Study On The Automatic Generation Of3D Assembly Dimension Chain

In the technology of Computer Aided Tolerancing (CAT), the automatic generation ofthe dimension-chain, which is based on the information of dimension and tolerance isexpressed by computer, specifies the closed loop firstly, and then the dimension-chain isautomatically generated on the principle of the automatic generation of the assemblydimension chain, this lays a solid foundation for the subsequent analysis and comprehensionof the tolerances. Nowadays, the changing of the design and manufacturing is fast, it’sneeded at initial design to ensure the correctness of the engineering program, if you want toreduce the costs and put the products into the markets ahead of the competition. In the wholestrategic decision, it’s a key factor for meeting the challenge to analysis the dimension andtolerance fast an accurately, which makes the demand for the analysis tool of dimension andtolerance very urgent in the manufacturing business. Therefore, in order to meet the3Ddesign software that has been mainstream, the research on the automatic generation of the3D dimension-chain has an extremely important significance both on the practicalapplication of the CAT and the improvement of the efficiency for the product design.The investigation of the method on the automatic generation of the3D assembledimension-chain is conduct in the paper. The system of the automatic generation of the3Dassemble dimension-chain is developed which takes the UG NX7.5as the platform for thedevelopment and application of the system by using the secondary development toolUG/Open and VC++6.0.The following is the main research contents of this dissertation:1.Introduces the Geometrical Product Specifications (GPS) and the basic conception ofthe theory for the control points of geometric features; Presents the contents of the GPS, thetheory for the control points of geometric features, and the representative model of theelements of the control points theory by importing the features type and property of theISO/TC213.2.Builds the assemble information model based on the theory of control points ofgeometric element. The characteristic of the model is that it takes the characteristic plane asnode, the mixed graph was consisted of undirected dimension and assembly edge andcomposition to geometric tolerances edge and other edge, this model can access theinformation of the assemble characteristic conveniently, and provide the data base for the lateranalysis and comprehension of the tolerance. 3. introduces the tolerance model and constraint mechanism of the UG software, presentsthe method on the normalization of the UG model before the generation of the assembledimension-chain.4.Proposes the method of automatic generation of the3D assemble dimension-chainbased on the fit characteristic plain. In the3D assemble model, after the closed loop isconfirmed by the user, the system extracts the fitting characteristic plain involved in theassembly constraints and related constraints information from the assemble informationmodel according to the search algorithm. The assemble dimension-chain is formed combinedassemble constraints chain generated by closed loop, and extracts the dimensions among thecharacteristic plain.5.The subsystem generated automatically from the dimension-chain integrated in the UGis developed by using VC++6.0and UG/Open secondary development package, then theapplication of the automatic generation system of the dimension-chain is explored combinedwith examples.