【作者】 邱化冬；

【导师】 路长厚；

【作者基本信息】 山东大学 ， 机械电子工程， 2011， 博士

【摘要】 直接标刻(Direct Part Marking,DPM)指直接在物体表面标刻机器可识读的代码,激光直接标刻二维条码在应用中最大的挑战是能否连续地产生机器可识读的高质量的二维条码。激光与材料之间复杂的相互作用机制不明,不同的激光参量、材料材质类型等对直接标刻条码等级产生重大影响。目前,国内外对直接标刻激光参量的研究大多将其转化为激光能量或激光功率,虽然具有研究方法直接、简便的特点,却无法指导实际加工和具体参量大小的设定,无法辨识激光参量对条码质量的影响。此外直接标刻条码的识读图像与一般打印条码图像相比,具有图像不规则、光学反差低以及标刻表面高反光等特征,这也限制了直接标识的应用。国外针对直接标刻二维条码的研究已开展,制定了一些标准,如ISO/IEC 16022、ISO/IEC 15415等,而国内的研究却比较少。基于此,本课题从激光直接标刻二维条码的加工和图像处理两个方面入手,以提高条码的标刻质量和条码图像质量为目的,对激光参量、标刻过程的物理机制以及低质量条码的图像处理技术进行相应的研究。本课题在山东省自然科学基金(Q2008G02)和山东大学自主创新基金(2010TS036)资助项目资助下,开展了如下研究工作：首先,从激光标刻二维条码加工方面对激光参量进行了研究。根据Data Matrix条码矩阵码结构,实验研究激光路径与激光线间距两参量,设计了单向光栅式、交叉光栅式和方形螺旋式三种标刻路径,通过对激光加工表面的粗糙度、符号对比度、对比均衡度进行分析,确定了单向光栅式模块填充激光路径和0.05mm的线间距为较优的选择。为了探明激光电流参量对标刻条码的符号对比度影响的规律,提出了一种基于多元非线性模型显著性检验的方法。通过建立激光电流和线间距两因素与符号对比度的多元非线性逐步回归数学模型,利用模型的显著性检验评估因素对符号对比度的影响,最后得出,随着激光电流的增大激光电流对条码质量衡量指标符号对比度的影响逐渐减小的规律。采用Nd:YAG激光器作为加工源,通过调节搭配激光有效矢量步长、有效矢量步间延时、Q频率和Q释放时间四参量实现3136种不同能量密度激光在铝合金表面标刻二维条码,并使用INTEGRA条码检测仪对标刻条码进行了分级。统计分析条码质量等级分布推得激光铝合金表面标刻条码的最优加工参量组。发现激光参量对条码质量影响的规律以及目前国际标准无法对黑色外观条码评级的原因。其次,研究了激光直接标刻条码微观形貌和生成物对条码质量等级的影响,探讨影响条码质量的深层次原因。将固溶体的概念引入激光标刻过程的物理机制研究中,提出基于材料元素熔点、沸点和比重的标刻物理机制的新理解,并进行了实验验证。采用物理机制新理解分析了铝合金表面直接标刻形成的六种外观及其对条码质量等级的影响。从激光标刻微观形貌方面研究黑白外观截然不同的两种条码,研究激光标刻微观形貌的度量,以及微观形貌与激光参量之间的关系。使用非线性内核在多尺度下对图像进行分层,从而改进了图像差分计盒算法,改进的算法具有较高的稳定性和准确性。将新算法应用于条码微观形貌扫描电镜图像,得出Nd: YAG激光加工的材料微观形貌维度数值,初步得到随着激光能量的增大,分形维度同时增大的规律。最后,以提高低质量条码图像质量为目的,针对激光标刻二维条码图像光学反差低、高反光等特征引入高动态范围图像合成技术。设计出覆盖全部灰度边缘的18阶灰度卡,提出一种基于此灰度卡的单幅图像相机响应曲线标定方法,解决目前相机响应曲线标定算法使用多幅图像和单幅图像灰度区域覆盖不全的问题。采用基于估算图像曝光分区的算法合成高动态范围图像,并将算法应用于激光标刻低质量二维条码图像,从实验结果上看高动态合成图像的灰度边缘比普通图像更加的陡峭,且获得更大的数据变化范围,这对二维条码识别图像的阈值确定和边缘准确定位有较大的意义。低质量二维条码高动态范围图像的色调映射研究中,采用了基于图像分层的各向异性边缘保护的色调映射算法,算法对光照不均和强反射体现出一定的鲁棒性。编写Data Matrix二维条码识别程序,使用高动态范围色调映射图像进行识别实验,实验结果表明借助此项技术提高了激光直接标刻二维条码图像的质量,从而可提高识别率推进激光直接标刻的工业化应用。更多还原

【Abstract】 Direct part marking refers to mark machine-readable permanently code on the surface directly. Certain applications have recently appeared in industry where a traditional barcode printed on a label will not survive because the item to be tracked has to be exposed to harsh environments. Laser direct part marking is a manufacturing process used to create permanent marks on a substrate that could help to alleviate this problem. The physical interaction of light with materials during the marking process plays an important role in theproduction of laser marks on different types of substrates. Over the last 20 years, the laser-material interaction has been explored by varying several different laser parameters and analyzing the effect of either a single substrate or multiple substrates. Laser parameters that consistently appear in these studies are laser power and pulse frequency. Although such studies will be more direct, it cannot.distinguish the influence of the independent laser parameter to the barcode quality and cannot guide the specific parameters setting in practical processing. Marks produced with a laser can be categorized as images, human-readable characters, or machine-readable symbols (e.g., bar codes). Compared with the general printing technology, machine-readable marks produced with a laser have its own features. For instance, irregular picture, lower optical contrast inconsistent module size and highly reflective surface of substrate materials are all the characteristics of the laser direct part marking.In order to effectively produce Data Matrix symbols on a specific substrate with a laser, it is important to establish a relationship between critical laser parameters and the resulting quality of the symbol. Once this relationship is understood, then laser parameters can be set so that the preferred properties of a laser-marked Data Matrix symbol can be obtained. Supported by Natural Science Foundation of Shandong Province (Q2008G02) and Shandong University innovation fund (2010TS036), the research carried out in this dissertation is as followings.First, we studied the laser parameters in manufacture of Data Matrix symbols. A Data Matrix symbol may be composed of several hundred individual modules, different tool path patterns may be used to produce a single module of a Data Matrix symbol onto the substrate with the laser. The effect of the laser tool path pattern was investigated via a separate experiment from those employed to assess the effects of laser parameters and type of substrate. We design single direction raster scanning, cross direction raster scanning and square spiral scanning to create Data Matrix minimum module. According to experimental data of laser processed surface roughness, symbol contrast and module illumination values’standard deviations, the best scanning path is single direction raster scanning path.Laser current is a key parameter in laser direct-part marking symbols on a substrate. Different laser current can create enormous impact on barcode contrast, but the influencing regularities are unclear. In this paper, a new significance test method based on multivariate nonlinear model was proposed to investigate the influencing regularities. First, the multi-element nonlinear stepwise regression model between the laser current, the laser line spacing and symbol contrast was established, and then the model significance test was employed to evaluate the influence between the two factors and symbol contrast. Finally, the influencing regularities were found by comparing the influence between the laser current and the laser line spacing. These regularities are that along with the laser current value increasing the influence of laser current on symbol contrast decreases and that the effect is much smaller and can even be neglected when the laser current reaches or exceeds a certain value. This certain value is 15 A in the Nd:YAG laser Direct-part marking symbols on aluminum alloy experiment.A 1064nm Nd:YAG laser was utilized to produce 3136 Data Matrix symbols onto aluminum substrates. The quality of the laser marked Data Matrix symbol was then evaluated according to the ISO/IEC 16022 bar code technology specification for Data Matrix. Several experiments were conducted to explore the effects that different parameters have on the quality of the laser direct-part marked symbols. The experiment focuses on all interval values of the vector step, inter-step time, laser Q frequency and laser Q release time. From the experiment results, the optimized parameters are the vector step of 0.005-0.009 mm, the inter-step time of 29-43μs, laser Q frequency of 7-10 KHz, and laser Q release time of 13-19μs. And then, by analyzing the higher and the lower power density processing module SEM images and EDS data, it was found that the interaction between the laser and the aluminum alloy can be divided into four stages.Second, we studied the laser parameters and materials influence on barcode grade in microstructure and micro-components. We introduced the concept of solid solution into the physical mechanism of laser marking. A new understanding of physical mechanisms, which based on the material elements melting point, boiling point and specific gravity, was bring forward. It was verified by the experimental data, and then the new understanding was used to analysis the six appearances of laser direct marking Data Matrix barcodes on aluminum.The micromor-phologies and microstructures of laser marking area were investigated by fractal analysis. We improved the image differential box-counting fractal dimension algorithm by using the non-linear kernel to divide the laser marking SEM image into multi-scale layering, and the box-counting principle also be improved. The experiment testifies the reformative algorithm has high stability and accuracy feature. This new algorithm was used to calculate the SEM image of laser marking, the microstructure was computed by fractal dimensions values. The fractal dimension of materials microstructure that the Nd:YAG laser processed concentrated in 1.7-1.8 range. The result shows that with the laser energy increases, the fractal dimension increased.Finally, according as the characteristics of low-quality barcode images to study the irregular, lower optical contrast and higher reflected DPM Data Matrix barcode recognition. The image fusion of high dynamic range algorithm and tone mapping algorithm were studied. We design the 18-ladder grayscale card that covers all the gray edges. Based on this grayscale card, a new algorithm of camera response curve calibration with a single image was advanced. It can solve the common used camera response curve calibration algorithm uses multiple images and single image gray-area coverage question.In high dynamic range images tone mapping, we present a new technique for the display of high-dynamic-range images, which reduces the contrast while preserving detail. It is based on a two-scale decomposition of the image into a base layer, encoding large-scale variations, and a detail layer. Only the base layer has its contrast reduced, thereby preserving detail. The base layer is obtained using an edge-preserving filter called the bilateral filter. This is a non-linear filter, where the weight of each pixel is computed using a Gaussian in the spatial domain multiplied by an influence function in the intensity domain that decreases the weight of pixels with large intensity differences. We build upon a different edge-preserving filter that is easier to control and more amenable to acceleration. The method is fast and requires no parameter setting.To my wife Wenshuang Bao I dedicate this PhD thesis in token of affection and gratitude.更多还原