A flexible shaft based travelling wave ultrasonic motor with high-precision positioning characteristics

• Published in: Precision engineering 2021-09, Vol.71, p.200-208
• Main Authors: Zhou, Ningning, Li, Jinbang, Chen, Pengfei, Qing, Tao, Cui, Yuguo
• Format: Article
• Language: English
• Subjects: Flexible shaft; High-precision positioning; Traveling wave; Ultrasonic motor
• ISSN: 0141-6359; 1873-2372
• DOI: 10.1016/j.precisioneng.2021.03.011

To improve positioning precision of the traveling wave ultrasonic motor (USM), a flexible shaft was used, and the structure was redesigned to reduce the fluctuations of step angles and speed. The start and stop response performances of the motor were analyzed theoretically and tested by a high-resolution test rig. The step characteristics were calculated, which showed the minimum step angle is below 0.20″ under different torques. The positioning process included two modes: continuous mode and step mode. In continuous mode, the speed of the motor was controlled by PID control based on the tests of frequency-speed characteristic of the motor. In step mode, the step characteristics of the motor was tested under different load torques and applied different lengths of driving voltage to find the minimum of step angle. From the tests, the step angle increases rapidly with the periods of driving voltage and the single-step angle fluctuations of the motor with flexible shaft is much less than that of motor with normal shaft. Finally, the positioning performances of USM were tested. The results showed that the minimum positioning error of the motor with flexible shaft could achieve 0.37″ (1.79 μrad) and the time costed was below 1 s. •A flexible shaft was used to improve positioning precision of the ultrasonic motor.•Step performance of the USM was utilized to a certain limit, which was below 1.0″.•The minimum positioning error of the USM with flexible shaft could achieve 0.37″.•Positioning accuracy of the USM can reach sub-arc seconds under different torques.