Research And Implementation Of Parametric Design Model

Parametric design and variational design are the key technology in the modern CAD/CAM systems. The work mainly concentrates on the research of product design oriented constraint representation model and the development of parametric design and drafting system. This thesis reports on the research of the model and the implementation of system.The main problems in parametric design models are: 1) The ability of design constraint representation. The constraint representations are not considered in the point of view of engineering design. It doesn't support the design variant constraint. 2) The interactive design process and the creation of the constraint model are divided into two phases. It can't take full advantage of the concealed design constraint knowledge and result in difficulties in solving the constraint model. To solve these problems the following works have been done:1. A constraint representation model based on an extended directed acyclic hypergraph is presented. It constructs the dependence relations between design objects based on one-way constraint and build the parametric graphics model by the basic graphic elements such as parameter values, dimensions, points, lines, and planes. The model can support the representation of dimensional constraints and geometric constraints. Moreover, the geometric structure changes and engineering design variants can also be represented.2. The method integrating constraint catch process into interactive design process is proposed to develop a more intuitive, graphically based parametric design system. A constraint recognition algorithm is used to automatically recognize geometric constraints between design entities (such as tangency, intersection, mid-point, parallel, perpendicularity, against) from system environment and manipulations. The parametric design model is finished while interactively constructing geometric objects.3. A constraint solver based on the mechanism of program explanation is developed. The constraints are satisfied constructively, by placing design objects in some order. Construction steps insure the constraint consistency.