Dynamometer power output measurements of piezoelectric actuators

Abstract

Abstract-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. In this work, to properly measure the energy output of a 10mg piezoelectric actuator, a custom dynamometer is designed and constructed to directly measure the power output at various frequencies and conditions. The dynamometer can simulate a pure resistive load at resonant frequencies from 1 to 100Hz. Due to low internal damping and fracture limits, actuators cannot be run in the matched condition at high fields (> 1 V/µm). Using the device, energy output per cycle at 1.6 V/µm was measured to be a maximum of 19.1 µJ/cycle (232 µm amplitude, 30Hz), giving a delivered energy density per cycle of 1.89J/kg. Internal actuator damping was measured at 1 V/µm to account for an energy loss of only 0.21µJ per cycle (232 µm amplitude, 30Hz).

The First Takeoff of a Biologically Inspired At-Scale Robotic Insect

“…For the sake of a performance metric, biological estimates place the body-mass-specific power density for flying insects between 29 W/kg [19] and 40 W/kg [20] and between 80 W/kg [21] and 83 W/kg [22] for the muscles alone. For comparison, the class of actuators used here have demonstrated power densities of 400 W/kg [23]. This is the first example of where a subsystem of the microrobotic fly exceeds the performance of its biological counterpart.…”

High lift force with 275 Hz wing beat in MFI

“…Future work includes scaling down the drive actuators while keeping them energetically capable of the same wing trajectory and repeating the lift result of 06-β. With the recent work in [6], the power density of 10mg bimorphs has been significantly improved, leading us to believe that takeoff using MFI technology is imminent. Our conjecture has recently been proven with the takeoff of a 60mg flapping air vehicle using MFI technology at Harvard [9].…”

“…Thus, the behavior of the thorax could be isolated without questioning the actuators. More recent work in [6] has further optimized and directly measured adequate power output from the 10mg bimorph actuators.…”

Challenges for 100 Milligram Flapping Flight

“…For Dipteran insects, power of 70-100 W kg −1 of body mass is estimated [16], with power plant power density of approximately 200 W kg −1 . Traditional electromagnetic motors, ubiquitous in larger robotic systems, are inappropriate for actuation of a robotic insect.…”

“…Extrapolation of actuator perfor- mance from DC measurements [22] predicted higher power than was actually observed. Hence, a miniature dynamometer system was developed [16], to measure real actuator output power for simulated damping loads at resonance. Fig.…”