Development of Ultrasonic Motors using Longitudinal and Bending Natural Vibration for Multi-Degrees of Freedom Motion

Abstract

Small and precise actuators for multi-degrees of freedom (DOF) motion is needed to construct a dexterous robot arms and manipulators. Ultrasonic motors are suitable for the multi-DOF actuation of the robot arms and manipulators because of its characteristics such as its output power per unit volume, high stationary limiting torque, high maximum operating torque, simple design, silence, and high controllability. In this study we develop a three-DOF ultrasonic motor. It is found that the three-DOF ultrasonic motor can be constructed when natural frequencies of two second bending modes and a first longitudinal mode of a bar-shaped stator correspond. A spherical rotor in contact with the stator head rotates around three perpendicular axes. Geometry and structure of the ultrasonic motor in detail is determined using finite element analysis. Measured natural frequencies and natural modes of bending and longitudinal vibrations of the stator agree well with calculated ones. The rotational speed of the spherical rotor around three perpendicular axes are measured.