MODELING AND CONTROL OF A MICROPOSITIONING TOWER

The design of a feedback controller for the z-motion of a positioning tower made up of a vertical motion micro-positioning stage situated on a pair of x-y Klinger stages is discussed. A three-degree of freedom dynamic model was built using frequency response experimental data to represent the dynamics of the micropositioning tower system in the ver tical direction. Based on this model, a controller was designed which combines a PID closed-loop controller and a 4th-order Chebyshev lowpas s filter in series. Both simulation and real-time tests were performed for the designed control scheme, and the: tracking control performanc e, disturbance rejection and oscillation suppression have improved usi ng this controller. The settling time of the designed closed-loop cont rol system is one third of that of the open-loop system, and frequency response tests on the real system show that a flat magnitude response with less than 3 dB attenuation is achieved over the frequency range of 0-75 Hz using this controller. (C) 1997 Elsevier Science Ltd.