Bar code scanning system composition structure principle

The bar code scanning system constitutes the structural principle. The main body of the scanning system is an optical structure. The structure should have the following two functions: 1. Have a scanning optical path to generate a light spot, which can be along a certain manual or automatic control. The trajectory moves in a straight line and passes through a left margin, a start character, a data character, a terminator, and a right margin of a bar code symbol. 2. A receiving system having a bar code symbol reflected light which is capable of and is good at receiving diffuse reflected light from which the scanning spot is reflected back from the bar code symbol. (Focus on micro-signal cloud collaborative intelligent manufacturing)

The bar code scanning system can adopt different light sources, scanning forms, and optical path design to achieve the above functions.

(1) Light source of the scanner

There are many types of light sources selected for bar code scanners, mainly semiconductor light sources, laser light sources, and light sources such as incandescent lamps and flash lamps. Here we mainly introduce semiconductor light-emitting tubes and lasers.

1 semiconductor light tube

A semiconductor light-emitting tube, also known as a light-emitting diode, is actually a diode composed of a P-type semiconductor and an N-type semiconductor. The light emitting diode emits light when a forward voltage is applied to the P-N junction.

2 laser

Laser technology has been developed for more than 30 years and is now widely used in various fields. There are many types of lasers. Early bar code scanners used krypton lasers as scanning sources. In the 1980s, semiconductor lasers developed rapidly due to their low power consumption, small size, low operating voltage, high reliability, and low price. These characteristics make the original krypton laser quickly replaced.

Our common semiconductor lasers are small in power and bulky like a normal triode, so semiconductor lasers are also called laser diodes. Because bar code scanners generally use laser diodes, their size and cost are greatly reduced. At the beginning, only laser diodes that can only emit infrared lasers appeared. After the 1990s, red laser diodes appeared (now there are blue laser diodes). The development of laser diodes has become an important aspect of the development of bar code technology in recent years.

Lasers have unique properties compared to other sources:

1, has a strong directionality.

2, monochromatic and coherent is excellent. Other light sources do not receive monochromatic light like lasers, regardless of the filtering technique used.

3. Extremely high light intensity can be obtained. The bar code scanning system uses low-power laser diodes to make it harmless to the human eye when it is suddenly injected into the human eye, but it still has illuminance that is difficult to achieve with other light sources.

(2) Scanning method

Scanner scanning scanning bar code symbols are mainly divided into manual scanning, automatic scanning and CCD scanning.

1 manual scan

Manual scanning is relatively simple. There is no scanning device inside the scanner. The position of the emitted illumination beam is fixed relative to the scanner. The scanning process requires a barcode scanner to scan the bar code symbol. This barcode scanner belongs to a fixed beam scanner. This type of scanning is used by the stylus and most card barcode readers. (Focus on micro-signal cloud collaborative intelligent manufacturing)

2 automatic scanning

Auto-scanning means that the bar code scanner contains devices for scanning the scanning beam, such as a rotating mirror, a mirror, and the like. The scanning source for automatic scanning is laser, which is the basic schematic of automatic scanning.

The scanning beam is emitted from the laser (LS), passes through the half mirror surface (BSP), and passes through the mirror surfaces of the periodically rotating prism (PG) to form a scanning motion of the laser beam. At the same time, the reflected light of the illumination spot on the bar code symbol passes through the mirror surface of the rotating prism, is reflected by the semi-reflex lens surface (BSP), and passes through the photodetector where the converging lens converges. In this scanning structure, the scanning beam of the laser light does not pass through the lens system that receives the light, and the laser beam is narrow and the light energy is concentrated. However, outside the lens system, the laser beam and the optical axis of the receiving system remain coincident, thus ensuring that the illumination point of the laser is the receiving point of the detector.

The scanning device of the handheld laser bar code scanning gun generally uses a pendulum mirror instead of a prism, and is swung under the driving of the internal vibration coil to realize scanning. In the supermarket, omnidirectional laser scanning guns generally use two methods: rotating prism scanning and holographic scanning. Both scanning methods can produce scanning in multiple directions and multiple positions.

In the scanning optical path, a plurality of mirror combinations of each of the plane mirror and the prismatic rotating mirror can form a plurality of scanning lines in a certain direction. The combination of the three mirrors and the rotating mirror constitutes a multi-line scan in three directions. The scanning spot is returned through the plane mirror and the rotating mirror, and then the composite lens is concentrated on the photodetector. (Focus on micro-signal cloud collaborative intelligent manufacturing)

The scanning principle of holographic scanning is more novel, and the scanning device is a rotating holographic disk, which replaces the rotating prism above.

The basic process of holographic scanning is that the laser beam 1 is incident on the holographic disk 2, the rotating holographic disk realizes beam scanning, then the scanning line sweeps over the bar code symbol 3, and finally the reflected light signal returns to the holographic disk 2, and is concentrated by the holographic lens to the photodetector 4 on.

On the holographic disc, there are up to 20 scanning lenses, plus pairing with multiple plane mirrors, which can sweep up to 100 scanning rays. Designed to be especially good at multi-directional multi-line scanning over multiple distances. In addition, the holographic scanning device has significant advantages such as compact structure, high reliability, and low cost.

3CCD scan

CCD (Charge Coupled Device) - A charge detector is an electronic detector that automatically scans a bar code scanner. The entire image of the bar code symbol is first presented on the CCD of the line array, and then the CCD is applied to it. The signal is photoelectrically converted and automatically scanned without the need to add any motion mechanism, so it is a special automatic scan.