Digital holographic cameras and data processing for remote monitoring and measurements of mechanical parts

Fast growing technology and requirements for testing of different types of materials and devices require new methods and systems for investigation of their parameters. Among the quantities of high interest are shape, deformation, roughness, local materials constants, displacement, and strain fields of elements under load. In the paper, we present novel solutions for digital holographic cameras, which allow for remote monitoring and measurement of the above mentioned quantities at small mechanical objects or at restricted areas of interest at big structures. The systems have compact design, “black box” measurement approach, and allows for fast and accurate measurements performed directly at the element and often in outdoor environment. The principles of digital and optoelectronic reconstruction and phase manipulation are described together with the exemplary measurement results obtained by means of the cameras presented.     

Three-dimensional analytical solution for a transversely isotropic functionally graded piezoelectric circular plate subject to a uniform electric potential difference

This paper studies the problem of a functionally graded piezoelectric circular plate subjected to a uniform electric potential difference between the upper and lower surfaces. By assuming the generalized displacements in appropriate forms, five differential equations governing the generalized displacement functions are derived from the equilibrium equations. These displacement functions are then obtained in an explicit form, which still involve four undetermined integral constants, through a step-by-step integration which properly incorporates the boundary conditions at the upper and lower surfaces. The boundary conditions at the cylindrical surface are then used to determine the integral constants. Hence, three-dimensional analytical solutions for electrically loaded functionally graded piezoelectric circular plates with free or simply-supported edge are completely determined. These solutions can account for an arbitrary material variation along the thickness, and thus can be readily degenerated into those for a homogenous plate. A numerical example is finally given to show the validity of the analysis, and the effect of material inhomogeneity on the elastic and electric fields is discussed. Supported by the National Natural Science Foundation of China (Grant Nos. 10472102 and 10432030) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20060335107)     

Neutron scattering by anharmonic crystals and the effect of sublattice displacements

A theory has been given for the scattering of neutrons by anharmonic crystals, for which terms of the typeV ⁽³⁾ (k _1j1; —k _1j1;o _j) which contribute to the sublattice displacements are not neglected. Using the standard perturbation theory in the interaction picture or Green’s function method, an expression has been derived for the differential scattering cross-section which brings in the shift and the width of the phonons in one-phonon energy exchange processes. It is shown that the sublattice displacements will modify the phase factor arising from the scattering by any atom in the unit cell, and the Debye-Waller factor also gets altered both by the sublattice displacements as well as by higher order terms arising from anharmonicity. It is shown that the differential scattering cross-section contains a term linearly depending on the third order anharmonicity coefficientV ⁽³⁾ (k _1j1;k _2j2;k _3j3) and neutron scattering by crystals should provide a useful method for evaluating the third order anharmonicity coefficients.     

Newton-Like Iteration Based on a Cubic Polynomial for Structured Matrices

We recall Newtons iteration for computing the inverse or Moore–Penrose generalized inverse of a matrix. Then we specialize this approach to the case of structured matrices where all input, output and intermediate auxiliary matrices are represented in a compressed form, via their short displacement generators. We design a new Newton-like iteration based on a cubic polynomial and show its effectiveness by some numerical experiments for matrices from the Toeplitz-like class and the Cauchy-like class.     

双频氦氖激光回馈位移测量系统的实验与应用研究

研究了一种全新的纳米尺度位移测量系统。将双折射元件插入He-Ne激光器谐振腔内产生频率分裂效应，使原本单模谐振的激光器输出变成了频差可调的2个正交偏振频率（o光和e光），而形成双频激光器。在激光谐振腔外放置沿激光轴线位移的反射表面，将输出的激光束反射回腔内，以便对激光的光强进行调制，可实现高分辨率非接触式可判向位移测量。提出了一种细分方法，该方法突破了传统干涉系统的衍射极限（1/2波长）。对于633nm波长He-Ne激光，本系统的理想分辨率为1/8波长（约为79nm）。     

光指针式微小位移测量仪

光指针式微小位移测量仪巧用光路将微小的位移量放大,从光指针终端的标度盘上可以直接读取实际的位移数值.     

带宽调制型单光纤光栅温变无补偿位移传感

报道了利用反射谱带宽调制和光强差分探测技术实现单一光纤光栅温变无补偿位移精确测量的新方法。设计了一种结构新颖的曲臂梁位移传感装置,结合光波导理论与材料力学原理分析了光纤光栅在高斯应变作用下光栅反射谱侧向梯度展宽的成因,理论推导了特殊结构梁在外力作用下光栅反射谱带宽/反射光强与压力之间的响应关系。光栅反射谱侧向梯度展宽的同时反射光强线性增加,利用光强差分检测方法消除光源出光抖动的影响,提高了位移测量精度。基于带宽调制的光纤光栅位移传感方法免受温度变化的影响,在-10℃~80℃的温度变化范围内,测量误差小于1.2%,实现了单光纤光栅温变无补偿位移测量。     

基于视觉测量的飞行器舵面角位移传感器标定

提出一种基于计算机单目视觉的飞行器副翼、襟翼、方向舵和升降舵角位移传感器的非接触标定方法.用共面的两个特征圆组成一标定靶固定在飞行器舵面上,用一台定焦数码摄像机对标定靶拍照,获得特征圆数字图像.经图像分析确定特征圆圆心及直径在像面上的透视投影位置和长度,根据透视投影逆变换原理建立物和像空间坐标关系的解算模型,进而导出靶面平面方程.飞行器舵面角位移则由标定靶面的法线方向余弦来表示.仿真结果表明,该方法具有标定过程快速、简单和准确的特点.不需事先标定摄像机内外部参量,其标定准确度优于0.2°.     

Parallel Plate Interferometer with a Reflecting Mirror for Measuring Angular Displacement

A parallel plate interferometer with a reflecting mirror for measuring angular displacement is proposed. A deflection angle of a beam caused by an angular displacement is amplified by use of a reflecting mirror to increase the optical path difference (OPD) in the plane-parallel plate, which provides high sensitivity of the phase measurement. Detection of light transmitted through the plane-parallel plate with a position sensitive detector (PSD) enables high accurate measurement of the initial angle of incidence to the plane-parallel plate with insensitivity to stray light. The improved parallel plate interferometer achieves a measurement repeatability of 10⁻⁸ rad.     

SUPERCONVERGENCE OF THE FULL-DISCRETE F.E.M. FOR COMPRESSIBLE MISCIBLE DISPLACEMENT: THE FULL TENSOR CASE

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