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Reading (Scanning) Bar Codes and Information

Input Devices 

An input device is simply a reader that provides a quick and efficient way to transfer encoded information into an application. Encoded data can be a bar code, magnetic stripe or even some physiological characteristic such as a fingerprint. Listed on the following pages are several input methods that are currently available. Some input devices require direct contact with the encoded data while others can read the data from a distance. Determining the input device is generally the first step when considering Automatic ID equipment. 

Scanning Devices

All scanning devices use a Light Emitting Diode (LED) and a photodetector to scan bar codes. The light generated from the LED falls on the bar code and is absorbed by the printed bars and reflected by the white spaces. The photodetector senses the reflected light and electro-optically converts the reflected light into a signal. The digitized signal is then sent to a decoder and converted into ASCII characters.

Wands

A wand is a pen-type scanner requiring physical contact with a bar code when scanning. The wand is simple to use but does require the user to maintain a tilt angle of 60º-85º above the label surface. This controls the reflectance of the light that is absorbed and a constant or continuous scanning motion across the bar code must be maintained to regulate the sample rate. The speed in which the user moves across the bar code is also important. If the continuous scanning motion is too slow or too fast, the decoder may not be able to detect the signal sent to it by the wand.

Often users are unaware that a wand may not be able to read certain bar code densities. The wand resolution must be less than the bar code density. For example, a 5 mil wand can read a 10 mil bar code, however, a 10 mil wand cannot read a 5 mil bar code. General purpose wands can typically read up to 5 mils.

A simple way of determining the correct wand resolution for a specific bar code application would be to multiply the X dimension of the bar code by 0.7 and round up to the next whole number. For example, if you are using a 15 mil bar code, multiply 15 mil by 0.7 (10.5) and round up to the nearest whole number (11). Any mil size less than 11 would normally suffice for the application in our examples.

In overall cost, Wands are about one-tenth the price of a laser gun and about one-fifth the price of a CCD reader. However there are a number of trade-offs that need to be considered before cost. First, a wand is a contact scanner and, therefore, must come into direct contact with the bar code. If the nature of the application does not permit the user to come into direct contact with the bar code, then another solution must be considered, such as a laser scanner. Secondly, a wand can not scan nearly as fast as a CCD reader or laser scanner. A wand is a manual scanning device in that a tilt angle and constant scanning motion must be met in order to obtain a good read. CCD readers and laser scanners simplify these procedures electronically through features such as automatic
gain control and self-scanning.

The wand works well in most applications and should be considered first when implementing a new bar code station or as a ÒhotÓ backup if an extra scanning device is required.

CCD

Charged Coupled Device (CCD) technology is a technique whereby a bar code is photographed, digitized, and electronically sampled by built-in photodetectors. The detectors process the measurement of every bar and space using the number of adjacent photodetectors which contrast a black mark and a white space. CCDs are lighter than most laser scanners and are generally
much more rugged since they have no moving parts.

CCD readers range from about 2 inches to approximately 4 inches in width. The most common CCD readers measure roughly 3 inches. Of all the scanning devices, a CCD reader is the easiest to use. The user simply covers the bar code with the head of the scanner and pulls the trigger to activate the scanner. 

The cost of a CCD scanner is about one-third the price of a laser scanner and about four times the cost of a wand. The CCD reader is a contact scanner in that user must have direct contact with the bar code label. If a wand is too difficult, too timely, or cumbersome to use, a CCD scanner could be an alternate solution.

A new technology related to CCD is Fixed Focus Optics (FFO). FFO technology utilizes the same principles as CCD technology, however, FFO scanners are non-contact readers. FFO readers can digitize a bar code from a distance of up to twenty inches from the label depending upon the resolution of the bar code. FFO promises to be a leading contender in the scanning market with the added capability of digitizing two-dimensional bar codes.

Laser Scanners

Laser scanning is in widespread use among a variety of applications and integrated in hand held laser guns, projection or fixed scanners used in conveyor systems, and in-counter scanners as seen in many supermarkets. Laser scanners project a beam of energy off an oscillating mirror or rotating prism and generate what appears to be a red scan line. An omnidirectional projection scanner creates a pattern or raster of red scan lines. In reality, the scan line(s) is a laser spot rapidly moving across at 30 or 40 times per second. Laser scanning is ÒautomaticÓ in a sense that it generates multiple scans activated either by sensing an object that is placed in front of the scanner (known as autosense) or by simply pulling a trigger. In comparison, a wand must be moved manually across a bar code by hand and thus is a manual scanning device.

One of the newest technologies regarding laser scanning is “Fuzzy Logic.” Fuzzy logic technology applies artificial intelligence to reading poorly printed bar codes and is ideal for low-contrast, high density bar codes. Fuzzy logic offers the highest level of performance and best first-time read rate across a range of bar code qualities including harsh environments and rugged operating conditions.

Projection scanners are commonly used in material movement configurations. Both tabletop and fixed mount projection scanners are popular units at many checkout counters and conveyors systems respectively. Grocery store clerks move items across tabletop scanners almost as fast as it takes to remove the items from a cart alone. Likewise conveyor systems scan at a much higher rates than anyone is able to without making mistakes.

Laser technology is very popular in the United States primarily due to patent grants. Only a hand full of companies hold the central patents in this technology preventing further domestic and foreign competition. CCD technology is more popular among other countries because of this legal issue.

Every laser scanner has a depth of field. The depth of field is the range between the minimum and maximum distance in which a laser scanner can successfully read a particular bar code, and it is directly related to the density of the bar code. For example, the higher the density of the bar code, the closer the laser has to be to read a symbol. Likewise, the lower the density of the bar code, the farther away the laser has to be to read a symbol. There will be some overlap between the range of various bar codes, but as a general rule, the user must keep this is mind when scanning. In regards to bar coding, some common problems may exist with the set up. The table on the next page outlines some of these problems and the appropriate step(s) to take.

Bar Slot

Bar Slot technology is similar to wand technology. From appearance alone, a bar slot reader looks very much like a magnetic stripe reader. However, rather than using the magnetic stripe technology to decode information, bar slot readers only decode bar codes. 
Bar slot technology is primarily used for access control and time and attendance applications. Typically, the front or back of a paper or plastic card is bar coded with the appropriate symbology. If paper is used, the card is usually laminated with a plastic coat to protect the card. Bar slot technology is primarily used over magnetic stripe when cards must be produced in-house. Bar codes have historically been easier to print and less expensive to produce than using magnetic encoders.

Magnetic Stripe

Magnetic stripe technology records magnetic data that is generally encoded on the front or back of a paper or plastic card similar to that of an audio or videotape. A magnetic stripe reader decodes the magnetic information on the card and translates it into ASCII characters.

The magnetic stripe found on the back of credit cards and ID badges have a possibility of up to three "tracks" of data - Track 1, Track 2, and Tack 3. Each track has a different encoded format. Track 1 contains up to 79 alphanumeric characters while Track 2 and 3 contain only numeric characters. Track 2 contains 40 numeric characters, and track 3 contains 105 numeric characters. The banking industry use Tracks 1 and 2. Regulations required the customer's name to be encoded on the magnetic stripe along with the account number. In addition, the card holder number and expiration date are usually encoded. ID badges, on the other hand, use Track 2.

There are two types of magnetic encoding schemes: low-coercivity and high-coercivity. In regards to magnetic stripe technology, coercivity is the opposing magnetic intensity that must be applied to a material to remove the residual magnetism when it has been magnetized to saturation. In other words, a card encoded with high-coercivity has a less of a chance of accidentally being erased with, for example, a magnetized screw driver or magnetic clasp than a low-coercivity encoded card. Most card systems support both types of media, but high-coercivity is generally recommended especially for creating ID badges.

The best known applications for magnetic stripe are credit cards, time and attendance, personnel identification, and banking cards. Standards have been adopted for data densities, encoding methods, data content, recording qualities, and data formats. Magnetic stripe standards are mandatory in all financial systems, however, few standards exists for most other applications. 

Other Identification Devices

Optical and Intelligent Character Recognition

Optical Character Recognition (OCR) technology has been used in commercial applications for nearly fifty years and uses OCR fonts (such as OCR-A and OCR-B) instead of bar codes for automated data entry. The fonts are electronically scanned and digitized into ASCII characters.

With the advent of the personal computer, OCR technology has expanded in translating other stylized fonts such as Courier, Times Roman, etc. that are commonly found in newspapers, magazines, and other reading materials. Many manufacturers now describe this as Intelligent Character Recognition (ICR) since today’s OCR equipment is much more capable and much more powerful.

There are three categories of OCR/ICR readers: transaction readers, page readers, and hand-held readers. Transaction readers scan relatively short character streams and have the highest accuracy of all three types of readers. Page scanners digitize pages of text. Hand-held scanners are primarily used when transaction scanners are impractical and too expensive to use. Hand-held scanners also allow the user to have greater flexibility in scanning data outside a relative boundary or fixed position, for example, locating and reading the International Standard Book Number (ISBN) found on most published books which is printed usually somewhere on the back cover.

OCR/ICR is better suited in applications where human readability is required and where it is impractical to convert to bar codes. One of the most common OCR fonts, E-13B (MICR), is found at the bottom of nearly all personal checks and frequently used in point of sale, payment processing, and libraries.

RF Identification and Proximity Readers

RF Identification (RF/ID) uses radio frequency technology for tracking and identifying vehicles, animals, pallets, etc. By affixing electronic tags to objects and encoding specific information, an object can readily be identified and tracked from a distance. RF/ID can have proximity ranges of up to a 100 feet with minimal interference. RF/ID provides both proximity and dynamic identification so
that tagged objects do not need to be physically contacted or stationary in order to be identified. RF/ID systems are extremely accurate, have no line-of-sight requirements, and cannot be erased easily from environmental conditions or strong magnetic fields.

RF tags are either active or passive. Active tags are usually more expensive because they can transmit a low-powered signal. These tags come with batteries and permit farther distances for RF identification. Passive tags do not come with batteries and are detected solely by the RF receiver.

The most common use of RF/ID is with toll tags. Other applications include personnel monitoring, security access, and package sorting.

Touch Memory

Touch Memories or memory buttons are electronic identification devices that are accessed when a touch probe comes into contact with a memory button. Memory chips are often packaged in coin-shaped stainless steel containers (buttons) to withstand harsh environments and are capable of holding large amounts of data (over 4,096 characters). Read and/or write operations between the probe and memory chip are performed with just a momentary contact. Thousands of reads and writes can be performed with a single chip and data integrity can last over 100 years. 

Touch memory is widely used by the US Postal Service for tracking collection times on its large collection boxes. Healthcare, transportation, and trade show organizations are other potential markets for this growing technology. Nearly any application where relatively large amounts of data need to be stored and randomly accessed are suitable candidates for this emerging technology.

Biometric Identification

Biometric Identification is a technology which digitizes an individual's physiological trait and uses it as a means of personal identification. Biometric identification is primarily used in access control applications and is predominantly used in high-security areas at government facilities and banks. 

Other biometric verification techniques include fingerprint, retinal scanning, hand geometry, facial characteristics, voice patterns, and blood-vessel arrangement in the wrist or hand. Fingerprint identification is the most popular.

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