Dual-loop Controller Design Considering Robust Vibration Suppression in Piezo-actuated Stage Systems

This paper presents a controller design approach considering robust vibration suppression against resonant frequency variations in piezo-actuated systems. In piezo-actuated systems, the improvement of suppression performance with respect to external disturbances and nonlinearities such as hysteresis and creep by the expansion of feedback control bandwidth is indispensable for achieving high-precision positioning. The vibration suppression approach is a key technology for the expansion of bandwidth. From a practical point of view, a minor feedback loop including a simple compensator with a few parameters to increase the design freedom is added to the general feedback control system. In the minor-loop design, the reduction of sensitivity gain at around the resonant frequencies is considered to suppress the residual vibration of the references and disturbances, and the loop-shaping approach based on the frequency domain is adopted to provide an intuitive and practical design guideline. A major-loop for an augmented plant, including the minor-loop, is designed by considering the system stability, servo bandwidth, and settling performance. The proposed approach is verified by conducting experiments using a commercial piezo-actuated stage system.