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Importance of Safety Light Curtain

August 08, 2018

When you buy a hot drink, there is often “careful hot” mark on the paper cup. When you enter the fast food restaurant, there is often warning sign stating “The floor is wet and slide carefully”. Safety warning signs can be seen everywhere in our lives, making our lives both colorful and secure.

However, sometimes there are only warning signs that are not enough. For presses of several hundred tons or even thousands of tons, a warning sign alone is not enough. When there are any small mistakes by the operator, it may cause serious injury or even life-threatening. In order to ensure the safety of machine operators such as presses and palletizers, we often need to install safety protection devices for the machine tools.

There are a variety of safety protection devices, the simplest of which is fence protection, but it has great limitations and makes operation extremely inconvenient. The two-hand control system can effectively protect the operator after it is correctly installed. It is economical and practical, and can be used in machine tools that cannot be immediately shut down. The limitation is that it can only provide protection for the operator himself, and it needs to install supplementary protection to ensure other The safety of the personnel; but its efficiency is low, because when the whole machine tool appears the dangerous state, the operator cannot leave the button with both hands; The utility palm type button, the labor intensity is high, is not suitable for many times repeated operation. At present, the use of electronic protection devices such as safety light curtains, laser scanning devices, safety mats, and radio frequency detection devices for area protection can effectively protect the personal safety of operators and others around them. Among them, the Safety Light Curtain has significant advantages, such as area protection, and at the same time protecting multiple operators, is easy to use, allows the operator to move freely, does not need adjustment, can directly observe and enter the work area, has high reliability, and is very useful in machine tools. widely.

Safety light curtains are essentially different from ordinary photoelectric switches. In general, ordinary photoelectric switches are prohibited from being used for personal safety protection because they can cause serious injury when the photoelectric switch fails. The same is the principle of photoelectric conversion. Why does the safety light curtain have a difference of two levels and four levels, then how do they divide it?

Different machine tools and danger levels require different degrees of protection. The European standard EN954-1 classifies the relevant safety control systems (safety light curtains) as follows:

Level 1: Using more safe components and principles, the control reliability is improved, but it is still possible to lose the safety function (more applications in home appliances, such as door switches of microwave ovens).

Level 2: Perform periodic safety function tests on the basis of level 1 and detect loss of safety function (single circuit).

Level 3: On the basis of Level 1, ensuring that the failure of a single component does not result in the loss of safety functions, but the failure of multiple components will result in the loss of safety functions (multi-loop/some failure detection)

Level 4: On the basis of Level 1, the failure of a single component does not result in the loss of the safety function and the safety system detects a failure at or before the next operation. Accumulation of failure does not result in the loss of the safety system (multi-loop/full failure detection).

For example, if a machine tool is in a dangerous state, the severity of the injury is S2, that is serious; the frequency of the dangerous state is F2, that is, it often occurs; if the possibility of danger avoidance is P2, it cannot be avoided, according to European standards. According to EN954's risk assessment form, we must install a 4-stage safety light curtain to achieve effective protection for machine tools and operators. So far, level 4 is the highest level of protection.

Similarly, the U.S. Office of Occupational Safety and Health also defined the control reliability of related safety products as follows: The control system should be designed such that the failure of the system should not prevent the normal shutdown of the machine tool. Multi-loop design is required to ensure that when any single failure occurs, the redundant loop can generate a shutdown action when needed.

The only difference between the European standard 4-level classification and U.S. control reliability concept is: the control reliability specification, single failure should be detected when the security system carries out the next command, and the four-level classification requirement, single failure should be performed in the security system. Command was detected before. In general, the four-level classification and control reliability are the requirements of relevant safety standards or institutions for related safety products to ensure the safety of machine tools and operators, ensure that the machine tool is reliable and efficient, and ensure that maintenance is simpler and more economical.

The safety light curtain also requires other auxiliary functions, such as blind spot function, upstroke protection function, and fault diagnosis display. The blind spot function is that within the effective protection area of the light curtain, a specific light beam can be ignored. Even if the light beam is blocked, the safety light curtain does not send a stop signal. The blind area function can be divided into drift blind area, positioning blind area, and fixed number blind area. The drift blind area can shield any set number of beams in the protection area, the positioning blind area can only block the specific position and the number of beams, and the fixed number of blind areas can only block a certain number of beams. The blind spot function makes the safety light curtain more flexible. The up-travel non-protection function makes the work efficiency of the machine tool higher on the basis of ensuring the safety of the machine tool. The fault diagnosis display can ensure the maintenance and use of the safety light curtain more easily.

At the same time, there are many precautions when using a safety light curtain. The safety distance is one of the important indicators for ensuring the reliable operation of the safety light curtain. The safety distance is the distance from the machine tool safety point to the safety light curtain, and it is also affected by the response time of the safety light curtain and the machine down time. In the process of using the safety light curtain, it is necessary to follow the correct use of the instruction manual, properly install auxiliary protective devices, and perform regular function tests of the safety light curtain.

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