A new thin cross type rotary ultrasonic motor has been proposed for further study of this type motors characteristics. As a stator, eight semi-circular piezoelectric ceramics were attached on the upper and bottom sides of a thin hollow cross brass plate. The stator was excited by two sinusoidal voltages with a phase difference of 90° and elliptical trajectories were generated at the contact points to drive a shaft rotor. The driving principle of the motor was illustrated by degenerating two orthogonal in plane vibration modes. Based on FEM analysis, the vibration shapes and frequencies of operation modes were simulated and the relationships between the maximum displacements of the contact points and various motor parameters were obtained. A prototype was fabricated and characteristics of the motor were measured. The relationship among rotation speed, pre-pressure and voltage are no-linear. The maximum rotation speed with no load was 22.9 rpm. The merits and shortcomings of the thin cross type rotary ultrasonic motor were discussed.
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