Research On The Conceptual Design Process Modeling And Scheme Solving Of Mechanical Products

A conceptual product, originating in the innovation requirement from the market, generally first goes through the multi-stage design process, then the manufacture and marketing stage, finally turns into reality. In this phase, conceptual design plays a key role, having critical influence on the overall performance and market competitiveness of the new product. Thus it is necessary to make research and investigation into the theories and methods relating to the issues with product conceptual design. From the researches on modern product design theory by the Academia at home and abroad in the last two decades, derived an amount of academic achievements concerning the essential points in process of conceptual design, ranging from the information gathering and managing of design requirements, product information modeling in conceptual design, conceptual design process modeling, to the generation and evaluation of conceptual product schemes. In this document, the literatures relating to the theories, ways and means of approaching conceptual design of mechanical products, at home and abroad since the mid 1990s in 20th century by now, have been collected, seriously sorted and studied; on this basis, to some key points and issues in conceptual design, which have not yet either been paid enough attention to or been fully settled, certain original viewpoints and methods are suggested. Design case study about special-used dynamic compaction machinery is done to exemplify the effectiveness and practicability of the suggested methods, aiming at combining this research work with engineering practice to a satisfying degree.The theoretical tools applied in this dissertation are introduced, including the fuzzy linguistic varible, sparse matrix corresponding to directed graph, fuzzy graph theory, and the pointwise fuzzy set-theoretic operations.Two key issues influencing the market competitive power of a conceptual product are studied intensively. Firstly, for the issue of quality assurance, this paper introduces a quality needs information modeling method, featured by the application of fuzzy linguistic variables. The decisive influence of the market conditions on the conceptual product quality needs can be dynamically represented through the properly-chosen fuzzy linguistic phrase and its corresponding quantitive parameter-value interval, which can be directly taken as constraints for conceptual design. Then, it is discussed that as for a conceptual mechanical product under innovation, the changes concerning its working environment and the varying market requirements have critical impact on the conceptual design process. Characterizing this kind of innovation process, a dynamic model of Environment-Requirement-Function-Behaviour-Structure (E-R-F-B-S) is put forward, which is featured by a series of mappings between the five kinds of variable sets. Named innovation chains, four kinds of innovation patterns depicting the designers' usual trains of creative thoughts in the mechanical product design activities are outlined, represented by the ordered combinations of the seven mapping units in the E-R-F-B-S model. The mathematical model of innovation chain is established by determining the correspondence between innovation chain and directed graph, then directed graph and sparse matrix, thus making it possible to suggest the set up of a computer-aided reasoning system for conceptual design, sparse matrices as its input variables.To fercilitate the visualization of the scheme generation process in conceptual design, the fuzzy graph theory is introduced and the concept space is represented as a fuzzy AND/OR tree. On the basis of the fuzzy comprehensive technical performance evaluation of the fundamental function carriers, the method with respect to optimal-level-value in fuzzy set-theory is used to select the appropriate carriers; then through the carrier combination, the candidate schemes can be generated and comprehensively evaluated. Thus, the scheme solving process in conceptual design can be optimized and the design efficiency improved.As a key issue in design evaluation, the conceptual product reliability estimate can be made by means of Fault Tree Analysis (FTA), with a fuzzy set defined on the unit interval whose elements correspond with the fuzzy linguistic expressions of the basic events' possibilities. The existing parameter-varying pointwise fuzzy set-theoretic operation model for FTA has obvious shortcoming, so the parameterized Schweizer(3) t-norm and parameterized Hamacher t-conorm are chosen, respectively as the means for the reliability estimate of AND/OR events. Respectively for the chosen parameterized t-norm and t-conorm, two parameter extrema are fixed refering to expert experience, to be used for making the most optimistic and the most pessimistic estimate, thus providing the necessary and reasonable reference for the designer to estimate a conceptual product's reliability according to its working environment-to-be.With broad prospect of application in ground foundation construction, dynamic compaction machinery has undergone the development from so-called "substitute machinery" to the special-used kind. As a new concept being explored, the special-used machinery is characterized by specific working environment, and its conceptual design can be taken as a representative as for mechanical products. Conceptual design of the type QH800 of special-used machinery is discussed here. Through the elaboration of innovative design of the main assemblies and sub-systems, followed by the reliability estimates of two kinds of main hydraulic circuit as well as three kinds of circuit control system, the application significance of Innovation Chain and FTA coupled with parameterized pointwise fuzzy set-theoretic operations can be validated in mechanical products' conceptual design.