基于单目视觉的微位移精确测量方法研究

发布时间：2019-04-10 06:30

【摘要】：随着机器视觉技术、图像处理技术、光电技术等技术的发展,视觉测量技术得到了飞速的发展与应用。单目视觉测量作为一种非接触性的视觉测量方法,在农业、工业、交通、医学等领域内有着重要的应用。本文利用单目视觉与激光点复合进行测量,获取深度信息,此方法具有系统简约、无需在被测物体上设置被动标记、无需摄像机内外参数标定等优点。本文首先介绍了小孔成像模型与透镜成像模型,分别分析了一般情况下的基于小孔成像与激光点复合的测量模型和基于透镜成像与激光点复合的测量模型。针对基于小孔成像与激光点复合的测量模型在微位移测量时,精度不高的问题,采用基于透镜成像与激光点复合的测量模型。此模型采用透镜成像原理,在像距等于两倍的焦距邻域附近,当物距有微小变化,激光点在CCD上的斑点图像位置变化明显,能够提高测量精度。由CCD相机获取激光点图像时,需要先对图像进行预处理,包含灰度处理,滤波处理、阈值分割和获取激光轮廓。激光点的中心位置对测量精度有着重要的影响,本文研究了不同的被测物体对阈值的影响,不同的阈值、开机工作时间、非激光光斑轮廓与光斑轮廓边缘奇异点对激光中心位置的影响;分析了非激光光斑轮廓与轮廓边缘奇异点产生的原因,提出了非激光光斑与轮廓边缘奇异点的去除方法,通过实验验证所提方法的可行性。根据测量模型中各个元器件之间的位置约束关系,设计了一种测量装置,分别对测量装置中的CCD相机、激光器、镜头、直线电机、物理基点、驱动器、镜头支架等零部件进行选型和设计。采用VS2010作为软件开发平台,选用面向对象的C++语言作为开发语言,根据界面设计原则与测量系统的要求,利用MFC与OpenCV相结合设计出单目视觉与激光点复合测量的界面。最后建立了实验平台,主要由三坐标测量机、六自由度位姿调节平台、测量装置、百分表等组成。首先利用三坐标测量机获得被测物体与物理基点之间的距离,利用图像处理技术获得激光光斑的中心位置,建立一一对应关系,然后多次移动被测物体,在每个位置获取CCD中激光点的中心位置,得到多组数据。利用这些数据,再根据理论测量模型,选用合适的拟合函数,采用最小二乘拟合方法得到理论测量模型的修正模型。得到测量模型的修正模型之后进行测量并与三坐标测量机测得的数据进行比较,分析修正模型的合理性,实验表明该方法能够进行微位移高精度测量,在1mm范围内测量的相对误差小于0.022%。
[Abstract]:With the development of machine vision technology, image processing technology, photoelectric technology and other technologies, vision measurement technology has been rapidly developed and applied. Monocular vision measurement, as a non-contact visual measurement method, has an important application in agriculture, industry, transportation, medicine and so on. In this paper, monocular vision and laser point are used to measure and obtain depth information. This method has the advantages of simple system, no need to set passive mark on the measured object, and no need to calibrate the inside and outside parameters of the camera. In this paper, the aperture imaging model and the lens imaging model are introduced firstly, and the measurement models based on the combination of small hole imaging and laser point are analyzed, respectively, and the measurement models based on lens imaging and laser point recombination are analyzed respectively. In order to solve the problem that the precision of the measurement model based on the combination of small hole imaging and laser point is not high in the micro displacement measurement, the measurement model based on the combination of lens imaging and laser point is adopted. This model adopts the principle of lens imaging. In the vicinity of the focal length equal to twice of the image length, when the object distance has a small change, the spot image position of the laser point on the CCD is obviously changed, which can improve the measurement precision. In order to obtain laser point image from CCD camera, it is necessary to pre-process the image, including gray-scale processing, filtering processing, threshold segmentation and obtaining laser contour. The central position of the laser point has an important influence on the measurement accuracy. In this paper, the influence of different objects measured on the threshold, the different threshold, the starting time, the working time, and so on, are studied in this paper. The influence of the non-laser spot contour and the singular point of the spot contour on the laser center position; The causes of non-laser spot contour and contour edge singularity are analyzed, and the removal method of non-laser spot and contour edge singularity is put forward. The feasibility of the proposed method is verified by experiments. According to the position constraint relation of each component in the measurement model, a kind of measuring device is designed. For the CCD camera, laser, lens, linear motor, physical base point, driver in the measuring device, respectively. Lens bracket and other components for selection and design. Using VS2010 as software development platform and object-oriented C language as development language, according to the principle of interface design and the requirement of measurement system, the interface of monocular vision and laser point complex measurement is designed by combining MFC and OpenCV. Finally, the experimental platform is established, which is mainly composed of three coordinate measuring machine, six degrees of freedom position and attitude adjustment platform, measuring device and percentile meter. Firstly, the distance between the measured object and the physical base point is obtained by using the coordinate measuring machine, the central position of the laser spot is obtained by using the image processing technology, and the one-to-one correspondence is established, and then the measured object is moved many times. At each position, the central position of the laser point in the CCD is obtained, and many sets of data are obtained. Based on these data and the theoretical measurement model, the modified model of the theoretical measurement model is obtained by using the least square fitting method and choosing the appropriate fitting function. After obtaining the modified model of the measurement model and comparing it with the data measured by the coordinate measuring machine, the rationality of the modified model is analyzed. The experiments show that the method can be used to measure the micro-displacement with high precision. The relative error is less than 0.022% in the 1mm range.
【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP391.41

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