Analysis neutral data structure for GD&;T

The fundamental issue for automatic geometric tolerance analysis is the representation model, which should, in conjunction with CAD models, accurately and completely represent the GD&T specification according to the GD&T standards. Furthermore, such a representation model should facilitate GD&T validation and tolerance analysis. Most GD&T representation models proposed so far are specific to the tolerance analysis method. Common tolerance analysis methods are min/max chart, Monte Carlo simulation and multivariate regions. This paper will propose a semantic GD&T model, which can be used for any of these methods. The model is a super constraint-tolerance-feature-graph (SCTF-Graph). This paper will demonstrate how the SCTF-Graph model can represent all the tolerance types in the standards, and can contain all the information that is needed for tolerance analysis: nominal geometry (i.e. trimmed features in this research), constraints, tolerances, degrees of freedom (DoFs) to be controlled, assembly hierarchy, and their respective inter-relationships. This paper will discuss the content of the model, how it can be automatically created from the CAD model containing GD&T information (e.g. attributed B-Rep model), and the implementation of such a model, along with some case studies.     

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。     

Exact Recognition of Compound Features by Feature Adjacency Matrix Elimination Algorithm

Aiming at the axiom of design for manufacture (DFM), this paper describes a recognition method for abstracting compound features from a part model and discloses the basic mechanism of compounding, also builds the corresponding 2D-simulation model. The inner association between feature neighboring and feature compounding is deeply discussed and, based on the essential transforming rule of two neighboring features, the corresponding feature adjacency matrix (FAM) of multi - feature entities are generated. For the manufacturing feature converted from the pure design feature; an innovative concept-homogenous compounding is presented to clarify the architecture of machining domain. Then, the FAM recurrence elimination algorithm is developed to determine all the compound features, and according to machining sequence, outputs a group of machining domains.     

根据工艺需要进行设计特征模型调整的方法

保持不同领域特征模型的一致性是多领域特征建模的一个核心问题。为有效地维护特征模型的一致性，提出一种根据对加工特征模型的修改要求自动确定设计特征模型调整方案的方法。该方法从加工特征修改所涉及的拓扑元素出发，通过搜索拓扑元素约束关系图找出相关的拓扑元素约束链，并以此为基础，利用有关准则自动确定设计特征调整的最优方案。该方法从加工的需求出发调整设计模型，保证设计与加工特征模型的一致性，可用于支持面向制造的设计。     

A surface based approach to recognition of geometric features for quality freeform surface machining

The paper presents a surface-based approach for geometric feature recognition for the purpose of automating the process planning of freeform surface machining. The proposed approach consists of the following four steps for recognition of the geometric features: conversion and preprocessing of the surface geometry data, subdivision of NURBS surface, reconstruction of surface orientation areas, and recognition of geometric features. The proposed scheme assumes that the input geometry data form is based on an IGES CAD model and the surface model can be represented in the form of trimmed NURBS surfaces. The connectivity relations of the product surfaces are analyzed and each surface is subdivided into orientation regions based on the surface normal vector over a certain point density grid, and then all the connected regions with the same orientation type are grouped into surface orientation areas. After that, the geometric feature will be recognized through the analysis of area connectivity and relationship. The paper describes the developed algorithms on surface orientation region subdivision, surface orientation area reconstruction, and geometric feature recognition. The verified feasibility study of the developed method is also presented.     

Hierarchical Geometric Constraint Model for Parametric Feature Based Modeling

A new geometric constraint model is described,which is hierarchical and suitable for parametric feature based modeling.In this model,different levels of geometric information are repesented to support various stages of a design process.An efficient approach to parametric feature based modeling is also presented,adopting the high level geometric constraint model.The low level geometric model such as B-reps can be derived automatically from the hig level geometric constraint model,enabling designers to perform their task of detailed design.     

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.     

基于局部特征识别的特征有效性维护方法

缺乏特征模型的有效性维护功能已经成为目前特征造型系统存在的一个严重而亟待解决的问题.在对特征有效性条件进行深入分析的基础上,提出了一个基于扩展属性邻接图（extended attributed adjacency graph,简称EAAG）的特征有效性表示方法,特别是提出了基于局部特征识别的特征有效性维护新方法.该方法不仅能够自动判别特征的有效性是否被破坏,而且能确定导致特征无效的原因和遭破坏后特征的状态,从而能够根据用户的意图自动维持特征模型的有效性.     

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.     

Admissible transformation volume for part dimensional quality gauging

Coordinate metrology aims to answer two questions: whether a manufactured part meets design tolerance specifications and how well the manufactured part meets the specifications. Existing methods for analyzing measured coordinate data are not adequate or effective for parts of complex tolerance zones.This paper presents a new approach to dimensional qualification of manufactured parts. In this paper, we view the part qualification problem as an issue of finding an admissible point in transformation space. Based on the concept of admissible point, we develop theories and algorithms for part geometric dimensioning and tolerancing (GD&T) conformance check. A formulation based on containment fit for tolerance check is developed. An admissible transformation volume (ATV) is used to quantitatively characterize the quality of manufactured parts with respect to design tolerance specifications.We examine our approach in three tolerance examples and conclude that admissible transformation volume is an effective metric for part dimensional quality gauging and it is especially useful for multi-tolerance zone check where traditional methods fail to address it effectively.     

加工面点云数据深度学习的加工特征自动识别

加工特征识别是实现CAD/CAPP/CAM系统集成的关键技术.针对传统基于符号推理加工特征识别模式存在鲁棒性问题,提出一种基于加工面点云数据深度学习的加工特征自动识别方法;基于PointNet点云识别框架,构建了一个面向加工面点云数据的加工特征自动识别卷积神经网络;通过收集CAD模型中的加工特征面集和采样点云,构建了适...     

Conceptual development of an enhanced tripod mechanism for machine tool

In this paper, a spatial three degrees of freedom parallel mechanism enhanced by a passive leg is proposed. The proposed parallel mechanism can be used in several applications, e.g. motion simulator, micromanipulator and machine tools. First, the geometric model of the three degrees of freedom parallel mechanism is addressed, in which a fourth kinematic link—a passive link connecting the base center to the platform center—is introduced. This last link is used to constrain the motion of the platform to only three degrees of freedom, i.e. the degree of freedom of the mechanism depends on the passive leg. The passive leg also enhances the global stiffness of the structure and distributes the torque from machining. Second, the kinematic analysis with the consideration of link flexibility is conducted. A kinetostatic model of the three degrees of freedom parallel mechanism with a passive link is then established and analyzed using lumped-parameter model. With the proposed method, a significant effect of the link flexibility on the mechanism's precision has been demonstrated. The influence of the change of structure parameters, including material properties, on the system behavior is discussed. Compliance mapping is also illustrated. The kinetostatic model proposed in the paper can be extended for optimal design and control of parallel kinematic machines. Finally, design optimization is conducted using genetic algorithms and some design guideline is given.     

特征的自动识别规则与提取

在对箱体类零件的加工特征及特征参数进行了分析,归纳和总结,在特征实体造型进行了研究的基础上,制定了各类特征的合理的识别规则和 识别算法,及提取的信息模型,实现了对复杂箱体类零件的加要特征信息自动提取,及CAD／CAPP系统的信息自动传递。     

新一代几何造型系统—GEMS4.0

ＧＥＭＳ４．０是清华大学ＣＡＤ中心在工作站上用Ｃ语言开发的新一代几何造型系统。和９０年代初问世的第三代几何造型系统相比，它具有如下特点：基于线框，表面，实体和特征表示的非流形造型；具有参数化设计，变量几何，尺寸驱动；扫描面，自由曲面和雕塑面用非均匀有理Ｂ样条（ＮＵＲＢＳ）表示，几何数据及属性的文件传送和数据库存取基于国际标准ＳＴＥＰ；基于窗口环境，面向对象的事件驱动和数据表格驱动的系统结构有利于开     

基于特征识别的3维人脸动画模型自动构造

针对3维人脸动画应用中,需要手工事先标定肌肉模型的控制点、工作区域和设置各种计算参数,造成工作量大、修改困难、移植性差等弊端,提出自动构造各种肌肉模型及确定它们计算参数的方法。研究工作包括:综合运用法向量变化率、高斯曲率、高斯纹理模型等参数研究3维人脸几何及纹理特征的快速检测方法;设计基于邻域生长和候选点聚类分析的识别算法来识别人脸五官部位的特征点;在此基础上,自动确定各种肌肉模型的位置结构、工作区域和计算参数,实现人脸动画所需的肌肉模型构造和装配的自动化。应用工作结果表明,基于特征识别的3维人脸动画肌肉模型自动构造方法移植性好、精度较高,提高了动画建模工作的效率。     

Viewer-centered geometric feature recognition

Computer aided design (CAD) and computer aided manufacturing (CAM) systems are now indispensable tools for all stages of product development. The flexibility and ease of use of these systems has dramatically increased productivity and quality of product while reducing lead times. These advances have been largely achieved by automating individual tasks. At present, these islands of automation are poorly linked. One reason for this is that current computer systems are unable to extract geometric and topological information automatically from solid models that is relevant to the down-stream application. In other words, feature information.The objective of the research reported in this paper was to develop a more generic methodology than heretofore, in order to find the generic protrusion and depression features of a CAD model. The approach taken is one relying on a more human type of analysis, one that is viewer-centered as opposed to the object-centered approach of most previous research in this area. The viewer-centered approach to feature recognition described is based on a novel geometric probing or tomographic methodology. A five-step algorithm is described and then applied to a number of components by way of illustration.     

自动特征识别技术综述

自动特征识别是从零件实体模型中抽取出具有特定工程意义的特征信息，由于自动特征识别构成ＣＡＤ与ＣＡＰＰ之间的智能接口，对实现ＣＡＤ，ＣＡＰＰ，ＣＡＭ集成具有重要意义，因此一直是ＣＡＤ／ＣＡＭ领域的研究热点，研究成果十分丰硕，另一方面，由于特征识别具有相当难度，该领域对仍存在的许多问题有待解决，本文对自动特征识别技术的历史和现状进行全面综述，介绍了具有代表性的特征识别方法，并阐述各个方法的特点，最后对     

语义特征造型系统中特征模型转换的研究

通过对新一代的语义特征模型的分析,参考Bidarra等人的研究成果,运用有效性标准,确立语义特征造型中特征转换的方法,在采用数学方法基础上,提出了怎样在数学模型中把设计特征表示转换成加工特征表示。设计过程中的设计特征由一组具有几何特征的面和一组属性（包括维数和具体特征）表示。加工过程中的加工特征由许多面和这些加工操作中面面之间有意义的关系来表示。特征转换中采用数学方法,能够在集合运算中形成加工特征,特征相交这种困难问题也可用数学描述,并且理论上能够转换,从而提高产品模型的可编辑性和易编辑性。     

用Pro/Toolkit应用程序实现产品模型更新的方法研究

在产品设计过程中,实现各阶段模型的快速更新,形成新的设计方案,是提高产品设计效率的有效途径。该文讨论的方法基于三维CAD软件Pro/Engineer,利用模型中尺寸标识id唯一的特点,通过加载Pro/Toolkit应用程序,建立模型几何特征与尺寸id之间的映射。利用这种映射关系,再读取零件详细设计后的尺寸数据,由id关联驱动模型尺寸,实现了产品设计时从初始几何模型到最终模型的自动更新。     

符号方案三维实体化的自动化方法研究

如何将创新设计过程中得到的符号方案生成直观的图形方案，是机械概念设计中的关键技术问题，通过对符号方案的邻接矩阵元素进行分析，得到机构的结构组成、构件连接关系等信息；运用符号方案的尺度矩阵确定各装配构件的二维几何尺度，在面向对象二次开发的环境下，基于三维参数化平台，实现构件的三维实体化；根据构件所处空间位置，按后台预置装配方法得到三维虚拟实体装配图。上述过程基于面向对象的环境，输入／读入概念设计得到符号方案后，系统自动地将符号方案生成三维虚拟实体方案。