Compared with the conventional contact ultrasonic motor, the non-contact type one 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 introduced a new non-contact ultrasonic motor with fluid medium. The structure, the operating principle and running characteristics of the motor are proposed. In the theoretical analysis and experiments, the saturated flow velocity of the motor is studied. This paper analyses the cause of the saturation, determines that the saturated flow velocity has relations with the depth of the fluid, the concentration of the solution, the nonlinear parameter of the fluid, and applies some methods to increase the saturated velocity. The relationship between the rotor structure and the motor's rotating speed has also been researched. The experiments show how the diameter, the height, the blade number and the material of the rotor influence the motor's rotating speed, and give guides to select the appropriate rotor structure that is advantageous to increase the motor's rotating speed.

The brushless DC motor (BLDCM) is receiving wide attention for industrial applications because of their high torque density, high efficiency and small size. Conventional controllers suffer from uncertain parameters and the non-linear of the BLDCM. The fuzzy control has been focus in the field of the control of the BLDCM. However, a systematic method for designing and tuning the fuzzy logic controller is not developed yet. In this paper, an auto-tuning method for fuzzy logic controller based on the genetic algorithm (GA) is presented. And the scheme is applied into the BLDCM control. Two closed loops are constructed in this paper. The inner loop is current feed back which is to adjust the torque of the motor. The outer loop is the fuzzy logic controller whose control rules are optimized off-line and parameters are adjusted based on the genetic algorithm. In this paper, a program is written in Visual C++ to adjust the fuzzy controller off-line. At last, a TMS320LF2407A digital signal processor (DSP) is used to fully prove the flexibility of the control scheme in real time. Excellent flexibility and adaptability as well as high precision and good robustness are obtained by the proposed strategy.

Being quite different from the contact ultrasonic motors, in the non-contact ultrasonic motor driving fluid directly the rotor immersed in the fluid doesn't contact with the stator directly. This motor solves many problems of the contact ultrasonic motor, such as shorter life expectancy and continuous running time, and becomes a new research direction in the field of the ultrasonic motor. This paper introduces the unique construction of this motor and the working mechanism. And then the course of transferring energy is discussed, in which the energy produced by the ultrasonic vibration is transferred to the rotor through the medium of fluid. It is revealed that the shearing Reynolds' stress is the driving force of the fluid flow. After that, this paper makes theoretical analysis on the acoustic streaming field and sets up the relationship between the acoustic streaming velocity and the rotating speed of the motor. Then the basic operating characteristics of the motor and the relationship between the rotating speed and the driving frequency, the driving voltage, the fluid circumstances and the rotor radius are simulated with MATLAB program. At last the simulation method is proved by experiments.

The stability of the rotor of ultrasonic motor driving fluid directly is a key to its applications and control. This paper introduced the acoustic streaming and acoustic viscous stress near the boundary layer. Following this, the effect of acoustic viscous force on the stability of the rotor of ultrasonic motor driving fluid directly was presented in detail. The result showed that this system can be equivalent to a mass-spring and the spring constant can be used to weigh the stability of the rotor. By this model and relevant experiments, factors that affect the stability of the rotor such as the driving frequency, the rotor's weight and radius, the saturated acoustic streaming velocity, the mode number of stator vibration, the fluid's height and type are investigated and useful guidelines for design and application are obtained.