METHOD AND APPARATUS FOR POSITION ERROR COMPENSATION

Positioning errors of a moveable machine member are reduced by compensation for cyclic errors attributable to anomalies of a position transducer. Compensation values are produced which are unique only within the pitch of transducer measurement and are applied to correct the representation of measured position produced by the transducer. Positioning errors not attributable to the position transducer are corrected by compensation of position commands using compensation values associated with fixed calibration points. Use of both compensations is effective to eliminate residual errors in position correction which arise from use of calibration data created without correction of transducer cyclic errors.