Correlative Reliability Analysis And Topology Optimization Of Failure Mode Of Mechanical Structure System Based On Vine Copula Function

There are a lot of uncertainties in the mechanical structure system,Such as load,material properties,structure size,etc.Dealing with these uncertainties often uses reliability methods.However,traditional reliability methods mostly assume that each random variable is independent of each other,However,in most cases random variables are correlated and the correlation between variables may have an impact on the analysis results.Therefore,this paper focuses on the theory and method of reliability modeling of mechanical parts and mechanical structural systems.At the same time,it must be reduced in weight to meet the requirements of system reliability.Lightweighting is one of the innovation themes of mechanical structural systems.This article takes an industrial robot as an example,Research on its dynamic characteristics and structural optimization,Discusses the topological optimization method of robot under dynamic conditions.The specific research content and results are as follows:1)Aiming at mechanical parts for multi-failure modes,the advantages of using Copula functions to describe correlations,a reliability modeling method for multi-failure mode related mechanical parts is proposed.Based on the Vine Copula function,the reliability problem of mechanical parts related to complex and multi-failure is transformed into the analysis of multiple two-dimensional Copula functions,optimal two-dimensional Copula function is identified by using maximum likelihood estimation and AIC information criterion.Mechanical parts failure mode is relatively small,access to less failure samples.To avoid the variability of AIC values,based on improved parameters is proposed to identify the optimal two-dimensional Copula function when the failure sample size is small.The feasibility of the improved parameter Bootstrap method is verified by Matlab simulation,then the reliability of the multi-failure mode related mechanical parts is solved by using the Vine Copula model.Finally,through the comparison between the calculation example of drive shaft and other methods,the method is rationality and validity.2)The dynamic reliability of mechanical system failure can be described by dynamic Vine Copula model.The Vine Copula function is used to transform the reliability problems of complex and multiple failures related to the analysis of multiple two-dimensional dynamic Copula functions,Using the nonparametric estimation algorithm,the empirical distribution function-local maximum likelihood two-step method is proposed to estimate the time-varying parameters in the dynamic Copula function.To established a dynamic Vine Copula model to describe the reliability of multi-failure dynamic related mechanical systems.And focus on the mechanical system of the series system reliability modeling and analysis,then the reliability of the mechanical system to solve,which provides a new method for characterizing the reliability of dynamic related mechanical systems between multiple failure modes.Finally,an example is given to demonstrate the rationality and validity of the method.3)Multi-body dynamics and finite element method are used to establish the rigid-flexible dynamic model of industrial robots.The dynamic load of the arm under the special working conditions of the industrial robot is obtained,and the dynamic structural strength of the arm is analyzed.The three-dimensional solid model of an industrial robot is established using Creo 1.0,imported into the finite element software Ansys,and the typical working conditions of the industrial robot are determinedaccording to the force curve of the robot,so that the static analysis is performed to find the dangerous part of the robot arm.,and get a steady load of working conditions.The solid model of the robot assembly was imported into Adams,and the rigid-flexible coupling model of the industrial robot was established for dynamic simulation,and the stress-time history curve of the robot arm was obtained.The analysis of the dynamic structural strength of the arm and the finding of the weak parts in the complete machine laid the foundation for the next step in establishing the appropriate topology optimization for the weak parts.4)Aiming at the multi-objective reliability topology analysis of structural systems,based on the optimization criteria of the SIMP material interpolation method and the reliability theory,a normalized sub-objective based on the compromised planning method was proposed,and the reliability index was used as a constraint to establish the machinery.The objective function of maximizing arm static stiffness and dynamic vibration frequency and component quality is used to determine the weight coefficient of the sub-target in the synthetic objective function by the analytic hierarchy process.Then the comprehensive target design of the arm structure is performed,and the new structure of the complete machine is obtained.The research results show that after optimization,the overall quality of the industrial robot is reduced under the condition of satisfying the reliability,and the overall stiffness performance is obviously enhanced,and the natural frequency of each order is improved to some extent.