Study on the Alignment and the Calibration of a Laser Structured Light Sensor

In this paper, the principle and the application of the two dimensional laser structured light sensor are introduced. A new method for the alignment and the calibration of the laser structured light sensor are proposed. In this method, the optical collimating and the computer graphic positioning technology are used. Therefore, the processing of the alignment and the calibration of the laser structured light sensor has been simplified and the required accuracy can be reached.     

Constructing feature points for calibrating a structured light vision sensor by viewing a plane from unknown orientations

To calibrate a structured light vision sensor, it is necessary to obtain at least four non-collinear feature points that fall on the light stripe plane. We propose a novel method to construct non-collinear feature points used for calibrating a structured light vision sensor with a planar calibration object. After the planar calibration object is moved freely in the range of measuring of the structured light vision sensor at least twice, all the local world coordinates of the feature points falling on the light stripe plane can be readily obtained in site. The global world coordinates of the non-collinear feature points in the local world coordinate frame can be computed through the three-dimensional (3D) camera coordinate frame. A planar calibration object is designed according to the proposed approach to provide accurate feature points. The experiments conducted on a real structured light vision sensor that consists of a camera and a single-light-stripe-plane laser projector reveal that the proposed approach has high accuracy and is practical in the vision inspection applications. The proposed approach greatly reduces the cost of the calibration equipment and simplifies the calibrating procedure. It advances structured light vision inspection one step from laboratory environments to real world use.     

一种高精度线结构光视觉传感器现场标定方法

针对现有线结构光视觉传感器标定方法存在的局限性,提出一种不需要求解光平面标定点的标定方法.根据光条图像求解平面靶标上光条在摄像机坐标系下的Plücker矩阵.在视觉传感器前合适位置将平面靶标摆放多次,联立所有光条空间直线的Plücker矩阵,求解光平面在摄像机坐标系的平面方程.最后通过非线性优化方法得到光平面方程在最大似然准则下的最优解.在标定过程中,所有光条点都参与光平面参数的计算过程,因此该方法标定结果精度高、稳健性强.实验证明,与现有方法相比该方法标定精度提高30%左右.     

Study on Calibration Methods of Structured Light Sensor

1　Ｉｎｔｒｏｄｕｃｔｉｏｎ　　Ａｌｉｎｅｓｔｒｕｃｔｕｒｅｄｌｉｇｈｔｓｅｎｓｏｒ (ａｌｓｏｎａｍｅｄｖｉｓｕａｌｓｅｎｓｏｒ)ｉｓｃｏｍｐｏｓｅｄｏｆｔｗｏｐａｒｔｓ ,ａＣＣＤｃａｍｅｒａａｎｄａｌｉｇｈｔｓｔｒｉｐｅｐｒｏｊｅｃｔｏｒ ,ａｓｓｈｏｗｎｉｎＦｉｇ .1 .Ｔｈｅｓｔｒｕｃｔｕｒｅｄｌｉｇｈｔｓｅｎｓｏｒｐｒｏｊｅｃｔｓａｌｉｇｈｔｓｔｒｉｐｅｏｎｔｈｅｐｒｏｆｉｌｅｏｆｔｈｅｏｂｊｅｃｔｔｏｂｅｍｅａｓｕｒｅｄｂｙａｌａｓｅｒ,ｔｈｅｎｔｈｅｓｃａｔｔｅｒｅｄｌｉｇｈｔｉｓＦｉｇ .1…     

Study on Calibration Methods of Structured Light Sensor

In this paper,advantages and disadvantages of existing calibration methods are presented.Based on the projective transformation which is the basic principle of a CCD camera,a new method of calibrating structured light sensor is presented.Steps and advantages of the calibration and experimental results are given.     

A novel 1D target-based calibration method with unknown orientation for structured light vision sensor

The problem associated with calibrating a structured light vision sensor is that it is difficult to obtain the coordinates of the world calibration points falling on the light stripe plane. In this paper, we present a novel method to address this problem by randomly moving a 1D (one-dimension) target within the sensor's view field. At each position where the target is set, the world coordinates with one calibration point on the light stripe plane that can be obtained based on at least three preset known points on the 1D target by a proposed two-stage technique. Thus, as long as the 1D target is at least set at three different positions, not less than three such calibration points can be obtained to perform the structured light vision sensor calibration. The simulation and real experiments conducted reveal that the proposed approach has an accuracy of up to 0.065 mm. The advantages of the proposed method are: (1) 1D target is easily machined with high accuracy, which reduces the cost of the calibration equipment; (2) the method simplifies the calibration operation and can be convenient in on-site calibration; (3) the method is suitable for use in confined spaces.     

基于三线结构光的相机平面标定方法研究

相机标定技术是结构光三维视觉测量的关键技术之一,结构光系统的相机标定的精度对三维测量的精度有很大影响。首先对三线结构光系统图的相机标定方法进行了分析,简单介绍了工业相机成像的几何模型及标定的原理;其次利用Harris角点检测方法提取特征点坐标,并选用了BP神经网络来校正工业相机的畸变模型,以提高标定算法的优化速度和标定精度;最后采用张正友的平面标定法对校正后的摄像机模型进行标定实验,由实验结果知,该方法具有一定的准确性和有效性,在一定误差范围内,基于神经网络畸变校正的张正友相机标定能够有效提高视觉检测的精度。     

平顶线结构光的中心检测算法及光刀平面标定

针对传统线结构光光刀平面标定方法测量精度不高,应用范围小的问题,提出基于平面标靶的线结构光系统光刀平面标定,对无激光的标靶图片进行迭代摄像机标定,有激光的标靶图片进行光刀平面标定.提出光强符合均匀分布的平顶激光检测中心算法,将平顶激光建模为矩形的台阶函数,估计背景亮度和前景亮度,确定亮条纹宽度,再将窗口内的有效像素参与重心计算,得到光条纹中心.用该算法对不同噪声及不同量块的图片进行处理,结果表明,处理后图像的均方根误差分别在0.149pixel和0.176pixel内,表明该算法抗噪声能力强、精度高.用该算法提取光条中心,计算光条在标靶上的位置,根据至少两个姿态下的光条中心三维点,基于最小二乘法拟合光刀平面.通过迭代摄像机标定和光刀平面标定,利用三角测量法,在立体视觉模型下获取物体的三维点云数据.实验测量两个距离为100.5mm的标准球,相机与标准球距离为500mm,比较两球心距离与标准距离,测得平均误差为0.236mm.表明平顶激光检测中心算法切实可行,光刀平面标定方法基本满足要求.     

一种基于机械式拼接的结构光扫描测量方法

测量大尺寸零部件一般需要较大的测量范围,而高精密扫描传感器往往视野较小。为了解决该矛盾,提出了一种基于机械式拼接的结构光扫描测量方法,通过结构光扫描仪获取局部高精点云,并利用高精十字平移台实现数据拼接。分析了测量系统的组成和测量原理,提出了一种基于加权非线性优化的外参标定方法,求解出结构光扫描仪和十字平移台之间非实物坐标系的变换关系。在实验中验证了系统在300 mm的测量范围内球心距的均方根误差（root-mean-square error,RMSE）优于45 μm;同时对实物进行了测量,检验了测量系统的实用性。     

Quantum efficiency calibration of opto-electronic detector by means of correlated photons method

A new calibration method of detectors can be realized by using correlated photons generated in spontaneous parametric down-conversion (SPDC) effect of nonlinear crystal.An absolute calibration system of detector quantum efficiency is performed.And its principle and experimental setup are introduced.A continuouswave (CW) ultraviolet (351 nm),diode-pumped,frequency-doubled,and solid-state laser is used to pump BBO crystal.The quantum efficiencies of the photomultiplier at 633,702,and 789 nm are measured respectively.The coincidence peaks are observed using coincidence circuit.Some measurement factors including the filter bandwidth of trigger channel,the detector position alignment and polarization of the pump light are analyzed.The uncertainties of this calibration method are also analyzed,and the relative uncertainties of total calibration are less than 5.8%.The accuracy of this method could be improved in the future.     

基于平面互补靶标的线结构光标定系统

为提升线结构光传感器的标定效率与精度,设计了一种集成自背光可调节位姿的平面棋盘格-同心圆互补线结构光标定系统。该系统基于同心圆圆心的真实投影位置与投影椭圆圆心位置的几何关系,建立非线性优化偏心误差补偿模型,精确得到透射投影下圆心偏心误差补偿位置。该方法与传统标定方法对比降低重投影误差84.7%,有效解决了圆形标志物偏心误差补偿的高精度标定难题。通过将相机坐标系下过光心、光条中心线的平面与靶标平面结合,多次获取空间交线的坐标信息增加特征点,并使用最小二乘法拟合光平面方程,解决了因特征点少从而平面拟合标定精度较低的问题。在复杂环境下重复实验测得大尺寸砂轮外径误差均值为0.005 1 mm,结果表明该标定系统具有一定的准确性和简便实用性。     

空间旋转多光轴平行性校准技术

空间旋转多光轴系统光轴平行性影响系统指向精度且校准难度高、耗时。基于空间旋转多光轴系统光轴校准原理,获得了校准理论模型;结合实验研究,建立了高精度光轴校准方案;以机械回转轴为基准,粗调准和精调准结合,以调整传感器安装面为粗调,借助双光楔实现光学量级的精校准;先校正可见光光轴与机械回转轴的平行性,再保证激光光轴与机械回转轴的平行性,最终保证可见光光轴与激光光轴的平行性。试验结果表明,该校准方案精度高,指标优于0.1 mrad,可用于实际工程装调。     

Line structured light vision sensor calibration using parallel straight lines features

Line structured light vision sensor (LSLVS) calibration is to establish the relation between the camera and the light plane projector. This paper proposes a geometrical calibration method for LSLVS via three parallel straight lines on a 2D target. The approach is based on the properties of vanishing points and lines. During the calibration, one important aspect is to determine the normal vector of the light plane, another critical step is to obtain the distance parameter d of the light plane. In this paper, we put the emphasis on the later one. The distance constraint of parallel straight lines is used to compute a 3D feature point on the light plane, resulting in the acquisition of the parameter d. Thus, the equation of the light plane in the camera coordinate frame (CCF) can be solved out. To evaluate the performance of the algorithm, possible factors affecting the calibration accuracy are taken into account. Furthermore, mathematical formulations for error propagation are derived. Both computer simulations and real experiments have been carried out to validate our method, and the RMS error of the real calibration reaches 0.134 mm within the field of view 500 mm × 500 mm.     

光纤湿敏球腔传感采集校准组合装置的技术问题初探

本文研制了一种光纤耦合湿敏监测装置,此装置采用MEMS微位移传感器来进行湿敏微腔耦合位置的辅助校准,再用光强传感器对耦合输出的光波进行湿度感测和量化。这种基于MEMS位移传感器的耦合位置校准方法与现有的校准平台相比,无需外加太多繁琐、庞大的仪器装置,就可获得精准又便捷的校准效果。另外在传感系统后端可进行可编程控制程序开发,用加载的数据采集卡来实现湿度敏感单元敏感量的采集与显示。     

Flexible and accurate implementation of a binocular structured light system

This paper presents a practical implementation of a binocular system for three-dimensional (3D) surface measurement. Manufacturing procedures are easy to implement because this system does not require that the optical axes of two cameras’ lenses be coplanar and the structured light sheets be perpendicular to that plane. The method of structured light calibration is proposed to obtain the parameters of the structured light sheets. This calibration method can tolerate the surface condition of the calibration board. To eliminate the effect caused by the distortion of projector lens, each structured light sheet is fitted to a conicoid. Meanwhile, data acquired from two cameras are transformed into a unique coordinate system to avoid 3D data matching. Experiments are conducted to validate the flexibility, accuracy, and desirability of our system.     

粒子加速器丝线位置测量电容传感器标定方法北大核心CSCD

在高能同步辐射光源中,为了提高磁铁的准直精度,采用磁中心代替机械中心进行磁铁标定,通过振动线或旋转线等技术获得磁铁的磁中心位置,以及通过电容式位移传感器测量得到丝线的位置,从而实现磁中心与准直靶标的关联。为了实现丝线位置的高精度测量,必须对电容传感器进行精确标定,因此介绍了一种电容式位移传感器,并对其标定方法进行了研究,提出了网格化的数据采集方式以及高阶多项式拟合的数据处理方法,搭建了传感器标定平台并开发了相应的标定控制程序,实现了对传感器的自动控制、数据采集和高精度标定过程。经过分析与对比,标定后的电容传感器达到μm级的位移测量精度,为磁铁的高精度准直提供了基础。     

A fast and accurate calibration method for the structured light system based on trapezoidal phase-shifting pattern

Calibration plays an important part in the structured light system. It used to be regarded as time-consuming, expensive and hard to implement. In this paper, we introduce a novel and fast method to calibrate the structured light system by using the camera to control the projector to “capture” images. Firstly, we projected just six trapezoidal grayscale pattern to establish the corresponding pixel between the camera and the projector, then we converted the camera image to its corresponding projector image. Thus the structured light system can be easy controlled by the camera calibration. Experiments showed that the present calibration method is fast, easy and accurate.     

基于多激光传感器装配的自由曲面法线找正方法研究

在国产化、技术自主化的大型飞机项目上,对孔位精度的标准正逐步升高,钻头的垂直度又是这一标准中最受关注的条件。机器人自动钻铆系统工作时,所产生的装配误差、磕碰、偏移等状况,不仅降低了制造及检测的准确度,还影响了整个结构件的疲劳性能。针对这一问题,提出了基于多激光传感器装配的自适应自由曲面法线检测技术,搭建了以该方法进行姿态找正的数学模型,并研究了检测装置的标定方法及流程。同时,着重讨论了在自适应方法检测时,利用电子经纬仪等装置进行误差补偿的相关技术。该方法的验证实验结果显示,多组实验数据均达到了法向精度<±0.5°的关键技术指标要求,找正后的法线平均偏差值为0.0667°。该方法能有效补偿在制孔工作中所产生的相关误差,进一步提高机器人的定位精度及法线方向检测精度。     

A novel calibration approach to structured light 3D vision inspection

Structured light 3D vision inspection is a commonly used method for various 3D surface profiling techniques. In this paper, a novel approach is proposed to generate the sufficient calibration points with high accuracy for structured light 3D vision. This approach is based on a flexible calibration target, composed of a photo-electrical aiming device and a 3D translation platform. An improved algorithm of back propagation (BP) neural network is also presented, and is successfully applied to the calibration of structured light 3D vision inspection. Finally, using the calibration points and the improved algorithm of BP neural network, the best network structure is established. The training accuracy for the best BP network structure is 0.083 mm, and its testing accuracy is 0.128 mm.     

一种改进的视觉传感器与激光测距雷达特征匹配点提取算法

激光测距雷达与视觉传感器的配准是视觉图像与激光距离信息融合的前提。激光测距雷达与视觉传感器的配准可分为点匹配与平面匹配。由于混合像素和非结构空间特征激光点丢失现象,使得基于点匹配的视觉传感器与激光测距雷达配准算法精度难以提高。通过对混合像素和非结构空间特征激光点丢失问题的分析,提出了一种结合平面建模思想,利用假想激光光束与平面模型相交提取匹配特征点的方法。验证了实验结果并进行了算法精度比较。实验结果表明,这种改进的特征匹配点提取算法解决了特征点缺失,并且提高了点匹配的精度,使匹配性能大大地改善。