Study and test of a double-rotor ultrasonic motor with symmetrical longitudinal-torsional converter

To obtain large torque, ultrasonic motors using longitudinal-torsional converters with diagonal slits are proposed. The converters have rather simple and tough structures and are driven by simply exciting the longitudinal vibration of the transducer. Stemming from the merits of such type ultrasonic motors, this paper proposes a double-rotor ultrasonic motor with a symmetrical longitudinal-torsional converter. The ultrasonic motor consists of four PZT-4 annular plates that vibrate longitudinally, two sonotrodes screw bonded atop the two end surfaces of the PZT plate stack, and two rotors pre-pressed against to the output surfaces of the sonotrodes by coil springs. To form identical directions of the output elliptical trajectory motions of the driving points, diagonal slits were symmetrically cut in the sonotrodes. To validate the proposed idea, principle description, FEM simulation, fabrication, and performance measurement of and prototype motor are presented in this paper. The tested performance of the prototype motor were no load revolution speed 30rpm and maximum torque 1.8N·m.