セーフティライトカーテン

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 

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.

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.