve, is a good indicator of machining precision. This paper presents a novel sliding mode contouring controller with nonlinear sliding surface to improve the machining accuracy for three-dimensional machining. Unlike the conventional sliding mode control design, the proposed nonlinear sliding surface depends on the output so that the damping ratio of the system changes from its initial low value to its 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 settling time, resulting in a smaller error. Because the 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. By using the proposed method, simulation and experimental results for a desktop three-axis machine show a significant performance improvement in terms of the contour error.