【作者】 肖振中；

【导师】 于德弘； 梁晋；

【作者基本信息】 西安交通大学 ， 机械工程， 2010， 博士

【摘要】 三维形貌与变形测量在产品质量控制、逆向设计、材料与工程结构测试、生物医学、文物保护等众多领域中的需求日益增加。过去传统的测量内容和测量方法已经不能满足需要,物体的三维尺寸、表面形貌和运动变形数据的获取成为测量领域的研究热点和前沿课题。本文针对目前光学三维形貌与变形测量研究中存在的不足,采用理论分析和实验研究相结合的研究方法,综合机械工程、光学电子、计算机视觉、数字图像处理和摄影测量学等多个学科对三维形貌与变形测量关键技术进行了系统、深入的研究。主要研究内容和研究成果如下:(1)讨论了光学三维形貌与变形测量技术原理和优缺点,对研究现状和发展趋势进行了系统的分析。研究了工业摄影测量和机器视觉中坐标转换、摄影几何约束、空间交汇和三维重建的基本理论。为本文的研究工作提供基本的理论依据。(2)机器视觉系统参数标定是三维测量技术中的关键问题之一,其标定精度直接决定后续三维重建的精度。为进一步提高视觉系统测量精度,提出了一种基于工业摄影测量的相机柔性标定方法,给出了相机成像模型和十参数镜头畸变模型,并进行了相机标定实验及重投影误差分析。该方法使用不同尺寸的标定板和标定十字架,无需标定物世界坐标,可以对不同视场单个或者多个相机进行标定。标定参数初始值由摄影测量中相对定向和直接线性变换方法得到,然后使用捆绑调整算法整体优化物方坐标及相机内外参数。实验结果表明,标定重投影误差小于0.05像素,标准尺(221.001±0.003mm)平均测量误差0.03mm,与传统方法相比,标定精度有较大提高。(3)系统地研究了单相机、双相机和多相机的高精度三维重建方法,推导了在不同情况下的三维重建方程。提出了基于外插多频相移的双目面结构光测量方法,并进行了精度实验验证和误差分析。基于外插多频相移的相位展开算法,相位展开过程主要依赖不同频率正弦光栅图像的相位主值,对被测物体表面颜色不敏感,无需表面处理,计算过程更稳定,且可对每种频率的相移均进行相位展开,后续三维重建时使用多个连续的相位值进行平均计算,提高了三维重建的精度。(4)针对大型结构件变形,提出了一种基于工业摄影测量的三维静态变形测量方法。该方法可以方便地获得大型结构件在不同载荷条件下的整体位移场信息。研究了同名点匹配和搜索算法,改进了坐标配准算法,提高了坐标配准的效率,并实现了静态变形测量数据中变形点的匹配,从而计算出实际的位移变形场。提出了一种相关拼合的算法,通过使用相关点进行坐标配准和相同变形点匹配,提高了相同变形点匹配的效率。(5)针对全场位移和应变测量,结合双目立体视觉,提出了一种基于数字图像相关的三维应变测量方法。研究了数字图像相关方法的基本原理,涉及的关键技术包括相关系数、相关搜索、相关区域校正和位移场数据的平滑等。通过引入盒滤波思想,改进了整像素相关搜索算法,提高了匹配效率,对影响测量精度的因素进行了分析并提出了散斑图像光照不均匀的校正方法。在上述理论与技术的基础上,将研制的双目面扫描系统、静态变形测量系统、动态变形测量系统在大型飞机全尺寸形貌测量、汽车钣金件、电力塔架真型试验、薄板焊接变形试验、材料拉伸试验中进行了应用和实验,并取得了良好的效果。更多还原

【Abstract】 In recent years, 3D shape and deformation measurement has become more and more important in many fields, such as quality control, reverse engineering, material testing, biomedicine, cultural relics protection and so on. As we all know, the traditional measuring content and measuring method can not meet the needs of practice. Acquisition of three dimensional geometry, surface shape and deformation data has already been the hot topics in the industrial measurement fields. The key technologies of 3D shape and deformation measurement are deeply and systematically researched in this thesis by means of combining theoretical analysis and experimental study, which are based on mechanical engineering, optical electronics, computer vision, digital image processing, photogrammetry and other disciplines. The main contents and achievements are listed as follows:(1) The technical principle, advantages and disadvantages, the present research and development trends of the 3D shape and deformation measurement are reviewed and discussed. The fundamental theory of computer vision and close range photogrammetry including coordinate transformation, photography geometric constraints, space intersection and three-dimensional reconstruction are explored in detail, which provide a good theoretical basis for our research.(2) Camera calibration in the computer vision system is one of the key technologies in 3D measurements. The calibration precision directly determines the accuracy of the 3D reconstruction. A flexible calibration method is proposed based on photogrammetry technique in order to improve the precision of the computer vision system. A cross-shaped calibration pattern which is portable and easy to be manufactured is designed. The cross target can be used to calibrate stereo vision systems with large measurement volume and obtain higher measurement precision conveniently. The mathematical model of the stereo vision system with 10 distortion parameters for each camera is presented. The calibration initial values are computed using the relative orientation method and the Direct Linear Transform (DLT) method of photogrammetry. The bundle adjustment algorithm is used to optimize the calibration parameters as well as the 3D coordinates of the feature points. Experiment results show that the RMS error of the reprojection in our method is less than 0.05 pixels and the distance measurement error is 0.031 mm with a high precision scale bar which length is 221.001±0.003mm.(3) A high accuracy method for 3D reconstruction is deeply researched which can be used to single-camera measuring, dual-camera measuring and multi-camera measuring. The 3D reconstruction equations in different situations are derived respectively. A stereo vision system is proposed based on digital fringe projection. A heterodyne multiple frequency phase-shifting algorithm is employed for overcoming the unwrapping problem of phase functions and for a reliable unwrapping procedure. According to the phase unwrapping algorithm of the heterodyne multiple frequency phase-shift technology, the phase unwrapping process is mainly dependent on phase principal value of the different frequency sinusoidal grating images. It is not sensitive to object surface color and needs no surface treatment. The redundant phase information is used to increase the accuracy of the 3D reconstruction.(4) According to large-scale structure deformation, a method of 3D static deformation measurement is presented. A correspondence points matching algorithm is researched in detail. The coordinate registration algorithm is improved to increase the efficiency and accuracy of the coordinate registration. A matching method based on correlation principle is proposed, which can realize coordinate registration and deformation points matching with good efficiency. Moreover, the deformation points matching of the static deformation measurement is implemented, which can be used to displacement field measurement.(5) According to 3D displacement and strain measurement, the principles and key technologies of the digital image correlation method (DICM) are systematically researched including correlation coefficient, correlation search, correlation area model and displacement field smoothing. A method of uneven illumination correction is proposed. It can be used to improve the accuracy of dynamic deformation measurement. The speckle matching and detection methods are implemented with high efficiency based on the improved DICM.According to above theories and technologies, the systems we developed including binocular surface scanning system, static deformation measurement system, the dynamic deformation measurement system have been used in 3D shape measurement for large airplane, automobile panel inspection, real-sized transmission tower loading test, welding deformation measurement of sheet metal, tensile test, and the results are encouraging.更多还原