Robust contouring control for biaxial feed drive systems

Contouring control is an effective method of providing precision machine tool control, and various such methods have been proposed to date. However, most existing methods require prior exact knowledge of feed drive dynamics. This paper presents a robust contouring control system design that takes into account dynamics modelling errors and disturbances such as friction. We first present a controller design for biaxial feed drive systems that enables assignment of controller gains, for reducing the error component orthogonal to the desired contour curve, independent of the tangential error component. Although this design provides better control performance with small control input variance, an inherent contour error exists because of the difficulty in calculating the exact contour error for any contour curve in real time. To address this problem, a reference adjustment method is used to estimate the actual contour error. A robust contouring controller is proposed based on the variable structure control. The effectiveness of the robust controller is demonstrated by experimental results using circular and non-circular contour curves.