Research On Laser Coloring Stability And Image Reconstruction Technology Of Color Direct Part Marking

Direct part marking(DPM)barcodes(such as Data Matrix)can ensure the traceability of the full life cycle of parts operating in harsh environments,and are now widely used in the automotive,aviation,medical equipment,pharmaceutical and electronic industries.Color DPM technology,which takes color as a dimension,can well meet the higher demand for data capacity in practical applications.It is an important development direction for intelligent product tracking in all links of the product,manufacturing,and service life cycle and corresponding systems.Aiming at the problem of color stability in the process of laser coloring on metal surfaces,research on the laser coloring stability and image reconstruction method of color DPM was carried out in this paper,mainly involving theories and new methods of nanosecond laser coloring mechanism,laser coloring stability evaluation and cause analysis,low-quality color DPM image reconstruction.It aims to improve the reading rate of the direct laser coloring Data Matrix and promote the further development of the full life cycle tracking of industrial products.The work of this article was mainly reflected in the following aspects:First,the mechanism of nanosecond laser coloring based on the electromagnetic scattering of the micro-nano structure on the coloring surface was studied.Laser scanning confocal microscope(LSM)and atomic force microscopy(AFM)were used to collect nanosecond laser colored surface micro-topography,and its relationship with scanning speed was analyzed.According to this,the actual rough surface was simplified to a one-dimensional rough surface composed of many forms of fundamental waves.Use finite difference time domain(FDTD)to study the electromagnetic scattering of one-dimensional laser-colored surface micro/nano structure model.The calculated color and the actual color were in the same color category,which proves the color effect of nanosecond laser-induced surface micro-nano structure and provides theoretical support for the application of color DPM technology and nanosecond laser coloring technology.Next,the stability evaluation and cause of laser coloring were studied.Twelve laser shading stability indexes were proposed,including four color features,two shape features and six texture features.The evaluation model of laser shading stability without reference color was trained by using BP neural network.The effects of cell position,cell size and scanning speed on the stability of laser shading were analyzed by taking the Data Matrix of direct laser shading as an example.The simulation results obtained by the laser heating process were consistent with the experimental results.It was proved that the temperature gradient change caused by different parameters is the main reason for the change of laser coloring stability,which provides a theoretical support for improving the laser coloring stability of color DPM.At the same time,because of the consistency of the laser coloring process,the conclusion in this paper can be extended to other laser coloring processes.Finally,based on the image processing technology,the low quality color DPM image reconstruction method was studied.By comparing different algorithms of grayscale,binarization and line detection,the preprocessing methods suitable for color DPM images were studied.Aiming at the distortion problem of acquired barcode,based on the characteristics of Data Matrix,an adaptive detection method for vertices of Data Matrix was proposed.Experimental results showed that the operation time of this method is much more acceptable than that of manual positioning in the near 1s under the same positioning accuracy.Then,a color barcode image reconstruction method based on K-means algorithm was proposed,which includes three steps:color recognition,bar code reconstruction and error correction.Finally,the digital matrix of the reconstructcd barcode was restored based on the color channel difference.The bar code reconstruction accuracy is more than 96%,which effectively improves the laser shading instability,greatly improves the color DPM readability,and provides a technical basis for the industrial application of color direct part technology.