Precise perimeter measurement for 3D object with a light-pen vision measurement system

A novel measurement scheme for a three-dimensional (3D) object's surface boundary perimeter is proposed. This scheme consists of three steps. First, a light-pen single-camera 3D coordinate vision measurement system is devised to obtain the 3D coordinates of a detected object's 3D surface boundary. Second, a novel 3D B-spline active contour is applied to converge to the object's 3D surface boundary accurately. Finally, for the convergent active contour, its true contour length is computed as the detected object's true perimeter. An experiment on a bent surface's perimeter measurement indicates that this scheme's measurement repetition error decreases to 0.6%.     

Calibration for stereo vision system based on phase matching and bundle adjustment algorithm

Calibration for stereo vision system plays an important role in the field of machine vision applications. The existing accurate calibration methods are usually carried out by capturing a high-accuracy calibration target with the same size as the measurement view. In in-situ 3D measurement and in large field of view measurement, the extrinsic parameters of the system usually need to be calibrated in real-time. Furthermore, the large high-accuracy calibration target in the field is a big challenge for manufacturing. Therefore, an accurate and rapid calibration method in the in-situ measurement is needed. In this paper, a novel calibration method for stereo vision system is proposed based on phase-based matching method and the bundle adjustment algorithm. As the camera is usually mechanically locked once adjusted appropriately after calibrated in lab, the intrinsic parameters are usually stable. We emphasize on the extrinsic parameters calibration in the measurement field. Firstly, the matching method based on heterodyne multi-frequency phase-shifting technique is applied to find thousands of pairs of corresponding points between images of two cameras. The large amount of pairs of corresponding points can help improve the accuracy of the calibration. Then the method of bundle adjustment in photogrammetry is used to optimize the extrinsic parameters and the 3D coordinates of the measured objects. Finally, the quantity traceability is carried out to transform the optimized extrinsic parameters from the 3D metric coordinate system into Euclid coordinate system to obtain the ultimate optimal extrinsic parameters. Experiment results show that the procedure of calibration takes less than 3 s. And, based on the stereo vision system calibrated by the proposed method, the measurement RMS (Root Mean Square) error can reach 0.025 mm when measuring the calibrated gauge with nominal length of 999.576 mm.     

Rapid and flexible laser marking and engraving of tilted and curved surfaces

We present a novel method for rapid and flexible laser marking and engraving of tilted, curved and freeform work-piece surfaces. The method is based on integrating a three-dimensional (3D) laser measurement system into a 3D laser marking system. We use the same laser source and optics for measurement and processing with a minimum of additional hardware components. A low power CW laser regime is used to measure the 3D shape of a work-piece surface while a high-peak power-pulsed laser regime is used for processing. The acquired 3D surface data are used to determine the 3D trajectory of the processing beam focus. Neither the 3D shape of the work-piece nor its orientation needs to be known in advance as long as the processed surface lies within the working range of the 3D laser processing system. This eliminates the need for exact work-piece positioning before processing and substantially improves processing flexibility (allowing, e.g. variations in work-piece shape or/and orientation from mark to mark). This paper discusses key issues concerning an implementation of the method and presents typical examples of markings and engravings, which demonstrate the advantages of the method with respect to the existing industrial 2D and 3D laser marking and engraving methods. The method can also be applied to flexible laser structuring and microprocessing of curved surfaces.     

无海面控制点的立体摄影海浪测量方法研究

介绍了一种无海面控制点的立体摄影海浪测量方法, 给出了其数学模型和相关算法. 文中利用海浪特性, 基于最小二乘法和海浪波面理论, 给出了一种新的外方位元素定标方式. 与传统的立体摄影定标方式相比, 该定标方式充分利用了平均海平面的性质, 既避免了海面控制点的需求, 又使测量数据更为直观, 同时还为基于运动平台的立体摄影海浪测量技术的发展提供了理论依据. 实验室实验表明基于本文发展的立体摄影测量系统精度较高, 可以用于海面微尺度波的测量; 现场实验表明基于本文发展的立体摄影测量系统测量面积可达10⁴ m² 量级, 是一种有效的大尺度海浪测量手段.     

Precise perimeter measurement for 3D object with a binocular stereo vision measurement system

A novel measurement scheme for a three dimensional (3D) object's surface boundary perimeter is proposed. This scheme consists of three steps. First, a binocular stereo vision measurement system with two CCD cameras is devised to obtain the two images of a detected object's 3D surface boundary. Second, two B-spline active contours are applied to converge to the object's contour edges accurately in the two CCD images to perform the stereo matching. Finally, for the reconstructed 3D active contour, its true contour length is computed as the detected object's true boundary perimeter. An experiment on a bent surface's perimeter measurement indicates that this scheme's measurement repetition error decreases to 0.6%.     

基于SfS的3D视觉测量研究

提出了一种将Shape from Silhouette(SfS)技术应用在三坐标机上的新方法,即用摄像机获取图像,用三坐标机作移动平台,构建视觉测量系统,应用SfS技术对物体进行三维测量。该视觉测量系统扩展了坐标机功能,扩大了其应用范围。实验结果表明,该视觉测量系统具有SfS技术和坐标机两者的优点,重构物体三维模型的过程简单快捷,精度高于0.4mm,其结果可作为坐标机智能测量的基础,是一种非常实用的方法。     

A three-step system calibration procedure with error compensation for 3D shape measurement

System calibration, which usually involves complicated and time-consuming procedures, is crucial for any three-dimensional （3D） shape measurement system based on vision. A novel improved method is proposed for accurate calibration of such a measurement system. The system accuracy is improved with considering the nonlinear measurement error created by the difference between the system model and real measurement environment. We use Levenberg-Marquardt optimization algorithm to compensate the error and get a good result. The improved method has a 50% improvement of re-projection accuracy compared with our previous method. The measurement accuracy is maintained well within 1.5% of the overall measurement depth range.     

A novel optimization method of camera parameters used for vision measurement

Camera calibration plays an important role in the field of machine vision applications. During the process of camera calibration, nonlinear optimization technique is crucial to obtain the best performance of camera parameters. Currently, the existing optimization method aims at minimizing the distance error between the detected image point and the calculated back-projected image point, based on 2D image pixels coordinate. However, the vision measurement process is conducted in 3D space while the optimization method generally adopted is carried out in 2D image plane. Moreover, the error criterion with respect to optimization and measurement is different. In other words, the equal pixel distance error in 2D image plane leads to diverse 3D metric distance error at different position before the camera. All the reasons mentioned above will cause accuracy decrease for 3D vision measurement. To solve the problem, a novel optimization method of camera parameters used for vision measurement is proposed. The presented method is devoted to minimizing the metric distance error between the calculated point and the real point in 3D measurement coordinate system. Comparatively, the initial camera parameters acquired through linear calibration are optimized through two different methods: one is the conventional method and the other is the novel method presented by this paper. Also, the calibration accuracy and measurement accuracy of the parameters obtained by the two methods are thoroughly analyzed and the choice of a suitable accuracy evaluation method is discussed. Simulative and real experiments to estimate the performance of the proposed method on test data are reported, and the results show that the proposed 3D optimization method is quite efficient to improve measurement accuracy compared with traditional method. It can meet the practical requirement of high precision in 3D vision metrology engineering.     

地震振动台实验三维全场位移测量的研究

提出一种基于高速相机双目立体视觉技术的大视场全场三维位移测量方法,用来测量地震振动台实验过程中的位移变化。给出了一种鲁棒的标志点匹配算法,基于VS2010开发环境,研发了用于振动台实验三维全场位移测量系统,设计了精度评估实验方案,验证该方法在大幅面位移测量中的精度,并利用该实验系统对高边坡模型振动台实验进行测量。结果表明:在3 m1.5 m视场范围,静态位移测量误差优于0.4 mm,动态位移测量误差优于0.5 mm,可以满足振动台实验的要求;该方法可以方便、直观地测量地震振动台实验中高边坡模型的位移场,并且测量得到X、Y、Z 3个方向位移曲线以及总位移曲线过渡自然、数据合理,是测量振动台实验全场位移变化的一种有效方法。     

三维形貌测量的扫描相移法研究

物体三维形貌测量中常用的光切法的主要优点是易于实现扫描测量大型物体表面,缺点是光刀中心位置难以精确确定;相移法的主要优点是可以用较宽的光栅提高测量的灵敏度与准确度,具有测量速度快和较好的抗静态噪声的能力,缺点是当待测范围较大时,采集图像的像差较大,不利于大型物面的测量.将这两种方法有机地结合起来,取长补短,提出了一种扫描相移法.实验结果表明,这个方法不但适用于长形大物面的形貌检测,而且又大大地减少了图像采集系统畸变误差的影响,从而提高了检测准确度.     

A composite-structured-light 3D measurement method based on fringe parameter calibration

This paper proposes a novel method for reducing measurement error caused by spectrum overlapping in composite-structured-light 3D measurement systems. For a composite-structured-light 3D measurement system, spectrum overlapping causes parameters of each deformed phase-shifting fringe to change, and therefore leads to phase measurement errors. The proposed fringe parameter calibration method is based on the fact that variations in each deformed fringe's parameters are independent of height and reflectivity of the measured object. Three frames of composite grating are projected on the reference plane, and each carrier channel includes the information of three phase-shifting sinusoidal gratings used in Phase Measuring Profilometry (PMP). With the parameter calculation formulas of PMP, the parameters of fringes demodulated from the same carrier channel can be calculated, and therefore parameter relation coefficients between fringes demodulated from different carrier channels may be obtained. When an object is measured, these relation coefficients can be used to calibrate the parameters of the deformed phase-shifting fringes. A new 3D measurement mathematical model is established to reconstruct the shape of the object. Experimental data proved that the proposed method can effectively restrain the effect of spectrum overlapping and improve measurement accuracy by more than three times.     

基于椭圆形光强分布光栅投影的三维面形测量方法

基于椭圆形光强分布光栅投影测量物体三维面形的方法,将椭圆形光强分布光栅投影到被测物体表面,用摄像机获取变形条纹图,通过系统参量和条纹图携带的相位信息求解出物体的三维面形.推导出通过椭圆形光强分布光栅条纹求解相位的计算公式并对提出方法作了计算机仿真.实验结果表明该方法可以比较准确地测量物体的三维面形,在噪音较大的情况下测量结果仍具有较高准确度.     

基于椭圆形光强分布光栅投影的三维面形测量方法

基于椭圆形光强分布光栅投影测量物体三维面形的方法,将椭圆形光强分布光栅投影到被测物体表面,用摄像机获取变形条纹图,通过系统参量和条纹图携带的相位信息求解出物体的三维面形.推导出通过椭圆形光强分布光栅条纹求解相位的计算公式并对提出方法作了计算机仿真.实验结果表明该方法可以比较准确地测量物体的三维面形,在噪音较大的情况下测量结果仍具有较高准确度.     

Single-lens 3D digital image correlation system based on a bilateral telecentric lens and a bi-prism: Systematic error analysis and correction

Recently, we proposed a single-lens 3D digital image correlation (3D DIC) method and established a measurement system on the basis of a bilateral telecentric lens (BTL) and a bi-prism. This system can retrieve the 3D morphology of a target and measure its deformation using a single BTL with relatively high accuracy. Nevertheless, the system still suffers from systematic errors caused by manufacturing deficiency of the bi-prism and distortion of the BTL. In this study, in-depth evaluations of these errors and their effects on the measurement results are performed experimentally. The bi-prism deficiency and the BTL distortion are characterized by two in-plane rotation angles and several distortion coefficients, respectively. These values are obtained from a calibration process using a chessboard placed into the field of view of the system; this process is conducted after the measurement of tested specimen. A modified mathematical model is proposed, which takes these systematic errors into account and corrects them during 3D reconstruction. Experiments on retrieving the 3D positions of the chessboard grid corners and the morphology of a ceramic plate specimen are performed. The results of the experiments reveal that ignoring the bi-prism deficiency will induce attitude error to the retrieved morphology, and the BTL distortion can lead to its pseudo out-of-plane deformation. Correcting these problems can further improve the measurement accuracy of the bi-prism-based single-lens 3D DIC system.     

基于机器视觉的马体尺测量系统设计与研究

传统马体尺的人工测量方法工作量大且存在安全隐患,对此提出基于线性回归理论和机器视觉技术的马体尺测量方法,旨在测量马体的基本数据如体高、体长、胸围、管围;首先,在Matlab中利用图像腐蚀方法得到马体轮廓,并在2D图像上精确定位马体坐标,获得体高、体长指标;然后,自定义胸径、管径指标,代入线性回归方程预测胸围、管围;最后利用Matlab GUI工具设计系统可视化界面,并初步完成系统的仿真测试;仿真结果表明,利用线性相关及线性回归理论解决3D指标的预测问题,具备测量依据和借鉴意义。     

Realtime 3D profile measurement by using the composite pattern based on the binary stripe pattern

In this paper, a one-shot composite pattern based on three-step binary stripe pattern is developed to meet the demand of real-time 3D shape measurement for complicated objects. Theoretical analysis and numerical simulation prove that the proposed pattern can provide higher accuracy than the composite pattern based on the traditional three-step phase shifting. Furthermore, the significant advantage for the proposed composite pattern is that it can provide the unique location of the stripe boundary, resulting in the elimination of the ambiguity which usually arises for measurement of complicated object with the phase shifting method. The proposed composite pattern has been implemented to measure three different complicated objects. The results demonstrate that it is appropriate for the real-time 3D shape measurement.     

三维虚拟动态测量系统构建方法研究

针对传统二维测量系统存在测量精度较低、稳定性差的不足,提出一种基于数据交互的三维虚拟动态测量方法。该方法采用三维构型与总线技术同步耦合的工作方式,对三维测量系统中模型驱动的关键问题进行了研究,探讨了三维测量系统中数据交互解决方法的可行性,并将该方法应用于煤矿排水系统,完成了三维虚拟动态测量系统的开发。试验结果表明由该方法实现的三维虚拟动态测量系统具有运行稳定、操作简单、直观性强、可靠性高的优点,应用前景广阔。     

Three-dimensional image reconstruction of V-grooves for damage analysis

In this paper, a novel method for the analysis of damaged V-grooves is presented. An optical sectioning system and image processing software were developed to determine the width of V-grooves at various heights. We succeeded in constructing a three-dimensional (3D) topographic image, which enabled the estimation of damage in each region of the V-groove. The necessity of replacing damaged wire guide rollers can be determined according to whether the damage in the V-grooves exceeds a given threshold. By altering the sampling rate, the proposed system can achieve an optimal balance between resolution and measurement speed. The proposed innovations represent a novel solution for engineering inspection technology and related applications.     

单目多视点立体图像提取及应用

设计并实现了一种基于广角相机和平面镜的单目多视点立体图像摄像系统,给出了硬件装置的设计指标和优化方法;同时,在研究了硬件系统的标定方法基础上,实现了其在三维测距方面的应用。多枚平面镜构成的对称斗型腔体被放置在广角相机前面,物体光线经过不同平面镜反射后,投影到相机图像平面的不同区域,在相机投影平面上生成物体多个影像,形成单目多视点投影图像。该类图像等价于视点不同的多幅图像,可以使用多视点立体视觉算法实现三维测量。     

一种单双目视觉系统结合的三维测量方法

在投影栅相位法的单日和双目三维测量结构的基础上,提出了一种单双目结合的三维测量方法.采用双目测量系统的架构,对两相机的公共区域使用双目的方法进行复现,同时分别将两个相机与投影仪组成两个单目测量系统,通过标定的统一可以将两者的世界坐标系统一到一个共同的基准上,利用单目的测量结果对双目测量的哪缺失区域进行填补.在对石膏头像的测量中,利用该方法避免了双目测量中在鼻梁附近出现的数据丢失.在保证双目复现区域精度的基础上,该方法有效地改进了测量结果的完整性.