A Hybrid Time-Varying Integrator-Gain Control Strategy for an Ultra-Precision Wafer Stage

The wafer stage is a crucial component in lithography machines, requiring nanometer-level motion control accuracy. To overcome the performance limitation between low-frequency trajectory tracking performance and high-frequency noise amplification of fixed-value hybrid integrator-gain system (HIGS), a novel hybrid time-varying integrator-gain control (HTVIGC) strategy is proposed for an ultra-precision wafer stage. Specially, a time-varying parameter design method is newly introduced into HIGS, and the integrator frequency and gain value in HTVIGC vary with the trajectory phase. Furthermore, the time-domain properties and approximate frequency-domain characteristics of HTVIGC are analyzed in detail, and the stability condition of the closed-loop system is obtained through an analysis similar to the circle criterion. Finally, experimental results on wafer stage demonstrate that the proposed method can achieve excellent control performance in both the acceleration and constant velocity phases of the trajectory.