AN ULTRASONIC MOTOR USING A METAL-CERAMIC COMPOSITE ACTUATOR GENERATING TORSIONAL DISPLACEMENT

An ultrasonic motor composed of three components; a stator, a rotor an d a ball bearing is proposed. The stator is made of an active piezoele ctric ring, poled in the thickness direction and bonded with two windm ill-like slotted metal endcaps. The stator is excited through its two electrodes, generating ultrasonic vibration in the radial direction at a radial mode resonance frequency. The two identical metal endcaps on both sides of the ring, bonded after shifting 45 degrees with each ot hers, transfers the radial vibration into longitudinal and tangential vibrations. The combination of these vibrations (longitudinal and tang ential) generates rotation due to frictional interaction between the c enter part of the top endcap and the periphery of the rotor. A prototy pe motor with 11.0 mm diameter was fabricated and its transient charac teristics were measured. The maximum torque of 1.36 mNm was obtained a t a speed of 480 rpm.