The Theory Of Structure And Experimental Research On SMA Linear Actuator

In the fields of modern technology,there are increasing high demands on linear actuators which are characterized by high thrust-weight ratio,high efficiency and displacement control whthin given volume and weight . While the traditional one has low thrust-weight ratio,and deceleration units are needed after drivers'revolving at high speed,both of which result in a complex transmission device and cumbrous structure . Therefore,it is impossible for conventional technology to meet the demands for development of technology.Nowadays, more and more smart materials are being adopted to driving parts. Among them,Shape Memory Alloy (SMA) , with such merits as high thrust-weight ratio,an integration of driver and sensor, as well as large strain , makes itself uniquely endowed with a latent application outlook in the field of application of smart materials .Firstly,in this thesis the categories of linear actuators are classified , the development trend of smart materials is analyzed, the smart materials which can be used in linear actuators are listed and an assay of their advantages and disadvantages is made , then a suitable driving material for this project---Ni-Ti memory alloy is sorted out. In addition, in this thesis the principle of operation of differential SMA actuators based on the theory of cumulative displacement is also expounded and a linear acuator capable of covering a long distance is designed and an experimental sample is manufactured.Afterwards, constitutive relation of SMA is included in it. In this thesis, the main characteristic parameters of alloy threads are acqiured through static experimental research on Ni-Ti alloy and then the relationship among SMA materials'stress,strain and temperature is analyzed ,which are presented as the theory basis of research on the phase transformation and properties of SMA linear acuators.Lastly, enamelled wires are chosen to heat the driver and semiconductors to cool it down. Also, a closed loop control system is constructed to control the heating and cooling of SMA driving parts precisely through PIC singlechips.These experiments show that this kind of acuators can output great force and lengthy displacement with a simple structure and a simple control system.Displacement and disformation rate rise along with the increasing in electricity current within a certain range . Except this merit, proper cooling measures do great promotion to raise the frequency and force .In order to measure the driving performance of SMA drivers, temperature control experiments and a overall test on its properties are conducted . These results indicate that this acuator is capable of meeting the design requirements of great force and long displacement. Due to the adoption of steping accumulation,the difficulties in intermediate state control are avoided ;thus relatively high precise displacement control can be achived .In conclusion,the correctness and feasibility of taking advantages of SMA to achive the cumulative displacement is proved on the foundation of theoretical analysis, the design and manufacture of the experimental sample as well as relevant experimental research . And the stimulation of electricity current can maitain the frequency of heating and cooling in control. As a consequence, this research provides some new trains of thought and methods for further research in SMA linear acuators.