Limit switches are tripping randomly during machine operation

[Gary Campbell]

If you needed to you could use NO switches in parallel and connect the alarm signal to the NC & Com terms of the relay (assuming relay has NO/NC terms

[slodat]

I'm not really worried about fail safe right now. This leaves me wondering why a NC contact/switch/circuit is "less prone to interference"...

The CNC12 issue mentioned on page two of this thread hasn't really been discussed.. Does anyone know for sure if this is a bug in CNC12?

Check with Keith,
I think there is an issue with home/limitOk setup at moment. I had an issue where home/limit kept re-tripping on axis 1 across a variety of switch types.
Only happened in first axis. Changed setup to home all & problem went away, just used soft limits after that.
Regards,
Michael

[mick41zxr]

I think so, was able to work around.
viewtopic.php?f=60&t=2193&start=20

[slodat]

Michael- Thank you for the reply. I'm not seeing anywhere that Centroid has taken this as a bug to be fixed in your thread.

Still not buying the NO contact is somehow noise sensitive vs NC contact. I am using 24vdc in the Omron proximity switches.

[mick41zxr]

Hopefully fixed in next version that is due soon (v4.14).
No i don't think its noise, however it is better practice to use NC switches (fail safe).
Wire all your homing switches in parallel (all actives together & all grounds together) to a single input then set that input to HomeAll - Normally open.
Set you soft limits & you should be good.
That's what I did, haven't had a problem since.
It will home a little slower as all axis have to home separately, however if you park the machine before shutting down it is of little consequence.
I bought N/O switched by accident (picked wrong model number on order).
Regards,
Michael

[martyscncgarage]

General statement:
I have used both NO and NC switches.
Never had a problem with either.

NC is standard and should be used. You might consider upgrading the switches to NC. I would buy at least one and replace one and test.

Electrical noise plays havoc with the motion controller.
Snubbers (Quencharcs) are a must on ALL relays and ALL solenoids.
All ground wires and cable shields need to be taken to ONE point and at that point earthground connected.

Take a look at Centroid Tech Bulletin TB206:
http://www.centroidcnc.com/dealersuppor ... ds/206.pdf

Marty

[slodat]

Marty,

Thank you so much for the reply! I have not come across best practice type of stuff for CNC machines in my travels yet. I will transition to NC switches. I think the direction I want to go is an inductive proximity sensor from Automation Direct with M12 connectors. When I removed the covers from my machine this weekend the wiring workmanship left a lot to be desired.

Thanks again!

[martyscncgarage]

Marty,

Thank you so much for the reply! I have not come across best practice type of stuff for CNC machines in my travels yet. I will transition to NC switches. I think the direction I want to go is an inductive proximity sensor from Automation Direct with M12 connectors. When I removed the covers from my machine this weekend the wiring workmanship left a lot to be desired.

Thanks again!

Yes, that is generally the case. Sometimes trying to work with someone else's "work" is not the best way to go. All the effort and time spent trying to sort it out, could have been spend just rewiring from scratch "the right way"
Even if the machine did operate, gremlins would pop up and make using the machine and learning the control, not so enjoyable.

Marty

[tblough]

Still not buying the NO contact is somehow noise sensitive vs NC contact.

Noise is extraneous voltage induced in the wires. If your switch is NO and the controller is looking for a voltage signal, a stray 1-2V spike can set it off. If the control is using a 24V NC switch, the control is seeing 24V when the is switch not made. A stray 1-2V spike just changes that from 24V to 26V - still not made. It's pretty easy for the control to notice the absence of 24V even with a few volts of noise in the system.

[Black Forest]

The main reason for NC E-stop and limits is safety. If you use NO switches and need an E-stop or reach a limit switch you won't know if you have a wiring failure until it is too late! NC switches will go into E-stop if there is a break in the circuit or a power supply failure, etc..