Development of a novel rotor-embedded-type multidegree-of-freedom spherical ultrasonic motor

An actuator system with multidegree-of-freedom (MDOF) motion and complicated action has recently gained interest in the field of robotic technology. In the present paper, a novel rotor-embedded-type MDOF spherical ultrasonic motor (SUSM) is proposed. The MDOF-SUSM consists of a spherical rotor and a stator vibrator with an all-in-one structure. The spherical rotor is embedded in the center of an almost annular stator vibrator with a spherical inner surface, and a motor shaft is mounted on the rotor. The stator vibrator with piezoceramic disks and plates adhered to the surfaces of the vibrator can excite five vibration modes, independently and simultaneously. The spherical rotor can rotate around three axes by combining two of the five vibration modes. The present paper describes the basic construction and the operating principle of the rotor-embedded-type MDOF-SUSM, modal analysis results for the stator vibrator, and some experimental results based on a trial manufacture. The proposed MDOF-SUSM confirmed the operating principle of the design, and it has a simple structure and is compact and lightweight, a large torque-to-weight ratio is expected to be realized.