A Rotary Ultrasonic Motor Operating in Torsional/Bending Modes With High Torque Density and High Power Density

In this article, to achieve high torque density and high power density of rotary ultrasonic motors (USMs), we develop a rod-shaped transducer operating in torsional/bending (T/B) modes and excite two elliptical motions on its bilateral ends to drive the rotor orthogonally pressed onto the transducer. Here, the torsional vibration, the driving structure, and the rod shape may enable the T/B motor to provide high driving force, large driving distance, and low weight, which facilitate the realization of high torque density and high power density. To assess the validity, first, we construct a transducer 43 and 110 mm in diameter and length, respectively. Then, we investigate the load characteristics of the T/B motor: When it works at the frequency of 21.64 kHz, the maximal torque and the maximal output power reach 10.1 N·m and 38.1 W, respectively. In the meantime, it yields the torque density and the power density of, respectively, 20.0 N·m/kg and 75.7 W/kg, which are, as predicted, relatively high compared to the values of most conventional rotary motors. This article not only validates the effectiveness of our proposal but also provides a new approach to design powerful rotary USMs.