Application Cases

Experiment Name: Finite Element Analysis and Experimental Research on High-Torque Radial Standing Wave Ultrasonic Motor

Research Direction: Ultrasonic Motors

Test Objective:
A high-torque radial standing wave ultrasonic motor is proposed, aiming to achieve high torque output while maintaining a compact structure. The structure and working principle of the motor were first designed and analyzed. The vibration characteristics of the stator were analyzed using the finite element method. Subsequently, an ultrasonic motor prototype with a diameter of 32 mm was fabricated. The resonant frequency and radial vibration amplitude of the stator were measured using a laser vibrometer; the measurement results agreed well with the theoretical analysis. Finally, a test platform for the motor's output characteristics was established, and the torque-speed characteristics of the motor under different voltages were measured. The experimental results showed that the resonant frequency of the stator's working mode was 73.3 kHz. When an excitation voltage with an amplitude of 100 V and a frequency of 74 kHz was applied, the motor's no-load speed was 45 r/min, and the stall torque reached 0.41 N·m. Compared with other ultrasonic motors of similar size, the proposed radial standing wave ultrasonic motor exhibits a larger stall torque.

Ultrasonic motors utilize the inverse piezoelectric effect of piezoelectric ceramics to convert high-frequency alternating current into ultrasonic vibrations of a metal elastic body. These vibrations are then converted into rotational or linear motion of the rotor or slider through friction transmission. Compared with traditional electromagnetic motors, ultrasonic motors offer advantages such as simple structure, self-locking when power is off, fast dynamic response, high control precision, and good electromagnetic compatibility. As actuators in control systems, ultrasonic motors have broad application prospects in fields such as aerospace, robotics, and medical devices. However, the limited torque output of ultrasonic motors restricts their application to some extent. Improving the torque output of ultrasonic motors would promote their further application in low-speed, high-torque scenarios.

Figure: Radial Standing Wave Ultrasonic Motor Prototype

Testing Equipment: ATA-4052 high-voltage power amplifier, magnetic hysteresis brake, DC power supply, signal generator, etc.

Experimental Procedure:

Figure: Experimental Platform for Radial Vibration Testing

To verify the output performance of the prototype, a test platform for the motor's output characteristics was built, as shown in the figure above. Considering the motor's low-speed, high-torque characteristics, a magnetic hysteresis brake was used as the load, powered by a DC power supply. The load magnitude was adjusted by varying the DC voltage. The motor's torque and speed were measured using a torque/speed sensor. The shaft of the magnetic hysteresis brake was connected via a flexible coupling to one end of the torque/speed sensor shaft, and the motor shaft was connected to the other end of the torque/speed sensor shaft via another flexible coupling. A signal generator was used to produce a high-frequency sinusoidal signal, which was amplified by the ATA-4052 high-voltage power amplifier and provided to the motor as the driving power.

Experimental Results:
This paper proposes a high-torque radial standing wave ultrasonic motor. The motor's structure was designed, its working principle was analyzed, the vibration characteristics of its stator were studied using the finite element method, a motor prototype was fabricated, an experimental platform was built, and the motor's vibration characteristics and output characteristics were measured. The fabricated prototype has a diameter of 32 mm. The motor utilizes the first-order radial expansion vibration mode of the stator as its working mode, with a resonant frequency of 73.3 kHz. When a sinusoidal AC voltage with an amplitude of 100 V and a frequency of 74 kHz was applied, the motor's no-load speed and stall torque were measured to be 45 r/min and 0.41 N·m, respectively. Compared with other ultrasonic motors, the proposed radial standing wave ultrasonic motor achieves high torque output while maintaining a compact structure. The dimensions and installation tilt angle of the elastic blades significantly affect the motor's performance. Therefore, in future studies, a contact model of the stator and rotor needs to be established to quantitatively analyze the influence of the elastic blade dimensions and arrangement on motor performance, thereby further optimizing motor performance. Furthermore, the motor proposed in this paper is a unidirectional rotating ultrasonic motor. By further improving and optimizing its structure, a bidirectional rotating ultrasonic motor could potentially be realized. For example, two stators could be driven in parallel: energizing one stator drives the rotor shaft in one direction, while energizing the other stator drives the rotor shaft in the opposite direction. The design and optimization of such a bidirectional rotating motor are also part of the future research outlined in this paper.

Aigtek ATA-4052C High-Voltage Power Amplifier:

Figure: Specifications of the ATA-4052C High-Voltage Power Amplifier