WHAT IS A LIGHT CURTAIN?
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.
SIGRA Controllers can operate up to four curtains (see fig C&D) with any mixture of sizes and ranges. This can be a useful feature if you wish to guard four sides of a machine.
Note: Although 4 Curtains are controlled, the Controller output will switch to stop the machine regardless of which light curtain is obstructed.
The Light Curtain Controller is connected to each transceiver using 4 core screened cable. The Controller determines from the signals from each transceiver, if the curtain area between the Transceivers is clear and provides outputs, which are used to stop the dangerous motion of the machine if the curtains are obstructed. This can be done by using the outputs to close or open valves to brakes or cylinders on the machine to stop the dangerous motion.
INTERFACING WITH MACHINERY
The Light Curtain Reset inputs have several uses. Resets can monitor the correct operation of the valves or other devices which the Light Curtain Outputs are controlling. They can be used with a push-button as a manual reset once the light curtain has been obstructed. They can also provide a very useful “anti-repeat” function, which does not allow the machine to re-start on it’s own once the curtain is unobstructed.
The Light Curtain Mute inputs effectively bypass the Safety Light Curtain. This can be useful for machine set up. These inputs can also be automatically activated by the machine during safe portions of a cycle, such as the opening stroke of the power press as shown in Figure E. This would allow the operator to step into the guarded area to remove the work-piece whilst the press was opening. The Mute inputs can also be used to make the Light Curtain UNIDIRECTIONAL, in other words product may be allowed to exit through the Light Curtain but nothing may enter through the Light Curtain.
Corner mirrors can be used to bounce the Light Curtain beams around corners. This would allow you, for example, to guard the application shown in the above Figure F with two corner mirrors and four less transceivers. Note, mirrors should not be used over distances totaling more than 12 metres. The main disadvantage of using mirrors is that they can be very difficult to align. Any mountings for mirrors should be very strong and robust. Mirrors are not recommended for use in high traffic areas as they will need constant re-alignment.
Other accessories include Chemical wash-down enclosures, Power Supplies, Dust Ignition Proof Enclosures, Pre-wired Cable assemblies and cables.