A linear ultrasonic motor driven by torsional/bending vibrations

A bonded-type linear ultrasonic motor via torsional/bending hybrid excitation was developed in this paper to not only enhance the actuating capability but also realize the lightweight. Here, the torsional vibration is excited by exciting out-of-phase longitudinal vibrations with diagonally arranged PZT plates rather than directly using the shear ones. Besides, four elliptic motions exist at the driving feet to drive the slider alternately. To examine the validity, first, the dynamic models capable of modelling the torsional vibration with the Mason circuits were constructed and a torsional/bending transducer was designed. Then, a prototype with the size of 35 mm x 10 mm x 5 mm was fabricated to test its vibration properties. Finally, the movement and load characteristics were measured and the results show that, at driving frequency of 34.68 kHz, the motor yielded the maximal thrust force of 2.175 N, no-load speed of 593 mm/s, and maximal output power of 179.8 mW. Moreover, the thrust force density and power density reach 265 N/kg and 21.9 W/kg, respectively, higher than those of some previously-reported linear USMs. This study validates the feasibility to achieve thrust force density and power density with torsional/bending motors and also paves a new way to design lightweight USMs.