Technology and Engineering of Barcode Scanners

Technology and Engineering

laser scanners : typical scanners utilise a 650nm laser diode, leveraging on the economies of scale of diodes manufactured for CD/DVD drives. The diode is normally housed in a metal casing for heat dissipation. The laser light emitted is focused through a lens and reflected off a rotating polygonal mirror, or an oscillating mirror. This produces a line or raster pattern which may be aimed at a barcode. The light reflected off the barcode is captured onto a photodiode whereby the current is amplified and interpreted by the decoding circuit. The signal obtained is the modulation of the laser spot (whose profile approximates that of a Gaussian beam), over the alternating black and white lines of the barcode. The performance of the scanner is a function of:
the signal to noise ratio (determined by the laser power, the size of the laser spot, reflectivity/transmittivity of the optical parts, receiving light collection area, distance to the barcode, the level of optical noise such as sunlight, fluorescent light as well as the ability to filter out that noise, etc). The laser power is usually limited by CDRH Class I/II safety requirements.
the scan speed of the device. Basically a trade-off between decode speed and the size of the decode zone.
the barcode (determined by difference in refectance of the barcode's alternating black & white stripes--print contrast ratio, defects, the size of the barcode, and the barcode's orientation in relation to the scanner). Generally, the laser has to pass a certain amount of the 'quiet zone' on the barcode before it hits the line patterns, in order to decode.
the decoding circuit's ability to decode and to handle errors in the barcode, optical noise as well as the range of frequencies at which the signal is modulated.

Types of Barcode Readers

Types of Barcode Readers
Many different types of barcode scanners are available. They can be distinguished as follows:





By light source
1. LED scanner : also referred to as CCD scanners, even though the CCD is in fact the photo imaging sensor, not the light source.
2. Laser scanner : more expensive than LED scanners but are generally capable of longer maximum scanning distances.
3. Linear Imager scanner : These scanners use a "linear Imaging Sensor" to take an image of the barcode. The sensor is a single row of light sensitive pixels generally used to scan one dimensional or "linear codes". Typically more rugged than laser scanners since they have no moving parts.
4. 2D Imaging scanner : These scanners take a 2D image of the barcode as in a camera and can be used to scan 2D barcode types such as Datamatrix as well as the more common linear barcode types.

By housing
1. Handheld scanner : with a handle and typically a trigger button for switching on the light source.
2. Pen scanner (or wand scanner) : a pen-shaped scanner that is swiped.
3. Stationary scanner : wall- or table-mounted scanners that the barcode is passed under or beside. These are commonly found at the checkout counters of supermarkets and other retailers.
4. Fixed position scanner : an industrial barcode reader used to identify products during manufacture or logistics. Most often used on conveyer tracks to identify cartons or pallets which need to be routed to another process or shipping location.
5. PDA scanner : a PDA with a built-in barcode reader.

Barcode Scanner

A barcode reader (or barcode scanner) is a computer peripheral for reading barcodes printed on various surfaces. Like a flatbed scanner, it generally consists of a light source, a lens and a photo conductor translating optical impulses into electrical ones. Additionally, nearly all barcode readers currently produced contain decoder circuitry analyzing the barcode's image data provided by the photo conductor and sending the barcode's content to the scanner's output port