Papers by Author: Jian Mei Li

Abstract: To evaluate the quality of the laser direct part marked Data Matrix symbols on titanium alloy substrates, the quality assessment methods at home and abroad were compared. A new quality assessment method of combining the effect of the laser on substrate materials and symbol grade of laser marked Data Matrix was put forward. Depending on previous research works, orthogonal experiment results were analyzed again and a modified nonlinear mathematics model was established. Analysis results indicate that this modified model can explain 90.6% of symbol contrast change and it is statistically significant. So it is better than previous linear regression model and can be used to estimate the quality of laser marked Data Matrix symbols on titanium alloy substrates. The nonlinear mathematics model can also explain the laser parameters influence on the symbol contrast.

Abstract: In the application of laser marking, the biggest challenge is that machine-readable barcodes with superior quality were not marked consistently. To solve this problem, laser direct-part marking Data Matrix barcode experiments were carried out on titanium alloy substrates, using a Q-switched light-pumped Nd:YAG laser. The microstructure of the symbols was analyzed using an environmental scanning electron microscope (ESEM). The internal micro-stresses of the marked areas were analyzed using X-ray diffractometer (XRD). The influence of the pulse frequency on the symbol contrast is analyzed. Results showed the interaction between the laser and the titanium alloy can be found. This can further explain the physical mechanism of laser direct part marking Data Matrix symbols on titanium alloy substrates.

Abstract: The image binarization of laser direct marking Data Matrix symbols on metal surface is a key procedure during recognition. Contrast and light uniformity of the symbols is greatly affected by the uneven illumination and reflection of the parts. To avoid the limitation of present binarized methods, an adaptive binarization method composed of Otsu method and Nearest neighbor pixels contributing threshold method is proposed. It takes global and local gray information into consideration, as well as the distribution of gray gradient. Experimental results show that the proposed method has a higher recognition rate and reliability.

Abstract: Laser current is a key parameter in laser direct-part marking symbols on a substrate. Different laser current can create enormous impact on bar code contrast, but the influencing regularities are unclear. In this paper, a new significance test method based on the 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 the aluminum alloy experiments.

Abstract: To improve the edge detecting effect of the pressed character, a novel method based on facet model and topographic structures is proposed. Firstly, the discrete gray scale image is approximated by a bivariate cubic function, then, the concerned features of the continuous function are computed to describe the discrete image. After every pixel in the image has been defined to Peak, Ridge, Saddle, Flat, Ravine, Pit or Hillside, the edge of the character is detected. To reduce the time in computing the coefficients of cubic function, an efficient separable algorithm is presented. In addition, an image enhancement method prior to edge detection is adopted to improve the detecting effect. The tests show that the proposed method is more suitable for complex edge detecting problems than common methods.

Abstract: In accordance with the obvious characteristics of the pressed raised character image and the shortages of the template matching method.
a new method of using the general radial-basis function neural network (GRBFN) for testing the quality of the pressed character is presented. The structures and training methods of GRBFN are fully analyzed, as well as the functionality of hidden layer, excited focus and area. The results show the checker based on GRBFN has highly checking ratio for the label pressed raised characters. It is suited to the quality testing of raised characters.