A Millipede-Inspired Miniature Self-Moving Ultrasonic Actuator with High Carrying Capability and Nanometer Resolution

To accomplish high carrying/positioning capability with compact structure, in this study, a miniature self-moving ultrasonic actuator (MSMUA) is developed by exciting a flexural traveling wave induced by dual longitudinal vibrations. Here, four lead-zirconate-titanite plates are bonded onto the bilateral ends of the bar-shaped vibrating body to efficiently generate the vibration. Interestingly, the MSMUA imitates the millipede in terms of the simple configuration and the operating principle. To test the validity, first, by using a Krimhertz-transmission-theory-based model, the key dimensions were adjusted to not only increase the driving-force-to-weight ratio but also make the elliptical motion shape close to the unity. Then, a prototype with the size of 87.5 x 9 x 9 mm(3) and the weight of 15.67 g was fabricated, its moving/carrying/positioning performance was evaluated, and an array of MSMUAs was constructed to achieve flexible movement. At 105.44 kHz working frequency, the MSMUA in a tethered manner yielded the maximum payload of 433 g (equal to 27.7 times of its own weight), the maximum speed of 378 mm/s, and the maximum towing force of 0.4 N. Meanwhile, it crossed the gully 21 mm in width and climbed the slope of 7.4 degrees Installed with an onboard circuit and 3.7 V batteries, the MSMUA provided the minimum step displacement of 19.2 nm. Moreover, the array of MSMUAs produced the turning movements (whose directions, angular speeds, and steering radii were adjustable) and the in-situ rotations. This study demonstrates the MSMUA's high carrying capability and nanometer resolution, and provides a new approach to design powerful ultrasonic actuators.