Light curtain controllers send stop signals to machines that are guarded by light curtains, photoelectric transmitters that project an array of synchronized, parallel infrared light beams to a receiver. When an opaque object interrupts one or more of the beams, the light curtain controller signals the stop. If a lockout condition occurs, an operator may need to reset a switch on the light curtain controller in order to return the machine to a run condition. Most light curtain controllers contain three relays: two control or safety relays and one auxiliary or status relay. They also include a power supply that receives AC or DC inputs. Integral light curtain controllers are packaged with a light curtain transmitter and receiver. External light curtain controllers are stand-alone units that are often positioned near the transmitter and receiver in order to provide a central wiring location. Typically, external light curtain controllers are housed in metal enclosures and mounted in racks or cabinets, or on walls or DIN rails.
Selecting light curtain controllers requires an analysis of product specifications and features. Devices differ in terms of the number of light curtain transmitters and receivers that can be controlled. Relay output specifications include maximum current rating, maximum AC voltage rating, maximum DC voltage rating, and maximum power rating. Controller features include visual indicators such as light emitting diodes (LEDs) and/or audible alarms. Lockable light curtain controllers require the use of a key to access the enclosure. Devices with muting, blanking or banking, and latching or guard mode activation are commonly available. Muting is the automatic, temporary deactivation of a safeguarding device during the non-hazardous portion of the machine cycle. Blanking or banking disables one or more fixed locations (beams) within the sensing field. Latching relays or guard mode activation causes a lockout condition when the light curtain’s sensing field is penetrated. The light curtain maintains the stop signal until the light curtain controller is reset manually.
Light curtain controllers are used with many different types of light curtains. For example, point-of-operation light curtains are used to protect the fingers and hands of personnel who operate mechanical and hydraulic power presses and molding presses or stamping, forming, riveting, and automated assembly machinery. Perimeter guarding light curtains are used to protect the perimeters or boundaries defined by machines, robots, or other equipment. In the United States, the Occupational Safety and Health Administration (OSHA) and the American National Standards Institute (ANSI) define standards for control reliability, the ability of machine control systems to achieve a safe state in the event of a safety-related failure.