Research And Application On Design Change For Complicated And Customized Products

It's inevitable that design should be changed if customer requirements, manufacturing processes, or design circumstances are changed, improved, or differentiated. Change or modification to existing products is fundamental to new product design processes. Design by modification applies particularly to complicated products where the inheritance and reuse of existing working parts and subsystems can reduce cost and risk whilst improve efficiency. However, change is rarely a matter of just reusing or modifying parts, change to one part of the product will, in most cases, result in changes to other parts, this knock-on effect of change propagation has been referred to as an'avalanche'of change or the'snowball effect'. Knock-on effect in design changes can lead to unexpected results, it is vital importance to make resolutions for design changes.Basing on analysis and overview of the literature of design change technologies, the technologies and methodologies including change propagation on Strong-tie and Weak-tie structures, impact prediction of network-flow system, and fast response of change in design process are deeply studied. With the actual project, the prototype systems for product design change are developed and validated in the application.The organization structure of the full text is as follows:In chapter 1, the reviews of product variant design are drawn out. The requirements of design change are analyzed, and the shortages of present research for design change are proposed. Then the research content and architecture of the dissertation are presented.In chapter 2, a methodology of design change on strong-tie structures based on assembly joint graph (AJG) is proposed. AJG takes all geometry features associated with assembly feature as research subject, connections between parts are expressed as assembly joint, and spatial relations among geometry features in the same part as transformation matrix. Change on a geometry feature is denoted as a transformation matrix in the geometry feature coordinate system. Propagation of changes on AJG is solved as the forward kinematics in robotics, and is dissolved in assembly joint according to DOF of joint. The layered recursively solving of change propagation on AJG and the implementation of change solution identified by manual intervention is performed by turns. The efficiency of this method is evaluated on the application developed based on Pro/Engineer platform.In chapter 3, a methodology of design change on weak-tie structures based on weak-tie relation graph (WtRG) is proposed. According to the propagation characteristics of design change on implied functional structures, a concept of weak tie structure is proposed and defined. When changes propagating, structures that associate with each other indeed closely but have no direct physical connection in the visual performance, or that have direct connection but can be easily overlooked cause of the implicit function in the structures, are defined as weak tie structures. On the fundamental of function-structure mapping model, the formal expression of weak tie structure is represented by weak-tie constraint primitive. WtRG is established by connecting constraint primitives, and realized the design change propagation on functional and systematic structures based on WtRG. A prototype system of product design change based on Solidworks platform was developed, and has been applied and verified on elevator products.In chapter 4, a methodology of impact prediction of design change based on network flow Petri net (NFPN) model is proposed. Impact prediction is incorporated with the dynamic expression of the network, Petri net is utilized to describe network flow and its design changes, and to establish the NFPN dynamic model. Based on the analysis of hierarchical network flow, the construction of full reachable graph of Petri net is associated with the impact prediction of change. The analysis of the integral network is recursively accomplished through the simplification of reachable graph by multi-level abstraction. Application to the reconstruction and design of distribution network verifies the feasibility and validity of the method, which greatly reduces the complexity of state space and demonstrates its applicable to large scale and complicated network. In chapter 5, a methodology based on ontology and process correlation for response design is presented. The Ontologies that act as the data support for the rapid response design are established in three forms, including flow ontology, domain ontology and process ontology. The design change process is described in a process-styled expression with additional fore-process and aft-process information. Fractionizes design into several phases and associates the phases with the project status data. Distributed design projects that cooperate according to their status data, and are integrated through the transformation of process-styled design data. Proposal has been evaluated on the reconstruction and design of distribution network, and proved to successfully carry out the fine-grained sharing of design data among distributed projects and can redound to the response speed of design changes.In chapter 6, the prototype systems for design change are developed. The prototype systems are applied in the design of elevator and distribution network products, which shows the validity and feasibility of the new theory and method proposed in this dissertation.In chapter 7, conclusions are given along with recommendations for the future research.