A piezoelectric motor using two orthogonal bending modes of a hollow cylinder

This paper proposes a compact ultrasonic motor with low manufacturing costs, a simpler driving circuit, and scalability. The stator of the motor presented in this paper consists of a hollow metal cylinder, whose outside surface was flattened on two sides at 90 degrees to each other, on which two rectangular piezoelectric plates were bonded. Because the cylinder has a partially square/partially circular outside surface, the stator has two degenerated bending modes that are orthogonal to each other. A wobbling motion is generated on the cylinder when only one piezoelectric plate is excited at a frequency between the two orthogonal bending modes. A rod through a pair of ferrules was used as the rotor of this motor. The prototype motor, whose stator was 2.4 mm in diameter and 10 mm in length, operated at 69.5 kHz, was experimentally characterized, and a maximum torque of 1.8 mNm was obtained.