Driving Characteristics of Robot Hand with Fingers using Langevin-Type Ultrasonic Motors : 2nd Report, Driving Characteristics under Pulse Width Modulation

Abstract

Loangevin-type ultrasonic vibrator works as an ultrasonic motor when it is pressed slantwise against the surface of an object. This paper describes a robot hand with three fingers that each works as an ultrasonic motor. This robot hand can simultaneously grasp a cylindrical body and rotate the body about its axis. We propose a PWM (pulse width modulation) Inethod for controlling the speed of ultrasonic motors by changing the duty ratio of the high frequency voltage applied to motors. The vibration of the ultrasonic motor and the driving characteristics of a robot hand were examined experimentally. It was confirmed that the vibration speed on the tip of the ultrasonic motor was approximately proportional to the duty ratio of the applied voltage. The velocity of the motor increases with an increase in duty ratio, except for at the offset region. The torque characteristic curves approach the origin, moving parallel as the duty ratio decreases.