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A piezoelectric ultrasonic motor is constructed by tightly contacting a rotor to a piezoelectric ultrssonic resonator with eliptical vibrstion (PUREV). The PUREV successfully operated with a torsion coupler in which a torsional mode coupled with a bending mode is excited by the same frequency longitudinal vibration. The typical values of the present motor are 120 r.p.m. with no load, and 90 r.p.m. with a load of 13 kg-cm, under a 40 kHz/100 volt sinsoidal voltage, i.e. 12 watts with 80% efficiency. These values correspond to a high output power density of 80 W/kg over the limit value 30 W/kg expected in the ordinary motors.
Akio Kumada (Tue,) studied this question.