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为提高ＣＡＤ／ＣＡＭ系统的智能化和集成化，本文提出了一种基于约束和特征设计的零件定义模型。该模型采用了一套新型的特征定义、分类、表达方法，并鉴于三维约束的特点，对三维特征约束进行高层抽象，分为特征内约束、特征间约束，特征内约束表示为定型约束Ｃｓ，特征间约束表示为依存约束Ｃｄ、定位约束Ｃｐ、形状依赖Ｃｓｄ。在此基础上，通过有向特征多叉树（ＤｉｒｅｃｔｅｄＦｅａｔｕｒｅＭｕｌｔｉｂｒａｎｃｈＴｒｅｅ，简写ＤＦＭＴ）建立起零件约束维护模型。同时也提出了零件模型的构造、修改及特征删除算法。
In order to improve the intelligence and integration of CAD / CAM system, this paper presents a part definition model based on constraint and feature design. In this model, a new set of features is defined, classified and expressed. Based on the characteristics of the three-dimensional constraints, a high-level abstraction of the three-dimensional feature constraints is performed. The model is divided into intra-feature constraints and inter-feature constraints. The inter-feature constraints are denoted as dependency constraints Cd, positioning constraints Cp, and shape dependence Csd. On this basis, the part constraint maintenance model is established by DirectedFeatureMultibranchTree (abbreviated DFMT). At the same time, the construction, modification and feature deletion algorithm of the part model are also proposed.