The basic principle of bar code reader
Bar code reader is used to read the information contained in the bar code equipment, bar code reader structure is usually the following parts: light source, the receiving device, photoelectric conversion components, decoding circuit, computer interface. Their basic working principle is: the light emitted by the light source through the optical system to the bar code symbol, the reflected light through the optical system imaging in the photoelectric converter, so that produce electrical signals, the signal amplified by the circuit to produce an analog Voltage, it is irradiated with the bar code symbol is reflected back to the light is proportional to, and then filtered, shaping, and the formation of analog signals corresponding to the square wave signal, the decoder can be interpreted as a computer can directly accept the digital signal.
Barcode readers generally use the following three bar code reader technology: light pen bar code reader, CCD bar code reader, laser bar code reader, they have their own advantages and disadvantages, not a bar code reader can have in all respects Advantages, the following discussion of each bar code reader works and advantages and disadvantages.
Light pen works
Light pen is the first to appear in a handheld contact bar code reader, it is also the most economical a bar code reader.
In use, the operator need to touch the light pen to the surface of the bar code, through the light pen of the lens to issue a small spot, when the light from left to right across the bar code, in the "empty" part of the light is reflected, ", The light will be absorbed, so a change in the internal voltage pen, the voltage through the amplification, shaping for decoding.
The advantages of the pen are: contact with the bar code to read, to be clear which is the bar code to be read; read bar code length can not be restricted; compared with other readers lower cost; internal no moving parts, relatively strong; Small, light weight. Disadvantages: the use of light pen will be subject to various restrictions, such as in some occasions is not suitable for access to reading bar code; the other only in the relatively flat surface to read the specified density, better print quality bar code, the pen can play its role; The operator must be trained to use, such as reading speed, reading angle, and the use of improper pressure will affect its reading performance; Finally, because it must touch reading, when the bar code due to improper preservation and damage, or above a Layer protection film, the light pen can not be used; light pen first read the success rate is low and high bit error rate.
CCD reader works
CCD for the electronic coupling device (Charg couple device), more suitable for close and contact reading, its price is not expensive laser reader, and there is no moving parts.
The CCD reader uses one or more LEDs, which emit light to cover the entire barcode. The barcode image is transmitted to a row of photodetectors, sampled by each individual photodiode, detected by adjacent detectors In other words, the CCD reader does not pay attention to reading each "bar" or "empty", but rather the entire part of the bar code, and converts it into a "bar" or "blank" Can decode the electrical signal.
Advantages: Compared with other readers, CCD reader price is cheaper, but also have a wide range of bar code reading, easy to use. It weighs less than a laser reader, and does not have to be readable like a light pen.
Disadvantages: CCD reader is limited in its reading depth of field and reading width, in the need to read printed on the arc surface of the bar code (such as beverage cans) when there will be difficulties in some distance reading, such as storage areas, Is not very suitable; CCD drop performance is poor, resulting in a higher failure rate; in the bar code to be read more wide, CCD is not a good choice, information is very long or very low density bar code is easy to scan Head reading range, resulting in bar code unreadable; and some to take more than one LED bar code reader, any one LED failure will lead to can not read; most of the CCD reader first read the success rate is low and the probability of error .
The working principle of laser gun
Laser scanner is a variety of scanners in the relatively high price, but it can provide the highest functional indicators, so in various industries are widely used.
The basic principle of a laser scanner is that a hand-held laser scanner emits a beam of light through a laser diode to a rotating prism or a mirror that swings back and forth. The reflected light passes through the reading window and illuminates the surface of the bar code. After a reflection of the bar or empty back to the reader, by a mirror to collect, focus, through the photoelectric converter into electrical signals, the signal will be scanned by the terminal or decoding software decoding.
Laser scanner is divided into handheld and fixed in two forms: hand-held laser gun connection is simple and convenient, flexible, fixed laser scanner for reading the largest bar code smaller occasions, the effective liberation of his hands work.
Advantages: Laser scanners can be used for non-contact scanning, usually in the reading distance of more than 30cm laser reader is the only choice; laser bar code reading density range, and can read the irregular bar code surface or through Because of the more advanced reading and decoding system, the first reading to identify a high success rate, the identification speed relative to the light pen and CCD faster, but also for the printing of the quality of the printing quality, Good or bad fuzzy bar code recognition effect; bit error rate is very low (only about three parts per million); laser reader shock and drop performance, such as: Symbol LS4000 series of scanners can be 1.5 m cement To fall.
Disadvantages: laser scanners only drawback is that its price is relatively high, but if the purchase cost and the use of the sum of the cost, and the CCD reader is not much difference.
The key parameters of a bar code scanner
Before selecting a barcode scanner, learn about several key technical parameters of the scanning device and select the appropriate device against these parameters, depending on the application.
1), resolution
For a bar code scanning system, the resolution is the width of the narrowest stripe to be read correctly, in English, MINIMAL BAR WIDTH (abbreviated as MBW). Select the device, not the equipment, the higher the better split rate, but should be based on the specific application of the bar code density to select the scanner with the appropriate resolution. In use, if the resolution of the selected device is too high, the impact of the system on the stripes, deinking, etc. will be more serious.
2), scanning depth of field
Scan depth refers to the difference between the farthest distance from the barcode surface and the closest point of the scanner to the surface of the barcode, that is, the effective operating range of the bar code scanner, to ensure reliable reading. Some bar code scanning equipment in the technical indicators did not give the scan depth of field indicators, but to give the scanning distance, that is, scanning head to allow bar code surface from the shortest distance.
3), scan width (SCAN WIDTH)
The swept width index refers to the physical length of the bar code information that can be read by the scanning beam over a given scan distance.
4), scanning speed (SCAN SPEED)
Scanning speed is the sweep frequency of the scanning beam per unit time on the scanning track.
5), a recognition rate
The primary recognition rate is the ratio of the number of tags read in the first scan to the total number of scanned tags. For example, if each barcode tag needs to be scanned twice for each read, the first recognition rate is 50%. From a practical point of view, of course, hope that each scan can be passed, but unfortunately, due to a variety of factors, requiring a recognition rate of 100% is not possible.
It should be noted that: a recognition rate of the test index is only applicable to hand-held light pen scanning identification. If the laser scanning method, the beam on the bar code label scanning frequency up to hundreds of times per second, by scanning the signal is repeated.
6), bit error rate
Bit error rate is a very important test index which reflects the situation of a machine identification system. The error rate is equal to the ratio of the number of times of error recognition to the total number of recognition times. For a bar code system, the bit error rate is lower than the first recognition rate is more serious problem.
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