μ-Synthesis Based Adaptive Robust Control of Linear-Motor-Driven Stages with High-Frequency Flexible Modes*

Linear motors have good potential to achieve high speed and high accuracy by eliminating gear related mechanical problems. By using the effective model compensation of nonlinear rigid-body dynamics, the close-loop bandwidth limitation due to the appearance of neglected high-frequency flexible modes has to be the main issue to maximize the achievable performance. In this paper, the modeling and identifications are carried out to verify the existing rigid-body and high-frequency dynamics. The μ-synthesis based adaptive robust control strategy is developed. The adaptive feedforward loop is used to keep good online parameter estimation and nonlinear model compensation, and also transfers the trajectory tracking problem into the traditional regulation problem which μ-synthesis control can more easily deal with. Since considering the fundamental flexible mode as a part of the nominal plant model, the μ-synthesis feedback loop can achieve higher close-loop bandwidth with the appearance of various model uncertainties. Comparative experiments have been done and the results show the excellent tracking performance of the propose algorithm.