Pre-compensation of contour errors in five-axis CNC machine tools

• Position commands to each axis are smoothed with quintic splines.
• Tracking errors of translational and orientation errors of drives are estimated.
• Contouring and orientation errors are predicted by considering servos and curved path.
• The position commands are pre-compensated to minimize five axis contouring errors.
• The algorithms are experimentally proven on a five axis machine.

This paper presents an analytical prediction and compensation of contouring errors in five-axis machining of splined tool paths. The position commands are first fitted to piecewise quintic splines while respecting velocity, acceleration and jerk continuity at the spline joints. The transfer function of each servo drive is kept linear by compensating the disturbance effect of friction with a feed-forward block. Using the analytically represented five-axis, splined tool path, splined tracking errors and kinematic model of the five-axis machine tool, contouring errors are predicted ahead of axis control loops. The contouring errors are decoupled into three linear and two rotary drives, and the position commands are modified before they are sent to servo drives for execution. The proposed method has been experimentally demonstrated to show significant improvement in the accuracy of contouring five-axis tool paths.