Dual-Stack Piezoelectric Device with Bidirectional Actuation and Improved Performance

Piezoelectric stacks can normally take significant compressive loads but cannot tolerate tension. Therefore, conventional piezoelectric stack actuators are mainly designed for the push-only actions and usually incorporate a compressive preload mechanism to protect the stack from experiencing tensile stresses. A common preload method is to include a mechanical spring in parallel with the stack, which may reduce the free stroke capability of the actuator and affect performance. In this research, a new bi-directional (can operate in both push and pull directions) actuator design is introduced, utilizing a pair of matching piezoelectric stack elements within the actuator housing. The stack elements are integrated in a mechanically opposing configuration and are electrically operated out of phase. To examine the performance advantages of the new concept, both analytical and experimental studies are conducted. The dual-stack actuator is compared with two internally preloaded single stacks integrated in a parallel configuration, thus both actuator systems are utilizing equivalent volumes of the piezoelectric material. The analysis indicates that the dual-stack actuator produces greater free stroke, output energy, and energy efficiency than the two parallel single-stack actuators. For experimental evaluations, a dual-stack actuator and an internally preloaded single-stack actuator are fabricated using the same materials, similar construction techniques, and the same piezoelectric stack elements. A testing procedure is formulated to determine the free stroke and blocked force of both the actuators. The experimental results verified the trends observed in the analytical predictions. That is, in addition to being bi-directional, the dual-stack arrangement can produce higher free stroke, blocked force, output energy, specific output energy, and energy efficiency, as compared to two preloaded, parallel-configured single-stack actuators. It is also concluded that by tailoring the dual-stack actuator, it will be 62% volume and weight of a conventional single-stack actuator that produces the same amount of blocked force and free strain.