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In Fourier transform profilometry (FTP), the zero frequency of the imaged patterns will influence the measurement range and precision. The π phase shifting technique is usually used to eliminate the zero order component, but this method requires the capture of two fringe patterns with a π phase difference between them, which will impede the real time application of the method. In this paper, a novel method is proposed, in which a composite structured light pattern is projected onto the object. The composite structured light pattern is formed by modulating two separate fringe patterns with a π phase difference along the orthogonal direction of the two distinct carrier frequencies. This method can eliminate the zero frequency by using only one fringe pattern. Experiments show that there is no decrease in the precision of this novel method compared with the traditional π phase shifting technique. 相似文献
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Sinusoidal fringe patterns are popularly used in conventional Fourier transform profilometry. There are numerous harmonics in the Fourier spectrum, so as to avoid spectrum overlapping; the maximum range of measurement is limited. The present paper studies FTP based on properly defocusing a binary square wave. There are only odd harmonics in the Fourier spectrum of a binary square wave, and the maximum range of measurement is expanded 1.5 times. Defocusing has a low-pass filtering effect and higher-order odd harmonics are suppressed. Therefore, the fundamental spectrum is easy to extract. The proposed method overcomes the filtering problem of conventional FTP. Measurement experiments show that the proposed method has a good measurement result and the measurement accuracy is improved. 相似文献
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窗口傅里叶变换轮廓术中窗口尺度选取的改进 总被引:1,自引:0,他引:1
多尺度窗口傅里叶变换法根据条纹信号的瞬时频率梯度来确定信号的局域平稳长度,再由局域平稳长度来控制窗口的尺度,即窗口的尺度和局域平稳长度成正比。使用多尺度窗口傅里叶变换法来使条纹信号的频谱局域化,可以在条纹信号的频率分辨率和空间分辨率之间达到一种较佳的调和。针对多尺度窗口傅里叶变换三维形貌测量技术中局域平稳长度提取算法的不足进行了改进,使窗口尺度的选取更具合理性,对变形光栅基频提取更精确,进一步减小了位相测量的误差。给出了理论分析、计算机模拟以及实验结果。 相似文献
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在传统傅里叶变换轮廓术的研究基础上,本文提出了一种倾斜式测量系统的傅里叶变换轮廓术,该技术放宽了传统傅里叶变换轮廓术测量系统的三个约束条件:CCD成像系统的光轴不需要与参考平面垂直,即有一定的倾斜度;投射系统的出瞳和CCD成像系统的入瞳中心之间的连线不需要与参考平面平行;投射系统的光轴和CCD成像系统的光轴不在同一平面内,且不交于参考平面上一点. 并且通过严格的理论分析,推导出高度与相位之间的关系式,与传统傅里叶变换轮廓术相比较,在保证一定的测量精度的前提下,倾斜式测量系统具有更强的实用性和可操作性.
关键词:
傅里叶变换轮廓术
倾斜式
测量系统
相位 相似文献
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Fourier transform profilometry: : a review 总被引:4,自引:0,他引:4
Fourier transform profilometry is one of the popular non-contact 3-D measurement methods, where a Ronchi grating or sinusoidal grating is projected onto a diffuse three-dimensional surface, and the resulting deformed grating image is detected by a CCD camera and processed by a computer. This method requires only one frame (or two frames) of the deformed fringe pattern in some algorithms to retrieve the surface of measured object, so it has obvious advantage for real time data acquisition and 3-D measurement of dynamic process. In this paper, we review some algorithms in FTP, discuss some important problems, including frequency spectra overlapping, phase unwrapping, sampling, and 3-D measurement of dynamic process. With the development of computer hardware and software and availability of high-resolution image grabber, FTP method will be a promising one for acquiring 3-D data of object, and more and more researchers pay attention to it. 相似文献
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A novel method for windowed Fourier transform (WFT) profilometry is presented. This method is based on improved S-transform. The impact of the second order derivative of the phase (φ'(b)) to the ridge of S-transform is derived, and how to estimate this deviation is discussed. An important conclusion that more accurate instantaneous frequency can be obtained after removing this deviation is shown. Thus, an accurate phase map of the fringe pattern is obtained by using the WFT based on the window size map, and this map is related to the instantaneous frequency. The method is compared with the WFT based on the wavelet transform. A numerical simulation and experimental example have shown its validity in practical applications. 相似文献
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动态液膜三维形貌的高速测量及重建,对于能源动力领域的工业过程优化十分重要。基于傅里叶变换轮廓术,对缓变表面和非缓变表面分别进行了模拟仿真,研究了物体表面形貌重建精度的影响因素,包括物体表面高度变化率、环境随机噪声以及条纹频率。并根据模拟结果对实验参数进行了优化,研发构建了高速三维结构光测量系统,对竖直壁面下降液膜表面形貌进行了动态测量。实验结果表明:随着液膜沿竖直壁面向下流动,液膜厚度呈现先增大后减小的趋势,高度方向的平均误差为0.1 mm,傅里叶变换轮廓术能够精确地应用于动态液膜高速测量。 相似文献
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The influence of sampling caused by 2-D solid-state image sensors (CCD) in FTP is discussed in this paper. As we all know, discrete fringe patterns processed by computer are obtained through two samplings. The first one is accomplished in the CCD image plane, and the second is accomplished in A/D convertor of frame grabber. In the previous analysis, sampling is just regarded as a point-sampling process because of ignoring the actual sensor structure of a CCD in the sampling process. Here we discuss the influence of the sensor structure of CCD in FTP, especially the influence from the light-sensitive area size variation. Certain formulas about sampling influence are given, and some simulations and a primary experimental demonstration are carried out to verify our analysis. 相似文献
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傅里叶变换轮廓术(FTP)复原三维形貌时,用来提取基频成分的带通滤波器对测量精度有很大影响。传统二维滤波器如汉宁窗或高斯窗为对称滤波器,其截止频率的大小受条纹空间频率即基频与零频间的距离所限,经常会导致基频成分提取不完整,有用信息缺失。为解决此问题,在二维汉宁滤波器基础上,提出一种椭圆形底部形状的二维非对称滤波器,在不同频率方向上具有不同的频率响应和截止频率,可提取出更为完整的基频成分。台阶和阵列物体的模拟实验表明,二维非对称滤波器对2个物体的复原精度相比于传统汉宁滤波器分别提高了39.5%和55.6%。 相似文献
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Windowed Fourier transform (FT) is introduced into Fourier transform profilometry (FTP) to extract zero component included in deformed fringe pattern without capturing two fringe patterns with π phase difference. First, we extract zero component of deformed fringe image using windowed FT and normalize it, then calculate the normalized Fourier spectra of deformed fringe image, finally subtract the zero component from Fourier spectra of deformed fringe image. We give the theoretical analysis of the proposed method. The experiment is carried out to demonstrate that the method can eliminate zero component and extend the measurable slope of height variation to nearly three times of the conventional FTP. 相似文献
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提出一种基于背景光调制的用于傅里叶变换轮廓术测量范围的复合光栅,该光栅通过调制一正弦条纹和不含任何相位信息的背景光来抑制零频,较基于相移技术的复合光栅有更大的优势:背景光只含直流分量,使得复合光栅的频谱更加简单,有利于滤出载波信息,提高测量精度;对从复合光栅中解调出来的背景光只涉及平均值校准,校准过程更为简单;解调出的背景光与物体表面的反射率成正比,具有潜在的应用价值。采用Matlab程序对该复合光栅进行了数值模拟,并对该光栅实用性进行了实验研究,结果证实了该光栅用于抑制零频、扩大傅里叶变换轮廓术测量范围的有效性,且提高了测量精度。 相似文献
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提出一种基于背景光调制的用于傅里叶变换轮廓术测量范围的复合光栅,该光栅通过调制一正弦条纹和不含任何相位信息的背景光来抑制零频,较基于相移技术的复合光栅有更大的优势:背景光只含直流分量,使得复合光栅的频谱更加简单,有利于滤出载波信息,提高测量精度;对从复合光栅中解调出来的背景光只涉及平均值校准,校准过程更为简单;解调出的背景光与物体表面的反射率成正比,具有潜在的应用价值。采用Matlab程序对该复合光栅进行了数值模拟,并对该光栅实用性进行了实验研究,结果证实了该光栅用于抑制零频、扩大傅里叶变换轮廓术测量范围的有效性,且提高了测量精度。 相似文献
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CCD抽样对傅里叶变换轮廓术的影响 总被引:1,自引:0,他引:1
从傅里叶变换轮廓术(FTP)原理入手,分析了傅里叶变换过程中频谱的产生,给出了CCD像元信号强度及其经抽样后的变形条纹的表达式,得出了变形条纹的傅里叶频谱式,其频谱是原连续函数的频谱在频域内的无限重复,即"频谱岛"。频谱中除了基频外,还产生了二级、三级等的高级频谱。给出了抽样条件及满足抽样条件的方法:当抽样频率与光栅基频的比值m>4时可以恢复物体的面形,反之不能;减小抽样间隔可以使m>4。给出了实验结果:当m=2.0883时,物体面形没有恢复;当m=16.6667时,物体面形得到了恢复。实验结果证明了理论分析的正确性。 相似文献
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The projecting grating method is used to measure the profile of the object. When the object has the steps shape or there are shadows in the grating stripes, the disconnected phase cannot be correctly unwrapped. In order to resolve these problems, the dual-frequency grating is programmed by the computer. And it is projected to the measurement object. The measurement object is placed on the exact rotary platform. After getting two images, the two images are mosaiced, the clear object image modulated by the grating is got. Then a novel Fourier transform profilometry is used to process the image, and the filter is designed to filter the high frequency and the low frequency. The phase difference of high frequency is worked out based on that of the low frequency. At last, the three dimension profile measurement is realized. Comparing with the traditional Fourier transform profile, the method cuts down three times frequency shifting reduces the calculation time and improves filter precision. The result indicates that the method is simple, with high precision. Three dimension profile measurement of the object that has the steps shape or there are shadows in its grating stripes can be successfully resolved. 相似文献
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Improved discrete fractional Fourier transform 总被引:8,自引:0,他引:8
The fractional Fourier transform is a useful mathematical operation that generalizes the well-known continuous Fourier transform. Several discrete fractional Fourier transforms (DFRFT's) have been developed, but their results do not match those of the continuous case. We propose a new DFRFT. This improved DFRFT provides transforms similar to those of the continuous fractional Fourier transform and also retains the rotation properties. 相似文献