Study On Theory And Methodology Of Tolerance Design Within The Framework Of The New Generation GPS Standards System

New generation GPS standards system is an information system of standard & metrology oriented the digitizing design, manufacturing and verification. The study on theory and methodology of tolernace design within the framework of the new generation GPS system has become the very important technology issue, which is in urgent need to settle during the course of establishing the system. On the basis of summarizing the latest research results in tolerancing both of at home and abroad, this dissertation aims to solve the key theories and technique problems on tolerance design currently unsolved in the GPS system. The main researches and creative points are as follows:A mathematical representation model of tolerance has been established oriented the new generation GPS system. According to the geometrical feature types and the operation methods extracting features newly defined in the GPS system, the SDT-based mathematical model of tolerance is studied by using the small displacement torsors (SDT) to characterize the deviations of shape, position, orientation and size of geometrical featrues. It also establishes theoretical basis for tolerance design from 1-D to 3-D assemblies, which is further studied in the following chapters.A comprehensive method of tolerance design for 3-D dimensional tolerances and geometrical tolerances is proposed. The description methods of various tolerance zones and kinematic links based on SDT are studied. Based on the surface model concept newly presented in new generation GPS system, we apply surface models to describe an assembly, and use the SDT to express the relative position between any two surfaces of an assembly. In order to determine the torsor between any two surfaces, two governing rules are defined: the union and the intersection. Based on the effect of each functional element on the whole functional requirements of products, the 3-D dimension-chain is created, and 3-D dimensional and geometrical tolerance design is realized. The engineering examples involving 3-D tolerance design are given to test the proposed method.Three-dimensional tolerance analysis technique based on the vector-loop tolerance model including the geometric feature variations is studied. In view of the needs for the new generation GPS system to integrate with CAD/CAPP/CAM/CAQ techniques, the tolerance analysis model based on the vector-loop is established at first. The discussions focus on the effects of dimensional variations and geometric feature variations of each individual component in the assembly, and variations due to small kinematic adjustments among components which occur at assembly time. And the effects of all variations are integrated in the tolerance analysis model so as to realize 3-D tolerance analysis including all geometric feature variations. The tolerance analysis examples of 2-D and 3-D assemblies are given to demonstrate the effectiveness of the proposed model, respectively.A concurrent tolerance design method for the products with correlated characteristics is presented based on the concept of concurrent engineering in the new generation GPS. On the basis of analyzing in detail manufacturing process plans of parts, the functional relationship between quality loss of products with correlated characteristics and process tolerances of correlated parts is derived. And a comprehensive model to concurrently allocate optimal design and process tolerances based on minimizing the combination of quality loss and manufacturing cost is established so that the concurrent tolerance design is realized, and product quality improvement and cost reduction are achieved. An example of the bevel gear assembly involving concurrent tolerance design is given to verify the presented method.An optimal tolerance design model for product life cycle is proposed within the frame of the new generation GPS system. Considering product degradation on quality characteristics over time, the multivariate quality loss function is used to model quality loss due to product degradation as a continuous cash flow function under continuous compounding. As a result, the functional relationship between the present worth of expected loss of product with correlated characteristics and its related tolerances is derived. The present worth of quality loss and product degradation over time is integrated into the total cost model, and a new optimization model for the tolerance design of products with correlated characteristics is presented. An example of the leaf spring involving optimal tolerance design is given to demonstrate the effectiveness of the proposed model.A prototype system for tolerance design within the framework of the new generation GPS system is developed. The software platform of the system is based on AutoCAD2007, development tools adopted involve ObjectARX, Visual C++ etc. The engineering examples are studied to demonstrate the effectiveness of this system.