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Photoelectric apparatus for detecting altered markings

  • US 4,250,393 A
  • Filed: 01/31/1979
  • Issued: 02/10/1981
  • Est. Priority Date: 03/20/1978
  • Status: Expired due to Term
First Claim
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1. An optical reading system comprising:

  • a document including an information carrier having information recorded thereon in the form of first and second types of optical markings,said first type optical marking comprising a first relief structure which deflects a reading light beam in at least one specific direction,said second type optical markings comprising the first relief structure and a superimposed second relief structure which causes the reading light beam to be dispersed; and

    apparatus for distinguishing between said first and second optical markings comprising;

    a light source providing a light beam directed toward said document,a first light sensor located on an optical axis to receive light within a cone including the light deflected from said first relief structure in said specific direction,a second light sensor located on an optical axis to receive light outside the cone of light deflected from said first relief structure in said specific direction to thereby detect said dispersed light from said second relief structure, anda comparator coupled to said first and second sensors for comparing the respective electrical signals therefrom and to indicate whether an optical marking being examined is of said first or second type.

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