Steady-state performance optimization for variable-gain motion control using extremum seeking

In this paper, we employ an extremum-seeking control strategy for steady-state performance optimization of variable-gain controllers for linear motion systems. Variable-gain control can balance the tradeoff between low-frequency disturbance suppression and sensitivity to high-frequency noise in a more desirable manner than linear controllers can. However, the optimal performance-based tuning of the variable-gain controller parameters is far from trivial. A model-based performance optimization method would require an accurate disturbance model, which may be hard to obtain in practice. The extremum-seeking controller proposed here does not require any plant- or disturbance model and therewith circumvents this difficulty. To illustrate the results, the variable-gain controller of a short-stroke wafer stage of a wafer scanner is optimized using extremum-seeking control.