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。     

一种新的二元条码设计与绝对式光电位置编码方法

提出一种新的二元条码设计方法,可用于绝对式光电位置编码.传统的光电编码器主要基于莫尔光栅条纹技术,把位移量变为电脉冲,结构简单,但由于增量式相对测量方式,从而使得光电编码器的应用受到了限制.本文提出的二元条码设计方法,在单码道上设计了包含三种频率信息的光栅,采用二元脉冲编码调制和误差扩散的方法形成二元条码标尺.在光电位置编码器中,标尺上某一段的条码就成像在线阵CCD上.对CCD获取的该段条码信息进行傅里叶变换,滤波和逆傅里叶变换,得到三种频率光栅的相位信息,采用小数重合法得到该段条码的绝对相位分布,从而得到绝对位置信息.新的方法保留了单码道光栅莫尔技术结构简单的优点,同时又能像多码道光栅编码器一样实现绝对位置测量.文中给出了编码方法的详细描述,条码信息处理方法,计算机仿真实验结果,最后给出了绝对式光电位置测量的实验结果.本文提出的方法在绝对式光电位置编码器和数字水准仪等领域具有一定的应用前景.     

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.     

双频光栅用于动态过程破裂表面的三维重建

针对在冲击炮轰等快变化过程的傅里叶变换轮廓术测量中,CCD的拍摄速度低于物体的运动速度导致对动态条纹的时间采样不足,提出了采用双频正弦光栅进行测量的三维轮廓术,以傅里叶轮廓术为基础,利用低频光栅条纹图的截断相位做标记条纹,跟踪锁定高频光栅条纹图的同一级次条纹,利用高频光栅的变形条纹进行动态破裂物体的三维面形重建,有效的解决了在快变化动态过程的三维测量中因时间采样不足和条纹断裂带来的问题,正确的获得了物体的面形分布.计算机模拟实验和对瓷砖破裂过程的实际测量验证了此种方法的正确性.     

基于白光干涉的空间频域算法研究

为了精确定位白光干涉条纹的零光程差位置,采用空间频域算法通过傅里叶变换提取白光干涉信号中心波长的相位信息并结合包络中心算法去除相位模糊从而实现零光程定位.实例测量了具有相位突变的计算全息元件的表面轮廓,其平均刻蚀深度为1.63 μm.测量表面形貌连续分布的微透镜阵列,0.32 mm×0.32 mm视场内表面PV为370...     

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。     

傅里叶望远术的实验室验证系统

本文介绍了傅里叶望远术成像的基本原理,为验证傅里叶望远术成像原理,在实验室中搭建了四光束的傅里叶望远术验证成像系统,对灰度透射式目标进行成像验证,利用LabVIEW软件完成了实验中相关控制软件,检测软件和信号处理软件程序设计.通过形成不同空间频率的干涉条纹提取目标的频谱值,利用相位闭合技术,消除与图像无关的相位因子,提...     

散斑分数傅里叶联合变换相关测量研究

提出数字散斑联合变换分数相关测量方法,利用分数相关可以锐化相关峰的作用,在数字散斑联合变换相关运算中用分数傅里叶变换代替傅里叶变换,提高测量精度。通过对散斑图像进行相位调制,有效地解决了分数傅里叶变换的移变性带来的谱移问题。编程模拟和对拉伸试件位移场测量的结果表明,只要选择合适的分数傅里叶变换级次和相位调制函数,可以使相关峰的半宽度从4～5pixel锐化到仅1pixel,得到优于傅里叶变换相关的理想输出。     

基于变窗口浮动阈值的调制结构光三维测量方法

为了解决结构光三维测量中深度信息的准确提取问题,提出了基于变窗口浮动阈值的调制结构光三维测量方法.该方法根据调制结构光相位信息得到被测物体的深度信息,分析条纹图像灰度输出信息与条纹轮廓之间的关系,对每一像素点灰度值在选定窗口内建立周期函数,并对其在整个图像域内进行周期延拓,利用窗口内灰度的极值构造新的权函数,并以此权函数为依据对不同点分配权值,使窗口内各点灰度满足单调性,从而得到不同的选定阈值.实验结果表明,应用这种变窗口浮动阈值法可以得到很好的分割效果,用于沟槽槽深调制结构光三维测量时,标定后其测量结果的重复性优于0.4μm.     

希尔伯特变换实时全息干涉条纹相位提取

实时全息干涉法可以观察记录整个测试过程中条纹图的动态变化,传统相位提取算法只适合于静态干涉条纹图相位的提取.根据实时全息干涉条纹和希尔伯特变换的特点,提出了利用希尔伯特变换提取实时全息干涉条纹相位值的方法,采用了高通滤波的方法减少背景光强的影响,对铝片受力变形实验中实时全息干涉条纹的相位变化分布进行了提取.实验表明:希尔伯特变换法适合于动态条纹的相位提取,可以自动提取实时全息干涉测量过程中全场各点在任意两个时刻间的相位变化值,且测量结果与实时全息干涉条纹人工分析结果一致.     

Image encryption based on a grating generated by a reflection intensity map

A virtual optical technique for image encryption and decryption is presented in this paper. The technique is carried out using optical operation and computational algorithms. In this technique, a grey-level image is captured by a charge-coupled device camera and encrypted using a linear grating superposed on the reflected intensity map of the object. The grating is generated as a fringe pattern by a computer algorithm. The reflected intensity map is determined using the grey level of the image. This reflected intensity map is included in the fringe pattern as an optical phase. It generates a grating, which is represented as a fringe pattern deformed according to the reflected intensity map. The decryption method is performed by a phase recovery method. The technique used here is a spatial synchronous method. This encryption and decryption technique has been used to encrypt real face images. To describe the accuracy of results obtained by this technique, the rms of error is calculated using decrypted and original data images. This encrypting technique is a virtual optical method because all the optical operations are performed by computer processes, and optical components are not required, which are advantages over optical methods, where some physical optical components are used. Simulated images are used in order to assess the technique. Finally, results on real images are presented.     

光栅调制和积分抽样

通过对光学图象调制和光电成像系统的抽样过程的研究，得出两条结论：１）光学图象的调制函数和抽样函数都具有周期重复特性，调制图象和抽样图象的频谱分布服从抽样定理；２）用谐频光栅进行图象调制和用点阵对图象抽样都可以精确恢复原图象，而阵列光栅的图象调制和光电成象系统中的积分抽样对图象恢复具有不同的效应。     

二维傅里叶变换法三维曲面检测

对投影光栅方法获得的位相调制空间载波图进行二维数字图象处理,实现了散射物体的三维曲面测量,利用二维快速傅里嚅变换将空域信号转变为频域信号,对一级频谱进行傅里叶反变换,逐步解调出其位相值,重建了被测物体表面的形貌。文中给出了对人体模型的实验测量结果。     

采用罗奇光栅离焦投影的位相测量轮廓术

本文提出一种采用罗奇光栅离焦投影的位相测量轮廓术。给出由离焦引起的光学低通滤波和N-位相算法表征的数字滤波的解析描述。证明由于采用罗奇光栅离焦投影而引起的误差只具有很小量级,在大多数实际应用中可以忽略。文中给出了计算机模拟和实验结果。     

Comparative analysis of low-pass filters for the demodulation ofprojected gratings in 3-D adaptive profilometry

In 3-D adaptive profilometry based on structured light projection, the choice of the low-pass filter to he used in the deformed pattern demodulation is crucial. In this paper, we have studied the performance of a typical finite impulse response (FIR) and of an infinite impulse response (IIR) Butterworth low-pass filter. Adaptiveness of the filters to both coarse and small variations of the grating frequency has been investigated. The ability of the filters to adapt to coarse changes of the grating frequency has been quantified in terms of their speed of synthesis, while the ability of the filters to tolerate small variations of the grating frequency has been quantified by measuring the residual phase errors. The analysis shows that the IIR Butterworth filter performs better than the FIR filter both in the coarse and in the fine grating frequency variation cases     

Three-dimensional profiling using the Fourier transform method with a hexagonal grating projection

We present three-dimensional profilometry based on triangulation in which a hexagonal pattern is projected on the object. To obtain an accurate result with a one-shot photographic image, the Fourier transform method and method of excess fraction are adopted. The three grating components of the hexagonal pattern are used. For compactness a new pattern projection scheme is introduced. The experimental results show that the constructed optical system works well for measuring the profile of a mannequin with a height resolution of ~ +/- 1 mm.     

Method to eliminate the zero spectra in Fourier transform profilometry based on a cost function

To increase the accuracy, speed, and robustness of 3D measurements in Fourier transform profilometry (FTP), this paper introduces a cost function according to the intrinsic features of the amplitude and frequency modulated (AF/M) signal and proposes two new algorithms to eliminate the background components of the fringe pattern based on the proposed cost function. Finally, the standard Fourier transform (FT) is used to calculate the phase of the pattern, which no longer contains background components. The two proposed methods are both data-driven and require no parameter adjustments in advance. Theoretical analysis and 80 experimental results show that the proposed cost function is valid. The results of more than 80 experiments with different types of fringe patterns, different carrier frequencies, and different noise variances with frequency overlap and sudden phase variation show that the proposed two methods are more accurate and robust than the 2D Gabor wavelet transform, the 2D Fan wavelet transform, and the 1D complex Morlet wavelet transform profilometry, and they are approximately 70 times faster than the 1D complex Morlet wavelet transform profilometry.     

Compensation for anamorphotic distortion in grazing-incidence interferometry testing planar specimens

One important feature of grazing-incidence interferometry is the anamorphotic distortion or the fore-shortened view of the interference pattern along the optical axis caused by the geometry of theinterferometer. To compensate for the consequential lower resolution along the optical axis, a setup was built in which the object plane is imaged onto a rectifying grating, ensuring sharp mapping of the whole specimen onto the detector. A volume hologram and a diffraction grating serve as rectifying elements and are applied to measure various types of planar objects such as mirrors and structured plastic samples. Accuracy, image sharpness, and residual distortion for both cases are discussed.