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Ultrasonic Motor with Coil type stator
Structure of ultrasonic micro motor
Fig.1 shows the schematic of the ultrasonic micro motor. The micro motor consists of an external vibrator, a wave guide, a stator and a rotor. The composition of the micro motor is very simple. The thin wire made stainless steel receives ultrasonic vibration from the vibrator that is attached to one end of the waveguide and propagates ultrasonic vibration to a helical coil (stator).
The progressive flexural wave in the helical coil generates micro frictional force at the contact points between the rotor and the coil type stator and the sum of these micro frictional forces can produce an elliptical motion to rotate the rotor. During this time, the micro frictional force works oppositely to the forward direction of the progressive wave. The rotor performs a rotary motion and a translational motion.

Development of miniature ultrasonic micro motor
To achieve the practical use of miniature IVUS system, an ultrasonic micro motor with casing part which is thinner than 1.0 mm in the diameter is developed. Fig.2 shows the photograph of the miniature motor. The dimension of this motor is 0.95 mm in outer diameter and 4.5 mm in length.

Future perspective
There still remain many technological barriers. They are, to make the driving principal of the motor clear, to simulate the mechanism using finite element method, to miniaturize, to increase torque and to be established IVUS using this motor. Moreover, this IVUS is going to be performed to observe the internal vessel in human blood vessel model and in the future it is desired that this IVUS is not only observed but also treated to the diseased part in blood vessel.
Fig.1 The schematic diagram

Fig.2 Miniature motor ( φ0.95 mm)


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