Research On Key Technologies Of3D Intelligent Dimensioning And Automatic Generation Of Dimension Chain

The intelligent dimensioning of3D parts and automatic generation of3D dimension chains areimportant research topics in the field of CAT. Based on TTRS tolerancing theory, the research on keytechnologies of3D intelligent dimensioning and automatic generation of dimension chain isinvestigated in this paper. The main research achievements are as follows:An intelligent dimensioning algorithm of3D parts is proposed based on TTRS theory. Firstly, theMinimum Geometric Datum Elements (MGDE) of Technologically and Topologically RelatedSurfaces (TTRS) are extracted and named dimension elements. The dimension element sets ofdimensions are constructed based on the classification of dimension elements and elimination ofredundant dimension elements. Secondly, function dimension set, non-function dimension set andTTRS dimension set are constructed. The dimensioning priorities for dimensions in non-functiondimension set are sorted according to the weights and the elimination of dimension redundancy basedon graph theory. Finally, the intelligent dimensioning of3D parts is achieved by using the applicationprogramming interfaces of CAA.An automatic generation algorithm of3D assembly dimension chains is proposed based onTTRS tolerancing theory. Firstly, dimensional tolerance information of each parts and assemblyconstraints in the assembly model are extracted according to inner tolerance expression and assemblyconstraints in CATIA. Then geometrical elements-dimension adjacent matrixes and geometricalelements-assembly constraint adjacent matrixes are built based on the extracted information. On thebasis of the above adjacent matrixes, graph and assembly constraints relation graph are constructed.The final graph named dimensional tolerance-assembly constraint is created by combing the abovegraphs. In the end, based on the information of closed loop, assembly dimension chain can begenerated automatically by searching the dimensional tolerance-assembly constraint graph.Dimension chain equation is designed according to the generated dimension chain. Nominaldimension and deviation of closed loop are calculated by extremum seeking method and probabilitymethod, and simulated by CAT software like Vis/VSA. And the results are compared with each other.Example shows that the automatic generation method of dimension chains in this paper is effectiveand reliable.