Real time implementation of a robust H∞ controller for a 2-DOF magnetic micro-levitation positioner

This paper presents a robust H_∞ controller for a two degree-of-freedom magnetic micro-levitation positioner and its real time experimental implementation. The experimental device described is designed for use in semiconductor manufacturing and consists of two U-shaped electromagnets and an actuator. First, we describe the system dynamics in state space form. Second, the system which is unstable in nature is stabilized using the H_∞ synthesis. The H_∞ control design problem is described and formulated in the standard form with emphasis on the selection of weighting transfer functions that reflect robustness and performance goals. The interactive computing environment MATLAB is used to calculate the controller. Third, the controller is implemented digitally using a digital signal processor with 16 bit A/D and 12 bit D/A converters. Finally, some simulation and experimental results are presented. The results obtained show that robust stability against model uncertainties is achieved and the performance goals are satisfied.