抄録
As actuators for an prosthetic arm, we use traveling wave ultrasonic motors because of their light weight, compact size and silent motion.
The prosthetic arm has to better move compliantly around every joint of it according to environmental force the same as the human arm. In order to realize the compliant motional prosthetic arm we think that the actuator have a compliant characteristic, but the traveling wave ultrasonic motor has no compliant characteristic in itself. Incidentally, the traveling wave ultrasonic motor is driven by two different phase sine-wave electric signals which propagate elastic traveling waves in its stator, then the traveling waves generate torque to its rotor. Though, usually the phase difference is adjusted to just +90deg or -90deg to get highest output torque and highest rotation speed, we adjust it in the range of -90deg to +90deg to regulate output torque and rotation speed continuously by the phase difference change. Then we control the phase difference with deflection angle of the output shaft from desired angle and with desired elastic coefficient.
We realized adjustable compliant motion on the traveling wave ultrasonic motor using the phase difference control of the two driving sine-wave electric signals. The motor acts as a spring with damping. The damping characteristic is observed as a constant speed response of the ultrasonic motor to the step change of the phase difference of the driving signals.
This system is useful for actuators of the prosthetic arm.
