Bar Code Scanner

Background

Many different types of bar code scanning machines exist, but they all work on the same fundamental principles. They all use the intensity of light reflected from a series of black and white stripes to tell a computer what code it is seeing. White stripes reflect light very well, while black stripes reflect hardly any light at all. The bar code scanner shines light sequentially across a bar code, simultaneously detecting and recording the pattern of reflected and non-reflected light. The scanner then translates this pattern into an electrical signal that the computer can understand. All scanners must include computer software to interpret the bar code once it's been entered. This simple principle has transformed the way we are able to manipulate data and the way in which many businesses handle recordkeeping. Bar code scanning emerged in the early 1970s as a way to improve the speed and accuracy of data entry into computers. Businesses were just beginning to exploit computer tracking of stock and billing. The challenge was to find a quick, efficient, and relatively fool-proof method of record entry for companies (for example warehouses or mail order companies) that maintain a small stock of high volume items. The use of bar codes enabled clerks to keep track of every item they sold, shipped or packed without a tedious and error-prone keyboard data entry process. Bar coding caught on quickly in clothing stores, manufacturing plants (such as car makers), airline baggage checks, libraries, and, of course, supermarkets. The supermarket scanners which are commonplace today are known as point-of-sale scanners, since the scanning is done when merchandise is purchased; point-of-sale scanning is perhaps the most challenging bar code scanning application in use today. Supermarket scanners represent the most advanced design of the various types of bar code scanners, because of the particular difficulties associated with reading bar codes on oddly shaped items or items that may be dirty, wet, or fragile. The first scanners required human action to do the scanning and used very simple light sources. The most common was the wand, which is still popular because it is inexpensive and reliable. Wand scanners require placing the end of the scanner against the code, because the light source they use is only narrow (focused) enough to distinguish between bars and stripes right at the wand tip. If the labeled products are oddly shaped or dirty, this method is impractical if not impossible. To make a scanner that works without touching the code requires a light source that will remain in a narrow, bright beam over longer distances—the best source is a laser. Using a laser beam, the code can be held several inches or more from the scanner, and the actual scanning action can then take place inside the scanner. Rotating, motor-driven mirror assemblies, developed in the mid-1970s, allowed laser light to be swept over a surface so the user didn't need to move the scanner or the code; this technology improved scanner reliability and code reading speed. Later, holograms were chosen to replace mirrors, since they can act just like a mirror but are lightweight and can be motorized more easily. A hologram is a photographic image that behaves like a three-dimensional object when struck by light of the correct wavelength. A hologram is created by shining a laser beam split into two parts onto a glass or plastic plate coated with a photographic emulsion. Whereas the previous generation of scanners worked by rotating a mirror assembly, holographic scanners operate by spinning a disk with one or more holograms recorded on it. Researchers at IBM and NEC simultaneously developed holographic point-of-sale scanners in 1980. Holographic scanning was chosen not only because the hologram disks could be spun more easily than mirror assemblies, but also because a single disk could reflect light in many different directions, by incorporating different hologram areas on the same disk. This helped to solve the problem of bar code positioning; that is, codes no longer needed to directly face the scan window. Modern bar code scanners will scan in many different directions and angles hundreds of times each second. If you look at the surface of a scanner in the checkout lane, you will see lots of criss-crossed lines of light; this pattern was chosen as the most reliable and least demanding on particular package orientation.