A Pole-Placement-Based Variable-Gain Observer for Precision Motion Stages: Addressing the Disturbance-Noise Trade-Off

Accurate pattern transfer in the lithography process demands extreme positioning accuracy. However, various external disturbances acting on the wafer stage can lead to positioning errors. To address this issue, this paper proposes a pole-placement-based Variable-Gain Extended State Observer (VGESO). First, the trade-off between disturbance rejection and noise attenuation faced by conventional Extended State Observers (ESOs) in precision motion systems is analyzed. Then, a modified ESO structure is introduced, in which two pole-related parameters are employed to adaptively adjust the observer gains. These parameters enable effective suppression of both low-frequency disturbances and high-frequency measurement noise within their designated ranges. Finally, simulation results verify the effectiveness and superior performance of the proposed method.