Application of a NDI method using magneto-optical film for micro-cracks

Leakage magnetic flux is occurred in the cracked area of magnetized specimens, and also it changes the magnetic domain area of the magneto-optical film positioned on the specimen. It causes the change of the optical permeability of the magnetic domain on the crack area. So crack images can be obtained easily using this principle. On the other hand, utilizing a laser in this method makes possible to perform a remote sensing by detecting the light intensity contrast between cracked area and normal area. This paper shows the application of non-destructive inspection system taking advantage of magneto-optical method for micro-cracks and presents examples applied to the several types of specimens having fatigue cracks and fabricated cracks using this method. Also the authors prove the possibility of this method as a remote sensing system under the oscillation load considering application to real fields.     

焊接缺陷磁光成像动态检测与识别

为了实现焊接缺陷的自动检测,研究一种交变磁场激励下焊缝表面及亚表面缺陷的磁光成像动态无损检测方法。分析了基于法拉第磁致旋光效应的焊接缺陷磁光成像机理,并结合交变磁场原理推导出励磁变化与动态磁光成像的关系。探索低碳钢板的亚表面焊缝磁光成像特征试验,验证了所提方法可用于检测焊缝亚表面的未熔合缺陷。最后对高强钢焊缝特征的动态磁光图像进行分析,采用主成分分析法和支持向量机(PCA-SVM)模式识别方法建立了焊接缺陷分类模型。试验结果表明,所提方法可以识别高强钢焊件中的焊缝特征(未熔透、裂纹、凹坑和无缺陷),缺陷分类模型的整体识别率达到92.6%,能够实现焊缝表面及亚表面缺陷的自动检测。     

Theoretical consideration of nondestructive testing by use of vertical magnetization and magneto-optical sensor

This paper describes a new magnetization method for non-destructive testing with magneto-optical sensor (denoted as MO sensor) which have the following characteristic; high observation sensitivity, independence of the crack orientation, and precise imaging of a complex crack geometry such as multiple cracks. When a magnetic field is applied normally to the surface of a specimen which is significantly larger than its defects, approximately the same magnetic charge per unit area occurs on the surface of the specimen. If there is a crack in the specimen, magnetic charge per unit area has the same value at the bottom of the crack. The distribution of the vertical component of the magnetic flux density, B_z, is almost uniform over the no-crack area (denoted as B_{Z, BASE}), while the magnetic flux density is smaller in the surroundings of the crack (denoted as B_{Z, CRACK}) : If B_{Z, BASE} is a bit larger than the saturated magnetic flux density of the MO sensor (B_S), then small magnetic domains occur over the crack area and a large domain over the non-crack area because B_{Z, CRACK} is smaller than B_s.     

Nondestructive evaluation of a crack on austenitic stainless steel using a sheet type induced current and a Hall sensor array

Austenitic stainless steels (hereafter A-STS) such as STS304 and STS316 are paramagnetic metals. However, a small amount of partial magnetization is generated in A-STS because of the imperfect final heat treatment and mechanical processing. Surface cracks on paramagnetic metal with a partially magnetized region (hereafter PMR) are difficult to inspect. In this paper, we propose a method for high speed inspection and evaluation of a crack on A-STS. Cracks can be inspected with high speed by using 64 arrayed Hall sensors (HSA) with 3.5 mm spatial resolution and a sheet type induced current (STIC). Then, a crack can be evaluated quantitatively by using the detailed distribution of the magnetic field obtained by using single Hall sensor scanning (SSS) around the inspected crack area. Several cracks on A-STS with partially magnetized areas were examined and the experimental formulas were derived.     

Defect inspection and extraction of the mobile phone cover glass based on the principal components analysis

Surface defect inspection is an important part of quality control in mobile phone cover glass manufacturing. The traditional method is usually carried out manually by experienced inspectors and thus lacks sufficient efficiency and accuracy. In this paper, an automatic defect inspection system based on the principal components analysis is proposed for five typical cover glass defects: scratch, crack, deformation, edge broken, and angle cutting. This inspection system is robust for the defect shapes and obtains high recognition accuracy. The inspection system includes three parts: pre-processing, PCA-based defect recognition, and defect edge extraction. After pre-processing, most of noise and outliers are eliminated and the pixels of defects in the image are well enhanced for inspection and recognition. The eigen-defect matrix is constructed to characterize the variation between defect images. Additionally, time consumption in constructing the eigen-defect matrix is also discussed. The experimental results show that the inspection system has achieved high accuracy for inspection and recognition.     

Scanning magneto-optical Kerr microscope with auto-balanced detection scheme

We have developed a scanning magneto-optical Kerr microscope dedicated to localization and measurement of the in-plane magnetization of ultra-thin layered magnetic nanostructures with high sensitivity and signal-to-noise ratio. The novel light detection scheme is based on a differential photodetector with automatic common mode noise rejection system with a high noise suppression up to 50 dB. The sensitivity of the developed detection scheme was tested by measurement of a single Co layer and a giant magnetoresistance (GMR) multilayer stack. The spatial resolution of the Kerr microscope was demonstrated by mapping an isolated 5×5 μm spin-valve pillar.     

Improvement of crack inspection possibility using gradient directional magnetization and linearly integrated hall sensors

A method for improving crack detection using scan-type magnetic flux leakage testing is proposed herein. Usually, the crack detection ability decreases when the crack length direction is parallel to the magnetization direction. We propose a gradient directional magnetization method that improves the probability of detection regardless of the direction of the sensor array, which is parallel to the magnetizer??s poles and perpendicular to the length of the crack. The effectiveness of the gradient directional magnetization method was verified using finite element method simulation and experimental tests.     

基于激光电磁超声的裂纹检测研究

为检测内裂纹,建立了一套基于脉冲激光激发、电磁超声探头接收的非接触型超声检测系统。为避免在试件表面产生烧蚀损伤,采用热弹性模式激发超声,采用EMAT探头接收信号。利用出平面EMAT探头和内平面EMAT探头,分别研究了横波与纵波在半圆铝制试块的传播情况。最后,结合阴影法,使用该试验系统测量了试件背面的裂纹,检测得到的裂纹深度与实际深度非常接近。证明在热弹性模式下,激光激发、EMAT探头接收信号的方法对于内裂纹的检测是可行的。     

机器视觉在工业测量中的应用与研究

基于普通双目视觉测量模型,针对视觉测量系统的关键技术-标定、特征提取、特征匹配,提出了一种实用的高精度摄像机标定方法,基于“多对一”的思想,讨论了一种改进的Hough变换方法;山外极约束理论,提出了一种基于角点的外极斜率特征匹配方法。实验证明.该方法能成功的应川于复杂零件的测量。     

基于改进人工势场法的电力巡检机器人自动避障轨迹规划

为了使巡检机器人在电力系统中避开障碍物,顺利完成电力巡检工作,提出基于改进人工势场法的电力巡检机器人自动避障轨迹规划方法。构建了电力巡检机器人的被控对象模型,分析电力巡检机器人的避障运动学,根据分析结果采用栅格法获取环境参数,实现环境建模,获取电力巡检机器人工作环境信息;引入改进人工势场法,叠加斥力势场和引力势场获得合力势场,判断环境中的障碍物并规划避障路线,完成电力巡检机器人自动避障轨迹的规划。实验结果表明,所提方法的避障准确率高、规划效果好、规划效率高。     

Apparatus for vectorial Kerr confocal microscopy

We present a confocal microscopy setup that is able to record magneto-optical hysteresis cycles separating the in-plane and out-of-plane magnetization components. This apparatus is based on a modified commercial microscope, where the light beam has been deviated from the cylindrical symmetry axis of the objective lenses by inserting a translating plate in the optical path. The instrument allows for the magneto-optical imaging with a lateral resolution of 600 nm at λ = 635 nm light wavelength.     

适用于磁光／涡流检测的铁石榴石磁光传感器

铁石榴石已在磁光涡流检测传感器上和到应用。磁光灵敏度和稳定性是依赖于包括磁光旋转系数在内等诸多因素的重要参数。本文简明介绍了几个影响石榴传感器的特性及其部分应用。     

基于主动磁化的钢板应力测量性能提升方法研究

提出一种提高基于磁弹效应的钢板应力测量灵敏度和一致性的方法。从力磁耦合理论模型出发,分析强磁化和弱交流磁化对力磁耦合所起的作用：强磁化能通过降低初始磁导率和统一力磁耦合参数,提高应力测量的灵敏度及一致性;弱交流磁化提供小幅振荡磁场,能有效消除干扰磁场影响。开展了基于磁弹法的钢板应力测量有限元仿真研究,表明当初始相对磁导率较低时,应力作用下的钢板法向磁感应强度变化率较大,即应力测量灵敏度较高。开展了不同强磁化条件下不同厚度钢板的拉伸试验,测量其法向磁感应强度变化。实验结果表明：与未磁化相比,强磁化后钢板应力测量灵敏度有数十倍提升,一致性有数倍至百倍提高。其中,3 mm厚度钢板采用单磁铁移动磁化方式的应力测量灵敏度和一致性参数提高至1.665 mGs/MPa和2%;5 mm厚度钢板采用双磁移动磁化方式的应力测量灵敏度提高至1.41 mGs/MPa,采用单磁铁移动磁化方式的一致性参数提高至0.2%;7 mm厚度钢板采用双磁铁移动磁化方式的应力测量灵敏度和一致性参数提高至1.2 mGs/MPa和1.8%。     

高压加氢反应器接管裂纹分析及检修

叙述了高压加氢裂化反应器接管焊缝裂纹现象，通过对裂纹管道的化学成分、宏观形貌、金相及微观形貌等分析，查找裂纹产生原因，并介绍了裂纹的检测方法、管道焊接方案及焊接后的质量检验方法。     

New generation solar telescope of operative predictions

The functional and metrological characteristics of a new solar telescope designed to obtain quantitative data on large-scale magnetic fields (LMF) of the Sun are considered. The full automation of measurements, the application of CCD matrices in image scanning and spectra recording systems, and the optical diagram corresponding to the main purpose of the telescope significantly increased the efficiency, quality, and accuracy of measurements of the LMF and expanded the range of tasks in comparison with existing telescopes. The developed automated system of telescope control, measuring system, and software for real-time processing of measurement results make it possible to obtain LMF magnetograms with the required accuracy for about 15 min.     

基于主动式全景视觉的管道内部缺陷检测方法

针对管道内表面检测空间受限的约束以及同时需要检测管道内壁功能性缺陷和结构性缺陷等需求,基于主动式全景视觉检测原理提出了一种既能视觉检测管道横截面几何尺寸又能获取和分析管道内壁表面缺陷的管道内部全方位视觉检测方法。利用携带有主动式全景视觉传感器的爬行机器人进入管道内部,分别实时获取内壁全景图像及激光横断面扫描全景图像。本文重点介绍基于管道内壁全景图像的缺陷检测方法,对管道内壁全景图像进行展开、预处理并提取管道病害区域的几何特征,最后判定缺陷类别及危害程度。经本文方法获取的缺陷几何特征实验数据验证,管道内表面存在的较为普遍的裂缝、腐蚀缺陷几何特征差异明显：腐蚀缺陷的圆形度较大,而裂缝缺陷的圆形度趋于0;腐蚀缺陷的凸度普遍大于裂缝缺陷;裂缝缺陷由于弯曲程度不同其边界离心率变化率大,而腐蚀缺陷的边界离心率趋于1。实验结果表明：该系统能够有效提取疑似缺陷区域并计算各几何特征,可通过合适的阈值判定其所属类别,为管道内表面缺陷检测提供了一种新的手段。     

Ultrasonic arrays for quantitative nondestructive testing an engineering approach

The Ultrasonic Pulse-Echo inspection method is extremely capable of detecting cracks that limit the structural integrity of loaded technical components and systems. However, the applied principles of ultrasonic material testing do not in general allow the characterization of flaws and the required measurement of crack dimensions. Appropriate wave field data sampling at the scanned surface with the subsequent field reconstruction improves both the resolution and the contrast sensitivity of inspection results. We use arrays with elements adapted for the inspection task with an optimized arrangement and element apertures of point source character. First results have been received applying linear arrays that are promising for the quantitative assessment of flaws by high-resolved high contrast imaging of inspection results in real-time.     

管道导波时反聚焦检测系统的设计与实现

在分析管道中超声导波时反聚焦原理的基础上,设计并实现了一套适合激励压电换能器阵列,并对管道中超声导波能量在缺陷处进行时间-空间聚焦的时反聚焦检测系统.该系统实现的关键技术为:改进DDS( direct digital synthesis)结构,实现脉冲激励电路对时反特征信号进行合成发射;采用脉冲方式,实现小体积大输出功率的宽带线性功放电路;通过时反聚焦检测过程,实现管道中超声导波能量在缺陷处的时间-空间聚焦.采用该系统进行八通道时反聚焦检测实验,其结果表明,对于所用的含缺陷的管道而言,在特定的检测条件下,缺陷回波信号的幅值相对常规检测可提高246％,并且很好地抑制了导波的频散和多模态特性,提高了回波信号的信噪比.     

Theoretical comparison of illumination and collection mode images of magneto-optical dots

We compare theoretical images of the same sample obtained with two different scanning near-field optical microscopes. The sample is a two-dimensional periodic array of magnetic sub-micrometric dots. The magnetization is perpendicular to the sample plane (polar magnetization). The first configuration is a scanning tunnelling optical near-field microscope (STOM) where the tip is used in the detection mode and the sample is illuminated by total internal reflection. The second configuration is an inverted STOM: the tip is used in the emission mode and the diffracted field is far-field detected in one direction. We present the models used to describe the two configurations and then explain the main lines of the formalism used to calculate the diffracted fields by a magneto-optical sample.     

Theoretical comparison of illumination and collection mode images of magneto-optical dots

We compare theoretical images of the same sample obtained with two different scanning near-field optical microscopes. The sample is a two-dimensional periodic array of magnetic sub-micrometric dots. The magnetization is perpendicular to the sample plane (polar magnetization). The first configuration is a scanning tunnelling optical near-field microscope (STOM) where the tip is used in the detection mode and the sample is illuminated by total internal reflection. The second configuration is an inverted STOM: the tip is used in the emission mode and the diffracted field is far-field detected in one direction. We present the models used to describe the two configurations and then explain the main lines of the formalism used to calculate the diffracted fields by a magneto-optical sample.