用自混合干涉测量振动

激光二极管自混合干涉信号的频率与外腔振动的速率成正比,为了从自混合干涉信号重建振动信号,采用频率电压变换的方法.用整形后的自混合干涉信号驱动模拟开关,来开关电容做电荷转移实现频率电压变换,用振动的激励信号驱动另一个模拟开关让电容的充电电源随振动的相位变化做极性变换,这样从自混合干涉信号中还原出振动信号.还原出来的信号的振幅与振动的振幅成正比,波形与正弦激励信号的波形一致.该方案操作简便、成本低廉,可以用于有确定激振方式的振动特性测量.     

浅谈激光计米器

一、激光计米器的原理 激光计米器用双光线的激光多普勒干涉测量技术,实现非接触式长度测量.激光源发射出的激光通过光束分离器产生两束光在被测物体表面产生明暗相间的干涉条纹,光检测器通过回收激光检测到干涉条纹的变化,输出相应的电信号.被测物体移动,光检测器获得信号,测出被测物体的速度,并精确计算出通过测量区域的该物体的长度.     

激光干涉波形解调测量振动相位新方法

激光干涉频比计数法广泛应用于绝对法振动标准装置,针对频比计数法只能测量振幅不能得到振动相位,提出一种利用激光干涉条纹与振动台运动位移之间的关系,实现测量振动相位的新方法,并给出激光干涉波形解调测量振动相位的数学模型。该方法基于零差的迈克尔逊激光干涉仪,利用高速采集器同步采集激光干涉信号和传感器信号,并在Lab VIEW虚拟仪器开发平台上,软件解调振动波形,实现振动幅值和振动相位的实时测量。测量结果与正弦逼近法相一致。     

薄膜定域干涉条纹清晰度探讨

一、引言图1是薄膜干涉光路示意图。从光源S来的两束光a、b经过薄膜后,其反射光a_1、b_1以一定的相位差在P点产生干涉,干涉光强为     

科氏质量流量计振幅对零点影响

针对科里奥利质量流量计振幅改变引起零点漂移的问题,首先通过简化模型建立流量管的弯曲振动方程,求解两检测点的位移响应,得到零点相位差与振幅之间的线性关系;然后采集不同振幅下的传感器放大信号,编写过零检测算法,计算零点相位差,建立零点与振幅之间关系的直线,实验验证零点与振幅的线性关系;最后结合检定规程和零点计算结果,定性和定量地分析振幅改变引入的零点漂移导致的测量误差,结果表明,振幅改变越大,引入的测量误差越大,当流量为10 kg/min时,振幅改变10 mV引入的测量误差达0.727%。     

一种正弦相位调制光纤干涉条纹相位稳定方法

为了消除环境因素(尤其是振动和温度波动)在物体表面三维形貌测量中的影响,基于正弦相位调制(SPM)发展了一种光纤干涉条纹相位稳定技术。利用马赫-泽德光纤干涉仪结构和杨氏双孔干涉原理实现高密度的余弦分布干涉条纹投射。利用两光纤干涉臂端面的菲涅尔反射生成迈克尔逊干涉信号,由光电探测器(PD)检测后送入相位控制系统。采用相位生成载波的方法提取干涉信号的相位,并将生成的补偿信号闭环反馈给压电陶瓷驱动器,与正弦相位调制信号相加后共同驱动压电陶瓷,补偿环境因素带来的相位漂移,实现干涉条纹相位的稳定。环境因素对条纹相位的影响低于57 mrad,实验结果验证了该方法可行性。     

高频振动方向和振幅测量的模糊图像处理方法

根据振动模糊图像和静止图像在频谱上存在的对应关系,即振动模糊图像频谱存在着对应于零阶贝塞尔函数零点的暗纹(贝塞尔条纹);提出对一幅振动模糊图像,经过二维傅里叶变换、灰度均衡以及Radon变换等步骤检测振动模糊图像频谱图上贝塞尔条纹的方向和位置,来实现振动方向和振幅测量的方法;试验证明可以实现平面内任意方向振动的测量,振幅测量精度亚像素级。     

一种基于Matlab的干涉条纹自动处理方法

对接触式干涉仪量块检定时产生的两种干涉条纹进行了研究,图像整体采用傅里叶级数曲线拟合法,实现干涉暗条纹大致定位.局部采用最小二乘二次曲线拟合法,确定干涉暗条纹中心的精确位置及暗条纹个数.利用Matlab和VC平台进行编程,快速有效地实现了干涉条纹中心位置的自动判读. 该方法已应用在中国计量科学研究院接触式干涉仪的量块检定中.     

光纤准白光干涉信号数字化处理方法

提出一种光纤准白光干涉信号数字化处理方法。该方法采用干涉条纹脉冲实现干涉包络信 号同步采集,克服了导轨移动速度不均匀造成的影响;通过高斯函数曲线拟合方法高精度确定干涉信号零光程差点;大大提高了准白光干涉信号定位精度。为消除包络信号采样边界点不确定性带来的误差,采用外插法进行补偿。实验表明,采用该方法对光纤准白光干涉信号零光程差位置的定位精度优于0.5个干涉条纹。     

基于光纤干涉仪的振动测量技术

本文介绍了基于光纤Mach-Zchndcr干涉仪的振动测量系统,用线阵CCD测量条纹动态位移,实现了光纤干涉条纹图像的连续采集.针对干涉条纹图像噪声的特点完成了低通滤波器的设计、图像的平滑处理,消除了干涉条纹中心的定位误差.文章绘制了干涉条纹位移曲线并对其进行了离散傅里叶变换,给出了所测振动的频谱特性.最后讨论了测量系统的灵敏度以及影响测量精度的因素,为了能够辨别条纹的移动方向,指出了条纹最大允许的移动速度限制,给出了实验结果.     

Time average vibration fringe analysis using Hilbert transformation

Quantitative phase information from a single interferogram can be obtained using the Hilbert transform (HT). We have applied the HT method for quantitative evaluation of Bessel fringes obtained in time average TV holography. The method requires only one fringe pattern for the extraction of vibration amplitude and reduces the complexity in quantifying the data experienced in the time average reference bias modulation method, which uses multiple fringe frames. The technique is demonstrated for the measurement of out-of-plane vibration amplitude on a small scale specimen using a time average microscopic TV holography system.     

Vibration Measurement Using Phase-shifting Stroboscopic Holographic Interferometry

A fringe-evaluation system for a vibration measurement is presented, which is based on the phase-shifting method in real-time holographic interferometry. Phase-shifted real-time holographic interferograms are acquired by a TV camera when stroboscopically illuminating the object of interest. An arctangent calculation with phase-shifted fringe patterns gives a phase distribution proportional to the displacement of the object, including the initial phase of the vibration. The effects of the time-integration of the real-time fringe, which involves a reduction in fringe contrast and phase error in the arctangent calculation, are analysed theoretically. Experimental demonstrations are also presented for two cases: vibration which is spatially uniform; and vibration in which the initial phase is non-uniform.     

Vibration-compensated interferometry system using phase-modulating interference fringe subdivision technology

An innovative vibration-compensation method, with phase-modulating interference fringe subdivision technology, is described. It simulates fringe movement by the phase difference of signals and can detect the fringe movement with an accuracy of 1/400 fringe spacing using this subdivision technology. A closed-loop vibration-compensation system is built, and the measurement of an interference fringe movement and a vibration-compensation test are successfully demonstrated. Because of this new method and a new feedback algorithm that was introduced, interference fringes can be stabilized at any preset phase position in real time. Compared with known methods, this method is simple and inexpensive, as well as effective.     

Vibration characteristics of composite piezoceramic plates at resonant frequencies: experiments and numerical calculations

The experimental measurement of the resonant frequencies for the piezoceramic material is generally performed by impedance analysis. In this paper, we employ an optical interferometry method called the amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) to investigate the vibration characteristics of piezoceramic/aluminum laminated plates. The AF-ESPI is a powerful tool for the full-field, noncontact, and real-time measurement method of surface displacement for vibrating bodies. As compared with the conventional film recording and optical reconstruction procedures used for holographic interferometry, the interferometric fringes of AF-ESPI are produced instantly by a video recording system. Because the clear fringe patterns measured by the AF-ESPI method will be shown only at resonant frequencies, both the resonant frequencies and corresponding vibration mode shapes are obtained experimentally at the same time. Excellent quality of the interferometric fringe patterns for both the in-plane and out-of-plane vibration mode shapes are demonstrated. Two different configurations of piezoceramic/aluminum laminated plates, which exhibit different vibration characteristics because of the polarization direction, are investigated in detail. From experimental results, we find that some of the out-of-plane vibration modes (Type A) with lower resonant frequencies cannot be measured by the impedance analysis; however, all of the vibration modes of piezoceramic/aluminum laminated plates can be obtained by the AF-ESPI method. Finally, the numerical finite element calculations are also performed, and the results are compared with the experimental measurements. Excellent agreements of the resonant frequencies and mode shapes are obtained for both results.     

干涉角度显微测量提高光子相关法空气声声压测量精度研究

在光子相关法测量自由场空气声声压中,光束夹角的准确测量影响着测量声压结果。提出了采用显微放大成像方法,利用CCD测量干涉区条纹间距,从而得到更为精确的光束夹角。首先,通过仿真分析高斯光束干涉条纹间距均匀性对光束夹角测量的影响,优化了声场测量的光路结构;然后,使用标准分辨率板对CCD显微成像的放大倍率进行标定并实现了干涉角度测量;最后,构建了光子相关法自由场空气声声压测量的实验系统。实验结果表明,相比于测量光的空间传播距离等传统三角方法获得的光束夹角,该方法得到的光束夹角提高了空气声声压测量的精度。     

Measurement of Surface Shape and Position by Phase‐Shifting Digital Holography

Abstract: Phase‐shifting digital holography is applied to measure the shapes and positions of rough surfaces from the averaged conjugate product of the reconstructed complex amplitudes, named complex coherence factor, corresponding to dual wavelengths. The phase of the averaged product at the object plane provides the shape of the surface, whereas the peak position of the modulus with respect to reconstruction distance provides the position of the surface. The phase is almost free from speckle noise and easy to be unwrapped. The resultant resolution of surface shape amounts to a few tens of micrometres. The sensitivity of the position measurement that requires no marking on the object is several per cent of object distance from a charge‐coupled device (CCD). The method corresponds to the detection of the position of maximum contrast of the fringes to be observed in conventional holographic interferometry. It makes use of fringe phase for shape measurement and fringe contrast for position measurement. Both the theory explaining the principle and experimental results are presented.     

Uneven fringe projection for efficient calibration in high-resolution 3D shape metrology

A novel uneven fringe projection technique is presented whereby nonuniformly spaced fringes are generated at a digital video projector to give evenly spaced fringes in the measurement volume. The proposed technique simplifies the relation between the measured phase and the object's depth independent of pixel position. This method needs just one coefficient set for calibration and depth calculation. With uneven fringe projection the shape data are referenced to a virtual plane instead of a physical reference plane, so an improved measurement with lower uncertainty is achieved. Further, the method can be combined with a radial lens distortion model. The theoretical foundation of the method is presented and experimentally validated to demonstrate the advantages of the uneven fringe projection approach compared with existing methods. Measurement results on a National Physical Laboratory (UK) "step standard" confirm the measurement uncertainty using the proposed method.     

Discuss the structure condition and sampling condition of wavelet transform profilometry

The structure condition and sampling condition of a wavelet transform profilometry are deduced in this paper and an exhaustive discussion is accomplished. As we all know, by the wavelet transform profilometry, the shape of an object can be obtained by a correlation operation, which provides an approach to retrieve the phase when to some extent there is frequency overlapping between the fundamental spectrum and other spectra. However, it is impossible to obtain the correct phase if the wavelet coefficient at the ‘ridge’ position is not correct. Therefore, it is necessary to discuss the measurement range of the wavelet transform profilometry. Here, from the point of view of the frequency analysis, the discussions, including the structure condition of the measurement system and the sampling condition introduced by digitizing the deformed fringe, have to be done. The conclusion shows that as long as both of the two conditions are met, the correct phase included in the deformed fringe pattern can be retrieved by this method. The computer simulations and experiments verify our analysis.     

White-light Phase-stepping Interferometry for Surface Profiling

Abstract

Interferometric profilers suffer from phase ambiguities if the measurement range involves a change in the optical path difference greater than a wavelength. This limitation has been overcome by using white light and scanning the object in height. We show how an achromatic phase shifter operating on the geometric phase can be used to evaluate the fringe contrast directly and to locate the position of the zero-order white-light fringe along the scanning axis.