Modeling and control of micropositioning systems using stewart platforms

The modeling and control of a 6-DOF Stewart micropositioning system with ea ch leg actuated by a respective piezoelectric actuator are considered in th is paper. The 12 multi-DOF passive joints are assumed to be well designed a nd fabricated so that guaranteed guiding precision and lack of backlash can be obtained. The dynamics model of the micropositioning system is derived first, and then a composite control strategy consisting of moving platform model-based feedback linearization and two sets of simple SISO fuzzy system s is proposed. By considering the internal axial forces of the six legs on the six spherical joints at the moving end as the virtual control inputs of the moving platform, feedback linearization can be easily used to derive t he desired control forces for the moving platform. The corresponding desire d Linear displacement of each piezoelectric actuator can then be computed b ased on the derived leg model, and each piezoelectric actuator's control vo ltage can be generated by the first set of independent leg fuzzy controls. The second set of fuzzy controls is suggested for the further enhancement o f robustness with respect to uncertainty. Computer simulations are presente d to illustrate the effectiveness of the suggested micropositioning control strategy. (C) 2000 John Wiley & Sons, Inc.