Design and experimental study of electromagnetic clutch-type variable pre-pressure ultrasonic motor

The traveling-wave rotary ultrasonic motor (TRUM) technique has become increasingly mature deepening of related research and development of related technology. The unique friction drive mode of a TRUM provides the advantages of a low speed, large torque, fast response, and a self-locking feature for power failure but also suffers from a relatively low efficiency. Regarding speed control, the commonly used approach of combining frequency modulation and speed regulation has provided the advantages of high precision and a wide range. Still, the load-carrying capacity of a TRUM is reduced when the driving frequency deviates from the resonant point, which is not conducive to the characteristics of low speed and large torque of the TRUM. To address this limitation, this study uses the pre-pressure and designs an electromagnetic clutch-type variable pre-pressure self-adjusting ultrasonic motor based on the TRUM-70 hollow ultrasonic motor. In addition, the force and motion analyses are conducted on the core components, and the basic parameters of the electromagnetic mechanism are calculated according to the specific design requirements. Furthermore, the Maxwell equation is used to simulate the designed magnetic circuit, and a prototype is fabricated and assembled. The feasibility of the proposed motor design is verified through experimental study, and the performance of the motor is compared with those of conventional ultrasonic motors. The experimental results show that the proposed electromagnetic clutch-type variable pre-pressure ultrasonic motor can effectively improve the output efficiency of the motor, especially when the load varies significantly.