Friction characterization and compensation of a linear-motor rolling-guide stage

In this article, characterization and compensation for the friction at the micro (plastic module and nonlinear spring) and macro modes (nonlinear Coulomb and Stribeck) of a linear-motor rolling-guide stage are reported. Because the system dynamics under the micro and macro modes are very different, the paradox to determine the optimal servo gains for both modes was solved by a two-stage fuzzy, PID controller. The fuzzy PID controller possesses a switching mechanism that continuously tunes the servo gains according to the system states. For the precision reversal path tracking at low speed, the system dynamics is dominated by the complicated and nonlinear friction characteristics. Due to the nonlinear spring characteristics, the friction was found unsymmetrical at the reversal points of the low speed path tracking. A simplified unsymmetrical friction model was proposed and proved to improved motion precision well. From the simulations and experiments, the proposed controller shows good tracking and positioning accuracy after friction compensation. (C) 2003 Elsevier Science Ltd. All rights reserved.