Development of a laser sensor for in-process guidance of an industrial robot

A pilot-type laser sensor for non-contacting distance measurement has been developed, which was aimed at application to in-process guidance of an industrial robot. A laser beam is emitted through a convex lens to an object and the reflected light is collected and focused by the lens. Diameter of its unfocused image is measured using one dimensional CCD-array, from which the distance is determined. Because the way of the beam emission and that of reflected light to the lens are the same, scanning of the beam to follow a path for robot guidance is easy and some geometric constraints, which may arise for a sensor using triangular principle, are removed. Geometric analyses for scanning the beam with a mirror are presented to determine the distance and position of an object point. A simple tracking control theory for the beam to follow a path and give informations about its position to a robot controller has been suggested and analyzed.     

Modeling outlier formation in scanning reflective surfaces using a laser stripe scanner

Scanning reflective surfaces using 3D laser scanners is a challenging task since reflective surfaces of complex geometry promote the formation of unwanted data outliers. These outliers are characterized with large measurement errors, which significantly deteriorate the quality of the scanned point cloud data. This paper experimentally investigates the formation of outliers in relation to scanning reflective surfaces using a commercial laser stripe scanner. Two outlier formation models are developed: mixed reflection and multi-path reflection. The undesirable specular reflections in both mixed reflection and multi-path reflection scanning situations cause multiple peaks in the image sensing arrays. The false image peaks are recorded and will eventually be observed as outliers because they are not part of the scanned object surface geometry. A series of scanning experiments have been conducted and the results confirm the validity of the developed outlier formation models. Potential applications of the developed models such as scan path evaluation and outlier filter design are also discussed.     

光针轮廓扫描技术测量内螺纹曲面

分析了激光光针扫描在测量内螺纹曲面时的特性及影响精度的因素。根据光斑在被测面的噪声分布特点,采用中值滤波与小波阈值去噪相结合的综合滤波算法对光斑图像进行了去噪处理,其中中值滤波可以有效地消除光斑图像中的脉冲噪声,而基于小波变换的阈值去噪算法可以消除图像中的高斯噪声。通过综合滤波算法对光斑图像进行处理,可以有效消除激光光斑噪声,消除图像噪声对测量精度的影响,同时保持了光斑图像的细部特征。根据激光光斑图像在倾斜被测物体表面光强分布特点,设计了近似圆拟合算法来确定光斑中心,该算法相对传统算法具有计算量小、计算效率高,适合在线检测的特点,可以克服测量面倾斜对激光光斑中心的影响。利用采用上述方法的坐标机激光光针扫描系统,对标准内螺纹量规进行测量,对比应用前后的测量结果,螺距精度提高了0.48 mm,中径测量精度提高了0.44 mm,牙型角精度提高0.57°。     

一种基于极线约束的激光条纹匹配算法

在逆向工程中为了获得产品的精确CAD模型，必须完成立体点的匹配．通过建立摄像机模型描述了三维世界坐标与计算机图像坐标之间的关系；提出了基于极线约束和连续性约束的激光条纹匹配准则，给出了一种直线和曲线求交的激光务纹匹配新方法，从而实现了激光条纹的快速精确匹配和激光扫描线的三维重建。     

便携式激光扫描三维形貌测量系统

介绍了基于双目立体视觉的便携式激光扫描三维形貌测量系统,该系统的测头部分安装了5个激光器,将 扫描速度提高了5倍,而且采用两个摄像机同时摄取扫描激光光条图像,避免了对投射激光的标定过程。根据立 体视觉原理,经图像匹配,可计算得到光条上所有点的空间位置和深度,即被测空间曲面的三维信息。阐述了非 接触三维形貌测量的原理和方法,试验结果证明了系统的可行性和适用性。     

激光速在视觉检测中的标定方法研究

计算机视觉检测技术在测绘、工业、军事、导航等领域已得到广泛的应用。而标定是视觉检测的关键技术之一。本文介绍一种用激光束对系统进行标定的新方法，即将激光器发出的平行光束投射到被测物表面上的光斑作为标定物，通过采集光斑图像并对图像进行预处理，包括噪声处理、图像分割技术等得到光斑图像，最后计算出图像象素与实际尺寸的对应关系。该方法能够在不便于或者不能使用常规标准件法的环境下进行快速标定。试验结果验证了该方法在一定精度下的稳定性和可用性。     

H-S波前传感器在大尺寸测量中的应用研究

针对目前激光大尺寸测量系统中的空气扰动问题,提出一种采用波前探测和图像恢复技术相结合的解决方法。该方法采用Hartman—Shack波前探测器,直接应用Zemike多项式来波前重构,然后运用图像解卷积运算进行图像恢复,以减小和消除测量激光束因大气扰动而产生的抖动、变形,从而提高测量精度。     

A prototype system of three-dimensional non-contact measurement

A prototype 3D measurement system is proposed in this paper which consists of a 1D laser displacement sensor, a 2D image system and a servo controlX,Y-table. The laser sensor and CCD camera are installed on theZ-axis perpendicular to theX,Y-table. The image-processing system employs the adaptive resonant theory (ART) neural networks to classify the outer shape of the measured object. The edge values of the object are then obtained by using the image processing procedures of sliding, stretching, edge enhancement and binary disposal. The 2D dimensions of the object are searched by employing the Hough theory based upon the edge values. The 3D dimensions of the object are measured and assembled by combining theX,Y-coordinates of the table and the scanning results of the 1D laser for the height of theZ-axis. A 3D plaster model is chosen as the specimen for non-contact measurement to verify the feasibility of this approach. The limitations and resolution of the 3D measurement of this system are discussed.     

Novel Method for Spatial Angle Measurement Based on Rotating Planar Laser Beams

Spatial angle measurement,especially the measurement of horizontal and vertical angle,is a basic method used for industrial large-scale coordinate measurement.As main equipments in use,both theodolites and laser trackers can provide very high accuracy for spatial angle measurement.However,their industrial applications are limited by low level of automation and poor parallelism.For the purpose of improving measurement efficiency,a lot of studies have been conducted and several alternative methods have been proposed.Unfortunately,all these means are either low precision or too expensive.In this paper,a novel method of spatial angle measurement based on two rotating planar laser beams is proposed and demonstrated.Photoelectric receivers placed on measured points are used to receive the rotating planner laser signals transmitted by laser transmitters.The scanning time intervals of laser planes were measured,and then measured point's horizontal/vertical angles can be calculated.Laser plane's angle parameters are utilized to establish the abstract geometric model of transmitter.Calculating formulas of receiver's horizontal/vertical angles have been derived.Measurement equations' solvability conditions and judgment method of imaginary solutions are also presented after analyzing.Proposed method for spatial angle measurement is experimentally verified through a platform consisting of one laser transmitter and one optical receiver.The transmitters used in new method are only responsible for providing rotating light plane signals carrying angle information.Receivers automatically measure scanning time of laser planes and upload data to the workstation to calculate horizontal angle and vertical angle.Simultaneous measurement of multiple receivers can be realized since there is no human intervention in measurement process.Spatial angle measurement result indicates that the repeatable accuracy of new method is better than 10".Proposed method can improve measurement's automation degree and speed while ensuring measurement accuracy.     

A new method for processing impact excited continuous-scan laser Doppler vibrometer measurements

A scanning laser Doppler vibrometer (LDV) can acquire non-contact vibration measurements from a structure with high spatial detail in an automated manner; one only need redirect the laser via computer-controlled mirrors to acquire measurements at additional points. However, since most LDV systems are only capable of measuring one point at a time, conventional scanning vibrometry cannot be effectively employed in some situations, for example when the time record is long at each measurement point or when the structure changes with time. Conventional scanning LDV systems are also difficult to employ with impact excitation because there is considerable variation in the impact location, angle and the character of the impacts, which leads to errors in the mode shapes that are extracted from the measurements. This paper presents a method by which one can determine the mode shapes, natural frequencies and damping ratios of a structure from as little as one response record by sweeping the laser continuously over the vibrating structure as the measurement is acquired. A novel resampling approach is presented that transforms the continuous-scan measurements into pseudo-frequency response functions, so they can be processed using standard identification routines to find the modal parameters of the structure. Specifically, this work employs a standard multi-input–multi-output identification routine and the complex mode indicator function to the continuous-scan laser Doppler vibrometry (CSLDV) measurements. The method makes no assumptions regarding the shape or properties of the surface and only requires that the laser scan periodically and that the structure vibrate freely. The method is demonstrated experimentally on a free–free beam, identifying the first nine mode shapes of the beam at hundreds of points from a few time histories. For this system, this represents a two-order of magnitude reduction in the time needed to acquire measurements with the LDV.     

加权空-谱与最近邻分类器相结合的高光谱图像分类

提出了一种基于加权空-谱距离(WSSD)的相似性度量方法 ,并将其应用到最近邻分类器(KNN)中,导出了一种新的高光谱图像分类算法。该算法利用高光谱图像的物理特性,通过引入空间窗口和光谱因子这两个参数来挖掘出图像中的空间信息与光谱信息,利用空间近邻点对中心像元进行重构。在最大限度减少图像冗余信息的基础上,增大了同类像元间的相似性以及异类像元间的差异性,获得了更为有效的鉴别特征,从而更好地实现了数据间的相似性度量。基于Indian Pines和PaviaU高光谱数据集进行了实验,结果表明:将提出的WSSD-KNN算法应用于高光谱图像分类时,其分类精度高于其他算法,总体分类精度分别达到了91.72%和96.56%。由于算法较好地融合了图像中的空间-光谱信息,提取出了更为有效的鉴别特征,故不仅有效地改善了高光谱数据的地物分类精度,而且可在训练样本较少时,保持较高的识别率。     

基于单次成像的三维形貌拼接技术

针对大型物体的三维形貌测量,研究基于辅助靶标的三维形貌拼接技术,并在此基础上提出单摄像机单次成像求解转换矩阵的方法.该方法通过单摄像机单次成像,结合控制点的边长约束,求解出全局坐标系同局部测量坐标系的转换关系,进而将局部测量数据统一到全局坐标系下,实现拼接.此方法避免采用单摄像机多摄站测量时带来的繁琐操作以及产生的相关问题,大大提高拼接的速度,并且可以保证较高的精度.     

机载设备安装姿态视觉校准中的靶板标定

基于飞机机载设备安装姿态视觉校准系统Archer-M的研发,提出针对系统中姿态测量辅助靶板的标定方法。首先,利用摄像机从不同方位拍摄靶板图像,在相差一个尺度因子的情况下确定靶点位置关系。然后,利用单个发光二极管（LED）靶点的多次精确移动和图像叠加的方法恢复绝对尺度,求解靶点的相对关系。最后,通过精确控制靶板的位姿运动,利用运动前后各坐标系之间的相对关系,求解出“靶/座"相对位姿,并进一步针对只用于物体姿态测量的靶板,提出了分别沿两个垂直方向运动的简化“靶/座"标定方法,从而大大降低了标定过程中对标定设备的要求。实验结果表明：距离为3~12 m时,姿态角度的测量标准差为0.004~0.017°,姿态测量精度与激光跟踪仪相当。     

联合光度立体视觉和图像校正的磨粒三维形貌重建

分析铁谱技术在机械装备磨损状态检测中发挥了重要作用,但其仅能提供磨粒二维图像,导致磨粒形貌信息不足。为实现磨粒三维形貌的精确重建,联合光度立体视觉和图像校正,为精确重建磨粒的三维形貌,联合光度立体视觉和图像。该方法首先采用大津阈值法由全光源图像识别磨粒与背景区域;然后为消除LED发光强度差异对磨粒形貌重建的影响,结合平面形状和朗伯反射模型确定背景区域的理想成像亮度,并校正各光度图像序列的亮度;最后根据光度立体视觉方法,由校正后光度图像序列重建磨粒的三维形貌。以不同类型的磨粒为测试样本,将所提出的方法的重建结果与激光共聚焦显微镜的测量结果进行对比。结果表明：重建磨粒的形貌参数误差小于15%,表明提出的方法能够精确重建磨粒的三维形貌。     

基于标准器的大尺寸测量系统坐标统一化方法

针对大尺寸测量系统坐标统一化过程中公共点的测量误差不可控制的问题,提出了利用可现场溯源的标准器取代传统的独立公共点的方法。设计了一种标准器,并用更高精度等级的三坐标测量机对标准器上各个目标点之间的空间几何位置关系进行标定,把这些几何位置关系作为约束条件。现场应用中多站大尺寸测量仪分别测量标准器上的目标点,计算出各个几何关系与通过标定的约束关系之差,将这个差值与设定的误差限进行比较,确定公共点的测量值是否有效。对该方法进行了理论分析和仿真证明。提出了7参数坐标配准算法对大尺寸测量进行空间坐标数据配准。用激光跟踪仪和激光雷达及4个标准器进行现场实验,实验结果与传统方法相比,坐标配准误差得到降低。为了进一步验证该方法的有效性,把一根经过检定的基准尺放置于测量空间的12个不同位置,使用标准器约束前后的两组坐标配准参数分别计算基准尺长度的平均值和标准差。实验结果表明,使用标准器约束方法能够提高大尺寸测量系统坐标统一化精度。     

Contour extraction of a laser stripe located on a microscope image from a stereo light microscope

A stereo light microscope has a special optical structure that consists of two optical paths. With two cameras fitted on its imaging planes, a microscopic binocular vision system can be constructed, and this system can be applied in three‐dimensional (3D) shape measurements of a microscopic object. A novel‐shape reconstruction system is developed in this article composed of laser fringe scanning and a stereo light microscope. A laser projector emits a thin light sheet and projects it onto the microscopic object's surface. The microscopic object is placed on a micro‐displacement mechanism and moved in a given direction. The entire surface of the object is scanned by the light sheet. This system captures a series of microscopic images of the laser stripe, which are used to restore the 3D shape of the object. In this article, we mainly focus on the study of the laser stripe detection method, which is derived based on the Canny rule. First, the Canny rule outputs pixels at the left and right edges of the laser stripe. Then, a subpixel edge extraction method is proposed based on polynomial fitting that outputs the center curve of the laser stripe. Finally, an edge filter is used to smooth the edge burrs, and the Hermite interpolation method is used to link the broken edges and construct continuous, smoothing edge contours. The results show that this method can effectively find the subpixel position of the laser stripe and output high‐quality edge contours. The method is suitable for extracting the contours of a laser stripe located in a microscope image.     

基于激光共焦扫描显微镜方法的磨损表面三维数字化描述

表面形貌的精确描述在许多领域诸如材料、生物医学、摩擦学和机器状态监测等领域变得越来越重要。开发了一种基于激光共焦显微镜和图像处理技术的研究磨损表面及表面参数的新方法。首先用B io-rad Rad iance 2000激光共焦显微镜方法获得精确的三维表面形貌,然后用计算机辅助图像分析技术自动计算出表面特征参数。应用示例表明本文所研究的方法是可靠的,能对工程表面的表面粗糙度特征进行精确描述。     

动态电容层析成像图像重建算法

提出了融合ECT测量信息和被测对象动态演化信息的新型图像重建模型;基于Tikhonov正则化方法,建立一个同时考虑了ECT测量信息、被测对象动态演化信息、时间与空间约束的新型图像重建目标泛涵,将图像重建问题转化为最优化问题;提出了集成分裂Bregman迭代法优势的新型算法求解该目标泛涵。数值仿真结果表明,所提出的图像重建算法其图像重建质量均优于OIOR算法、STR算法及PLI算法;同时由于所提出的图像重建算法同时考虑了测量数据和重建模型的不精确性,其抵抗测量噪声的能力得以提高。     

Station-transfer measurement accuracy improvement of laser tracker based on photogrammetry

Laser tracker has been used in a diverse range of applications due to its high accuracy and efficient, specifically as measuring the coordinates of points or scanning shape of objects. In real applications, we often need to measure common points on multi-stations by using this technology if objects are large scale. To ensure every common point within the range of laser tracker, common points are usually placed far from the laser tracker. However, the long distance between common points and laser tracker will decrease the accuracy of the result. In this research, we proposed a new method where photogrammetry and laser tracker are integrally used to measure common points to reduce measurement error. With the help of photogrammetry, we first constructed the geometric constraints of common points. Then, by using graphic correction method, the coordinates of common points on laser tracker will be corrected. Both of the theoretical and experimental study results indicated the great success of improving the measurement accuracy of laser tracker. We consider that this method we reported can highly increase the accuracy of measurement on laser tracker station-transfer.     

散乱数据的曲面重构与深度图像多视匹配技术

针对激光扫描测量系统得到的大量散乱数据点 ,制定了基于曲率特征的自适应采样策略 ,研究了一种基于Delaunay三角剖分的三角Bezier曲面造型与NURBS曲面造型相结合的实用曲面重构技术 ,采用改进后的迭代最近点算法对深度图像数据多视匹配技术进行了研究。