Working Principle and Composition of Safety Light Curtain?

Figure 1: Safety light curtains.
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1. Overview

Safety light curtain is generally used in high-risk mechanical equipment such as punch press, stamping and non-standard machinery to protect workers from personal injury.

1. Working Principle

The infrared light is sent out by the sender and received by the receiver to form a protective light curtain. If an object passes through the light curtain, it will block the corresponding infrared light. And the photoelectric sensor will detect it, convert the optical signal into electrical signal and transmit it to PLC or alarm circuit, so as to stop the equipment or send out safety alarm and ensure the safe production of the equipment and the personal safety of operators.

Figure 2: An object passes through the light curtain.

2. Composition

Sender: it is composed of several light-emitting devices and it emits infrared light.

Receiver: it is composed of several light receiving devices, which receive infrared light and correspond with the light-emitting devices of the light-emitting device one by one to form a protective light curtain. They generate light transmission signal and shading signals and transmit the signals to the controller through the signal cable to control the external equipment.

Signal cable: It is used to transmit the signal between the light sender and light receiver.

Figure 3: Sender, receiver and controller.

3. Features

The installation method of light curtain is flexible and simple. The light curtain also has waterproof function and dustproof function, photoelectric cycle self inspection, line synchronization technology, strong anti-interference ability, SMD patches, short response time and high reliability.

Safety light curtains protect people from harm. When the machine is running it greatly facilitate the loading and unloading of materials, and it simplifies the adjustment and maintenance of the machine.

4. Notes

The density of the light determines how large the body part can be detected through the light curtain. According to the data of ergonomics, the finger diameter of adults are longer than 14mm, the thickness of the palm are longer than 30mm, and the diameter of the wrist are longer than 40mm. For example, if the optical axis spacing of the light curtain is 40mm, the optical axis diameter is 20mm, and its resolution is 40 + 20 = 60mm. Then the fingers, palm, wrist and arm may pass through the light curtain without being found. Therefore, if you want to obtain higher security, you need to use a light curtain with higher resolution.

Figure 4: How large the body part can be detected through the light curtain.

When using safety light curtain, there are certain requirements for installation. It is not allowed for personnel to bypass the light curtain and enter the dangerous area. It is also not allowed to have a surface reflecting light near the safety light curtain, so that the receiver will receive the reflected light and cannot output the safety switch signal.

In addition, there are certain requirements for the use environment of grating and light curtain. If there is too much dust in the environment, it will affect the emission of light affecting the use of grating and light curtain.

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