光电编码器单莫尔条纹测速方法

为了提高编码器的测速精度,研究了基于希尔伯特-黄变换的光电编码器单莫尔条纹测速方法。首先,利用AD采集编码器的单路莫尔条纹光电信号,并将信号序列通过EMD变换,滤除直流分量;然后,利用希尔伯特变换求出信号的相位变化,并通过差分运算求取信号的瞬时频率;最后,结合编码器的具体参数求取编码器的转速。实验结果表明:对某21位编码器进行测速实验,测速误差均方差由0.022 4 rad/s降低到0.013 4 rad/s。此方法测速稳定性高,抗干扰能力强,可用于速度精度要求较高的测速场合。     

Moiré properties of Walsh functions

A new type of moiré experiment is presented. Each grating is synthesized by Walsh functions. These functions have the property of being cyclically periodic, and the resulting moiré is also cyclically periodic. Gratings synthesized by different Walsh functions were employed and a contouring measurement is described.     

The Effects of Motion on Dynamic Moiré Interferometry

Experimental techniques (e.g. laser interferometry, photoelasticity) that generate fringe data are currently being utilized for analyzing full-field surface deformations in a variety of dynamic problems in experimental mechanics. As opposed to static problems, the transience of surface deformations in dynamic problems poses a unique problem in accurately resolving the fringe data that is acquired. Neumann determined that for time-lapse, double-exposure holographic interferometry the fringe contrast depends on the data acquisition time, wavelength of the light source, and transience of the dynamic phenomena. Dally performed a similar analysis for dynamic photoelasticity, where the dependence was on the stress gradients instead of the wavelength of the light source. This paper attempts to extend the analysis of Neumann and Dally to the analysis of transient fringe intensity data obtained from using dynamic moiré interferometry. It is found that the fringe contrast can depend on the frequency of the fringe field rather than the wavelength of the light source or stress gradients, and the fringe contrast will decay more rapidly for Gaussian light sources than constant intensity light sources. © 1997 Elsevier Science Ltd. All rights reserved.     

Moiré superstructures of silicene on hexagonal boron nitride: A first-principles study

Using first-principles calculations, we predicted hexagonal boron nitride (h-BN) with flat surface is an ideal substrate for silicene. Van der Waals interactions hold silicene and h-BN together, forming silicene/BN moiré superstructures. The moiré superstructures open a band gap of about 30 meV at the Dirac point of silicene at equilibrium distance. The band gap is almost independent of the rotation angle between the two lattices, but can be effectively tuned by changing the interlayer spacing. The high Fermi velocity of silicene is well preserved in these superstructures. These features are helpful in achieving applications of silicene in nanoscale electronic devices.     

Determination of residual stresses within plasma spray coating using Moiré interferometry method

In this paper, residual stresses of the Ni-Cr-B-Si coatings prepared by supersonic plasma spray processing were measured by moiré interferometry and X-ray diffraction method. Moiré interferometry method was used in measuring the distribution of residual stresses of the Ni-Cr-B-Si coatings alongside the specimen thickness direction, then the distribution of residual stresses both in the substrate and the coating was also analyzed. Experimental results showed that residual stresses in the coating and the substrate are tensile and compressive separately; residual stresses of the coating are diminished with the increase of the distance from the coating surface and almost zero at the coating-substrate interface; the maximum of compressive residual stresses of the substrate are present to the vicinity of the coating-substrate interface. It could be concluded that residual stresses in the specimen would result from the dismatch of thermophysical properties between the coating and substrate during the spray process, and the distribution of residual stresses of the substrate would be influenced by the sandblasting prior to spraying.     

Phase determination in holographic Moiré in presence of nonsinusoidal waveforms and random noise

This paper proposes a subspace parameter estimation method which besides allowing for accommodating multiple PZTs in an optical interferometer permits for extracting in real time values of phase shifts between data frames at each pixel point. The technique enables to freely choose values of phase shifts between 0 and π. A generalized phase measurement algorithm allows for computing multiple phase information present in the interferometer. The method facilitates the use of spherical beams, addresses errors arising from the miscalibration of the phase shifting devices, and is capable of handling nonsinusoidal waveforms in an effective manner. Numerical simulations demonstrate that phase distributions can be measured with high accuracy even in the presence of noise.     

基于Talbot-Moiré法测量透镜焦距的莫尔条纹的图像处理

利用Ronchi光栅的Talbot效应和Moiré条纹测量了长焦透镜焦距,并根据焦距与莫尔条纹斜率之间的定量关系可求得透镜焦距.为获得条纹斜率,用CCD采集莫尔条纹图像后,利用数学形态学滤波方法进行图像滤波平滑等预处理,有效地增强了图像的对比度.通过二值化、细化获得单像素宽连通的条纹,通过对条纹进行标记,为条纹斜率的直线拟合计算提供了可靠的数据,采用这些数据计算的焦距的误差为0.10%.     

End-wall errors in temperature measurement of external convective heat transfer with Moiré deflectometry

Moiré deflectometry is a robust and simple optical method that allows obtaining the temperature field in flows with uniform pressure and two-dimensional and axisymmetric flows. Since in real configurations it is not possible to keep exactly the hypothesis of two-dimensional flow, it is necessary to asses this influence. Therefore this work studies a procedure to estimate the errors due to the end-wall and 3-D effects when Moiré deflectometry is used for measuring the temperature field of an external convective heat transfer flow with free edges.According to the value of the parameter Gr/Re², results show two tendencies. The error in temperature measurement is smaller than 1% for ratios of thermal boundary layer thickness to the test field width lower than 0.4, in turbulent forced convection flows for temperature differences of 40 K. Temperature effects are significative, multiplying the error by two for a temperature difference 50% greater. These results enable researchers to evaluate the errors of this measurement technique associated with the end-wall effect.     

A moiré fringe alignment aid

The task of accurately superimposing two photographic transparencies is frequently encountered in some areas of optical metrology. By recording a suitable line structure, along with the image, on each photograph, moiré fringes formed when two of the structures are superimposed can be used to give an accurate indication of the alignment of the transparencies.     

Binarization of scanning Moiré fringe pattern

This paper describes a digital picture processing method to obtain a binary scanning moiré pattern. In this method, a bias component due to the illumination light distribution is eliminated from the scanning moiré fringe pattern to detect the zero-crossing points of the moiré profile. The binary fringe pattern is then obtained from the zero-crossing points. Experiments indicate that the method is useful for facilitating three-dimensional automatic measurement using moiré topography.     

Generation of millimeter-wave in optical pulse carrier by using an apodized Moiré fiber grating

A novel scheme is proposed to transform a Gaussian pulse to a millimeter-wave frequency modulation pulse by using an apodized Moiré fiber Bragg grating in radio-over-fiber system. The relation between the input and output pulses is analyzed theoretically by Fourier transformation method and the requirements for the proposed fiber grating are presented. An apodized Moiré fiber Bragg grating is designed and its characteristics are studied. It is shown that the proposed device is feasible, and the new scheme is believed to be an effective solution for the generation of millimeter-wave sub-carrier in future radio-over-fiber systems.     

相移阴影莫尔基于迭代LSM拟合

相移阴影莫尔技术相位高度存在着非线性关系,无法在全场获得均匀相移,因而致使经典的相移算法不能得到精确解.对此,提出了一种基于最小方差迭代的相移阴影莫尔技术,该技术通过垂直光栅面等间距移动光栅来产生相移,但光栅移动距离可不采用固定值,所以相移过程灵活|使用在高度解调过程中确定的逐点相移增量来抽取精确的测量相位,实现了相移阴影莫尔技术中固有的相位高度非线性误差补偿.结果表明,该方法可通过干涉图计算光栅的移动量,具有相移器的自标定特性.     

Automatic fringe analysis for moiré topography

Two digital systems are developed for the automatic measurement of 3-D shapes using moiré techniques—an automatic 3-D shape measuring system using the scanning moiré method and an interactive fringe analysing system for moiré fringe photographs. In the automatic 3-D shape measuring system, a deformed grating is scanned and sampled with an electronic image scanning device so that moiré fringes are generated in a computer. This technique of electronic fringe generation eliminates ambiguity with regard to the sign of the moiré fringes. The interactive fringe analyser provides a flexible and versatile tool for moiré fringe analysis. Medical applications of these analysing systems are discussed.     

An algorithm for estimating both fringe orientation and fringe density

In this paper, an algorithm is proposed which can estimate good fringe orientation and estimate fringe density at the same time. This algorithm accumulates differences along four orientations and then obtains the local orientation and estimates local fringe density according to the differences. The obtained orientation results are more accurate and more robust than the plane-fit method. And it will be shown both theoretically and experimentally that the accumulated differences can estimate fringe density roughly.     

A fringe carrier technique for unambiguous determination of fringe orders in shearography

Shearography is an interferometric method which measures displacement derivatives. This paper presents a technique which eliminates the ambiguity in shearographic fringe interpretation. The technique is based on generating a carrier fringe pattern. Introduction of the carrier fringes results in the formation of a fringe pattern which has monotonically increasing fringe orders, thus allowing fringe orders to be determined in a straightforward manner and without ambiguity. The phase change due to deformation alone is then obtained by simply subtracting the known undeformed carrier fringe orders from the deformed carrier fringe orders. Elimination of fringe ambiguity has paved a way for automatic data acquisition in shearography.     

基于二进制条纹加相位编码条纹离焦投影的三维测量方法

复杂表面的精密三维测量在工业无损检测中非常重要。二进制条纹离焦投影方法在快速三维测量中有重要的应用前景,但该方法难以实现复杂表面高精度三维测量。为此,提出了基于二进制条纹加相位编码条纹离焦投影的三维测量方法。由于离焦投影滤除了高次谐波和高频噪声,可以克服投影仪的非线性伽马效应,与传统投影正弦条纹方法相比,提高了其测量精度。针对离焦投影时,随着相位编码条纹频率增大,条纹级次判决困难,出现周期错位,导致相位解包裹出错,提出了相移编码方法来解决以上问题。采用相移编码方法校正周期错位,使条纹级次判决准确,进一步提高其测量精度。实验结果表明,其测量精度可以达到0.044 mm,验证了本方法的有效性和实用性。     

Refractive fringe diagnostic of spherical shocks

The refractive fringe diagnostic was applied to a spherical shock wave in air generated by an arc discharge. A pulsed ruby laser, synchronized with the shock generation, was used as the probe beam. Both fine and coarse fringes were observed and were modelled computationally. Agreement with the broad features of the density profile predicted by theory was obtained, but the gradient of the theoretical shock rear was found to be too shallow. The shock tail was seento be stationary over a duration of hundreds of microseconds.     

Masker fringe and binaural detection

Yost [J. Acoust. Soc. Am. 78,901-907 (1985)] found that the detectability of a 30-ms dichotic signal (S pi) in a 30-ms diotic noise (No) was not affected by the presence of a 500-ms dichotic forward fringe (N pi). Kollmeier and Gilkey [J. Acoust. Soc. Am. 87, 1709-1719, (1990)] performed a somewhat different experiment and varied the onset time of a 25-ms S pi signal in a 750-ms noise that switched, after 375-ms, from N pi to No. In contrast to Yost, they found that the N pi segment of the noise reduced the detectability of the signal even when the signal was temporally delayed well into the No segment of the noise and suggested that the N pi segment of noise acted as a forward masker. To resolve this apparent conflict, the present study investigated the detectability of a brief S pi signal in the presence of an No masker of the same duration as the signal. The masker was preceded by quiet or an N pi forward fringe and followed by quiet, an No, or N pi backward fringe. The present study differs from most previous studies of the effects of the masker fringe in that the onset time of the signal was systematically varied to examine how masking changes during the time course of the complex fringe-masker-fringe stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Computer aided evaluation of fringe patterns

The crucial step in computer aided evaluation of interferometric fringe patterns is the determination of the interference phase distribution from the recorded and stored intensity pattern. Methods for determination of the interference phase distributions from fringe patterns are presented and the most important methods, which are skeletonising, temporary heterodyning, phase shifting and Fourier transform evaluation are compared with regard to experimental requirements, achievable resolution and precision, as well as inherent noise suppression and image enhancement. The comparison shows that whenever phase shifting is possible, it is the best choice. If only one interference pattern is offered, Fourier transform evaluation is recommendable. For demodulation of the wrapped phase a path-independent algorithm is presented. Practical examples are given from holographic interferometric measurements.