Suppression of harmonic positioning errors in ball-screw drives using Adaptive Feedforward Cancellation

Harmonic positioning errors can negatively affect the positioning accuracy of the ball screw drive system. This paper addresses the problem of harmonic positioning error suppression in ball-screw drives using Adaptive Feedforward Cancellation (AFC). AFC method is integrated with the dual (i.e., rotational and translational) feedback structure used in ball-screw drives. The ability of AFC to quench harmonic positioning errors originating from multiple input sources is analyzed, considering the effects of the commanded trajectory, motor torque ripples, rotary encoder measurement errors, and lead errors coming from the ball-screw mechanism. A new approach for parameter tuning of the AFC resonators is proposed which considers both the performance deterioration issue at frequencies outside the target harmonics, and also the robust stability requirement in the sense of limiting the peak loop sensitivity value. Effectiveness of the proposed AFC scheme for ball-screw drives is validated in experiments, demonstrating successful rejection of time-periodic machining force disturbances, as well as mitigation of displacement-periodic lead error and misalignment type errors. In the case of machining force rejection, 50-78% improvement is achieved in the standard deviation of the translational positioning error. In the case of position dependent disturbances, the improvement is typically in the 10-20% range and is most effective during constant velocity motion.