What is a vending machine?
A vending machine is a machine that can automatically pay according to the input coins. Vending machines are commonly used equipment in commercial automation. They are not restricted by time or location, can save manpower and facilitate transactions. It is a brand new form of commercial retail, also known as a 24-hour micro supermarket. It can be divided into three types: beverage vending machines, food vending machines, and comprehensive vending machines. There are currently two types of vending machines that can recognize coins and banknotes.
As fake renminbi continue to be exposed, we can’t help but ask, how can vending machines be identified? How does it identify banknotes?
1. Fluorescence detection
The working principle of fluorescence detection is to detect the paper of RMB. RMB is made of special paper (containing more than 85% of high-quality cotton). Counterfeit banknotes are usually made of ordinary paper that has been bleached. The bleached paper will appear under the irradiation of ultraviolet light (blue light with a wavelength of 365 nm). Fluorescence reaction (diffracts blue light with a wavelength of 420 - 460 nm under the excitation of ultraviolet rays), while RMB has no fluorescence reaction. Therefore, the authenticity of the banknotes can be determined by using an ultraviolet light source to illuminate the banknotes and simultaneously using a silicon photocell to detect the fluorescence response of the banknotes. In order to eliminate the interference of ambient light on counterfeit identification, a set of color filters whose transmission wavelength is consistent with the fluorescence reaction wavelength of the fake RMB must be installed on the surface of the silicon photovoltaic cell. In fluorescence detection, two issues need to be paid attention to:
1. Detect space occlusion. External light entering the detection space will cause false alarms;?
2. Dust protection of UV light sources and photocells. There is a large amount of dust during the banknote counting process. The adhesion of this dust to the surface of the light source will weaken the detection signal and cause false alarms. For the fifth edition of RMB, fluorescent characters can be detected at the same time (printed with colorless fluorescent ink and detected with another silicon photocell, the transmission wavelength of the color filter is consistent with the fluorescence reaction wavelength of genuine banknotes) to improve the identification effect.
2. Magnetic detection
The working principle of magnetic detection is to use certain parts of large-denomination real banknotes (20 yuan, 50 yuan, 100 yuan) to be printed with magnetic ink. A set of magnetic heads detects the magnetism of the banknotes, and the magnetism is analyzed through a circuit to identify the authenticity of the banknotes. In magnetic detection, it is required that the magnetic head and the banknote have good friction. If the magnetic head is too high, the impact signal will be large, resulting in false alarms; if the magnetic head is too low, the signal will be weak, resulting in false alarms. Detection needs can be met by controlling the height of the magnetic head (guaranteed by processing and assembly) and installing a banknote pressing rubber wheel above the magnetic head.
3. Infrared penetration detection
The working principle of infrared penetration is that the RMB paper is relatively strong and dense, and the thickness of the ink printed with gravure printing technology is higher, so It has strong ability to absorb infrared signals to identify the authenticity of banknotes. There are certain differences between the paper characteristics of RMB and that of counterfeit RMB. When infrared signals are used to detect penetrating banknotes, their absorption capabilities of infrared signals will be different. Using this principle, counterfeiting can be achieved. It should be noted that the color and thickness of the ink will also cause differences in infrared penetration capabilities. Therefore, mathematical operations and comparative analysis must be performed on the signals of infrared penetration detection.
4. Laser detection
Using an infrared laser of a certain wavelength to illuminate the fluorescent characters on the fifth edition of the RMB will cause the fluorescent characters to produce a laser of a certain wavelength. Through the detection of this laser Can identify the authenticity of banknotes. Because it is difficult to imitate, it is very accurate for identifying fakes.
5. Anti-sandwich detection
The so-called anti-sandwich detection is to pick out banknotes of different denominations from a stack of banknotes.
Banknotes of fundamentally different denominations have different characteristics, such as paper quality, magnetism, format size, etc., which can be used for anti-sandwich detection. The current counting machine only detects the paper and magnetic width of banknotes. Therefore, for banknotes with the same or similar paper, magnetic and width, such as the fourth edition of 1 yuan and 2 yuan, 5 yuan and 10 yuan, the fifth edition of 10 yuan. It is difficult to distinguish between 1 yuan and 20 yuan. If a set of infrared tubes are added to detect the length of the banknote at the same time, this problem can be effectively solved.
Related reading: The principle of coin recognition by vending machines
There are many types of metal coin recognizers, but the coin storage and refund mechanisms are basically divided into two categories: one is a flat coin storage , the solenoid valve returns the coins; the other type is the cylindrical coin storage, and the stepper motor returns the coins. When the coins are put in and the electrical signal is recognized, the counterfeit coins and foreign matter are discharged, and the genuine coins are distributed by several groups of electromagnetic fields according to their face value. The valves are allocated to different coin storage chambers for backup. After receiving the electrical signal for coin return and change, the coins in the lower part of the coin storage chamber are pushed out according to the electrical signal program through the coin return solenoid valve or the coin return motor pull rod, completing the operation of the vending machine. Return coin change function.
Identification principle
Main identification indicators: diameter, material, thickness.
The material is measured electromagnetically, using air-core coils or magnetic core coils. The number of coil groups is only one group, and the common number is six groups. Under working conditions, the coil and its peripheral circuits will oscillate at a special frequency (the frequency will be different if there are multiple coils). When a coin passes perpendicularly or parallel to the plane of the coil (different products have different methods), oscillation will occur. Frequency changes. The amplitude and direction (increase, decrease) of frequency changes caused by different materials are also different. After recording the changing characteristics of a certain coin, it becomes the basis for identifying the coin in use.
There is nothing specifically measured for thickness. In fact, this indicator is measured together with the material. Because even coins of the same material have different thicknesses, the resulting frequency changes will be quite different.
Diameter - The old-fashioned identification device uses a photoelectric tube array to identify the diameter. If the arrangement and combination are appropriate, the identification accuracy is not low (can answer 0.5mm). The newer ones all use eccentric or special-shaped coils for measurement. The basis is that the coin with a small diameter has less overlap with the coil, which also brings about differences in frequency changes.
Common anti-counterfeiting principles
Mainly rely on the frequency change characteristics mentioned above. For acceptable genuine coins, the changes are limited to a certain range, while fake RMB often falls within a certain range. If there is any discrepancy between the indicators and the real ones, they will be identified and kicked out.
The coin entrance should have a detection element (usually a photoelectric tube). After detecting the entry of a coin, the coil behind it will oscillate and start recording the frequency value, and at the same time calculate the change.
Under normal circumstances, a coin is stuffed into the entrance, and then rolled in along the structurally designed groove. It will have a certain speed. The time for passing through the aforementioned coil is very limited (within 500ms), and the speed Relatively even. So, as a metric, a coin that is put in slowly will not be accepted.
Relevant information and pictures are all from the Internet: search through Baidu
Relevant reference sources are as follows:
Zhihu.com:
/ question/21145447/answer/17337386
CSDN (see attachment)
/download/adusemail/2235594