Sliding Mode Contouring Control for Biaxial Feed Drive Systems with a Nonlinear Sliding Surface

Control input variance is one of the important criteria in machining because it affects the surface roughness, machining precisions and consumed energy. This paper presents a nonlinear controller design for biaxial feed drive systems for reducing the control input variance while maintaining the motion accuracy. The contour error, which is defined as the error component orthogonal to the desired contour curve, is considered to design the controller because it directly affects the precision of machined work-piece profile. The proposed nonlinear controller allows to adjust a controller gain from its low value to high value as the contour error changes from low value to high value and vice versa, and hence a closed-loop system simultaneously achieves low overshoot and settling time, resulting in a smaller error. In order to design the variable controller gain, a sliding mode control based on a nonlinear sliding surface is employed. Experimental results demonstrate a significant performance improvement in terms of control input variance while maintaining the motion accuracy.