Research On The Laser Direct Part Marking Parameters And Physical Mechanism Based On 2D-barcodes Quality

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.