Research On Automatic Generation Of Assembly Dimension Chain Based On Analytic Hierarchy Process

Automatic generation of dimension chain is a key technology in computer aided tolerance design.In this paper,aiming at the problem of low accuracy of automatic generation technology of dimension chain,the automatic generation technology of assembly dimension chain based on AHP is studied.The main research contents are as follows:This paper presents the rules of weight allocation based on Analytic Hierarchy Process(AHP).According to the steps of AHP,taking dimension and tolerance constraints B₁,interference fit B₂ and gap-or-transition fit B₃ as evaluation factors,and dimension chain paths C₁,C₂,…,and C_n as indicators,a hierarchical structure model for dimension chain path selection was established,and the weight of each evaluation factor on assembly dimension chain path selection was calculated.The rule of degree elimination based on graph theory is proposed.The concept of degree in undirected graph is studied,and a method of eliminating points and edges independent of assembly accuracy is proposed.The method first counts the degrees of the points except closed rings,then eliminates the points with degrees 0 and 1 and the corresponding edges,and repeats them many times until the degrees of the remaining points except closed rings are greater than 1,then stops the statistics of the degrees.The concept of property set of geometric elements is proposed and its generation method is given.Based on the new generation of product geometry technology specification theory,the geometric elements are divided into component elements and derived elements,and the size and tolerance constraints among the elements are studied.According to the spatial position relationship,assembly constraints are divided into interference fit and clearance fit or transition fit,and the assembly constraints among various elements are studied.According to the requirement of automatic search of dimension chain,the property set of geometric elements is constructed and its generation method is given.Build the assembly information model of dimension chain.In order to express the dimension chain information of assembly completely,constraint transfer graph between features is constructed.Finally,the assembly information model of dimension chain is built.An automatic generation strategy of assembly dimension chain is proposed.The realization of Floyd search algorithm is studied.After the closed loop is determined,the system obtains the information of dimension and tolerance constraints and assembly constraints,and generates the constraint transfer diagram between geometric elements.The dimension chain can be obtained by searching the transfer diagram.The generation technology of dimension chain is studied.Finally,an example is given to verify the effectiveness of this method.The prototype system of automatic generation of dimension chain and the application of engineering examples are given.Finally,an example is given to verify the effectiveness of this method.This paper summarizes the research contents of the full text and looks forward to future research work.