【作者】 朱根松；

【导师】 周天瑞；

【作者基本信息】 南昌大学 ， 材料加工工程， 2009， 博士

【摘要】 反求工程是进行产品设计、开发和创新的先进制造技术,其中产品外形表面的数字化和几何模型重建是反求工程的两项关键技术,而对反求得到的数字模型进行再创新是反求工程的核心。由于基于三角形和四边形网格的曲面重构方法易丢失产品设计意图,从而造成产品再创新的困难。而几何建模应服务于产品的再创新与制造,特征技术是实现信息共享与系统集成的有效手段,本文以基于截面特征的反求策略为基础,对反求工程中特征建模的关键技术进行了研究,主要的研究结果如下。(1)探讨了反求工程中特征的定义、数据结构及反求工程系统的模型。本文从实现基于特征建模的反求工程系统的需要和结合反求工程的实际特点,定义了反求工程中的各种特征。并在分析了当前各种CAD模型系统后,提出了易于扩展和维护的基于组件技术的面向对象的CAD系统来实现基于特征建模的反求工程CAD系统,并定义了符合组件技术和面向对象技术的要求的数据结构和特征类。(2)探讨了点云模型的数据结构与预处理技术。随着测量技术的发展,实物数字化后数据点规模越来越庞大。如何高效地实现点云数据的拓扑重建,加快数据的检索是目前反求工程研究的难点。本文以点云数据的外包围盒和空间网格划分技术为基础,实现了自适应K近邻拓扑结构重建。利用自适应K近邻拓扑结构重建得到的点云易于检索点及相邻点的特点,用基于弦高误差控制自适应删减技术直接对点云数据删减,在保持点云形状特征的前提下,大大减小的点云数据规模,取得约90%的压缩率。(3)重点讨论了任意方向切片技术的快速实现及平面无序点集有序化方法。切片算法是实现截面特征反求策略的前提,本文利用切片平面与点云数据外包围盒的交线快速定位相交子立方格,从而快速求得与切片平面相交的数据点集。对于由切片得到的无序点集,分别探讨了用改进的Dijkstra最短路径逼近算法和蚁群算法来实现平面无序点集有序化。由于首次将蚁群算法引入反求工程曲线重建过程中,因此重点研究了蚁群算法在平面无序点集有序化过程中各种参数的设置和实现过程,经实验验证,取得了很好的效果。(4)着重讨论了平面特征的识别和曲线匹配方法。平面特征识别和曲线匹配是图像图形学中的难点。本文用角度差分法和最小二乘曲线拟合法相结合的方法实现平面特征的识别,即首先用角度差分法初步识别角点,然后用最小二乘曲线拟合法识别出角点中的特征点,最后再识别出直线、圆弧和自由曲线。由于传统基于曲线各种属性的曲线匹配算法不能很好地实现曲线匹配和对比,本文提出用Fourier-Mellin变换的图像配准技术来实现曲线匹配和对比,不仅能实现一般曲线的匹配,而且能对经过平移、旋转和缩放的曲线实现匹配,经实验验证,效果很好。(5)着重讨论了简单三维特征的识别。本文采用增量最小二乘法自动分区并识别平面和球面。而对于拉伸体、回转体及扫描体等较为复杂平面,首先用高斯球曲率映射法得到曲面的拉伸(扫描)方向或旋转轴,然后用切片技术和Fourier-Mellin曲线匹配技术,实现了拉伸体、回转体及扫描体等造型特征的识别。(6)结合实际应用,利用快速成型实验验证了基于本文算法开发的反求工程原型软件TrSurf1.0的有效性和实用性。本文结合正向工程的特征技术和反求工程几何建模特点,提出了基于截面特征的反求工程特征建模系统模型并开发了系统原型软件TrSruf1.0。用TrSruf1.0得到的反求模型具有高层次的信息,为后续的再创新与制造提供了更强大的支持,符合现代产品设计的发展趋势。更多还原

【Abstract】 Reverse Engineering (RE) technology is an advanced manufacturing technology which is used to design and exploit new product. Shape data acquisition and geometric reconstruction are two key technologies, and recreation of product’s CAD is its soul in reverse engineering.Traditional surface reconstruction based on triangle model or rectangle model is easy to lost design intention of product. It leads to modify difficultly. And reverse engineering geometric modeling (REGM), referring to create CAD model from points cloud data, should be serving for recreation and machining etc. Feature technology is efficient approach to realize information share and system integration. In the dissertation, some key technologies of feature modeling based on section feature technology in RE are researched, the main conclusions of research read as follows.(1). Definition and data structures of features in RE and system model of RE CAD prototype are studied. Features in RE, such as points, curve, surface, are defined considering implementation STEP (the STandard for Exchange of Product model data) which is benefit to realize feature modeling. Based on the shortcoming analysis of three CAD system models, CAD system based of object oriented and group assembly is proposal to implement RE CAD prototype system. Classes and data structure of feature based on OOP and GA are also defined.(2). Data structure of points cloud and points reduction method are studied through analyzing the shortcoming of existing algorithms. It’s important to reconstruct topology of points cloud to find the point quickly in points cloud, especially points cloud include points more and more larger with measuring technique more and more advanced. Firstly, the min-max box of points cloud is divided into a set of uniform grids, and then the indexes of points stored into appropriate cell for finding k-nearest neighbors. After reconstruction of topology, a new point’s reduction method based of chord-arc distance estimation is used to reduce the points cloud. It can reduce points greater with near 90 percent reducing ratio, while keeping former shape. (3). Quick-implementation of arbitrary slice technology is studied on emphasis, and order reconstruction also discussed on emphasis. Slice technology is foundation of strategy of reverse engineering based of section feature. The intersection of an arbitrary plane and three-dimensional cube-cell is realized, and all the subordinate cells intersected with the plane are got rapidly and briefly. Base on it all the scattered points on the slicing plane are got quickly. Getting serial points data from scatter points calls curve reconstruction. At firstly, simplified Dijkstra algorithm for curve reconstruction is introduced and illustrated by experiments. Then, curve reconstruction implementation of Ant Colony Optimization (ACO) algorithm in reverse engineering is researched, emphasis on ACO parameters setting. After experimenting, the conclusion is that the curve reconstructed by ASO-curve reconstruction is better smooth and reflect better the shape of scatter points as other curve reconstruction, but needs more time.(4). A novel method for plane feature recognition is proposed, curve matching algorithm is also researched. It’s difficulties of photography and geometry science that plane curve recognition and curve matching. Plane feature recognition method is by combining the angle-difference method and conicoid least square curve fitting method to recognize the curve feature. Firstly, comer points are extracted by angle-difference method, and then feature points are recognized from the corner points with conicoid least square curve fitting method. Fourier-Mellin image registration for curve matching and contract is presented based on analysis shorting of traditional curve matching which is invariant to rotation, scaling and translation (RST). It is effective and feasible illustrated by experiments.(5). Simple three-dimension (3D) feature recognition based on Fourier-Mellin curve matching method is discussed. Extracting algorithm that extruded surface, revolved surface and scanned surface are presented and some samples are given to illustrate the feasibility of feature extracting algorithm.(6). To make the theory research be used in practice, two surface reconstruction is given and the CAD model are got. The practicalities of two CAD model are made by FDM. From the results, the conclusion is drawn that the feature reconstruction software, TrSurf1.0 which programmed based on algorithms presents in the dissertation, is feasibly and efficiency.Combining feature technology in forward-engineering with reverse engineering geometric modeling, the reverse engineering feature modeling based on section feature technology is put forward. And the prototype RE-CAD system software, TrSurf1.0, is programmed by C++. The geometry model reconstructed by TrSurf1.0 includes high-level semantic information, serving for recreation and machining etc, which is according with the developing intent of modern production design.更多还原