Browse Prior Art Database

Analog "First Bar Find" for a Bar Code Scanner

IP.com Disclosure Number: IPCOM000120750D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Cato, RT: AUTHOR [+2]

Abstract

Disclosed is a technique for improving the capability of a bar code scanner to distinguish between the bar code signal and the "paper noise" that arises from the granular nature of the paper that the bar code is printed on.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Analog "First Bar Find" for a Bar Code Scanner

      Disclosed is a technique for improving the capability of
a bar code scanner to distinguish between the bar code signal and the
"paper noise" that arises from the granular nature of the paper that
the bar code is printed on.

      One method for analyzing the analog video signal in a bar code
scanner is to create a "white follower circuit" that tracks and holds
the peaks of the signal and a "black follower circuit" that tracks
and holds the valleys of the signal.  A threshold signal is created
from the follower signals, tracking midway between the white follower
and black follower.  Whenever the analog video signal crosses the
threshold, a bar edge is detected.  A digital video signal created
from these transitions is used as the input to the bar code decode
algorithms.

      Circuits that perform these functions are well known.

      One problem with existing circuits is that they switch on the
"paper noise" transitions that occur when a laser beam sweeps across
the wide margin area of a bar code.

      These paper noise transitions lead to spurious bars in the
digital video, and these spurious bars can complicate the decoding
process.  The purpose of the disclosed technique is to create a
signal that marks the position of the first true bar code bar in the
digital video signal, allowing the decode logic to ignore the
spurious bars.

      In the margin area of the bar code (the quiet zone preceding
the bars), both the peaks and the valleys of the signal have a much
lower amplitude than the signal from a true bar.  The first-bar-find
circuit detects the large black follower transition that occurs when
the laser beam moves from the margi...