Robotic Guarding: Light Curtains Versus Fencing

Industrial robots can improve process efficiency and quality, but they can also be dangerous. Unlike other automated equipment, it’s never clear when or where a robot arm will pivot or swing. This means, to avoid crush injuries, workers must always be kept clear of the work envelope. Another hazard is the risk that the gripper or end-of-arm tooling will drop something while moving quickly, potentially injuring anyone in its path.

To prevent these types of injuries, ANSI/A3 developed the R15.06-2025 standard, which requires manufacturers (using robots) to implement appropriate safety measures for their employees. This is done either by installing physical fences around robotic cells or using light curtains that automatically shut down the cell if a risk is detected.

This article explores the differences between these two robotic guarding options.

Light Curtains

As the name suggests, light curtains produce a beam of light from a transmitter to a receiver. The beams are infrared, making them invisible to the human eye. Any interruption in the beams is detected and can initiate an emergency stop.

The transmitter and receiver look like two “sticks” and can be as tall or short as needed. Beam spacing and the maximum and minimum distances between sticks are determined by the stick design. When choosing light curtains, it’s important to consider these factors for maximum safety.

The gap between beams determines the smallest object that can pass through. This also determines how far away from the robot the curtain must be. Finger protection requires a narrower gap than hands. Curtains set to trigger only on objects the size of a hand must be further away from the hazard.

Modern light curtains incorporate blanking and muting features to allow beam breakage without triggering a shutdown. Blanking involves telling the curtain controller to disregard the temporary obstruction of one or more beams. Muting refers to temporarily stopping detection, as needed to let a container pass into or out of a cell on a conveyor.

Benefits

• Provide rapid equipment shutdown when the beam is interrupted.
• Allow good visibility into the workspace or cell.
• Allow items to move in and out without stopping production.

Limitations

• Must be set back far enough to ensure hands or fingers can’t reach through to the hazard.
• Prone to false triggers (and equipment stoppage) when a beam is inadvertently blocked.
• Require regular cleaning for good light transmission and detection.
• Do not protect against flying objects, like a tool or package, released from a robot gripper.

Best Use Cases

• Hand-loaded/unloaded equipment, like presses.
• Points where conveyors enter/exit a cell.

Safety Fencing

Safety fencing provides a physical barrier that prevents people and other objects, such as forklifts or flying debris, from passing through. Fencing for robot cells and other industrial equipment is usually constructed with a metal frame with an inner filler. This inner filler is usually wire mesh, but it can also be a clear or opaque solid material, provided it has the strength to resist impacts. Fence panels are fixed securely to upright posts mounted to the floor.

Opening panels (gates) are interlocked with the cell safety system. If the gate is opened, the robot or other equipment stops immediately. Operating switches can be locked and integrated into Lockout/Tagout (LOTO) systems.

For access into a cell, fence panels can be hinged or sliding. Hinged panels need mounting on a sturdy vertical post and a floor area to move on. Sliding fence panels move in a floor-mounted track and take up less space.

Benefits

• Provides a physical barrier that prevents unauthorized access.
• Can be mounted close to the robot (no offsets needed to allow for finger/hand reach).
• Guards against flying objects (solid panels protect against smaller debris).
• Versatile (available in many sizes and can be moved and reinstalled with ease).
• Inexpensive.

Limitations

• Can reduce visibility into the work area.
• Need space to swing open, unless they’re sliding.
• Extensive design planning is needed to prevent bottlenecks.
• Mesh panels will allow small debris to pass through (consider solid panels if this is a concern).

Best Use Cases

• Robot cells.
• Welding equipment or operations.
• Restricting access to storage areas (protecting hazardous materials).
• Preventing unauthorized access to conveyor or hoist systems.
• Protecting industrial equipment from unauthorized access.
• Protecting equipment from collisions with pallet trucks, forklifts, or autonomous mobile robots.

Get Help Designing Robotic Guarding

Every robot cell should be suitably guarded to protect workers from injury. A formal risk assessment should be conducted beforehand to determine existing hazards and identify the most appropriate corrective actions.

When considering your guarding options, it’s important to remember that fencing provides a physical barrier. There may be situations where light curtains are effective in some, possibly all, parts of a robot cell, but they do have significant limitations.

If you’re designing guarding for a new or existing cell, ROBO FENCE® is here to help. Our experts can provide both product recommendations and design assistance based on your facility’s unique risks. Visit our website to learn more about our guarding solutions, or contact us today to get started with a design consultation.