Study On Theories And Methods Of Geometric Tolerance Design Based On Variational Geometric Constraints Network

Based on the "Study on Simultaneous Design of Blueprint Tolerance and Process Tolerance" (National Nature Science Fund Project, No: 59575076) and the "Study on Computer Aided Tolerancing System" (National Nature Science Fund Project, No: 59705022), the theories of variational geometric constraints network are presented. Based on the theories, the methods of generation of geometric tolerance types and optimization of geometric tolerance values are studied. The prototype system for computer aided geometric tolerance design 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. Based on those, the key techniques and development trends of CAT system are proposed. At last, the background, main contents, general structure scheme and innovation points of mis dissertation are presentIn the second chapter, based on new feature type defined by ISO/TC 213, the theoretical basis and classification is studied. Based on group theory, seven kinds of symmetrical Lie subgroups are analyzed. This then lead to a classification of the symmetrical features into seven classes. Variational geometric constraints (VGC) are classified as self-referenced VGC, cross-referenced VGC and mating VGC. Seven kinds of self-referenced VGC, twenty-seven kinds of basic cross-referenced VGC and six kinds lower-pair mating VGC, are classified. The chapter establishes mathematic basis of the theories of variational geometric constraints network, which is presented in the following chapter.In the third chapter, the concepts of loop circuit (LC) and variational geometric constraints network (VGCN) are firstly presented. Based on mate tree (MT), the generation rules of well-constrained loop circuit are presented. Evaluation rules of well-constrained VGCN are studied. Leading evaluation method into design process, the generation strategies of well-constrained VGCN is discussed, and the theories of variational geometric constraints network are established.In the fourth chapter, classifying tolerances into self-referenced tolerance and cross-referenced tolerance, the corresponding rules between self- & cross- referenced VGCs and tolerance types are studied. The generation method of well-referenced tolerance types is presented. The generation strategies three-dimensional tolerance network (TN) is discussed.In the fifth chapter, using the method of kinematic analysis in robotics, the kinematicmodel of VGCN is established. The screw parameter and matrix of all kinds of VGCs is defined. The accumulation of screw matrixes in VGCN is studied. The general expressions of kinematic model of 3-dimensional VGCN are presented, which is the equation constraint in optimization of tolerance values. Screw parameters in VGCN specified by tolerances in TN are expressed as inequation, which is inequation constraint in optimization of tolerance values.In the sixth chapter, application of VGCN to optimise tolerance values is studied. The mathematic model of optimization allocation of tolerance values is established. In the model, the objective function of the optimization is production cost-tolerance function, and the constraints of the optimization are equation and inequation in the fifth chapter. Based on genetic algorithm, the method of optimization geometric tolerance values is studied. The method can be used to synthetically design dimensional tolerance and geometric tolerance. Examples are analyzed to show the scheme to be effective.In the seventh chapter, the prototype system for three-dimensional geometric tolerance design is studied. The system comprises three tolerance design module and two tolerance evaluation module. Three examples are studied to demonstrate that the system can effectively design dimensional tolerance and geometric tolerance, and integrate tolerance design and tolerance evaluation.In the eighth chapter, all of the work in this dissertation is summed up, and the future research of computer-aided tolerancing is prospected.