Speed Characteristic of A New Type Ultrasonic-motor and Impedance Matching System by Novel Method

An impedance of rehabilitation and assisting robot should be matched with that of human in order to carry out cooperative works harmoniously. If not so, we could not set our expectations highly to get stability and effectivity in the cooperative works of human-robot. In this paper, we develop the cooperative work system to adjust the impedance of a robot driven by ultrasonic motor (USM) to that of human's arm. There is reason to adopt a USM for the robot's actuator. It has many good characteristics like high torque at low speed. When we use the adjusting phase difference method among the various control methods of USM, we have to consider cautiously how to set the value of the driving frequency because the characteristics of USM is changed according to which value of the driving frequency is set. Therefore, we suggested a novel method that the suitable driving frequency is supplied according to each the phase difference. Using this method, we could change the mechanical impedance of USM such as viscosity and stiffness. To evaluate the proposed cooperative work system, we conduct the two types of tasks.