Linear (One-Dimensional) Bar Code Symbologies

Bar codes in their most familiar format - a series of varying-width parallel bars and spaces - have been with us for over 25 years. These linear, or 1D (one dimensional as opposed to two dimensional bar codes discussed below) symbologies continue to be the most widely used optical recognition technology. Well over 100 encodation schemes or symbologies have been invented over the years, but the most common 1D symbologies are Code 39, pioneered by the defense and automotive industries; the Universal Product Code (U.P.C.), first employed by the supermarket industry in 1973; Codabar, used early on by blood banks, Interleaved 2-of-5 (ITF), and Code 128.

Depending upon which symbology is used, bar codes may encode only numeric data (U.P.C. and ITF, for example), or all or part of the American National Standard Code for Information Interchange (ASCII) character set (e.g., Codes 39 and 128) by the width of the bars, and in most cases by the width of the spaces as well. As a scanning device is moved across the symbol, the width pattern of the bars and spaces is analyzed to extract the original encoded data.

The width of the narrowest bar or space is referred to as the X dimension, usually given in mils (thousandths of an inch). The X dimension dictates the width of all other bars and spaces, and ultimately the length of the bar code. The greater the X dimension, the more easily a bar code will scan; however, the tradeoff for easier readability is the greater cost of bigger labels. For proper scanning, most bar codes have a quiet zone, i.e., clear space, at either end whose width is at least 10 times the bar code's X dimension.

All bar codes use special patterns at each end, called start and stop characters. These characters identify the symbology and also enable the scanner to read the symbol bidirectionally, decoding the data in the correct order. Bar codes also often include a check digit at the end that is determined according to an algorithm based upon the preceding characters. The check digit validates that all characters have been decoded correctly.

Most bar codes include an interpretation line - the encoded data printed in human readable characters directly below the symbol. It is interesting to note that bar code technology made necessary the "human readable" designation for what used to be called simply numbers or text when humans were the only "readers."

Standardization within and across industries has been, and continues to be, essential to the phenomenal growth and widespread implementation of bar code technology. Bar code standards apply to printing, scanning, and verification of bar code symbologies. AIM, the leading standards developing organization for the AIDC industry, has published standard specifications for many symbologies. Additionally, the Uniform Code Council (UCC) and EAN has published specifications for the EAN/U.P.C. symbology.

These publicly available specifications allow AIDC vendors to produce labels, printers, scanners, verifiers, and entire integrated systems that can interact in an open business environment. The standardization of bar code label formats, under the aegis of ANSI (American National Standards Institute), CEN, and ISO/IEC has resulted in manufacturing, warehousing, and distribution cost savings and efficiencies across industries throughout the supply chain.

Reprinted with permission from AIM, Inc.
www.aimglobal.org

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