【作者】 刘俊；

【导师】 何建英；

【作者基本信息】 华中科技大学 ， 机械设计及理论， 2007， 硕士

【摘要】 逆向工程(Reverse Engineering,RE)也称反求工程,是消化、吸收先进技术时采取的一系列分析方法和应用技术的结合。作为新产品开发和消化、吸收先进技术的重要手段,逆向工程(RE)的研究正受到各国工业和学术界的高度重视。并已经在汽车,模具,家电,文物修复与仿制等领域得到了广泛的运用。逆向工程中的产品建模一般按照如下流程进行:通过测量使实物成为数字化的点云,测量数据点云的预处理,CAD模型重构。在上述这些步骤中,点云质量的好坏和曲面拟合重构方案的选择成为最终影响CAD模型质量的关键性因素。在用激光三维扫描仪对被扫描对象扫描的过程中,由于受到扫描对象、现场环境、扫描速度和时间等的限制,导致三维物体的某些部分获取的数据不完整,造成三维数据的残缺。本文将探讨两种测量数据的修补方法:基于截面数据的测量数据修补方法和基于三维散乱数据的修补方法。基于截面测量数据的修补方法通过把某一坐标轴方向坐标等值化处理,将三维数据转化为基于神经网络二维曲线拟合的方式;另外一种基于BP网络的三维散乱点云的神经网络修补方法,采用将三维曲面某一坐标看成是其他两个坐标的输出的方式直接对点云坐标进行预测。另外,本文将针对现有的工程实际中使用的曲面拟合方案中不适应处理数据量庞大的点云或与现有CAD软件的兼容性问题,探讨了一种曲面拟合流程,采用将曲线、曲面在不同环境下分步拟合的策略。从而综合利用了专业反求软件点云处理能力强、曲线拟合质量高和大型CAD软件面拟合手段丰富、建立体模型时兼容性好的特点。研究表明,基于截面数据的测量数据修补方法和基于三维散乱数据的修补方法取得了较好的效果,丰富了不同形态点云的修补手段;新的曲面拟合的方案较大程度上克服了传统方案的弊端,探索了一种具有实际工程运用价值的逆向流程。更多还原

【Abstract】 Reverse Engineering (Reverse Engineering RE), also known as reverse engineering, considered as a feedback-loop design from upstream to downstream, and then develop more advanced technology products, as well as absorb advanced technologies from series of analytical methods and application technology.As an important method of developing new products and absorbing advanced technologies. Reverse-engineering (RE) is understudied by industrial field and academia in many countries. So far, it have applied in wide range of fields such as vehicles, mold , household appliances , the restoration and imitation of cultural heritage. Industrial engineers, in the use of free-form surface reconstruction technique, can significantly shorten the product design and manufacturing cycles, improving product development efficiency.Modeling of the products in Reverse Engineering is in accordance with the following general procedures: acquire the data-point cloud through measuring the product, Pretreatment data-point, CAD model reconstruction. In these steps, The quality of point cloud and surface fitting reconstruction program eventually to be a crucial factor affecting the quality of CAD models.During the scanning process by 3D laser scanner, due to the limit of scan target site, scanning speed and time , data from certain parts of the 3D object was not in integrity, which caused defects of 3D data. Some scholars have already given a cross-section measurements remedy , used to coordinate the equivalent of a particular axis direction, in this way,3D data into 2D curve fitting based on neural network approach. But its application is very narrow, Because the nature of the cloud patterns must followed to a stringently limit. This article will explore another unorganized point cloud repairing method based on BP neural network, and compared these two methods. At last ,give an introduction for the methods on will be of various types of cloud shows targeted for repairing incomplete data.In addition, the surface fitting programs in actual engineering can divided into two major categories :one is directly rebuild the surface base on professional software, the other is using CAD software to Complete the surface-reconstruction based on data point cloud, such as Pro-E. I-DEAS and UGII. These existed programs are not suited to deal with big amount of data point or have compatibility problems with CAD soft wares. This article will explore a new surface fitting program, taken into account of two items: professional reverse software‘s processing ability on data point cloud and CAD software’s large high-quality surface fitting means, which also have good compatibility features with other CAM soft wares. For Specific, the fitting of the curve and the surface are under different environments. This strategy resolve these contradictions. and the merits of the two programs are integrated. This article gives a rather good treatment process, and also have actual value in implementation.Research shows that: the three-dimensional artificial neural network repairing on data-point cloud achieved good results, enriched the forms of repairing ways; The new surface fitting program greatly overcome the shortcomings of the traditional program, give a valuable exploration which have actual implementation value in engineering.更多还原