Nearly all of the automatic identification technologies consists of three principal components,
Encoded data: A code is a set of symbols or signals representing alphanumeric characters. When data are encoded, the characters are translated into a machine-readable code. A label or tag containing the encoded data is attached to the item that is to be later identified.
Machine Reader or Scanner: The device reads the encoded data, converting them to alternative form, usually an electrical signal.
Decoder: This component transforms the electrical signal into digital data and finally into the original alphanumeric characters.
ADC Technologies can be divided into the following six categories:
Optical: Most of these technologies-use high contrast graphical symbols that can be interpreted by an optical scanner. They include linear and two dimensional bar codes, optical character recognition and machine vision.
Magnetic: Which encode data magnetically, similar to recording tape. The two important techniques in this category are
Magnetic stripe, widely used in plastic credit cards and banking access card
Magnetic ink character recognition, widely used in the banking industry for check processing.
Data Accuracy: Accuracy of data collected is improved with ADC. The error rate in bar code technology is approximately 10,000 times lower than in manual keyboard data entry.
Timeliness: the second reason is to reduce time required by human workers to make data entry. The speed of data entry for handwritten documents is approximately 5-7 characters per second. Automatic identification methods are capable of reading hundreds of characters per second.
Labor Reduction: The time savings in using automatic identification techniques can mean substantial labor cost benefits for large plants with many workers.
Fixed beam readers: these are stationary units that use a fixed beam of light. they are usually mounted beside a conveyor and depend on the movement of the bar code past the light beam for their operation.
In this technique , light-colored paper labels are coated with a heat sensitive chemical that darkens when heated.
The printing head of the thermal printer consists of a linear array of small heating elements that heat localized areas of the label as it moves past the head , causing the desired bar code image to be formed.
Bar codes by direct thermal printing are of good quality ,and the cost is low.
This technology is similar to direct thermal printing , except that the thermal printing heads is in contact with a special ink ribbon that transfers its ink to the moving label in localized areas when heated.
This process can be used to mark bar codes onto metal parts . The process provides a permanent identification mark on the item that is not susceptible to damage in the harsh environments that are encountered in many manufacturing processes.