Driving Characteristics of Robot Hand with Fingers using Vibration-Type Ultrasonic Motors (3rd Report, Detection of Grasping Force by Decrease in Vibration and Influence of Disturbances)

A vibration-type ultrasonic vibrator works as an ultrasonic motor when it is pressed slantwise against the surface of an object. In our previous paper we made a trail robot hand with three fingers that each works as an ultrasonic motor. This robot hand can simultaneously grasp a cylindrical body and rotate it about its axis. High torque is obtained when an optimum contact force is used for the ultrasonic motor. We propose a detection method to measure the grasping force of the robot hand by the change in the amplitude of vibration. It was confirmed that the vibration amplitude detected by a piezo-element on the vibrator was decreased almost linearly with increase in the grasping force of robot hand. The grasping force affects very little change in the resonance frequency of the vibrator in comparison with the temperature by its self-vibration.