Load characterization of high displacement piezoelectric actuators with various end conditions

Piezoelectric ceramic transducers are characterized by relatively small strains on the order of 0.1%. One method of achieving significantly larger displacements is to utilize flexural mode actuators, such as unimorphs or bimorphs. In this paper, we investigate a particular type of stressed unimorph flexural actuator, viz. the 'THUNDER' actuators. (THUNDER (TM) is a trademark of Face International Corporation). These stressed unimorphs are of interest due to their particularly large flexural strains. To determine their versatility as high displacement actuators, it was necessary to investigate their actuation capability as a function of load. In addition, our investigation determined that end conditions have an appreciable effects which has also not been reported in the literature. Therefore, experimental results of the load capabilities of these high displacement actuators with various end conditions are presented here. Commercially available rectangular actuators were chosen for this study. The actuators had been constructed by bonding thin PZT ceramics (0.152 turn thick 1.37 cm. wide, 3.81 cm long) to stainless steel sheets (0.20 mm thick 1.27 cm wide, 6.35 cm. long). They were operated in a flexural mode. It was shown that progressively restrictive end conditions increased the stiffness, ranging from 2.5 to 23 N/m, enhancing the load capabilities of the actuator. In some cases, displacement actually increased as a function of load. This enhanced stiffness was obtained at a cost of reduced no load flexural strain (defined as the ratio of flexural displacement and ceramic length), ranging from 1.08% for free-end conditions to 0.2% for highly restricted end conditions. The load bearing capabilities were tested out to 10 N for most end conditions. (C) 2001 Published by Elsevier Science B.V.