Development of an auto-focus system by the moiré method

Ju Yi Lee, Yu Ju Lin, Yung Hsing Wang, Chien Sheng Liu

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

Abstract

An auto-focus system based on the moiré effect and the P control method is presented. First, a collimated laser beam passes through a focusing lens and 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, where three types of moiré patterns are observed and received by a linear CCD. A new formula is derived for finding the focus value (FV) in order to calculate the spiral angle of the moiré pattern and to determine the defocus distance from the sample. The results show that auto-focus should be achieved in a very short time by means of the defocus distance calculation and P control method.

Original languageEnglish
Title of host publication10th International Symposium on Measurement and Quality Control 2010, ISMQC 2010
Pages485-488
Number of pages4
StatePublished - 2010
Event10th International Symposium on Measurement and Quality Control 2010, ISMQC 2010 - Osaka, Japan
Duration: 5 Sep 20109 Sep 2010

Publication series

Name10th International Symposium on Measurement and Quality Control 2010, ISMQC 2010

Conference

Conference10th International Symposium on Measurement and Quality Control 2010, ISMQC 2010
Country/TerritoryJapan
CityOsaka
Period5/09/109/09/10

Keywords

  • Auto-focus
  • Moiré
  • Spiral grating

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