3 - Single-axis arm designed with an ultrasonic motor: basic active/passive joint torque control

Abstract

This chapter highlights the active and passive joint torque control methods of a single-axis arm designed with an ultrasonic motor. Recently, many studies on assist robots have been conducted in which the development of a unique system is required to support aged persons, physically handicapped persons and/or carers. One of the representative systems is called the assist suit and is partially developed. The assist suit is a mechatronics device which can assist physical human actions. However, the current assist suit has a few problems with respect to cost, size, weight, longevity and so on. In this chapter, a fundamental study concerning a compact assist device is conducted. Where the assist device supports is one spot on the body such as a knee, an elbow or a shoulder. First of all, a simple single-axis arm is designed by using an ultrasonic motor which can generate high torque from a low velocity range. Then, a servo system with holding torque, a torque control system and a passive torque control system are proposed and their characteristics are evaluated. Here, the passive torque control includes a stiffness control, a compliance control and an impedance control.