Hybrid control for motion systems with improved disturbance rejection
In this paper a hybrid control design for motion systems is
proposed that aims at improved disturbance rejection under equal noise response. Typically performance-relevant frequency contributions in the error response are up-scaled through linear filtering, subjected to a nonlinear weighting, that is, inducing extra controller gain when large enough and otherwise neglected, and subsequently down-scaled as to maintain closed-loop stability. At a wafer stage of an industrial wafer scanner such a strategy is demonstrated to improve low-frequent disturbance suppression while limiting the amplification of high-frequent noise.