采用标记条纹跟踪的冲击过程三维轮廓术

针对在冲击、爆轰等快变化过程的三维轮廓术中,CCD拍摄速度低于物体的运动速度而导致对动态条纹的时间采样不足和物体表面发生破裂而分成数块的动态过程,提出一种采用标记条纹进行跟踪的动态过程三维轮廓术.以傅里叶变换轮廓术为基础,通过采用标记条纹进行跟踪锁定变形条纹中同级次条纹的变化以及Gerchberg迭代算法在破裂区域迭代生成伪条纹,对破裂表面分块进行处理,有效地解决了在快变化动态过程的三维重建中因时间采样不足和条纹断裂对三维相位场的展开所带来的问题,获得了物体正确的面形分布.实验证实了此种方法的正确性.     

动态傅里叶变换轮廓术实现路面形变快速检测

公路表面的三维结构对于判断公路路面破损状况具有重要的意义。基于光栅投影的傅里叶变换轮廓术将物体的高度信息编码在投影到待测物面上的正弦条纹的形变信息中,可以实现对物体的垂直测量。探讨了傅里叶变换轮廓术在高速公路路面面形测量-动态实时系统中的应用,提出了利用自适应标准模版匹配,基于特征图像识别的方法,分选破损的公路路面,从而实现对高速公路路面形变的快速实时检测。     

基于彩色双通道投影的快速调制度测量轮廓术

针对传统调制度轮廓术测量速度较慢的问题,本文提出了彩色双通道投影的调制度轮廓术.该方法将两个正弦光栅通过不同的通道同时成像在被测物体上,两光栅像面不重合(相互离焦),采用彩色CCD采集条纹图,利用彩色CCD的色通道性质,分离出两个单一通道的条纹图,得到其调制度分布.由于调制度比值和物体高度存在一一对应关系,由此可重建物体三维面形.文中给出了实验的设计方案、信息获取的方法、实验结果及误差分析,讨论了影响测量精度的几种原因.实验结果表明,该方法测量深孔等面形复杂物体,测量速度快,算法简单,且可以达到较高测量精度.     

气球快速泄气过程动态面形测量方法

提出一种气球快速泄气过程中动态三维面形的测量方法。用正弦光栅投影到处于快速泄气 过程中的气球表面,使用高帧频CCD获取随时间变化的一系列变形条纹,再采用傅里叶变换轮廓术的方法进行处理,能再现气球快速泄气的整个变化过程。该方法为诸如爆轰、膨胀和萎缩等相关领域的动态过程的研究提供了一种新的方法。     

自动搜索匹配区域消除阴影影响的拼接算法

针对基于结构照明的三维面形测量中阴影和条纹裂断的存在会影响物体面形重建质量的问题,提出一种新的获得整个物体三维面形的方法.在同一参考面内,旋转被测物体,并对旋转前、后的物体分两次进行测量,利用调制度信息确定重建物体高度数据的可靠区域,用最小二乘法找出两次重建的高度数据的坐标变换关系并在可靠区域内拼接,从而得到整个物体的正确三维面形分布.该方法操作简单,有效解决了传统方法不可避免的阴影和条纹裂断问题,保证了傅里叶变换轮廓术(FTP)的测量精度,通过实验证明了此方法的有效性.     

一种提高光栅投影轮廓术精度的方法

在光栅投影三维轮廓术中,直接条纹位移分析法存在着垂直条纹方向分辨率低的缺点。在分析产生低分辨率原因的基础上,提出移物法,该方法通过多次移动物体来提高测量的采样精度。测量结果表明,在不提高对光栅投影系统的要求的情况下,对物体移动N次分别进行测量,每次移动的距离为条纹宽度的1/(N 1),这样就可以使得测量精度提高N倍。     

大量程纳米级光栅干涉位移测量

针对传统光栅干涉仪中测量范围和分辨率难以同时提高的问题,提出利用单根大长度、低线数光栅实现大量程、高分辨率位移测量的方法.首先利用长度400mm,栅距10μm计量光栅的±5级衍射光生成条纹图,实现了条纹的10倍光学细分.然后提出一种基于傅里叶变换时移特性的条纹细分新方法,利用相邻两帧条纹图同一位置处相位的变化实现了高达1000倍的条纹电子细分.在此过程中,针对能量泄漏对傅里叶变换法相位提取精度的影响,提出条纹图整周期裁剪的方法,使条纹细分精度至少可达到1/1000条纹周期.仿真和实验结果表明,系统具有纳米级的分辨率和优于10nm的测量精度.     

神经网络获取三维面形研究

针对基于传统三角原理的结构光三维测量方法难以测量阶梯形物体的问题，应用神经网络对获取的变形条纹进行处理，获取物体的三维面形信息。该方法通过对神经网络的训练，直接建立条纹图分布与物体高度之间的对应关系，完成对物体的三维测量，即使在投影系统参数未知的情况下，也能取得较好的结果。论文中提出的神经网络三维面形测量方法测量时间短，测量过程中只需要一幅条纹图就能恢复阶梯物体的高度信息。计算机模拟及试验验证了方法的可行性。     

自适应窗口傅里叶变换三维面形检测技术

通过小波脊变换,得到局部条纹的最佳变换窗口,在傅里叶变换三维测量时,可以保证窗口尺寸随变形条纹频率变化而自动调整。实验研究表明,此方法克服了窗口傅里叶变换空间．频率分辨率无法调整的问题,可以最大限度地抑制变形条纹的频谱混叠,准确地提取基频信息,大大地提高了测量精度,误差范围由-2～8mm降低为-1～1mm。并且,由于只需要从一帧条纹图中获取物体的三维分布,适合于动态测量。     

基于傅里叶变换的微结构全彩色三维面形重构

分析表明,在傅里叶成像光谱仪的干涉信号中,不仅含有光谱信息,同样也包含三维面形结构信息。因此,本文基于傅里叶变换光谱技术,提出一种彩色三维面形检测方法,不仅可以测量物体表面各个点的光谱反射率分布,还可以获得物体表面三维面形数据,达到三维面形超光谱成像。通过纹理映射将光谱像和三维面形相融合,实现了微结构彩色物体全彩色三维面形数字重构。     

Surface profiling of a transparent object by use of phase-shifting Talbot interferometry

Talbot interferometry is used to study the surface profile of a transparent object. Periodic patterns are produced by illuminating a grating with a collimated laser beam. The object is placed on the self-image plane of the grating. The deformed grating image, which interferes with another grating, results in the Talbot interferometric fringes. The fringe pattern is recorded on a CCD camera for subsequent analysis, and the phase variation is achieved by a linear translation stage. In this application two specimens are tested to demonstrate the validity of the method; one is a transparent object with a spherical shape with a height of less than 350 microm, and the other is a transparent object with an uneven surface of 50-microm average height. The experimental results are compared with the test results obtained with the mechanical stylus method.     

Shape measurement by use of liquid-crystal display fringe projection with two-step phase shifting

The use of an optical fringe projection method with two-step phase shifting for three-dimensional (3-D) shape measurement of small objects is described. In this method, sinusoidal linear fringes are projected onto an object's surface by a programmable liquid-crystal display (LCD) projector and a long-working-distance microscope (LWDM). The image of the fringe pattern is captured by another LWDM and a CCD camera and processed by a phase-shifting technique. Usually a minimum of three phase-shifted fringe patterns is necessary for extraction of the object shape. In this method, a new algorithm based on a two-step phase-shifting technique produces the 3-D object shape. Unlike in the conventional method, phase unwrapping is performed directly by use of an arccosine function without the need for a wrapped phase map. Hence, shape measurement can be speeded up greatly with this approach. A small coin is evaluated to demonstrate the validity of the proposed measurement method, and the experimental results are compared with those of the four-step phase-shifting method and the conventional mechanical stylus method.     

虚拟光栅变频投影三维测量技术的研究

虚拟光栅变频投影三维测量技术采用多光束干涉条纹形成虚拟余弦光栅,将虚拟余弦光栅投影到被测物体上得到被物体形貌调制的变形虚拟光栅。通过调整多光束干涉的楔角改变虚拟光栅频率,将两幅不同频率的变形虚拟光栅经过光学接收系统成像在CCD像机上,对CCD像机记录的变频变形光栅图像进行综合处理从而获取被测物体的三位形貌。本文给出了这种测量技术的原理,实验结果表明,采用变频虚拟光栅投影三维形貌测量技术可以有效地解决三维测量中被测物体高度变化率过大引起相位展开困难的问题。     

非整数倍双频光栅投影的相位测量轮廓术

采用整数倍双频光栅投影的借助低频相位导向的双相位图成整数比例相位展开方法不可避免误差积累传递,由此提出了一种采用非整数倍双频光栅投影的新光学三维传感方法。非整数倍双频光栅条纹投影到物体上,两相位同时分别以特定相位间隔增长,CCD依次获取16帧变形条纹图,通过这16帧条纹图的强度,可有效地分离出两组受物体调制的对应频率变形条纹的截断相位。利用两组截断相位关系,进行绝对相位展开,避免相位展开中误差的传递,较好地重建了被测物体的轮廓。计算机模拟试验结果证实,该方法与采用整数倍双频光栅投影相比,测量高度为105mm的同一不规则物体时,标准偏差由0.821mm降低到0.760mm。     

基于相位法的三维面型测量及曲面重建技术

文中采用相位法对三维面型测量和曲面重建技术进行了探讨,实现了三维信息获取和曲面重建的方法。该方法是用非相干光源投射的虚拟光栅和 CCD 摄像机构成的视觉系统对物体进行一次扫描获取物体表面的三维测量数据,这些数据经过处理后转换成*.ibl 文件,借助于 Pro/Engineer 软件重建三维物体表面。该方法快速、简便,适合于实时测量、加工,同时可实现测量、处理、加工的一体化,从而为反求工程的发展提供了一个很好的新方法。最后给出了实验,实验结果证明了方法的可行性和有效性。     

Profiling of objects with height steps by wavelet analysis of shadow moiré fringes

A temporal wavelet analysis algorithm is proposed for shadow-moiré-based three-dimensional surface profiling on objects having discontinuous height steps. A grating is positioned close to an object, and its shadow is observed through the grating. The moiré fringe patterns vary when the grating is in-plane rotating. A series of fringe patterns are captured by a CCD camera at different rotating angles. Phase values are evaluated point by point with the continuous wavelet transform. From the phase values of each point on the object, the distance between the object and the grating can be retrieved. The surface profile is obtained without temporal or spatial phase unwrapping. This technique is applicable to objects with discontinuous height steps, which are impossible to measure with conventional shadow moiré topography. Two specimens are tested to demonstrate the validity of the method: One is an object with a height step of 1.6 mm, and another is a small coin with unevenness of less than 0.2 mm. The experimental results are compared with test results by use of the mechanical stylus method.     

An online triple-frequency color-encoded fringe projection profilometry for discontinuous object

Abstract

An online triple-frequency color-encoded fringe projection profilometry is proposed to measure the complex and discontinuous object at straight-line movement. N frames of color fringe patterns are specially designed. Three grayscale sinusoidal grating patterns with geometric progression frequency growth are encoded into red (R), green (G), and blue (B) channels separately to compose a color-encoded fringe pattern. If these three grayscale sinusoidal grating patterns are phase-shifted N steps with an equivalent shift phase of 2π/N, they can compose the corresponding N frames of color-encoded fringe patterns as above respectively. In order to avoid the movement’s interference to the phase shifting, position adjustment should be done to guarantee the phase-shifting direction to be perpendicular to the moving direction. While these N frames of specially designed color-encoded fringe patterns are projected onto the moving object one by one, the corresponding deformed color patterns are captured by a CCD camera in real time. By color separating, color crosstalk compensation, pixel matching, and phase calculation, three wrapped phase at different frequencies can be extracted. The unwrapped phase can be solved by a simplified algorithm based on temporal phase unwrapping method from the relationship of the three wrapped phase at the same pixel. Thus, it is very suitable to measure the online complex and discontinuous objects at straight-line movement. The experimental results show the feasibility and the validity of the proposed method.     

基于结构照明和BP神经网络的三维物体识别

提出一种具有旋转不变性的三维物体识别的新方法,该方法通过结构光照明的方法,使物体的高度分布以变形条纹的形式编码于二维强度图中,由于条纹图包含有物体的高度分布信息,因此对条纹的相关识别具有本征三维识别的特点.旋转不变性是通过BP神经网络实现的.计算机模拟结果表明,用二维强度像的基频分量做训练样本设计BP神经网络,选择训练样本和隐藏层神经元的数目,基于结构光编码的BP神经网络对三维物体具有良好的旋转不变识别效果.     

Complex phase tracing method for fringe pattern analysis

We present what we believe to be a novel complex phase tracing method for fringe pattern analysis related to the phase-locked loop idea. The image with deformed complex fringes is analyzed with lexicographic scansion that leads directly to the investigated phase without unwrapping. Robustness of the procedure is ensured by the delay mechanism in the process of calculating the reference value. A numerical model and examples of application of the presented method are given.