Performance test and improvement of piezoelectric torsional actuators

This paper presents the design, test and improvement of a newly developed piezoelectric torsional actuator which generates large angular displacement using piezoceramics and a torsion bar. Because the proposed piezoelectric torsional actuator can generate torsional displacement, directly invoking the shear mode of the piezoelectric material, no complicated additional mechanism is needed. The electrodes are formed from a cylindrical piezoceramic poled along the axial direction and divided into six segments that are arranged radially and bonded to each other in opposite poling directions with conductive adhesive. The key to designing such an actuator is to match the torsional resonant frequency of the actuator with the excitation frequency. Finite element analysis for the piezoelectric actuator is performed to find the torsional resonant mode; an experimental investigation in terms of electrical impedance and torsional displacement measurement was conducted to verify the mode. As a result a maximum angular displacement of 0.18 degrees was measured. To magnify the torsional displacement, a torsion bar was attached on top of the actuator. Thus, the torsional displacement was magnified by a factor of three. A resonance decrease due to the added mass of the torsion bar was observed and a theoretical investigation was performed using a two degrees of freedom lumped model.