| Computer-aided design(CAD) system is currently applied in many fields: such as mechanical engineering, electrical engineering, aerospace engineering, industrial design and architectural design. At present the popular solid modeling system is a feature-based modeling system. One of the important features of CAD is the capability of analyzing and modification even under the circumstance of no physical model yet, another important feature is that assembly modeling can be done through CAD, so that models can be reused, reducing the cost of the design aspects . The complete definition of assembly Modeling was demonstrated based on the the semantic feature modeling method, the main thesis of paper is as follows:Firstly, Advantages and disadvantages of current practical CAD were analyzed. based on the concept of the semantic feature modeling and cellular unit, combined with geometric constraints and topological model of constraints, a new set of model definition, assembly modeingl is defined with precision and persistence, and the scope of parameters can be resolved.Secondly, a new model of geometric constraint was demonstrated through the analysis of geometric constraints on the model, the model of geometric constraints method can be divided into three categories: a subset of the full constraint, expanding and radiological subset. Through the solution of these three types of subsets to achieve the model geometric constraint solving purposes.Thirdly, Through the analysis of the Topological constraints model, a new feature model solving method contained the Boolean variable mapping method, the topological constraint solving problem was transformed into a Boolean satisfiability problem which was solved with less complexity, thus topological constraint problem was solved.Lastly, The model definition methods was prgrammed into a CAD software,The new method has been tested in many trials. The performance will be recorded and analyzed, thus the modification can be done to complete the new method. |
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