High displacement piezoelectric actuators: characterization at high load with controlled end conditions

Piezoelectric ceramic transducers are characterized by relatively small strains on the order of 0.1%. Methods of achieving larger displacements include mechanical amplifiers and flexural mode actuators, such as unimorphs or bimorphs. A particular type of stressed unimorph flexural actuator, the "THUNDER" actuator, provides enhanced flexural strain. (THUNDER/sup TM/ is a trademark of FACE International Corporation). However, displacement has generally not been characterized as a function of load, which was needed for our application. We found that load and displacement were very sensitive to end conditions, which has also not been reported in the literature. The commercially available THUNDER/sup TM/ model 8-R rectangular actuators were chosen for the research presented here. They were operated in a flexural mode, and used to characterize displacement as a function of load under well-controlled end conditions. Our experimental results show that progressively restrictive end conditions increased the stiffness, ranging from 2.5N/m to 23N/m, which increased the load capabilities of the actuator. In some cases, displacement actually increased as a function of load as well. 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 10N for most end conditions.