| Linear piezoelectric motors show wide application prospects in the micro-nano electro mechanical system, micro operating system and the field of aeronautics and astronautics with its advantages of simple structure, good reliability and high precision. In Occident and Japan, linear piezoelectric motors have already begun to be industrialization and used for Mars exploration, optical focus, biomedical and other high and new technology industry as mature products. Unfortunately, its core technology is in strict secrecy.In view of the urgent need of large travel and high precision drive technology in the emerging fields, it is significant to research and develop linear piezoelectric motors which have good stability, large stroke and high precision independently. Also, it is of great significance to break the foreign technology blockade and to promote the development in the field of emerging technologies in our country. Linear piezoelectric motors can be divided into resonance type and non-resonance type. Resonance type linear piezoelectric motors have poor stability and put high demand on the machining precision. By now, they cannot solve the problem of the stability for both large travel and high precision positioning, so their displacement resolution and speed control characteristics are poor. To improve displacement accuracy and operation stability, high precision friction drive technology had been achieved utilizing piezoelectric stacks with their outstanding features of large output force and displacement repetitive.To conclude, main contributions of this dissertation are as follows.1. Through the analysis of the advantage and the shortage in the existing linear ultrasonic motor and non-resonance linear piezoelectric motors, the need for the study of linear ultrasonic motors is proposed. By analyzing the electrical and mechanical properties of piezoelectric stack, the dynamic characteristics of piezoelectric stack system were researched on to provide the basis for the flexible design method of piezoelectric stack system.2. Combining friction drive mechanism of ultrasonic motor and the existing technology of non-resonant piezoelectric motor, the friction drive technology of linear piezoelectric motor in non-resonant conditions was put forward using the flexible triangle displacement transformation principle. With reference to the ellipse trajectory theory of ultrasonic motor, the formation of the ellipse trajectory theory of flexible stator non-resonant was described in detail and the operation mechanism of this type of motor was further analyzed. Then, both the motor stator structure with bidirectional flexible and the stator clamping unit with ideal single degree of freedom were advanced. Through design, fabrication and experimental test of prototype, the design method was produced for friction drive piezoelectric stack linear motor with flexible stator and its overall structure. Experimental results show that the above linear piezoelectric motor can run in 1 k Hz frequency domain and has good stability. Unfortunately, its output force is not large.3. In order to compensate for the shortage of the small thrust which caused by the flexible stator, piezoelectric stack actuators system named "sandwich" stiffness structure was proposed and nonresonance friction drive piezoelectric linear motor with a rigid stator structure was also constructed. Through systematic researches on the theory of the elliptical trajectory of the drive foot, the characteristics of motor speed of the type were acquired. Through the establishment of the stator vibration mathematical model and the dynamics analysis of the motor stator, the relationship between the vertical amplitude and the thrust Characteristics of non-resonant piezoelectric linear motors were built. The overall design criterion of rigidity stator friction drive piezoelectric laminated linear motor was summarized and its stator through the design, fabrication and testing of the prototype. Experimental results show that friction drive linear motor with rigid stator can run smoothly over a wide frequency range, the speed of the motor appear approximately linear relationship with the excitation frequency and excitation voltage. Compared with the flexible stator structure, the type motor output force has an order of magnitude increase.4. Analyzing the ideal model of non-resonant friction drive linear piezoelectric motors, two methods of achieving elliptical trajectories in the non-resonant state were proposed with piezoelectric stack actuator system. Based on the system longitudinal vibration model, the vibration detachment characteristics were analyzed for the non-resonant friction drive motors. In view of the intermittent contact characteristics for non-linear resonant piezoelectric motor between stator and the mover, the contact interface between the stator and the mover were studied. A non-resonance contact model is established based on coulomb law of friction, which were simultaneously used to study the output characteristic of the motors. Experimental results shows that the model can reflect the working characteristic of the motor in general trend, which benefits for the motor performance prediction and structure optimization.5. Friction differential drive principle was proposed based on the friction drive mechanism, and then the structure and electric excitation of the motor were also put forward. Based on studies of the working mechanism of the differential friction type piezoelectric stack linear motor, the main parameters of the motor were analyzed and the influence of frequency and preloading which applied to differential friction drive performance was researched on. Through researches on the movement characteristics of the motor both with constant pressure difference and with variation pressure difference, three operation modes in different frequency domain were proposed for difference friction drive non-resonance linear piezoelectric motors. Research results show that the motor can work stably in a lower frequency domain(20Hz) and that its open loop resolution can reach micron grade in the medium and high frequency domain and can reach nanometer grade in low frequency domain.All in all, the friction driven piezoelectric stack linear motors proposed in the paper have low demands on the processing accuracy of stator and are almost not affected by temperature and other environmental factors. Therefore, they can realize stable non-resonance friction drive in broad frequency domain( the working frequency range is about 1 k Hz), while the differential friction type motor can achieve open loop resolution up to 12 nm. |
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