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CSME 2018/06
Volume 39 No.3
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267-274
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Fabrication and Evaluation of Reflected Type Optical Linear Encoder Using Femtosecond Laser
Mohammad Hossein Goudarzi a, Jeng-Ywan Jengb and Ji-Bin Horngc
aDepartment of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan, ROC.
bDepartment of Mechanical Engineering, Engineering School, National Taiwan University of Science and Technology, Taipei, Taiwan, ROC.
cIndustrial Technology Research Institute (ITRI) , ITRI Southern Region Campus, 8 Gongyan Road, Liu-jia District, Tainan, Taiwan 73445ROC.
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Abstract:
This paper explains the fabrication method of linear diffraction grating by femtosecond laser. Several gratings were made using two setups: chirped pulse FS laser and mode locked fibre laser. Laser direct writing with different optical paths was used to fabricate two gratings with pitches of 5mm and 20mm. The average power, scanning speed and repetition rate of the laser were changed to determine optimal grating. The ablation threshold of Invar36 was calculated for NOPs of 389 and 1.1, resulting in 0.122J/cm 2 and 0.42 J/cm 2 respectively. And an online non destructive performance testing procedure was applied to assess the reflective diffraction grating for optical linear encoding applications, based on the Talbot effect. The contrast of self imaging was used as a comparison parameter. These results were verified by measuring the diffraction efficiency and traveling distance, using a Renishaw encoder. The best and poorest samples were the same in all setups, as was the trend. Specifically, the worst case couldn’t deliver a self image with acceptable contrast, or generate uniform signals from an optical Tonic read head, since it diffracted laser light to different points and its diffraction efficiency was very low. In addition, the traveling distance error of the best sample was only 0.1mm.
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Keywords: Femtosecond phenomena, Diffraction gratings, Talbot and self-imaging effects.
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©
2018
CSME , ISSN 0257-9731
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