A cross-coupled controller, designed to improve high-speed contouring accuracy independently of tracking accuracy in biaxial machine tool feed drive servomechanisms, is presented here. The controller parameters depend on the instantaneous slope of the desired contour and hence vary with time for curved contours, resulting in a time-varying controller. An approximate stability analysis of the controller is presented. The proposed controller is evaluated experimentally on a microcomputer controlled two-axis positioning table and compared to a more traditional uncoupled controller. Controller performance is evaluated for straight line, cornering and circular contours at feed rates varying from 2.25 m/min to 7.2 m/min. The experimental results show that the proposed controller reduces contouring error as compared to the uncoupled controller and leaves the tracking error practically unchanged. The cross-coupled controller is simple to implement and is practical.
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.
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