大型定子叶片铸件的数字化测量及误差评定

随着航空、航天、船舶、汽车和模具工业的飞速发展,复杂曲面的数字 化测量与误差评定技术对曲面加工精度起着越来越重要的作用。利用激光跟踪测量设备对大 型定子叶片铸件进行了数字化测量,对测量点云进行了去噪、精简等数据处理,并将测量点 云与理论模型进行了基准匹配,计算出了定子叶片铸件各部位的误差分布,实现了对大型定 子叶片铸件的误差评定;测量及误差分析结果可以用于优化叶片在后续加工中的装夹姿态, 使叶片各部位的加工余量趋于均匀,有效提高产品制造精度和加工效率。     

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。     

基于激光测量的航发叶片表面几何缺陷识别技术

针对航发叶片修复检测的应用,提出了一种基于截面线一阶导矢法的叶片型面缺陷识别方法.该方法是以等高线法处理测量点云中的截面数据,通过B样条插值函数拟合成光滑曲线;再由B样条曲线的一阶导矢公式求出每个测点的一阶导数,然后以点斜公式求出截面曲线上各个测点的切线;如果曲线光滑,曲线上测点的斜率变化在两端点斜率值之间,否则表明曲线上有缺陷存在;根据k-d树的最近点搜索算法,遍历整个叶盆(叶背)就可以找到叶盆(叶背)上的缺陷区域.通过与三坐标测量实验比对,该技术可以实现3μm精度的缺陷识别.     

A robot hand-eye calibration method of line laser sensor based on 3D reconstruction

In the robotic eye-in-hand measurement system, a hand-eye calibration method is essential. From the perspective of 3D reconstruction, this paper first analyzes the influence of the line laser sensor hand-eye calibration error on the 3D reconstructed point clouds error. Based on this, considering the influence of line laser sensor measurement errors and the need for high efficiency and convenience in robotic manufacturing systems, this paper proposes a 3D reconstruction-based robot line laser hand-eye calibration method. In this method, combined with the point cloud registration technique, the newly defined error-index more intuitively reflects the calibration result than traditional methods. To raise the performance of the calibration algorithm, a Particle Swarm Optimization - Gaussian Process (PSO-GP) method is adopted to improve the efficiency of the calibration. The experiments show that the Root Mean Square Error (RMSE) of the reconstructed point cloud can reach 0.1256 mm when using the proposed method, and the reprojection error is superior to those using traditional hand-eye calibration methods.     

隐式B-样条曲线重建的直接Greville纵标法

提出了一种以隐式B-样条曲线为表达形式,基于直接Greville纵标的曲线重建方法。根据点云建立有向距离场,并作为B-样条函数的Greville纵标,然后根据高影响区内的平均代数误差优化Greville纵标;得到一个隐式B-样条函数,该函数的零点集即为重建曲线。该方法具有模型简单,重建速度快,无多余分支,无需手工调节任何参数的优点。实验结果证实了该直接法的效率明显高于点拟合法和普通场拟合法,以几何误差为准则的精度亦优于普通场拟合方法。     

基于MATLAB的汽轮机叶片型面误差分析

汽轮机叶片型面制造误差分析是其制造过程中的重要环节,本文研究叶片型面制造误差分析方法,并基于该方法利用MATLAB开发误差分析系统。应用实例表明,该系统能够很好地分析叶片型面制造误差,并能同时对多组数据进行分析,提高了分析效率。     

基于B 样条曲面插值误差控制的内超环面齿轮齿面建模

针对内超环面齿轮齿面数控加工精度难以保证的问题,提出一种基于B 样条曲面 插值误差控制的内超环面齿轮齿面建模的方法。该方法以内超环面齿轮理论齿面原型为依据, 运用B 样条曲面构造插值曲面,计算插值曲面片与理论齿面之间的误差。通过插值误差分析, 根据误差分布特点,将型值点网格不断细化,获得一组型值点阵,经插值重构后可得到满足精 度要求的内超环面齿轮齿廓模型。最后,通过数控加工验证了建模的有效性。基于B 样条曲面 插值误差控制的内超环面齿轮齿面建模方法为获得高精度的内超环面齿轮实体模型奠定了理 论基础。     

An integrated approach of reverse engineering aided remanufacturing process for worn components

The worn mechanical components/parts arrived in the remanufacturing system exhibit highly uncontrolled variabilities in failure conditions as well as structures and shape complexities. With the aid of reverse engineering (RE) technologies, a quick and accurate acquisition of the damaged areas of the worn part is attainable and thereby facilitates remanufacturing operations necessary to bring the parts back to like-new conditions. In this paper, a reverse engineering based approach is proposed to aid the remanufacturing processes of worn parts. The proposed approach integrates 3D surface data collection, nominal model reconstruction, fine registration, extraction of additive/subtractive repair, tool path generation and actual machining process, seeking to improve the reliability and efficiency of manual repair process. For nominal model reconstruction, a Prominent Cross-Section algorithm embedded with curvature constraint is proposed to automatically identify the boundary of the part's damaged area and thereby eliminate the defective point clouds from the reconstruction process. With the nominal reconstruction model and the 3D model of the worn part, a modified ICP algorithm integrating curvature and distance constraints is proposed to achieve a best-fit position of the two models by automatically identifying and eliminating the unreliable corresponding pairs through iterations. The proposed approach is demonstrated through remanufacturing of two different mechanical components and is approved to be efficient and effective.     

基于中心线匹配的导管三维重建技术

针对工业领域中导管的三维重建效率低的问题,提出了一种基于中心线匹配的导管三维重建方法.该方法首先通过导管的平面灰度图像提取出中心线和边缘线,根据立体视觉原理,以非均匀有理 B样条(Non-uniform rational B-spline, NURBS)曲线作为导管中心线的描述工具和匹配基元,利用其透视投影不变性,重建导管的空间中心线,并通过边缘线计算导管的外径,最后利用三维建模技术重建导管的CAD模型.相对于现有导管三维重建方法,该方法具有测量效率高,操作简单的特点.实验结果表明,该方法的导管三维重建时间可控制在1分钟内,重投影误差为0.284像素,导管两端面中心点的测量误差为0.242mm,外径测量误差为0.158mm.     

基于特征点动态选择的三维人脸点云模型重建

针对典型的点云配准方法中伪特征点过多导致配准效率低和配准结果不精确的问题,提出一种基于特征点动态选择的三维人脸点云模型重建方法。该方法在粗配准阶段,采用动态特征矩阵求解法获取粗匹配特征变换矩阵以避免伪特征点的干扰。在精配准过程中,采用二次加权法向量垂直距离法在人脸流形表面选择更有效的特征点以减少伪特征点的数量,并采用基于特征融合与局部特征一致性的迭代最近点方法进行精配准。经过对比实验验证了算法的可行性,实验结果表明,提出算法能够实现高精度且快速的三维人脸点云模型重建,且均方根误差达到1.816 5 mm,相较于其他算法,在模型重建精度和效率方面都有所提升,具有良好的应用前景。     

A general approach for the machining quality evaluation of S-shaped specimen based on POS-SQP algorithm and Monte Carlo method

In S-shaped specimens which are frequently used to reflect the machining ability of machine tools, the surface error refers to the distance between the points on the actual machining surface to their relevant points on the design surface. The proper measurement of this error is crucial for evaluating the machining quality of S-shaped specimens. During the process of error measurement, improper registration between the measurement coordinate system and the design coordinate system, as well as neglected uncertainty remain the main obstacles for the quality evaluation of S-shaped specimens. This study proposes a general method for the high-precision machining quality evaluation of S-shaped specimens that overcomes both problems. By applying the non-uniform rational B-spline (NURBS) surface molding technology, the surface of S-shaped specimen was reconstructed. Based on the minimum area principle and the particle swarm optimization-sequential quadratic programming (POS-SQP) algorithm, a surface error model of S-shaped specimen was developed. This model minimizes the maximum distance of the transacted measurement points to the design surface. It can be used to obtain the optimal registration matrix of the measurement coordinate system, with minimal surface error of S-shaped specimen. Additional common algorithms were also adopted to search the optimal registration matrix for comparison. Accounting for the random characteristics of basic parameters and the nonlinearity of surface error model, an uncertainty model of the surface error of S-shaped specimen was established based on the Monte Carlo method. This could obtain the actual tolerance zone of the surface error, according to which, the allowable tolerance zone of the surface error was optimized and a defined evaluation result of machining quality of S-shaped specimen was obtained. Then, a general approach for the evaluation of the machining quality of S-shaped specimen was developed based on POS-SQP algorithm and Monte Carlo method. This approach was implemented in a case study though a series of experiments. The experimental results identified the proposed approach as effective in improving the measurement quality and the evaluation of the machining quality of S-shaped specimens can thus be performed within an allowable tolerance zone.     

航空叶片打磨余量分析及轨迹生成

针对航空发动机叶片打磨加工前,叶身余量分布不均且较小的问题,提出一种基于毛坯点云配准的加工余量分析和自适应打磨轨迹生成方法。利用精确扫描测绘技术获取毛坯三维点云,形成了毛坯/零件数模二者点云配准方法;通过基准对齐、点云轮廓包含等条件约束,实现了毛坯三维加工余量分析;在余量分布点云基础上,通过截面获取加工点云轨迹,对轨迹点云进行珠链排序,将轨迹排序点有效化,计算出连续合适的打磨路径,实现自适应余量打磨。最后在Vericut软件中进行了打磨仿真,验证了提出方法的有效性。     

基于改进麻雀搜索算法的B样条曲线拟合方法

航空发动机叶片气动性能设计的改进要求叶片加工系统采用高精度、高效率的加工工艺，基于传统建模方法的叶片加工系统已难以满足当前的加工需求。提出一种基于改进麻雀搜索算法(SSA)的拟合方法，旨在利用最少控制点高效地达到曲线拟合的目标精度，进而提升传统建模方法的精度和效率，建立适用于数字孪生生产环境的高精度、高实时性的三维叶片模型，提高航空发动机叶片的加工合格率。启发式优化算法在B样条曲线拟合中存在收敛慢的问题，而SSA不断跃向最优解的特性使其能快速收敛。基于此，改进SSA的位置更新函数并给出内节点向量更新范围的概念，通过自动迭代内节点向量配置，利用最小二乘法计算最优控制点，依据局部和全局误差计算适应度值并参与下次迭代，多次迭代后得到符合目标精度的拟合曲线。此外，为提高SSA搜索最少控制点的效率，设计一种二分搜索方法。采用某型叶片截面数据进行拟合验证，结果表明，与传统定义节点向量方法和经典优化算法相比，该方法具有较高的拟合精度和收敛效率，在20和80个控制点下分别取得了1e-3 mm和1e-5 mm左右的拟合精度，在5e-3 mm目标精度下，收敛效率较粒子群优化算法、标准SSA分别提升了14....     

三次B样条插值的网格拼接和融合

目的 网格模型的拼接和融合是3维模型编辑的一个重要方面。为了提高3维模型之间拼接曲面的精度和效率,提出一种基于三次均匀B样条曲线曲面的网格融合方法。方法 首先,利用协变分析和数据驱动方法在目标模型上选定融合区域、确定要融合模型的大小及方向;其次,根据选定的3维网格模型,确定待拼接区域的边界,识别并记录边界点集,利用三次B样条插值边界点集;然后,对边界曲线进行双三次B样条曲面插值得到拼接区域连续曲面,并以此作为两模型拼接时的过渡面;最后,对拼接区域重采样,并对其三角化,以实现网格模型的无缝光滑拼接和融合。结果 为了验证本文方法对3维模型拼接的有效性,选取4组不同的模型,分别对其使用本文提出的融合拼接方法进行实验,对前两组模型的拼接效果进行了对比试验,实验结果表明,本文方法可以达到很好的拼接效果,对于融合区域以外的部分能够保持源模型的细节特征,拼接部分的过渡区域光顺平滑,拼接后的模型完整性佳。在运行时间相差0.05 s内,与数据驱动的建模方法相比,本文方法可以处理的节点数至少多2 000个,面片数至少多5 000个。结论 本文方法能够适用于具有任何边界的模型,在选取模型时,对于模型的形状、大小、拓扑结构等的要求较低,适用于新模型的快速建造,因此,该算法可应用于医学、商业广告、动画娱乐以及几何建模和制造等较为广阔的应用领域。     

复杂曲面造型原理及其工程应用

复杂曲面的逆向造型是曲面造型的核心。针对目前CAD／CAM系统存在复杂曲面造型方面的不足,开发了数据预处理程序,对测量得到的实体数据进行平滑滤波处理,消除由此带来的噪声影响,再利用预处理后的数据实现从型值点到控制点的反算以及B样条曲面的重构。结合Pro／E软件,较好的实现了复杂曲面的实体造型,从而为后续的数控加工打下了基础。     

叶片破损区域边界的自动提取算法研究

为了提高叶片的维修效率,提出一种叶片破损区域边界的自动提取算法．该算法主要包括两部分：区域分割和边界重构．在区域分割算法中,通过曲率估算、种子栅格选取和区域生长等步骤将破损区域的数据点从原始点云中分离出来;在边界重构算法中,通过多边形细分和离散光顺算法重构破损区域边界．应用实例表明,文中算法效率高、稳定性好,能够从散乱的点云数据中直接获取高质量的区域边界信息。     

多阈值提取平面点云边界点的方法

针对基于切片技术的点云数据重建算法需要提取切片内点云边界点,及现有算法效率低、提取效果不好等问题,提出一种多阈值提取平面点云边界点的算法。通过选取判断点的k个近邻点,计算相邻两点与判断点连线间夹角,由于边界点必存在最大夹角,通过判断最大夹角是否超过设定阈值,从而快速提取边界点。通过对阈值设值分析,不同点云数据的边界提取实验及几种方法间比较,该方法不受点云形状影响,均能较好提取边界点,且优于其他3种算法。结果表明该方法在保证原始点云特征信息的前提下,可较好提取边界点,提高后续点云重建速度与效率。     

飞行时间三维相机的多视角散乱点云优化配准方法研究

针对目前基于飞行时间(TOF)原理的三维相机实现物体完整表面的三维点云重建过程中,多视角散乱点云配准精度低的问题,本文提出了一种多视角散乱点云优化配准方法。该方法通过构建一个目标功能函数,并结合相邻点云的变换矩阵对该目标函数进行最小化求解,直接获取任意位置的点云到基准坐标系的绝对变换矩阵,避免了对相邻点云的变换矩阵进行累积而引起误差的累加。实验结果表明,该方法提高了多视角点云配准的精度,同时增强了物体点云模型重建的效果,在三维曲面重建中具有较强的实用性。     

Curve reconstruction based on an interval B-spline curve

Curve reconstruction that generates a piece of centric curve from a piece of planar strip-shaped point cloud is a fundamental problem in reverse engineering. In this paper, we present a new curve-reconstruction algorithm based on an interval B-spline curve. The algorithm constructs a rectangle sequence approximating the point cloud using a new data clustering technique, which facilitates the determination of curve order implied in the shape of the point cloud. A quasicentric point sequence and two pieces of boundary point sequences are then computed, based on which a piece of interval B-spline curve representing the geometric shape of the point cloud is constructed. Its centric curve is the final reconstructed curve. The whole algorithm is intuitive, simple, and efficient, as demonstrated by experimental results.     

Contour curve reconstruction from cloud data for rapid prototyping

In this study, a method for generation of sectional contour curves directly from cloud point data is given. This method computes contour curves for rapid prototyping model generation via adaptive slicing, data points reducing and B-spline curve fitting. In this approach, first a cloud point data set is segmented along the component building direction to a number of layers. The points are projected to the mid-plane of the layer to form a 2-dimensional (2D) band of scattered points. These points are then utilized to construct a boundary curve. A number of points are picked up along the band and a B-spline curve is fitted. Then points are selected on the B-spline curve based on its discrete curvature. These are the points used as centers for generation of circles with a user-define radius to capture a piece of the scattered band. The geometric center of the points lying within these circles is treated as a control point for a B-spline curve fitting that represents a boundary contour curve. The advantage of this method is simplicity and insensitivity to common small inaccuracies. Two experimental results are included to demonstrate the effectiveness and applicability of the proposed method.