Study On Auto-generation Of Dimension Chain Faced To 3D Assembly Drawing

Based on the "Study on Computer Aided Tolerancing System" and "Design Theory of Integration Tolerance based on Geometrical Product Specifications" (National Nature Science Fund Project, No: 59705022, 50275136), the technology of the auto-generation of dimension chain faced to 3D assembly drawing is presented. The prototype system is developed and proved by examples.In the first chapter, State-of-the-arts of computer aided tolerancing (CAT) system at home and abroad are summarized. The technology of the auto-generation of dimension chain is also analyzed. Main contents and general structure scheme of this dissertation are present.In the second chapter, the concept of geometrical product specifications (GPS) is introduced. Based on tolerance definition and feature type defined by ISO/TC 213, contents of the geometrical specifications, TTRS theory and several sorts of feature are analyzed.In the third chapter, the constraints mechanism of MDT is studied. Dimension constraints, geometric constraints and assembly constraints of MDT are analyzed. Combined with new feature type defined by ISO/TC 213 and Variational geometric constraints (VGC) theory, a kinds of Variational geometric constraints network (VGCN) faced to dimension chain is proposed.In the fourth chapter, the assembly characteristic is studied. Several common assembly information models are analyzed. Top-down assembly database way is adopted and the assembly information model is improved with the concern of the characters of the CAT. The assembly database faced to dimension chain is put forward and realized. At last, the definition of the part class, assembly class and feature class of the assemble database are given.In the fifth chapter, the auto-generation principle of the dimension chain faced to 3D assemble drawing is put forward. First, the closing loop is specified in the assembly drawing by the user. Then system can get the assembly constraints from the drawing and generate the VGCN faced to the dimension chain. The parts' related dimension information is also obtained. The dimension chain is auto-generated later.In the sixth chapter, the prototype system for auto-generation of dimension chain faced to 3D assembly drawing is introduced.In the seventh chapter, all of the work in this dissertation is summed up. The future research of computer-aided tolerancing is prospected.