复杂结构件CAD模型碎面缺陷自动识别与修正方法

针对复杂结构件数模中常存在碎面缺陷,易导致零件在数控加工自动编程时出现特征识别错误、特征提取困难等问题,提出基于属性邻接图的自动识别与修正方法.首先分析复杂结构件碎面缺陷的特征,给出碎面缺陷的定义;然后建立结构件CAD模型的有效属性邻接图,计算面和边的属性并对图中元素赋值,识别碎面缺陷;再根据碎面的几何类型和几何参数构造相应类型的基面,并对基面进行拟合完成碎面缺陷的修正;最后给出文中方法的实现流程并开发了相应的算法,结合实例证明了该方法的正确性和有效性.文中算法已在CATIA V5平台上实现,并集成在飞机复杂结构件快速数控编程系统中,应用于实际生产,取得了良好的效果.     

基于知识与图的形状特征层次识别方法

为解决特征识别中对特征间关系缺乏有效处理的问题,提出基于知识与图的形状特征层次识别方法。将形状特征进行分层识别,由低到高依次分为面关系图、简单形状特征关系图、组合形状特征关系图,给出模型的数据结构及特征识别算法。实验证明,该方法可以简化零件的属性邻接图表达方法,丰富图表示法的工程含义,为建立零件间的关联功能级装配特征提供一条新的途径。     

飞机结构件槽腔内面间最短距离计算算法

摘 要：在飞机结构件数控加工自动编程系统的开发过程中,由于零件的特征层面的工艺 性缺陷,特别是槽腔内面间的最短距离过小,容易导致零件加工复杂、成本过高甚至无法加工。 目前针对该模型问题主要采用人工检查的方式,不仅效率低且易出错。针对具有复杂形状,并 且包含开闭角、内陷等复杂特征的飞机结构件槽腔,其侧壁面间最短距离无法直接获取的问题, 提出飞机结构件槽腔内面间最短距离计算算法。首先给出槽腔以及与距离相关的术语定义,接 着在特征几何参数提取的基础上,将侧壁面间最短距离计算转化为线线间最短距离计算,并根 据槽特征的几何特性提出线线距离有效性判断准则以简化计算,求得槽特征内侧壁面间最短距 离。最后,以某飞机结构件模型为例,验证了该算法的可行性和有效性。     

基于特征分离的飞机结构件特征识别技术研究

为了有效识别并分离出飞机结构件的加工特征,论文通过定义飞机结构件的加工特征面,利用CAA二次开发技术,将加工特征定义为加工特征与辅助特征两种类型。利用邻接矩阵面节点间连接弧的凹凸性定义加工特征与辅助特征,并进行分离;将加工特征离散为点云数据,并采用DBSCAN算法对加工特征进行区分,得到单一特征与相交特征点云数据;输入点云数据至DGCNN模型的分类分割网络,实现单一特征的分类与相交特征的分割。开发CATIA应用插件对该方法进行验证,结果表明该方法能够准确识别出结构件中的复杂特征。     

机械加工MBD毛坯模型的特征识别设计方法

为了解决基于模型的定义(MBD)环境下机械加工毛坯辅助设计问题,采用特征识别技术辅助创建三维毛坯模型.首先分析了机械加工工艺设计环节MBD毛坯模型的组成要素与模型要求,并建立零件模型的属性面邻接图;根据零件模型上加工特征的特点划分简单特征、体积特征和表面特征;通过属性面邻接子图的模式从特征集合中识别出简单特征与体积特征,并利用补特征法与半空间法抑制这2种特征;最后,根据工艺员输入的表面加工余量创建抑制表面特征的实体.在整个毛坯设计推理过程中研究了三维制造标注的维护方法,最终达到辅助工艺员快速设计MBD毛坯模型的目的.     

基于遗传算法的复杂型腔类零件刀具优化

针对复杂型腔数控加工的刀具组合优选问题,提出了一种基于遗传算法的复杂型腔类零件刀具优化方法.首先通过偏置环算法构建可行的型腔加工刀具集;其次为解决型腔类零件每个特征与整体最优刀具组合的差异性问题,建立以加工效率和刀具成本为优化目标的复杂型腔零件刀具组合优化模型,并通过有向图和改进的遗传算法对多刀具组合优化模型进行求解;最终,以某复杂型腔零件数控加工刀具组合优选为例进行实验,验证了方法的可行性.     

从几何实体重建设计特征模型

根据几何元素间的典型关系，提出多种将面邻接属性图分解为更小的子图的方法，如利用内环、夹在几个邻接面之间的环等来分解面邻接属性图．为提高识别的速度和稳定性，依次采用如下步骤：提取可识别的简单特征；根据序列的规则来区别未识别的子图并识别出复杂特征；最后用ACIS5．0中REM模块相应的函数检验所识别的特征．文中算法的有效性用NIST零件库中的标准测试零件予以验证．     

反向工程中三角网格的加工特征识别

为实现反向工程中的特征重构,提出一种在三角网格上由Morse-Smale复形转换为分割面属性邻接图进行加工特征提取的算法.首先通过移动最小二乘曲面法计算网格顶点曲率,构建曲率特性指标函数,消除因网格连接引起的误差,达到降噪的作用;然后在三角网格上建立和简化Morse-Smale复形,精确提取特征线,将网格分割为边界清晰连续的区域,并获得各区域的邻接关系;最后判断关键点和特征线的性质,将Morse-Smale复形直接转换为分割面属性邻接图进行加工特征识别.实验结果表明,该算法准确、高效,而且不需要人工干预,对于反向工程中大规模、带噪声的网格具有较好的识别效果.     

基于径向基函数神经网络的特征识别技术研究

特征表示和识别效率是基于神经网络特征识别技术所面临的基本问题。在研究特征拓扑结构信息的基础上，提出一种应用特征构成面及其邻接边信息构成特征编码的特征表示模型，并在此基础上，提出基于径向基函数神经网络的特征识别方法。最后，应用此方法实现了对典型加工特征的识别。     

设计特征向加工特征转换的扫体重构法

针对同时需要铣削和车削加工的零件,提出一种基于扫体的从设计特征向加工特征转换的统一方法.采用扫体方式重构零件和毛坯模型,并将毛坯与零件之间的差体沿着这些扫体扫掠路径拆分出各种新的加工扫体,最后将这些加工扫体依照它们之间的邻接关系和加工特征形状结构选择合并成加工特征.该方法实现了同一零件中直扫体和回转扫体2种特征的统一转换,能够产生对应各种不同加工方法和方向的加工特征,有利于工艺优化.文中方法已应用于一个CAPP系统,其结果证明了该方法的可靠性.     

混合加工特征识别方法

介绍一种集成了自动特征识别和用户交互特征定义的混合特征识别方法，该方法采用基于广义痕迹的特征识别建立零件的加工特征模型，通过交互特征定义对已建立的加工特征模型进行局部修改和再解释，在交互特征定义中，用户只需通过选取要修改的特征面定义自己的特征，剩余的面则调用自动特征识别算法处理，特征参数由系统提供的统一算法计算，从而减少了交互的工作量，这种混合特征识别方法有助于提高加工特征识别系统的实用性和健壮性。     

Recognition of machining features for cast then machined parts

Mechanical parts are typically manufactured using multiple manufacturing processes. Primary processes such as casting realize the primary shape of the part, while secondary processes such as machining generate more detailed shape of the part. This paper presents a feature recognition method to support machining process planning for cast-then-machined parts. From the part model including the specification of machined faces, we generate the starting workpiece for machining, which represents the casting output in sufficient detail to support machining process planning. The starting workpiece is generated by identifying faces to be made by casting followed by machining, then offsetting the part through these faces by a uniform machining thickness to obtain cast faces, and combining the halfspaces induced by machined faces and the halfspaces induced by their bounding cast faces to enclose removal volumes. Machining features are then recognized from the removal volumes using a volume decomposition method called Alternating Sum of Volumes with Partitioning.     

面向网络基于分治策略的加工特征识别算法

提出一种面向网络,基于分治的加工特征识别算法,首先将零件剖分成若干个适当大小的分解体;然后对每一分解体进行加工特征识别;最后通过对相关分解体的识别结果进行合并生成零件的加工特征模型,实验结果证实了文中算法的有效性。     

Automatic Narrow-Deep Feature Recognition for Mould Manufacturing

There usually exist narrow-long-deep areas in mould needed to be machined in special machining.To identify the narrow-deep areas automatically,an automatic narrow-deep feature (NF) recognition method is put forward accordingly.First,the narrow-deep feature is defined innovatively in this field and then feature hint is extracted from the mould by the characteristics of narrow-deep feature.Second,the elementary constituent faces (ECF) of a feature are found on the basis of the feature hint.By means of extending and clipping the ECF,the feature faces are obtained incrementally by geometric reasoning.As a result,basic narrow-deep features (BNF) related are combined heuristically.The proposed NF recognition method provides an intelligent connection between CAD and CAPP for machining narrow-deep areas in mould.     

一种卷积神经网络和极限学习机相结合的人脸识别方法

卷积神经网络是一种很好的特征提取器,但却不是最佳的分类器,而极限学习机能够很好地进行分类,却不能学习复杂的特征,根据这两者的优点和缺点,将它们结合起来,提出一种新的人脸识别方法。卷积神经网络提取人脸特征,极限学习机根据这些特征进行识别。本文还提出固定卷积神经网络的部分卷积核以减少训练参 数,从而提高识别精度的方法。在人脸库ORL和XM2VTS上进行测试的结果表明,本文的结合方法能有效提高人脸识别的识别率,而且固定部分卷积核的方式在训练样本少时具有优势。     

回转体逆时序右特征识别及内外轮廓自动重构

特征自动化识别与解读是回转体零件加工代码自适应生成的重要基础,而回转体内外轮廓的几何特征信息是加工轨迹生成的重要依据。针对多种信息混合的CAD载体中回转体零件几何特征解读问题,提出了顺时序最右侧判别法自动识别回转体零件的内外轮廓特征。利用DXF结构化存储的图形信息和回转体零件对称性的特点去除尺寸标注,剖面线、粗糙度标注,形位公差标注等多余线,最后沿着逆时针寻找相对于当前轮廓最右侧的路径为下一轮廓。与传统方法相比,所提出算法的复杂度进一步降低,能够准确可靠地在干扰信息中识别出零件的内外轮廓精确信息。     

智能化图象编程系统GNCPPPS的设计原理

本文介绍了一个智能化的图象编程系统.文中论述了系统的设计原理,提出了采用加工单元的方法编程,加工单元先从三维模型中识别出来,然后自动选择刀具和安排加工单元加工顺序,最后自动选择刀具轨迹计算模块,使工艺过程设计和数控编程结合为一体.系统研究中应用了人工智能技术,提出了用概念模型、超级概念模型及规则表示知识,而规则只是对概念模型的一种属性约束.     

Feedback method from inspection to process plan based on feature mapping for aircraft structural parts

The feedback from results of computer aided inspection is used by process planners (though a manual process) to improve machining processes to achieve desired quality. Mapping from inspection features to machining features is a practical method to automate this process. In NC machining of aircraft structural parts, composite machining features, surface joining and complex topological adjacency between free-from surfaces make this kind of mapping (one-to-many mapping mostly) much more complicated. In this research, a new feature mapping based feedback method from inspection to process plan is proposed. The geometry of inspection features are categorized into three kinds of basic inspection elements: Axis, Plane, and Surface. Then, the one-to-many mapping is simplified into one-to-one mapping. The correspondence relationships between basic inspection elements and machining features are abstract as mapping rules to obtain the associations between the basic inspection elements and candidate machining features. Through geometric reasoning, the basic inspection elements are mapped into machining features. Then, the measure data as feedback can be transferred to process planner for improving machining process. The optimized machining process will be stored in knowledge base for reusing. A case study is presented in this paper to demonstrate the proposed method. A prototype feature-based on-line inspection system has been developed and applied for machining aircraft structural parts in a large aircraft manufacturer.     

A flexible and effective NC machining process reuse approach for similar subparts

NC machining process reuse is widely accepted as an effective strategy for engineers to generate the process plan with less time and lower cost. However, there has been very little research on how to reuse the NC machining process of similar subparts. As a result, most reusable NC machining process still has to remain in the repository as tacit knowledge, which can easily get lost due to oblivion. This paper proposes a novel NC machining process reuse approach for similar subparts in which existing NC machining process cases are described in association with machining features. First, a feature-based parameter-driven model is established to formalize the links between information imbedded in the machining feature and the parameters of cutting tools, drive geometries, and machining strategies. Then, the NC process parameter-driven characteristic of similar feature is revealed from the perspective of machining geometry, machining precision of the feature, and cutter geometry. Moreover, an NC process reusability assessment approach of similar pocket/subpart is presented using the pocket’s medial axis transform. Finally, the NC machining process inheritance mechanisms are explored to implement the NC machining process reuse automatically and efficiently. A prototype system based on CATIA has been developed to verify the effectiveness of the proposed approach.