【作者】 干江红；

【导师】 何岭松； 周莉萍；

【作者基本信息】 华中科技大学 ， 机械电子工程， 2012， 博士

【摘要】 物体三维形貌可提供丰富直观的信息,在现代生活和生产的众多领域存在巨大的潜在应用。近年来,随着数字投影设备、图像传感器及图像处理设备的发展,基于数字条纹投影的三维形貌测量技术得到广泛研究与应用,提供了物面形貌全场、大量程的测量手段。但是,物体形貌三维全场精密测量仍面临许多技术难题。现有的基于条纹投影的三维形貌测量技术由于投影设备精度,系统模型等限制,无法获得物体表面形貌的精密测量结果,不能满足精密测量和计量的要求。如何提高基于条纹投影的三维形貌测量范围、测量精度及适应性,是三维形貌测量的重要研究及发展方向。本文提出了一种三维形貌精密测量系统,其利用条纹对比度高,强度呈正弦分布的无衍射栅型结构光作为投影光源,并借助机器视觉相关技术,实现物体三维形貌精密测量。本文对提出的三维形貌精密测量系统中关键技术,包括栅型结构光条纹投影实现、摄像机标定、投影系统标定、条纹图像处理及形貌还原算法等,展开研究,并提出系统的潜在应用。主要工作与创新点如下：提出基于无衍射栅型结构光条纹投影的三维形貌精密测量模型,即根据摄像机针孔成像几何模型和投影光平面方程间的几何关系直接获得物体表面的空间坐标,该三维形貌还原模型不存在近似等效,保证了三维形貌还原精度。提出利用双三角棱镜为主要光学元件实现无衍射栅型结构光的方法。利用几何光学分析了所产生的栅型结构光条纹的特性,包括条纹间距、强度分布、最大投影距离等；进一步利用衍射理论及数值仿真分析了基于双三角棱镜产生的栅型结构光的无衍射特性,并首次讨论了双三角棱镜的边缘孔径及棱脊衍射对产生的栅型结构光强度的影响。利用改进的马赫-泽德(Mach-Zehnder)干涉光路及488nm蓝光DPSS(Diode Pumped Solid Satae)激光器实现了投影视场大的类无衍射栅型结构光条纹投影,该波段的激光可使荧光素钠激发出黄绿色荧光,便于扩展应用。研究并提出了基于摄像机针孔模型透视投影关系的小视场摄像机的精密标定方法,实现摄像机光心及工作范围内焦距的精确标定。提出了栅型结构光投影系统投影光平面方程与光平面相位关系的标定方法。对系统进行了实际标定实验,验证了所提标定方法的可靠性与准确性。提出一种基于功率谱密度的无衍射栅型结构光条纹图像散斑抑制的算法。通过分析散斑噪声与载波条纹的功率谱密度分布,发现散斑噪声的功率谱密度分布比有用的载波条纹及物面变化的功率谱密度小的多,利用带有散斑噪声的物面条纹图像功率谱密度分布构建合适的滤波器,去除由于采用相干光照明引起的图像散斑,获得很好的散斑抑制结果。并利用条文强度散斑系数评估滤波效果。条纹相位计算是采用傅里叶变换的方法,该方法只需一副条纹图像,适合于快速形貌测量。利用投影线结构光条纹为参考对投影栅型结构光条纹进行编码,并提出利用相位跳变点实现整体相位解包裹算法,可有效抑制由噪声引起的孤立相位跳变及累计误差。实际测量实验验证了算法的通用性与可靠性。利用所提的三维形貌测量模型,结合所提相关关键技术进行了实际物体三维形貌测量,并与商用三维扫描设备测量结果进行比较,分析了相关测量误差。对涂有荧光素钠的物面进行了投影测量,根据获得荧光条纹图像进行了三维形貌还原,扩展了该系统的应用范围；并对滴有荧光素钠溶液的兔子角膜进行了三维形貌测量,获得很好的效果,为进一步生物医学应用打下基础。更多还原

【Abstract】 3-D shape measurement can provide direct information about the measured object, which has potential application in modern life and many industry applications, such as production inspection, quality control, machine vision, plastic and artificial limb, and etc. With the rapid development of digital projection equipment, image sensor and image process tools,3-D shape measurement with digital fringe projection is widely researched as a nod-contact, whole field measurement approach. There are many problems about 3-D shape precision measurement to be solved. The existing fringe projection technique for 3-D shape measurement can not satisfy precision measuring and testing application because of the limitation of projection equipment and system measurement model. How to improve the measurement range, measurement accuracy and universality is an important research orientation.In this dissertation, a 3-D shape precision measurement system is presented, which uses non-diffracting grating structure light with high contrast, sinusoidal intensity distribution as projection source. The major techniques about 3-D shape precision measurement, such as, realization of projection fringes, camera calibration, projection system calibration, algorithm of fringes image process and 3-D shape reconstruction, are in-depth studied. The prospect application of this measurement system is given in the dissertation. The main outlines and innovations of this dissertation are as follows:Model of 3-D shape precision measurement based on non-diffracting grating fringes projection is proposed, which is consist of camera model, fringe phase obtaining, height-phase relationship mode. There is no approximation in this model, which can satisfy the precision measurement.Implementation method to generate non-diffracting grating structure light using biprism is presented. The generated fringe features such as fringe space, intensity distribution, the maximum nondiffraction distance, are analyzed by geometric optics method. Non-diffracting property of grating structure light is confirmed by Diffraction theory and numerical simulation. The diffraction effect of biprism edge aperture is also discussed. Utilize the approved Mach-Zehnder interferometer and 488nm Diode Pumped Solid State (DPSS) laser to project wild field grating structure light. The light with 488nm wavelength can make laser induced fluorescence.The calibration approaches suitable for small field camera and grating structure light projection system are investigated. The relationship between phase and function of the non-diffracting structure light is obtained by calibration. The actual calibrate experiments prove the veracity of the proposed calibrate approach.The property of speckle on the captured fringe image is analyzed and an effective speckle reduction algorithm based on power spectrum intensity (PSF) of fringe image is described. The PSF of speckle is small enough than the carrier wave. Speckle index is induced to evaluate the result of filter. Wrap phase of fringe is calculated by FFT and unwrap phase is obtained by whole period phase compensation algorithm, which can restain the error inducded by noise.Set up a 3-D shape precision measurement system according to the proposed technique and conduct some real measurement experiments. Resolution and error of the system is discussed and give some error reduction methods. The surface coated by Fluorescein Sodium is measured and the result shows the potential application of the presented system. A good 3D shape of rabbit cornea is obtained by the system to further the biomedical application.更多还原