基于曲面的实体编辑方法探讨及实现

适应零件设计越来越复杂的要求，在Parasolid平台上研究开发了利用曲面编辑实体的3种曲面编辑方法：曲面链接、曲面替换和曲面转换。曲面编辑利用了曲面造型技术比较成熟的优势，极大地增强了对实体的编辑能力。详细论述了这3种曲面编辑的功能及实现过程。     

复杂船体曲面NURBS造型技术的研究与实现

根据采集到的数据点阵，对NURBS曲面模型反求中的若干问题进行了深入分析与研究，实现了复杂船体曲面的三维实体造型．获得了满意的效果。     

雕塑实体的精确求交算法

提出了一个雕塑实体布尔操作中的精确求交算法．为了确保算法的高效率、精确性和鲁棒性,采用了先确定拓扑、再跟踪的策略来进行曲线－曲面求交,以及层次求交和交线跟踪的方法,来保证裁剪曲面片分割和区域分类的一致性,从而克服实践中常见的退化情况．该算法已经在一个基于Ｗｉｎｄｏｗｓ／ＮＴ平台的雕塑实体造型器ＴｉｇｅｒＳｕｒｆ上实现,并通过大量造型实体实例的测试．     

模具的曲面造型和三轴联动加工案例

对复杂形状模具的加工。必须先进行模具的三维设计。设计一般采用实体造型的方法,而采用曲面造型完成三维设计是一种更快捷便利的造型方法。该文作者以使用CAXA制造工程师设计和加工一个小汽车上凸模这一案例。介绍了利用CAD／CAM软件进行曲面造型和使用数控机床进行加工的具体方法。该文的意义在于教学示范性。如果要用于生产实际还需做相应的改进。     

逆向工程中IGES数据接口的实现

逆向工程是当前先进制造技术研究的热点之一,通过对IGES标准及曲面实体数据的结构分析,进行逆向CAD软件的IGES接口设计,实现逆向软件与通用CAD造型软件之间曲面数据转换。     

流线型结构特征造型方法及其在高速列车设计中的应用

提出了一种基于自由曲面的流线型结构特征造型方法,并将其应用于200km／h电动车组“先锋号”的流线型结构设计之中,流线型结构特征所描述的实体模型对自由曲面外形的变化具有自适应性,该方法便于流线型结构数据存取和修改,可在自由曲面外形和流线型结构各种参数多次修改的情况下自动生成流线型结构实体;大幅度地减少了人机交互时间,解决了高速列车流线型结构实体造型过程中设计周期过长的问题。     

汽车发动机风扇叶片的逆向造型与分析

以汽车发动机风扇为研究对象,采用ATOS光学测量系统对风扇表面数字化得到其三角网格模型,利用三角网格数据预处理技术、过渡曲面特征提取方法、三维重构及实体造型原理对叶片进行逆向造型,并对重构的模型进行光顺性和精度校检。获得符合设计要求的叶片实体模型。     

基于NURBS曲线曲面造型理论的产品外形系统设计

为了设计一个适用于产品外形设计的系统,文中重点对曲线曲面造型模块进行了研究,在NURBS曲线曲面造型模块中融入了实体造型的功能,设计了便于扩充和维护的曲线曲面类层次结构,并讨论了曲面造型模块的应用流程,通过与数据导入导出功能的衔接实现了与其它造型软件之间的数据共享,提高了系统造型效率,缩短了产品设计周期。在内核的显示模块设计中,提出了一个包含两个显示链表的显示类结构,用以加快图形对象的显示速度。     

异型曲面造型初探

本文讨论了“陶瓷产品CAD集成系统”中异型曲面造型技术。我们运用ARX工具进行AutoCAD R14的二次开发，利用ARX库设计一个新类，为AutoCAD实体数据库增加了一个实体，使Auto-CAD在三维曲面造型上的功能得到了加强。通过简单的操作，即可生成AutoCAD R14本身不易生成的复杂的陶瓷产品造型。     

曲面造型方法在工程中的应用

本文结合CAD／CAM软件UGII的应用实践，阐述了曲面造型的方法，介绍如何从各种不同角度进行曲面造型，并给出一些实例说明各种思路的应用效果。     

基于代数张量积B样条的隐式曲面重构

提出一种以代数张量积B-样条曲面作为几何表示形式的方式,采用Sampson距离来度量数据点与曲面之间的误差,它不仅是几何距离的很好近似且具有齐性和刚体不变的良好性质.建立了近似几何误差和薄板能量极小化的最优化隐式曲面重构模型.同时结合最优化理论中的信赖域思想和拟牛顿法,给出自适应的选代求解算法及其实现.理论上由信赖域法的收敛性分析,迭代算法具有总体收敛性.最后基于散乱点数据集,给出曲面重构的实例,并作简单的讨论.     

Weld-seam identification and model reconstruction of remanufacturing blade based on three-dimensional vision

Remanufacturing technique has been widely used for repairing the damaged regions of aero-engine blades. As the irregularity of weld-seam shape and uneven residual height pose great challenges for the subsequent precision grinding and polishing, it is necessary to use the high efficiency and precision measurement method to obtain a true and accurate weld-seam model, especially in the boundary areas. Therefore, a measurement approach for weld-seam identification and model reconstruction of the remanufacturing blade based on self-developed binocular vision system is presented in this work. The calculation of three-dimensional reconstruction and the complexity of subsequent point cloud processing were reduced by coarse positioning firstly, and then the weld-seam was located precisely by point cloud segmentation based on the region growth algorithm and point cloud normal filtering method. On this basis, a true weld-seam model with precise boundary was obtained. The average error of the boundary extracted by proposed method is about 0.263 mm lower than that of the traditional method. In addition, the B-spline surface was fitted according to the point cloud without weld-seam feature, and a theoretical machining model was obtained by cutting of B-spline surface along the weld-seam boundary. Furthermore, the results of verification experiment indicated that the smoothness error of machined blade surface was less than 0.025 mm and the machining error was less than 0.07 mm. This method has obvious advantages in calculation efficiency and reconstruction accuracy of theoretical machining model while compared with traditional measurement methods for the remanufacturing blade, which is beneficial to improve the machining quality and efficiency of the remanufacturing parts.     

基于B样条的平面轮廓重构闭合曲面算法

由一组平行轮廓线重构三维闭合表面是三维可视化研究的主要内容之一。文中通过对B样条插值算法的研究,提出了一种新的公共节点矢量确定方法,利用该方法首先对经过预处理的CT牙齿图片提取轮廓线获得三维数据点,之后对轮廓线数据点进行B样条曲线的拟合,在每条拟合曲线上根据所确定的节点矢量值重新采样,由重新采样的三维数据点利用B样条曲面插值算法构造闭合曲面．所构造的闭合曲面是对原始轮廓数据的拟合。通过实例验证可看出该方法可获得较好的拟合曲面,经过误差分析检测,满足拟合条件,因此该方法可以保证几何重建的准确性。     

四边形网格生成中的前沿边生长改进算法

为提高B样条曲面重构中点云四边形网格的生成效率和质量,对现有的四边形网格Q-Morph前沿边生长算法进行改进,提出面向四边形网格生成的三角网格拓扑优化方法,通过设定生长限制条件和调整网格顶点度,保证全局四边形网格质量,实现适合复杂曲面重构的规则四边形网格获取。实例结果表明,该算法效率高、适应性好,生成的四边形网格具有分布均匀、不规则网格数量少的优点。     

医学图象三维表面的快速重构方法

介绍了基于CT等值面数据的脸部面貌及颅骨的曲面生成方法，以双三次B样条曲面技术区别于传统的蒙皮曲面生成方法，采用截面数据的重采样，解决了复杂实体在曲面生成时的局部扭曲及数据量过大等问题，在等值线的曲面造型方法及医学可视化领域有广泛应用前景。     

基于闭环理论的自由曲面测量与实时重构

寻求更优的测量方法和更精确的重构模式一直是逆向工程中的研究重点。基此,对具有自由曲面特征的产品逆向,提出一种自适应测量、实时重构和在线评价的方法。依据几何特性,测量实物外形并用高次Bézier曲线拟合,微分推演探测点及矢量,指导三坐标测量机CMM（Coordinate Measuring Machining）自适应探测完整实物点云;借助非均匀B-spline架构曲面模型,基于扫描网格和实物特征从以上重构的曲面上抽取关键检测点,在线引导CMM确定上述检测点在实物上的准确位置并评价已构曲面误差,若误差高于阀值就将检测点加入更新曲面,逐步提高直至满足几何精度,集成测→构→评→添的全闭环逆向过程,建立精确的实物数字化模型。实例验证表明,该方法可利用曲面的几何特性,让测点分布随曲面曲率变化而呈疏密变化,以获得高质量的原始数据点云,实时模型重构、在线评价并及时添加检测点修正模型,可完整表述曲面的几何信息,可使重构模型精度达微米级。     

A study of a reverse engineering system based on vision sensor for free-form surfaces

Reverse engineering can quickly create a CAD model of a new product, in which, the sensor, sampling planning and surface reconstruction are three crucial elements. In this paper, a reverse engineering system involving a new vision sensor, an improved sampling planning module and a fine surface reconstruction module is developed. A characteristic of the proposed sensor is strong linearity between output and input, obtained by the structure optimization when a simple lens replaces the asperic lens. Back propagation (BP) neural network error compensation heightens accuracy. To increase efficiency of digitization, an improved sampling planning approach is proposed; it is based on surface curvature and tangent line slope of a measured point. In surface reconstruction, a new adaptive extracting approach based on curvature of surface reconstructs the non-uniform rational B-spline (NURBS) surface for the scattered data. The accompanying reverse engineering experiment proves the proposed system to be reliable and efficient.     

任意NUBS曲线的小波分析和造型技术

为了对任意NUBS曲线进行精确的分解和重构，提出了半正交B样条小波分解和重构的新算法，同时给出了处理非均匀B样条曲线的非整数阶分辨率的小波分解和重构算法，并实现了任意非均匀B样条曲线的多分辨率表示，对于任意非均匀B样条或NUBS曲线，无论它有多少个控制点，均可以对它进行半正交分解和重构，而不受控制点数必须等于2＋3的限制，从这个意义上讲，该方法不仅可以实现连续分辨率水平（continuous-resolutionlevel)的非均匀B样条曲线造型，还可以对非均匀B样条和NURBS曲线进行精确的分解和重构，这对于B样条曲线曲面的多分辨率造型与显示具有重大应用价值。     

Fitting unorganized point clouds with active implicit B-spline curves

In computer-aided geometric design and computer graphics, fitting point clouds with a smooth curve (known as curve reconstruction) is a widely investigated problem. In this paper, we propose an active model to solve the curve reconstruction problem, where the point clouds are approximated by an implicit B-spline curve, i.e., the zero set of a bivariate tensor-product B-spline function. We minimize the geometric distance between the point clouds and the implicit B-spline curve and an energy term (or smooth term) which helps to extrude the possible extra branches of the implicit curve. In each step of the iteration, the trust region algorithm in optimization theory is applied to solve the corresponding minimization problem. We also discuss the proper choice of the initial shape of the approximation curve. Examples are provided to illustrate the effectiveness and robustness of our algorithm. The examples show that the proposed algorithm is capable of handling point clouds with complicated topologies.     

Scattered data interpolation with multilevel B-splines

The paper describes a fast algorithm for scattered data interpolation and approximation. Multilevel B-splines are introduced to compute a C² continuous surface through a set of irregularly spaced points. The algorithm makes use of a coarse to fine hierarchy of control lattices to generate a sequence of bicubic B-spline functions whose sum approaches the desired interpolation function. Large performance gains are realized by using B-spline refinement to reduce the sum of these functions into one equivalent B-spline function. Experimental results demonstrate that high fidelity reconstruction is possible from a selected set of sparse and irregular samples