Patent Document ID: 5380992
Application ID: 07924372
Patent Status: 1

Claim One:
1. A method for detecting a bar code from a response light signal of a first predetermined light wavelength received from a luminescent bar code pattern on a background surface of a moving carrier, which signal is responsive to light of a second predetermined wavelength irradiating said bar code pattern, the bar code pattern including a number of successive bar code positions each containing a bar code element from a predetermined set of two possible bar code elements, such as bar/no bar or thin/thick bar, the response light signal occurring during steady relative movement of said carrier with respect to a signal pick-up device for said response light signal, which device is equipped with a source of said light irradiating said bar code pattern, said response light signal pick-up device having means for converting said response light signal into an electric response signal, said electric response signal including a background signal produced during movement of said carrier by light emanating from said background surface of said carrier and a pulse signal produced by light emanating from each bar code element corresponding to a bar, which pulse signal is additive to said background signal, said method comprising the main steps of: storing in memory the electric response signal during each said steady relative movement of said carrier with respect to said signal pick-up device for facilitating the performance of other substeps with the assistance of a processor, sub-dividing said electric response signal on a time basis by determining successively, in terms of relative movement of said carrier, a number of electric signal segments each of which corresponds with a bar code position, and classifying each said electric signal segment according to the bar code element contained in the corresponding bar code position, the main step of classifying each said electric signal segment comprising the following substeps: deriving an approximated local background signal value from the electric response signal value corresponding to the background response light signal from a background corresponding to an electric signal segment under classification, generating a bar criterion signal which is a function of said approximated local background electric signal value, comparing the electric response signal of said electric signal segment under classification with said bar criterion signal, and generating a classification signal in a first sense if said electric response signal of said electric signal segment under classification exceeds said bar criterion signal and generating a classification signal in a second sense if said electric response signal of said electric signal segment under classification fails to exceed said bar criterion signal.