Analysis of a novel longitudinal-bending hybrid ultrasonic motor using vibration coupling

A novel longitudinal-bending (L-B) hybrid ultrasonic motor using vibration coupling is proposed. Different with the previous L-B ultrasonic motors, only longitudinal PZT plates are used; and the longitudinal-bending hybrid vibrations of the motor are excited synchronously. Fixed boundary condition is applied on one side surface of the flange, which locates at the wave node of a longitudinal transducer. The working principle of the motor is analyzed. By using finite element method, comparison between the proposed ultrasonic motor with fixed boundary condition and a transducer with free boundary condition are developed by modal analysis, harmonic analysis and transient analysis. It is found that the longitudinal-bending hybrid vibrations can be produced by the longitudinal piezoelectric elements under a fixed boundary condition of the flange. It should be noted that the bending vibration is not generated by the bending piezoelectric elements, but excited by a vibration coupling effect under an unsymmetrical boundary condition. The change of the boundary condition also shows minute effects on the resonance frequency and the electromechanical coupling factor. Oblique elliptical movements are formed on the two end tips of the transducer. These motions can push the runners linearly by frictional forces if preloads are applied.