二维分布规则尺寸的激光在线测量方法的研究

本文对二维分布规则尺寸的激光在线测量进行了研究,提出了激光—傅里叶变换测量方法。与传统测量方法相比,它具有测量精度高,可靠性强、速度快并能实现自动在线测量的优点。该方法可用于能够产生规则傅里叶变换频谱的所有被测物体的几何量。     

用二维傅里叶变换识别兰姆波模式的研究

本文用二维傅里叶变换信号处理进行了兰姆波模式分析。通过理论计算与实验结果的比较表明,二维傅里叶变换技术能有效地分析识别兰姆波模式。实验中,采用直探用与可变角探头作为超声波换能器做了接收宽带兰姆波信号的对比。     

激光扫描实验回波信号的分析

利用激光回波信号的强度变化来测量物体边缘轮廓的新型激光雷达,并利用二维扫描、直接探测等技术建立了一套激光扫描实验系统。振镜在X、Y方向分别以不同的频率振动,当激光经过振镜反射后,就以X、Y方向进行二维扫描,激光二极管接收到的信号经过滤波后被分为两个不同频率的信号,分析这两个不同频率的信号,就可以得到物体的轮廓信息。实验测量表明,通过测量回波强度变化来测量物体边缘轮廓的方案是可行的。     

金属丝网激光在线检测仪系统

本文讨论金属丝网激光在线检测仪系统。该检测仪系统利用了“激光-傅里叶变换法”,并对被采样信号进行实时处理,实现了金属丝网二维分布尺寸的在线检测。     

傅里叶变换轮廓术测量方法的分析研究

对传统傅里叶变换轮廓术（FTP)、π相移法以及灰度图法测量结果进行对比分析。结果证明,随着被测物体高度梯度的增加,基于灰度图和π相移技术的改进傅里叶变换轮廓术取得了很好效果,特别是在梯度大于3的情况下适合采用π相移法,能更有效地提高傅里叶变换轮廓术的测量精度。     

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。     

基于频率-波数分析的激光Lamb波传播特性试验研究

Lamb波的频散和多模态特性,使得利用Lamb波信号的时域或频域特征实现缺陷的定量检测具有一定的困难。提出了一种在频率-波数内分析激光Lamb波传播特性的方法。基于全光学型激光超声检测系统,脉冲激光在固定位置激励,连续激光一维线扫描接收,获得时间-空间波场信号,可直观地显示激光Lamb波信号的传播特性以及激光Lamb波与缺陷之间的作用规律。采用二维傅里叶变换将波场信号从时间-空间域转换到频率-波数域,可有效识别信号中包含的各模态信息。为了保留空间信息,借鉴短时傅里叶变换的思想,采用短空间二维傅里叶变换得到沿扫描路径上波数的分布,从中可直观看出缺陷的位置。采用带通滤波结合连续小波变换的方法对短空间二维傅里叶变换的结果进行了优化。分别在有、无缺陷铝板中进行了试验研究,试验结果验证了该方法的有效性。     

用光子相关法测量振动频率

提出了一种测量振动物体振动频率的新方法,搭建了实验系统,并做了大量的实验.该系统通过接收振动物体的散射光并对其做自相关处理而得到振动物体的振型,通过对自相关数据的快速傅里叶分析给出振动物体的振动频谱.由于采用光纤传输光信号,用光电倍增管作为光子探测器,并采用了自相关和快速傅里叶变换相结合的数据处理方法,使得该系统对光源和被测物体均无特殊要求,适用范围广,操作简便,能够很容易的实现非接触、远距离、网络化在线测量.模拟实验表明,该系统的测量范围可达1～10~5Hz.     

提高Fourier变换轮廓术测量精度的新方法

在傅里叶变换轮廓术测量方法中,对离散的条想方设法进行DFT（离散傅里叶变换）运算,存在“栅栏效应”,离散频谱不能完全无误地代表原连续频谱分布,相当于在频域内发生了谱信息损失。为了减小由“栅栏效应”引入的位相误差,采用了对条纹进行空域数值加权和外插补零方法,从而提高FTP的测量精度。计算机模拟证实了所提方法的有效性。     

一种在微型计算机上提高二维快速傅里叶变换速度的方法—子矩阵算法

本文介绍一种在微型计算机上提高二维快速傅里叶变换速度的算法——子矩阵算法。其关键是在行变换和列变换之间,通过把数据矩阵划分为若干子矩阵的方法,来减少进行矩阵转置的时间,从而达到提高二维快速傅里叶变换速度的目的。     

Noise-free normalized fringe patterns and local pixel transforms for strain extraction

Noise reduction is one of the most exciting problems in automatic fringe processing. We propose a two-dimensional (2-D) envelope transform for normalization of fringe patterns, coupled with spin filtering, to construct so-called noise-free normalized fringe patterns. The 2-D envelope transform uses correct fringe intensity envelopes for normalization of fringe patterns, i.e., for making the fringe background and amplitude constant over the whole field. Spin filtering is applied to fringe patterns for removal of random noise taking into account fringe flow. With spin filtering and the 2-D envelope transform, a noise-free normalized fringe pattern is constructed for postprocessing. Based on this improved fringe pattern, two local pixel transforms for strain extraction from a single moiré pattern are developed, in which the digital pure secondary moiré method is improved and the strain-field image method with division is developed.     

Technique for phase measurement and surface reconstruction by use of colored structured light

We present a new method for improving the measurement of three-dimensional (3-D) shapes by using color information of the measured scene as an additional parameter. The widest used algorithms for 3-D surface measurement by use of structured fringe patterns are phase stepping and Fourier fringe analysis. There are a number of problems and limitations inherent in these algorithms that include: that the phase maps produced are wrapped modulo 2pi, that in some cases the acquired fringe pattern does not fill the field of view, that there may be spatially isolated areas, and that there is often invalid and/or noisy data. The new method presented to our knowledge for the first time here uses multiple colored fringe patterns, which are projected at different angles onto the measured scene. These patterns are analyzed with a specially adapted multicolor version of the standard Fourier fringe analysis method. In this way a number of the standard difficulties outlined above are addressed.     

A New Calibration Procedure for 3-D Shape Measurement System Based on Phase-Shifting Projected Fringe Profilometry

An original procedure is presented for the calibration of fringe-projection-based 3-D vision systems. The proposed approach estimates both the phase-to-depth and transverse relationships by directly measuring the phase maps for only three planes placed within the calibration volume and then estimating the phase maps for a number of other ldquovirtual planes.rdquo Experimental tests conducted on a fringe projection system show the effectiveness of the proposed procedure.     

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.     

用于沙体三维形态检测的二维傅立叶变换轮廓术

提出一种二维傅立叶变换轮廓术，对于在变换条纹图象中存在不连续条纹和类散斑结构噪声时，这种方法比传统的傅立叶变换轮廓术方法优越，能够正确地恢复物体三维面形，本文中给出这种方法的理论推导和沙体三维形态检测的实验结果。     

Phase recovery from a single fringe pattern using an orientational vector-field-regularized estimator

Recent studies have demonstrated that the phase recovery from a single fringe pattern with closed fringes can be properly performed if the modulo 2pi fringe orientation is estimated. For example, the fringe pattern in quadrature can be efficiently obtained in terms of the orientational phase spatial operator using fast Fourier transformations and a spiral phase spectral operator in the Fourier space. The computation of the modulo 2pi fringe orientation, however, is by far the most difficult task in the global process of phase recovery. For this reason we propose the demodulation of fringe patterns with closed fringes through the computation of the modulo 2pi fringe orientation using an orientational vector-field-regularized estimator. As we will show, the phase recovery from a single pattern can be performed in an efficient manner using this estimator, provided that it requires one to solve locally in the fringe pattern a simple linear system to optimize a regularized cost function. We present simulated and real experiments applying the proposed methodology.     

High-resolution two-dimensional angle measurement technique based on fringe analysis

A novel angle-measurement technique based on fringe analysis for phase-measuring profilometry is proposed. A two-dimensional (2-D) angle between two mirror surfaces is determined by least-squares fitting of a plane to the 2-D distribution of the phase difference introduced by the 2-D tilt angle. To evaluate the performance of the proposed technique, numerical simulations that use the Fourier-transform technique and the phase-shift technique for fringe analysis were performed, and the results are compared. A 2-D angle-measurement interferometer based on a Mirau interference microscope was developed that demonstrated the validity of the proposed principle. It is shown by simulation and experiment that the proposed 2-D angle-measurement technique can achieve both a wide measurement range and a high angular resolution simultaneously.     

Phase retrieval errors in standard Fourier fringe analysis of digitally sampled model interferograms

We investigate the reliability of phase retrieval by use of the fringe Fourier analysis method for measuring the displacements of facets during the growth of equilibriumlike-shaped crystals. The mean phase change between two successive interferometric images contains an inherent error that emerges from the noninteger number of fringes in the image field. The magnitude of the retrieved phase error of the ideal fringe pattern is investigated as a function of spatial carrier frequency, of the initial phase setting, and of the deviation of the number of fringes from the nearest integer value. The suggested modified algorithm suppresses the error more than threefold.     

Color fringe-projected technique for measuring dynamic objects based on bidimensional empirical mode decomposition

A triple-frequency color fringe-projected technique is presented to measure dynamic objects. Three fringe patterns with a carrier frequency ratio of 1:3:9 are encoded in red, green, and blue channels of a color fringe pattern and projected onto an object's surface. Bidimensional empirical mode decomposition is used for decoupling the cross talk among color channels and for extracting the fundamental frequency components of the three fringe patterns. The unwrapped phase distribution of the high-frequency fringe is retrieved by a three-step phase unwrapping strategy to recover the object's height distribution. Owing to its use of only a single snapshot, the technique is suitable for measuring dynamically changing objects with large discontinuity or spatially isolated surfaces.     

Modulo 2pi fringe orientation angle estimation by phase unwrapping with a regularized phase tracking algorithm

The fringe orientation angle provides useful information for many fringe-pattern-processing techniques. From a single normalized fringe pattern (background suppressed and modulation normalized), the fringe orientation angle can be obtained by computing the irradiance gradient and performing a further arctangent computation. Because of the 180 degrees ambiguity of the fringe direction, the orientation angle computed from the gradient of a single fringe pattern can be determined only modulo pi. Recently, several studies have shown that a reliable determination of the fringe orientation angle modulo 2pi is a key point for a robust demodulation of the phase from a single fringe pattern. We present an algorithm for the computation of the modulo 2pi fringe orientation angle by unwrapping the orientation angle obtained from the gradient computation with a regularized phase tracking method. Simulated as well as experimental results are presented.