Call the education bureau of the city where you took the exam. When the province encounters such a test paper, it will call the admissions office and ask the admissions office to find out your test papers and check them one by one. The examination papers will not be sent to the province. The staff of the recruitment office told me clearly that it would not affect the performance, but it would cause trouble to the staff.

I. Introduction

Bar code is a graphic identifier that arranges a number of black bars and blanks with different widths according to certain coding rules to represent a group of information. Common bar codes are parallel lines composed of black bars (referred to as bars) and white bars (referred to as spaces) with great differences in reflectivity.

Barcode can indicate the country of production, manufacturer, commodity name, production date, book classification number, starting and ending place, category and mailing date, and so on, so it has been widely used in many fields such as commodity circulation, book management, postal management, banking system and so on.

Automatic bar code identification system consists of bar code label, bar code generating equipment, bar code reader and computer.

Bar code technology (BCT) is an automatic identification technology which is produced and developed in the practice of computer application. It aims to realize automatic scanning of information and is an effective means to collect data quickly, accurately and reliably. The application of bar code technology solves the bottleneck problem of data entry and data collection, and provides favorable technical support for logistics management.

Bar code is a symbol composed of a set of regular bars and corresponding characters, which is used to represent some information. The core content of bar code technology is to read these bar code symbols through photoelectric scanning equipment, realize automatic identification of machines, and quickly and accurately input data into computers for data processing, thus achieving the purpose of automatic management.

The research object of barcode technology mainly includes five parts: standard symbol technology, automatic identification technology, coding rules, printing technology and application system design.

Second, the principle of recognition

Bar code symbol is an information symbol composed of "bars" and "spaces" with different reflectivity according to certain coding rules.

Because the "bar" and "space" in the bar code symbol have different reflectivity to light, the bar code scanner receives reflected light signals with different intensities and generates electric pulses with different potentials accordingly. The width of "bar" and "empty" in bar code symbols determines the length of electric pulse signals with different potentials.

The optical signal received by the scanner needs to be photoelectrically converted into an electrical signal and amplified by an amplifier circuit. Because the scanning spot has a certain size, the edge in bar code printing is blurred and other reasons, the bar code electrical signal amplified by the circuit is a smooth fluctuation signal, which is called "analog electrical signal".

"Analog electrical signals" need to be shaped into ordinary "digital signals". According to the coding rules corresponding to the coding system, the decoder can read the "digital signal" as digital and character information.

Bar code scanner converts the detected optical signal into electrical signal by photoelectric element, and then converts the electrical signal into digital signal by analog-to-digital converter, and transmits it to computer for processing.

For one-dimensional barcode scanners, such as laser scanners and image scanners, scanners read barcode information by emitting light beams to labels from a certain angle and receiving light reflected from the labels. Therefore, when reading bar code information, the beam should be at an oblique angle with the bar code, so that the whole beam will diffuse and the analog waveform can be converted into digital waveform.

If the light is perpendicular to the bar code, some analog waveforms will be too high to be converted into digital waveforms normally, so that information cannot be read.

For a two-dimensional barcode scanner, such as a photographic scanner, the scanner reads in an omni-directional and photographic manner. Therefore, when reading, the light is required to be perpendicular to the bar code, and the positioning cross and positioning frame are consistent with the scanned bar code.

Bar code scanner is generally composed of light source, optical lens, scanning module, analog-to-digital conversion circuit, plastic or metal shell, etc. Every barcode scanner has certain requirements for ambient light sources. If the ambient light source exceeds the maximum fault tolerance requirement, the barcode scanner will not be able to read normally.

When the bar code is printed on the surface of metal, silver-plated layer, etc. , the light beam will be reflected by the high brightness surface. If the light reflected by the metal enters the light receiving element of barcode scanner, it will affect the reading stability of the scanner. Therefore, it is necessary to cover or coat the metal surface with black paint.