一种钣金件拓扑元素命名和辨识方法

拓扑元素的命名与辨别是特征技术中存在的一个困难和待解决的问题.本文在对钣金件特征研究和"零厚度"假设的基础上,提出了一种钣金件拓扑元素命名和辨别的新方法.该方法采用元素编号的方法对拓扑元素进行命名,并根据钣金件的拓扑点和拓扑边编号与旧模型中的编号是否一致来辨识点和边的拓扑元素.实验表明该方法在钣金件的拓扑结构发生变化时能有效地辨识出拓扑元素的前后对应关系.     

TopSolid 专用模块

一、TopSolid钣金和级进模设计 TopSolid有一个专用的钣金模块TopSolid/Fold和专用的钣金标准件库.此模块可以自动创建钣金特征,自动折弯,自动展开,钣金件排样,并可将普通零件识别为钣金零件.TopSolid/Fold提供了一整套的工具(展开工具、切割工具和毛刺工具等),用户也可以加入自己的工具.     

面向设计意图不变的三维CAD模型重用方法

为了解决目前检索到的三维CAD模型难以重用的问题,提出一种针对B-rep表示的CAD模型重用方法.首先提出一种自动识别B-rep模型中对称特征的算法,依据面的属性对B-rep模型所有的面进行排序,将具有相同属性的面分为一类,并通过不同类之间的合并形成B-rep模型中的对称特征,同时提取该对称特征的约束知识;然后交互式地定义B-rep模型的其他特征,使B-rep模型中的任一面都属于模型的某一特征(主形状特征或局部形状特征);最后以B-rep模型的主形状特征为特征树的根节点,依据特征之间的邻接关系逐次递归地建立特征之间的依赖关系,并自动创建B-rep模型的特征树.与NXTM同步建模方法进行比较的实验结果表明,文中方法利用模型高层次的设计知识重用已有模型,使模型在修改过程中始终保持原有的设计意图,在模型的重用过程中具有一定的优越性.     

基于关键特征相对位置关系的钣金零件检索算法

针对二维钣金类CAD零件相似性的检索,提出一种适用于钣金展开件的相似性检索算法.在分析钣金零件形状特点的基础上,选取设计过程中常用的36种关键特征,建立了关键特征的位置关系模型.该模型以构建关键特征之间的相对位置三角形为基础,具有坐标系无关和旋转无关的特性;以关系模型为依据,提出了钣金件关键特征的相对位置检索算法,并通过实例计算了不同钣金零件之间的相似度.实验结果表明,文中算法是有效的,可满足钣金零件的检索要求,具有实用价值.     

基于知识的设计过程保存与重构

提出基于知识的广义特征信息模型和记录设计历史的广义特征CSG树的表示方法.通过对设计知识与广义特征的封装,构建了广义特征信息模型,在该模型基础上用CSG树的方法表示了设计过程.广义特征信息模型和广义特征CSG树存储于XML格式的广义特征信息表中,实现了设计过程的保存.通过对广义特征信息表的导入和解析,重构了设计过程,实现了设计过程和设计知识的重用.最后给出了在涡轮叶片设计中的实例.     

基于SolidWorks二次开发的钣金箱体三维建模

以VB为开发工具,通过调用solidworks对象和API函数,实现尺寸驱动的钣金箱体的三维建模及自动装配。通过对钣金箱体实际产品数据进行归类管理,总结出通用的设计流程。模拟主特征面逐步添加面上辅助特征及阶梯面特征的设计过程,调用相应特征函数实现钣金件的三维建模。通过改变钣金件在装配环境下的位姿矩阵达到虚拟装配的目的。此辅助设计系统,减少了设计过程中大量重复劳动,提高了产品的设计效率。     

面向设计重用的工程零件设计特征模型构建

随着CAD技术的蓬勃发展和广泛引用,设计重用受到了越来越多的关注,然而由于缺乏有效的底层模型表征,现有的三维CAD模型检索算法普遍存在难以支持设计重用的问题.针对设计重用需求,提出一种设计特征模型的表征结构及构建方法.通过扩展特征树的设计模型表征结构,准确地刻画设计模型中不同粒度、不同形式的特征及特征间的关联关系,有效地捕捉模型中包含的设计语义;通过人工交互定义主形状特征和辅形状特征、系统自动建立特征间关系的方式构建设计特征模型,确保模型表征的唯一性及稳定性.实验结果表明,文中提出的设计特征模型表征结构及构建方法能够有效地捕捉工程零件中包含的设计语义,进而支持面向设计重用的检索.     

IPv6网络攻击事件溯源中的攻击树节点特征定位

在网络普及的现代,各类网络协议层出不穷,而在当下最为普遍的便是IPv6网络协议,其虽然优化解决了前网络协议中存在的部分问题,但是依旧存在各类安全隐患,为了能更好地预防并构建网络防御系统,需要对过往攻击事件中的攻击树节点特征实施提取。为此,提出了IPv6网络攻击事件溯源中的攻击树节点特征定位。该方法首先利用攻击类型实施扩展,得到攻击树模型,并以此展开计算,之后结合深度学习网络对攻击树的节点特征实施提取,最后利用DV-Hop方法对提取到的攻击树节点特征实施定位。所提方法在定位过程中不仅能耗低,而且误差小,不易受环境干扰,定位稳定性较好,定位效率较高,可以更有效地为改进网络防御系统提供数据支持。     

钣金件中匹配孔的半径差及轴线重合度自动检查

摘 要：针对汽车钣金件中匹配孔的半径差及轴线重合度人工检查效率低、易遗漏等问题, 提出了钣金件中匹配孔的半径差及轴线重合度自动检查方法。首先将获得的 B-Rep 三维模型以 面壳封闭的方法拓扑分解为面基本单元;其次根据圆柱面具有 2 条半圆弧线和 2 条直线的特征 对圆柱面进行筛选,并以其为基本单元对圆孔和槽孔进行提取;然后分别获取圆孔和槽孔的半 径及轴线,并利用点到点和点到线距离方法,根据孔匹配原理对匹配孔进行检查分析;最后对 半径差不满足要求和轴线不重合的孔对进行标注。借助 CATIA 的 CAA 开发平台对相关算法进 行了系统设计,并验证方法的可行性。实例检查结果表明,该方法能够高效、准确的对钣金件 中匹配孔的半径差及轴线重合度自动检查。     

Pro／ENGINEER的钣金展开与数控加工

一、钣金加工工艺特点 在钣金件的折弯过程中,由于钣金零件折弯区产生塑性变形,所以展开图的尺寸与几何计算的尺寸不一致,考虑到折弯钣金件的展开尺寸与钣金件的厚度、折弯角、折弯半径和材料伸缩率等因素有关,需要进行专门的计算.     

Three‐dimensional localization of thin‐walled sheet metal parts for robotic assembly

This article presents a technical demonstration of a system for determining the three‐dimensional spatial location of complexly shaped, thin‐walled sheet metal parts grasped by robots during assembly. For successful part assembly, the precise location of grasped parts (essential for successful mating of parts) must be achieved. A localization system is implemented to determine the accurate position and orientation of a sheet metal part that has been picked up by a robot from an arbitrary location. The proposed localization system employs a novel sensing method, utilizing laser‐based proximity and edge detectors, to extract the part feature data in real time. These geometrical feature data are incorporated into an existing localization algorithm, which is based on the singular value decomposition formulation of the part localization problem. The sensing method is particularly effective in measuring 3‐D feature geometry (i.e., thin edges) of sheet metal parts. An experimental single‐robot test bed has been developed to demonstrate the feasibility of the part localization concept for a single sheet metal part. The experimental results obtained from the test bed demonstrate that the system can be effectively used for the localization of thin‐walled sheet metal parts. © 2002 Wiley Periodicals, Inc.     

Evolutionary path planning for robot assisted part handling in sheet metal bending

While the bending sequence planning has been intensively studied, design of the motion path of a sheet metal part in the bending operation tends to be ignored by researchers. Because during the bending operation, the space for maneuvering a sheet metal part is very small, collisions between the part and bending tools are likely to occur. When a robot is used to handle the part, the role of an automatic path-planning tool becomes more significant. In this study, an evolutionary path-planning approach for robot-assisted handling of sheet metal parts in bending is firstly proposed and implemented. The proposed approach globally searches the motion path space to identify feasible paths. Collision detection algorithms based on segment intersection are used to check if the generated paths are feasible or infeasible. This method can automatically design feasible handling operations for a robot. Simulation examples on a simple “V” shaped part and a part with multiple bents demonstrate that the approach is efficient and practical.     

一种基于自动特征识别确定模具脱模方向的方法

判定脱模方向是实现模具自动设计的第一步,也是评估塑件或浇注件能否模具成型的重要因素,文中以基于广义痕迹的自动特征识别方法来识别塑件模型中的所有特征。首先,通过确定每类塑件特征的候选和可行脱模方向,针对每个识别出的特征,自动产生该特候选的脱模方向,然后把所有具有机或完全相反的候选的脱模方向组成一组,并对每组方向,进行选定的模具因子计算,最终胡定优选的脱模方向。实例测试表明,本文提出的方法具有很高的效     

基于实体模型的产品形状特征识别

依据实体造型的特点,从模型空间的特征层入手,搜寻模型空间中的简单形状特征,并根据造型特点获取单个特征在零件模型上的几何拓扑关系,从而实现形状特征的自动识别.通过分析特征实体造型,提出一种基于实体模型的产品形状特征识别方法,并结合微波器件产品开发特征参数提取模块,实现复杂零件模型形状特征的自动识别与提取.该方法为快速建立企业零件库提供途径,也为网络环境下的协同设计和数据共享奠定基础.     

Automatic recognition of features from freeform surface CAD models

This paper reports the design and implementation of a system for automatic recognition of features from freeform surface CAD models of sheet metal parts represented in STL format. The developed methodology has three major steps viz. STL model preprocessing, Region segmentation and automated Feature recognition. The input CAD model is preprocessed to get a healed and topology enriched STL model. A new hybrid region segmentation algorithm based on both edge- and region-based approaches has been developed to segment the preprocessed STL model into meaningful regions. Geometrical properties of facets, edges and vertices such as gauss and mean curvature at vertices, orientations of facet normals, shape structure of triangles, dihedral edge angle (angle between facets), etc. have been computed to identify and classify the regions. Feature on a freeform surface is defined as a set of connected meaningful regions having a particular geometry and topology which has some significance in design and manufacturing. Feature recognition rules have been formulated for recognizing a variety of protrusion and depression features such as holes, bends, darts, beads, louvres, dimples, dents, ridges/channels (blind and through) etc. occurring on automotive sheet metal panels. The developed system has been extensively tested with various industrial sheet metal parts and is found to be robust and consistent. The features data can be post processed and linked to various downstream CAD/CAM applications like automated process planning, sheet metal tool design, refinement of FEM meshes and product redesign.     

Classification,representation, and automatic extraction of deformation features in sheet metal parts

This paper presents classification, representation and extraction of deformation features in sheet-metal parts. The thickness is constant for these shape features and hence these are also referred to as constant thickness features. The deformation feature is represented as a set of faces with a characteristic arrangement among the faces. Deformation of the base-sheet or forming of material creates Bends and Walls with respect to a base-sheet or a reference plane. These are referred to as Basic Deformation Features (BDFs). Compound deformation features having two or more BDFs are defined as characteristic combinations of Bends and Walls and represented as a graph called Basic Deformation Features Graph (BDFG). The graph, therefore, represents a compound deformation feature uniquely. The characteristic arrangement of the faces and type of bends belonging to the feature decide the type and nature of the deformation feature. Algorithms have been developed to extract and identify deformation features from a CAD model of sheet-metal parts. The proposed algorithm does not require folding and unfolding of the part as intermediate steps to recognize deformation features. Representations of typical features are illustrated and results of extracting these deformation features from typical sheet metal parts are presented and discussed.     

故障诊断系统中的冗余特征处理

特征参数是故障诊断的基础和关键,然而特征参数中总是存在很多冗余特征,影响故障诊断的准确率;根据设备的结构特点提出了基于故障树分解的冗余特征处理方法;首先,采用基于分类的粗糙集算法对不同部件的冗余特征进行约简,根据故障树结构分层处理;进而采用Apriori算法挖掘隶属于同一父节点的部件的频繁特征,降低不同部件特征参数的相关性;仿真实验证明,对原始特征进行冗余处理后,故障诊断系统的性能有较大提高。     

Hidden Markov model-based process monitoring system

Sensor signals produced in industrial manufacturing processes contain valuable information about the condition of operations. However, extracting the appropriate feature for effective fault diagnosis is difficult. Moreover, the adaptability and flexibility of current fault diagnosis systems are often found wanting in real-world applications. Unfortunately, it is essential to rebuild most fault diagnosis systems when new fault types emerge. This paper presents an intelligent fault diagnosis system based on a hidden Markov model. Introducing the concepts of time marginal energy and frequency marginal energy, the features of which can be acquired by the wavelet packet technique satisfy the requirements for fault diagnosis. By utilizing the best tree principle, this method not only extracts the feature automatically without a priori experience but also compresses the data; both of which ensure a system that is practical for real-time application. The new diagnosis system developed here is efficient and effective, as demonstrated by the model developed and applied to a real-time sheet metal stamping process. Based on tests conducted during two experiments (one based on simple blanking, the other on progressive operations) and related comparisons, the proposed method is substantially more effective than other approaches. In addition, the new method requires that only related models be created for new fault types, which results show are ideal for shop floor applications.