【作者】 秦大辉；

【导师】 黄树槐； 史玉升；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2009， 博士

【摘要】 现有测量装备大致分三类,一是以三坐标测量机和关节臂为代表的接触式测量装备,其特点为精度高、柔性低,难以满足现场测量的需求;二是以结构光测量技术为代表的光学非接触式测量装备,其特点是速度快、无法进行单点测量且有断光干扰;三是以光笔测量机为代表的视觉坐标测量装备,其特点为无线、无臂、无断光干扰、柔性高、探针直接采点,可以实现随时随地测量。因此,光笔能够在现场测量光线难以到达的工件内腔曲面、深孔等特征,为零件装配的定位和零件的工装检测提供一种新方法。目前,光笔视觉测量技术在工业界具有非常大的需求,但是被挪威迈卓诺公司垄断,价格昂贵,技术保密。因此,本文对光笔测量技术中的关键技术进行系统研究,以研制出具有自主知识产权的光笔测量系统。硬件的合理选择和正确使用能够提升系统的性能。本文针对组成光笔视觉坐标测量系统的硬件特性进行了深入的研究,包括CCD的特性和误差源,镜头的特性和误差源,标志点材质对定位精度的影响,CCD摄像机不同的接口对精度和性能的影响等。最后构建了实验样机。光笔图像滤波处理是降低图像噪音的有效途径。通过对光笔图像的背景特点和对不同类型滤波器特性的深入研究,选取了具有线性和旋转对称性的高斯平滑滤波器,该滤波器能够显著的降低噪声水平,同时还能够控制标志点图案边缘位置的准确性。光笔图像中标志点区域分割是实现标志点追踪的重要一步。在对不同的阈值分割技术进行系统的研究的基础上,选取数学形态学中的顶帽变换算法,该算法能够有效的补偿图像背景光的不均匀性,实现目标区域的准确分割。并通过研究标志点区域的特点,提出了一种综合形状和面积判别准则,实现了对光笔标志点区域的准确识别与提取。光笔图像圆形标志点中心位置的精确求解是保证标志点精确定位的关键技术。在系统的研究各种中心位置获取算法的基础上,提出了一种利用梯度幅值作为权重因子的最小二乘拟合算法来求取标志点椭圆中心,并通过严格的实验证明了拟合算法的稳定性和准确性。相机的准确标定是保证视觉测量的精度的前提。通过研究标定板不同的材质和不同的图案对标定过程和精度的影响,设计了一种具有圆形图案的平面标定板,实现了标定板图案椭圆靶标准确的自动编码技术,提高了标定过程的自动化程度。在微软研究院张正友博士提出的标定算法基础上,对镜头三阶径向畸变和二阶切向畸变系数进行了准确的标定,从而进一步提高了摄像机的标定精度。)光笔结构参数标定是光笔测量系统能够进行三维坐标测量的关键。采用光束法平差原理进行光笔标志点的三维坐标的精确求取,并提出了基于单点多姿态的光笔测头自标定算法,实现了对光笔结构参数的完整标定。最后通过实验验证了标定算法的准确性。测量数据的真实感显示对直观地观察测量结果具有重要意义。提出基于反射光的三维点云真实感显示算法。该算法利用微切平面法矢来近似三维数据点在测量曲面处的法矢,通过OpenGL为每个点添加法矢并定义光源和材质,得到具有反射光的三维点云真实感显示效果。以上研究成果构成了一套完整的光笔视觉坐标测量技术,在此基础上开发出了一套光笔视觉坐标测量系统,并通过具体的应用案例证实了本文的所提出的理论与技术是切实可行的。更多还原

【Abstract】 Measurement equipments can be divided into three categories. First one is contacting measurement equipments which contain coordinate measuring machine and artificial measuring arm, their measuring precision is very high, but they can hardly satisfy the complex production requirements. The second is structure-light measuring machines which represent non-contacting measuring equipments, and they are credited with fast speed, but they can’t be used to position single point and have light discontinuity situations. The last one is Light Pen Measuring System (LPMS) which is more flexible, and its structure is much easier and has no light discontinuity situations. So it performs well in measuring hiding points and deep holes that light can hardly reach and it provides a new way for assembling and detection. At present, the demand of the LPMS is increasing very fast. However there is only one company called Matrix that has developed the light-pen measuring system and its price is too expensive. So this paper makes researches on the key technology of the LPMS to develop our own system which has independent intellectual property rights.The right choice and proper use of the LPMS’s hard device will improve the whole performance of this system.This paper makes a deep research of the hardware device on many aspects. It contains the feature and error source of CCD and Lens, the effect of circle marks’ material and the effect of different CCD cameras’ interface on the precision. Experimental prototype is successfully built.It is an effective way to use filter to reduce noise of the LPMS’s images. By studying the features of the LPMS’s images and different kinds of filters, the Gaussian smoothing filter with linear and rotational symmetry is chose.This filter can remarkably reduce the noise and guarantee the accuracy of edges of circle marks.Regional threshold segmentation of the LPMS’s images is the first step to track the marks. On the base of research on different threshold segmentation technology a mathematical morphological pseudo top-hat algorithm is employed to compensate the non-uniformity of LPMS’s digital image’s background light, and realize accurate threshold segmentation in circle mark areas. After the feature of marks’ areas is studied, criteria based on integration of shape and area is proposed to realize accurate regional recognition and extraction.The extracting precision of positioning the center of marks is guaranteed by the center of the marks. A least-squares fitting algorithm which take gradient amplitude as a weighting factor is proposed to fitting the marks’ centers. And this algorithm is proved to be accurate and robust by experiments.Camera calibration is one of the most important steps in photogrammetry. This paper designs a circle-mark calibration board and realizes the automated coding technology of calibration marks. So automation level of the calibration process is increased. On the base of Zhang’s flexible calibration method, 3-order radial distortion and 2-order tangential distortion mathematic mold is under consideration, so the precision of camera calibration will be improved.Calibration of LPMS’s structure parameters is the key step before measurement. This paper uses bound adjustment to obtain the marks’ coordinates, and single point multi-posture self-calibration method is proposed. Then the LPMS’ parameters can be accurately calibrated. The precision of this method is authenticated by experiments. The realistic display of measurement data is mean. This paper proposes the realistic display of three-dimensional point cloud algorithm based on reflected light. This algorithm takes the normal vector of micro tangent plane as the normal vector of the point and the light source and texture will be defined by OpenGL. Finally each point can get realistic display.Finally a complete LPMS technology is completed by the research of above and the LPMS is developed. And this technology is proved to be feasible and robust by applications.更多还原