Desired Compensation Adaptive Robust Contouring Control of an Industrial Biaxial Precision Gantry Subject to Cogging Forces

To obtain a higher level of contouring motion control performance for linear-motor-driven multi-axes mechanical systems subject to significant nonlinear cogging forces, both coordinated control of multi-axes motions and effective compensation of cogging forces are necessary. In addition, the effect of unavoidable velocity measurement noises needs to be carefully examined and sufficiently attenuated. To solve these problems simultaneously, in this paper, a discontinuous projection based desired compensation adaptive robust contouring controller is developed by explicitly taking into account the specific characteristics of cogging forces in the controller designs and employing the task coordinate formulation for coordinated motion controls. Specifically, based on the largely periodic nature of cogging forces with respect to position, design models consisting of known sinusoidal functions of positions corresponding to the main harmonics of the force ripple waveforms with unknown weights are used to approximate the unknown cogging forces. Theoretically, the resulting controller achieves a guaranteed transient performance and final contouring accuracy in the presence of both parametric uncertainties and uncertain nonlinearities. In addition, the controller also achieves asymptotic output tracking when there are parametric uncertainties only. Comparative experimental results obtained on a high-speed industrial biaxial precision gantry driven by linear motors are presented to verify the excellent contouring performance of the proposed control scheme and the ef∗THE WORK IS SUPPORTED IN PART BY THE US NATIONAL SCIENCE FOUNDATION (GRANT NO. CMS-0600516) AND IN PART BY THE NATIONAL NATURAL SCIENCE FOUNDATION OF CHINA (NSFC) UNDER THE JOINT RESEARCH FUND FOR OVERSEAS CHINESE YOUNG SCHOLARS (GRANT NO. 50528505). Address all correspondence to this author. fectiveness of the cogging force compensations.