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Light emitting diode scanner

  • US 5,136,147 A
  • Filed: 08/27/1990
  • Issued: 08/04/1992
  • Est. Priority Date: 08/27/1990
  • Status: Expired due to Term
First Claim
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1. A system for reading symbols, comprising:

  • (a) light source means for generating a light beam;

    (b) focusing means for focusing the light beam to a scan spot of predetermined area at scan plane and for positioning the scan spot on a symbol located in a working distance range in the vicinity of the scan plane;

    (c) scanning means for sweeping the scan spot across the symbol in a scan, thereby reflecting off the symbol reflected light, at least a returning portion of which travels away from the symbol back in the direction of the light source, the returning portion of the reflected light having a variable intensity over the scan;

    (d) a sensor for viewing and detecting the variable intensity of the returning portion of the reflected light over a field of view, and for generating an electrical signal indicative of the detected variable light intensity;

    (e) a signal processor for processing the electrical signal and generating therefrom data descriptive of the symbol, the signal processor including(i) a converter for receiving the electrical signal and developing an amplified, filtered, and inverted first voltage signal relative to the electrical signal,(ii) a delay circuit for developing a delayed version of the first voltage signal(iii) a peak-locating comparator for receiving the first voltage signal and the delayed version of the first voltage signal, the peak locating comparator changing state whenever the first voltage signal and the delayed version of the first voltage signal are equal, and the peak-locating comparator generating an output,(iv) a gating comparator for receiving the first voltage signal, for changing state on pulses of the first voltage signal that are greater than positive and negative noise thresholds, and for generating an output, and(v) a latch comparator for receiving the outputs of the peak-locating comparator and the gating comparator, the latch comparator changing state only if the gating comparator has changed state since the last change of state of the peak-locating comparator, the latch comparator providing data descriptive of the symbol; and

    (f) imaging means for imaging a viewing window of the sensor means, said viewing window having an area smaller than that of the scan spot, and for positioning the viewing window at a viewing plane that is spaced away from the scan plane.

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