Light curtains are opto-electronic devices that are used to safeguard personnel in the vicinity of moving machinery with the potential to cause harm such as (but not limited to) presses, winders and palletisers. Light curtains can be used as an alternative to mechanical barriers and other forms of traditional machine guarding. By reducing the need for physical guards and barriers, light curtains can increase the maintainability of the equipment they are guarding. The operability and efficiency of machinery can also be improved by the use of light curtains by, for example, allowing easier access for semi-automatic procedures.
Light curtains fall into a category of equipment known as presence detection devices. Other common presence detection devices are pressure-sensitive safety mats and laser scanners (often used on Remotely Operated Vehicles (ROV) when in industrial settings).Most important application of safety relays is in automation industries dealing with robotic cell set up .
Light curtains are supplied as a pair with a transmitter and receiver. The transmitter projects an array of parallel infrared light beams to the receiver which consists of a number of photoelectric cells. When an object breaks one or more of the beams a stop signal is sent to the guarded equipment.
The light beams emitted from the transmitter are sequenced, one after the other, and pulsed at a specific frequency. The receiver is designed to only accept the specific pulse and frequency from its dedicated transmitter. This enables the rejection of spurious infrared light and thus enhances their suitability as components within a safety system.
Typically, light curtains are connected to a safety relay which will remove motive power from the hazard in the event that an object is detected. Safety relays can be provided with muting functionality which enables the temporary disabling of the safety function to allow objects to pass through the light curtains without tripping the safety relay. This is particularly useful for machinery which has some semi-automatic procedures.
What Is a Light Curtain and how it work? Very simply, a Safety Light Curtain is a device used to protect persons from dangerous machinery. A Safety Light Curtain is made up of two electronic sensor bars (Transceivers), which send and receive invisible infra-red beams between each other. These transceivers are connected, as per Figure A, to a Controller, which receives electronic signals from the transceivers and from these signals decides whether or not the area between the transceivers is clear or obstructed.
The Safety Light Curtain is placed between a machine operator and a dangerous machine as per Figure B, so that if the operator puts any part of their body into the machine, then some of the infra-red beams between the Transceivers will have been obstructed. The Controller will then send a stop signal to the machine, before the operator can be injured.
The following partial list of standards should be used for guidance when implementing light curtains:
ISO13855 (EN 999);