Simulation Analysis and Experimental Research of Non-Contact Ultrasonic Motor Based on Acoustic Streaming

Traditional ultrasonic motors can produce low speed and strong torque because the stator and rotor are in direct contact with one another. However, the contact surface will experience significant friction wear and temperature increase. Complex phase control is necessary for the traditional ultrasonic motor in order to maintain proper motor operation. These issues can be completely avoided by using a non-contact ultrasonic motor. The non-contact ultrasonic motor is driven by the principle of acoustic streaming effect. There is not need for the control system to realize the rotation of the rotor. In this paper, a novel kind of non-contact ultrasonic motor based on acoustic streaming was developed in order to circumvent the mentioned problems. The rotor was driven to revolve by the motor through four wedge-shaped driving grooves on the rotor surface. The stator disk and rotor were built of the 7075-T6 aluminum alloy for machinability and rotor quality. The wedge-shaped driving grooves were evenly spaced throughout the circumferential direction, and the groove depth gradually increased from 0 to 0.3 mm. The radial stability force prevented the rotor from falling off the surface of the stator disk in the absence of a positioning shaft. By changing the direction of the wedge drive slot to change the rotation direction of the motor, the two-way rotation of the motor was realized. The Reynolds stress method was used to examine the motor′s running performance in order to determine the suggested motor′s operating principle. Incorporating the stator disk′s bending vibration mode into the governing equation for the acoustic streaming field. The governing equation of the acoustic streaming field also taken into account the acoustic wave perturbation theory, the fluid continuity equation, and the N-S equation. Finite element analysis (FEM) was used to determine the motor′s resonance frequency as well as the amplitude and vibration mode of the stator disk. By contrasting the model′s viability with the outcomes of the experiment, it was confirmed. The development of an ultrasonic motor test system was used to conduct the experimental measurements. The experimental outcomes were consistent with those predicted by the model. The empirically measured resonant frequency was 19.5 kHz, while the resonant frequency obtained using FEM was 21.7 kHz. The results of the harmonic response analysis indicated that the stator′s amplitude in the second-order mode could reach 9.35 μm. And the two pitch circles had radii of 18.26 and 47.93 mm, respectively. Theoretical and practical results indicated a strong correlation between motor speed and driving voltage. The lowest and greatest measured rotational speeds for the experimental voltage range were 18 and 28 r/min, respectively. The FEM yielded a minimum rotational speed of 18 r/min and a maximum rotational speed of 26 r/min. By combining the two methods, the maximum rotational speed error was 9.45%. When the rotor surface was not machined with driving grooves, the sound pressure distribution and the vibration mode were strongly associated. It displayed the properties of the second-order vibration mode distribution. When the processing of the driving groove was complete, the change in sound pressure corresponded to the change in depth of the driving groove. The sound pressure decreased as the driving groove depth increased. With an increase in excitation voltage, the motor′s speed increased gradually. The rotational speed would increase together with the sound pressure, which was proportional to the excitation voltage. Following the stable acoustic streaming, a vortex also developed at the acute structure, which caused the sound flow velocity to suddenly increase. The accuracy of the theoretical calculation was demonstrated by both the motor′s harmonic response analysis and the speed comparison results.