基于自适应采样的自由曲面偏置算法

应用基于形状的自适应采样算法，给出了一种自由曲面的偏置.算法。首先从微分几何的观点出发，建立了原曲面与偏置曲面之间曲率上的对应关系。然后在原曲面上根据偏置曲面的曲率分布进行数据点的采样计算，并将采样结果进行偏置处理，最后得到给定精度下的偏置曲面。算例表明，给定相同的允许误差，本方法能明显减少所需偏置点的个数，降低了偏置曲面插值及进一步处理的难度。     

一种用于飞机识别的三维建模方法

提出了基于垂距逐步递推的自由曲面自适应数据采样的新算法,给出了应用该算法对复杂曲面物体外形重构和建模方法。自由曲面自适应数据采样时,首先运用逆向工程测量方法,获得曲面的截面数据点列,用非均匀三次B样条曲线拟合出截面轮廓曲线;然后利用基于垂距的数据采样算法,对拟合曲线上的数据点进行重新采样,达到优化数据点的分布及减少描述曲线数据量的目的。最后运用蒙面法完成物体外形轮廓曲面重构和建模。仿真结果表明算法简便、有效。     

融合几何特征的ICP改进算法在数字化测量评价中的应用

针对ICP算法对初值依赖程度高、在配准过程中可能陷入局部最优解的问题,提出了一种融合几何特征的ICP改进算法。利用零件具有丰富几何参数的特点,首先对实测点云进行基于曲率的体素采样,尽可能保留几何特征,再将点云的曲率差值和法向量夹角差值引入算法的目标误差函数中进行迭代计算,当目标误差函数达到设定阈值时迭代结束,得到最终配准结果。利用复杂曲面标准件进行了点云配准实验验证,结果表明：相较ICP算法,融合几何特征的ICP改进算法的收敛速度更快、误差更低;相较快速全局配准加ICP配准算法,融合几何特征的ICP改进算法在保证配准准确性的同时,减弱了对初值的需求,简化了点云配准过程。融合几何特征的ICP改进算法为促进零件的准确数字化测量评价提供了有力支撑,具有技术借鉴价值。     

参数曲面点元离散求交法

提出了一种基于点元的参数曲面求交交互式新算法。该算法在参数曲面上进行自适应的离散点元采样,将点元组织为空间八叉树结构进行求交运算,最后进行交点排序并得到最终的求交结果。与以往的参数曲面求交方法相比,本算法更简单高效。实验结果表明,本算法稳定可靠,误差可控,而且可以达到交互速度。     

求解集装箱装载问题的混合蚁群模拟退火算法

目的 针对物流行业中存在的大规模、复杂、多规格货物的集装箱装载问题,提出一种基于塔装载启发式算法、二维装载点启发式算法、蚁群模拟退火算法的混合算法。方法 首先,采用塔装载启发式算法将三维待装箱装载成塔集,即将三维装箱问题降为二维装箱问题,有效降低集装箱的装载规模;其次,蚁群算法通过融入信息素选择更新策略,并利用自适应信息素挥发系数来提升算法整体的收敛速度,同时结合模拟退火算法对每代优秀路径集进行局部搜索,避免算法因收敛过快而陷入局部最优;最后,将蚁群模拟退火算法与二维装载点启发式算法相结合,优化每座塔的装载顺序和放置姿态,寻找最优的装载方案。结果 实验证明,在250组算例中,采用混合算法后,集装箱的平均空间利用率为90.92%,优于其他3种对比算法。结论 设计的混合蚁群模拟退火算法适用于解决大规模集装箱装载问题。     

面向四面体网格生成的曲面Delaunay三角化算法

提出了一种曲面域Delaunay三角网格的直接构造算法。该算法在曲面网格剖分的边界递归算法和限定Delaunay四面体化算法的基础上,利用曲面采样点集的空间Delaunay四面体网格来辅助曲面三角网格的生成,曲面上的三角网格根据最小空球最小准则由辅助四面体网格中选取,每个三角形都满足三维Delaunay空球准则,网格质量有保证,并且极大的方便了进一步的曲面边界限定下的Delaunay四面体化的进行。     

基于采样保真性的点模型去噪

提出了一种基于采样保真性的点模型去噪算法.该算法通过移动最小二乘曲面,计算每个采样点的保真性;由法向张量投票方法,测量采样点的特征性;利用改进的双边滤波算子获得各个采样点的滤波方向,结合保真性和特征性对点模型去噪.实验结果表明,算法是鲁棒的,在剔除噪声的同时能够有效地保持曲面的几何特征.     

改进PSO-2D Otsu在连铸坯缺陷图像分割中的应用

为更准确有效地提取连铸钢板坯图像中的各类缺陷,通过改进标准PSO算法以优化二维Otsu的阈值选取。将二维Otsu类间方差函数作为粒子的适应度函数,根据适应度值使粒子的惯性权重自适应地优化,根据迭代次数对粒子的变异概率进行改进,提高全局寻优能力和收敛精度。最后选取连铸坯不同种类的缺陷图像进行分割实验,对比二阶振荡PSO-Otsu、二维Otsu、SPSO-二维Otsu法和改进算法的分割结果,多次实验结果表明,改进算法对各类缺陷的分割准确率和成功率分别在90%和96%以上,且算法运行快,具有较好的实用性。     

采用分形技术的二维纹理在曲面上的贴图方法

利用分形理论生成的个性化分形图案在纹理贴图中的应用比较广泛。文章阐述了分形技术中仿射变换的二维不规则纹理生成原理,提出了矢量化离散细分二维纹理图案的方法。该方法把纹理图案表示为一系列离散的点,寻找出离散点与曲面空间中任取一局部小三角形面片中各点的对应关系,根据点对点的转换原理,实现由二维纹理空间到曲面空间的贴图。开发了相应系统对上述方法进行了验证。     

室外大型场景多机位三维数据全局快速配准

以激光采样点为配准单元,提出了一种新的基于反向投影的室外大型场景多机位三维数据全局快速配准算法。算法直接利用激光采样点的点位和激光反射强度两重属性通过马氏距离搜索最近点,并利用反向投影加速最近点搜索,依靠插值方法修正最近点,避开采样分辨率影响。根据最小生成树原则生成了多机位三维数据最佳配准路线图,在PC机上自动将多机位三维数据无缝拼合在同一坐标系。经过实际应用,验证了算法的稳定性,给出了满意的配准结果。     

Domain-specific Gaussian process-based intelligent sampling for inspection planning of complex surfaces

Precision measurement of complex surfaces requires intensive sampling for fully characterising the surface geometry and reducing the measurement uncertainty, which is, however, less efficient when the data are costly to acquire. This paper presents a Gaussian process (GP)-based intelligent sampling method for achieving well balance between the measurement efficiency and accuracy. The method makes use of GP to model the surface with domain-specific composite covariance kernel functions. The statistical nature of the GP makes it capable of giving credibility to the arbitrary prediction over the entire established model which can be used in a critical criterion to perform intelligent sampling of the surfaces. The method is independent from the coordinate frames, which makes the sampling plan easily utilised without accurate pre-positioning in actual measurement. The effectiveness of the method is verified through a series of comparison study and actual application in measuring a multi-scaled complex mould insert on coordinate measuring machine.     

Automatic sampling for CMM inspection planning of free-form surfaces

Coordinate measuring machines (CMMs) are used to examine the conformity of the produced parts with the designer's intent. The inspection of free-form surfaces is a difficult process due to their complexity and irregularity. Many tasks are performed to ensure a reliable and efficient inspection using CMMs. Sampling is an essential and vital step in inspection planning. Efficient and reliable approaches to determine the locations of the points to be sampled from free-form surfaces using the CMM were developed. Four heuristic algorithms for sampling based on the NURBS features of free-form surfaces are presented. The sampling criteria are equiparametric, surface patch size and the surface patch mean curvature. An algorithm for automatic selection of sampling algorithms performs complexity checks on NURBS surfaces, including the surface curvature changes and surface patch size changes, and selects the suitable sampling algorithm. Extensive simulations were performed using the developed methodologies to evaluate their performance using free-form surfaces with different degrees of complexity and compared with the uniform sampling pattern. The CMM measurement errors and manufacturing form errors have been simulated in these studies. The developed algorithms provide a useful tool in selecting the effective sampling plans for the tactile CMM inspection planning of free-form surfaces.     

叶片型面测量编程与误差处理技术

针对航空发动机叶片三坐标测量机(CMM)测量,进行了自动测量编程与误差处理两个方面的研究。提出了一种基于已知叶片CAD模型提取测量点理论坐标值与计算法向矢量的方法,矢量计算采用微平面法。数据处理时,采用ICP算法进行配准消除了系统误差,从而得到叶片型面误差。开发了测量点坐标值与矢量计算以及配准程序。实例证明该方法可靠、有效。     

An adaptive design and interpolation technique for extracting highly nonlinear response surfaces from deterministic models

Response surface methodologies can reveal important features of complex computer code models. Here, we suggest experimental designs and interpolation methods for extracting nonlinear response surfaces whose roughness varies substantially over the input domain. A sequential design algorithm for cuboid domains is initiated by selecting an extended corner/centre point design for the entire domain, then updated by decomposing this domain into disjoint cuboids and taking the corners and centre of these cuboids as new design points. A roughness criterion is used to control the domain decomposition so that the design becomes space-filling and the coverage is particularly good in the parts of the input domain where the response surface is strongly nonlinear. Finally, the model output at untried inputs is predicted by carefully selecting a local neighbourhood of each new point in the input space and fitting a full quadratic polynomial to the data points in that neighbourhood. Test runs showed that our sequential design algorithm automatically adapts to the nonlinear features of the model output. Moreover, our technique is particularly useful for extracting nonlinear response surfaces from computer code models with two to seven input variables. A simple modification of the outlined algorithm enables adequate handling of non-cuboid input domains.     

基于曲率弦高法的海量测量数据精简

针对视觉测量的点云数据过大而不利于计算和重构的问题,在分析视觉测量点云数据特征的基础上,将曲率原则和弦高法相结合,提出基于曲率弦高法的海量测量数据精简方法。该方法在考虑曲线曲率变化的基础上构建弦高函数,并通过迭代得到各测点变化的弦高值,再根据弦高法的数据精简原则确定需要保留的测量点。仿真实验表明,该方法在平均误差小于0.2 mm时,精简率为89.8%,能够有效地对海量点云数据进行精简,并实现精简后测点按曲面曲率的合理分布。     

一种基于测点生成的间隙面差名义值算法

本文提出一种白车身装配CAD模型间隙面差名义值的算法,该算法基于UG二次开发测点生成,在零件需要保证精度的匹配关键位置生成测点,并由点生成截面,获得两个匹配零件该截面处信息,该信息包括测点坐标、截面线,从而计算的出该匹配零件间隙面差的名义值.该名义值将用于实际测量真实值的比对,来判断两匹配零件匹配实际信息是否合格.由于...     

Profilometry of toroidal surfaces with an improved ronchi test

An implementation of the well-known Ronchi test technique, which allows for the profilometric measurement of nonrotationally symmetrical surfaces, is presented and applied to the measurement of toroidal surfaces. Both the experimental setup and the data-processing procedures are described, and parameters such as the radius of curvature of the sample surface, the orientation of its principal meridians, and the position of its vertex are measured by means of the values of the local normal to the surface obtained at a set of sampling points. Integration of these local normal values allows for the reconstruction of the three-dimensional profile of the toroidal surface considered with micrometric accuracy, and submicrometric surface details may be calculated by use of surface-fitting procedures. The density of sampling points on the surface may be tailored to fit test requirements, within certain limits that depend on selection of experimental setup.     

五轴加工中心的在机检测系统研究

为了避免加工与检测过程中出现重复定位误差,研究了用于复杂空间型面的在机检测方法。通过将测头系统应用于五轴加工中心,分析对应机床在机检测的运动学模型并开发了后置处理程序。将传统的旅行商问题转化为最优匹配问题进行局部快速求解,获取行程段路径规划轨迹。同时提出一种干涉检验方法,利用图形求交判断的方式对检测干涉进行预处理。实现了“S”试件曲面的在机检测,并将获取偏差数据与三坐标测量机的采样数据进行对比,在数据整体一致的条件下,前者的变异系数相对后者降低了7.3%。     

基于误差分解定权的工业测量空间线面拟合算法

针对工业工件拟合中测量数据由于测量仪器特性导致的不同方向误差分量差异问题进行了研究,提出了基于误差分解定权的工业测量拟合算法。该算法考虑了工件姿态以及测量仪器和测点的空间关系,分析了纵向误差和横向误差分量对空间直线和空间平面拟合的影响,然后通过影响量对测量数据进行定权,从而削弱仪器测量误差对拟合结果的影响,提高工件拟合精度。实验结果表明,该算法相比等权拟合精度可提高约16%。