Optimal Contouring Control of Multi-Axial Feed Drive Servomechanisms

Abstract

The capability of multi-axial machine tool feed drives to follow specified trajectories accurately is an important requirement for precision machining and especially so in applications involving high contouring speeds. In current generation machine tools, contouring is achieved by coordinating the commands to the individual feed drives, and implementing closed position loop control for each axis. The present paper deals with the evaluation of a cross-coupled compensator aimed specifically at improving contouring accuracy in multi-axial feed drives. The controller design is formulated as an optimal control problem. The performance index to be minimized weights the contour error explicitly. The controller is evaluated experimentally on a microcomputer controlled two-axis positioning table. Controller performance is evaluated for straight line, cornering and circular contours at feed rates varying from 2.25 m/min to 5.63 m/min. Measures of the steady state and transient contour errors are considered. The experimental results show that the proposed controllers reduce contouring errors considerably as compared to conventional uncoupled control of the multiple axes. The control action of the optimal controller is compared with that of more conventional uncoupled controllers.