一种基于结构光条纹投影的微小物体测量系统

为了通过结构光投影的方法测量微小物体,构建了一套微小物体三维形貌测量系统,视场范围可达1.8 cm×1.6 cm。这套测量系统利用了Light Crafter 4500数字投影组件的高速投影、立体显微镜的低畸变缩放、远心镜头的大景深与低畸变成像的特性。先利用立体显微镜对Light Crafter 4500投影的相移条纹图进行低畸变缩小,再投影到待测物体表面,采用配有远心镜头的相机同步记录受到物体表面形貌调制而发生形变的条纹,利用三步相移法计算出条纹对应的截断相位图,再根据可靠路径跟踪相位展开算法求取连续的相位分布,重建被测物体的三维表面形貌。实验成功重建了以BGA芯片为代表的微小物体表面三维形貌。实验结果表明,系统测量精度达到11 μm,系统的有效深度测量范围为700 μm。     

利用散斑嵌入条纹和查找表进行三维面形测量

为了快速、准确地重建复杂场景的三维面形,提出了一种利用散斑嵌入相移条纹图案和截断相位-高度查找表的三维面形测量方法。将散斑作为辅助信号嵌入到四步相移条纹图案的相位分布中,得到待投影的复合条纹图案。利用相移算法解调出被测物体的截断相位和额外的散斑信息。利用查找表得到截断相位对应的多个候选高度,再利用散斑对条纹周期进行标记以解决高度歧义问题,唯一确定截断相位所对应的正确高度,以实现被测物体三维面形的快速重建。该方法直接从截断相位信息中重建三维面形,无需投影任何附加图案,也无需进行相位展开。理论分析和实验结果表明,该方法可以实现动、静态复杂场景三维形貌的高精度测量且鲁棒性好。     

基于正弦和三角波条纹投影的三维测量方法

在现有的针对复杂物体表面形貌的三维测量方法中, 为了完成绝对相位的测量, 通常需要处理至少6幅条纹图像, 限制了测量速度。提出了采用2幅正弦条纹和2幅三角波条纹图来获得物体三维形貌的方法。利用两步相移正弦条纹和两步相移三角条纹得到截断相位, 再利用两步相移三角波条纹得到条纹级次, 减少了投影条纹幅数, 提高测量速度。在得到条纹级次时, 计算三角波条纹强度调制和强度对比度, 与计算相位相比, 可以减少数据处理的时间, 进一步提高测量速度, 同时能减小物体表面反射率的影响, 提高了测量精度。测量最大高度为39 mm的阶梯状标准块, 得到的最大绝对误差和最大的RMS误差分别为0.045 mm和0.041 mm。验证了该方法的有效性和实用性, 在高速实时的复杂形貌三维测量中有广泛的应用前景。     

一种无需标记的在线三维测量方法

提出了一种无需标记的物体在线三维面形测量方法。将一固定的正弦条纹投影到待测运动物体上,借助物体运动产生等效的相移变形条纹。基于傅里叶变换轮廓术的调制度对各帧变形条纹计算,提取其具有某一特定分布的特征区域,采用相关度最大法,检测各帧变形条纹对应的调制度特征区域的位移量来检测出物体的移动,从而实现像素匹配,得到一组像素坐标完全一一对应的等效相移变形条纹图。利用Stoilov相移算法得到物体的截断相位,利用位相展开算法展开位相,通过位相和高度映射即可实现在线移动物体的面形测量。通过计算机仿真验证了该方法的可行性。     

基于自适应条纹投影的彩色物体三维形貌测量

针对三维形貌测量技术中彩色物体表面反射率的非均匀性影响测量结果的问题,提出一种基于自适应条纹投影的三维形貌测量技术,该方法可避免彩色物体表面反射率非均匀的影响,提高系统的测量精度。彩色相机采集RGB光强图像,并根据物体表面颜色的反射特性计算每个像素点的最优投射光强和颜色;采集水平和垂直的正弦条纹序列,利用计算所得绝对相位值将相机图像坐标系中每一个像素点的最优投射光强和颜色映射到投影仪像素坐标系;投射自适应条纹序列进而测量彩色物体的三维形貌。实验结果表明,该方法能够有效测量彩色物体三维形貌,具有很高的测量精度。     

基于几何约束的自适应相位解包裹算法

提出一种通过相机和投影仪的空间几何约束来展开相位包裹的方法,只需要对结构光投影测量系统进行标定,不需要进行传统的时间或空间相位展开.通过投影单周期条纹得到物体的大致高度信息以确定虚拟深度平面,在虚拟平面z0min处,根据结构光系统的标定参数创建最小绝对相位图,物体的包裹相位逐像素与进行比较,即确定条纹级数,实现相位解包裹.该方法具有良好的鲁棒性,对硬件要求低,采集图像少并且不需要额外的物体来获得z0min,能够实现自适应动态测量.实验结果表明,在同等条件下,与传统时间相位展开方法相比,该方法的相对误差降低了14.33%,同时简化了测量方法,能够有效实现物体的三维形貌测量.     

基于相位预测的在线三维测量像素匹配方法

物体的运动使变形条纹图中物体像素点不对应,因此需要对物体做像素匹配。提出了一种基于相位预测的在线三维测量像素匹配方法。仅投一帧正弦光栅条纹到在线运动的物体上,CCD同步采集相同步距时刻受物体调制的变形条纹图。采用傅里叶变换轮廓术(FTP)方法对采集的变形条纹预测物体不同位置的相位信息,并以该相位信息的特征做像素匹配,实现了物体在各帧条纹图中的像素一一对应,同时匹配后的变形条纹产生等效的等步相移,进而采用等步长相移算法来重构在线运动物体的三维面形。计算机模拟与实验验证了该方法的有效性和可行性。同时,与在线FTP方法进行比较,在线FTP方法和本文方法的均方根误差分别为1.013mm和0.024mm,表明该方法对在线三维测量具有较高的测量精度。     

基于统计逼近的Stoilov改进算法

Stoilov算法是近几年提出的一种相移量任意的等步长相移算法,它无须知道相移量的大小,只要保证相移步长相等,就可以解算出物体表面的截断相位,因而在三维测量领域中倍受人们关注.但Stoilov算法的表达式过分依赖采集的变形条纹图像的光强,存在对光强的减法、除法和开方等运算,使相位计算时在某些位置会出现分子分母为零,开方出现复数等奇异现象,会导致算法算错或者相位展开出错,致使三维重构表面会出现畸变、失真,甚至无法进行三维重构.因此提出了一种基于统计逼近的方法对Stoilov算法进行修正,有效抑制了奇异现象引入的相位误差,提高了三维测量精度.实验验证了其算法的有效性和适用性.     

复杂刚性运动物体的高精度三维测量算法

基于相移法的三维形貌重建精度高,对环境噪声和阴影等不敏感,但由于多幅条纹解相位,难以应用于动态物体的三维测量中,为此,提出了一种新的算法.基于Harris算法提取刚性运动棋盘格的角点,确定相邻两帧采集条纹图像之间的像素偏差并校正采集条纹图像;根据投影仪和摄像机的标定参数建立投影图像和采集图像之间的空间变换矩阵,并根据变...     

基于圆形条纹投影的相位测量轮廓术研究

编码的圆形正弦条纹在圆心具有零相位,该点可以作为后续相位计算和展开的参考。但是圆形条纹提供的载频相位具有非线性特点,当其用于三维面形测量时,如果圆心在物面上,获取物面高度信息的方法与投影单频直条纹的情况不同。研究基于圆形条纹投影的相移轮廓术,讨论了物面高度引起的图像点坐标的位移量和绝对相位的计算方法,并完成相应的误差分析。对3.5 mm平面测量误差的标准差为0.019 mm。计算机模拟和实验验证了该方法能直接得到离面物体的绝对相位,用于重建物体的三维面形。     

三维时域散斑动态干涉测量系统的集成化设计

三维电子散斑干涉技术（3D ESPI）具有非接触、高精度、高灵敏度和全场测量等优点,被广泛应用于许多领域。为了实现非接触动态全场三维测量,设计并建立了一个紧凑、完备的三维测量系统。用一个多波长光纤耦合激光器代替3个独立光源,产生的离面、面内散斑干涉图仅用一台彩色CCD相机就能捕捉和处理;整个测量系统采用笼式结构,具有高度的灵活性和稳定性;对基于小波变换的相位展开算法进行了编程,实现了被测物体三维位移信息的完整提取。实验证明该测量系统可以实时获取被测物体的三维位移,在测量实验中,获得的三维位移值17.68 μm、36.23 μm、13.85 μm,相比于实际位移值18.1 μm、36.4 μm、14.0 μm它们的绝对误差分别为0.42 μm、0.17 μm、0.15 μm,相对误差分别为2.3%、0.5%、1.1%。     

3D shape measurement of larger complex objects based on fringe cycle correction

The grating fringe on the reference plane is broadened in the intersecting axis system because of oblique-angle projection. In order to solve this problem, we study the theoretical model of the temporal phase unwrapping method based on the fringe cycle correction. We also study the 3D shape measurement theoretical model of the larger complex objects after considering the coordinate deviation and lens distortion. Experimental results demonstrate that the fringe cycle on the reference plane can be corrected to a constant value, the lens distortion can be corrected, and 3D shape of larger complex objects can be accurately measured.     

基于相位展开及拼接算法的一种高精度大量程宽光谱干涉显微术

宽光谱干涉显微术广泛应用于高精密检测领域,它测量样品形貌通常采用垂直扫描干涉术对亚微米至毫米级特征进行测量,以及相移干涉术对纳米级特征进行测量。其中,相移干涉术精度可达纳米级,但量程有限,高度变化对应的相位需限制在区间内。采用包裹相位展开算法可以扩展相移干涉术的量程,也仅适用于平滑表面,当高度起伏超出焦深或者光源相干长度的限定范围时,干涉条纹模糊或对比度丧失,所解算的结果将产生较大误差甚至错误。提出一种基于相位展开及拼接算法的高精度、大量程宽光谱干涉显微测量方法,以干涉条纹调制度量化条纹质量,条纹对比度高、成像清晰的区域对应调制度较高,定义当前焦面条纹调制度高于阈值的区域为理想区域,定义焦面条纹调制度低于阈值的区域为问题区域。以相位展开算法获得理想区域中的样品相位分布,问题区域的包裹相位不进行展开。使用微位移结构纵向移动物镜焦平面,选择合理的步长,使相邻焦面位置理想区域展开后的真实相位保持部分区域重合,根据重合区域的相位值均差可以实现不同焦面位置的高精度相位拼接,最终获得扩展量程的高精度真实相位结果,进而可以恢复样品完整的表面形貌分布。该算法通过对理想区域的筛选,避免了相位在问题区域展...     

Surface normal guided method for two-dimensional phase unwrapping

A novel phase unwraping method has been presented and evaluated in this paper. This method works by first constructing a quality map based on the characteristic of the active triangulation system from the wrapped phase data. The quality map is then used to guide the unwrapping. In order to reduce the execution time of phase unwrapping, we tessellate the whole wrapped phase map into blocks. Blocks with higher confidence will be unwrapped first. Experiment shows that this method can unwrap the wrapped phase map derived from the digital moiré system successfully. In data integration stage, only data with higher confidence will be reserved and used to merge together to form a complete 3D model.     

Surface normal guided method for two-dimensional phase unwrapping

A novel phase unwraping method has been presented and evaluated in this paper. This method works by first constructing a quality map based on the characteristic of the active triangulation system from the wrapped phase data. The quality map is then used to guide the unwrapping. In order to reduce the execution time of phase unwrapping, we tessellate the whole wrapped phase map into blocks. Blocks with higher confidence will be unwrapped first. Experiment shows that this method can unwrap the wrapped phase map derived from the digital moiré system successfully. In data integration stage, only data with higher confidence will be reserved and used to merge together to form a complete 3D model.     

两步相移实现投影栅相位测量轮廓术

提出一种新的投影栅相位测量方法--两步相移法。该方法只需两幅相移条纹图，因此计算量小，速度快。给出了实验及计算结果，并同四步相移法进行了比较，证明了该方法具有较高的精度。     

Iterative two-step temporal phase-unwrapping applied to high sensitivity three-dimensional profilometry

Although temporal phase unwrapping method can be applied to solve some problems to measure an object with steep shapes, isolated parts or fringe undersampling in three-dimensional (3D) shape measurement, it needs to acquire and process a sequence of fringe pattern images which would take much time. Servin et al. proposed a 2-step temporal phase unwrapping algorithm, which only needs the 2 extreme phase-maps to achieve exactly the same results as standard temporal unwrapping method. But this method is only validated by computer simulation, shortage of experimental demonstration, its sensitivity coefficient G is limited, and it cannot be used when the G value is larger. We proposed an iterative two-step temporal phase-unwrapping algorithm which is an extension of Servin׳s method. First, add a fringe pattern with an intermediate sensitivity, project the fringe patterns of different sensitivity onto the tested object’s surface, and collect deformed fringe patterns with a CCD camera. Then we obtain the unwrapped phase with larger sensitivity coefficient G by cascading the sensitivity coefficients. And we derive the initial phase conditions of the 2-step temporal phase unwrapping algorithm. Finally, the experimental evaluation is conducted to prove the validity of the proposed method. The results are analyzed and compared with Servin׳s method. The experimental results show that the proposed method can achieve higher sensitivity and more accurate measurement, and it can overcome the main disadvantages encountered by Servin׳s method.     

3-D shape measurement based on complementary Gray-code light

A combination of phase-shift with Gray-code light projection into a three-dimensional (3-D) measurement system has been exploited to digitalize 3-D shape information of a tested object, even with a discontinuous surface. Unfortunately, the phase unwrapping will fall into an error, when an improper value of Gray coding is caused by mistake at the partial boundary of two adjacent binary words. To this end, a new complementary Gray-code method is proposed in this paper as well as the corresponding phase-unwrapping method. This problem of phase unwrapping could be cleverly solved by projecting an additional Gray-code pattern to extend this code and using the different and complementary boundary locations of the traditional and additional codes. The results of computer simulation and experiment confirm that this proposed method based on complementary Gray-code can reliably reconstruct the nature phase distribution of the tested object with only one extra fringe pattern.     

基于多频外差原理的相位校正及匹配方法研究

利用多频外差原理推导四频光栅条纹相位解包裹过程,同时,为了减小相位解包裹误差,提出一种相位校正的方法,并分析了相位校正对匹配结果的影响;通过将校正后的绝对相位值作为匹配的依据,利用极线对上基于相位的亚像素匹配方法;利用三维重建技术获取物体的三维点云数据。实验结果表明:平面测量的匹配率提高了4.97%,测量精度达到0.189 5 mm。     

Noise immune unwrapping based on phase statistics and self-calibration

Unwrapping is an important step for precise phase measurement in an interferometric technique. Due to the effects of noises and speckles, an accurate unwrapping has been quite difficult. To address this issue, a new phase unwrapping method is proposed. The new method uses the wrapped phase statistics together with the limited smoothness characteristics of the interference phase. In this method, statistical parameters of the wrapped phase are firstly obtained. The step is then followed by a self-calibration process to identify and correct corrupted data points to obtain preliminary unwrapped phases. Finally, a phase revision step is taken to remove the effects of the residual errors. A computational testing was carried out to demonstrate the performance of the proposed method at six different levels of noise injection. An experimental test was also carried out using a lateral shearing interferometer. The success and the precision achieved using the proposed algorithm show that the method is quite effective and accurate for phase recovery under the condition of noise contaminations.