Development of an auto-focus system based on the moiré method |
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Authors: | Ju-Yi Lee Yung-Hsing Wang Lyu-Jhen Lai Yu-Ju Lin Yu-Hsiu Chang |
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Affiliation: | aInstitute of Opto-Mechatronics Engineering, National Central University, 300 Jhongda Rd., Jhongli City, Taoyuan County 320, Taiwan;bOpto-Electronics Sensing Department of Laser Application Technology Center, Industrial Technology Research Institute, Tainan County 734, Taiwan |
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Abstract: | An auto-focus system based on the moiré effect and a feedback control method is presented. First, a collimated laser beam passes through a focusing lens then falls incident on the surface of the sample. The deviation of the angle of the light reflected back is proportional to the defocus distance from the sample. The reflected light then passes through two spiral gratings, producing three types of moiré pattern which can be observed and recorded by a linear CCD. The defocus distance can be derived from the spiral angle in the moiré pattern. The results show that auto-focusing can be achieved by the moiré method for glass and mirror samples in a cycle time of less than 0.1 s. |
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Keywords: | Auto-focus Moiré Spiral grating |
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