Hurry up and call the Education Bureau Admissions Office in the city where you are taking the exam. When the province encounters such a test paper, it will call the city Admissions Office and ask the Admissions Office to find out your test papers and check them one by one. . Exam papers are not sent to the province. The staff of the Admissions and Examination Office clearly told me that it would not affect the scores, but it only caused more trouble for the staff.
1. Introduction
Barcode is a graphic identification that expresses a set of information by arranging multiple black bars and blanks of different widths according to certain coding rules. symbol. A common barcode is a parallel line pattern composed of black bars (referred to as bars) and white bars (referred to as spaces) with very different reflectivities.
Bar codes can indicate the country of production, manufacturer, product name, production date, book classification number, starting and ending location of the mail, category, date and many other information. Therefore, they are widely used in commodity circulation, library management, and postal management. , banking systems and many other fields have been widely used.
The barcode automatic identification system consists of a barcode label, a barcode generation device, a barcode reader and a computer.
Bar code technology (BCT) is an automatic identification technology produced and developed in the application practice of computers. It is designed to realize automatic scanning of information. It is an effective means to collect data quickly, accurately and reliably. The application of barcode 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, spaces and corresponding characters, used to represent certain information. The core content of barcode technology is to realize automatic recognition of machines by using photoelectric scanning equipment to read these barcode symbols, and to quickly and accurately enter data into computers for data processing, thereby achieving the purpose of automatic management.
The research objects of barcode technology mainly include five parts: standard symbol technology, automatic identification technology, coding rules, printing technology and application system design.
2. Recognition Principle
The barcode symbol is an information symbol composed of "bars" and "spaces" with different reflectivities according to certain encoding rules.
Since the "bars" and "spaces" in the barcode symbols have different reflectivities for light, the barcode scanner receives reflected light signals of different strengths and correspondingly generates electrical pulses with different potentials. . The width of the "bar" and "space" in the barcode symbol determines the length of the electrical pulse signal with different potentials.
The optical signal received by the scanner needs to be photoelectrically converted into an electrical signal and amplified by an amplification circuit. Due to the certain size of the scanning light spot, the edge ambiguity during barcode printing and some other reasons, the barcode electrical signal amplified by the circuit is a smooth fluctuating signal, which is called an "analog electrical signal".
"Analog electrical signals" need to be shaped into ordinary "digital signals". According to the encoding rules corresponding to the code system, the decoder can read and translate the "digital signal" into digital and character information.
The barcode scanner uses photoelectric elements to convert the detected optical signal into an electrical signal, and then converts the electrical signal into a digital signal through an analog-to-digital converter and transmits it to the computer for processing.
For one-dimensional barcode scanners, such as laser type and image type scanners, the scanner reads the barcode information by emitting a beam to the label from a certain angle and receiving the light reflected back. Therefore , when reading barcode information, the light must be at an oblique angle with the barcode, so that the entire light beam will produce diffuse reflection, which can convert the analog waveform into a digital waveform.
If the light shines perpendicularly to the barcode, it will cause a part of the analog waveform to be too high to be converted into a digital waveform normally, making it impossible to read the information.
For two-dimensional barcode scanners, such as photo-type scanners, the scanner uses omnidirectional and photo-taking methods for reading. Therefore, when reading, the light is required to be perpendicular to the barcode, and the positioning cross and positioning frame are in line with the required positioning. Scan the barcode to match.
Barcode scanners generally consist of a light source, optical lens, scanning module, analog-to-digital conversion circuit, and plastic or metal casing. Each barcode scanner has certain requirements for the ambient light source. If the ambient light source exceeds the maximum error tolerance requirement, the barcode scanner will not be able to read normally.
When barcodes are printed on metal, silver-plated surfaces, 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 the barcode scanner, it will affect the reading accuracy of the scanner. Stability, therefore, requires covering or applying black paint to the metal surface.