Research On Characteristics Of The Ultrasonic Motor Driving Fluid Directly

Compared with the conventional contact ultrasonic motor, the non-contact type one which the stator and the rotor do not contact directly resolves the problems caused by friction, such as shorter life expectancy and continuous running time. So it is a new research direction in the field of the ultrasonic motor. This paper researched a new non-contact ultrasonic motor with fluid medium. An ultrasonic motor driving fluid directly is such a micro-motor whose rotor is driven by the acoustic streaming field that is caused by stator vibration in the fluid. It has the advantages of easier microminiaturization due to its simple structure and longer working life due to non-direct contact. At first, the motor structure and the operating principle are proposed. The unique structure of the motor is analyzed in detail. The production of the vibration, the formation of the standing wave, the combination of the traveling wave and the process of energy transmission in the fluid are discussed. Then a practical driving circuit for the motor is designed. The ultrasonic motor is a typical mechanical and electrical composite, so its performance is affected directly by the quality of its driving circuit. A driving system is designed according to the peculiarity of the motor, where a signal whose frequency is adjustable is generated by the Voltage Controlled Oscillator, then the signal is shifted in phase, so four sets of square-wave signals that differ 90 degrees in succession are generated, which can be applied to drive two sets of push-pull circuits, then the two square-wave signals can be used to drive the motor after their transformation. And the driving frequency and voltage is easy to regulate. So this circuit meets the requirement of the experiments very well. Next, the rotating speed characteristic of the motor was investigated from two aspects of the fluid character and the rotor structural parameter. The fluid characters include the height, viscosity and non-linear parameter. The rotor structural parameters are the radius, the blade height, the blade number and the material density. The experiments proved that the rotating speed increases as the depth of the fluid increases, decreases as the viscosity coefficient increases and is in reverse to the non-linear parameter. The rotors that have good operating characteristic have been found, which have given guides to select an appropriate rotor. And some methods were deduced to increase the motor's rotating speed. At last, the saturated flow velocity of the motor was studied. It is the phenomenon that the fluid velocity does not increased anymore correspondingly when the stator vibrating velocity exceeds a speed limit. It restricts the performance of the motor, so is worth studying. The cause is analyzed from the nonlinear acoustics and the experiments proved it. The relationships were determined between the saturated flow velocity and the fluid character and the rotor structure. These are the foundation for optimizing the operating characteristic of the motor.