A rotary ultrasonic motor using radial bending mode of ring with nested PZT excitation

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Abstract
This study presents and verifies a new idea for constructing a rotary traveling wave ultrasonic motor (USM) that uses the radial bending mode of a ring. In the new design, 20 trapezoid cross section slots are cut symmetrically in the outer surface of a thick duralumin alloy ring, where 20 PZT stacks are nested. In each slot, two wedging blocks are set between the PZT stack and the two sides of the slot respectively to apply preloading on the PZT ceramics. Two radial bending modes of the stator that have a phase difference of a quarter wavelength on space are generated by using the d33 operating mode of the PZT elements, and then a flexural traveling wave is formed by the superimposing of two standing waves whose amplitudes are equal and phases are different by 90° temporally. Two conical rotors are pressed to each end of the ring type stator by a coiled spring. The finite element method (FEM) simulation is developed to validate the feasibility of the proposed motor. The maximal speed and torque of the prototype are tested to be 126 r/min and 0.8 N·m, respectively.

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