Improvement of Characteristics of Noncontact Ultrasonic Motor Using Acoustically Coupled Two Air Gaps

The improvement of the rotational characteristics of a noncontact ultrasonic motor using a flexural traveling wave vibration disk was experimentally tried using an acoustic reflector and a double-disk rotor. By attaching the acoustic reflector over the single-disk rotor, a revolution speed of about 2300 rpm was obtained, which was about 1.4 times the maximum value without the reflector. Using a double-disk rotor instead of a single-disk rotor, a revolution speed of about 2800 rpm was achieved. From the observation of the air flow in the air gap, it was confirmed that the increase in revolution speed is attributed to the acoustic streaming induced in the air gap newly formed by the reflector and the double-disk rotor. The acoustic streaming in the new air gap is caused by the acoustic coupling between the double air gaps through the open edges of the air gaps.