A coordinate design of two-degrees-of-freedom controller for fast and precise positioning

This paper presents a novel robust 2-degrees-of-freedom (2-DOF) positioning controller design methodology against frequency perturbations in mechanical vibration modes. The authors have already proposed an LMI (linear matrix inequality)-based feedforward (FF) compensator design to provide robust properties in positioning against the perturbations, where a feedback (FB) controller has been independently designed to ensure the robust stability on the basis of the 2-DOF controller design framework. A problem, however, still remains that the undesired response in the FB system due to the perturbations deteriorates the ideal response by the FF compensation. The proposed controller design, therefore, considers the FB system in the FF compensator design to solve the problem. In addition, the FB controller is redesigned to improve the positioning performance as a coordinate design between the FB and the FF controllers. The effectiveness of the proposed approach has been verified by numerical simulations and experiments using a prototype of galvano scanners.