Mechanical Symmetry-Breaking Theory And Its Application In Design

Symmetry-breaking phenomenon widely exists in mechanical products. Numerous design cases demonstrated that symmetry-breaking played a vital role in implementing functions, improving performance and satisfying constraints. Despite its importance, there were few studies on mechanical symmetry-breaking at present. The thesis reviewed the literature of symmetry-breaking in inter-disciplines and discussed the deficiencies in current studies on the mechanical symmetry-breaking. Then the research on the concept system of mechanical symmetry-breaking and its application in mechanical design was carried out. The major work can be classified into following four aspects:Firstly, the concept system of mechanical structure symmetry-breaking was established. Based on the analysis of design instances of symmetry-breaking structure, the definition of mechanical structure symmetry-breaking was proposed. Furthermore, the formulation mechanism of symmetry-breaking structure in mechanical parts and components was studied and symmetry-breaking patterns are summarized.Secondly, the concept systems of space-time symmetry-breaking of general requirements and working principle were established. By analyzing of mechanical instances which had symmetry-breaking feature in general requirements or working principle, and also taking concept system of mechanical function and principle space-time symmetry for reference, the concept system of space-time symmetry-breaking of general requirements was built which contained three symmetry-breaking types:function requirements, performance requirements and constraint requirements space-time symmetry-breaking. The concept system of space-time symmetry-breaking of mechanical principle was built as well.Thirdly, application knowledge of mechanical symmetry-breaking was concluded. Based on the concept systems referred above, the connections between symmetry-breaking and product design requirements were analyzed. And then application knowledge of mechanical symmetry-breaking was concluded into7design principles or guidelines.Fourthly, mechanical symmetry-breaking knowledge mining and application software platform was studied. In knowledge mining respect, a process of knowledge mining of symmetry-breaking was proposed and repositories of design cases, basic knowledge and association rules were built. In knowledge application respect, a process of applying knowledge of symmetry-breaking was proposed. Besides, a design method and process of symmetry-breaking structure was proposed. Finally, a design case of a novel chain drive device was presented in order to verify the effectiveness of design theory.