Theoretical and Experimental Study on Rotor Stability of Ultrasonic Motor Driving Fluid Directly

The ultrasonic motor driving fluid directly is a new type of non-contact ultrasonic motor, which can be used the actuator in micro-mechanical system. Its rotor doesn´t contact with the stator and is driven by acoustic streaming. The rotor stability is a key factor to its application and control. By means of finite element analysis, the velocity distribution of acoustic streaming was analyzed. The simulation results show that, radial streaming and tangential streaming occur at the same time, whose amplitude and direction are influenced by the exciting voltage and parameters of the fluid. The radial streaming acting on the rotor causes it unstable. To analyze easily, it is assumed that the rotor axial was not fixed. Following this, the influence on the rotor stability shows that this system can be equivalent to a mass-spring and the spring constant K can be used to weigh the stability. In the end, factors that affect the stability such as the exciting voltage, the rotor thickness, the fluid height and type are investigated and useful guidelines for design and application are suggested