Development of a novel radial-torsional hollow ultrasonic motor and contact interface coating test.

• A novel radial-torsional hollow ultrasonic motor is designed, optimized and tested. • The rotary motor has a novel hollow design working by converting the radial in-plane mode into torsional motion of the inner ring. • A new method of coating Si 3 N 4 film on contact interface by magnetron sputtering is presented. • The maximum torque and speed of the prototype are 0.27 mN m and 600 r/min respectively before coating. • After Si 3 N 4 film was coated on the contact surface of the motor, the maximum torque of the motor can be increased by 55.56% to 0.42 mN m. A novel miniature radial-torsional hollow ultrasonic motor is proposed in this work, which is mainly composed of a base, a hollow rotor, a stator. One piece of piezoelectric wafer bonded on the bottom face of the stator is used to excite the radial in-plane vibration mode of the outer ring, which is converted into the revolved motion of the inner ring through the connection beams. The revolved motion of the inner ring can drive the rotor pressed on the inner ring to rotate through friction. The finite-element method was performed to verify the working principle of the motor and optimize the key dimensions of the motor. One prototype motor with the appearance size of Φ35 mm × 12 mm and weight of 20.1 g is fabricated and characterized. In addition, Si 3 N 4 thin film is coated on the contact interface of the stator by the magnetron sputtering coating machine to improve the output performance of the ultrasonic motor. The experiment results show that the locked-rotor torque of the motor with coated stator can reach 0.42 mN m, which is 55.56 % higher than that of the uncoated motor. [ABSTRACT FROM AUTHOR]