用于激光超声非接触检测的面型测量技术研究

发布时间：2019-01-11 10:36

【摘要】：随着工业的迅速发展,激光超声无损检测技术的应用范围越来越广阔。目前,激光超声无损检测的对象已不再局限于平面和圆筒圆柱等具有规则形状的工件,在航空航天及核电等工业领域,也通常需要采用激光超声无损检测技术对一些具有自由曲面形状的曲面工件进行一系列的检测工作。为了解决复杂曲面工件的激光超声自动探测问题,国家质检总局开展了基于激光超声技术的高温曲面工件自动探测设备研制这一公益性科研专项。在激光超声曲面自动探测系统研制背景下,为了保证激光超声探测时需保证检测激光沿被测物体表面法向方向扫查,以提高系统的检测精度,本文采用了基于单目相机多轮廓遮挡技术的物体三维模型重构方案来实现目标曲面法矢量提取。本文建立了以CMOS相机、镜头、自动转台及计算机为基础的图像采集系统,利用张正友标定法及数学计算的形式对系统进行内外参标定,并通过计算机完成目标物体多角度图像序列的自动采集;对采集到的图像序列进行二值化、滤波去噪、去小面积等处理,提取了图像中目标物体的轮廓数据,并将多角度轮廓序列及其对应的光心点坐标数据进行了坐标转换,实现了数据在世界坐标系下的统一;与3D-Rhino软件结合,根据体相交法原理获取目标物体近似三维模型;针对基于遮挡轮廓原理体相交法得到的三维模型大于目标物体实际尺寸这一问题进行了相关理论和实验研究,得到了模型尺寸与光心点到物体的距离之间的线性变化规律,提出了基于模型尺寸相较于目标物体实际尺寸的扩大倍数反向缩小的方法将所得模型还原到目标物体实际尺寸,并进行了实验验证;在缩小后的目标物体三维模型上通过点坐标分析的方式提取了目标曲面法矢量。同时通过两个外形由简单到复杂的物体作为实验对象验证了论文方案的可行性。最后描述了如何将所获取的目标物体法矢量用于激光超声自动检测系统进行探头扫描方位的控制。论文实现了三维重构技术与激光超声无损检测技术的结合,法矢量的成功提取解决了激光超声复杂曲面工件自动探测系统的探头扫描方向的控制问题,由此为激光超声曲面自动探测系统的研制提供了依据。
[Abstract]:With the rapid development of industry, laser ultrasonic nondestructive testing technology is more and more widely used. At present, the objects of laser ultrasonic nondestructive testing are no longer confined to regular workpieces, such as plane and cylinder cylinders, but also in the fields of aerospace, nuclear power and other industries. Laser ultrasonic nondestructive testing (NDT) is also usually used to detect some curved surfaces with free-form surfaces. In order to solve the problem of laser ultrasonic automatic detection of complex curved surface workpiece, the State Administration of quality Supervision, Quarantine and Quarantine has carried out the development of the high temperature surface workpiece automatic detection equipment based on laser ultrasonic technology, which is a public welfare scientific research project. Under the background of the development of laser ultrasonic surface automatic detection system, in order to ensure the laser scanning along the normal direction of the object surface, in order to improve the accuracy of the system, In this paper, the object 3D model reconstruction scheme based on the multi-contour occlusion technology of monocular camera is used to extract the normal vector of the target surface. In this paper, an image acquisition system based on CMOS camera, lens, automatic turntable and computer is established. The calibration method of Zhang Zhengyou and mathematical calculation are used to calibrate the internal and external parameters of the system. The multi-angle image sequence of the target object is automatically collected by computer. The contour data of the target object in the image are extracted by binary processing, filtering and denoising, de-noising, and the coordinate transformation of the multi-angle contour sequence and its corresponding optical center point coordinate data are carried out. The unification of data in the world coordinate system is realized. Combined with 3D-Rhino software, the approximate three-dimensional model of object is obtained according to the principle of volume intersection. Aiming at the problem that the 3D model based on the principle of shading contour is larger than the actual size of the object, the linear variation law between the model size and the distance from the center of light to the object is obtained. Based on the inverse reduction of the expansion multiple of the model size compared with the actual size of the target object, the model is restored to the actual size of the target object, and the experimental results are verified. The normal vector of the object surface is extracted by point coordinate analysis on the reduced object 3D model. At the same time, the feasibility of the scheme is verified by two objects with simple to complex shapes. At last, how to use the normal vector of the target object to control the scanning azimuth of the probe in the laser ultrasonic automatic detection system is described. The paper realizes the combination of 3D reconstruction technology and laser ultrasonic nondestructive testing technology. The normal vector is extracted successfully to solve the problem of scanning direction control of the probe in the automatic detecting system of laser ultrasonic complex curved surface workpiece. This provides the basis for the development of laser ultrasonic surface automatic detection system.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB559

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