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

Robust H-infinity optimal control theory has proven to be one of the best techniques in linear control system design. The achievable robust stability and performance are high, but the resulting controllers are very complex and difficult to implement. As a result, few practical implementations of H-infinity control can be found in the literature. This paper presents a robust H-infinity controller for a two-degree-of-freedom magnetic micro-levitation positioner and its real time experimental implementation. The experimental device used in this study is designed for use in semiconductor manufacturing and consists of two U-shaped electromagnets and a manipulator. First, we describe the system dynamics in state space form. Second, the system which is unstable in nature is stabilized using the H-infinity synthesis. The H-infinity 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.