Displacement Control of Piezoelectric Actuators Using Current and Voltage

This paper introduces a feedforward charge control scheme, which controls the velocity of a piezoelectric actuator by the current fed to the actuator. The velocity-current relation, however, is not linear over the entire motion range, and therefore, information about the actuator voltage is also utilized. The required current is estimated using an actuator model, which is separated in two phases combining individual models for a motion phase and a static phase. The method is verified by a series of experiments, where a piezoelectric actuator is moved with variable velocities and displacements. During the experiments, the current is fed to the actuator using a current driver consisting of a voltage amplifier, a precise current meter, and a controller. The results show a significant improvement in comparison to open-loop voltage control; the hysteresis is less than 2% and the drift approximately 1%. This indicates that the motion of piezoactuators is a function of current and voltage, and does not depend considerably on the motion history. Therefore, a sensorless control scheme to overcome the hysteresis and drift would be feasible.