Study On The Methods Of Assembly Error Analysis Based On Skin Model Shapes

Supported by the National Nature Science Fund Project "Tolerance analysis theory and methods for complex assembly based on number theory(No.51575484)",this thesis studies the methods of tolerance analysis for mechanical assembly,realizing the modeling of actual manufacuturing surface,the construction of the error cumulative calculation model with consideration of manufacturing error and part deformation comprehensively,and the tolerance analysis of assembly.1)To satisfy the requirement of new generation GPS for tolerance representation model in product life cycle,the geometric tolerance-oriented surface model of parts is developed.Considering different tolerance principles,the strategy for calculating dimension error and corresponding compensation amount is proposed,and then the skin model shape of part with full tolerances is generated.2)The assembly error analysis method based on Jacobian-Skin Model Shape model is studied,in which the skin model shape is adopted for tolerance representation,and the Jacobian matrix is used for tolerance propagation.The most common types of serial and parallel joints between parts are given,then the solution of small displacement variation of serial and parallel connections based on relative positioning method is presented,the assembly analysis model including tolerance information and joints information is established.3)Aiming at the limitations of the Jacobian-Skin Model Shape in the application of fully parallel structural assembly,a unified Polytope-Skin Model Shape method is proposed.The toleranced features are represented by skin model shapes,the geometric and contact polytopes are built to indicate the corresponding geometric and contact deviations,and according to the assembly structure,Minkowski sum or Intersection operations are carried out on the polytopes to obtain the functional requirements.4)Considering the deformation of parts caused by environmental factors in the actual working process,the influence of actual working conditions on the manufacturing parts is analyzed.The finite element analysis is performed on the skin model shape,the surface with manufacturing errors and deformation errors taken into account is obtained.On this basis,the small displacement variation is obtained by relative positioning,and then the Jacobian model is modified to be the tolerance mathematical model considering the cumulative manufacturing and deformation errors;Based on the geometric and contact polytopes calculated from the deformed surfaces,the accumulated error is given.5)The software prototype system for skin model shape simulations and assembly error analysis is developed based on MATLAB.The modules of the system are elaborated and the workflow of the system is demonstrated with an example.