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Optical scanner with fixed focus optics

  • US 5,777,314 A
  • Filed: 11/05/1996
  • Issued: 07/07/1998
  • Est. Priority Date: 02/27/1992
  • Status: Expired due to Fees
First Claim
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1. An optical assembly within an optical scanner for scanning a symbol comprising a plurality of contrasting regions representative of encoded information, each contrasting region having a bar width, wherein said symbol is illuminated by incident light to produce modulated reflected light providing a square wave input representative of said plurality of contrasting regions, said optical assembly comprising:

  • at least two LEDs for generating the incident light;

    a detector array for detecting the square wave input and generating an electrical signal representative of the square wave input, said detector array comprising a plurality of CCDs and having an array area;

    a fixed focus multi-element lens system having a pre-selected magnification for receiving the modulated reflected light and providing focused reflected light to said detector array, the pre-selected magnification being selected so that the focused reflected light impinges upon a substantial portion of said array area over a range of distances to said symbol;

    wherein said at least two LEDs, said detector array, and elements of said multi-element lens system are selected by determining a spatial frequency of said plurality of contrasting regions, calculating a square wave modulation transfer function using the Fourier transform of the square wave input to determine an initial optical resolution, comparing the initial optical resolution to a minimum required optical resolution for a given density of the plurality of contrasting regions to determine whether a particular symbol with the given density can be read at a given distance from the symbol, and varying the elements of said multi-element lens system to provide an adjusted magnification and an adjusted optical resolution greater than the minimum required optical resolution at the given distance and to obtain equal resolvability for an entire field of view.

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