点激光测头激光束方向标定

为了使点激光测头能在任意方向上实现测量功能,提出一种逆向工程中标定激光束方向的方法,设计了一种标定面方向可调的标定块配合标定。标定过程中,让激光测头在标定面上分别沿X、Y、Z3个轴方向做等间距运动,根据进给步长与激光束长度变化量之间的关系确定激光束的方向。以三坐标测量机为平台,给出了以任意方向安置点激光测头时,测量值从传感器坐标系到基准坐标系的转换过程,并对标定算法及整个标定过程进行了详细描述。最后,通过与接触式测量进行对比实验,验证标定后点激光测头的测量效果。实验结果表明,用该方法标定的点激光测头在3σ范围内沿任意方向的测量误差为(0.0452±0.0168)mm,满足逆向工程的测量要求。     

基于图象处理的复杂指针式仪表的识别

根据仪表的结构特点,提出了复杂的指针式仪表的识别方法.对实现其功能的主要方法做了介绍,如阈值迭代二值化、边界跟踪、Hough变换的目标信息的提取、模板匹配.     

Influence of flow disturbances on the performance of industry-standard LNG flow meters

In the last decade significant progress has been achieved in the development of measurement traceability for LNG inline metering technologies such as Coriolis and ultrasonic flow meters. In 2019, the world's first LNG research and calibration facility has been realised thus enabling calibration and performance testing of small and mid-scale LNG flow meters under realistic cryogenic conditions at a maximum flow rate of 200 m³/h and provisional mass flow measurement uncertainty of 0.30% (k = 2) using liquid nitrogen as the calibration fluid. This facility enabled, for the first time, an extensive test programme of LNG flow meters under cryogenic conditions to be carried out to achieve three main objectives; the first is to reduce the onsite flow measurement uncertainty for small and mid-scale LNG applications to meet a target measurement uncertainty of 0.50% (k = 2), the second is to systematically assess the impact of upstream flow disturbances and meter insulation on meter performance and the third is to assess transferability of meter calibrations with water at ambient conditions to cryogenic conditions. SI-traceable flow calibration results from testing six LNG flow meters (four Coriolis and two ultrasonic, see acknowledgment section) with water in a water calibration facility and liquid nitrogen (LIN) in the LNG research and calibration facility under various test conditions are fully described in this paper. Water and LIN calibration data were compared and it was observed that the influence of removing the meter insulation on mass flow rate measurement accuracy can be more significant (meter error > ±0.50%) than the influence of many typical upstream disturbances when the meter is preceded by a straight piping length equal to twenty pipe diameters (20D) with no additional flow conditioning devices, in particular for ultrasonic meters. The results indicate that the correction models used to transfer the water calibration to cryogenic conditions (using LIN) can potentially result in mass flow rate measurement errors below ±0.5%, however, the correction models are specific to the meter type and manufacturer. This work shows that the target measurement uncertainty of 0.50% can be achieved if the expanded standard error of the mean value measured by the meter is smaller than 0.40% (k = 2). It is planned to repeat these tests with LNG in order to compare the results with the LIN tests presented in this paper. This may reveal that testing with an explosion safe and environmentally friendly fluid such as LIN produces representative results for testing LNG flow meters.     

通用机器人视觉检测系统的全局校准技术

介绍了基于通用机器人的车身在线柔性视觉检测系统的工作原理和在复杂现场环境下使用激光跟踪仪和测量臂进行全局校准的实用方法。基于测量姿态的全局校准方法利用机械约束将传感器坐标系和靶标坐标系统一起来,实现测量姿态时传感器坐标系与系统基准坐标系的坐标转换。基于机器人运动学模型的全局校准方法利用机器人末端关节位姿可通过正向运动学获知的特点,在现场构建机器人基坐标系,并通过坐标变换获得与机器人运动精度无关的手眼关系,实现了任意姿态时的全局校准。实际测量的结果表明,应用两种校准方法后系统的重复性精度都十分理想,测量装置重复测量标准差和系统重复测量标准差分别为0.07mm和0.13mm,能够满足在线监控白车身加工尺寸变化的精度要求;系统进行坐标测量时的误差分别为±0.2mm和±0.8mm。     

变电站指针式仪表检测与识别方法

受限于复杂的电磁环境,变电站中的大量模拟式仪表需要人工读取示数,不利于变电站自动化管理。而目前针对仪表自动读数方法的研究大多基于预先获取到的高质量图像,其中仪表目标位于图像中央且占比较大,仪表表盘与相机平面平行,这需要大量预先的仪表测量与相机标定工作,不能满足实际电站环境下的使用要求。为解决上述问题,提出了一种完整的变电站指针式仪表的自动检测与识别方法。首先利用卷积神经网络模型检测当前视野下仪表目标的包围框位置,计算其距离视野中央的偏离值与图像占比,据此调整相机位置和缩放倍数。通过透视变换消除表盘平面与相机平面偏差造成的仪表图像畸变,通过霍夫变换检测仪表的表盘与指针,完成仪表读数识别。变电站实际测试实验结果表明,本方法最大读数误差仅为1.82%,对于复杂背景下多类别仪表的自动检测与识别任务具有良好的准确性与稳定性,可满足变电站实际应用需求。     

Water meter pointer reading recognition method based on target-key point detection

With the rapid development of video image technology and fifth-generation mobile network technology, the automatic verification of mechanical water meters has become an increasingly important topic in smart cities. Although much research has been done on this subject, the efficiency and accuracy of existing water meter pointer reading technology can still be improved. This paper proposes a new water meter pointer reading recognition method based on target-key point detection. Our method consists of a target detection module and a key point detection module. The target detection module uses a modified YOLOv4-Tiny network to detect and classify the areas where the dials and pointers are located in water meter images with distinct characteristics. The key point detection module is used to detect the key point of the pointer image. In this module, the structure of the RFB-Net network is improved to introduce multiple layers of low-level feature information, therefore, it can make full use of the information between multi-scale feature layers for key point detection. In addition to, aiming at the problem of dial rotation, a method of establishing a right-angle coordinate system based on key point is proposed to realize pointer reading. The whole method proposed in this paper is compared to the Hough transform feature matching algorithm and traditional machine learning algorithms through experiments which test the detection and recognition of the water meter dial, pointer and key points. The experiment results show that the missed detection rate of the model in this paper is 1.88% and 1.07% for the dial region and the pointer region, respectively. And the accuracy rate reaches 98.68%, the average processing time per image is 0.37 s. This implies that the water meter inspection task is completed quickly and accurately with strong robustness. Thanks to the lightweight algorithm of our approach, the model can also be fully automated and easily deployed on mobile devices.     

基于三点透视模型的线结构光系统标定方法

针对现有线结构光传感系统标定过程中对设备要求高、标定过程繁琐等问题,提出一种基于三点透视模型的快速标定方法。引入一个可自由移动的平面靶标,靶标上只需要共线、且相互位置确定的三个特征点,利用共线三点建立三点透视数学模型,根据三个特征点以及光条纹在摄像机像面的成像信息,就可以获取光平面上标定点在摄像机坐标系下的坐标。平面靶标在视觉范围内任意移动几个位置,得到光平面上多个标定点坐标,从而确定光平面方程。实验证明,该方法平均相对测量误差小于0.8%。该方法不需要昂贵的辅助调整设备,也不需要求解坐标系之间的转换矩阵,简单、快速,适合现场标定。     

Water density formulations and their effect on gravimetric water meter calibration and measurement uncertainties

In the gravimetric calibration method of water meters, the volume of water that has passed through the equipment under test (EUT) is generally collected into a tank and the quantity (mass) determined by weighing. The mass of water collected is then converted into a volume. This conversion of mass into volume requires knowledge of the water density, which can be estimated, measured directly or determined by other means. The error of measurement of the EUT is determined by comparing the volume recorded by the EUT and the volume collected in the tank. The density of water is, therefore, one of the major causes of measurement uncertainty in laboratory calibration of water meters using the gravimetric method. Water meter calibration facilities commonly use density formulations proposed by the International Standards Organisation (ISO) and the Organisation for International Legal Metrology (OIML). In Australia, additional guidance in water density determination is provided by the National Measurement Institute (NMI). In this study, testing was undertaken using ten positive displacement water meters arranged in series in the test rig to evaluate some of the common water density formulations used in Australia. The effect of these different formulations on the water meter error measurement was determined, as well as the effect on the measurement uncertainties. The results shows that the use of these different density formulations evaluated do not significantly affect the water meter error of measurement or the uncertainty of measurement. There was no apparent correlation between the water meter error and the meter position in the test rig. It was also determined that if the water density was adjusted only for temperature effects, a maximum of 0.05 and 0.15% drift in meter error and measurement uncertainty respectively, can be expected.     

一种应用于视觉测量标定的亚像素级特征点提取算法

在应用视觉测量系统时 ,视觉传感器的标定是必要的步骤 ;当采用标定图案标定时 ,角点图像坐标的提取精度会影响最终标定的结果 ,方法的易操作性也会影响该项技术的应用 ;本文提出一种基于亚像素级的特征点提出方法 ,该方法的主要思想是先采用了自动提取的初始点为引导进行边缘提取和哈夫变换 ,再通过直线拟合求交的方法获得角点的精确坐标     

A study on a vision sensor system for tracking the I-Butt weld joints

In this study, a visual sensor system for weld seam tracking the I-butt weld joints in GMA welding was constructed. The sensor system consists of a CCD camera, a diode laser with a cylindrical lens and a band-pass-filter to overcome the degrading of image due to spatters and arc light. In order to obtain the enhanced image, quantitative relationship between laser intensity and iris opening was investigated. Throughout the repeated experiments, the shutter speed was set at 1/1000 second for minimizing the effect of spatters on the image, and therefore the image without the spatter traces could be obtained. Region of interest was defined from the entire image and gray level of the searched laser stripe was compared to that of weld line. The differences between these gray levels lead to spot the position of weld joint using central difference method. The results showed that, as long as weld line is within ±15° from the longitudinal straight line, the system constructed in this study could track the weld line successfully. Since the processing time is no longer than 0.05 sec, it is expected that the developed method could be adopted to high speed welding such as laser welding.     

三坐标测量机驱动的摄像机标定技术

为了降低摄像机的标定费用和提高标定精度,提出了一种基于三坐标测量机平动的摄像机标定技术,对该技术的原理、数学模型、标定步骤和标定精度进行了研究。根据摄像机标定的基本原理,利用三坐标测量机沿X、Y、Z轴移动和正交精度都很高的特点,以三坐标测量机带动待标定摄像机产生和白色陶瓷标准球球心(标定特征点)在X、Y、Z轴方向上的相对平动,得到标定特征点在测头坐标系中不同位置的坐标;在每一个确定位置,摄像机拍摄标定特征点的像,经图像处理后,计算出像点在计算机帧存坐标系中的坐标。引入测头坐标系,建立了该项摄像机标定技术的数学模型,给出了标定步骤,组建了标定系统。比对标定实验结果表明,基于三坐标测量机平动的摄像机标定系统与专用标定系统的标定精度相当,数据相差在±1μm以内,满足工程实际精度要求,成本低、标定效率高。     

基于线结构光参考平面的多摄像机标定方法研究

多摄像机视觉测量系统中不同视觉传感器空间分布广,无公共视角,现场标定十分困难。针对多摄像机标定问题,研究了一种基于线结构光参考平面的灵活标定方法。标定过程中,以空间中同时覆盖相邻摄像机视角的结构光平面作为标定参考基准,在不同摄像机视角中,自由移动平面靶标多次,确保每次移动后靶标与结构光相交,并能在各自摄像机中清晰成像,摄像机拍摄靶标图像。提取靶标图像中角点坐标、激光光条特征点坐标。借助靶标平面与摄像机坐标系外部参数矩阵,求解激光光条特征点在对应摄像机坐标系中坐标。通过结构光基准平面内,不同摄像机坐标系中至少3组非共线特征点坐标信息,求解相邻摄像机外部参数。分别进行标定试验和精度验证试验,试验结果表明该方法切实可行。     

基于激光三角法和嵌入式的微位移实时检测系统

基于激光三角法和嵌入式的微位移实时检测技术,采用激光三角法测距和灰度重心法提取激光条纹中心的原理,使线结构光、透镜、CCD位置信息满足Scheimpflug共轭清晰成像条件。通过图像处理获取像面坐标系位移信息,得到待测物体物面坐标系的位移,利用灰度重心法实时提取结构光条纹中心的特点,结合嵌入式系统尺寸小、稳定、便携的特性,实现对待测物体进行实时、非接触和微位移测量。     

Calibration and analysis of eccentric error of the laser rotary-scanning measurement system

A laser rotary-scanning measurement system was developed for the reverse engineering of 360° objects. The system is constructed by an optical head and a rotary indexing. The optical head is composed of a laser diode strip-light projector and dual CCD cameras. Based on the principle of structured-light triangulation, a laser line is projected onto the object upon which the distorted line is captured by dual CCD cameras from left and right simultaneously. By processing a series of line fittings from the discrete angular positions of an object, the entire 3D profile can be reconstructed. Since the actual space coordinates of the object are computed according to the geometric relationship between the coordinate of optical head system and the coordinate of the rotary indexing systems, if these two coordinate systems are not in good alignment, errors in the computed coordinates will be introduced.This paper describes the influences of the alignment and eccentricity errors of the laser rotary-scanning measurement system on the computed geometrical profile. Calibration procedures are then proposed to adjust the alignment to avoid image distortions and thus enhance the system accuracy. Experimental results show that this easy-to-use calibration procedure can significantly improve the accuracy of the system.     

In-situ water level measurement using NIR-imaging video camera

Water level is a critical component for observation and management of water resources. Since video surveillance is becoming a standard configuration of gauging stations, more attentions have been paid on the image-based water level measurement techniques in recent years. Instead of human eyes, images of staff gauge can be captured by a camera and automatically processed to detect the readings of water line. However, it is quite unreliable to identify the readings on staff gauges due to low imaging resolution, tilt viewing angle and complex illumination in field conditions. For that reason, most of the existing methods failed to make effective automatic measurements in practice. To resolve difficulties of poor visibility, image distortions and ambient noises in in-situ water level measurement with standard bicolor staff gauges, an all-weather, real-time and automatic flow measurement system using single near infrared (NIR)-imaging video camera is developed. Lab and in-situ experiments demonstrate that NIR-imaging is efficient to enhance image contrast and suppress reflection noises on the water surface, which successfully overcomes the limitation of water line detection with current visible light (VIS)-imaging systems in clear water and low velocity conditions. The proposed water level conversion method is based on image ortho-rectification. It requires no on-site calibration by utilizing natural corresponding points to build the perspective transformation between the staff gauge Region of Interest (ROI) and an orthographic template image. The measurement resolution of water level (1 mm) is controlled by the physical resolution (1 mm/pixel) of the template. The proposed water line detection approach is integrated by a series of algorithms: the Order-Statistic Filtering for adaptive thresholding, the Morphological Opening Operation for local noise suppression, the Multi-points Continuity Criterion for water line locating and the Median Filtering for random noise elimination. It overcomes the deficiency of traditional Otsu method for images with uneven illumination. The reliability of system under various weather and illumination conditions is proved with water level accuracy up to 1 cm and Effective Data Ratios up to 95%.     

A flexible method for multi-view point clouds alignment of small-size object

Alignment is a key step of the point cloud processing. We propose a flexible, easy-implemented, low-cost alignment method for multi-view point clouds of small-size objects (≦50 cm). The method is based on the idea of rotating measurement, firstly more than three pieces of point clouds of cylinder calibration pattern are used for calibrating the center axis of a single-axis turntable in the scanner’s coordinate system, so the rigid relationship of the turntable and scanner can be obtained. Then the rotation matrix can be calculated using the known angle parameter of the turntable, and finally an arbitrary view of point cloud can be easily transformed into a unified coordinate system by the rotation transformation. Our method does not require overlapping feature or co-markers constraint between point clouds, and only the rigid relationship between the scanner and the turntable and rotate angle need to be known. More importantly, the calibration of the turntable is flexible and low-cost: (1) the calibration pattern can be a common cylinder objects (such as cup, paper tube, caddy, water pipe, etc.), (2) the turntable and the alignment method can be integrated with variety 3-D scanners. The result of experiment has demonstrated the efficiency and automatic characteristic of the alignment method compared with other two convention methods.     

In-situ calibration of permanent magnet flow meters in PFBR using noise analysis technique

In Fast Breeder Reactor sodium circuits, permanent magnet flow meters (PMFM) are extensively used to measure the liquid sodium flow rate. The performance of PMFM can degrade with respect to time due to various reasons. This degradation results in reduction in output voltage and affects flow meter stability. The distortion of the magnetic field in the large diameter flow meters makes its characteristics nonlinear. Further, the performance of the flow meter is also affected by vibrations, shocks, temperature and change of reluctance within the magnetic circuit. Hence, it is desirable to calibrate the PMFM at periodic time intervals for ensuring accuracy and stability. However, it is very difficult and almost impossible to calibrate large size flow meters once installed in the system under actual flow conditions in a sodium test loop. Therefore, it is necessary to calibrate the flow meter in-situ without disturbing its normal operating conditions.Experiments were carried out in different sodium loops in Fast Reactor Technology Group (FRTG) and Fast Breeder Test Reactor (FBTR) with permanent magnet flow meters of different sizes to develop an in-situ calibration procedure. Cross-correlation technique is studied and the flow rate is estimated from the transit time with a deviation of ±5.5%, which is comparable with that of calibration of the flow meter in actual sodium test loop. In this paper, in-situ calibration of PMFM is discussed with experimental details, data acquisition, cross-correlation technique and the results obtained.     

基于视频图像的工业仪表高速自动识别

针对工业现场高速变化的灯板仪表全自动检测的问题,提出了一种基于图像识别的检测方法。本方法采用高速工业相机获取仪表视频图像,并采用数字图像处理技术,对单帧图像用OSTU算法进行二值化分割,运用邻域平均法进行平滑处理,通过闭运算以完成去噪,运用Hough变换以实现对灯的逐一定位,并用灰度检测法对灯状态进行判读,最后保存视频。研究结果表明,该算法可靠有效,系统能够高速准确地应对仪表位置的变化,为进一步的一般化视频检测奠定了基础。     

焊接模型的非线性方程组参数估计法

图像的标定就是确定世界坐标系和图像坐标系的几何关系。在透视光变换模型的基础上,运用非线性方程组参数估计中的牛顿法对焊接模型进行了重新标定。通过对非线性估计法实验数据的分析可以看出,当图像有干扰时,标定的参数值能够最大限度地接近真实值,用估计法求解降低了传统标定过程中因过参数化而导致的求解结果误差较大的问题,为进一步的自动焊缝跟踪提供了准确的焊缝尺寸信息。     

大轴弯曲激光精密自动测量系统

提出了用激光扫描技术测量汽轮机转子弯曲量的新方法。测量系统用平面转镜进行扫描,采用双狭缝进行扫描自校准,由光电探测器完成光电转换,最后由微机完成数据处理、显示及打印。实验表明,该系统能远距离非接触测量大轴弯曲,测量精度达±5μm,测量距离达4m。