Robust µ control and repetitive control for precision motion control of a pneumatic actuating table

Abstract

Because of uncertain and time-varying parameters influenced by air pressure and thermal parameters, applying H∞ robust control techniques to a pneumatic servo design has proven to be an efficient control strategy over the past few decades. However, because this method is a worst-case design that must yield robustness under given uncertainties, the inevitable trade-off may be too conservative and thus deteriorates its motion control performance. This study presents a robust µ control and repetitive control method for attaining precise dynamic tracking control of a pneumatic actuating table. The applied hybrid control structure consists of two feedback controllers. The first is a repetitive controller used to improve periodic tracking performance, and the second is a µ controller used to manage the dominant nonlinearities and uncertainties in pneumatic servo systems. This study presents an independent design of two controllers and takes advantage of the synergetic effect that results in an enhanced robust repetitive control design. In this study, a weighted average method is applied to determine optimal performance weights between these two control actions without violating robust stability. The experimental results on tracking dynamic motion profiles at perturbed operating regions for a heavy-duty pneumatic actuating table demonstrate the effectiveness of the proposed control method.