6.1. Bar Codes This section provides a brief introduction to bar code technology. The chief aspects of bar codes are discussed together with some of the most popular standards in use today. 6.1.1. What Is a Bar Code? A bar code is a scheme in which printed symbols represent textual information. The printed symbols generally consist of vertical bars, spaces, and squares and dots. A method that encodes alphanumeric characters using these symbol elements to a printed symbol is called symbology. Two symbologies may use the same or different symbol elements to encode the same character string. Some characteristics of a symbology are as follows: Encoding technique. A symbology with better encoding techniques allows for efficient and error-free encoding. Character density. A symbology that offers better character density can represent more textual information per unit physical area. Error-checking techniques. A symbology with better error-checking capability can allow the data to be read correctly even if some of the symbol components are damaged or missing.
About 270 different symbologies have been invented to support specific requirements, and approximately 50 are in widespread use today. Each symbology falls into one of the following three categories: Linear. Linear symbologies consist of vertical lines with different widths with white space separating two adjacent lines. The maximum number of characters that can be encoded with a linear symbology is up to 50. Two dimensional. Two-dimensional symbologies have the most data-storage capacity. The maximum number of characters that can be encoded with a two-dimensional bar code symbology is 3,750. Three dimensional (also called a bumpy bar code). A three-dimensional symbology is actually a linear bar code embossed on a surface. This type of bar code is read using the "bumpiness" or the three-dimensional relief of the bar code. A bumpy bar code is thus not dependent on the contrast between the bar code lines and spaces for its reading (discussed in the next section). This type of bar code can be painted and subject to harsh environmental conditions, whereas a paper bar code in similar scenarios is easily destroyed.
Subsequent sections discuss symbologies in more detail. For now, however, the discussion turns to operating principles of bar codes and bar code readers, followed by the advantages and disadvantages of the technology. 6.1.2. How Are Bar Codes Read? Bar code readers, also called scanners, read bar codes. A bar code scanner uses a light beam to scan across the bar code. The direction of scanning, in general, is irrelevant. However, during scanning, the light beam cannot move out of the bar code region. Therefore, in general, an increase in a bar code length also means an increase in scanner height to accommodate for larger deviations of the light beam outside the bar code region during scanning. During the scanning process, the reader measures the intensity of the reflected light by the black and white regions (for example, vertical bars) of this bar code. A dark bar absorbs light, and white space reflects light. An electronic device called a photodiode or a photocell translates this light pattern into an electric current (or analog signal). Electric circuits then decode this generated electrical current into digital data. This data is what was originally encoded by this bar code. The digital data is represented as ASCII characters. A single bar code reader can read several symbologies. Figure 6-1 shows the process just described. Figure 6-1. Steps in reading a bar code. 
6.1.3. Bar Code Readers Today, the following four types of bar code readers are available: Pen readers (also called wands or contact wands). This type of reader looks like a wand or a pen with the light source focused at the tip. The bar code needs to be in contact with the reader at all times while being read. The advantage of this reader is that it has no moving parts; the user does the scanning manually. As a result, these readers are inexpensive and lightweight (besides being rugged). One of the drawbacks of this type of reader is when a bar code is placed on a roughly textured object. If the bar code's surface is not sufficiently flat, a reader might not be able to read the data correctly. Figure 6-2 shows an example wand reader. Figure 6-2. A wand bar code reader from Intermec Corporation.
Reprinted with permission from Intermec Technologies Corporation 
Laser readers. This type of reader is the most frequently used bar code reader. A laser beam located inside the reader automatically scans a bar code. One of the advantages of this reader type is its capability to read a bar code even if the bar code surface is not flat. It can do so because laser beams of such readers can be focused precisely into a small beam. The laser beam of a reader of this type can either move automatically or be stationary. The laser beam in an self-scanning reader moves back and forth rapidly at the rate of 40 to 800 times per second. Generally, just one scan is needed to read a bar code. Therefore, this type of reader can read bar codes at a high rate, even if a bar code is of bad quality. A static beam reader is frequently used in industrial operations where the object that has the bar code is moving at a constant speed (for example, on a conveyor belt). In this case, there is no need for a moving scanning beam. A reader of this type can be either stationary or handheld. The maximum reading distance for this type of reader is about 30 feet (9 meters approximately). Figure 6-3 shows an example laser reader. Figure 6-3. A laser bar code reader from Intermec Corporation.
Reprinted with permission from Intermec Technologies Corporation 
Charged coupled device (CCD) readers. This type of reader can read a bar code in a contactless manner. An array of several hundred small light sensors is located at the front of the reader. When the image of a bar code is projected into these photo-detectors, they generate a voltage pattern. This pattern is identical to the voltage pattern generated by a laser reader for this bar code. Some of these systems use additional sources of light, such as a flash, to increase the focal distance. The maximum reading distance for this type of reader is 6 inches. One of the drawbacks of these types of readers is that they cannot read long bar codes because of their limited field of view. In addition, the number of photo sensors in a reader determines the bar code density it can read. Figure 6-4 shows an example of a CCD reader. Figure 6-4. A CCD bar code reader from Intermec Corporation.
Reprinted with permission from Intermec Technologies Corporation 
Camera readers. These readers are the result of recent advances in bar code technology. A small camera inside this reader captures the bar code image. This image is then processed using digital image-processing technology to determine the bar code data. A drawback of this reader type is that it is sensitive about the quality of the bar code for an accurate reading. For example, the bar code must have sufficient contrast between its white and dark symbols and cannot have spots or empty spaces. Camera-based imaging scanners have become smaller, faster, and cheaper. A large number of end users are replacing laser scanners with imagers for two-dimensional bar code applications. Figure 6-5 shows an example of a camera reader. Figure 6-5. A camera bar code reader from Intermec Corporation.
Reprinted with permission from Intermec Technologies Corporation 
6.1.4. Benefits The major benefits of bar codes include the following: Rapid and accurate data collection. A bar code automates data collection. Using laser readers, you can scan several bar codes in a short period of time. Bar code reading is accurate, with an average error rate of one in three million reads. Table 6-1 (shown later in this chapter) shows a bar code accuracy survey result. Table 6-1. Bar Code Accuracy (Summary of Ohio University's Findings)Symbology | Worst Case | Best Case |
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DataMatrix | 1 error in 10.5 million | 1 error in 612.9 million | PDF417 | 1 error in 10.5 million | 1 error in 612.4 million | Code 128 | 1 error in 2.8 million | 1 error in 37 million | Code 39 | 1 error in 1.7 million | 1 error in 4.5 million | UPC | 1 error in 394,000 | 1 error in 800,000 |
Increased operations efficiency. The data decoded by a bar code reader can be fed directly to an application running on a computer system. Therefore, you can automate various operations, such as price retrieval, personnel identification (e.g., library member), inventory monitoring and control, and so on. Reduced operations cost. Bar code use offers cost savings by reducing the data- collection errors, reducing manual labor cost, and eliminating process inefficiencies.
6.1.5. Drawbacks The major drawbacks of bar codes include the following: Easily damaged. A bar code can be damaged by dirt, paint, fading due to bright sunlight, and moisture. Reader (contactless) operations can be affected by moisture in the environment. Light rays from a reader are refracted by suspended water particles in the environment, resulting in distortion of focus. Therefore, this reader might experience a loss in read accuracy. Presence of obstacles. A bar code reader needs to have a line of sight to the bar code it is supposed to read. Any obstacle between the reader and the bar code will prevent reading of this bar code. Speed. A bar code reader might not be able to read every bar code if they move at a high speed (for example, when the scan rate of a reader is exceeded by the movement speed of the bar codes).
Now, some major bar code symbologies are discussed. 6.1.6. Example Symbologies It is beyond the scope of this book to explain every symbology that exists today. Therefore, this book discusses only a few of the major symbologies in widespread use today, as follows: 6.1.6.1. UPC UPC stands for Uniform Product Code and is managed by the Uniform Code Council (UCC). Two major UPC types are as follows: UPC-A. This symbology consists of 12 digits, of which the last digit is used as a check digit. The first digit represents the product type, the next five digits the manufacturer code, and the subsequent five digits identifies the actual product. This symbology is used extensively in retail. UPC-E. This consists of seven digits, of which one is used as a check digit. UPC-E is also sometimes called zero suppressed UPC because it can compress a UPC-A code into a six-digit code by suppressing its trailing zeros for the manufacturer code and leading zeros of the actual product. The seventh digit is used as a check digit for the first six digits. Thus, UPC-E can always be converted back into UPC-A. This symbology is used for small retail items.
A supplemental two- or five-digit number can be appended to both UPC-A and UPC-E. Periodicals and publications use this supplemental. Figures 6-6 and 6-7 show example UPC-A with a two- and five-digit supplemental, respectively. Figure 6-8 shows an example UPC-E bar code. Figure 6-6. An example UPC-A bar code with a two-digit supplemental. 
Figure 6-7. An example UPC-A bar code with a five-digit supplemental. 
Figure 6-8. An example UPC-E bar code. 
6.1.6.2. EAN EAN stands for the European Article Numbering system, which is the European version of UPC. Two major EAN types are as follows: EAN-13. This symbology is the European equivalent of UPC-A. Compared to UPC-A, an EAN-13 symbology contains an additional digit, which together with the twelfth digit generally represents the country code. This symbology is used by the publishing industry to represent ISBN numbers for books. An ISBN code is an EAN-13 bar code with the first three digits as 978 and the remaining nine digits representing the first nine digits of the actual ISBN number. EAN-8. This consists of eight digits, of which the first two are used for the country code. The next five digits are used for data, and the last one is used as a check digit.
A supplemental two- or five-digit number can be appended to both EAN-13 and EAN-8. Periodicals and publications use this supplemental. For ISBN codes, this supplemental number starts with 5, and the remaining four digits are used to encode the price of the book. Figures 6-9 and 6-10 show example EAN-8 and EAN-13 bar codes, respectively. Figure 6-9. An example EAN-8 bar code. 
Figure 6-10. An example EAN-13 bar code. 
6.1.6.3. Code 128 This variable-length symbology uses both alphabetic symbols and digits. This symbology is widely used and is generally considered to be the optimal choice for a variety of bar code applications. It uses characters from the following three sets: Uppercase alphabets and ASCII control characters Uppercase and lowercase alphabets Numbers from 00 through 99
The first character is a special character that signals which of these sets is used initially. Three special shift codes, one for each set, also allow changing the character set after the initial set. This symbology also uses a check digit. Figure 6-11 shows an example Code 128 bar code. Figure 6-11. An example Code 128 bar code. 
6.1.6.4. PDF417 PDF stands for Portable Data Format. This high-density, two-dimensional symbology, invented by Symbol Technologies, Inc., can encode all 256 ASCII characters. A maximum of 2,525 characters can be represented by a bar code of this type. This symbology consists of smaller bar codes stacked on top of each other. This is a mature symbology that provides several options such as data security and compression, error detection and correction, and so forth. This bar code offers the next-best read accuracy (see Table 6-1) after DataMatrix. Figure 6-12 shows an example PDF417 bar code. Figure 6-12. An example PDF417 bar code. 
6.1.6.5. Aztec Code This high-density symbology can encode all 256 ASCII characters. A maximum of 3,750 characters can be encoded by a bar code of this type (when the characters are all digits). The basic building blocks of this symbology are shaped like a square and are called modules. At the center of this bar code is a square-shaped bulls-eye surrounded by layers of encoded data. A bar code of this type can be read independent of its orientation. Figure 6-13 shows an example Aztec bar code. Figure 6-13. An example Aztec bar code. 
6.1.6.6. DataMatrix This high-density symbology can encode all 256 ASCII characters. A maximum of 3,116 characters can be encoded by a bar code of this type. A distinguishing characteristic of this symbology is its perimeter pattern. The new version of this symbology, called ECC200, offers better encoding and better error-detection and -correction schemes. This bar code offers the maximum read accuracy (see Table 6-1). Figure 6-14 shows an example DataMatrix bar code. Figure 6-14. An example DataMatrix bar code. 
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