Fast three-DOF control for multi-DOF ultrasonic servo motor by online adaptation

A multi degree of freedom (DOF) ultrasonic motor can rotate in three degrees of freedom and does not generate noise. In addition, it generates high torque with an appropriate pre-loading mechanism. This motor is therefore anticipated for use as a servomotor in robots in the next generation. This paper proposes a pre-loading mechanism and control algorithm for the multi-DOF ultrasonic motor for its application to an actual auditory tele-existence robot, TeleHead. The proposed methods realize fast multi-DOF rotating motion with little time delay. The pre-loading method generates pre-loading force by using tensioned springs, and compensates for the torque generated by the weight load on the motor by using these springs and a counter weight. The control algorithm uses feed forward control based on online feedback error learning. Experimental results show the high performance of these proposed methods.