Development of machine vision system and dimensional analysis of the automobile front-chassis-module

In the present research work, an automated machine vision system and a new algorithm to interpret the inspection data has been developed. In the past, the control of tolerance of front-chassis-module was done manually. In the present work a machine vision system and required algorithm was developed to carryout dimensional evaluation automatically. The present system is used to verify whether the automobile front-chassis-module is within the tolerance limit or not. The directional ability parameters related with front-chassis-module such as camber, caster, toe and king-pin angle are also determined using the present algorithm. The above mentioned parameters are evaluated by the pose of interlinks in the assembly of an automobile front-chassis-module. The location of ball-joint center is important factor to determine these parameters. A method to determine the location of ball-joint center using geometric features is also suggested in this paper. In the present work a 3-D best fitting method is used for determining the relationship between nominal design coordinate system and the corresponding feature coordinate system.     

Compensation of installation errors in a laser vision system and dimensional inspection of automobile chassis

Laser vision inspection systems are becoming popular for automated inspection of manufactured components. The performance of such systems can be enhanced by improving accuracy of the hardware and robustness of the software used in the system. This paper presents a new approach for enhancing the capability of a laser vision system by applying hardware compensation and using efficient analysis software. A 3D geometrical model is developed to study and compensate for possible distortions in installation of gantry robot on which the vision system is mounted. Appropriate compensation is applied to the inspection data obtained from the laser vision system based on the parameters in 3D model. The present laser vision system is used for dimensional inspection of car chassis sub frame and lower arm assembly module. An algorithm based on simplex search techniques is used for analyzing the compensated inspection data. The details of 3D model, parameters used for compensation and the measurement data obtained from the system are presented in this paper. The details of search algorithm used for analyzing the measurement data and the results obtained are also presented in the paper. It is observed from the results that, by applying compensation and using appropriate algorithms for analyzing, the error in evaluation of the inspection data can be significantly minimized, thus reducing the risk of rejecting good parts.     

Evaluation of circularity from coordinate and form data using computational geometric techniques

Data for evaluating circularity error can be obtained from coordinate measuring machines or form measuring instruments. In this article, appropriate methods based on computational geometric techniques have been developed to deal with coordinate measurement data and form data. The computational geometric concepts of convex hulls are used, and a new heuristic algorithm is suggested to arrive at the inner hull. Equi-Distant (Voronoi) and newly proposed Equi-Angular diagrams are employed for establishing the assessment features under different conditions. The algorithms developed in this article are implemented and validated with the simulated data and the data available in the literature.     

基于坐标配准的牙颌测量点云拼合技术研究

针对牙颌等待测物非接触式光学三维测量,提出了一种融入标定功能的夹具设计方法,实现了测量过程中待测物与标定靶的空间一致性;定义了单目视觉测量过程涉及到的坐标系统;提出了一种基于坐标配准的点云拼合技术,简化了点云拼合流程,实现了点云拼合理论零误差;应用张正友标定方法对摄像机进行了标定;通过实验验证,得到了具有一定精度的牙颌三维模型点云拼合数据,实现了较快的测量速度,为提高牙颌测量系统的整体精度提供了有力支撑。     

大尺寸动态视觉测量系统的并行加速

由于现有以大数据量和计算量为基础的大尺寸动态视觉测量系统处理速度较慢,本文建立了一个高速大尺寸动态视觉测量系统,并对该系统涉及的特征点中心定位、编码点识别、相机定向等算法进行了并行化研究。首先,分析了在不同测量条件下各个主要算法的时间消耗情况及每个主要算法的并行性;然后,对常规的特征点中心定位和编码点识别算法做了介绍,分别提出了特征点中心并行快速定位和编码点并行快速识别算法,并详细说明了这两种并行快速算法的实现原理。最后,针对大量原子操作的问题,提出了线程束集体原子操作的优化方法。实验结果表明:在不损失定位精度和识别率的前提下,图像中包含300个点时的并行方案比串行方案的时间开销减少了42%,当点数达到20 000时,时间开销减少91%以上。实验显示提出的并行设计方案有效地提高了处理速度,解决了大尺寸动态视觉测量系统实时性差的问题。     

宽厚板板形测量系统与标定方法研究

针对当前宽厚板板形在线智能化检测的需求,设计一种单激光器多相机的宽厚板板形测量系统,提出一种基于唯一激光平面的多相机坐标系姿态校准标定方法。板形测量系统由分别位于宽厚板矫正机前后的两个相同的子系统组成,子系统采用多相机测量视野拼接的方式,实现宽厚板板形的检测;利用相邻相机公共视野中同一姿态标定板世界坐标系的唯一性,将多个相机的坐标系映射在基准坐标系下,根据实际激光平面的唯一性将多个相机坐标系统一为同一姿态,并通过统一坐标后相邻相机点云数据的位置关系,实现多相机测量数据的快速拼接,完成多相机结构光测量系统坐标系的标定。试验结果表明,该方法准确有效,为大视场结构光三维测量提供了一种有效的测量标定方法。     

反求工程中复杂曲面测量规划研究

数据采集是反求建模的第一环节，测量数据的好坏决定了反求CAD模型的品质和精度。针对目前应用广泛的三坐标测量机，提出了产品反求建模过程中复杂曲面测量规划的基本规则，并对测量误差进行了分析，为最终构造出精度高、品质好的CAD模型奠定了基础。这些规则在汽车、飞机零部件的测量造型过程中得到了广泛应用，并取得了良好的应用效果。     

汽车传感器电路板涂胶质量视觉检测系统研究

提出了基于视觉检测技术的车用传感器电路板涂胶质量视觉检测系统,采用多次模板匹配对目标图像进行定位和计算角度,并将图像平移和旋转,从而使零件图像与最初选定的图像位置和角度基本一致。然后,将从最初选定的图像获得的电路板应该有胶和无胶区域坐标应用到零件图像上,截取出相应区域的图像,利用图像分割等算法计算各个区域中涂胶部分的面积占总面积的百分比,与给定的面积百分比限制值进行比较,要求有胶区域的面积百分比大于对应的限制值,无胶区域的面积百分比小于对应的限制值则认为零件涂胶合格。结果表明,系统控制自动定位精度达到像素级,保证了检测精度,解决了目前在现场检测过程中人工操作工作量大、判断不准确以及效率低等问题。     

Volumetric error modelling of a stereo vision system for error correction in photogrammetric three-dimensional coordinate metrology

Optical three-dimensional coordinate measurement using stereo vision has systematic errors that affect measurement quality. This paper presents a scheme for measuring, modelling and correcting these errors. The position and orientation of a linear stage are measured with a laser interferometer while a stereo vision system tracks target points on the moving stage. With reference to the higher accuracy laser interferometer measurement, the displacement errors of the tracked points are evaluated. Regression using a neural network is used to generate a volumetric error model from the evaluated displacement errors. The regression model is shown to outperform other interpolation methods. The volumetric error model is validated by correcting the three-dimensional coordinates of the point cloud from a photogrammetry instrument that uses the stereo vision system. The corrected points from the measurement of a calibrated spherical artefact are shown to have size and form errors of less than 50 μm and 110 μm respectively. A reduction of up to 30% in the magnitude of the probing size error is observed after error correction is applied.     

采用光学定位跟踪技术的三维数据拼接算法

为了实现大型自由曲面的三维面型测量,提出了采用光学定位跟踪技术的数据拼接方法。平面靶标作为中介,固定在测量系统上,靶标上的特征点在测量坐标系中的坐标通过中介坐标转换法获得。利用双目立体视觉构建跟踪定位系统,并以跟踪坐标系为全局坐标系,获取平面靶标上特征点的三维全局坐标,求得测量坐标系到全局坐标系的转换矩阵,将测量传感器在不同位置下所测的各子区域的三维数据统一到全局坐标系下,完成大型自由曲面的全局测量。对平面靶标上100个点进行两次测量,实验结果表明：单次测量精度为0.08mm,拼接均方误差小于0.237mm。该方法操作简单、可行,能满足一般的精度要求。