Failure Analysis For Conceptual Design Of Redesigning Products Based On Qualitative Reasoning

In the total life cycle of mechanical products, conceptual design is the most important stage,because it affects product’s quality, performance, cost and the design time. The conceptual designscheme plays a key role in product development life.Redesign is an important means for upgrading the existing products. The safety and reliabilityof a product is one of its important attributes to be considered for redesign of existing products, andfailure analysis is an important means to ensure its safety and reliability in the design phase. Basedon a study of the conceptual design methods and design characteristics, this thesis appliesqualitative reasoning fault diagnosis technology into product conceptual design stage, to investigatethe failure mode in conceptual design scheme, and to discuss the fault diagnosis methods of theactual system.Firstly, the thesis reviews the conceptual design researches, summarizes the theories andmethods of conceptual design, and expounds the research purpose and significance of this work.The thesis also reviews the current qualitative reasoning researches.Secondly, the thesis uses the failure mode and effects analysis (FMEA) to analyze the failureof system in the conceptual design phase, decomposes the main function of the system, and buildsa function to structure map. By assuming possible function failure, the corresponding structure isidentified as the failure reason, and then the failure cause is evaluated and assigned with ranking todetermine the main failure reason, the possible measures, and finally, get an FMEA form.Thirdly, based on the qualitative simulation and directed graph faulty diagnosis methods, thethesis presents a qualitative constraint-based directed graph failure diagnosis method. By addingthe qualitative constraints into symbol directed graph model, the failure state is compared with thenormal state of the system, to identify the failure state, where the corresponding variables are usedas input, and the backtracking method is employed to reason out the root fault based on the symboldirected graph model.Finally, an example case is studied to demonstrate the effectiveness of the proposed method.