Design and Experimental Investigation of a Compact Traveling-Wave Piezoelectric Angular Motion Motor

This paper presents the design, numerical analysis, and experimental investigation of a compact traveling-wave piezoelectric motor for continuous and incremental angular motion. The key advancement of the proposed design is a compact coaxial direct-drive architecture that combines a single ring-shaped piezoelectric stator with four independently excited electrode sections, three discrete spherical contact elements, a cone-shaped rotor, and an adjustable spring-based preload mechanism. In contrast to conventional traveling-wave motors employing continuous annular or toothed contact interfaces, the proposed configuration localizes the stator-rotor interaction at three predefined contact points while allowing both continuous bidirectional rotation and incremental angular positioning within the same actuator. Numerical analysis identified the operating mode at 39.95 kHz and confirmed the formation of elliptical displacement trajectories at the spherical contact elements. The calculated resonance frequency and effective electromechanical coupling coefficient were 39.93 kHz and 4.36%, respectively. Experimental measurements showed resonance of 39.94 kHz with an effective coupling coefficient of 4.47%. The motor achieved a maximum rotational speed of 87 ± 2.2 RPM at 180 V_p-p. The maximum stall torque reached approximately 8.3 N·mm and 8.4 N·mm for clockwise (CW) and counterclockwise (CCW), respectively, at 180 V_p-p. Depending on the excitation amplitude, the angular step varied from 0.082 ± 0.015° to 3.038 ± 0.120°. The results confirm that the proposed compact motor can provide controllable continuous rotation and incremental angular positioning.