Robust reset control design by loop shaping for piezoelectric-actuated positioner in presence of nonlinearity

Loop-shaping is widely used in precision motion control, but conventional approaches — focused on phase margin and open-loop gain — are inadequate for piezo positioning systems where open-loop phase critically affects performance. This paper proposes generalized loop-shaping guidelines tailored for nonlinear piezo-actuated stages. A constant-in-gain lead-in-phase reset controller is developed to implement the guidelines by overcoming waterbed effect in linear control. An intuitive methodology for shaping filter design is presented to ensure reliable reset control implementation. Using (higher-order) sinusoidal input describing functions, nonlinear motion control is designed. Experiments demonstrate closed-loop bandwidth flatness ( ± 1 dB) and enhanced sensitivity function.