Credit: Mühlbauer
Beside cashless payments, coins are still a part of modern life. Approximately one thousand billion coins are circulating worldwide; among them 33 billion euro (as of the end of November 2023). Minting, circulating and recirculating of coins remains a great responsibility for mints and central banks. Depending on the quality of the coin, the lifespan of hard cash can be 10 years or more.
In recent years, banks have begun to refine the process of coin recirculation. Raw materials and energy consumption for coin production are expensive, so the goal should be to bring every coin still fit for circulation back into our wallets and reduce the amount of coins destroyed as scrap.
Another aspect is counterfeit coins. The number of fake coins is still rising. The €2 coin is a favourite target for forgers, with a total share of more than 90% among counterfeit euro coins. It is important to prevent such counterfeits from being recirculated to bring down the amount of fake coins used for payment transactions.
Without doubt, high volume automated inspection is the key. For coin fitness checks, machines based on camera technology as used by mints for the quality check of freshly minted coins seem to be the indicated method.
However, used coins are so much more demanding. Different designs of the same denomination are challenging. The range of expectable quality variations is huge; and for every denomination, one big decision has to be made: what is still acceptable and what is scrap? This will always remain the responsibility of the bank. Knowing this helps to realise that the inspection of used coins cannot be a one-way street. It is a close cooperation between the provider of the inspection machine and the bank. Even artificial intelligence needs input before it can work.
The basis of a successful coin fitness check is an efficient inspection technology working at high throughput rates – for example Mühlbauer’s COIN INSPECT, which checks the coins on two parallel tracks at high speed.
When trying to understand how such a camera-based inspection works, it is useful to be aware that you cannot compare a camera image one-to-one to what you see with the human eye. Furthermore, it is impossible to change the viewing angle of a coin lying flat on a conveyer, as you would do when you hold a coin in your hand and turn and flip it to see all the details under different angles of incident light.
This is the reason why inspection machines such as COIN INSPECT work with different inspection units, using different illuminations like coaxial, dome, and ring light to obtain different images of the same coin.
Each image is important since it will highlight different characteristics of the coin to provide the best impression of its condition. In one image, discolouration caused by corrosion, peeling, and dirt are visible; in another image, you will see mechanical damages like cracks, bending, and rim defects, and still another image gives the clearest impression of the wear of the coin. This enables the detection of a great variety of possible defects.
Another factor is determining coin dimensions such as thickness, diameter, and even the height of the coin profile.
One method is 3D measurement using a camera, which scans a laser line to generate a height profile. This seems to be an obvious approach but, without going too much into technical details, it raises several problems: the precision drops with rising speed and consequently, the expected performance cannot be effectively achieved in a high throughput inline process. Coin surfaces are highly reflective. The 3D image becomes noisy and can include a variety of misinformation. Minor vibrations of the conveyor belt, not visible but still effective, cause varying measurement values. Consequently, no absolute figures are available.
Due to these factors, the COIN INSPECT inspection machine relies on 2D optical inspection of the minting profile and uses backlight with a mirror array to measure the diameter and the thickness of the coin silhouette.
For inspecting used coins, it is important to run as many unacceptable quality coins as possible through the machine. The software uses this information to learn the desired quality and build a basic set of inspection parameters.
These values are not etched in stone. Authorised persons can modify them any time, even software engineers based hundreds of kilometres away, if required. Inspection of used coins is like life in general. You learn every day; and if quality standards change, you can adapt your inspection parameters at anytime.
A special aspect of used coin inspection is the detection of counterfeit coins. Basically, there are two groups of characteristics that can distinguish a genuine coin from a fake coin: general parameters, which indicate a high probability that the coin is not genuine; and individual special features known from experience, which mark a fake coin.
The first and often used method is measuring the electromagnetic signature (EMS) of the coin by an EMS sensor. This has been common practice for many years. They can be found in slot machines as well as in high technology inspection solutions. The measurement result allows conclusions on the material of the coin to be made, and unmasks a high percentage of fake coins since forgers often use cheaper materials to make counterfeiting profitable.
So why is there still such a high amount of fake coins in circulation? The answer is easy: forgers are smart and they improve their methods constantly. To stop them we need high volume inspection solutions, which use more than one technology to check the coin. Machines like the COIN INSPECT combine optical inspection methods with EMS measurement to uncover counterfeits. The great advantage is the opportunity to combine a variety of inspection parameters for a detailed analysis within a split second. This not only increases the detection rate, it also improves reliability.
Coins show different signs of wear, damage and corrosion after several years of circulation. These variations influence the optical appearance and may also alter the EMS signature. Consequently, differentiating a fake coin from a worn but still recyclable coin can be a delicate task. Every piece of information gained by the inspection system is valuable; all data is correlated before a quality decision is reached.
The inspection software has to handle a huge amount of data within a very short processing time, eg. data from eight vision units and one EMS sensor for obverse and reverse inspection of around 1,500 used coins per minute. Despite artificial intelligence and years of experience incorporated in machines like the COIN INSPECT, such a demanding task can never be a simple plug-and-play solution. The exchange of information remains inevitable and technology is not the only factor that counts. The cooperation between trustworthy reliable parties is essential.
Certainly, an inspection machine for used coins should not be seen in isolation. It is just a part of a complex process of supply, unpacking, pre-sorting, inspection, counting, weighing, and packing.
Banks want to establish complete cash centres to automate and optimise their processes of receiving, checking and recirculating used coins. Consequently, it is important that such a machine provides all the necessary mechanical, electrical, and software interfaces to perfectly interact with up and downstream equipment.
More than that, potential partners like Giesecke+Devrient Currency Technology, to cooperate with and rely on when being part of such large-scale projects, is a real advantage. By engaging experts from all industrial fields involved, banks can optimise their processes for a sustainable and cost-efficient cash handling.
