Multiple‐view Shape and Deformation Measurement by Combining Fringe Projection and Digital Image Correlation

Abstract: We present a new method that combines the fringe projection and the digital image correlation (DIC) techniques on a single hardware platform to simultaneously measure both shape and deformation fields of three‐dimensional (3‐D) surfaces with complex geometries. The method in its basic form requires only a single camera and single projector, but this can be easily extended to a multi‐camera multi‐projector system to obtain complete 360° measurements. Multiple views of the surface profile and displacement field are automatically co‐registered in a unified global coordinate system, thereby avoiding the significant errors that can arise through the use of statistical point cloud stitching techniques. Experimental results from a two‐camera two‐projector sensor are presented and compared with results from both a standard stereo‐DIC approach and a finite element model.     

反向条纹投影技术及其在数字地球仪中的应用

本文提出一种基于反向条纹投影原理的数字地球仪.在数字地球仪中,显示屏是一个球面的漫反射屏,通过投影的方法可以实现数字地球仪任意方向的旋转显示.首先通过投影正弦条纹到球面显示屏上,从观察数字地球仪的方向用CCD相机获取变形条纹图像,通过相移算法,建立投影器和摄像机像素之间的几何传递关系.基于地球三维图形信息数据库,根据期望图像为投影器产生投影图像.本文建立了地球三维信息提取模型,可快速获取从任意角度观察地球的图形信息.实验使用一半径为25 cm的漫反射球体作为显示屏,将计算得到反向地图投影其上,得到相当好的实验结果.     

High Temperature Gratings for the Moiré and Moiré Interferometry Methods and their Application to Deformation Measurement - A Review

Abstract: This paper gives a general review of the production of high temperature gratings and their application to deformation measurement. The fabrication techniques for gratings and deformation measurement methods using the gratings are discussed. The review is confined to in-plane moiré and moiré interferometry methods. Some typical applications in high temperature deformation measurement are briefly discussed.     

基于条纹投影的复杂曲面测量技术

如何快速、高精度地测量复杂曲面的三维轮廓是目前的一个热点研究方向。与现有的测量方法相比,条纹投影轮廓测量技术具有非接触测量、测量速度快和重构点云密集等优点,在逆向工程等领域得到了广泛的应用。本文搭建了基于条纹投影轮廓测量技术的复杂曲面测量装置,并且对相位误差标定及补偿、投影仪精确标定、高阶系统模型简化以及有效点云快速识别等条纹投影轮廓测量的关键技术进行了深入地研究。最后使用该装置进行了叶片表面轮廓测量实验,实验结果表明,本文设计装置的测量偏差最大值不超过0.05 mm。     

相移条纹投影三维形貌测量技术综述

结构光三维形貌测量系统目前得到了越来越广泛的应用和研究,相移条纹投影三维形貌精密测量技术是其重要的发展方向。对结构光相移条纹投影三维形貌测量系统的应用发展、工作过程、不同系统构成方式、相移条纹的各种形式及特点、相位误差校正方法、不同相位解包裹算法及其优缺点和适用场合、测量系统数学模型的实现方法及其相应的优缺点、高动态范围测量技术等进行了详细的分析。对相移条纹投影系统的工作流程、实现方法、关键技术的发展及其存在问题等进行了比较全面的梳理,为三维形貌精密测量技术进一步满足先进制造中更高精度的要求指出了后续的研究方向。     

Measurement of the Appearance and Growth of Tow Buckling Defect in the Frame of Complex Shape Manufacturing Process by Using Fringe Projection Technique

During the manufacturing of composite complex shape parts, defects such as tow buckles characterised by out of plane elevation may appear. The parameters controlling the appearance and growth of the defect are not completely understood and need to be investigated. A device capable of reproducing tow buckles has been used to study the tow buckling phenomenon. Several techniques able to measure out of plane elevations are discussed to detect the appearance and evaluate continuously the growth of the tow buckle in relation to its size and shape. The fringe projection technique was chosen as it gives the best compromise between the size of the defect to measure and its resolution. If the in‐plane bending angle is the main criterion at the origin of the tow buckle appearance and growth, it is not the only one. This work shows that the fabric architecture such as the space between the tows perpendicular to the one showing the buckle is also crucial to control the buckle's appearance and growth. It also shows that the differential bi‐axial loading of the fabric as well as the stiffness of the tows in the three main directions greatly influences the appearance of the defect.     

显微栅线投影相关法及其在三维形貌测试中的应用

基于数字图像相关法解调被物体高度调制的投影栅线平移量的原理，提出了显微栅线投影相关法的概念。该方法是栅线投影法和数字图像相关方法相结合的产物，用于测量微结构的三维形貌和离面变形。系统阐述了该方法的测量原理和详细的标定过程，研究了该方法在微薄膜挠度测量中的应用。测量结果表明，显微栅线投影相关法简单易行，测试结果可靠，配合高速图像采集系统，可用于微结构的动态测试，从而为实现微结构动、静态测试展现了新的应用前景。     

基于EMD算法的光栅莫尔条纹信号去噪方法研究

针对计量光栅莫尔条纹信号的质量问题,提出了基于经验模态分解（EMD）算法对非平稳光栅莫尔条纹信号模型的去噪方法。建立非平稳的光栅时变信号模型,利用EMD算法不需要定义滤波器参数的自适应性优点,对添加不同噪声的多组光栅信号模型进行了滤波分析的仿真实验,其信噪比和均方根误差两项指标优于均值滤波、小波阈值去噪方法。对两路正余弦理想信号添加高次谐波分量,通过对比EMD算法抑制高次谐波前后的李萨如图形,验证了该方法在去噪过程中对光栅莫尔条纹信号正弦性误差补偿的良好效果。     

基于条纹反射的镜面测量及三维重建算法分析

本文详细介绍了依据条纹反射术测量镜面,类镜面的原理和方法,分析了经由梯度数据重建三维面形的主要算法和关键问题.通过计算机模拟和波面实际测量,对十字路径积分法、傅里叶变换积分法和区域波前重构法三种主要算法的重建精度进行了对比研究.研究表明:区域波前重构法不但对高频噪声有较强的抑制作用,同时也可以处理复杂的连通区域和非等间距分布梯度数据的复杂情况,因此更适用于基于条纹反射术的波面测量.     

Analysis of Digital Speckle‐Pattern Interferometry Fringe Patterns Issued from Transitory Mechanical Loadings

Abstract: During a dynamic mechanical loading, we cannot use a phase‐shifting technique because the mechanical parameters evolve according to the time. This problem can be avoided by the development of algorithms which can extract the mechanical information from only one fringe pattern. In this way, we present two algorithms, the modulated phase correlation (MPC) and the polynomial modulated phase correlation (pMPC). These processes are based on the use of the virtual fringe pattern which locally approaches the real fringe morphology. The similarity degree between real and virtual fringe pattern is estimated by digital correlation technique. When the best similarity is obtained, we suppose that the virtual phase function is very close to the real phase function. Some examples are presented to show the low noise sensitivity of these techniques. So, we propose to use the MPC or the pMPC algorithms to extract the relief from a single interferogram obtained by digital speckle‐pattern interferometry. In this paper, we present experimental tests of impact loading on plates. The frame rate is adapted to the dynamic conditions of loading. Recorded fringe patterns and results of the unwrapped phase demodulated with our algorithms are shown.     

屏幕上点的斜面透视投影坐标式及计算机的绘图

推导出来的屏幕上点的斜面透视投影坐标式，完全满足计算机易于使用的参数方法的要求。用它编程，不但可以把正投影中点的坐标或曲线的参数方程转换成屏幕上能够直接显示点的透视投影的坐标或曲线的透视投影的参数方程，而且除了赋值不同外，对绘一点透视，二点透视和三点透视都具有通用性。此法与矩阵法相比，数学知识简单，易运用，特别是完全可以直接应用曲线的参数方程，更显示其优点。     

基于投影寻踪模型的纸和纸板质量综合评价

采用基于遗传算法的投影寻踪模型(GA-PP)用于纸和纸板质量分类与评价。该模型依据样本数据类内密集度和类间散开度最大构建目标函数,寻求最优的投影方向,将多维分类指标综合成一维指标,然后利用一维投影值特征信息,根据相近原则进行样本的聚类与排序。实例研究表明:投影寻踪模型得到的各指标权重客观地反映了各评价指标之间的影响关系,用于纸和纸板质量分类与评价切实可行,分析结果和其它方法具有较好的一致性,并更为合理和可靠。     

基于投影寻踪模型的区间数群决策权重确定

扩展了可直接处理特征空间为区间数的PROMETHEE II多属性群决策方法,从最佳投影角度构造了专家信息前处理群决策权重确定的投影寻踪模型。考虑到传统的优化方法很难获得群决策权重的最优解,文中应用遗传算法来全局优化确定群决策权重。该方法特别适合于决策方案比较多的场合。应用实例表明了该方法具有一定的可行性、有效性和推广应用价值。     

微显示背投电视的技术和市场新进展

背投影电视机是现代电视技术、光学技术和新材料技术结合的产物，其显示系统可采用CRT（阴极射线管）、PDP（等离子显示器）、LCD（液晶显示器）、DLP（数字光处理器）和LCoS（硅基液晶）等显示技术，后三种又称微显示技术，因为采用的是微型的显示器和电子元件，因而大大降低功耗和生产成本，减小体积和厚度。而且微显示背投影电视机图像较CRT背投亮度强，清晰度高，屏幕可以做大，寿命长，综合性能明显优越，极有发展前途。本文对此进行综述和分析。     

Projection and Contraction Method for the Valuation of American Options

An efficient numerical method is proposed for the valuation of American options via the Black-Scholes variational inequality. A far field boundary condition is employed to truncate the unbounded domain problem to produce the bounded domain problem with the associated variational inequality, to which our finite element method is applied. We prove that the matrix involved in the finite element method is symmetric and positive definite, and solve the discretized variational inequality by the projection and contraction method. Numerical experiments are conducted that demonstrate the superior performance of our method, in comparison with earlier methods.     

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.     

Three‐Dimensional Printing of Multifunctional Nanocomposites: Manufacturing Techniques and Applications

The integration of nanotechnology into three‐dimensional printing (3DP) offers huge potential and opportunities for the manufacturing of 3D engineered materials exhibiting optimized properties and multifunctionality. The literature relating to different 3DP techniques used to fabricate 3D structures at the macro‐ and microscale made of nanocomposite materials is reviewed here. The current state‐of‐the‐art fabrication methods, their main characteristics (e.g., resolutions, advantages, limitations), the process parameters, and materials requirements are discussed. A comprehensive review is carried out on the use of metal‐ and carbon‐based nanomaterials incorporated into polymers or hydrogels for the manufacturing of 3D structures, mostly at the microscale, using different 3D‐printing techniques. Several methods, including but not limited to micro‐stereolithography, extrusion‐based direct‐write technologies, inkjet‐printing techniques, and popular powder‐bed technology, are discussed. Various examples of 3D nanocomposite macro‐ and microstructures manufactured using different 3D‐printing technologies for a wide range of domains such as microelectromechanical systems (MEMS), lab‐on‐a‐chip, microfluidics, engineered materials and composites, microelectronics, tissue engineering, and biosystems are reviewed. Parallel advances on materials and techniques are still required in order to employ the full potential of 3D printing of multifunctional nanocomposites.     

Non-destructive evaluation of fatigue and creep-fatigue damage by means of the induced-current focused potential drop technique

Quantitative evaluation of damage accumulation including crack initiation and propagation is one of the major concerns of industrial plant management and plant licence renewal. In order to develop a novel non-destructive testing (NDT) and non-destructive evaluation (NDE) technique for damage evaluation, the induced-current focused potential drop (ICFPD), originally proposed for a defect inspection, was employed. In this study, ICFPD was successfully applied to a non-destructive damage evaluation based on crack measurements. The measurements were taken on fatigued specimens with various degrees of fatigue damage. The ICFPD can clearly detect and differentiate the damage accumulation processes including crack initiation, small crack growth and subsequent macroscopic crack growth. In order to demonstrate the applicability of damage evaluation assessments based on small crack measurements, ICFPD has also been applied to creep–fatigue loading where damage evaluation of a fusion reactor material is based on small crack measurements by the ICFPD technique and a novel methodology is proposed.     

Performance Analysis and Evaluation of Geometric Parameters in Stereo Deflectometry

This paper presents a novel geometric parameters analysis to improve the measurement accuracy of stereo deflectometry. Stereo deflectometry can be used to obtain form information for freeform specular surfaces. A measurement system based on stereo deflectometry typically consists of a fringe-displaying screen, a main camera, and a reference camera. The arrangement of the components of a stereo deflectometry system is important for achieving high-accuracy measurements. In this paper, four geometric parameters of a stereo deflectometry system are analyzed and evaluated: the distance between the main camera and the measured object surface, the angle between the main camera ray and the surface normal, the distance between the fringe-displaying screen and the object, and the angle between the main camera and the reference camera. The influence of the geometric parameters on the measurement accuracy is evaluated. Experiments are performed using simulated and experimental data. The experimental results confirm the impact of these parameters on the measurement accuracy. A measurement system based on the proposed analysis has been set up to measure a stock concave mirror. Through a comparison of the given surface parameters of the concave mirror, a global measurement accuracy of 154.2 nm was achieved.