Study on Multidegree-of-Freedom Ultrasonic Motor Using Vibration Mode Rotation of Metal Spherical Stator

Most of the multidegree-of-freedom ultrasonic motors (MDOF-USMs) use a spherical rotor, and the design of the stator is restricted due to the use of the resonance mode. (1) Therefore, there is almost impossible to freely design the overall shape, resulting in a complicated structure. (2) To solve such an inconvenience, an MDOF-USM using a metal spherical stator was proposed. The vibration mode rotation on the stator was designed by theoretical analysis of spherical vibration and finite element method analysis. Multilayer piezoelectric actuators (MPAs) were embedded in the sphere to excite the vibration mode. Cylindrical projections were attached to the surface of the stator to magnify the vibration displacement and worked as the driving part. Their effects were evaluated using an electronic circuit simulator method of performance analysis. (3) As a result, two types of vibration mode rotation methods for the 3-DOF rotation were confirmed. It was also confirmed that the rotor covering the outside stator rotates around three axes. However, tiny torque, low power factor, and slow speed were obtained. (4) An MDOF-USM using a spherical stator was realized according to the operating principle. However, since the cause of such a low performance is the excitation method of the sphere and the rotor structure, research for improvement is required in the future.

Automated summary

Most multidegree-of-freedom ultrasonic motors (MDOF-USMs) use a spherical rotor, which restricts the design of the stator and results in a complicated structure. To address this inconvenience, a metal spherical stator design for MDOF-USM was proposed. The rotational vibration mode on the stator was achieved through theoretical analysis and finite element method analysis. However, the obtained torque, power factor, and speed were found to be low, indicating the need for further research to improve the excitation method and rotor structure.