Model reference adaptive control of air-lubricated capstan drive for precision positioning

Because friction-induced nonlinearities in positioning systems an generally range of motion-dependent, dual-model or dual-stage strategies are often a dopted to deal with the inconsistencies encountered when a system moves fro m submicrometer steps (micro mode) to larger scale strokes (macro mode). Al though good performance is usually obtained when each model/stage operates in its designed range of motion, a system frequently performs less satisfac torally when operating near the switching point between models or stages. A n air-lubricated capstan drive was used in this study to minimize the discr epancy between macro and micro modes, and a single-mode MRAC was developed to control the capstan drive system for precision positioning. Accuracy bet ter than +/-15 nm with no overshooting was achieved in all conditions teste d (including 50 nm, 500 nm and 10 mum steps). Disturbance resistance of the system also proved to be satisfactory. (C) 2000 Elsevier Science inc. All rights reserved.