Dynamometer Power Output Measurements of Miniature Piezoelectric Actuators

Piezoelectric bending actuators are an attractive option for driving microrobots due to their light weight, scalability, ease of integration, and high bandwidth. However, the only existing energy or power output measurements for piezoelectric bending actuators have been extrapolated from dc values or unloaded ac values, and are most likely overestimates. For microrobot applications such as flapping flight, accurate measures of power density are critical for design variables. In this paper, to properly measure the energy output of a 10-mg piezoelectric actuator, a custom dynamometer is designed and constructed to directly measure the power output at various frequencies and conditions. The dynamometer can simulate resonance with a tunable resistive (damping) load at frequencies from 1 to 100 Hz. It was found that due to low internal damping and fracture limits, actuators cannot be run in the damping matched condition at high fields (>1mum). Using the device, energy output per cycle at a drive field of 1.6 V/mum was measured to be a maximum of 19.1 muJ/cycle (232-mu m amplitude, 30 Hz), giving a delivered energy density per cycle of 1.89 J/kg. Internal actuator damping was measured at 1 V/mum to account for an energy loss of only 0.21 muJ per cycle (232-mu m amplitude, 30 Hz). These results are the first measurement of real power output of a piezoelectric bending actuator operating in real-world conditions (at ac and driven by high fields), and demonstrate power output measurement techniques that are applicable to other miniature actuators that are designed for operation in resonance.