AB 440R-EM4R2 triggered by Point IO safety output

[creativepaper]

I have a Point IO safety chasis with some safety IO (1734-OBV2S cards in it). This is controlled by a GuardLogix PLC.

I have two robots that I want to add their safety interlock into. Their diagrams show a standards dual channel safety relay in the schematics.
To me, I cannot use the outputs from 1734-OBV2S cards since they don't use the same 24V as the robot is from a different electrical panel.

Can I have the output from the OBV2S go to a 440R-EM4R2 terminal L12 and wire the robots into this?
I have two robots (both separate breakers), so need a total of four 'dry contacts'

Other alternatives are:
- use a 1734-FPD and another 1734-OBV2S card so the OBV2S sources the robot 24V. Would need 2x 1734-FPD and 2x 1734-OBV2S.
- Use a 440R-D22R2 relay and a 440R-EM4R2 and have the existing OBV2S trigger the DI safety relay. This is the same as what I would like, just an additional relay in the way.

 

[joseph_e2]

I would be surprised if you can control the EM4R2 expansion relay directly from the 1734 chassis. I've never used the 1734 safety outputs, though, so I don't know if they support SWS. I doubt it, but wouldn't rule that out. All of the wiring examples I've seen with the 440R-EM* modules show them connected to another 440R safety relay. It would be pretty cool if it worked, though...

 

[creativepaper]

I agree that it would be nice.
Since a 'dumb' relay can control the expansion card, I am hoping that the Point IO can as well.
Best way is that we all learn and I have a spare 440R-D22R2 to use on another project.

 

[joseph_e2]

Being a safety application, I would want to get AB's blessing on that configuration *in writing*, even if it seems to work.

 

[James Mcquade]

check with your ab distributor for part quotes AND delivery dates !!
our items are 26-54 week delivery times.
james

 

[ASF]

Other alternatives are:
- use a 1734-FPD and another 1734-OBV2S card so the OBV2S sources the robot 24V. Would need 2x 1734-FPD and 2x 1734-OBV2S.

I don't think this would work. I'm not 100% certain, but I believe that the outputs on the safety output modules are supplied from bus power, not field power. That is, if you put an 1734-FPD before the 1734-OBV2S, the 24V you supply to the FPD will appear on the V and COM terminals, but the O0 through O3 terminals will receive their 24V and 0V from the 1734-AENT(R).

If I'm right about this, you could instead use a 1734-EP24DC, which creates a new "bus" as well as new field power. However that may not be practical, because if you have no bus power on a section of the bus, your connection to the whole rack will fault because the AENT(R) can't see the modules in that section. If there's the possibility that one robot would turn off, but that you'd still need to be able to run things (even just jog things for maintenance, etc), then that's probably a non-starter.

If I were in this situation I'd take one of two approaches:
1. Investigate whether the robot safety circuit can be modified to remove the safety relay (since you've got a far more powerful safety PLC at your disposal) and wire your safety outputs directly to the safety output devices in the robot. E.g. if the safety relay in the robot has a pair of safety contactors wired to its outputs, could you dispense with the safety relay and just wire those safety contactors directly to your safety PLC? There are a lot of caveats with this method - you'd have to bring the feedback loops and reset pushbutton into your safety PLC as well, you'd have to consider whether there were any other safety input devices also associated with that safety relay, and you'd only ever touch it if you had good support from the robot OEM and they were happy to work with you to modify their machine and sign off together on the safety solution. But if you could do it, you'd have a really neat, elegant, highly visible solution.

2. Just put some force guided relays on your 1734-OBV2S like the Omron G7SA - or even a standard safety contactor - and wire the 24V from the robot's safety relay directly through the dry contacts of your relay. At that point you could revert from 2x OBV2S and 2x FPD/EP24DC to 1x OB8S. Again you'll have to consider a feedback loop from your relays, and it IS slightly more complicated - but it keeps the two systems well contained and doesn't blur the line between "your system" and "my system", which in many cases is an important thing to be able to do.

 

[joseph_e2]

...
2. Just put some force guided relays on your 1734-OBV2S like the Omron G7SA - or even a standard safety contactor - and wire the 24V from the robot's safety relay directly through the dry contacts of your relay. At that point you could revert from 2x OBV2S and 2x FPD/EP24DC to 1x OB8S. Again you'll have to consider a feedback loop from your relays, and it IS slightly more complicated - but it keeps the two systems well contained and doesn't blur the line between "your system" and "my system", which in many cases is an important thing to be able to do.

I should have thought of that, because that's exactly what we did on a palletizing robot system here. We used a Keyence GC-1000 programmable safety controller to handle the doors, light curtains, and area scanners in the cell and it controlled 4 force guided relays: 2ea for the robot "e-stop" signal and 2ea for the robot's "fence" signal.

 

[creativepaper]

Thanks guys.
I think having the Safety PLC trigger a safety relay is the best option.
Just weird that I need this.
Must be a technical reason why AB won't create a pure safety relay point IO card.