【作者】 方萃浩；

【导师】 叶修梓；

【作者基本信息】 浙江大学 ， 计算机科学与技术， 2006， 博士

【摘要】 CAD／CAM技术及计算机网络技术的发展，改变了现有工业的运作模式，促进了全球化设计与生产浪潮，使得产品开发涉及的领域和人员发生了变化，从而形成了网络化几何造型技术。在网络化几何造型技术中，多分辨率造型、模型共享及协同安全是三个最为关键的技术，本文将针对这三方面相关技术进行深入的理论与应用研究。 本文首先回顾了几何造型技术的发展历史，重点介绍了特征造型技术的相关理论及特点；然后针对多分辨率造型技术、模型数据传输和协同安全技术的研究现状和存在问题进行综述和分析。 现有普通的多分辨率造型方法一般都是基于网格模型，根据最终模型的几何形状信息对模型简化，得到的简化模型往往与设计分析需求不一致，导致它无法满足CAD／CAM相关领域的特殊要求。在分析了现代产品设计模式及基于历史的参数化特征造型方法的基础上，本文提出了—种新型的三维CAD特征模型的多分辨率表示方法。该方法的核心思想是利用模型的复杂度与操作特征集的相关性，通过选择不同的特征集作集合运算，得到不同细节层次的特征模型。考虑到设计特征间存在着相互依赖关系，不能任意独立抑制某个特征，本文提出了一种去依赖特征抑制操作。它从分析特征依赖关系的产生原因入手，通过拓扑对象替换实现任意特征的单独抑制，从而可以创建任意细节层次的特征模型。注意到某些应用对某些特征有特殊的要求，如模型分析阶段中非常忌讳模型含有诸如倒角、圆角等细小特征，本文还提出了一种混合型LOD标准，以能优先处理这些特殊类型特征。 为验证所提出的多分辨率表示方法的可行性及其应用价值，作者自主开发了一个多分辨率造型集成原型系统。本文详细阐述了特征模型的多分辨率造型的具体实现过程，主要介绍了零件体和装配体模型的多层次几何建模的具体算法和注意事项，其中关键算法有：模型的特征序列计算、特征的去依赖抑制、系列LOD层次模型创建、和零件体及装配体细化等。注意到模型的某些细节是由草图轮廓细节所产生，它无法通过特征抑制法消除，本文还提出了—个基于草图简化的模型简化方法。该简化方法通过分析草图轮廓信息实现草图的最优简化，通过草图简化实现模型简化。 相对于以往的多分辨率造型方法，本文所提出的特征模型的多分辨率造型方法得到的简化结果模型更加符合设计意图。由于多层次简化模型创建过程中的操作对象为高层语义特征，它与模型的具体底层表示无关，因此该多分辨率造型方法具有更好的通用性和语义性，可以在当前任意特征造型系统中实现。更多还原

【Abstract】 The development of CAD/CAM and internet techniques has changed the way the product design and manufacturing is working. Globalization of design and manufacturing activities becomes prevalent, which led to a new field called network-centric geometric modeling, and multi-resolution modeling, model sharing and security in a collaborative environment are the three most important techniques in network-centric geometric modeling. The thesis intends to do research on the theory and application of these three techniques. The thesis introduces the history of the development of geometric modeling with a focus on feature-based modeling technologies. Then related research on multi-resolution modeling, model transmission, sharing and security in a collaborative environment are surveyed.Existing multi-resolution simplification methods are mainly developed for polygonal meshes, which don’t fit well in CAD/CAM applications. In this thesis, a new method for multi-resolution modeling of feature-based CAD models has been proposed. The new method is based on the observation that in a feature-based CAD modeler with history dependences, different sets of design features can result in different level-of-details (LOD) of the CAD model. Since children features are depend on their parent features, all children features will be suppressed automatically when suppressing a parent feature. This means that we cannot suppress a feature alone without affecting other features. To solve this problem, we propose in this thesis a De-dependence Feature Suppressing operation in order to suppress a feature alone for various LODs of feature models, together with a scheme for topology entity replacement. A mixed type of LOD criterion is defined to sort different types of features with different priorities in sorting the features.To verify the feasibility and effectiveness of the new method, an integrated prototype system has been developed. The implementation details for multi-resolution modeling of parts and assemblies are presented. Key algorithms are presented in details, including feature sorting, de-dependence feature suppressing, series simplification, refinement of simplified parts and assemblies. Techniques for sketch simplification which is basis of many feature creations are also introduced. Sketch simplification can further simplify the feature model by removing unwanted details resulted from small sketch segments which can’t be removed by feature suppressing. A post repairing operation is performed to validity the model.Compared with existing multi-resolution methods, the new method for feature-based CAD models can produce more intuitive results that are much closer to designer’s intents. Since only更多还原