Hybrid Integral Reset Control with Application to a Lens Motion System

A hybrid integral controller with reset is proposed. This hybrid controller ensures improved low-frequency disturbance rejection properties under double integrator (PI²D) control without inducing the undesired increase of overshoot otherwise resulting from adding an extra linear integrator to a PID controller. The controller is applied to an optical lens motion system that requires PID control in one operating mode and PI²D control in the other, therewith motivating a hybrid integral control strategy. The reset element in the controller is included to improve transient performance. To guarantee closed-loop stability, a conditional (and partial) reset rule is introduced that restricts the input-output behavior of the dynamic reset element, i.e., the hybrid integrator with reset, to a bounded sector. As a result, stability can be guaranteed on the basis of a circle criterion-like argument and checked by (measured) frequency response data. Stability and performance of the hybrid integral control design with conditional (and partial) reset are investigated by application to a piezo-actuated lens system that is part of an industrial wafer scanner.