CN101566461B - Method for quickly measuring blade of large-sized water turbine - Google Patents

Method for quickly measuring blade of large-sized water turbine Download PDF

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CN101566461B
CN101566461B CN2009100225767A CN200910022576A CN101566461B CN 101566461 B CN101566461 B CN 101566461B CN 2009100225767 A CN2009100225767 A CN 2009100225767A CN 200910022576 A CN200910022576 A CN 200910022576A CN 101566461 B CN101566461 B CN 101566461B
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blade
point
points
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point cloud
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CN101566461A (en
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梁晋
刘建伟
肖振中
唐正宗
史宝全
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Xian Jiaotong University
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Abstract

The invention discloses a method for quickly measuring a blade of a large-sized water turbine, which is characterized by comprising the following steps: firstly, sticking a mark point to the surface of the blade, then shooting a group of photos from different angles as measured primary data, and inputting the data to a computer to carry out analytic processing; by carrying out image detection for the group of photos in a measurement software, identifying the mark point in each photo and positioning the center of the mark point, and matching the mark points with the same name; finally, reconstructing a three-dimensional coordinate of corresponding object points according to a plurality of two-dimensional coordinates of the mark points, fitting a sparse framework model of a target by the reconstructed three-dimensional mark points, then scanning the surface of the blade block by block by using a binocular grating scanning method to acquire a local dense point cloud, and aligning the dense point cloud to an overall coordinate system according to the local mark points to acquire a dense point model of the blade; and by comparing the dense point model with a CAD designed model after aligning, calculating a three-dimensional processing error of the surface of a workpiece.

Description

大型水轮机叶片快速测量方法 Rapid Measuring Method for Large Water Turbine Blades

技术领域technical field

本发明涉及一种对大型水轮机叶片进行快速测量的方法,特别涉及一种应用视觉测量技术对中大型水轮机叶片尺寸及型面进行快速测量的方法。The invention relates to a method for rapidly measuring blades of large water turbines, in particular to a method for rapidly measuring the size and profile of blades of medium and large water turbines using visual measurement technology.

背景技术Background technique

对于造价昂贵的大型水轮机组,叶片是水轮机的“心脏”,其表面的质量及制造精度将直接影响到整个机组的水力性能、发电效率、运转的稳定性及使用寿命。但由于大型水轮机叶片的型面为复杂的自由曲面,其体积和重量庞大,因此在制造和加工的过程中,对叶片外型尺寸及型面的全尺寸检测一直是业内的一个难题。For expensive large hydro turbine units, the blade is the "heart" of the hydro turbine, and its surface quality and manufacturing precision will directly affect the hydraulic performance, power generation efficiency, operation stability and service life of the entire unit. However, since the profile of the large water turbine blade is a complex free-form surface, its volume and weight are huge, so in the process of manufacturing and processing, the full-scale detection of the overall size and profile of the blade has always been a difficult problem in the industry.

文献“水轮机转轮检修装备的研究现状及发展趋势”(何清华等,大电机技术,2003)总结了当前大型水轮机叶片检测中几种主要的方法,按使用的设备仪器不同有:立体样板法、样板法、梳齿法、三坐标测量机法、机械臂法、激光干涉仪法、光电径纬仪法、激光跟踪仪法、光切法以及水下摄影法等。立体样板法所使用的组合样板为手工制造,刚性差、容易变形,已逐步被淘汰。三坐标测量机虽然精度高,但对测量环境要求高、不便携、测量范围小;特别是巨型三坐标机极其昂贵,水轮机叶片在三坐标机台上摆放调整困难,前期还需要耗时进行检测坐标系的建立及测量编程。关节臂、激光跟踪仪、经纬仪可以在现场进行高精度测量,但由于是逐点测量方式,测量效率偏低,无法达到全尺寸反求设计和生产检测所需的密集点云采集要求。因此目前的研究热点集中于融合计算机视觉技术和摄影测量技术的非接触式光学测量方法,这种方法有着严谨的理论基础,量程具有较大的弹性,并能提供相当高的精度和较高的测量效率,是解决中大型工件三维全尺寸检测难题一种可行的方案。The literature "Research Status and Development Trends of Hydraulic Turbine Runner Maintenance Equipment" (He Qinghua et al., Large Motor Technology, 2003) summarizes several main methods in the current large-scale hydraulic turbine blade inspection. According to the equipment used, there are three-dimensional model method , template method, comb method, coordinate measuring machine method, mechanical arm method, laser interferometer method, photoelectric pathodolite method, laser tracker method, light section method and underwater photography method, etc. The combined template used in the three-dimensional template method is hand-made, has poor rigidity and is easy to deform, and has been gradually eliminated. Although the three-coordinate measuring machine has high precision, it has high requirements on the measurement environment, is not portable, and has a small measurement range; especially the giant three-coordinate measuring machine is extremely expensive, and it is difficult to place and adjust the turbine blades on the three-coordinate machine, which requires time-consuming work in the early stage Establishment of detection coordinate system and measurement programming. The articulated arm, laser tracker, and theodolite can perform high-precision measurement on site, but due to the point-by-point measurement method, the measurement efficiency is low, and it cannot meet the dense point cloud collection requirements required for full-scale reverse design and production inspection. Therefore, the current research hotspots are focused on the non-contact optical measurement method that integrates computer vision technology and photogrammetry technology. Measurement efficiency is a feasible solution to solve the problem of 3D full-scale inspection of medium and large workpieces.

基于计算机视觉方法的检测系统是指利用CCD摄像机作为图像传感器,综合运用图像处理、精密测量等技术进行非接触二维或者三维坐标测量的检测系统。文献“视觉测量技术及应用”(叶声华院士,中国工程科学,1999)总结了视觉测量技术发展的不同方向及其应用领域,提出了几种视觉检测原型系统。但由于计算机运算速度和图像获取精度等条件的限制,并没有实际的检测系统被应用。A detection system based on computer vision methods refers to a detection system that uses a CCD camera as an image sensor and comprehensively uses image processing, precision measurement and other technologies for non-contact two-dimensional or three-dimensional coordinate measurement. The document "Visual Measurement Technology and Application" (Academician Ye Shenghua, China Engineering Science, 1999) summarizes the different directions of development of visual measurement technology and its application fields, and proposes several prototype systems of visual inspection. However, due to the limitations of computer computing speed and image acquisition accuracy, no actual detection system has been applied.

近几年,由于计算机技术和有关光学、数字图像处理、计算机视觉理论等方面的光电技术不断发展,研究基于光学、数字图像处理和计算机视觉理论的大型复杂曲面三维测量已成为可能。因此,研究新的基于光学、数字图像和视觉信息融合的大型复杂曲面便携式快速三维测量方法,并将检测步骤、数据处理等标准化,即具有重要的理论意义,又具有重大的实用价值。In recent years, due to the continuous development of computer technology and optoelectronic technology related to optics, digital image processing, and computer vision theory, it has become possible to study 3D measurement of large and complex surfaces based on optics, digital image processing, and computer vision theory. Therefore, it is of great theoretical significance and great practical value to study a new portable and rapid three-dimensional measurement method for large and complex surfaces based on the fusion of optics, digital images and visual information, and to standardize the detection steps and data processing.

发明内容Contents of the invention

针对大型水轮机叶片在加工过程中的型面及尺寸的检测问题,如何在保证精度满足要求的前题下,提高检测的速度,降低测量成本,如何实现现场检测及避免环境中振动、温度变化、湿度、粉尘等干扰。本发明提出了一种基于摄影测量和立体视觉原理的光学测量方法,并经过实验验证,能够对大型水轮机叶片尺寸及型面进行现场快速测量。Aiming at the detection of the shape and size of large turbine blades during processing, how to improve the speed of detection and reduce the cost of measurement under the premise of ensuring that the accuracy meets the requirements, how to realize on-site detection and avoid vibration, temperature changes, Humidity, dust and other interference. The invention proposes an optical measurement method based on the principle of photogrammetry and stereo vision, and through experimental verification, it can quickly measure the size and profile of large water turbine blades on site.

为达到以上目的,本发明是采取如下技术方案予以实现的:To achieve the above object, the present invention is achieved by taking the following technical solutions:

一种大型水轮机叶片快速测量方法,包括下述步骤:A method for quickly measuring blades of large water turbines, comprising the following steps:

第一步,在叶片的表面及其周围放置圆形标志点和带有环形编码的标志点,标志点包括编码点、非编码点;将标志点粘贴在磁性像胶垫上,并吸附在叶片表面,根据后边密集点云采集设备的要求间隔粘布置;The first step is to place circular markers and markers with ring codes on the surface of the blade and its surroundings. The markers include coded points and non-coded points; paste the markers on the magnetic rubber pad and absorb them on the surface of the blade , according to the requirements of the dense point cloud acquisition equipment behind the sticky layout;

第二步,放置全局标尺,标尺是恢复叶片实际尺寸的依据,其两端是固定好的编码标志点或非编码标志点,两端标志点之间的距离经过严格的校准;The second step is to place a global ruler, which is the basis for restoring the actual size of the blade. The two ends of the ruler are fixed coded or non-coded markers, and the distance between the markers at both ends is strictly calibrated;

第三步,采用专业数码相机,全方位对被测叶片进行拍照,获取包含编码标志点、非编码标志点、全局标尺信息的一组照片;The third step is to use a professional digital camera to take photos of the measured blade in all directions, and obtain a set of photos including coded marker points, non-coded marker points, and global scale information;

第四步,计算标志点坐标,运行测量软件,在计算机中导入所拍照片组,进行图像处理,测量出照片组中标志点的二维坐标,然后根据二维坐标计算出所有标志点在空间中的三维坐标,结果中非编码标志点点云即构成了被测叶片的全局稀疏点模型,该模型作为下一步局部密集点云采集后进行全局坐标对齐的依据;The fourth step is to calculate the coordinates of the marker points, run the measurement software, import the photo group into the computer, perform image processing, measure the two-dimensional coordinates of the marker points in the photo group, and then calculate the space of all the marker points according to the two-dimensional coordinates. The three-dimensional coordinates in the result, the non-coded landmark point cloud in the result constitutes the global sparse point model of the measured blade, which is used as the basis for global coordinate alignment after the local dense point cloud collection in the next step;

第五步,被测叶片表面密集点云采集及对齐,采用双目光栅扫描方法,用两摄相机同步拍摄由投影机投向物体表面的编码条纹,测量软件自动进行立体匹配和三维重建后获得叶片表面局部的标志点及密集点云,根据该局部的标志点在全局稀疏点模型的位置完成该局部密集点云的全局坐标对齐;重复采用上述双目光栅扫描方法得到所有已全局坐标对齐的局部密集点云。The fifth step is to collect and align dense point clouds on the surface of the measured blade. Using the binocular raster scanning method, two cameras are used to simultaneously capture the coded stripes projected from the projector to the surface of the object. The measurement software automatically performs stereo matching and 3D reconstruction to obtain the blade. The global coordinate alignment of the local dense point cloud is completed according to the position of the local landmark point and the dense point cloud on the surface of the global sparse point model; the above-mentioned binocular raster scanning method is used repeatedly to obtain all the local coordinates aligned with the global coordinates. Dense point cloud.

第六步,密集点云预处理及建模,由于得到的叶片密集点云模型有一定的数据冗余,在进行建模之前先对其进行处理,删除重叠部分点云,并将各局部密集点云进行合并,得到叶片外表面的整体密集点云模型,也即叶片测量模型;The sixth step is dense point cloud preprocessing and modeling. Since the obtained blade dense point cloud model has a certain amount of data redundancy, it should be processed before modeling, and the overlapping part of the point cloud will be deleted, and each part of the dense point cloud will be The point clouds are merged to obtain the overall dense point cloud model of the outer surface of the blade, that is, the blade measurement model;

第七步,将叶片测量模型与叶片CAD模型的坐标系对齐,对测量模型进行坐标转换;The seventh step is to align the blade measurement model with the coordinate system of the blade CAD model, and perform coordinate transformation on the measurement model;

第八步,叶片测量模型与叶片CAD模型对比,对两个模型进行简单的矢量减运算,即可得到叶片铸件表面每一个位置与设计模型的偏差,通过编程实现并以3D的形式显示,或借助商业对比软件根据各个位置和方向的剖面图,生成2D的偏差数据。The eighth step is to compare the blade measurement model with the blade CAD model, and perform a simple vector subtraction operation on the two models to obtain the deviation of each position of the blade casting surface from the design model, which is realized by programming and displayed in 3D, or With the help of commercial comparison software, 2D deviation data is generated according to the profile diagrams of various positions and directions.

上述方法中,所述第三步全方位对被测叶片进行拍照,设置摄像站位置采用三个依次增加的高度,每个高度均环绕360度,拍摄要求如下:In the above method, the third step is to take pictures of the measured blade in all directions, and set the position of the camera station to adopt three successively increasing heights, each of which surrounds 360 degrees, and the shooting requirements are as follows:

1)以叶片三维尺中最大值作为拍摄距离正直拍摄。1) Take the maximum value in the three-dimensional ruler of the blade as the shooting distance and shoot upright.

2)尽可能使每个标志点被4个以上不同位置的摄像站所拍摄。2) Try to make each marker point be photographed by more than 4 camera stations in different positions.

3)尽可能使每个标志点的交会角在60°~120°。3) Try to make the intersection angle of each marker point between 60° and 120°.

4)尽可能使每个标志点的入射角小于45°。4) Make the incident angle of each marker point smaller than 45° as much as possible.

5)尽可能使每个摄像站都能拍摄尽量多的标志点,保持相邻摄像站拍摄的照片间有60%以上的重叠和公共点。5) Try to make each camera station capture as many landmarks as possible, and keep more than 60% overlap and common points between the photos taken by adjacent camera stations.

所述第四步的测量照片组中标志点二维坐标,具体步骤如下:The two-dimensional coordinates of the marker points in the measurement photo group of the fourth step, the specific steps are as follows:

1)采用Canny算法检测图像中的边缘,得到单像素宽的闭合边缘集;1) Use the Canny algorithm to detect the edges in the image to obtain a closed edge set with a single pixel width;

2)用梯度幅值作为权值来计算沿梯度方向的位置加权值,对边缘位置沿梯度方向作子像素级校正:2) Use the gradient amplitude as the weight to calculate the weighted value of the position along the gradient direction, and perform sub-pixel level correction on the edge position along the gradient direction:

δdδd == ΣΣ ii == 11 nno gg ii dd ii ΣΣ ii == 11 nno gg ii ,,

其中,di是一个像素沿梯度方向与检测到的边缘点的距离,gi是梯度幅值;Among them, d i is the distance between a pixel and the detected edge point along the gradient direction, g i is the gradient magnitude;

3)采用圆度准则鉴别出边缘集中的椭圆,并利用如下先验信息去除不合条件的椭圆,包括椭圆的面积太小、椭圆轮廓呈凹性、非封闭性、与相邻椭圆距离太近;3) Use the circularity criterion to identify the ellipses in the edge concentration, and use the following prior information to remove unqualified ellipses, including the area of the ellipse is too small, the ellipse outline is concave, non-closed, and the distance between the ellipse and the adjacent ellipse is too close;

4)两次采用最小二乘法拟合出椭圆的中心,第一次拟合后去除掉距离大于3倍标准差的边缘,再进行第二次拟合;4) The center of the ellipse is fitted twice using the least squares method, and the edges whose distance is greater than 3 times the standard deviation are removed after the first fitting, and then the second fitting is performed;

5)判断椭圆外围是否有环带,如果没有即为非编码点;如果有则径向作内外边界的连线,在连线上等距离采样5次,以5次采样的中值与标记点的灰度阀值作比较,大于阀值则本环带的编码为1,否则为0;每36°(对应于10位编码点)重复上述操作,旋转一周后得到形如“0100100111”的二进制编号;5) Determine whether there is a ring on the periphery of the ellipse, if not, it is a non-coded point; if there is, make a radial connection between the inner and outer boundaries, and sample 5 times at equal distances on the connection, and use the median value of the 5 samples to match the marked point If it is greater than the threshold, the code of this ring is 1, otherwise it is 0; repeat the above operation every 36° (corresponding to 10-bit code points), and after one rotation, a binary format like "0100100111" is obtained serial number;

6)查表得到编码点的ID,如果查不到则看作非编码点。6) Look up the table to obtain the ID of the code point, if it cannot be found, it is regarded as a non-code point.

与现有技术的立体样板法、激光跟踪仪法、关节臂法等相比,本发明基于视觉测量方法具有如下优点:Compared with the three-dimensional template method, laser tracker method, articulated arm method, etc. of the prior art, the present invention has the following advantages based on the visual measurement method:

1、由于采用CCD作为传感器,为非接触式测量方式,不会伤及叶片表面,也不受叶片表面形状及粗糙度的影响,也不会损耗测量设备。1. Since CCD is used as the sensor, it is a non-contact measurement method, which will not damage the surface of the blade, and will not be affected by the shape and roughness of the blade surface, and will not damage the measurement equipment.

2、由于采用逐区域扫描并由软件自动对齐,测量时间主要取决于叶片表面的分区块数,对大型叶片还可以采用多台扫描设备并行工作,相对于逐点测量方式,现场测量效率较高,后期的点云处理及模型对比可以离开现场处理。2. Due to the use of area-by-area scanning and automatic alignment by the software, the measurement time mainly depends on the number of partitions on the blade surface. For large blades, multiple scanning devices can also be used to work in parallel. Compared with the point-by-point measurement method, the on-site measurement efficiency is higher. , the later point cloud processing and model comparison can be processed off-site.

3、由于采用密集点云扫描方式,特别适用于叶片表面测量点众多的任务,测量结果是密集点云表示的叶片完整模型,可以在此基础上进行任意几何量的测量。3. Due to the dense point cloud scanning method, it is especially suitable for the task of measuring many points on the surface of the blade. The measurement result is a complete model of the blade represented by the dense point cloud, and any geometric quantity can be measured on this basis.

4、由于测量结果是完整的叶片三角面模型,在对比软件的帮助下,可以自动地进行全尺寸三维色谱分析、随意的定制偏差容限进行合格判定,检测结果直观、快捷。4. Since the measurement result is a complete triangular surface model of the blade, with the help of the comparison software, it can automatically perform full-scale three-dimensional chromatographic analysis and arbitrarily customize the deviation tolerance for qualification judgment, and the test results are intuitive and fast.

5、作为测量中间结果的叶片点云模型,可以作为原始数据,进行逆向工程设计。5. The blade point cloud model as the intermediate result of the measurement can be used as the original data for reverse engineering design.

6、由于采用CCD作为传感器,本方法中采用的测量设备价格便宜,测量成本低。6. Since the CCD is used as the sensor, the measuring equipment used in the method is cheap and the measuring cost is low.

附图说明Description of drawings

图1是本发明叶片测量安放基座图。Fig. 1 is a diagram of a blade measurement and placement base of the present invention.

图2是非编码标志点和编码标志点参考方案图。Fig. 2 is a diagram of a reference scheme of non-coded marker points and coded marker points.

图3是粘贴标志点后被测叶片的照片。Figure 3 is a photo of the tested blade after pasting the marker points.

图4是计算机生成的三维标志点叶片稀疏模型图。Fig. 4 is a diagram of a sparse model of a leaf with three-dimensional marker points generated by a computer.

图5是双目光栅扫描法采集系统原理图。Fig. 5 is a schematic diagram of the binocular raster scanning acquisition system.

图6是逐块表面密集点云采集及对齐的叶片模型照片。Fig. 6 is a photo of the blade model collected and aligned with dense point clouds on the surface piece by piece.

图7是密集点云预处理及建模后的叶片模型照片。Figure 7 is a photo of the blade model after dense point cloud preprocessing and modeling.

图8是叶片测量模型与设计模型的3D对比照片。Figure 8 is a 3D comparison photo of the blade measurement model and the design model.

图9是叶片某一剖面偏差的2D正面絮状照片。Figure 9 is a 2D frontal floc photo of a certain section deviation of the blade.

图10是图9叶片剖面偏差的2D侧面絮状照片。Fig. 10 is a 2D side flock photo of the deviation of the blade section in Fig. 9 .

图11是编码标志点编码环方案示意。Fig. 11 is a schematic diagram of the scheme of encoding mark point encoding loop.

图12是摄像站布置示图。Fig. 12 is an arrangement diagram of camera stations.

具体实施方式Detailed ways

以下结合附图及实施例对本发明作进一步的详细描述。The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

大型水轮机叶片尺寸及型面的一种快速检测方法:A rapid detection method for the size and profile of large turbine blades:

水轮机叶片的放置,水轮机叶片由于体积较大,部分位置壁厚较薄,自由态的放置会带来一定的形变,对测量结果有影响。而视觉测量需要从不同的位置对被测对象进行拍照,因此需要考虑叶片的放置方式。遵循原则:一是便于摄影拍照;二是不会产生形变而方便现场操作,提高效率。可以加工如图1的叶片测量基坐。基座可以重复使用。The placement of the turbine blades. Due to the large volume of the turbine blades and the thin wall thickness at some positions, the free placement will bring certain deformation and affect the measurement results. Visual measurements, on the other hand, require taking pictures of the measured object from different positions, so the placement of the blades needs to be considered. Follow the principles: first, it is convenient for taking pictures; second, it will not cause deformation, so it is convenient for on-site operation and improves efficiency. The blade measuring base as shown in Figure 1 can be processed. The base can be reused.

第一步:在叶片表面和周围布置标志点。标志点包括编码点、非编码点;使用圆形标志点可以获得比较高的定位精度。带有环形编码的标志点则可以方便识别其编号,选择合适的标志点图案及材料,由于叶片大多使用铸钢材料,因此可将标志点粘贴在磁性像胶垫上,方便布置和撤掉。并可重复使用。如图2所示。Step 1: Arrange marking points on and around the blade surface. Marker points include coded points and non-coded points; high positioning accuracy can be obtained by using circular marker points. Marking points with ring codes can easily identify their numbers, and choose the appropriate marking point pattern and material. Since the blades are mostly made of cast steel, the marking points can be pasted on the magnetic rubber pad for easy arrangement and removal. And can be used repeatedly. as shown in picture 2.

人工标志点要有明显的特征,本发明中标志点中心为实心圆,经过投影变换为椭圆,用来对标志点进行定位;编码标志其内部是一个非编码标志,外部有一个和中心的圆同心的扇环,如图11所示,根据编码规则的不同,编码标志又分为8位、10位、12位、14位、15位等几种编码,n位编码表示将外部的圆环等分成n份,每一位上若颜色和中心的圆同色,则编码为1,否则为0。另外,根据颜色的不同,又可以把编码标志以及非编码标志分成白底黑点标志和黑底白点标志。标尺是恢复叶片实际尺寸的依据,其两端是固定好的编码标志点或非编码标志点,两端标志点之间的距离经过严格的校准,并考虑温度的影响。布置标志点及标尺前应对叶片表面及周围进行清理,去除铁屑、油污等,保证标志点和标尺不会发生掉落及移位。The artificial marker point will have obvious features, and the center of the marker point in the present invention is a solid circle, which is transformed into an ellipse through projection, and is used to locate the marker point; the inside of the coded marker is a non-coded marker, and there is a circle with the center outside Concentric fan rings, as shown in Figure 11, according to different coding rules, the coding signs are divided into 8-bit, 10-bit, 12-bit, 14-bit, 15-bit and other codes, and the n-bit code means that the outer ring Divide into n equal parts, if the color of each bit is the same as the color of the center circle, it is coded as 1, otherwise it is 0. In addition, according to the different colors, coded signs and non-coded signs can be divided into black dot marks on white background and white dot marks on black background. The scale is the basis for recovering the actual size of the blade. Its two ends are fixed coded mark points or non-coded mark points. The distance between the mark points at both ends has been strictly calibrated and the influence of temperature is considered. Before arranging the marking points and scales, the blade surface and its surroundings should be cleaned to remove iron filings and oil stains, so as to ensure that the marking points and scales will not fall or shift.

如图3所示,在叶片表面均匀粘贴非编码点,点的密度应与双目光栅扫描设备的单次采集幅面相配合,保证每次扫描区域内至少有3~5个非编码点;在叶片表面均匀粘贴编码点,密度为非编码点密度的1/5~1/3;在叶片周围放置若干编码点,使全体标志点构成空间分布。As shown in Figure 3, non-coded points are evenly pasted on the surface of the blade, and the density of the points should match the single acquisition format of the binocular raster scanning equipment to ensure that there are at least 3 to 5 non-coded points in each scanning area; The coding points are evenly pasted on the surface of the blade, and the density is 1/5 to 1/3 of the density of non-coding points; a number of coding points are placed around the blade to make all the marking points form a spatial distribution.

第二步:在叶片周围放置与叶片尺寸相当的标尺,尽量使3个维度上都有标尺。Step 2: Place rulers around the leaves that are equivalent to the size of the leaves, try to make sure there are rulers in 3 dimensions.

第三步:拍摄全局标志点照片序列。环绕叶片从各个水平角度拍摄照片,摄像站位置设置可以参考图12。根据待测叶片尺寸将摄像站分布于三个水平高度,如高度为2m的叶片,可选择1m,2m,3m三个水平高度;每个高度旋转360度设置摄像站;为保证标志点三维坐标解算的精度,除了选择高分辨率、镜头畸变小的专业相机外,照片组拍摄原则如下:Step 3: Take a sequence of photos of global marker points. Take photos from various horizontal angles around the blades, and the position setting of the camera station can refer to Figure 12. According to the size of the blade to be measured, the camera stations are distributed at three horizontal heights. For example, for a blade with a height of 2m, three horizontal heights of 1m, 2m, and 3m can be selected; each height is rotated 360 degrees to set up the camera station; in order to ensure the three-dimensional coordinates of the marker points For the calculation accuracy, in addition to choosing a professional camera with high resolution and small lens distortion, the principles of photo group shooting are as follows:

3.1以叶片三维尺中最大值作为拍摄距离正直拍摄。3.1 Take the maximum value in the three-dimensional ruler of the blade as the shooting distance and shoot upright.

3.2尽可能使每个标志点被4个以上不同位置的摄像站所拍摄。3.2 Try to make each marker point be photographed by more than 4 camera stations in different positions.

3.3尽可能使每个标志点的交会角在60°~120°。3.3 Try to make the intersection angle of each marker point between 60° and 120°.

3.4尽可能使每个标志点的入射角小于45°。3.4 Try to make the incident angle of each marker point less than 45°.

3.5尽可能使每个摄站都能拍摄尽量多的标志点,保持相邻摄像站拍摄的照片间有60%以上的重叠和公共点。3.5 Try to make each camera station capture as many landmarks as possible, and keep more than 60% overlap and common points between the photos taken by adjacent camera stations.

第四步:测量照片组中标志点坐标。对得到的照片组先进行二维的图像处理,识别出每张照片中的标志点及编码,测量出各标志点的中心坐标,具体算法如下:Step 4: Measure the coordinates of the marker points in the photo group. Perform two-dimensional image processing on the obtained photo group first, identify the marker points and codes in each photo, and measure the center coordinates of each marker point. The specific algorithm is as follows:

4.1采用Canny算法检测图像中的边缘,得到单像素宽的闭合边缘集;4.1 Use the Canny algorithm to detect the edges in the image, and obtain a closed edge set with a single pixel width;

4.2用梯度幅值作为权值来计算沿梯度方向的位置加权值,对边缘位置沿梯度方向作子像素级校正:4.2 Use the gradient magnitude as the weight to calculate the weighted value of the position along the gradient direction, and perform sub-pixel level correction on the edge position along the gradient direction:

δdδd == ΣΣ ii == 11 nno gg ii dd ii ΣΣ ii == 11 nno gg ii ,,

其中,di是一个像素沿梯度方向与检测到的边缘点的距离,gi是梯度幅值。Among them, d i is the distance between a pixel and the detected edge point along the gradient direction, and g i is the gradient magnitude.

4.3采用圆度准则鉴别出边缘集中的椭圆,并利用如下先验信息去除不合条件的椭圆,包括椭圆的面积太小、椭圆轮廓呈凹性、非封闭性、与相邻椭圆距离太近。4.3 Use the circularity criterion to identify the ellipses in the edge concentration, and use the following prior information to remove unqualified ellipses, including the area of the ellipse is too small, the outline of the ellipse is concave, non-closed, and the distance to the adjacent ellipse is too close.

4.4两次采用最小二乘拟合出椭圆的中心,第一次拟合后去除掉距离大于3倍标准差的边缘,再进行第二次拟合。4.4 Use least squares to fit the center of the ellipse twice, remove the edges whose distance is greater than 3 times the standard deviation after the first fitting, and then perform the second fitting.

4.5判断椭圆外围是否有环带,如果没有即为非编码点;如果有则径向作内外边界的连线,在连线上等距离采样5次,以5次的采样的中值作与标记点的灰度阀值作比较,大于阀值则本环带的编码为1,否则为0;每36°(对应于10位编码点)重复上述操作,旋转一周后得到形如“0100100111”的二进制编号。4.5 Determine whether there is a ring on the periphery of the ellipse, if not, it is a non-coded point; if there is, make a radial connection between the inner and outer boundaries, sample 5 times at equal distances on the connection, and mark with the median of the 5 samples Point gray threshold for comparison, if it is greater than the threshold, the code of this ring is 1, otherwise it is 0; repeat the above operation every 36° (corresponding to 10-bit code point), and get a shape like "0100100111" after one rotation binary number.

4.6查表得到编码点的ID。如果查不到则看作非编码点。4.6 Look up the table to get the ID of the code point. If not found, it is regarded as a non-coding point.

第五步:计算标志点的三维坐标并建模。具体算法如下:Step 5: Calculate the three-dimensional coordinates of the marker points and model them. The specific algorithm is as follows:

5.1编码标志点根据唯一的ID号实现匹配。5.1 The coded markers are matched according to the unique ID number.

5.2根据共面方程实现各照片间的相对定向。5.2 Realize the relative orientation between each photo according to the coplanar equation.

5.3利用DLT法实现各照片的绝对定向。5.3 Use the DLT method to realize the absolute orientation of each photo.

5.4利用光束平差法实现相机的高精度标定。5.4 Use bundle adjustment method to achieve high-precision calibration of the camera.

5.5利用前方交会法计算编码标志点的三维坐标。5.5 Use the forward intersection method to calculate the three-dimensional coordinates of the coded marker points.

5.6利用多张照片外极线约束实现非编码标志点的匹配。5.6 Use the epipolar line constraints of multiple photos to realize the matching of non-coded landmark points.

5.7利用前方交会法计算非编码标志点的三维坐标。5.7 Use the forward intersection method to calculate the three-dimensional coordinates of the non-coded marker points.

5.8利用光束平差优化全部的解算结果。5.8 Use bundle adjustment to optimize all solution results.

5.9导出全部的三维非编码标志点,由此得到叶片的稀疏模型。5.9 Deriving all the three-dimensional non-coding marker points, thus obtaining the sparse model of the blade.

第六步:叶片局部密集点云采集及对齐。Step 6: Acquisition and alignment of local dense point clouds of blades.

采用双目光栅扫描方法,其系统原理如图5所示,左右两相机同步拍摄由投影机投向物体表面的编码条纹,测量软件自动进行立体匹配和三维重建后获得叶片表面局部的标志点及密集点云。根据该局部的标志点在全局稀疏点模型的位置完成该局部密集点云的全局坐标对齐。The binocular raster scanning method is adopted, and its system principle is shown in Figure 5. The left and right cameras simultaneously shoot the coded stripes projected by the projector onto the surface of the object, and the measurement software automatically performs stereo matching and 3D reconstruction to obtain local landmarks and density on the blade surface. point cloud. The global coordinate alignment of the local dense point cloud is completed according to the position of the local landmark point in the global sparse point model.

具体步骤如下:Specific steps are as follows:

6.1将非编码点云表示的叶片模型数据从摄影测量软件中导出,导入密积点云采集软件中,作为局部密集点云对齐时的参考。6.1 Export the blade model data represented by the non-coded point cloud from the photogrammetry software, and import it into the dense point cloud acquisition software as a reference for local dense point cloud alignment.

6.2撤去叶片表面粘贴的编码标志点,保留非编码标志点。6.2 Remove the coded marking points pasted on the blade surface, and keep the non-coding marking points.

6.3将双目光栅扫描设备正对叶片表面某区域,左右两相机拍摄两张局部照片,由于两相机相对位置及方向事先已标定出,为已知数据,因此根据空间前方交会法可计算出局部标志点的空间相对位置关系。6.3 Put the binocular grating scanning device facing a certain area on the blade surface, and the left and right cameras take two partial photos. Since the relative positions and directions of the two cameras have been calibrated in advance, they are known data, so the local area can be calculated according to the spatial forward intersection method. The spatial relative positional relationship of the marker points.

6.4调整双目光栅扫描设备与目标的相对位置,使得计算出的非编码标志点的数目多于3个。在三维空间,利用子图同构算法匹配区域标志点和全局关键点云:局部标志点表示为“子图”,待匹配的全局标志点云表示为“大图”,在“大图”中搜索同构子图。6.4 Adjust the relative position between the binocular raster scanning device and the target, so that the calculated number of non-coding marker points is more than three. In the three-dimensional space, use the subgraph isomorphism algorithm to match the regional landmark points and the global key point cloud: the local landmark points are represented as "subgraphs", and the global landmark point cloud to be matched is represented as "big picture", in the "big picture" Search for isomorphic subgraphs.

6.5匹配成功后,计算出区域到整体的旋转矩阵R和平移矩阵t。6.5 After the matching is successful, calculate the rotation matrix R and translation matrix t from the region to the whole.

6.6由投影装置向叶片局部投射编码结构光,左右相机同步拍摄序列照片,经过图像上处理,立体匹配,三维重建后生成局部的密集点云数据。如果叶片反射性能太差,则需要在扫描前喷涂显影剂。6.6 The projection device projects coded structured light to the blade part, and the left and right cameras take a sequence of photos synchronously. After image processing, stereo matching, and three-dimensional reconstruction, local dense point cloud data is generated. If the blade reflectivity is too poor, you need to spray developer before scanning.

6.7局部密集点云数据根据上一步中的旋转矩阵和平移矩阵[R|t]转换到全局坐标系下。6.7 The local dense point cloud data is transformed into the global coordinate system according to the rotation matrix and translation matrix [R|t] in the previous step.

6.8逐区域扫描得到整体密集点云模型。6.8 Scan area by area to get the overall dense point cloud model.

6.9移动光栅扫描设备,在保证不留缝隙的情况下,逐区域扫描叶片表面并自动对齐,得到有一定数据冗余的叶片整体密集点云模型。见图6。6.9 Mobile raster scanning equipment, under the condition of ensuring no gaps, scans the surface of the blade area by area and automatically aligns it to obtain an overall dense point cloud model of the blade with certain data redundancy. See Figure 6.

第七步:点云预处理及三角化建模。采用K平均聚类法进行多视点云重叠面的删除及数据融合处理。利用通用逆向工程软件(如Geomagic)对叶片点云模型进行降噪、去孤、平滑、抽稀后,进行三角化生成三角网络模型,最后对由标志点覆盖产生的空洞进行补洞处理。由此得到了叶片的整体三角网络模型,见图7。Step 7: Point cloud preprocessing and triangulation modeling. The K-means clustering method is used to delete the overlapping surfaces of the multi-view point cloud and to process the data fusion. Use general reverse engineering software (such as Geomagic) to perform noise reduction, de-isolation, smoothing, and thinning on the leaf point cloud model, then perform triangulation to generate a triangular network model, and finally fill in the holes generated by the marker point coverage. As a result, the overall triangular network model of the blade is obtained, as shown in Figure 7.

第八步:测量模型与CAD设计模型的坐标对齐。假如叶片在加工过程中有加工基准面,那么可以根据三个以上相互垂直的面确定叶片设计坐标系,将测量得到的标志点云模型根据“面——线——点”即“3-2-1”方式进行坐标转换,以便对齐到设计坐标系下。应在得到由标志点点云模型后,密集点云采集之前完成此项坐标转换。Step 8: Align the coordinates of the measurement model with the CAD design model. If the blade has a processing datum plane during processing, then the design coordinate system of the blade can be determined based on more than three mutually perpendicular surfaces, and the measured mark point cloud model is based on "surface-line-point" or "3-2 -1” mode for coordinate transformation in order to align to the design coordinate system. This coordinate transformation should be completed after obtaining the point cloud model from the landmark points and before collecting the dense point cloud.

如果待测叶片没有加工基准面,可以利用商用的对比软件(如GeomagicQualify)读入测量模型和设计模型,执行“最佳全局配准”命令,以完成两模型的最优匹配。If the blade to be tested has no processing datum plane, the measurement model and design model can be read in by commercial comparison software (such as GeomagicQualify), and the "best global registration" command can be executed to complete the optimal matching of the two models.

第九步:叶片测量模型与设计模型的偏差对比。Step 9: Comparison of the deviation between the blade measurement model and the design model.

将测量模型和设计模型对齐后,可编程或使用商业对比软件(如GeomagicQualify),运行“三维比较”命令,得到测量数据和叶片设计数模的三维色谱偏差,见图8。After aligning the measurement model with the design model, program or use commercial comparison software (such as GeomagicQualify) to run the "3D comparison" command to obtain the 3D chromatographic deviation of the measurement data and the blade design model, as shown in Figure 8.

根据工艺、检测要求进行任意关注位置的剖切,可以方便的得到叶片各位位置2D色片拍逆差絮状图,见图9、图10。According to the process and inspection requirements, any position of interest can be cut, and the 2D color film deficit flocculus of each position of the blade can be easily obtained, as shown in Figure 9 and Figure 10.

Claims (3)

1.一种大型水轮机叶片快速测量方法,其特征在于,包括下述步骤:1. A method for quickly measuring a large water turbine blade, is characterized in that, comprises the following steps: 第一步,在叶片的表面及其周围放置圆形标志点和带有环形编码的标志点,标志点包括编码点、非编码点;将标志点粘贴在磁性橡胶垫上,并吸附在叶片表面,根据后边密集点云采集设备的要求间隔粘贴布置;The first step is to place circular mark points and mark points with ring codes on the surface of the blade and its surroundings. The mark points include code points and non-code points; paste the mark points on the magnetic rubber pad and absorb them on the surface of the blade. Paste and arrange at intervals according to the requirements of the dense point cloud acquisition equipment behind; 第二步,放置全局标尺,标尺是恢复叶片实际尺寸的依据,其两端是固定好的编码标志点或非编码标志点,两端标志点之间的距离经过严格的校准;The second step is to place a global ruler, which is the basis for restoring the actual size of the blade. The two ends of the ruler are fixed coded or non-coded markers, and the distance between the markers at both ends is strictly calibrated; 第三步,采用专业数码相机,全方位对被测叶片进行拍照,获取包含编码标志点、非编码标志点、全局标尺信息的一组照片;The third step is to use a professional digital camera to take photos of the measured blade in all directions, and obtain a set of photos including coded marker points, non-coded marker points, and global scale information; 第四步,计算标志点坐标,运行测量软件,在计算机中导入所拍照片组,进行图像处理,测量出照片组中标志点的二维坐标,然后根据二维坐标计算出所有标志点在空间中的三维坐标,结果中非编码标志点点云即构成了被测叶片的全局稀疏点模型,该模型作为下一步局部密集点云采集后进行全局坐标对齐的依据;The fourth step is to calculate the coordinates of the marker points, run the measurement software, import the photo group into the computer, perform image processing, measure the two-dimensional coordinates of the marker points in the photo group, and then calculate the space of all the marker points according to the two-dimensional coordinates. The three-dimensional coordinates in the result, the non-coded landmark point cloud in the result constitutes the global sparse point model of the measured blade, which is used as the basis for global coordinate alignment after the local dense point cloud collection in the next step; 第五步,被测叶片表面密集点云采集及对齐,采用双目光栅扫描方法,用两摄相机同步拍摄由投影机投向物体表面的编码条纹,测量软件自动进行立体匹配和三维重建后获得叶片表面局部的标志点及密集点云,根据该局部的标志点在全局稀疏点模型的位置完成该局部密集点云的全局坐标对齐;重复采用上述双目光栅扫描方法得到所有已全局坐标对齐的局部密集点云;The fifth step is to collect and align dense point clouds on the surface of the measured blade. Using the binocular raster scanning method, two cameras are used to simultaneously capture the coded stripes projected from the projector to the surface of the object. The measurement software automatically performs stereo matching and 3D reconstruction to obtain the blade. The global coordinate alignment of the local dense point cloud is completed according to the position of the local landmark point and the dense point cloud on the surface of the global sparse point model; the above-mentioned binocular raster scanning method is used repeatedly to obtain all the local coordinates aligned with the global coordinates. Dense point cloud; 第六步,密集点云预处理及建模,由于得到的叶片密集点云模型有一定的数据冗余,在进行建模之前先对其进行处理,删除重叠部分点云,并将各局部密集点云进行合并,得到叶片外表面的整体密集点云模型,也即叶片测量模型;The sixth step is dense point cloud preprocessing and modeling. Since the obtained blade dense point cloud model has certain data redundancy, it should be processed before modeling, and the overlapping part of the point cloud will be deleted, and each part of the dense point cloud will be The point clouds are merged to obtain the overall dense point cloud model of the outer surface of the blade, that is, the blade measurement model; 第七步,将叶片测量模型与叶片CAD模型的坐标系对齐,对测量模型进行坐标转换;The seventh step is to align the blade measurement model with the coordinate system of the blade CAD model, and perform coordinate transformation on the measurement model; 第八步,叶片测量模型与叶片CAD模型对比,对两个模型进行简单的矢量减运算,即可得到叶片铸件表面每一个位置与设计模型的偏差,通过编程实现并以3D的形式显示,或借助商业对比软件根据各个位置和方向的剖面图,生成2D的偏差数据。The eighth step is to compare the blade measurement model with the blade CAD model, and perform a simple vector subtraction operation on the two models to obtain the deviation of each position of the blade casting surface from the design model, which is realized by programming and displayed in 3D, or With the help of commercial comparison software, 2D deviation data is generated according to the profile diagrams of various positions and directions. 2.如权利要求1所述的大型水轮机叶片快速测量方法,其特征在于,所述第三步全方位对被测叶片进行拍照,设置摄像站位置采用三个依次增加的水平高度,每个高度均环绕360度,拍摄要求如下:2. The method for rapidly measuring blades of large water turbines as claimed in claim 1, characterized in that, the third step is to take pictures of the blades to be measured in all directions, and the position of the camera station is set to adopt three successively increasing horizontal heights, each height All surround 360 degrees, and the shooting requirements are as follows: 1)以叶片三维尺中最大值作为拍摄距离正直拍摄;1) Take the maximum value in the three-dimensional ruler of the blade as the shooting distance and shoot upright; 2)使每个标志点被4个以上不同位置的摄像站所拍摄;2) Make each marker point be photographed by more than 4 camera stations in different positions; 3)使每个标志点的交会角在60°~120°;3) Make the intersection angle of each marker point between 60° and 120°; 4)使每个标志点的入射角小于45°;4) Make the incident angle of each marker point less than 45°; 5)使每个摄像站都能拍摄尽量多的标志点,保持相邻摄像站拍摄的照片间有60%以上的重叠和公共点。5) Each camera station can take as many landmarks as possible, and keep more than 60% overlap and common points between the photos taken by adjacent camera stations. 3.如权利要求1所述的大型水轮机叶片快速测量方法,其特征在于,所述第四步的测量照片组中标志点二维坐标,具体方法如下:3. the large water turbine blade fast measuring method as claimed in claim 1, is characterized in that, the two-dimensional coordinates of marker points in the measurement photo group of described 4th step, concrete method is as follows: 1)采用Canny算法检测图像中的边缘,得到单像素宽的闭合边缘集;1) Use the Canny algorithm to detect the edges in the image to obtain a closed edge set with a single pixel width; 2)用梯度幅值作为权值来计算沿梯度方向的位置加权值,对边缘位置沿梯度方向作子像素级校正:2) Use the gradient amplitude as the weight to calculate the weighted value of the position along the gradient direction, and perform sub-pixel level correction on the edge position along the gradient direction: δdδd == ΣΣ ii == 11 nno gg ii dd ii ΣΣ ii == 11 nno gg ii ,, 其中,di是一个像素沿梯度方向与检测到的边缘点的距离,gi是梯度幅值;Among them, d i is the distance between a pixel and the detected edge point along the gradient direction, g i is the gradient magnitude; 3)采用圆度准则鉴别出边缘集中的椭圆,并利用如下先验信息去除不合条件的椭圆,包括椭圆的面积太小,椭圆轮廓呈凹性、非封闭性,与相邻椭圆距离太近;3) Use the roundness criterion to identify the ellipses in the edge concentration, and use the following prior information to remove unqualified ellipses, including that the area of the ellipse is too small, the ellipse outline is concave and non-closed, and the distance between the ellipse and the adjacent ellipse is too close; 4)两次采用最小二乘法拟合出椭圆的中心,第一次拟合后去除掉距离大于3倍标准差的边缘,再进行第二次拟合;4) The center of the ellipse is fitted twice using the least squares method, and the edges whose distance is greater than 3 times the standard deviation are removed after the first fitting, and then the second fitting is performed; 5)判断椭圆外围是否有环带,如果没有即为非编码点;如果有则径向作内外边界的连线,在连线上等距离采样5次,以5次采样的中值与标记点的灰度阀值作比较,大于阀值则本环带的编码为1,否则为0;每36°,对应于10位编码点,重复上述操作,旋转一周后得到形如“0100100111”的二进制编号;5) Determine whether there is a ring on the periphery of the ellipse, if not, it is a non-coded point; if there is, make a radial connection between the inner and outer boundaries, and sample 5 times at equal distances on the connection, and use the median value of the 5 samples to match the marked point If it is greater than the threshold, the code of this ring is 1, otherwise it is 0; every 36° corresponds to a 10-bit code point, repeat the above operation, and get a binary format like "0100100111" after one rotation serial number; 6)查表得到编码点的ID,如果查不到则看作非编码点。6) Look up the table to obtain the ID of the code point, if it cannot be found, it is regarded as a non-code point.
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