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 b est 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 im plementations of H-infinity control can be found in the literature. Th is paper presents a robust H-infinity controller for a two-degree-of-f reedom magnetic micro-levitation positioner and its real time experime ntal implementation. The experimental device used in this study is des igned for use in semiconductor manufacturing and consists of two U-sha ped electromagnets and a manipulator. First, we describe the system dy namics in state space form. Second, the system which is unstable in na ture is stabilized using the H-infinity synthesis. The H-infinity cont rol design problem is described and formulated in the standard form wi th emphasis on the selection of weighting transfer functions that refl ect robustness and performance goals. The interactive computing enviro nment MATLAB is used to calculate the controller. Third, the controlle r is implemented digitally using a digital signal processor with 16 bi t A/D and 12 bit D/A converters. Finally, some simulation and experime ntal results are presented. The results obtained show that robust stab ility against model uncertainties is achieved and the performance goal s are satisfied.