Development of an arrayed-type multi-degree-of-freedom ultrasonic motor based on a selection of reciprocating vibration modes

This paper presents a novel type of a multi-degree-of-freedom (MDOF) ultrasonic motor. In recent years, ultrasonic motors are attracting attention as a new type of actuator well suited for MDOF actuation. Ultrasonic motors can be divided into two types, either driven by a single phase and by dual phases. Ultrasonic motors driven by a single phase are easier to downsize and have simpler form than those driven by dual phases, because plural frequencies must correspond to each other completely. However, a single ultrasonic motor driven by a single phase cannot generate MDOF movement. Hence, we proposed of a MDOF ultrasonic motor composed of plural vibrators driven by a single phase. First, its principles and structure are designed. Secondly, we decided the form of the vibrators, the layout of the piezoelectric ceramic (PZT) and excitation methods through finite element analysis. Then, we manufactured the motor and confirmed that the rotor could rotate upon three axes. And also, the maximum torque of the rotation upon the x-axis was about 15 mN-m. As a result, we developed a novel type of MDOF ultrasonic motor driven by a single phase, which can rotate a spherical rotor upon three axes. In the future, this motor may be used for a number of applications, such as adjusting the lens on cameras, and joints of robot arms.