Perfect tracking control considering generalized controllability indices and application for high-precision stage in translation and pitching

Abstract

High-precision stages are widely used for manufacturing semiconductors and flat panels. These high-precision stages have become multi-input multi-output (MIMO) systems with six-degrees-of-freedom (DOF); hence, the coupling between the translation and pitching motion deteriorates the control performance. This study proposes the multirate feedforward control for MIMO systems and applies it to these high-precision stages. The multirate feedforward control designs the stable inversion for the unstable discretization zero problem. In addition, the design of the MIMO multirate feedforward controllers has a degree of freedom to design the B matrix according to the selection of the generalized controllability indices. In conventional control methods such as precompensated decoupling controllers, it is theoretically impossible to achieve perfect tracking because unstable discretization zeros are generated. In this study, the proposed method is applied to the translation and pitching motion of a high-precision stage, and it achieves perfect tracking in the simulation. The effectiveness of the proposed method is verified experimentally.