Research On Combined Ultrasonic Actuator Connected By Low Stiffness Beam And Its Motion Form Of Driving Point

Piezoelectric ultrasonic actuator has the advantages, such as direct drive, fast response, without electromagnetic interference, high positioning accuracy, simple structure, flexibility of design and so on. In recent three decades, ultrasonic actuator develops markedly and can be widely applied in the fields, such as aeronautics and astronautics, optical instruments, micro- electromechanical system, robot, semiconductor manufacture and medical instruments. At present, how to expand the driving function of actuator,realize multi-function, such as multi-DOF driving, and integrate it with the mechanism or the system have become important research areas of ultrasonic actuator and need to be studied systematically. In addition, the mode degeneration is a common problem for actuator excited by composite modes of different type. And the result of mode degeneration directly affects output performance of actuator. Therefore, it’s a valuable research topic to simplify the process of mode degeneration and guarantee the degeneration result in design phase.In this thesis, the motion form of driving point and the combined ultrasonic actuator connected by low stiffness beam are researched. The actuators are constructed by transducers connected by low stiffness beams. The mathematical models of the beams are established. The motion form of driving point of actuator is taken as the research object, and the methods to generate and adjust the motion form are analyzed. Then the theoretical basis is established. By integrating theory, finite element simulation and experiment, the principle prototypes of new type ultrasonic actuators with single, two and multi driving points are developed, and the driving functions are realized, such as two-degree of freedom, two output driving and one-degree of freedom. The targets are realized, which are to test the theory, simplify the mode degeneration process or avoid the mode degereration problem and acquire new driving characteristics.The output characteristics are decided by the motion form of driving point of piezoelectric-metal composite ultrasonic actuator. To identify the method of generating and adjusting the motion form of driving point, the characteristics of piezoelectric ceramic, vibration modes of beam and vibration theory of beam excited by piezoelectric ceramic are analyzed. Then, to realize the driving function, the method is studied to generate elliptical motion trajectory of driving point in spatial plane by one transducer excited by composite modes.To simplify the mode degeneration process and avoid the interference of modes of transducers, the vibrator is constructed by multi transducers, which are connected by low stiffness beams. Two kinds of beam are designed, and the mathematical models are established to analyze the method to generate elliptical motion trajectory of driving point and the effects of major influence factors. By the research of the above contents, the theoretical basis is established for the combined actuator, which is consists of multi-transducer and can generate acticipated elliptical motion trajectory by driving point.Multi-DOF driving function is one form of expression of multi-function of ultrasonic actuator. In order to realize 2-DOF driving, the motion form of driving point and the exciting methods are studied, and two actuators with one driving point are developed. The multi mode excitation and mode switching methods are utilized to generate and adjust the motion form of driving point, and the one DOF and two DOF driving function are realized, respectively. By the research of the actuators, the facts are tested: the effectiveness of the method to generate and adjust the motion form based on the low stiffness triangular beam connection way, the effect of combining low stiffness beam and mirror symmetrical structure of vibrator on simplification of mode degeneration process.It is another form of expression of multi-function of actuator that is to driving multi moveable bodies by one actuator. Therefore, facing the miniature mechanism with two independent rotors, the driving way of coordinating two driving points of one vibrator is put forward and used. The motion forms of two driving points and the exciting methods of actuator are studied. The principle prototype with two driving points is developed. The multi operation modes are designed, and the working principle of actuator and the methods to generate and adjust the motion form of driving point are studied. The vibration characteristics and driving characteristics are tested. The actuator can drive two independent rotors rotating with same or contrary direction and with different speeds.According to research, the mode degeneration problem can be avoided by using the two orthogonal vibration mode of a rotational symmetrical structure to excite an actuator. To utilize the characteristic and realize rotary driving function, the combined drive way by multi points, the motion forms of driving points and the exciting methods of actuator are studied. Firstly, four longitudinal transducers are connected in parallel to generate an actuator with rotational symmetrical structure. To weaken the interference of transducers and merge the local longitudinal modes with entire orthorgonal lontigudinal modes, the transducers are connected by low stiffness beams. Then, using the finite element simulation method, the vibration modes, working principle and the generation and adjustment methods of elliptical motion trajectory of driving points on the two sides of the vibrator are analyzed. The principle prototype of the actuator is developed. And, the facts are tested: the effectiveness of the method to generate and adjust the motion form based on low stiffness direct beam with tooth, the effect of combining low stiffness beam and rotational symmetrical structure of vibrator on avoiding mode degeneration problem.