Initial Friction Compensation Using Rheology-Based Rolling Friction Model in Fast and Precise Positioning

This paper presents an initial friction compensation by a disturbance observer which is designed on the basis of a rolling friction model (RFM) for the fast and precise positioning of ball-screw-driven table systems. Rolling friction in the table drive mechanism behaves as a nonlinear elastic component in the microdisplacement region, deteriorating the fine settling performance. The effects of the rolling friction on the positioning, therefore, should be compensated to provide the desired control performance. In the compensator design, a feedback control with a disturbance observer allows the plant system to behave as a nominal one with a robust stability and compensates for the effects of nonlinear friction on the positioning performance. The disturbance observer, however, inherently includes an estimation delay at the starting motion due to low-pass filters and delay components. In this paper, therefore, an RFM is adopted as an initial value compensation of the disturbance observer to compensate for the initial friction behavior, providing the delay-free estimation. The proposed compensation method has been verified by numerical simulations and experiments using a prototype for industrial positioning devices.