Product Description:Laser scanning bar code readers because of its unique large depth of field area, high scanning speed,
wide scanning range of other advantages have been widely used. In addition, the whole point of the laser scanning reader reading due to an arbitrary direction through the high-speed scanning of bar code symbols, has been widely used in a variety of high degree of automation, logistics and large areas .
Laser scanning bar code readers from the laser source, optical scanning, optical receiver, photoelectric conversion, signal amplification, shaping, quantization and decoding components. Discussed in detail below these components .
Laser source
Using MOVPE ( metal oxide vapor phase epitaxy ) technology to produce a visible semiconductor laser has a low power consumption, can be directly modulated, small size, light weight, solidification, high reliability and high efficiency . It appeared that quickly replaced the original use of the He-Ne laser.
Semiconductor laser beam emitted axisymmetric non- elliptical beams. Of the incident light beam perpendicular to the junction plane direction of the P-W divergent angle V ⊥ ≈ 30 °, parallel to the junction plane direction of the divergence angle of V ‖ ≈ 10 °. Such as the use of traditional techniques beam collimation, the beam focal point of the elliptical spot of the long side, the short axis direction switching will occur . Obviously, this would make only a small scanner scanning depth of field. JayM.Eastman and put forward as shown in Figure 3 collimated beam technology to overcome this exchange, greatly improves the scan depth of field . This elliptical beam can only be used in single-line laser scanner. Arranged in the optical path, so that the spot to be the major axis direction of the ellipse perpendicular to the light scanning direction . For single scan reader, this elliptical light spot due to the insensitivity of the printing noise, than the following characteristics of said circular spot better .
The whole point of the bar code scanner reader, because the beam scanning bar code reading, sometimes a larger tilt angle swept barcodes. Thus, the beam spot should be made oval. Usually put it round the whole form . Shaping scheme currently used in front of the collimating lens of a small circular aperture . Such beam characteristics available holes Fresnel diffraction characteristics of a good approximation . Using this scheme, UPC bar code for standard size, depth of field can do about 250mm to 300mm. This is normal commercial POS systems have been sufficient. But for such as airport baggage conveyor lines require a large depth of field of the occasion, it becomes insufficient. The most commonly used solution is to increase the size or the bar code symbol scanning pattern consisting of different scanning light is focused on different areas to form a " multi- focal plane ." But the more attractive solution is to use special optical collimating element, the field of light passing through it so as to have a particular distribution of the beam divergence angle small, to obtain a large depth of field.
Optical scanning system
Emitted from the laser light source by a laser beam scanning system need to form the scanning lines or scanning pattern . Omnidirectional barcode scanner reader generally use rotating prism scanning and holographic scanning two programs . Holographic scanning system has a compact structure, high reliability and low cost and other significant advantages . Since the type of IBM Corporation in 3687 first applied on the scanner since been widely used, and innovation. It is anticipated that the market share will be increasing .
Rotating prism scanning technology more historic, more technologically sophisticated . It uses the rotating prism to scan the beam, with a plane mirror to fold the optical path changing multi -direction scan light. The use of more scanner products such as MS-700 also makes different rotating prism wedge angle of the different surfaces to form a scanning direction has several scan lines. By a number of multi-line scanning rays to form a high-density scanning pattern . This approach may bring another advantage of laser radiation can harm reduced.
This concept was first scanned the whole point is to increase the velocity of circulation of supermarkets put forward, and designed with the corresponding UPC code . For the UPC code two -scanning direction "X" scanning pattern, been able to achieve full scan angle . With the development of scanning technology, bar code applications to broaden and increase the degree of automation of the urgent need now is to scan the whole point of this concept to other code systems, such as 39 yards, 25 yards, etc. interleaved . The bar code system aspect is relatively small, in order to achieve full angle scan will require a lot more number of scan direction . This will be needed in addition to rotating the prism to add another moving element, for example, in Figure 4 the fold rotational plane mirror groups, etc.
Optical receiver system
Onto the bar code symbol scanning beam after scattering by the receiving system receives the scattered light enough . The whole point of the laser scanning reader, the commonly used back to the receiving system . In this structure, the received light beam is emitted main axis ray axis . In this way, the scattering light spot is always in the axis of the receiving system . The instantaneous field of this structure is very small, can greatly improve the signal to noise ratio, but also improve the bar code symbol suppression of specular reflection, and the requirements of the receiving lens is also very low . In addition, it allows the sensitive surface of the receiver is small. High-speed optical receiver is sensitive area is generally not large, and is small and sensitive areas of the receiver is relatively low cost, so it is very important. Its disadvantage is that when scanning beam scanning system located in the edge of each component to produce vignetting phenomenon Apart from structural measures to minimize vignetting, we must also abandon characteristic bad scan angle.
The whole point of the scan reader is also commonly used in optical AGC system, so that the light intensity of the received signal does not vary with the distance bar code symbol is changed . This can reduce the signal dynamic range, it is beneficial to subsequent processing.
Hand gun scanning reader with a scanning speed is slower, lower frequency signal characteristics . The low frequency response of the receiver, such as silicon photovoltaic cell having a large sensitive area, and this system is also easy to achieve high low SNR . Therefore, in addition to the receiving program can be used outside of the back can also take other programs . For example, using a semiconductor laser easily modulated, the outgoing laser beam is modulated to a higher frequency . Then, again when the signal processing technique using synchronous receiver amplifier Remove barcode signal. As long as the modulation frequency is much larger than the bar code signal frequency, it brings the bar width error will be negligible . Synchronous receiver technology with high noise rejection capability, and therefore do not necessarily go back to the receiver using the structure . This will give the arrangement of the optical receiving system brings considerable flexibility . With this flexibility will enable readers some aspects of performance can be improved. For example, the return to the receiving program, the moving element is also part of the receiving system, which requires a certain pore size sufficient to ensure that the received signal light . However, if the moving element is only emitted from the light beam scans the role can be made small . Obviously small moving elements both for the selected power components or increased life expectancy and reliability are extremely beneficial.
Photoelectric conversion, signal amplification and shaping
The received optical signal to an electrical signal by the photoelectric converting . The whole point of the barcode reader scans the signal frequency of a few MHz to tens of MHz. Requires such a high frequency signal having a high frequency response of the photoelectric conversion ability avalanche photodiode (APO) or PIN photodiode. The whole point of the scan readers are generally long continuous use, for the safety of users, requiring less energy emitted laser source . Therefore, the energy of the last received very weak . In order to obtain a higher signal to noise ratio ( which determined by the bit error rate ), low noise, are usually discrete components to the low-noise pre-amplifier circuit to amplify the signal.
From the above mentioned case, we can see the high signal frequencies brings great technical difficulties and cost increase. Reading capability for a certain angle scanning reader full, its data rate R is proportional to n / (H × Cosα-W × sinα). Where, n is the number of scan direction, H, W respectively, for the bar code symbol height, width, α relative to the scanning patterns of bar code symbols in the most unfavorable values of the scan angle when reading, for each scanning line uniformly distributed α = π / 2n, if n = 2, α is 45 ° From this formula we can estimate the UPC code, if the left portion and the right half of the scan and splicing program, n is 3, the lowest data rate, for completely through before reading the program code, n is 5, the minimum data rate . Scanning system is required in the design of this into account .
Further, low-speed scanning module may be combined into an array to achieve the full performance of the angle speed scanning bar codes . Obviously, this solution should be applied over the pipeline occasions .
Company Contact:

Contact Name: Chloe
Company Name: Shenzhen Longview Technology Co., Ltd.
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Tel: 86-755-83233013-814
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Street Address: Tongjian Buildings
2, Shennan Road, Futian District,
Shenzhen, Guangdong, China
Shenzhen, Guangdong
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https://www.aliexpress.com/store/907376
Member name: chloezeng
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China
Member Since: 24 October 2013
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47 chloezeng Import Export Business Leads
Business focus: Barcode Scanner, Barcode Scanner Module, Barcode Printer, Ribbon, Data Collector, Pos System, Cable, Label Sticker
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