Offenburg University of Applied Sciences

Bar codes / Barcodes - An Overview

by

 Andreas Brodmann

Table Of Contents

1 Identification Technologies 6

1.1 Mechanical/Electromechanical Identification 7
1.2 Magnetic Identification 8
1.3 Optical Identification 9
1.4 Electronic / Electromagnetic Identification 11

2 Bar Cod 12

2.1 Generation 13
2.2 Acquisition 15
2.3 Decoding And Processing 16

3 1D Code18

3.1 Sructure 18
3.2 Error Detection 19

4 2D & 3D Codes 21

4.1 Structur 22
4.2 Error Detection & Correction 23

Abstract

Automatic identification became part of our life′s nowadays. Bar codes, ID cards and chip cards can be found everywhere in trade, industry and logistics to name only some areas. This document gives an overview on the different identification technologies and focuses especially on bar codes which belong to the optical identification technology. First the generation, acquisition and decoding & processing is shown. The different types and methods of 1D, 2D and 3D codes and their structures are explained. The most common bar codes, its typical fields of application are presented and its advantages and disadvantages are shown.

1 Identification Technologies

Identification technology is used for management of production, logistics and delivery of products and goods. Over the years the work flow of production speed up also because the identification methods were improved and faster processing and identification became possible. Identification technology uses the following principles:

• mechanical/electromechanical
• magnetic
• optoelectronic
• electronic/electromagnetic

Figure 1: Identification Technologies 

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1.1 Mechanical/Electromechanical Identification

The mechanical/electromechanical identification utilizes switches and cams. E.g. one way to encode information is to use movable metal sheets which are placed on the object and metal brushes are placed next to the object on the assembly line. If the distance between the metal sheets matches the distance of the metal brushes an electrical impulse triggers the actions to be taken. Another possibility are cams placed on the moving object. While passing a certain point on the assembly line the cams eventually trigger switches in the same distance and measures can be taken.¹

Figure 2: Mechanical/Electromechanical Identification 

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1.2 Magnetic Identification

Magnetic Identification is based on the magnetic forces. The forces are either coupled on ferromagnetic metals or used to induce electrical impulses in induction loops.¹
Permanent magnets on the object either trigger a signal in a reed contact or an induction loop. With an loop the inducted voltage is proportional to the speed of the relative speed of the magnet.
Furthermore magnetic strips can be applied to ID cards and documents. The data is written and read by inductive read / write heads. The data can also be deleted from the magnetic stripe1. Figure 3 shows a magnetic slider with permanent magnets.

Figure 3: Magnetic Slider

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Magnetic-visible characters have the advantage that they are visual and automatic readable. The colour of the characters contains iron oxide. Before automatic reading the characters are magnetized and then scanned by the read head. There are analogue and digital magnetic fonts called MICR fonts. Analogue means, the single characters are distinguished by the signal variation with time. The characters of digital fonts are printed with a bar code texture. Each character has its own bar code pattern. An example of the analogue font E13B and the digital font CMC-7 are shown in Figure 4.

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1 Lenk, B., Handb. d. autom. Identifikation Band1, 2000, p. 9-11

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1 Lenk, B., Handb. d. autom. Identifikation Band1, 2000, p. 12