Modeling and control of a micro-positioning 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 vertical direction. Based on this model, a controller was designed which combines a PID closed-loop controller and a 4th-order Chebyshev lowpass filter in series. Both simulation and real-time tests were performed for the designed control scheme, and the: tracking control performance, disturbance rejection and oscillation suppression have improved using this controller. The settling time of the designed closed-loop control 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.