Research On Multi-joint Shape Memory Alloy Drive System Based On Forced Thermal Convection

The current thesis is about the investigation on a multi joint driving system by using shape memory alloy spring actuated via forced thermal convection.The shape memory alloy(SMA)spring has been studied by many researchers due to its special performance.Due to its high energy density,SMA has been used in many different scenarios.However,the response speed of SMA is usually low,which is a limitation to the applications of the material.The system put forward in the current thesis is tend to overcome the limitation to expand the using of SMA.The current research is focused on the design and analysis of the system,in order to get a quick response.By analyzing the actuation mechanism of SMA,a new heat convection method is proposed to improve the response frequency of SMA systems.After verifying the feasibility of the new system,the structure was designed and fabricated,different experiments are performed to test the real response frequency of the driver.The main work of the thesis is listed as follows:In the first chapter,the background and significance of the thesis is presented and the application potential and limitation of the SMA spring is also elaborated in detail.SMA actuating system have been studied for many years,however,the low response frequency of the system is still one of the major obstacles in its applications.Based on a comprehensive analysis of the existing systems,a new system is proposed.In the second chapter,the constitutive relation of SMA spring is elaborated to explain the behaviors.Some models and typical theories on shape memory phenomenon are introduced to support the design of the whole system.By using the models and theories,the feasibility of the proposed system is verified.In the third chapter,the dynamic model of the system was established on the basis of the analysis.The actuating mechanism and structure are put forward.The structure design is an essential step for the current thesis.All the components used in the current system are manufactured,and then assembled together in the lab.The SMA springs are also made according to the specific need.In the fourth chapter,based the previous design and analysis,numerical simulations and experimental tests are performed.Firstly,by using the models elaborated before,numerical simulations of the actuating system working in different situation are carried out.Secondly,the characters of the SMA springs are identified by fitting the numerical data with tensile experiments.At last,the experimental investigation of the actuating system under different conditions are performed,and the comparison between numerical and experimental results is also presented.It is shown by the comparison that a reasonable agreement is achieved.In the last chapter,a conclusion about the work presented in the current thesis is drawn.The results of the experimental tests are analyzed.Based on numerical and experimental results,some prospective research topics are put forward.