Optimization Design Of Spect Mechanical System Based On Fatigue Reliability

SPECT is a kind of precise medical imaging equipment,which is widely used in the functional research of human organs and the diagnosis of diseases.The mechanical system of SPECT has the characteristics of multi-degree of freedom,high load and variable load.The fatigue reliability of the mechanical system is greatly tested.At the product design stage,in order to ensure the fatigue reliability of SPECT mechanical system,the fatigue life of SPECT mechanical system was analyzed by virtual fatigue test,and the key components were optimal designed.S-N curve method was used to analyze fatigue life.Firstly,a 3d model of SPECT mechanical system was established,and dynamic simulation analysis was performed based on SPECT motion characteristics to obtain the load time history of key connections such as lead screw,guide rail slider and bearing block.Then,finite element analysis was carried out on the substrate assembly,X platform assembly and Y platform assembly.Unit load was added at the key joints of each component,and the solution was obtained by using the inertia release method to obtain the static analysis results.Finally,s-n curve method is selected for fatigue life analysis.The linear superposition method is used to obtain the stress spectrum by multiplying the load spectrum with the static stress analysis results of unit load.The fatigue characteristics of the parts themselves,namely the S-N curve,are combined to make life prediction.On the basis of ensuring that the fatigue reliability of SPECT mechanical system meets the requirements,the optimal design of SPECT mechanical system is carried out to improve the material utilization and reduce the equipment weigh and cost.A method combining topological optimization and size optimization is adopted.The topological optimization method is used to reduce the structure,and the response surface method is used to control the local size.The finite element model of the detector translation mechanism under four typical working conditions is established.During topological optimization each working condition is weighted according to the strain energy result of the finite element analysis.The multi-working condition topological optimization model is established to search the optimal material distribution and obtain the optimal topological structure.Parametric modeling was carried out based on the improved topology structure,and parameters with great influence on quality,such as thickness and weight reduction hole size,were selected as the optimized design variables,and a reasonable range of design variables was set according to the assembly relationship and motion range.Experiment design is carried out by applying the method of optimal space filling.The test sample points is took within the value range.The response surface is built by CCD or Non-parametric regression method.With the minimum volume of quality as the goal,the size of the parts as the design variables and the results of the fatigue life as constraint conditions optimize the design.The genetic algorithm is used to solve.X platform assembly quality reduce 11.2%.Y platform assembly quality reduce 15.9%.Base board assembly quality to reduce 15.1%.The fatigue life of optimized structure meets the requirements and the lightweight design is achieved.