Several key issues in developing of cylinder type 3-DOF ultrasonic motor

A cylinder type 3-DOF ultrasonic motor consists of a cylinder-shaped stator and a spherical rotor. Two bending vibration modes with orthogonality and a longitudinal vibration mode are excited in the stator by three groups of piezoelectric ceramic elements, respectively. The combinations of any two modes mentioned above push the rotor to rotate in one plane. Totally, the rotor can rotate around x, y or z-axes. This paper summarizes some key issues in developing the motor whose output properties and efficiency can be improved. These key issues include selection of the vibration modes, consistency of the modal frequencies, placement of the piezoelectric ceramic elements and the supporting plane, setting of pre-pressure and rotor–stator contact angle, influence of interfering modes.