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【中文 5700 字】逆向工程在产品设计中的应用本文在阐述了逆向工程在产品设计中的应用范围和发展条件，有效的解决造型设计与后续的工程设计、制造环节相脱节的问题，提出了一种在产品设计过程中采用Pro/Designer与Pro/Engineer无缝连接的方法，为工业产品造型设计与后期的工程制造的连贯开辟了一个新的途径，其设计流程的过程为产品设计系统化提供行之有效的措施，从而缩短了产品设计开发周期，实现了产品造型设计的系统化。1 逆向工程的内容及其应用范围随着计算机技术的发展，CAD技术已成为产品设计人员进行研究开发的重要工具，其中的三维造型技术已被制造业广泛应用于产品及模具设计、方案评审、自动化加工制造及管理维护各个方面。在实际开发制造过程中，设计人员接收的技术资料可能是各种数据类型的三维模型，但很多时候，却是从上游厂家得到产品的实物模型。设计人员需要通过一定的途径，将这些实物信息转化为CAD模型，这就应用到了逆向工程(Reverse Engineering).所谓逆向工程技术，是指用一定的测量手段对实物或模型进行测量，根据测量数据通过三维几何建模方法重构实物的CAD模型的过程。逆向工程技术与传统的正向设计存在很大差别。而逆向工程则是从产品原型出发，进而获取产品的三维数字模型，使得能够进一步利用CAD/ACE/CAM以及CIMS等先进技术对其进行处理。一般来说，产品逆向工程包括形状反求、工艺反求和材料反求等几个方面，在工业领域的实际应用中，主要包括以下几个内容:(1)新零件的设计，主要用于产品的改型或仿型设计。(2)已有零件的复制，再现原产品的设计意图。(3)损坏或磨损零件的还原。(4)数字化模型的检测，例如检验产品的变形分析、焊接质量等，以及进行模型的比较。逆向工程技术为快速设计和制造提供了很好的技术支持，它已经成为制造业信息传递的重要而简洁途径之一。而传统的产品造型设计，一般是在市场调研，制定需求表之后，先展开平面简图的构思，形成稍微完整的方案之后，开始绘制三维简图，完全定型后再根据需要绘制效果图、三视图或制作简易的模型。在造型设计的过程中，需要工程技术人员、产品造型人员与工人的通力合作，用样品实物模型来表达设计者的构思，但对每一种方案都制作实物样品，要付出大量的劳动，还存在着精度低、修改调整困难、设计周期长及成本费用高等问题。2 CAD技术应用于产品设计计算机技术的发展，带来第三次技术革命浪潮，计算机辅助设计(computer aided design,简称CAD)技术则是计算机在工业领域应用中最为活跃的一支。它集数值计算、仿真模拟、几何模型处理、图形学、数据库管理系统等方面的技术为一体，把抽象的、平面的、分离的设计对象具体化、形象化，它能够通过“虚拟现实”技术把产品的形状、材质、色彩，甚至加工过程淋漓尽致地表现出来，并能把产品的设计过程，通过数据管理，实现系统化、规范化，这正是工业设计与CAD技术必然结合的基础所在。逆向工程技术实施的软件条件目前，比较常用的通用逆向工程软件有Surfacer, Delcam. Cimatron以Strim。具体应用的反向工程系统主要有以下几个:Evans开发的针对机械零件识别的逆向工程系统;Dvorak开发的仿制旧零件的逆向工程系统:H.H.DanzdeCNC CMM系统。这些系统对逆向设计中的实际问题进行处理，极大地方便了设计人员。此外，一些大型CAD软件也逐渐为逆向工程提供了设计模块。例如Pro/E 的ICEM Surf和Pro/SCANTOOLS模块，可以接受有序点(测量线)，也可以接受点云数据。其它的象UG软件，随着版本的提高，逆向工程模块也逐渐丰富起来。这些软件的发展为逆向工程的实施提供了软件条件。而这些软件相对与尽管目前一些高端的设计软件，已经具备了产品复杂造型的设计与渲染功能，但要艺术类的设计师掌握并运用这类软件，至今还不是一件容易的事。所以从事结构设计的设计师们大都是机械工程师出身，设计的思维与方式完全不同于造型设计师，他们思维是一种完全符合机械设计标准的设计思维方式。那么,两种设计将如何在产品的设计中得到结合，且得到较好的结合，并且更好地完成从设计到加工程序的转换?成为我们进行产品设计所要考虑的问题。3 产品设计-逆向工程CAD技术(1) Pre/E参数化设计在工程中的应用参数化设计(Parametric)(也叫尺寸驱动Dimension-Driven)是CAD技术在实际应用中提出的课题，它不仅可使CAD系统具有交互式绘图功能，还具有自动绘图的功能。目前它是CAD技术应用领域内的一个重要的、且待进一步研究的课题。利用参数化设计手段开发的专用产品设计系统，可使设计人员从大量繁重而琐碎的绘图工作中解脱出来，可以大大提高设计速度，并减少信息的存储量。参数化设计的关键是几何约束关系的提取和表达、约束求解以及参数化几何模型的构造。1988年，美国参数技术公司首先推出参数化设计CAD系统Pre/Engineer(简称Pre/E)充分体现出其在许多通用件、零部件设计上存在的简便易行的优势。它的主要特点就是:基于特征、全尺寸约束、全数据相关、尺寸驱动设计修改。这样我们可以采用PTC:公司的工业设计软件Pre/Designer(简称Pre/D)进行曲面设计，由于Pre/D与Pre/E采用的是同一数据库，两者之间是无缝连接的，因而在设计中造型设计师和结构工程师可以更好的协作(2) Pre /D的曲面设计能力对于工业设计人员和那些想构建曲面模型的工程人员来说，Pre/I正是他们需要的工具，Pre/D可以构建高质量的自由曲面模型，并且可以很容易的转换到其它基于制造工程的CAD系统中。Pre/D能够创建真实而精确的几何体，利用它可以更加容易的创建模型，缩短设计周期。利用Pre可以把视觉上的美学要求和模具制造过程中的工程要求很好的结合起来，这一点在创建自由曲面模型的过程中现得尤其显著。(3) Pre /D与Pre/E之间的致据传抽Pre /Designer与Pre/Engineer之间交换数据有两种方式:一种是与Pre/Engineer直接交换数据，另外还有一种就是以文件的方式与Pre/Engineer交换数据。(4) 造型复杂产品三维设计的CAD应用对于造型装饰性强，特别是包含复杂曲面的产品，可以使用Pre/D与Pre/E组合起来进行，造型设计师在Pre/D里面做ID、做曲面建模，直接从Pre/I里启动Pre/E，把数据导到Pre/E由结构设计师进行结构设计，在整个设计过程中甚至结构设计全部做完了，由于客户的要求或设计师对方案的局部要进行更改，这时只须在Pre/D里面改动，改好后存好再原名称送给Pre/E，那么Pre/E里也得到改变，而结构不用重做(当然修改要使结构有存在的条件，即它的父特征不会有问题)。长久以来，工业产品的传统开发方式均是遵循严谨的研发流程:从产品需求的构思、功能与规格预期指标的确定，进而到各个组件的设计、制造、组装、性能测试等。每个组件都保留有原始的设计图，此设计图目前通常以CA文件的形式来保存。这种开发模式被称为“预定模式”(Pre-scriptive Model)，此类开发工程亦通称为“正向工程”(Forward Engineering).然而 ，随着工业技术水平的提升以及生活水准的提高，任何通用性产品在消费者对于高品质的要求下，功能上的需求已不再是赢得市场竞争力的唯一条件。产品不单单是功能要先进，而且更多着重于产品的外观造型，这已不是传统的机械工程师们所能胜任了。设计师们先通过手工方式塑造出模型，例如:蜡模、木模、石膏模、粘土模、工程塑料模等等，然后再以三维尺寸测量的方式生成自由曲面的CAD文件，这就是所谓的“逆向工程”(Reverse Engineering,RE)。这时摆在设计者和制造者面前的是实物样件，需要将实物模型转化为CAD模型，因为产品信息模型是实现CAD/CAM无缝制造技术的关键。逆向工程 (ReverseE ngineering)是在没有设计图纸或者设计图纸不完整以及没有CAD模型的情况下，按照现有零件的模型(产品原型或油泥模型)，利用各种数字化技术及CAD技术重新构造CAD模型而克隆或创造实物产品的过程。正向工程是从CAD模型向实物模型转化的过程，而逆向工程则是从实物模型向CAD模型的转化过程，两者的设计流程正好相反，逆向工程和正向工程有不同的应用领域，随着数字化测量技术的飞速发展，逆向工程技术在制造业中的应用日益广泛、成熟，关于逆向工程的研究也成为CAD领域的研究热点之一。4 逆向工程建模技术包括了从数据测量到CAD模型构建的一整套技术步骤，概括起来主要有以下几方面的关键技术:(1)测量数据处理由于数字化测量设备的广泛应用，海量数据点(百万数量级)的获取成为十分容易的事。百万级的数据无论对于数据读人还是模型重构等方面都为我们带来十分不便，因此需要的重构CAD模型前对测量数据进行预处理。(2)网格模型构造三角网格模型是逆向工程中常用的模型表示方式。三角网格模型很容易表达复杂的物体表面形状，同时网格模型对于重构曲面模型是一个非常好的基础模型。(3)基本曲面模型构造逆向工程造型的最终目的是为通用CAD系统提供一个有价值的基本曲面模型，最终在通用CAD系统中完成产品模型的重构。因此逆向工程中的基本曲面模型重构对于重构高品质的CAD模型十分重要。(4)模型品质分析逆向工程模型是在测量数据基础上重构的CAD模型。在重构过程中由于对数据的各种处理(如压缩、去噪等)不可避免的回使数据产生误差。最终的CAI模型是否在允许的误差精度内是评价重构模型品质的重要指标之一。以下将分别对这几方面的内容进行系统阐述。4.1 测量数据预处理技术现在随着三维扫描设备的发展，得到的测量数据点数量也越来越大，含有几百万测量数据点的文件已经是很常见的。这么多的数据点，带来的好处是显而易见的，可以把模型上微小的特征全部获取，但对于处理系统，则是很大的一个障碍。这不但大大加大了系统的负荷，而且降低处理效率，以致会影响整个逆向工程建模的过程。所以测量数据的预处理成为现在逆向工程建模技术一个重要的方面。测量数据预处理，除了要对大量的数据进行压缩以外，还要去除扫描中产生的噪声数据。无论测量设备如何先进，噪声的影响总是不可避免的。虽然噪声点不多，但噪声的影响还是很大的，去除噪声的工作可以大大提高生成模型的质量。由于某些模型的形状比较复杂，往往无法一次扫描获得全部的数据。这样，一个模型的测量数据有好多块，所以在进行模型构建之前，必须将多块数据拼接，融合成一个模型。该过程在逆向工程中成为Register，即数据重定位。4.2 三角网格模型构造三角网格模型在逆向工程中有广泛的应用。测量得到的数据点我们一般称之为点云。点云数据不包括任何拓扑信息，为了重构曲面模型以及快速原型制造(Rapid Prototype Manufacture,RPM)等加工的需要我们需要在点云数据的基础上构造出三角网格模型。三角网格模型包含了丰富的拓扑信息，可以用于诸如特征重构、曲面分割等后期处理阁。三角网格也可以很真实的显示出模型的形状，可以达到很好的视觉效果。此外，足够细密的三角网格还可以直接用于零件的加工。根据处理对象和采用的测量技术和手段不同，逆向工程CAI建模内容可以分为两个方面:一种是研究整个形体的CAD建模问题，另一种以处理复杂型面为主要特点的表面CAD建模。这也决定了三角网格模型的构造方法有两个主要类别。整个形体的CAI)建模问题，主要在医学图像可视化领域应用。这方面的研究比较多，也比较深人，一般是利用CI，等设备获取器官的截面轮廓线，然后从这些轮廓线构造三角网格，其主要难点是处理“分叉”和“内孔”情况的模型。这种根据截面轮廓线构造三角网格模型的算法现在已经很成熟，也能达到很高的效率。大量 机 械 零件的建模，一般都是处理复型面的表面CAD建模。这方面的算法很多，但效果都不是很尽如人意，算法都是从一个种子三角形开始，遍历周围的点，来构建三角网格。现在有待提高的是算法的效率和网格的质量。目前大多数的三角化算法都不是对原数据点的插值算法，这就造成了三角网格模型与原数据点的误差，这部分误差将会累积到后续的曲面重构。4.3曲面的重构自由曲面模型在逆向工程产品建模中占有重要地位，自由曲面由于形状表达灵活，在航空、航天、汽车、模具等行业有大量应用，同时，这些行业也是逆向工程应用的重要领域，因此基于自由曲面模型重构一直是逆向工程CAD领域的重要研究内容。曲面重构(亦称曲面建模)是通过建模可以将离散的测量数据重构出连续变化的曲面，曲面拟合包括曲面插值和曲面逼近，曲面插值要求插值后的曲面严格地通过数据点;曲面逼近是基于离散数据构造出一个曲面，使这些点在某种意义下最为接近所构造的曲面。依据曲面拓扑形式的不同，常见的曲面重构方式有两种。以三角Bezier曲面为基础的三边域曲面构造方法，和以B样条101和NURBS曲面为基础的四边域曲面构造方法。基于 三 角 Bezier曲面的三边域曲面构造方法。基本处理思路是将待处理的原始数作为一个整体考虑。首先根据点云暑假构造三角网格，构建出三角网格以后，运用三角Bezier曲面在网格基础上构建光滑曲面121。三角Bezier曲面插值在三角网格的每个三角形上构造初始二变量的三次三角Bezier曲面片，再将每个三角曲面片升阶到四次，然后将每个曲面片进行C-T (clough-tocher)分割，再调整每个子曲面片的控制顶点，使整个组合曲面达到一阶几何(GCI)连续。4.4 基于特征的模型重建技术由于逆向工程处理的对象是空间三维数据，如何在重构曲面模型过程中，准确再现产品的特征，是逆向工程产品模型能否于通用 CAD 系统融会贯通的重要标志。现在的逆向工程，特别是在通用机械零件的重构方面，纷纷转向自动提取模型特征方面。不仅自动提取出产品的特征，如倒角，过渡面等，更是把基于特征的思想引人到逆向工程的各个方面，把特征提取作为逆向工程建模的一种辅助手段。在特征重建方面主要有两种重建方式:一是基于点云数据的特征提取;二是基于网格模型的特征提取。基于点云的特征提取算法依据点云数据的局部微分几何特征提取其特征线，并以这些特征线为基础构建三角网格，再根据测到的数据点根据几何特征插到三角网格中实现三角网格的细分，这样得到的网格在变化剧烈的地方集，变化平缓的地方稀疏。可以大大提高三角网格构造的效率和质量。基于三角网格提取特征。三角网格由于拥有了拓扑关系，可以得到比点云数据更多的特征。三角网格模型中的特征提取可以大大提高逆向工程产品造型过程中曲面区域划分的自动程度。因为一般情况下，一个完整的产品表面模型无法用一张曲面充分表达，需要采用多张曲面组合表达，根据特征来分割，可以使得曲面的划分更加合理，曲面的质量也更高。逆向工程是一项开拓性、实用性和综合性很强的技术，逆向工程技术己经广泛应用到新产品的开发、旧零件的还原以及产品的检测中，它不仅消化和吸收实物原型，并且能修改再设计以制造出新的产品。这对于CAD 技术的产品设计，不仅意味着设计手段的改变，同时改变了工业设计的思维方式。推动着制造业从产品设计、制造到技术管理一系列深刻、全面、具有深远意义的变革，这是产品设计、产品制造业的一场技术革命，实现产品设计的系统化，缩短产品开发周期，从而创造出实用、经济、美观宜人的产品。Reverse Engineering in the application of product designThe application that is in expatiate contrary engineering in the product design with develop the term, effectively of solution shape design with follow-up engineering design, manufacturing link mutually the problem that become disjointed, put forward on sowing in adopt in the product design process the Pro/Designer have no with Pro/Engineer to sew to connect method, design for the industry product shape with the in the late engineering makes of linking up and developing a new path, the process of its design process is a line of for valid measure that product design systematize to provide, from but shortened the product design development, period, realizes the product shape design of systematize.1 reverse engineering of the content and scope of applicationWith the development of computer technology, CAD technology has become a product design staff an important tool for research and development, of which three-dimensional modeling technology has been widely used in manufacturing products and mould design, program evaluation, automated processing and management of all aspects of maintenance. In the actual development of the manufacturing process, design staff to receive technical information may be all kinds of data types of three-dimensional model, but a lot of time, it is from the upstream manufacturers have the physical product model. Designers need to adopt a certain way, this kind of information into the CAD model, which applied to reverse engineering (Reverse Engineering). The so-called reverse engineering, refers to a means of measuring the physical model or measured, according to survey data 3D modeling methods through physical reconstruction of the CAD model of the process.Reverse engineering technology and traditional design is very positive difference. And reverse engineering is starting from a prototype and then obtain three-dimensional digital model of the product, make it possible to further use of CAD / ACE / CAM and CIMS and other advanced technology to process.In general, reverse engineering products, including the shape reverse, the summation of the anti-reverse, and several other materials, in the industrial field in the practical application, including the following: (1) the design of new parts, mainly for the product imitation or modified design. (2) Have been parts of the copy, reproduce the original intent of the design of the products. (3) damaged or worn parts of the reduction. (4) digital model of detection, for example, the deformation of product testing, welding quality, as well as a model for comparison. Reverse engineering technology for the rapid design and manufacturing provided a good technical support ，it has become an important manufacturing information transmission and concise way. And the traditional product design, market research in general, the development requirements table after the plane started to sketch the idea of forming a little integrity of the program, started drawing three-dimensional map, then completely stereotyped as required draw results map, three view or create a simple model. In the process of design, engineering and technical personnel needs, product modeling staff and workers work together, using samples physical model to express the idea of designers, but for every kind of a program have produced samples, to pay a lot of labor, There is a low accuracy, modify adjustment difficulties, the design cycle length and cost of higher issue.2 CAD technology in product design issues.The development of computer technology, brought about the third wave of technological revolution, computer-aided design (computer aided design, referred to CAD) technology is the computer industry in the area of application of the most active one. It sets numerical simulation, geometric model of processing, graphics, database management systems, and other aspects of technology integration, the abstract, flat, separation of the specific object of design, visualization, it can through the virtual reality technology The product of the shape, texture, color, and even brought process demonstrated, and can product design process, through data management, and systematic, standardized, and this is industrial design and integration of CAD technology will inevitably the basis.Reverse engineering software implementation of the conditionsAt present, relatively commonly used generic reverse engineering software Surfacer, Delcam. Cimatron to Strim. The specific application of reverse engineering system is mainly the following: Evans for the development of machine parts to identify the reverse engineering system; Dvorak development of the imitation parts of the old reverse engineering system: HHDanzdeCNC CMM system. These systems to reverse the practical problems in the design process, greatly facilitate the design staff. Besides, Some large CAD software is gradually provided for reverse engineering design module. Such as Pro / E and the ICEM Surf Pro / SCANTOOLS module can accept and orderly points (measurement line), can also accept the point cloud data. UG as other software, with versions of the increase, reverse engineering module is gradually enriched up. These software reverse engineering for the development of the implementation of the software conditions. These software and despite some relatively high-end design software, already the product of complex design and modeling exaggerated features, but the art designers to master and use of such software, so far is not an easy task. So in the structural design of the major designers who are mechanical engineers, design and way of thinking completely different from the modeling designer, their thinking is a fully consistent with the design of mechanical design standard way of thinking. So, how will the two designs in the design of the products are in combination, and receive better integrate and better processing from design to completion of the conversion process of our product design to consider the issue.3 product design - CAD reverse engineering technology(1) Pre / E of the design parameters of the projectParametric Design (Parametric) (also known as drive size Dimension-Driven) is in the practical application of CAD technology in the subject, it will not only CAD system is an interactive graphics capabilities, but also with automatic mapping capabilities. Currently, it is the application of CAD technology in the field of a major, Judai further study the issue. Use of the design parameters of the development of the means for product design system will enable designers from the large number of heavy and trivial mapping out relief work, can greatly improve the design speed, and reduce the storage of information. Parametric design, the key is to extract the geometric constraints and expression, and the parameters of constraint solving geometric model of the structure. 1988, the United States launched the first technology companies parameters of the design parameters of CAD system Pre / Engineer (referred to Pre / E) to give full expression to their common in many parts, components, the simple design of the advantages. Its main features are: Feature-based, full-size constraints, all data related to the size of drive to amend the design. So that we can use PTC: the companys industrial design software Pre / Designer (referred to Pre / D) of surface design, the Pre / D and Pre / E is using the same database, is the seamless connection between the two, thus Design modeling designers and structural engineers can better collaboration(2) Pre / D surface design capabilities for industrial designers and those who want to build surface model for the engineering staff, Pre / I is precisely the tools they need, Pre / D can build high-quality free surface model, and Can easily switch to the other based on the manufacturing engineering CAD system. Pre / D to create a true and accurate geometry, the use of the more easily it can create a model to shorten the design cycle. Pre able to use visual aesthetic requirements and die manufacturing process in the engineering requirements combined with a very good, this point in the creation of free surface model now in the process was particularly notable.(3) Pre / D and Pre / E of the rumored pumped Pre / Designer and Pre / Engineer data exchange between There are two ways: one is with the Pre / Engineer direct exchange of data and another is a way to document and the Pre / Engineer data exchange. (4) three-dimensional modeling complex product design for the CAD application form decorative strong, especially products containing complex surface, you can use the Pre / D and Pre / E combination, modeling designer in the Pre / D inside do ID, so Surface modeling, directly from the Pre / I started in the Pre / E, the data lead to the Pre / E designers from the structural design of the structure of the entire design process of structural design or even all done, the customers request or designer Local to the program to make changes, then only in the Pre / D changes inside, to better keep good again after the original name given to Pre / E, then Pre / E has also been changed, but do not have to redo the structure (of course, to amend For structural conditions for the existence of, the father of characteristics that it will not be a problem).Over the years, the development of the traditional industrial products are to follow strict form of research and development process: from the idea of demand for products, features and specifications of the expected target identification, then to the various components for the design, manufacture, assembly, testing performance. Each component is retaining the original design, the design usually to CA in the form of documents to save. This development model known as scheduled mode (Pre-scriptive Model), the development of such projects also known as positive work (Forward Engineering). However, with the level of industrial technology upgrading and improving the standard of living, Any GM products in the consumer demand for high-quality, functional needs of the market has ceased to be competitive to win the only condition. Products not only to advanced features, and more focused on modeling the appearance of products, this is not the traditional mechanical engineers to the competent. Designers to shape the way through the manual model, for example: wax model, wood model, cast, clay model, engineering plastics, etc.-and then three-dimensional measurement methods generate free surface of the CAD file, which is the so-called Reverse engineering (Reverse Engineering, RE). Then put in front of the designer and manufacturer of the physical kind, will need physical model into a CAD model, as product information model is the realization of CAD / CAM technology seamlessly create the key.Reverse Engineering (Reverse Engineering) in the absence of design drawings or design drawings incomplete and not the CAD model and in accordance with the existing parts of the model (or sludge prototype model), the use of digital technology and CAD technology re-structure the CAD model And cloning to create physical products or processes. Project is positive from the CAD model to the physical model into the process, and reverse engineering is from the physical model to the CAD model of the transformation process, both the design process just the opposite, reverse engineering and forward the application of different areas, with the Digital measurement of the rapid development of technology, reverse engineering in the manufacturing sector of the increasingly widespread and mature, on the reverse engineering of CAD has also become one of the hot areas of research.4 modeling technology, including reverse engineering from the measurement data to the CAD model of a set of technical steps can be summed up in the following several aspects of key technologies: (1) measurement data processing - As the number of measurement equipment by the wider use of massive data point (in millions of orders of magnitude) access to a very easy matter. 1000000 data regardless of the person or read data, and other aspects of reconstruction model for us is very inconvenient, and in need of reconstruction CAD model before the measurement data pretreatment. (2) grid model construction three grid model of reverse engineering is commonly used in the model that way. three grid model can easily express complex shape of the objects surface, while grid model for the reconstruction surface model is a very good foundation model. (3) basic model surface structure - reverse engineering modeling is the ultimate goal of universal CAD system to provide a valuable basic surface model, in the final completion of GM products in the CAD system model of reconstruction. So reverse engineering of the basic surface model for the Reconstruction of high-quality reconstruction of the CAD model is very important. (4) model of quality - reverse engineering model is based on measurement data in the reconstruction CAD model. In the reconstruction process because of the various data (such as compression) so that data back to the inevitable errors. The ultimate CAI model is in error to allow the evaluation of the accuracy of reconstruction is an important indicator of the quality of model one. Following this will be a few aspects of the systems described.4.1 Data pretreatment technology Now with three-dimensional scanning equipment development, the measurement data are also increasing the number of points, with millions of data points measured in the paper is already very common. So many data points, the benefits are obvious, able to model all the characteristics of the small acquisition, but processing system, it is a lot of obstacles. This will not only greatly increase the systems capacity, but also reduces efficiency, which will affect the whole process of reverse engineering modeling. Therefore, the measurement data pretreatment reverse engineering modeling now become an important aspect of technology. Survey data preprocessing, in addition to the large amounts of data compression, but also to remove the noise generated in the scan data. No matter how advanced measuring equipment, the impact of noise is always inevitable. Although not much noise points, but the impact of noise or great, the work of removing the noise generated model can greatly improve the quality. Because the shape of certain models more complicated, often unable to get a scan all the data. In this way, a model of the measurement data have many pieces, so in model building, must be multi-block data connection, integration into a model. The process works in reverse as in the Register, that is re-positioning data.4.2 grid model construction Grid model in the reverse engineering of a wide range of applications. Measured data points we generally referred to as point cloud. Point cloud data does not include any topology information, in order to reconstruction surface model and rapid prototyping (Rapid Prototype Manufacture, RPM), and other processing needs we need to point cloud data constructed on the basis of triangular grid model. 1.30 Mesh topology contains a wealth of information that can be used, such as special Reconstruction of the levy, such as surface divided post-processing Club. grid can also show a real model of the shape, can achieve good visual effects. In addition, the triangle enough detailed grid can be directly used for processing parts. According to deal with the object and the use of different measuring techniques and tools, reverse engineering CAI modeling content can be divided into two aspects: one is to examine the entire body of CAD modeling, the other to deal with a complex of the main characteristics of CAD surface modeling. It also determines the triangular grid model of the construction method has two main categories. The whole body of the CAI) modeling, mainly in the field of medical image visualization applications. This kind of research more and relatively deep, is generally used CI, access to facilities such as the organ section contour, and then from these contour triangular grid structure, and its main difficulty is the handling of the bifurcation and Holes The model. According outline cross-section of this structure of the triangular grid model algorithm is now very mature and can achieve high efficiency. Modeling a large number of mechanical parts, are generally dealt with rehabilitation of the surface of the CAD modeling. Many aspects of this method, but the effect is not very satisfactory, algorithms are from a seed triangle, traverse around the point, to build triangular grid. Now is the algorithm needs to be raised the efficiency and quality of the grid. Most of the triangulation method is not the original data points of the interpolation algorithm, which caused a triangular grid model with the original data points of error, this error will be accumulated up to the surface reconstruction.4.3 Surface ReconstructionFree surface model in reverse engineering products play an important role modeling, because of free-form shape of a flexible, in aviation, aerospace, automotive, mould and other industries a large number of applications, at the same time, these industries are
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