Contour Controller Design For Biaxial Table System Based On Friction Observer

For the high precision permanent magnet linear synchronous motor (PMLSM) direct drive X-Y table system, the influences to the system were analyzed, including the nonlinear dynamic friction forces, the velocity mismatch between two axes and the problem of the free-form contour error model. The real-time contour error method applicable for multi-axis nonlinear motion system was adopted to establish free-form contour errors model, and to enhance the contour error precision of X-Y table linear servo system, a robust control strategy based on combining the friction observer and contour controller was proposed.Nonlinear friction forces inevitably debase the contour error accuracy of X-Y table linear servo system. Firstly, the development and application, performance, construction, existing compensating method, dynamic and static model of friction forces were introduced in this paper. To represent all the friction force dynamics fully, this paper employ the LuGre friction model that include overall the static, dynamic and Stribeck nonlinear friction forces.Secondly, the development, application, construction and work principles of direct drive X-Y table were introduced in this paper. Mathematical models of single axis permanent magnet synchronous linear motor (PMLSM) and X-Y table were established according to the characters of PMLSM direct drive X-Y table. The factors that affect the contour precision were analyzed, so the contour error models of the linear and circular trajectory were established. For the time-varying free-form contour trajectory, real-time contour error method is adopted to establish free-form curve contour error model and eliminate the influences of the contour model error for the contour accuracy. of error dynamic system. Through feedback linearization and pole assignment control, the equivalent errors approached zero.Last, to eliminate nonlinear friction forces and improve the robust performance of the servo system, the friction observer base on LuGre model is designed. The influences to the servo contour performance by the velocity mismatch between two axis cannot be entirely eliminate by the friction observer, so the dynamic properties between two axes and the three kinds of observer states were combined to design the contour controllers of the direct drive X-Y table. Yokogawa LM110 permanent magnet linear synchronous motor X-Y table is considered as the controlled object, its mathematical model is established, and it is necessary to simulate and analyze above control strategies using MATLAB software. Simulation results show that the proposed contour controller base on friction observer can enhance the robustness and contour precision of X-Y table linear servo system.