Patent ID: 6354503
Filing Date: 2002-03-12
Classification: G06K

Abstract:
Apparatus for scanning for a bar code on a surface that moves past the apparatus, where the apparatus includes a scanning laser beam source which scans along a predetermined distance and a detector for detecting reflections of the laser beam and for generating analog signals representing the magnitude of the detected reflections, comprising:an analog circuit that records transitions, of at least a predetermined magnitude, of the light amplitude detected by said detector, and that generates a signal indicating that a bar code is not present in an area that includes a first transition and an area immediately following said first transition, when a second transition fails to be detected within a predetermined distance following said first transition,said analog circuit being constructed to generate a signal representing MAX minus MIN, wherein: said MAX value continuously decreases in value at a controlled MAX rate, from a magnitude representing substantially complete reflection until the magnitude of a bright reflection is detected with a reflection magnitude greater than the instantaneous MAX value and with the MAX value then immediately increasing to said value of said bright reflection and then continuously decreasing again at said controlled MAX rate; said MIN value continuously increases in value at a controlled MIN rate from a magnitude representing substantially no reflection until a low detected reflection is detected with a brightness level less than the instantaneous MIN value and with the MIN value then immediately decreasing to the value of said low detected reflection and then continually increasing again at said controlled MIN rate; said analog circuit includes a circuit part that generates said signal indicating that a bar code is not present in said area that includes said first transition when the signal representing MAX minus MIN decreases below a predetermined level.