Research On Support Technology For Knowledge-based Computer Aided Mechanism Design

Modern Mechanism design involves the stages of function and principle design, scheme design, dimension synthesis, kinematics, dynamic analysis and evaluation decision-making and so on, with the characteristics of complexity, uncertainty, creativity, high precision, synthetically, cross-subject and etc. This is a design process based on experience. The current CAD on mechanism is limited to the phase of dimension synthesis, which only meets the requirements of calculation , drawing and 3D modeling, and the design precision needs to be further improved. Furthermore, the current CAD mechanism requests designer to own abundant experiences and creative design technique and methodology, Therefore, how to use modern design methodology during the whole process of mechanism design to formalize and digitize mechanism design knowledge so as to preserve them in explicit forms and to use knowledge model accordingly with design idea and technique to dispose knowledge and extend, enlighten and improve design ability of designer in the process of CAD is a key issue in modern mechanism design.Based on problems in technique research of modern mechanism design, this paper aims at research techniques on CAD of mechanism which joins modern design methodology into the process of mechanism design. This research focuses upon the classification, description of knowledge resource on mechanism, construction, hierarchy and application technology of knowledge resource base and key techniques of function and principles solution, scheme design solution and dimension synthesis solution and develops computer aided mechanism design support system based on knowledge. The achievements of this research are highlighted as follows:(1) The software functional model in support of computer aided mechanism design system which is composed of knowledge resource subsystem, knowledge management subsystem, mechanism design process subsystem, design process management subsystem and information exchange subsystem is presented on analysis of function requirements of the supporting system of computer aided mechanism design based on knowledge, and the intelligent design platform oriented to the mechanism design process is built up.(2) Multi-dimension classification model of mechanism design knowledge is put forward, which classify according to design process, accuracy, represent formation, description method as well as the characters of mechanism design knowledge is analysised. A unified design knowledge description method based on knowledge element and composing scheme of knowledge resource base oriented to the process of mechanism design is proposed. The organization method of case base based on the way of MOP and TOPS and a clustering analysis arithmetic of case based on multi-level abstract case base organization model,organization method and formalization description , the composing of model base and storage hierarchy are studied as well as the management model of knowledge resource is set up, application technology of knowledge resource is explored.(3) The method of function description by nature language description at the stage on function and principle design and by precision description of function information model based on function basis at the stage on knowledge reasoning are proposed and the information model of function and behavior are set up. By analyzing the method of function and principle design regarding the solution method of function-behavior-structure as main method and function-process-behavior-structure as supplement one is put forward; furthermore, the solution model of process of function abstraction and function disassembling is set up. and the tool base of function analysis in support of function and principle design is set up, and the movement restrictions of input and output and movement characteristic is coded.(4) Model synthesis and model construction of mechanism are two stages in the process of mechanism scheme design, the model synthesis of mechanism mostly rely on design case and basic mechanism model, so this paper studied the technique principle based on case-reasoning, put forward a kind of method of three layer search to model synthesis and the foundation method of information model of basic mechanism function carrier base and case. This paper also probed into the reasoning step on case, the way of conflict clearing up and case search in nearest neighbor method. Furthermore, the paper research the arrangement of scheme reuse, the expression of symbol cluster of semantics element of design request, the tree-like structure of design scheme and its symbol and reconstruction technique of scheme structure tree.(5) The mechanism parametric design is a precise and idiographic parametric design oriented to mechanism of structure invariability relatively. The paper analysised the limitation of traditional parametric design and studied the characteristics of the parametric design based on knowledge fusion and the key parametric techniques based knowledge fusion in the process of mechanism design: the method of establishing knowledge constraint model and developed software of slippage helix transmission. (6) Dimension synthesis of planar linkages may come down to the request which is to fulfil given track and/or given location. At present, the key of CAD of dimension synthesis of planar linkages is to ascertain the optimized algorithmic. This paper analysised the characteristics of planar linkages and several optimized algorithmic, probed into methods to use genetic algorithmic to optimize synthesis. Furthermore, based on the example of path synthesis solution for adjustable five-bar mechanism, this paper set up an optimized model to use genetic algorithmic to optimize synthesis, and at last an example of optimized synthesis was given.