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Products What is a Light Curtain? Types Resolution Safety Light Grids Operation Broken Beams Special Functions

Kategori 4 emniyet ışık bariyerleri çalışma noktalarına erişimi, bölgeleri ve çevreyi koruyarak personelin yaralanmasını ve makinaların zarar görmesini önler. Kategori 2 emniyet ışık bariyerleri ise düşük riskli uygulamaları için uygun maliyetli bir emniyet çözümü sunar.

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Ağır Ortam Şartlarına Dayanıklı Kategori 4

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Type 2

Cost-effective safety light curtain for lower risk applications.

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What Is a Light Curtain and What Does It Do?

A light curtain, or safety light curtain, is a presence-sensing device that protects operators from hazardous equipment. At the most basic level, it is an invisible barrier made of multiple infrared beams sent from one device, an emitter, to a second device, a receiver. If these infrared beams are broken by a person or object, the machine stops. But there’s a lot more to protecting operators than just breaking a beam of invisible light.

Light curtains typically have two main machine guarding duties: access guarding or perimeter guarding. When a light curtain is used for access guarding, it protects specific access points to a hazardous area. This area can be large or small, depending both on the area that needs to be safeguarded as well as what may trigger the light curtain. When used for perimeter guarding, larger light curtains are set around a machine or other piece of equipment and prevent access to the surrounding area. This takes up more floor space, but allows greater flexibility in approaching equipment.

Applications in which light curtains may be a preferred protection method include:

Guarding against moving parts on machines
Avoiding pinching or crushing hazards
Controlling personnel access to restricted areas
Managing items on packaging and sorting lines
Preventing machine startup during maintenance

Because light curtains offer non-contact machine guarding, they typically last much longer than mechanical devices like door switches, which can wear over time due to repeated locking and unlocking. Also, less floor space is needed because there’s no physical door needing room to swing open.

Different Types of Light Curtains for Different Machine Guarding Needs

The two most common types of light curtains are Type 2 and Type 4, each of which satisfies different levels of safety requirements. Type 4 safety light curtains are used when there’s greater risk of injury, whereas Type 2 light curtains are designed for lower-risk applications. Think of it like this: Type 2 light curtains protect personnel from light wounds and injuries that may need treatment with a first-aid kit, while Type 4 light curtains guard against severe injuries that would necessitate a trip to the hospital. Type 2 curtains typically offer hand and body protection and are less expensive than Type 4 curtains, which will stop equipment when something as small as a finger passes through two or more beams.

Opposed-mode sensing offers the highest level of excess gain (sensing energy)
Long sensing range
Most robust for harsh environments
Precise position sensing
Small-part detection using lens apertures
Impervious to surface reflectivity (the color or finish of the object)

Why Is Resolution So Important?

When discussing different levels of protection, such as hand or finger, what we are really talking about is the smallest size of object a light curtain can detect any place in the sensing field. This is called the resolution, which is measured from the outside of one beam to the far side of an adjacent beam. Any object larger than the resolution will not be able to pass through the light curtain without breaking the beams and causing a fault.

Safety light curtains are available in many different resolutions. Smaller resolutions (14 millimeters to 40 millimeters) are used for machine guarding, in which light curtains protect a specific access point to the machine. Larger resolutions (50 millimeters and greater) are used for perimeter guarding, which use less floorspace than physical guards, such as fences, to protect the area around equipment. Common resolutions include:

14 millimeters: finger detection
23 to 30 millimeters: hand detection
35 to 40 millimeters: arm detection
50 millimeters and greater: legs, bodies, and other large objects

Guarding Larger Areas with Safety Light Grids

Similar to light curtains are safety light grids. They also use both an emitter and a receiver, but these have low resolutions, often using only two, three, or four beams with 300 millimeters to 500 millimeters between them. They are designed for body protection in long-range perimeter guarding applications, and are not a substitute for higher-resolution safety light curtains closer to machinery. Whereas safety light curtains are designed to guard shorter ranges up to 20 meters, safety light grids can monitor across much longer ranges, with some models covering distances up to 60 meters.

How Light Curtains Operate

No matter which type of safety light curtain you are using, they all essentially function the same. Each curtain requires two devices: an emitter and a receiver. Both devices must be paired with each other so they can communicate. They must also be aligned with each other in order to function (this can be aided using alignment indicators, such as those on Banner’s S4B Series of heavy-duty safety light curtains). The emitter sends an array of infrared light beams to the receiver, which is tuned to recognize only these specific light beams. This minimizes the effects of ambient light.

What Happens after Light Curtain Beams Are Broken

Once the light curtain has been tripped, the safety interlock needs to be reset so the equipment can begin operating again. This may be manual or automatic, depending on the application, the light curtain capabilities, and the design of the machine guarding system being used.

In an automatic reset, the light curtain determines that the beams are no longer blocked, then turns its two output signal switching device (OSSD) outputs ON. This is an efficient way of restarting equipment, though it should only be used when a person cannot be inside the guarded area, such as finger or hand guarding access points to small machines. For situations in which a person could potentially be inside the protected area when a hazard is restarted, a manual reset is typically used. This requires an operator to press a button located outside the protected area, keeping the operator out of harm’s way as the equipment is powered back up. When pressed, the button sends a signal to the relay or controller, which tells the light curtains to turn the OSSD outputs ON and again let power flow to the machine but does not start the hazardous motion. The normal machine start process is required to restart the hazardous motion after the safety circuit is turned back on.

Special Light Curtain Functions

Sometimes light curtains need to allow objects to pass through without shutting off equipment and interrupting workflow, such as preventing operator access to a conveyor while still allowing pallets through, or maintaining operation when a fixed object would otherwise trip the system and halt production. These optional functions are referred to as muting and blanking. Other applications may also benefit from cascading, connecting light curtains in a chain.

Light Curtain Muting

Muting lets a safety system temporarily ignore the breaking of a light curtain when objects or materials need to pass through a protected area without halting the production process. This is often used to allow objects through a light curtain, such as goods on a conveyor moving from one area to another.

To accomplish this, a pair of muting sensors are mounted so they detect objects as they come to the light curtain. If the sensors detect an object, the light curtain is momentarily disabled as the object passes through. After the object has passed through the light curtain, sensors detect the object again and re-enable the curtain. However, a person reaching through the light curtain will trigger the machine to stop.

Light Curtain Blanking

Similar to muting, blanking also lets certain objects pass the light curtain. In this case, blanking only disables adjacent light beams in a certain part of the curtain’s field, ignoring either moving or stationary items of a certain size.

There are two types of blanking: fixed and floating. In fixed blanking, a predetermined set of beams is disabled, allowing an object to remain in a portion of the light curtain’s sensing field while the rest of the light curtain continues operating. This is useful when a piece of fixed equipment would normally block beams.

Reduced resolution (sometimes called floating blanking) can change the number of disabled beams based on the size of object passing through. For example, boxes of slightly different heights passing through a light curtain may break an extra beam or two without shutting down the line.

Cascading Light Curtains

Certain applications may be well-served by using cascading light curtain technology, connecting pairs of light curtains in a series with other light curtain pairs to reduce wiring and connections to a safety controller. Typical uses of cascaded light curtains are for creating U-shaped sets of light curtains placed around a piece of equipment for three-sided operator protection, L-shaped pairs that protect both the entrance to a machine as well as the approach area, and perimeter guarding of hazardous areas.

Each successive light curtain added to a cascade adds its own detection delay time, slowing safety response times and requiring the curtains to be set back farther from the hazard in order to achieve required safety levels. However, Banner Engineering’s safety light curtains are designed to minimize this extra response time, adding as little as two milliseconds for each additional curtain. This allows Banner’s safety light curtains to be placed closer to the hazard while still maintaining proper protection, creating a smaller footprint and saving valuable floor space.

Find out More about Safety Light Curtains from Banner

From basic safety to advanced machine guarding applications, Banner has intuitive, easy-to-use light curtains to protect personnel in nearly any industrial application. Contact an engineer today to maximize machine safety in your facility.

Emniyet Işık Bariyerleri

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Ağır Ortam Şartlarına Dayanıklı Kategori 4

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