Characteristics and stability mechanism of non-contact ultrasonic motor with a longitudinal transducer.

Ultrasonic motors (USMs) as a kind of smart drive actuator have potential in space explorations, optical system, precise instrument, biomedicine, etc. However, a series of challenges, such as complex phase control system, severe friction and wear between the stator and rotor, unpractical motor structure, restrict the development and commercialization of ultrasonic motors. To tackle these problems, a non-contact ultrasonic motor with a longitudinal transducer based on near-field acoustic levitation was presented to simplify the structure and improve motor performance. Acoustic levitation force can separate the stator and rotor during operation, completely eliminating friction and wear between the stator and rotor. The driving torque is generated by the high-frequency squeezing vibration of the stator. In addition, restoring force caused by acoustic levitation can enhance the stability of rotor operation. The widely used longitudinal transducer as a stator can promote commercial applications. To assess the validity, a theoretical model based on Navier-Stokes equations was constructed to discuss the characteristics and stability mechanism of the proposed motor. A prototype was designed and manufactured and the levitation force tests and restoring force experiments have been carried out. The analysis shows that the rotational speed increases with increase of the driving voltage. The restoring force get enhanced by considering the grooves on the surface of rotor. At 1430 V voltage, the motor yielded the rotational speed and restoring force of 30 rpm and 8.5 mN, respectively. This study sheds a new light on the design of ultrasonic motors and further promotes application to automatic industries.