Most travelling wave ultrasonic motors uses two phase signal with a 90° time phase difference to generate a traveling wave, this paper propose a novel nut-type travelling wave ultrasonic motor which uses only a single phase driving signal to excite two bending modes in r - θ plane of a nut-type stator simultaneously. Thus, both the motor structure and the driving circuit will be simplified. The working principle of the new single phase drive traveling wave nut-type ultrasonic motor was described. The working modes are observed with a finite element method software. A prototype nut-type ultrasonic motor was fabricated, and its electrical impedance was tested to observe the two working modes. The prototype motor worked at frequencies between two resonance frequencies under single phase drive as expected, and it also rotated bi-directional successfully.
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