Принцип работы магнитных пряжек для супермаркетов

In today’s large supermarkets, more and more goods, such as socks, clothes, hats, slippers, etc., are locked with magnetic buckles. When the customer checks out at the checkout counter, the cashier will open it with the help of a strong magnetic unlocking device, and then the customer can take the product out of the supermarket. If customers secretly take out products with magnetic buckles from the supermarket, the alarm will automatically sound when passing by the cash register. But without the use of external force for violent demolition, no matter how much force you use, it is difficult to open it smoothly in a short period of time. Therefore, the magnetic buckle, also known as the EAS hard tag, has a shape as shown in Figure 1. So, what is its structure and working principle?

Figure.1 Anti theft buckle

1. Internal structure of EAS hard tag

The materials used to make EAS hard tags mainly include organic synthetic materials and metal materials. As shown in Figure 2, the EAS hard tag is composed of three parts: a steel needle, a plastic shell, and a lock cylinder, while the lock cylinder is a simple combination device composed of three steel balls, a steel ring, and a spring.

2. Working principle of EAS hard tag

The implementation of the EAS hard tag function is indispensable to metal and iron. The components of the EAS hard tag, such as steel balls, steel rings, and steel needles, are all made of metal materials and are made of iron alloys with ferromagnetism. This is a property that other metals do not have.
Lock principle: As shown in Figure 3, there are three small grooves on the rod of the steel needle, which are like the barb of a fish hook. When the steel needle is inserted from the bottom of the EAS hard tag, the three small steel balls in the lock cylinder will slide smoothly to the groove position on the steel needle and tightly buckle in the gap between the steel needle and the lock cylinder shell; In addition, the steel rings above the steel balls are firmly clamped in the grooves under the pressure of the top spring. Therefore, it is difficult to pull the steel needle out of the bottom again with ordinary brute force.
Unlocking principle: When a strong magnetic force is applied to the top of the EAS hard tag (as is the practice at the supermarket checkout counter), the steel ring and small steel ball are attracted by the strong magnetic force and compress the spring to move up, so that the steel needle can be easily removed from the bottom of the EAS hard tag. When the supermarket EAS hard tag is opened, it mainly relies on magnetic steel with a capacity of 8000GS or above to suck the three small steel balls containing the steel needles inside the lock cylinder away from the steel needles, so that the steel needles can be smoothly pulled out of the EAS hard tag. Magnetic steel with a magnetic capacity of 8000GS or above is a commonly used strong magnetic unlocking device for cashiers.
So, why does the alarm automatically sound when the EAS hard tag passes through the cash register in a locked state? This is the result of the combination of the supermarket EAS hard tag and the anti-theft antenna system at the supermarket exit.

Alarm principle: There is also a magnetic coil and a chip inside the steel ring. When you are holding the product without checking out at the checkout counter (the EAS hard tag is not removed), when this EAS hard tag passes through the exit anti-theft door, the anti-theft door will automatically beep and alarm when it senses magnetism.

Figure.2 Latch Status

Figure.3 Unlock Principle