Limit switches and E-Stop

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30 Apr 2020 11:21 #166205 by SPH
Hey all, I'm back working on my Rover having finally got the correct encoder cables for my chinese servos.

I want to start getting the axis' set up but I'm not keen to start without getting the e-stop and limits set up.

I'm mostly concerned with the hardware side of things. I want to make sure that when I hit the e-stop it disables the drives. Same goes for the limit switches, disable the drives.

The e-stop and limit switches were connected via safety relays but they've been removed. I might look at re-installing a safety relay down the track but I just need a basic setup for now to get to work safely.

The drives allow an input to be setup as e-stop so that's the likely option, send the limit/e-stop circuit to the drive (drive's, jumped to the three seperate e-stop inputs) and then have the drives e-stop output sent to the 7i77.
From what I've read I want the limits and e-stop connected NC to avoid a possible wire break from disabling the circuit. So that would mean the drive e-stop input pins need to be set active low? Dc voltage going to the input under normal operating conditions?
Alternatively if the input active state can't be changed (the manual is not the easiest to read) I could connect the circuit to a relay to flip the high/low condition?

Ultimately I understand there are many ways to achieve the circuit but I'd appreciate some advice on the best way to handle it.

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30 Apr 2020 11:50 #166207 by rodw
Replied by rodw on topic Limit switches and E-Stop
Have a look at estop-latch
linuxcnc.org/docs/devel/html/man/man9/estop_latch.9.html

If you can't wire them together in a chain with external wiring, you can chain all of your estops together using this component and turn iocontrol.0.emc−enable−in false when you press a button. You can then trigger a relay or output pin to disable the drives.

I'm not sure its a wise idea to disable the drives if you hit the limits becasue then you won't be able jog off using ignore limits. Trust me things stop quickly when you hit one!

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30 Apr 2020 12:07 #166209 by SPH
Replied by SPH on topic Limit switches and E-Stop
Fair enough, I'll have a look at it. I was under the impression though that e-stop at least should have a direct physical connection to the drives rather than relying on software to kill the machine in the event of a problem? Pretty sure this machine would tear its self to pieces if it tried to run over the limits.

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01 May 2020 17:27 #166346 by Aciera
Replied by Aciera on topic Limit switches and E-Stop
At the end of the day it all comes down to how much you trust the software and the driver board. If you want to go the secure way you need hardware switches to disconnect the drives in an emergency situation. In a commercial setup this can cause a fair bit of headache and can also incur a fair bit of cost. Doing this properly requires the safety relays you mentioned and that is also why those are pricey things to buy.
The following user(s) said Thank You: thefabricator03

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05 May 2020 22:33 - 05 May 2020 22:35 #166810 by Becksvill
Replied by Becksvill on topic Limit switches and E-Stop
SPH I have just done this same thing with my retrofit on my cnc mill. So I will try and help out here. I am pretty happy with my estop now.

I wasn't happy with the other options in Hal like the latch component for my big machine. like you say a E stop should always cut power/stop the machine regardless of what the computer says. but I also want the computer to be able to cut power without me if needed eg if I go up for breakfast I want to know that I am now going to come back to a fire lol.

On my machine I use Classic ladder for my e stop circuit and use the e stop circuit that is included with linuxcnc when you install it. if you make your config with either step config or pncconf they both make this circuit for you by default if you tick the correct box so that makes this pretty much plug and play.

Limit switchs are separate to home switches on my machine and never get touched normally. they are wired in NC so that if something ever breaks I will get a error on linuxcnc. the limit switches do not cut power to the drives. (well they throw the estop, I think that cuts power, but then you can override the limits and power the machine back up and move off the limit switches if you want

anyway I made a long and involved video to help the next guy that had this problem so here it is. I use this on a 5 ton cnc mill and it works perfect. my e stop classic ladder video

ps I am planning on fixing the video quality. sorry about that hopefully you can still work it out

this video here was the best thing ever to understand the Hal layer. You need to learn to use Halcmd if you are not already it makes life so much better! Hal is no longer a mystery lol. E stop video by SAM (Watch this!)


hopefully these videos should help. if not I am happy to help

best way to contact me if you are struggling is (carbidecutters.co.nz) just find my email on the contact page

all the best
Last edit: 05 May 2020 22:35 by Becksvill. Reason: forgot to say something
The following user(s) said Thank You: tommylight, thefabricator03

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06 May 2020 00:59 #166825 by SPH
Replied by SPH on topic Limit switches and E-Stop
Thanks, I'll definitely take a look. Sounds like we came to similar conclusions, more or or less.
Same kind of thoughts I had, it's not that I don't trust the software, I'd just rather the drives cut power directly and lcnc get an estop at the same time.
I've got it working in a way I'm happy with at the moment. Was just getting ready to tune th axis' when my pc hardware failed. Don't known yet if it's the 7i77, pc or something else. Frustrating.

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06 May 2020 02:08 #166829 by Becksvill
Replied by Becksvill on topic Limit switches and E-Stop
sweet. the good thing about my e stop system is that the classic ladder part is already made and included with linuxcnc and you only have two lines of Hal connections to add. can't get much easier.

btw what brand of chinese servos did you buy?

Regards

Andrew

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06 May 2020 03:56 #166835 by SPH
Replied by SPH on topic Limit switches and E-Stop
Uhhh, yes. Ympc I think? There are a lot of generic looking servos available. They all appear to be pretty much the same. Can't comment on how good they are yet as I haven't got anything more than a jerky jog out of any one axis.

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06 May 2020 11:43 #166862 by Becksvill
Replied by Becksvill on topic Limit switches and E-Stop
hey SPH

long shot here. I have about 8 old yaskawa servo drives here that I got free. and no motors. I was browsing the forum and randomly say your post about your cnc router retrofit. I don't know if my drives take 0-10 volt or not (eg if they are usable... ) but just wondered if you kept the motors from your retrofit as I know you bought new chinese drives like me. I need more servos for a cnc lathe retrofit and since you are only in Aus i just thought I would ask/

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06 May 2020 11:44 #166863 by Becksvill
Replied by Becksvill on topic Limit switches and E-Stop
just in case you don't get a notification from my reply here it is here also. just wondering if you still have your yaskawa servo motors?

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