共查询到20条相似文献,搜索用时 15 毫秒
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In this paper, two categories of transform coding and subband coding are comparatively studied for compressing ultrasonic NDE images. The data compression performance of the discrete cosine transform-, the Karhunen-Loève transform-, and the discrete wavelet transform-based codecs are examined by being applied to ultrasonic NDE images. The effects of these compression methods on the analysis of ultrasonic information in compressed ultrasonic images are examined. Moreover, evaluation of the main elements in image coding system is performed to explore the important factors, which are worth paying more attention when developing a special image compression technique for ultrasonic NDE images. 相似文献
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Miniature robotic vehicles are receiving increasing attention for use in non-destructive testing (NDT) due to their attractiveness in terms of cost, safety and their accessibility to areas where manual inspection is not practical. Cameras can play several roles in a robotic system as a result of the information rich nature of the 2D image signal including object/shape recognition, motion estimation and ranging. This paper considers a robot configured with a single camera that monitors the surface of the structure under the robot as it moves. Visual odometry is demonstrated that can reliably track the robot's position. An image mosaicing approach is presented that calculates the robot's path using the complete image set, taking account of overlapping images that were not consecutive in the image stream. It is shown that this significantly reduced the absolute error of the positional estimate. The system was found to work well on surfaces that were not highly reflecting including steel which is common in industrial plant. 相似文献
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NDE using ultrasonic signals is a very useful technique for the assessment of solid materials, construction, food, and biomedicine. Among many NDE methods, the ultrasonic inspections may involve the extraction of an appropriate set of features or a neural network for the classification of the signals in the feature space. This paper presents an approach that uses a geometric method and the LMS (Least Mean Square) algorithm to determine the coordinates of the ultrasonic probe followed by the SAFT (Synthetic Aperture Focusing Technique) and centroid searching technique to estimate the location of the ultrasonic reflector. The proposed method is employed to classify ultrasound NDE signals from cracks and deposits within steam generator tubes in a nuclear power plant. 相似文献
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采用同步辐射白光貌相术研究了快速降温温度梯度法合成的大颗粒金刚石单晶体的晶体缺陷。晶体生长的早期形成了沿±[100]和±[010]方向延伸的平直位错,位错线均起源于种晶表面。晶体生长中期向[001-]方向生长,未生成新位错。在晶体生长的末期,形成了大量位错束,这些位错束由多条直线形位错组成,每个位错束中的所有位错生成于同一位错源,分布在扇形区域内,扇形夹角大多数在30°以内。这些扇形位错束的位错源均位于靠近晶体外表面的晶体内,在靠近(1-00)的晶面附近分布最多,(100)晶面附近比较多。少部分靠近(010)和(01-0)晶面。位错束的生长方向主要分布在[1-00]至[1-01-]区域和[001-]附近区域,少量向[010]、[01-0]方向延伸。位错束的形成和晶体合成末期的快速降温具有密切的关系。 相似文献
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A focused ultrasonic transducer is used for precise, step-by-step, surface ultrasonic scanning inspection of spot welds. Two methods for generating characteristic data matrices of ultrasonic echo signals of the spot welds are established. One is based on the ultrasonic echo amplitude and the other is based on frequency spectrum. Both methods generate scanning inspection data arrays and provide clear C-scan images. Based on C-scan noise reduction, the Krisch edge detection operator for edge detection-a gray window transform-reflects the shapes of the spot welds and allows quantitative determination of their size. The method based on the ultrasonic echo amplitude provides a greater quantitative detection accuracy. 相似文献
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M. J. Jackson G. M. Robinson L. J. Hyde R. Rhodes 《Journal of Materials Engineering and Performance》2006,15(2):223-229
Small milling cutters are susceptible to very small changes in geometry on the surface of the cutting edge that are substantial
when machining at the microscale. The purpose of this paper is to show how to design a neural image processing program to
accurately determine the amount of wear accumulated on small milling cutters after successive machining operations. After
determining the amount of wear on a small milling cutter, the program creates the appropriate amount of compensation to be
used for a computer numerical control (CNC) machining program that will account for in-process tool wear.
This paper was presented at the fourth International Surface Engineering Congress and Exposition held August 1–3, 2005 in
St. Paul, MN. 相似文献
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With rising feed rates of wood working machines, it is important to realize a process-integrated quality assurance. The quality
control of produced workpieces is mainly carried out by the operator. As his capabilities are limited, an automated quality
control system can help to assure a constant quality level. Due to the high production speeds, only an optical measurement
can be used. While CCD-camera-based control systems are generally applied in wood working, no approach has been made so far
to measure the surface roughness which is caused by the machining of the workpiece. This paper presents two different quality
control systems for an assessment of the surface quality of a workpiece. In planing of solid wood, the size of the waves on
the surface is most significant for workpiece quality. An image processing system has been developed which measures the width
of the waves by means of a special illumination. In machining chipboards, the size and number of cracks in the edge are very
important. Here, a camera-based system is presented which is able to measure the complete workpiece edge even at high feed
rates with a sufficient resolution. 相似文献
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Routine inspection of oil and gas pipes for time dependent degradation is essential. Pipelines are most commonly inspected using In-Line Inspection (ILI), however restrictions from pipe geometry, features or flow rate can prevent its use. Facility pipework rarely facilitates ILI, and external inspection often warrants the undesirable removal of the pipe insulation and cladding. This work investigates the applicability of a current deflection non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly focusing on corrosion. Magnetic sensors are used to monitor variations in the spatial distribution of the induced magnetic flux density outside a pipe that arise from deflection of an injected electric current around inner or outer wall defects. An array of orthogonal magnetoresistive sensors has been used to measure the magnetic flux density surrounding six-inch schedule 40 seamless and welded carbon steel and austenitic steel pipes. The measurements were stable and repeatable to the order of 100 pT which suggests that the defect detection or growth monitoring of corrosion-type defects may be possible with a few amps of injected current when measurements are taken at around 50 mm lift-off. The sensitivity of the technique is dependent on factors including defect geometry, sensor lift-off, bends, variations in nominal pipe geometry or material properties, and the presence of ferromagnetic objects, each of which were investigated using either experiment or a validated finite element model. 相似文献
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提出了一种基于互信息的改进匹配算法,将灰度图像互信息匹配算法扩展到二值化图像匹配领域,保留了原灰度图像的信息量,该算法的执行速度与源图及模板大小无关,仅与二值化后的源图和模板的前景点个数成线性关系。在GPU上的运算结果表明,该算法定位结果可信度高,速度快,可以有效克服图像中存在的遮挡、噪声、形变、旋转、缩放、光照变化等问题,能够满足实时焊缝跟踪应用的需要。 相似文献
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It is difficult to acquire satisfied weld pool image by CCD sensor during gas metal arc welding(GMAW), for arc disturbs violently, welding current is great and working frequeacy is high. By using CMOS vision sensor to GMA W process, the vivid weld pool image is collected at any time, furthermore, whose gray compression ratio is controllable by sensor hardware circuit developed. Acquired weld pool image is firstly pre-processed by using Wiener filter and Ostu threshold segmentation algorithm. Subsequently separation between weld pool intage and cathode mist region is conducted by means of mathematical morphological algorithm, and the edge of weld pool image is extracted by using Prewitt algorithm. 相似文献
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Lin Liu Taiwen Huang Min Qu Gang Liu Jun Zhang Hengzhi Fu 《Journal of Materials Processing Technology》2010,210(1):159-165
The heat transfer during directional solidification by Bridgman-type directional solidification has been analyzed and a relationship has been established that reflects the effect of alloy properties, process parameters and equipment characteristics on thermal gradients. Based on this relationship, some methods for obtaining high thermal gradients have been developed. By using zone-intensified overheating and liquid-metal cooling, high thermal gradients of up to 800 K/cm were achieved. Application of these methods in the processing of single crystal superalloys indicated that high thermal gradient directional solidification produced more uniform microstructures and optimized mechanical properties. 相似文献
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为了精确定位开口裂纹的端部在铝合金厚板对接焊缝中的位置,对其超声衍射时差法(TOFD,time off flight diffraction)的 B 扫描图像进行了处理.为了提高图像的横向分辨率,引入了合成孔径聚焦技术(SAFT, synthetic aperture focusing technique).根据缺陷端部和换能器之间的几何关系,建立了图像SAFT处理的数学模型,实现了B扫描图像的SAFT重建.为了提高图像的纵向分辨率,先将原始图像进行了线性化处理,从而提出了一种新的超声TOFD法B扫描图像处理技术L-SAFT(linearization-SAFT).结果表明,该技术有效地提高了图像的分辨率.利用该技术能快速、准确地捕捉裂纹端部在试件中的横向和深度位置,实现缺陷的精确定位与定量. 相似文献