A Traveling-Wave Linear Ultrasonic Motor Driven by Two Torsional Vibrations: Design, Fabrication, and Performance Evaluation

In this study, we design and fabricate a tank-track-shaped stator working in two torsional modes to form a traveling-wave (TW) linear ultrasonic motor (USM). The stator comprises two torsional transducers and two kidney-shaped vibrating bodies. When voltages with a certain phase are applied to the transducers, two in-phase TWs are excited on the vibrating bodies to frictionally drive the slider. Here, the torsional vibration guarantees strong electromechanical coupling, and meanwhile, the tank-track shape ensures plural driving points and low weight; these features may facilitate realizing high thrust force density and high power density of linear motors. To examine the feasibility, first, we constructed a stator prototype 116 mm in length, 91 mm in width, and 32 mm in thickness and explored its vibration properties. The minimal standing wave (SW) ratio reaches 1.21 and the small SW components are desirable for TW motors. Then, we measured the load characteristics and found that, at the working frequency of 54.34 kHz and the phase shift of -110°, the maximal thrust force and maximal output power were 96.1 N and 27.8 W, respectively. Moreover, the thrust force density and power density reached respectively 234.1 N/kg and 67.8 W/kg, relatively high compared to the values of most conventional linear motors. This study verifies the feasibility of our proposal and paves a new way of designing powerful linear USMs.