Key Technologies For Multi-skeleton Based Top-down Design Of Mechanical Products

The frequent modification of design,the low reuse rate of existing design and the uncontrollability of design process have seriously affected the design efficiency of the customized one-off large mechanical product and increased the burden of designers.Different from the mass production of ordinary products,the design for the customized oneoff or small-batches of large products need to meet the challenges of multi-dimensional complexity,hierarchical structure,iterative process,gradual innovation,nonlinear evolution and information uncertainty.The top-down design is a rapid and effective design method,nevertheless,the traditional top-down design theory and approach could not applied to the design of these type products effectively without consideration of information management,inheritance mechanism,reuse of the existing design and optimization of design activities,etc..In view of the above problems and challenges,two scientific issues are proposed for top-down design: 1)the design issue of product oriented to coupling,iteration and reuse,2)process planning issue for the hierarchical and uncertain information of design tasks.The focus is on the research of three key technologies to improve design efficiency,which are construction of the modular function structure for mechanical product,layout design and process planning.The main research contents are as follows.(1)The modular function structure construction approach for product based on community detection of weighted and directed complex networks is proposed.First,the approach of constructing a function model of weighted and directed complex network is proposed.After the function base model for product is implemented,the function bases are mapped to the network vertices,and the function flows are mapped to different directed edges between vertices,then the different directed edges between two vertices are merged to obtain weight of the every directed edge between vertices,thus,the weighted and directed networks function model is established.Second,the method of partitioning the complex weight network module with random walk and community detection is introduced.Based on the LinkRank community detection algorithm and the simulated annealing algorithm,the construction of the functional structure of product is realized.(2)A multi-skeleton modeling approach layout design for mechanical product is proposed.First,through studies on the inheritance mechanism between design descriptions on different levels in the hierarchical modelling architecture and the interface relationships between different modules,design information is classified into five categories: locations,interface features,design spaces,key features and kinematic constraints.Second,these different types of design information are modelled using three types of skeletons: location skeletons,interface skeletons and published skeletons.Third,a multi-skeleton modelling scheme is introduced for the design of product descriptions from relative abstract levels to more detailed levels in recursive and iterative manner with relatively independent modules.This multi-skeleton modelling approach can be used to propagate changes of product descriptions on different levels,to improve design efficiency by reusing and modifying the existing modules,and to evaluate the design at early design stage without detailed design descriptions.In addition,the multi-skeleton model can be implemented in most CAD(computer aided design)systems.(3)A top-down design process planning method based on hierarchical fuzzy design structure matrix is proposed.First of all,according to the product structure and multiskeleton layout design method,the planning product design process is mapped to hierarchical structure matrix and the coupling design activities are identificated.Second,due to the uncertainty of the design information,the expert scoring is introduced to construct the coupling design structure matrix based on the triangular fuzzy number.Third,the coupling degree of the design activities are calculated.Final,according to the coupling degree,the process of the design activities is optimized through activities merging,decomposing or rearranging.(4)The achievements of this research are implemented in a typical large mechanical product— a heavy-duty crawler crane,providing a practice application.The proposed framework and technologies are carried out in the top-down design process step by step,which includes constructing the modular function structure,implementing the multiskeleton modelling layout,and evaluating the design process planning.The proposed topdown design methodology strengthens the capability of iterative change,rapid modification and design reuse in design process of heavy-duty crawler crane.The heavy-duty crawler crane case illustrates the feasibility and effectiveness of the proposed approaches.Multiskeleton modeling layout design technology applied to a satellite design company,the design efficiency has been significantly improved.This research carries out a deep exploration for the rapid design of mechanical product,and provides approaches and technolgies for the construction of modular function structure,layout design and process planning,which are to lay foundation on further research.The positive effects were received from the practical application of the cooperation projects— top-down design for the heavy-duty crawler crane.