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Abstract: 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. [Copyright &y& Elsevier]

Abstract: This paper introduces an optimization design method for a three-degree of freedom (three-DOF) ultrasonic motor stator using constrained variable metric algorithm (CVMA). It is a circular cylindrical stator with a spherical rotor attached at its end. A mathematical model of the stator is established with combining the finite element method (FEM) and the optimal analysis method. Based on the model, the authors code an optimal program, which is implemented with MATLAB. The object is to optimize the characteristic length L 1, and L 2 of the stator in order to satisfy its vibration and contained conditions. According the optimization results, the stator is manufactured and tested. The experiments show that the stator''s mode frequencies and shapes agree well with those predicted by the program. The program is easy to operate, and that is time saving. [Copyright &y& Elsevier]