Dynamic Contour Error Estimation and Feedback Modification for High-Precision Contouring

Cross-coupling control (CCC), which acts on contour error, is intended to improve contouring precision of multiaxis servosystems. The contour error estimate (CEE) significantly affects contouring precision. Conventional CEE methods rely on static single-point techniques to reconstruct contour error using current position error and an estimate of the reference map at the lead point. The performance of such static CEE methods deteriorates dramatically with increasing contour feedrate and at sharp corners. Hence, a dynamic CEE algorithm based on the Newton update algorithm is proposed to achieve high-precision CEE. Since the convergence rate of the Newton algorithm is user assignable and independent of the reference contour, the proposed CEE stays almost identical to the contour error for vastly different feedrates or sharp corners. Multiaxis cross-coupling adds more design steps for the position control loops. Therefore, in this paper, feedback signals are modified such that a separate cross-coupling controller is no longer needed. It has been shown, analytically and experimentally, that the modified feedback in combination with integral sliding mode control provides simpler design and fewer steps in comparison to conventional CCC designs. Moreover, the proposed CEE and the concept of modified feedback together result in reduced contour error. Various experiments are reported to show the effectiveness of the proposed algorithm at high feedrates and for sharp corners.