Robust feedback control for automated force/position control of piezoelectric tube based microgripper

This paper addresses the problem of automated grasping tasks using a piezoelectric microgripper, based on two piezoelectric tube actuators, for an accurate and rapid micro/nano manipulations. For this matter, we propose a strategy to control the position of one actuator and a hybrid approach that switches between force and position control of the second actuator. However, the nonlinearities and the uncertainties that characterize the piezoelectric actuators and the different properties of the manipulated objects make the control of such system not a trivial task. To handle this problem we propose to model the microgripper system by linear interval system, that embraces the parameters uncertainties, and synthesize a robust controller to control the interval system based on the classical output-feedback control design. The robust control synthesis consists on the search of robust gains for the controller that ensure the inclusion of the eigenvalues of the interval closed-loop system in a desired region of the complex plane. The effectiveness of the control strategy is illustrated by a real experimentation where the position and the manipulation force control show to maintain the desired performances under system uncertainties.