Safety Relays for Robot Cell

  • Hello - setting up a new robot cell with a Fanuc RJ3 controller. I am having trouble identifying what safety relay hardware to purchase, which can connect to the RJC fence circuit. I know the circuits to the RJ3 is dual channel and needs to be switched simultaneously. So I need a unified relay to control those circuits, but also to monitor the 2 safety devices I'm integrating (1 light curtain, and 1 walkdoor interlock).


    Anyone have guidance on safety relay hardware that can accomplish this? Tips?


    Thanks!

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  • How do you want to wire these devices? It might actually be possible to simply wire them in series with each other, as if they were a pair of double-throw relays, and the RJ's safety "output" would connect to its associated safety "input" only when both "relays" were closed.


    In this case, I'm assuming that you want the Gate and Light Screen to close the "safety gate" circuit on the RJ.


    If your safety devices won't tolerate that, then you might need to find a safety relay with inputs for two devices, that combines them into a single "output" channel pair that would close the RJ's safety contacts.

  • I recommend you research first just what your local regulations, machinery directives you need to satisfy before actually purchasing and integrating anything as even if it works, it may not satisfy your local regulations or machinery directives.


    From what you have written it suggests you want to drive the dual channel safety fence input to the controller from both light curtain and door interlock .

    ie 2 dual channel states to drive 1 dual channel input.


    I agree with what SkyeFire mentioned, this can simply be accomplished using a single safety relay and series linking the volt free output states or your safety devices to the dual channel input of the safety relay.


    You do need to be aware of your chosen safety relay start/reset circuit regarding automatic or manual reset configurations and whether they are monitoring the inputs for short circuits etc.


    When a safety relay goes in to fail safe ie when there is a problem with the inputs, usually it latches and remains latched until the re-evaluation of the inputs (balanced state) is conditionally correct.

    Some require you to power cycle the safety relay in order to reset/restart to re-evaluate and some have independent reset/start configurations without the requirement of power cycling.


    So you need to consider this when selecting an appropriate device(s).


    What would help is for you to study a datasheet from an OEM for a safety relay as they often have wiring schematic examples and obtain one of them and do some bench testing if you are not familiar in how they operate and construct your simple circuit outside of the robot.


    I have attached one from PILZ for your reference.

    Notice in the feedback loop example, it shows how the safety output(s) are driving force guided relays instead of being directly connected to the safety input of the safety device it is controlling.


    This type of configuration is much more flexible to use as the additional relays are used to control the safety device (safety fence input etc), but also allows for their states to permit/prevent the start/reset of the safety relay and also allow for independent monitoring of the safety devices used in the topology.


    Again, make sure to follow your local regulations, machinery directives when integrating safety monitoring.


    If in doubt, hire a specialist in this area to ensure safety practices are ensured to be correct.

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