【作者】 王俊；

【导师】 何庆；

【作者基本信息】 东北大学 ， 控制科学与工程， 2022， 硕士

【摘要】 实际生产中大量存在的与真实缺陷相似的伪缺陷,如氧化铁皮、压痕、水痕等,这些伪缺陷都是表面的纹理,而真实缺陷则对铸坯造成了实际的损伤,两者具有明显的三维结构上的区别。目前基于二维成像的检测方法没有办法获取铸坯的三维信息,在检测过程中难免会出现一定程度的误检和漏检。因此本文希望通过三维测量方法准确地获取铸坯三维形貌,从而为更精准的铸坯缺陷检测提供便利。光栅投影三维测量方法以其非接触、低成本、高速、高精度等优点,广泛应用于工业检测、文物保护、逆向工程和医学诊断等领域。因此本文选择该方法进行铸坯的三维测量。运动问题是主要难点。普通的相移算法在运动条件下不再适用。在运动过程中,被测物体在相机平面和投影仪平面的位置会发生移动,一方面相移量会发生改变,不再是静止条件下的固定相移,另一方面由于铸坯表面反射率差异较大,运动后同图像坐标下的背景值和调制度也不相同。本文详细分析了铸坯运动的特点并在此基础上提出了运动相移算法,主要包括质点跟踪、相位校正和快速解包裹三部分。首先,物体上的一点在运动前后的反射率可以认为保持不变,即背景值和调制度不变,这在运动幅度相对不大的情况下基本可以得到保证。于是为了构建出相移方程就需要对质点的运动情况进行跟踪,而铸坯平面比较平整,因此可以通过透视变换矩阵来描述质点位置的变化。其次,在构建出相移方程后,由于相移量未知,因此没有办法直接求解出包裹相位。在局部小区域内的相移量可以近似认为是一致的,于是可以通过迭代的方法计算出每个小区域的相移量,并根据相移分布拟合出全局相移分布,并计算出包裹相位。最后,由于铸坯表面比较平整,不存在比较大的相位突变,因此本文提出了基于参考平面的快速解包裹算法,不需要额外投影图片便能求解出精确的展开相位。高动态范围是铸坯测量面临的另一个问题。铸坯表面的反射率差异较大,而相机的测量范围有限,在获取图像时很容易出现图像的情况,使得正弦信号被截断,无法准确测量。本文分析了铸坯表面反射模型,提出了基于多视角的三维测量方案,通过两个视角的测量结果互相弥补,从而获取完整的三维测量结果。本文主要围绕铸坯三维测量中运动和高动态范围两个要点展开研究并取得了良好的测量效果,经实验验证,平均测量误差不超过0.05mm。更多还原

【Abstract】 There are a large number of pseudo defects similar to real defects in actual production,such as iron oxide scale,indentation,water mark,etc.these pseudo defects are surface texture,while the real defects cause actual damage to the slab.The two have obvious differences in three-dimensional structure.At present,the detection method based on two-dimensional imaging has no way to obtain the three-dimensional information of slab,so it is inevitable to have a certain degree of false detection and missed detection in the detection process.Therefore,this paper hopes to accurately obtain the three-dimensional shape of the slab through the three-dimensional measurement method,so as to provide convenience for more accurate slab defect detection.With the advantages of non-contact,low cost,high speed and high precision,grating projection three-dimensional measurement method is widely used in the fields of industrial detection,cultural relics protection,reverse engineering and medical diagnosis.Therefore,this method is selected for three-dimensional measurement of slab.Movement is the main difficulty.The ordinary phase-shifting algorithm is no longer applicable in motion.During the movement,the position of the measured object in the camera plane and the projector plane will move.On the one hand,the amount of phase shift will change,which is no longer a fixed phase shift under static conditions.On the other hand,due to the large difference in the reflectivity of the slab surface,the background value and adjustment system under the same image coordinates after the movement are also different.In this paper,the characteristics of slab motion are analyzed in detail,and on this basis,a motion phase shift algorithm is proposed,which mainly includes particle tracking,phase correction and fast unwrapping.First of all,the reflectivity of a point on the object before and after the movement can be considered to remain unchanged,that is,the background value and modulation are unchanged,which can be basically guaranteed when the movement amplitude is relatively small.Therefore,in order to build the phase shift equation,it is necessary to track the motion of the particles,and the slab plane is relatively flat,so the change of the particle position can be described by the perspective transformation matrix.Secondly,after constructing the phase shift equation,because the phase shift is unknown,there is no way to directly solve the package phase.The phase shift in local small areas can be approximately considered as consistent,so the phase shift in each small area can be calculated by iterative method,and the global phase shift distribution can be fitted according to the phase shift distribution,and the package phase can be calculated.Finally,because the slab surface is relatively flat and there is no large phase mutation,a fast unwrapping algorithm based on reference plane is proposed,which can solve the accurate unwrapping phase without additional projection pictures.High dynamic range is another problem in slab measurement.The reflectivity of the slab surface varies greatly,and the measurement range of the camera is limited.It is easy to get images when obtaining images,which makes the sinusoidal signal truncated and unable to measure accurately.In this paper,the slab surface reflection model is analyzed,and a three-dimensional measurement scheme based on multi angle of view is proposed.The measurement results of the two angles of view complement each other,so as to obtain the complete three-dimensional measurement results.This paper mainly focuses on the two key points of motion and high dynamic range in the threedimensional measurement of slab,and has achieved good measurement results.The experimental results show that the average measurement error is less than 0.05mm.更多还原