Force estimation in a 2-DoF piezoelectric actuator by using the inverse-dynamics based unknown input observer technique

The aim of this paper is the estimation of force in a two degrees of freedom (2-DoF) piezoelectric actuator devoted to microrobotic manipulation tasks. Due to the limited space and to the small sizes of the actuator, the use of external sensors to measure both the displacement and the force played into role during the tasks are impossible. Therefore the deal in this study consists to propose observer techniques to bypass the use of force sensors. Based on the unknown input observer (UIO) technique, force along the two directions (y and z axes) of the actuator can be estimated precisely and with convenient dynamics. Additionally to the force, the state vector of the actuator is also estimated. Experimental tests are carried out and demonstrate the effectiveness of the method.