Load characterization of high displacement piezoelectric actuators with various end conditions

Piezoelectric ceramic transducers are characterized by relatively small str ains on the order of 0.1%. One method of achieving significantly larger dis placements is to utilize flexural mode actuators, such as unimorphs or bimo rphs. In this paper, we investigate a particular type of stressed unimorph flexural actuator, viz. the 'THUNDER' actuators. (THUNDER (TM) is a tradema rk of Face International Corporation). These stressed unimorphs are of inte rest due to their particularly large flexural strains. To determine their v ersatility as high displacement actuators, it was necessary to investigate their actuation capability as a function of load. In addition, our investig ation determined that end conditions have an appreciable effects which has also not been reported in the literature. Therefore, experimental results o f the load capabilities of these high displacement actuators with various e nd conditions are presented here. Commercially available rectangular actuat ors were chosen for this study. The actuators had been constructed by bondi ng thin PZT ceramics (0.152 turn thick 1.37 cm. wide, 3.81 cm long) to stai nless steel sheets (0.20 mm thick 1.27 cm wide, 6.35 cm. long). They were o perated 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 condition s to 0.2% for highly restricted end conditions. The load bearing capabiliti es were tested out to 10 N for most end conditions. (C) 2001 Published by E lsevier Science B.V.