Investigation of a rotary ultrasonic motor using a longitudinal vibrator and spiral fin rotor

• A novel ultrasonic motor presented which compose of a Langevin transducer as stator and spiral fin as rotor.
• The transducer only works in longitudinal vibrating mode.
• The rotor composes of a shaft and spiral fins.
• The spiral fins acted as elastic coupler between stator and rotor.
• The spiral fins convert the longitudinal vibrating into elliptical motion to make the rotor rotary.

A Langevin transducer can provide longitudinal vibration with larger amplitude while also possessing a greater fatigue life than other types of piezoelectric vibrators. A novel rotary Ultrasonic Motor (USM) was proposed based on the use of a longitudinal transducer (acting as the stator) and a spiral fin rotor: the front cover of the Langevin transducer was designed as a double-layer cup-shaped structure, with the rotor sustained by the inner-layer, and the bearing cover fixed to the outer-layer; the rotor consisted of a shaft and spiral fins which acted as the elastic coupler. It is different from a traditional traveling USM, because the stator provides longitudinal vibration and the rotor generates the elliptical motion. This paper analyzed the motion locus equation of the fin contact points. Additionally, a theoretical analysis was performed in regards to the mechanism and the motor’s rotor motion characteristics, which demonstrates the relationships among the motor’s driving force, the torque, the revolution speed, and the motor structure parameters. A motor prototype has been manufactured and surveyed to demonstrate the motor performance. The relationships between the amplitude and the preload on the rotor, the free revolution speed, and the torque of the motor have also been studied.