Automatic Analysis of the Phase Object Using Projection Moire Deflectometry

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一种新的光栅投影轮廓术

提出了一种新的光学全场轮廓术，它采用了一种可由计算机控制的，可变空间频率的莫尔条纹投影仪，利用不同空频的两次变精度测量，以适应待测物体形面的突然起。以以上理论基础以及一台具体实验装置的配合下，得到出了令人满意的测量结果。     

自由立体显示器中锯齿状交错狭缝光栅的设计

光栅式自由立体显示由于易存在莫尔条纹和串扰的问题而影响其显示效果.利用斜光栅可减轻莫尔条纹但增加了视点间的串扰.本文提出一种减轻莫尔条纹的光栅设计方法,同时对可视区域影响较小.设计中对光栅进行分段,并将相邻两段狭缝错开一定距离.该方法能减小通过同一狭缝看到两相邻子像素之间的黑条的比例,获得较宽且较淡的莫尔条纹,从而减轻了视觉干扰.仿真结果表明该光栅相比传统垂直光栅,莫尔条纹亮度下降了108.1%,而可视区域仅减小32.8%,具有较高的实用价值.     

双计算机光栅莫尔拓扑术

提出了利用双计算机光栅实现莫尔拓扑检测的方法.理论分析表明,投影光栅核的横向偏导数为常数是实现灵敏度均匀性检测的必要条件.适当设计光栅核,就可用等间距直条纹来表征标准面形.被测实物面形的缺陷就可通过莫尔条纹相对于背景直条纹的偏移而定量且直观地反应出来.最后,以轮胎镜为例进行了计算机模拟和实验验证.     

莫尔条纹技术的三维测角方法研究

针对传统莫尔条纹技术在测量物体偏转角度中不能对多维角度变化进行测量的问题,采用了一种分区间设计的组合光栅方法,并结合光学自准直成像方法构建了一种新的实验系统装置,利用该系统通过测量莫尔条纹的变化实现了对被测量物体偏转角度的三维测量,对合作光学反射镜的偏转角度测量精度优于1”,绕轴转动测量精度优于2”。     

自由立体显示器中锯齿状交错狭缝光栅的设计

光栅式自由立体显示由于易存在莫尔条纹和串扰的问题而影响其显示效果.利用斜光栅可减轻莫尔条纹但增加了视点间的串扰.本文提出一种减轻莫尔条纹的光栅设计方法,同时对可视区域影响较小.设计中对光栅进行分段,并将相邻两段狭缝错开一定距离.该方法能减小通过同一狭缝看到两相邻子像素之间的黑条的比例,获得较宽且较淡的莫尔条纹,从而减轻了视觉干扰.仿真结果表明该光栅相比传统垂直光栅,莫尔条纹亮度下降了108.1％,而可视区域仅减小32.8％,具有较高的实用价值.     

Improvement for optical mechanics method of coherent gradient sensing

Coherent gradient sensing (CGS) is double grating lateral-shearing interferometric technique with the simplicity of the optical set-up, non-contact, real-time, full-field optical information and variable resolution, which has shown many applications in the study of quasi-static as well as dynamic crack-tip field in both homogeneous and composite materials. It can be used both in a reflection mode (for opaque materials) and in a transmission mode (for transparent materials). The accuracy of the fringe order in the CGS interference image will deeply influence the precision of experimental study. Because of the difference in the optical principle from other optical methods, the fringe order of CGS cannot be obtained through the phase-shift technology. In this paper, a kind of modified CGS method is introduced and analyzed, which can accurately obtain the fringe order of random position in the CGS interference image. This method does not need additional optical set-up and complicated image processing techniques, but only needs several (greater than two) CGS interference images under different loadings. Static fracture experiments show that this method can evidently improve the precision of the CGS method.     

基于彩色光栅投影的快速三维测量方法

 针对条纹投影术提取物体高度信息的问题,提出了一种新的基于彩色光栅投影的三维测量方法。对选取G分量为255,R,B分量各取0或255而组成的青、白、黄、绿四色遵循格雷码原理进行编码,然后将G分量作正弦调制形成投影光栅投向被测物体。提取采集到的光栅变形图中G分量,利用傅里叶变换方法得到其初始相位;同时对采集到图像中的R,B分量作阈值迭代分割而G分量自动赋值为255,综合三分量信息得到条纹颜色信息进而获取条纹的周期信息,从而展开相位。全过程仅需投影一幅彩色光栅图就能完成三维测量,实验结果表明该算法易于实现,在测量实时性和精确性上表现良好。     

An in-plane insensitive multiaperture speckle shear interferometer for slope measurement

A modified two-aperture speckle shear interferometer that eliminates the contribution of the in-plane component and its derivative to the phase change, and yields a fringe pattern corresponding to the first-order partial derivatives of the out-of-plane displacement component, is reported in this note. In this method, two laterally sheared object points are viewed axially. The wave fields from these points are independently combined at the image plane of the imaging system.     

Fringe projection profilometry based on complementary color-encoded fringe patterns

3D measurement techniques based on color-encoded fringe pattern projection have been widely used in various fields of engineering recently. There is one problem that the surface color of measured object may interfere with the color of projected fringe pattern. To solve this problem, a novel method based on complementary color-encoded fringe projection is proposed. Two color-encoded fringe patterns whose fringe colors are complementary are designed. The first pattern is with the sinusoidal fringe embedding into the green color channel which is used to evaluate phases by Fourier transform method. The fringe color of the captured image is established with the help of the complementary color fringe pattern, which is based on the feature of color complementation. Thus, the influence brought by the color of object surface can be eliminated, and decoding errors can be further reduced. Experiment results indicate that the proposed method is valid and can be applied to the measured colorful objects.     

Vibration analysis and non-destructive testing with real-time shearography

Real-time laser speckle shearography coupled with vibration stressing is shown to be an effective means of vibration analysis and non-destructive testing. The shearograms are modulated by a system of live fringes. These fringes are shown to be described by the zeroth-order Bessel function of the first kind and their visibility decreases with increasing fringe order. In vibration analysis, the instantaneous fringe pattern depicts the out-of-plane surface displacement gradient of the object surface at various resonance modes. In non-destructive testing, the flaw depth in a component can be determined without having to determine fringe orders. There is good agreement between the results obtained using the method and those from theory and time-average holography. A major advantage of real-time shearography is its facility for continuous assessment of a vibrating object without the need for secondary shearogram reconstruction.     

Recording and optical processing of images of projected fringes in the study of objects with a periodic surface texture

Specific features of application of the fringe projection method to the study of objects with a periodic surface texture are analyzed. It is shown that a moire pattern is formed in the image recording process. It is caused by the superposition of two periodic structures, namely, the image of the texture of the surface under study and the system of projected fringes. The bending of moire fringes in the pattern is determined by the summary effect of two functions, which describe the bending of the images of surface texture and the system of projected fringes, because of the deviation of the relief shape from the comparison plane. A method for the optical processing of a photographic image by two coherent light beams is described, which makes possible a separate interferometric visualization of the aforementioned functions. Results of experimental studies are presented.     

High-speed fringe analysis by using stair-shaped virtual grating demodulation

This article describes a novel fringe analysis technique using stair-shaped virtual grating demodulation algorithm for extracting the phase information from a single fringe pattern. In contrast to the Fourier transform technique and quadrature multiplicative moire method, the new method processes a fringe pattern in the integer signal domain instead of the frequency domain and real-signal domain. The spatial carrier of fringe image is not limited to any particular frequency as long as it fulfills the sampling theorem. The errors analysis of this technique is conducted by computer simulation and experiments.     

A modified moiré interferometer for three-dimensional displacement measurement

This paper presents a new optical interferometric system, MMI-T/G, composed of a modified four-beam moire interferometer and a Twyman/Green interferometer. The MMI-T/G system can measure threedimensional displacement fringe patterns with a single loading on the specimen, and the in-plane and out-of-plane displacement fields can be measured independently and defined clearly. The optical setup has the advantages of structural novelty, flexibility, and high fringe contrast. Moreover, the in-plane displacement sensitivity is twice of that of the normal moire interferometer. The measuring techniques to obtain the fringe patterns and displacement fields using the MMI-T/G system axe described. The experimental results of thermal displacement of an electronic device are shown.     

A novel color fringe projection based Fourier transform 3D shape measurement method

A novel Fourier transform 3D shape measurement method based on color fringe projection is proposed in order to solve the spectrum overlapping and phase unwrapping problems existed in Fourier transform profilometry (FTP). The R and G components of the color fringe are set to two sinusoidal patterns with different frequencies and the B component is set to the average value of R or G component. Then this pattern is projected to the object and the deformed fringe image is captured. Three gray patterns are separated from the color fringe, the background and high frequency noise can be eliminated using our method and the accurate unwrapped phase can be got. Only one shot color pattern is projected to get the 3D information of the object. Experiment results show that the 3D information of an object can be obtained rapidly and accurately.     

成像型任意反射面速度干涉仪数据处理方法

 采用傅里叶变换方法,列出了对成像型任意反射面速度干涉仪得到的干涉条纹图进行处理的过程。利用文献结果,处理了冲击波整形时产生的有间断干涉条纹图,对处理结果进行了分析。结果表明：条纹图要干净,条纹间距清晰、均匀,应使用１维傅里叶变换的方法处理条纹图,减小滤波的难度。研究了冲击波测试当中条纹丢失的问题,提出了间断条纹图间断起始点相位确定的方法。对透明和不透明靶产生条纹图的不同进行了讨论,得出对透明靶产生的条纹图应采用适当的条纹外延技术进行预处理后再进行常规处理。     

Fourier fringe processing using a regressive Fourier-transform technique

Since the introduction of a fourier fringe algorithm by Takeda, it has been possible to determine the phase of a particular light source impinging on an object from one sole image. This has led to applications in many whole field optical measurement techniques such as ESPI, holography, profilometry and so on. However, the basic processing technique, in case of the 2D-Fourier transform, is subject to a major drawback. Because this technique supposes periodicity in a fringe image, the so-called leakage effects occur. This gives rise to non-negligible errors, which can be resolved by using a regressive Fourier transformation technique. In the method introduced in this article, the fringe signal is represented by a model using sines and cosines where the frequency is not fixed (which is the case for classical FFT-techniques). The coefficients of those sines and cosines together with the frequency components are then estimated locally by means of a frequency domain system identification technique. This allows the fringe pattern to be unwrapped without any distortion. This method will be applied in particular to Fourier-transform profilometry (determines object geometry using shifts of projected fringes) although it can be used in any of the techniques mentioned above. Moreover, it will be shown that the proposed method can deal with other distortions that occur in practice such as over-modulation and varying fringe visibility. The proposed technique will be validated on both simulations and on a profile measurement of a pipe section.     

A new method for photoelastic fringe analysis from a single image using elliptically polarized white light

A new two-dimensional photoelastic method for the analysis of fringe order and the principal direction of birefringence from a single image combining an elliptically polarized white light and color image processing is demonstrated. To determine fringe order, a database-search approach based on the primary color analysis is employed. After determining fringe order, the principal direction of birefringence is obtained by solving a non-linear equation. The equation of emerging light intensity is derived and the theory of the proposed method is described. Then, the successful application of the method to photoelastic analysis is shown. It is emphasized that the proposed method can be applicable to time-varying phenomena since multiple exposures are not necessary for sufficient data acquisition for the completion of stress analysis.     

Neural network applied to reconstruction of complex objects based on fringe projection

The neural network has been introduced into the reconstruction of the complex object based on fringe projection. In this method, the neural network with powerful property of approximation is used to get the continuous approximate function of a discrete fringe pattern captured by an image frame grabber. The depth-related phase of the measured object modulated into the fringe pattern can be demodulated by dealing with the approximate function. Compared with the Fourier transform profilometry (FTP), in the network method, one deformed fringe pattern is needed to reconstruct the tested object, and a high spatial resolution is maintained for no filtering process. Therefore, this method performs better than FTP in the measurement of the complex object. Moreover, the network method is capable of demodulating more depth-related phase even in the case that the local shadow exists in the fringe pattern. Computer simulations and experiments validate the feasibility of this method.     

实时全息术检测透明物的一种新方法

介绍了实时全息术检测透明物的一种新方法,它采用物光再现的参考光和参考光通过全息图的直透光所形成的干涉图纹检测透明物体的变化。证明了这组干涉图纹与用参考光再现的物光和物光通过全息图的直透光所形成的干涉图纹分布规律相似,仅在相位上相差π。还讨论了这组干涉图纹的衬比和获得最佳衬比的条件。此方法可消除物光光路上某些因素带来的相位畸变,避开待测物体自发光的干扰,并可在全息图后方任意位置进行记录,这使实时全息术在实践中更具有灵活性,有助于它在更广阔领域内的应用。