Influence of sampling on three-dimensional surface shape measurement

In order to accurately measure an object’s three-dimensional surface shape,the influence of sampling on it was studied.First,on the basis of deriving spectra expressions through the Fourier transform,the generation of CCD pixels was analyzed,and its expression was given.Then,based on the discrete expression of deformation fringes obtained after sampling,its Fourier spectrum expression was derived,resulting in an infinitely repeated"spectra island"in the frequency domain.Finally,on the basis of using a low-pass filter to remove high-order harmonic components and retaining only one fundamental frequency component,the inverse Fourier transform was used to reconstruct the signal strength.A method of reducing the sampling interval,i.e.,reducing the number of sampling points per fringe,was proposed to increase the ratio between the sampling frequency and the fundamental frequency of the grating.This was done to reconstruct the object’s surface shape more accurately under the condition of m>4.The basic principle was verified through simulation and experiment.In the simulation,the sampling intervals were 8 pixels,4 pixels,2 pixels,and 1 pixel,the maximum absolute error values obtained in the last three situations were 88.80%,38.38%,and 31.50%in the first situation,respectively,and the corresponding average absolute error values are 71.84%,43.27%,and 32.26%.It is demonstrated that the smaller the sampling interval,the better the recovery effect.Taking the same four sampling intervals in the experiment as in the simulation can also lead to the same conclusions.The simulated and experimental results show that reducing the sampling interval can improve the accuracy of object surface shape measurement and achieve better reconstruction results.

Multi-objective strategy to optimize dithering technique for high-quality three-dimensional shape measurement

Dithering optimization techniques can be divided into the phase-optimized technique and the intensity-optimized technique. The problem with the former is the poor sensitivity to various defocusing amounts, and the problem with the latter is that it cannot enhance phase quality directly nor efficiently. In this paper, we present a multi-objective optimization framework for three-dimensional(3D) measurement by utilizing binary defocusing technique. Moreover, a binary patch optimization technique is used to solve the time-consuming issue of genetic algorithm. It is demonstrated that the presented technique consistently obtains significant phase performance improvement under various defocusing amounts.

A method for phase reconstruction in optical three-dimensional shape measurement

In optical three-dimensional shape measurement, a method of improving the measurement precision for phase reconstruction without phase unwrapping is analyzed in detail. Intensities of any five consecutive pixels that lie in the x-axis direction of the phase domain are given. Partial derivatives of the phase function in the x- and y-axis directions are obtained with a phase-shifting mechanism, the origin of which is analysed. Furthermore, to avoid phase unwrapping in the phase reconstruction, we derive the gradient of the phase function and perform a two-dimensional integral along the x- and y-axis directions. The reconstructed phase can be obtained directly by performing numerical integration, and thus it is of great convenience for phase reconstruction. Finally, the results of numerical simulations and practical experiments verify the correctness of the proposed method.

Balanced Functional Maps for Three-Dimensional Non-Rigid Shape Registration

Three-dimensional(3D)shape registration is a challenging problem,especially for shapes under non-rigid transformations.In this paper,a 3D non-rigid shape registration method is proposed,called balanced functional maps(BFM).The BFM algorithm generalizes the point-based correspondence to functions.By choosing the Laplace-Beltrami eigenfunctions as the function basis,the transformations between shapes can be represented by the functional map(FM)matrix.In addition,many constraints on shape registration,such as the feature descriptor,keypoint,and salient region correspondence,can be formulated linearly using the matrix.By bi-directionally searching for the nearest neighbors of points’indicator functions in the function space,the point-based correspondence can be derived from FMs.We conducted several experiments on the Topology and Orchestration Specification for Cloud Applications(TOSCA)dataset and the Shape Completion and Animation of People(SCAPE)dataset.Experimental results show that the proposed BFM algorithm is effective and has superior performance than the state-of-the-art methods on both datasets.

A fast and precise three-dimensional measurement system based on multiple parallel line lasers

This paper conducts a trade-off between efficiency and accuracy of three-dimensional(3 D)shape measurement based on the triangulation principle,and introduces a flying and precise 3 D shape measurement method based on multiple parallel line lasers.Firstly,we establish the measurement model of the multiple parallel line lasers system,and introduce the concept that multiple base planes can help to deduce the unified formula of the measurement system and are used in simplifying the process of the calibration.Then,the constraint of the line spatial frequency,which maximizes the measurement efficiency while ensuring accuracy,is determined according to the height distribution of the object.Secondly,the simulation analyzing the variation of the systemic resolution quantitatively under the circumstance of a set of specific parameters is performed,which provides a fundamental thesis for option of the four system parameters.Thirdly,for the application of the precision measurement in the industrial field,additional profiles are acquired to improve the lateral resolution by applying a motor to scan the 3 D surface.Finally,compared with the line laser,the experimental study shows that the present method of obtaining 41220 points per frame improves the measurement efficiency.Furthermore,the accuracy and the process of the calibration are advanced in comparison with the existing multiple-line laser and the structured light makes an accuracy better than 0.22 mm at a distance of 956.02 mm.

THE APPLICATION OF SPLINE FUNCTION IN THE GEOMETRIC REPRODUCTION OF LOG SHAPE

The paper introduces a method to get three-dimensional reproduction of log shape by adopting Spline Function in fitting the curve of the finite log data. The method has ad-vantages of higher accuracy, less acquired data, easier to use, etc. Making use of high-precision drawing function of computer, the graphs of log geometric shape in different visual angles can be achieved easily with this method. It also provided a firm foundation for the determination of optimum saw cutting scheme.

Three-dimensional multiple optical cages formed by focusing double-ring shaped radially and azimuthally polarized beams

We propose and simulate a method for generating a three-dimensional （3D） optical cage in the vicinity of focus by focusing a double-ring shaped radially and azimuthally polarized beam. Our study shows that the combination of an inner ring with an azimuthally polarized field and an outer ring with a radially polarized field and a phase factor can produce an optical cage with a dark region enclosed by higher intensity. The shape of the cage can be tailored by appropriately adjusting the parameters of double-mode beams. Furthermore, multiple 3D optical cages can be realized by applying the shift theorem of the Fourier transform and macro-pixel sampling algorithm to a double-ring shaped radially and azimuthally polarized beam.

“活性碱”对出土干缩变形木质文物的润胀复原研究

为使干缩变形木质文物恢复原有形状,采用"活性碱"作为润胀剂,对干缩变形的出土木质文物进行了复原试验,并采用环境扫描电镜、傅立叶红外光谱、X射线衍射仪对复原前后的木质成分、结构进行了表征。结果表明,经"活性碱"处理后,干缩木材试样中木质素的含量、纤维素结晶度明显降低;干缩木材中原本塌陷的细胞腔结构得以恢复,同干缩状态相比,复原后木材体积的最大膨胀值达420%,使得干缩变形的木材试样基本恢复了原有形状。

一种治理主溜井特大塌方的新方法——托斗法

介绍一种治理主溜井特大塌方的新方法——托斗法。该方法的技术核心是:采用箱式结构梁跨越塌空区,成为卸矿支承结构使其放矿功能得到恢复;在溜井卸矿水平以下局部施工一倒锥台体的漏斗式结构,兼有储矿和溜矿功能,同时对上部和周围井壁给予支撑。该项技术通过对特大塌方现场的局部加固,获得整个系统稳定的工程效果,既实现对系统功能的全面恢复,又在本质上解决对特大塌方的综合治理和预防,是结构设计理念上的突破。

近代民间服饰门襟形式研究与裁剪工艺复原

针对近代民间服饰门襟形式与裁剪工艺进行了研究.通过对江南大学传习馆内收藏的近代民间服饰的观察和测量以及走访了中式传统服装制作的工艺传人,对近代民间服饰中门襟的种类、形式逐一进行了记录、分析和研究,并对其裁剪工艺进行了复原.

新型螺纹联接接触恢复应力的计算表征

基于铁基形状记忆合金新型防松螺母的防松机理,对由该新型螺母组成的新型螺纹联接的接触恢复应力进行了计算表征。并以M10×1.5的螺纹连接为例,对该新型螺纹联接的接触恢复应力进行了计算,通过与实验结果的比较论证了该恢复力计算模型的正确性。

SFS方法在车身重建中的应用研究

提出了一个基于Shape From Shading(SFS,基于阴影恢复形状)方法进行车身重建的方法,该方法从车身二维照片入手,采用图像处理技术对图像进行必要的处理,并由图像的亮度进行车身三维形状的重建,利用VC++6.0和OpenGL开发了一个重建平台,实现了车身外形的重建。

基于TDLAS的天然气泄漏空间动态分布监测技术及应用研究

天然气泄漏污染空气,易造成爆炸事故,危害人身安全,长期泄漏造成资源浪费,因此天然气泄漏监测成为天然气站亟待解决的问题。相较于其他各种测量原理,可调谐激光二极管吸收光谱(TDLAS)技术因其响应迅速、非接触式测量等优点,广泛应用于开放环境下天然气泄漏监测。目前天然气站一般采用多点多线布置多个开放式激光气体遥测仪监测或采用多个扫描式激光气体遥测仪巡航监测的方案,监测区域范围小、漏洞大。本文基于TDLAS的奇次谐波信号建立吸收率函数在线重构算法,提出了一种天然气泄漏空间监测方法及系统,该系统基于GIS平台对天然气站进行三维建模,将监测数据融合处理,采用空间浓度场反演算法,在动态扫描后生成整个场站的浓度动态分布图。该系统实施后的试验结果表明,天然气泄漏监测系统响应迅速、灵敏度高、报警联动及时,三维场景及浓度动态分布图显示直观,泄漏点判断准确。

Ti-22Nb-6Zr(at%)合金的超弹性和形状记忆效应

用弯曲法和拉伸法测定Ti-22Nb-6Zr(at%)合金的超弹性和形状记忆效应,研究固溶处理温度对Ti-22Nb-6Zr合金组织结构及性能的影响。结果表明:固溶处理后Ti-22Nb-6Zr合金的室温组织为单一的β相,晶粒尺寸随固溶处理温度升高而增大;合金的静态弹性模量小于30GPa;Ti-22Nb-6Zr合金具有良好的超弹性和一定的形状记忆效应。室温下变形,合金的超弹性和形状记忆效应随固溶处理温度升高而提高。900℃固溶处理后的合金在室温下拉伸变形,应变为5%时,总的最大回复应变达4.12%,其中超弹性回复应变为3.91%,记忆回复应变为0.21%。

快速凝固Cu-Al-Ni合金的记忆性能及时效稳定性

采用快速凝固淬火法获得Cu-Al-Ni合金带,并对其合金的转变特性、记忆性能、时效对临界点的影响以及应变与回复率的关系进行了研究,为了进一步开发和应用提供了依据。

基于傅里叶变换轮廓术的钢轨三维面型复原

随着现代化轨道交通的飞速发展,在线非接触式检测技术已成为钢轨面型检测的趋势。本文基于傅里叶变换轮廓术(F T P)提出实现钢轨的三维面型复原的新方法。通过生成虚拟光栅,再将其投影在被测钢轨上,得到被测钢轨的变形光场图。再由滤波和相位展开等步骤成功恢复出被测钢轨的三维面型,为控制钢轨的外形尺寸,提高外观质量提供了新的方法。

Emplacement Mechanism of the Akebasitao Pluton:Implications for Regional Tectonic Evolution of West Junggar,NW China

Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we reported new anisotropy of magnetic susceptible （AMS） data combine with detailed field study and audio magnetotelluric （AMT） sounding to assess the three-dimensional shape and magmatic emplacement mechanism of the Akebasitao pluton. The geological features and the AMT sounding indicate that the pluton had a slightly oblique movement of magma from northwest to southeast, which was most likely to correspond to an asymmetrical torch with a laccolith-shaped upper part, and a lower part formed by sub-vertical ＂root＂ that was located within its northwestern part, probably controlled by the NE-trending Anqi fault. The AMS fabrics of all the specimens reveal a low Pj value （mean of 1.02） and a low T value （mean of -0.024）, suggesting that the deformation of the AMS ellipsoid is relatively weak. The specimens exhibit both oblate and prolate shapes of the AMS ellipsoid. Magnetic lineations and foliations are randomly distributed throughout the pluton without any preferred orientation. These AMS patterns indicate that the pluton formed in a relatively stable structural environment with no regional extrusion. Therefore, we propose a complex emplacement process in which the magmas reached the shallower crust levels via deep-faults and subsequently occupied the room created by doming, accompanied by stoping near the pluton roof. Additionally, the regional tectonic setting was relatively stable during the emplacement of the Akebasitao pluton, indicating the termination of compressional orogeny during the late Late Carboniferous in the West Junggar region. This conclusion perfectly coincides with the regional tectonic paleogeography, magmatic system, and paleostress field.

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.

提高SMW工法桩型钢回收率技术研究

南京青奥轴线地下隧道工程J3区围护结构采用SMW工法桩围护结构形式,工法桩共2 102组,需型钢3 154根。通过对以往类似工程型钢未回收的原因进行调查分析,借鉴相关经验,积极进行技术创新,施工中加强过程管控,主体工程完工后,型钢回收3 035根,总体回收率达到96.24%。

Estimation of the Scale of Artificial Reef Sets on the Basis of Underwater 3D Reconstruction

The creation of three-dimensional models from an unorganized set of points is an active research area in computer graphics.One of the purposes of this study is to explore the 3D reconstruction of a cube-type artificial reef(CTAR)set by linear structured light and binocular stereo vision technology in an underwater environment.The experimental setup is composed of two ca-meras in a stereo vision configuration.The alpha shapes method can be used to construct a surface that most closely reflects the arti-ficial reef set described by the points.A parameter study is conducted to assess the scales of the set(i.e.,usable volume,surface area,projected area,height,and base diameter)on the basis of 3D reconstruction.Experimental results show that the quality of 3D recon-struction in an underwater environment is acceptable for estimating the scale size of the CTAR set.According to the measurement of the scale sizing of the CTAR set,the relationships between the parameters of the CTAR set and the number of CTAR modules were determined.Moreover,the usable volume of the CTAR set can be estimated depending on the basis of the number of CTAR modules.