This paper presents the experimental and theoretical considerations on characteristics of a noncontact ultrasonic motor with an acoustically levitated rotor. The results can be used to optimize the motor design. It is shown that a linear relation between the revolution speed and the stator vibration velocity exists. The revolution speed can be increased by utilizing the resonance of the air gap between the stator and the rotor, by increasing the mode number of stator vibration, by narrowing the gap, and decreasing the stator inner diameter. The miniaturization of the motor is tried, and a maximum revolution speed of 1000 r.p.m. is observed for the motor of stator inner diameter of 6.0 mm. From the transient characteristics, it is known that the rise time of revolution can be shorten by using the same methods as increasing the revolution speed. Finally, the effect of the stator vibration velocity on the rotor stability is investigated.
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