Piezoelectric motor and method of exciting an ultrasonic traveling wave to drive the motor

A method of exciting a shear-shear mode vibration in a piezoelectric ceramic disc for a rotary ultrasonic piezoelectric motor having a rotor and a stator, said method comprising the steps of:

• polarizing the piezoelectric disc for the stator in a radial direction, wherein the piezoelectric ceramic disc is bounded by a top electrode positioned on an upper side of the ceramic disc, and a bottom electrode positioned on a lower side of the ceramic disc, and the bottom electrode is divided into segments;
• applying a pair of alternating voltages with a phase shift of 90 degrees to the bottom electrode segments from a power source;
• exciting a shear-shear mode vibration in the stator;
• and
• producing a shear-shear mode flexure traveling wave in the stator causing a portion of the rotor in contact with the stator to rotate through a frictional force between the rotor and the stator due to the traveling wave deformation of the stator.

A rotary ultrasonic piezoelectric motor comprising:

• a stator having a piezoelectric ceramic disc polarized in the radial direction, and bounded by a top electrode positioned on an upper side of said ceramic disc and a bottom electrode positioned on a lower side of said ceramic disc, and the bottom electrode is divided into segments;
• a metal ring having a plurality of teeth disposed on said ceramic disc;
• a power source, wherein said power source applies two pairs of alternating voltages to said bottom electrode segments to excite a shear mode vibration in said stator, resulting in a shear-shear mode flexure traveling wave in said stator;
• and
• a rotor operatively connected to said stator, wherein a portion of said rotor in contact with said stator is driven to rotate through a frictional force between said rotor and said stator due to said traveling wave deformation of said stator, and said stator and said rotor are each supported on a shaft extending through a centrally located aperture in said rotor and a centrally located aperture in said stator.