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Pattern detecting apparatus

  • US 4,441,206 A
  • Filed: 12/14/1981
  • Issued: 04/03/1984
  • Est. Priority Date: 12/17/1980
  • Status: Expired due to Term
First Claim
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1. A pattern detecting apparatus comprising:

  • means for illuminating a positioning pattern formed on a sample with illumination light;

    means for defining a range illuminated with said illumination light, said positioning pattern being illuminated in said range;

    means for optically focusing reflected light from said positioning pattern on a predetermined image plane;

    means for electrically detecting a bright and dark image on said image plane in accordance with positions on said image plane;

    means for removing a signal corresponding to a region outside said illumination range from a detection signal and for holding, in place of said removed signal, a level of said detection signal produced within said illumination range of said illumination light, said detection signal being obtained by said detecting means; and

    means for detecting a position of the center of said positioning pattern from an output signal of the holding means.

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