Light curtain
Encyclopedia
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 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.
KEYENCE, Omron STI, Banner Engineering (EZ-SCREEN), Leuze electronic, OMRON, Pilz, Rockwell, Guardmaster; Schmersal Inc.; Sick and Pinnacle Systems, Inc.
Machine press
A machine press, commonly shortened to press, is a machine tool that changes the shape of a workpiece.-Servomechanism:A servomechanism press, also known as a servo press or a electro press, is a press driven by an AC servo motor. The torque produced is converted to a linear force via a ball screw....
, winders
Winder (machine)
A winding machine or winder is a machine for wrapping string, twine, cord, thread, yarn, rope, wire, ribbon, tape, etc onto a spool, bobbin, reel, etc.-In textiles:...
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.
Description
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
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
beams to the receiver which consists of a number of photoelectric cells
Solar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
. 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
Motive power
In thermodynamics, motive power is an agency, as water or steam, used to impart motion. Generally, motive power is defined as a natural agent, as water, steam, wind, electricity, etc., used to impart motion to machinery; a motor; a mover. The term may also define something, as a locomotive or a...
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.
Standards
The following partial list of standards should be used for guidance when implementing light curtains:- ANSI B11.19
- IEC61496-1/-2
- IEC/TS 62046;
- ISO13855 (EN 999);
Suppliers
The following is a partial list of light curtain suppliers:KEYENCE, Omron STI, Banner Engineering (EZ-SCREEN), Leuze electronic, OMRON, Pilz, Rockwell, Guardmaster; Schmersal Inc.; Sick and Pinnacle Systems, Inc.