圆柱面任意方向裂纹的双线阵激光热像检测

Dual linear array laser thermography detection of arbitrary direction cracks on cylindrical surface

圆柱铁氧体磁芯为黑色柱体,裂纹对比度不高,传统机器视觉裂纹成像效果不佳。激光红外热成像技术根据试样表面的温度分布情况检出裂纹缺陷,可用于解决低对比度微小裂纹的检测问题。常用的线激光、点激光在检测裂纹时,平行于激光扫描方向裂纹往往因两侧热流较小而无法检出。双线阵激光热成像检测系统,线阵激光错位排布,营造多方向热流,可实现任意方向裂纹检测。为验证双线阵激光对任意方向裂纹的检测可行性,仿真模拟了0°、45°、90°裂纹的双线阵激光扫描过程。线阵激光由于各点光斑功率分布存在较大的非均匀性,不同参数设计对裂纹检测效果影响大。因此,优化点光斑半径、点光斑中心距、线阵激光错位间距、线阵激光间距、运动速度等设计参数实现裂纹检测信噪比提升。裂纹成像算法根据温度空间梯度成像裂纹,由于光斑的非均匀性,裂纹在两束激光间不同相对位置的梯度大小各不相同。算法选取裂纹在两束激光间具有较大相对梯度的位置,通过多幅梯度图像融合,实现任意方向裂纹检测。对4个具有水平、垂直、倾斜自然裂纹的铁氧体样品进行实验,成像结果清晰直观地显示出所有裂纹。

Cylinder ferrite magnetic core is a batch of black cylindrical samples and its crack contrast is low.The crack imaging result of traditional machine vision is not good.Laser infrared thermography detection technology relies on the sample surface temperature distribution to detect the crack defects,which solve the problem of low contrast micro crack detection.When the crack is detected by line laser or point laser,the cracks parallel to the laser scanning direction is hard to detect because of the small heat flow on both sides.Dual linear array laser thermography system with dislocation arrangement creates multi-direction heat flow,which can detect arbitrary direction cracks.In order to verify the feasibility of dual linear array laser to detect arbitrary direction cracks,simulation took the laser scanning process of 0°,45°and 90°cracks.Linear array laser had great non-uniformity in the power distribution of each spot,so different parameter design had great influence on crack detection.Therefore,the design parameters such as spot radius,spot center distance,linear array laser dislocation distance,linear array laser distance,and motion velocity were optimized to improve the SNR in crack detection.Crack imaging algorithm generated cracks based on temperature spatial gradient.Due to the non-uniformity of the laser spots,the gradient of the crack at different relative positions between two laser beams was different.Algorithm selected the position of the cracks with large relative gradient between two laser beams.Through the fusion of multiple gradient images,crack imaging algorithm achieved arbitrary direction crack detection.The imaging algorithm was designed according to the crack spatial temperature gradient characteristics excited by dual linear array laser.Four cylinder ferrite samples with horizontal,vertical and inclined natural cracks were tested,and the imaging results showed all the cracks clearly and intuitively.