现代CAD/CAM系统中的几个技术问题

CAD／CAM系统已发展到第三代系统，也称为现代CAD／CAM系统。现代CAD／CAM系统在其核心技术──建模技术方面有了很大的发展，基于特征的、参数化、变量化建模技术已得到了应用，有些技术仍在研究发展中。本文就现代CAD／CAM系统中大家所关心的几个技术问题:几何建模与基于特征的建模之间的区别；变量化建模与参数化建模之间的区别；全部约束建模与部分约束建模之间的差别；用显式技术与隐式技术设计的系统之间的区别；真正的参数化设计系统与几何模型生成后再将参数和尺寸加入模型中的设计系统之间的区别；用基于特征的建模系统…     

Pro/ENGINEER中的公差标注

一、引言 尺寸公差标注是设计建模的重要内容之一,也是机械设计制图国标化的基本要求,而尺寸公差的识别与提取是实现CAD/CAPP/CAM/CAE信息集成的关键,公差分析与综合则是面向创新设计的虚拟产品开发的重要环节,本文从尺寸公差标注的便捷性、国标化以及系统集成应用等方面对Pro/ENGINEER软件进行了分析研究.     

Pro/ENGINEER中的公差标注

一、引言 　　尺寸公差标注是设计建模的重要内容之一,也是机械设计制图国标化的基本要求,而尺寸公差的识别与提取是实现CAD/CAPP/CAM/CAE信息集成的关键,公差分析与综合则是面向创新设计的虚拟产品开发的重要环节,本文从尺寸公差标注的便捷性、国标化以及系统集成应用等方面对Pro/ENGINEER软件进行了分析研究.……     

CAD/CAPP/CAM集成系统的IDEF方法建模技术

本文讨论了采用IDEF方法建立CIMS环境下的CAD／CAPP／CAM集成系统的功能模型与信息模型的相关技术。针对CAD／CAPP／CAM系统集成的特点，结合实例，给出了相应的建模步骤、建模思路以及有效的建模过程管理方法。     

计算机辅助公差设计的发展与现状

<正> 随着计算机技术、自动化技术和人工智能技术的迅速发展,计算机集成制造(CIM)技术已成为现代制造技术中的核心高技术之一.目前CIM的核心问题是计算机辅助设计(CAD)和计算机辅助制造(CAM)的一体化,而实现CAD/CAM一体化的一个重要环节则是计算机辅助公差设计(Computer Aided Toleranc-ing,简称CAT).CAD和CAM从一开始就是在各自的领域中独立发展.CAD是从计算机图形学发展起来的,虽然已从简单的二维几何图形绘制发展到三维实体造型,但目前所生成的形体模型绝大多数并不是信息完善的模型,它们还不能完整地表达公差信息,无法直接为CAM提供加工精度信息.CAM是从数控机床的计算机编程自动控制发展起来的,机床加工所需的尺寸公差都是由人工赋值.虽然计算机辅助工艺规划(CAPP)有了很大发展,但加工精度信息仍由人机交互输入.因此,要想实现CAD/CAM一体化,就必须开发能表达公差信息的计算机造型技术.     

一个CAD/CAPP/CAM集成系统

CAD／CAPP／CAM集成系统是整个CIMS系统的重要信息来源，影响整个CIMS的水平。作者结合在钻井用牙轮钻头制造厂建立CIMS工程的实际，研究了CAD／CAPP／CAM系统的集成问题，本文介绍其主要功能和结构。     

特征模型CAD/CAM信息集成的研究

特征建模技术是实现CAD／CAM集成的核心，本文对建立在I-DEAS之上特征建模的研究为基础，针对板块类零件，提出了基于特征的集成模型总体结构和数据的组织方法，该模型以面为纽带，将零件的几何信息加工工艺信息有机地联系在一起，以便使CAD的数据能方便地被CAPP、NC等后续环节所使用，从而为CAD／CAM的集成奠定基础。     

现代CAD／CAM系统中的几个技术问题

CAD/CAM系统已发展到第三代系统,也称为现代CAD/CAM系统。现代CAD/CAM系统在其核心——建模技术方面有了很大的发展。尽管有些技术仍在研究发展中,但它与传统的几何建模系统相比,基于特征的、参数化的和变量化的建模技术均得到了不同程度的应用。本文就现代CAD/CAM系统中的几个技术问题:几何建模与基于特征的建模之间的区别;变量化建模与参量化建模之间的区别;全部约束模型与部分约束模型之间的区别;用显式技术与隐式技术设计的系统之间的区别;依赖于历     

面向终端用户的CAD／CAM人机接口

本文阐述了面向终端用户的CAD／CAM人机接口设计思想，分析了CAD／CAM系统中人机交互的特点，并以此为基础构造了一个菜单生成器。按照这种新思想构造的CAD／CAM软件，既是一个CAD／CAM工具，同时又是一个CAD／CAM系统开发工具。     

CAD/CAM软件在电子组装领域中应用技巧实例

如今CAD/CAM软件已被广泛应用于电子行业,摆在我们面前一个很现实的问题就是如何从CAD/CAM系统中得到用于生产的必要数据,建立起CAD设计系统和自动化组装设备之间的有机联系,提高电子制造的效率和质量。本文以作者的经验为例。介绍了CAD／CAM软件在电子组装领域中的一些应用技巧实例,希望能对相关技术人员有所帮助。     

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.     

Tolerance Representation and Analysis in Industrial Inspection

In this work we address the problem of tolerance representation and analysis across the domains of industrialinspection using sensed data, CAD design, and manufacturing. Instead of using geometric primitives in CAD models todefine and represent tolerances, we propose the use of stronger methods that are completely based on the manufacturingknowledge for the objects to be inspected. We guide our sensing strategies based on the manufacturing process plans for theparts that are to be inspected and define, compute, and analyze the tolerance of the parts based on the uncertainty in thesensed data along the different toolpaths of the sensed part. We believe that our new approach is the best way to unifytolerances across sensing, CAD, and CAM, as it captures the manufacturing knowledge of the parts to be inspected, asopposed to just CAD geometric representations.     

TolRM:面向三维CAD的公差建模系统

提出了面向三维CAD的公差建模系统T01RM的设计思想、系统结构、核心功能等．通过设计层次式的公差表示与基于类的公差类型定义，实现了公差与三维CAD系统的有机集成；研究了保证公差合理、完整、有效的评价方法．讨论了公差工程语义的解释方法，并给出了基于变动体的公差效果体现方法．为提高系统效率，分析了公差域的各种情况并对其进行预处理．经过较多的测试表明，TolRM具有较好的鲁棒性、实用性和先进性。     

Manufacturing applications of octrees

It is well understood that effective and comprehensive CAD representation methods are necessary for modelling all the design and manufacturing functions in an automated environment. Recent research work has concentrated on using Constructive Solid Geometry (CSG) methods and Boundary Representation (B-Rep) schemes for representing design and manufacturing functions. This paper presents several novel ideas on the application of octree and quadtree based representation schemes in several manufacturing areas such as robotic task planning, tolerance representation and inspection, feature-based design, and assembly modelling and verification. Suggestions on the application of extended octrees for modelling metal forming operations are also presented.     

Feature-based representational scheme of a solid modeler for providing dimensioning and tolerancing information

Presently available CAD data models have no problem handling the basic shape design of an object as required but they are not properly manufacturing-oriented. It is not possible to represent the dimensioning and tolerancing information or other technological information (such as material data, the surface roughness and accuracy data, feature information, etc.). This paper discusses the requirements of a new CAD data model and proposes a feature-based representation scheme based on the hybrid CSG/B-Rep data structure. This hybrid structure exploits the advantages of both CSG and B-Rep models in representing tolerance information. A relational graph structure (face-based data model of B-Rep) of the object is maintained at each hierarchical level of object construction for associating tolerance and other attributes.     

A survey of CAD model simplification techniques for physics-based simulation applications

Automated CAD model simplification plays an important role in effectively utilizing physics-based simulation during the product realization process. Currently a rich body of literature exists that describe many successful techniques for fully-automatic or semi-automatic simplification of CAD models for a wide variety of applications. The purpose of this paper is to compile a list of the techniques that are relevant for physics-based simulations problems and to characterize them based on their attributes. We have classified them into the following four categories: techniques based on surface entity based operators, volume entity based operators, explicit feature based operators, and dimension reduction operators. This paper also presents the necessary background information in the CAD model representation to assist the new readers. We conclude the paper by outlining open research directions in this field.     

基于非精确图匹配的CAD模型搜索方法

为了弥补现有的三维CAD模型搜索方法难以搜索到不同近似程度的相似模型的缺陷,提出一种基于面属性化邻接图非精确匹配的CAD模型搜索方法.首先提取CAD模型中的B-rep信息将CAD模型转化为面属性化邻接图;然后计算目标模型与被搜索模型的面属性化邻接图之间的顶点相容程度矩阵和边相容程度矩阵,并由此建立2个模型相似程度的度量作为选择不同顶点匹配矩阵M的优化目标函数;在对匹配矩阵M进行连续化松弛后,运用Sinkhorn行列交替规范化方法求解匹配优化问题.实验结果表明,采用该方法能够搜索到不同近似程度的相似模型;并且由于避免了具有NP复杂性的精确图匹配过程,检索效率也能满足实际要求.     

基于面上下文码匹配的CAD模型检索方法

为弥补现有的基于图的形状描述应用图匹配或子图匹配实现CAD模型检索时,存在着检索效率低下或检索结果不够准确的缺陷,提出一种基于面上下文码匹配的CAD模型检索方法。提取CAD模型的B-rep信息生成面属性邻接图;依据面的上下文邻接关系,将模型面属性邻接图转化为上下文层状面属性邻接图,生成面上下文码;由检索模型与数据库模型的面上下文码匹配排除筛选不匹配的面,得到与检索模型相匹配的面。实验结果表明,该方法能够实现CAD模型的整体和局部检索,并且检索效率和精准程度能够满足实际需要。     

面向对象的特征设计系统的开发与研究

本文结合面向对象的特征设计原型系统（ＯＯＦＤＳ）的开发，论述了面向对象机制的实现方法，面向对象的特征表达以及特征设计的方法，原型系统基于ＡｕｔｏＣＡＤ环境，并应用其接口语言ＡｕｔｏＬＩＳＰ进行开发。     

GHCAD：一个产品模型为基础的CAD／CAM集成系统

ＳＴＥＰ是关于产品数据表达和交换的国际标准，如何将ＳＴＥＰ的方法和规范应用于系统开发是解决计算机集成制造系统（ＣＩＭＳ）开发的关键问题之一。集成化ＣＡＤ／ＣＡＭ系统是ＣＩＭＳ的核心，实现将ＣＡＤ的工程设计功能和ＣＡＭ的制造功能的结合。本文介绍一个产品模型为基础的ＣＡＤ／ＣＡＭ集成系统－ＧＨＣＡＤ。系统采用ＳＴＥＰ的数据交换、建模思想，以产品模型为核心，通过ＳＴＥＰ的标准数据接口ＳＤＡＩ实现了系统的集成。