Precision Motion Control Methodology for Complex Contours

A general precision motion control methodology for complex contours is proposed in this paper. Each motion servomechanism dynamic model is divided into a linear portion and a portion containing nonlinear friction, unmodeled dynamics, and unknown disturbances. A full state feedback controller, based on a state space error system model, is developed to track general reference trajectories. The lumped static, Coulomb, and Stribeck friction effects are described using the Tustin friction model. Unmodeled dynamics and unknown disturbances are estimated using a Kalman filter that employs a first-order stochastic model. The nonlinear friction, unmodeled dynamics, and unknown disturbances are directly canceled by the controller. In the proposed motion control methodology, complex contours (i.e., contours whose radii of curvature constantly change along the contour) do not need to be decomposed into line segments and arcs and the reference signals do not need to be prefiltered. Also, the controller structure does not need to be adjusted to track different types of contours. Experiments are conducted on a two-axis laboratory grade machine tool for elliptical, limacon, and free-form contours. The results demonstrate the excellent tracking performance of the proposed motion control methodology. They also demonstrate that the performance is independent of the contours’ complexity.