Development of a Laser Speckle Interferometer to Measure Two-dimensional In-plane Vibration in Real-time Based on Fourier Transform with Electronic Circuit

为了研制高性能、高精度实时测量多维位移的振动仪，提出了一种基于四孔法的二维傅里叶变换干涉像位相检测激光散斑干涉仪，并对其进行了理论和实验验证。然后设计了二维傅里叶变换的模拟电子电路。主要研究成果如下：(1)搭建了四孔径法激光散斑干涉仪样机。通过相关法检测点阵式干涉图像的二维位移，即可测量出目标的二维位移。(2)从理论上推导了点阵式干涉图像的二维傅里叶变换。结果表明，在干涉像基频的两倍空间频率处，目标的位移与相位谱成正比，与相关法相比，计算成本显著降低。(3)对二维静态位移进行了测量实验，并讨论了引起测量误差的因素。结果表明，干涉图像的平均能见度越高，图像的相位变化越小，测量误差越小。(4)通过选择激光照射点，使干涉图像的平均能见度高，图像的相位变化小，并对图像进行25点中值滤波，减小了测量误差。(5)设计了一种模拟电路，可以根据二维傅里叶变换实时计算C-MOS图像传感器获得的干涉图像的基频分量的相位。

Aiming to develop a high-performance vibrometer which can measure multi-dimensional displacement with high accuracy in real-time, a new laser speckle interferometer based on the quad aperture method with a phase detector of interference image using two-dimensional Fourier transform was proposed and was theoretically and experimentally examined. Analogue electronic circuit for two-dimensional Fourier transform was then designed. The results obtained are summarized as follows.(1)A prototype of a laser speckle interferometer with the quad aperture method was built. And by detecting a two-dimensional displacement of lattice type interference image with correlation method, a two-dimensional displacement of a target can be measured.(2)Two-dimensional Fourier transform of the lattice type interference image was theoretically derived. It was then revealed that displacement of the target was in proportion to the phase spectrum at the spatial frequency twice as high as the fundamental spatial frequency of interference image and that the calculation cost could be remarkably reduced in compare with that of the correlation method.(3)Experiments to measure the two-dimensional static displacement were carried out and then the factors to cause measuring error were discussed. It was revealed that the measuring error became smaller as the average visibility of the interference image was higher and as the phase variation in the image was smaller.(4)By selecting laser irradiation point so that the average visibility of the interference image is high and that the phase variation in the image is small, and by applying the 25 points median filter to the image, the measuring error becomes reduced.(5)An analogue electronic circuit which can calculate the phase of the fundamental frequency component of the interference image obtained with C-MOS image sensor according to two-dimensional Fourier Transform in real-time was designed.