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Author Topic: Possible to keep limits enabled during home?  (Read 5673 times)

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Possible to keep limits enabled during home?
« on: April 04, 2011, 12:29:26 AM »
Hi Guys and Gals,
I have a 3 axis mill with all limits and home switches wired to separate inputs on my BOB. Yep nine inputs.
I Set up the mill b4 I had Mach running and wired the limits this way because it lets you safely jog off a limit without disabling the limit, and it's normal practice here at work for motion control systems. ( would be great if I could replicate this in Mach as well)

Is it possible to edit the homing routine (DoButton24 etc) to leave the limit inputs enabled during the home all sequence.

My home positions are 20mm inside the closest limit and if I inadvertently home from within that space the limits are of no use at all, the mill will drive to the end stops and stall the steppers.
I understand why Mach is set up this way, I just want to keep the fail safe features that I have implemented enabled during home.

Cheers,
Phil

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Re: Possible to keep limits enabled during home?
« Reply #1 on: April 04, 2011, 02:58:39 AM »
It is something I have asked for and hopefully will be included in Rev4 but dont think there is a way at the moment.
One thing you can possibly do which may help you. If you have the home switches trigger set up so that once the table reaches and passes the home switch it is always triggered then there is an option on General Config page  called Home Switch Safety, if you have that chosen you get a message saying a home switch is active and the axis wont home, if however you dont have that chosen then the axis with the active home switch will home the opposite way from normal thus moving off the switch.
Hood
Re: Possible to keep limits enabled during home?
« Reply #2 on: April 04, 2011, 04:08:16 AM »
Thanks Hood,
I run separate hall effects and one magnet for the limits and home, I think maintaining the home active mechanically will be a bit of a challenge.

While I wait for Rev4, I might install some electronics to sort the issue out.
I think if I wire the limit signal and home signal through a logic OR gate (74LS32) to the home switch input it will solve the issue.
If the home is missed then the limit will trigger a home and when the home sequence finishes and the limits are re-enabled, the still active limit will trigger an E-stop. That way I'll know that the home was missed. (if I remember the set up)

Thanks again,
Phil

Offline Hood

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Re: Possible to keep limits enabled during home?
« Reply #3 on: April 04, 2011, 04:26:08 AM »
Sounds like it would work.
I am in the fortunate position that my homing is done in my drives so Mach knows nothing about me homing until my drives signal its complete, so the Limits are always active.
Hood
Re: Possible to keep limits enabled during home?
« Reply #4 on: April 04, 2011, 07:59:17 AM »
Phil, Hood,
  Could you just use OEM Triggers for the limits that are near the home pos. ?
Assign OEM Trigger 1003 (STOP) to those three inputs. Tried 1021 (RESET) but it never goes into EStop.
Seems to work OK here in sim. and allows all jogging afterwards.
Just a thought,
Russ

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Re: Possible to keep limits enabled during home?
« Reply #5 on: April 04, 2011, 08:02:18 AM »
Possible I suppose Russ. Not sure if they would be as quick as actual limits but probably not far behind if they were  slower.
Hood
Re: Possible to keep limits enabled during home?
« Reply #6 on: April 04, 2011, 08:14:05 AM »
Appears to be instantaneous here in sim., surely would be quick enough unless homing at near 100%.
I'd try it with caution though, start slow.
Russ

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Re: Possible to keep limits enabled during home?
« Reply #7 on: April 04, 2011, 08:24:31 AM »
Yes should be fine, not sure if limits are via the driver or not, if they are then they will be faster but its likely they are not, and even if they were  the difference likely be so minimal that it probably wouldnt matter.
Hood
Re: Possible to keep limits enabled during home?
« Reply #8 on: April 04, 2011, 10:10:38 AM »
Quote
Phil, Hood,
  Could you just use OEM Triggers for the limits that are near the home pos. ?
Assign OEM Trigger 1003 (STOP) to those three inputs. Tried 1021 (RESET) but it never goes into EStop.
Seems to work OK here in sim. and allows all jogging afterwards.
Just a thought,
Russ

Thanks for the Idea Russ,
I'll give it a try when I get back to the mill tomorrow night and let you know how it went.

I home at 20% and the limit stays active for about 3mm before the magnet travels too far past.

Cheers,
Phil
Re: Possible to keep limits enabled during home?
« Reply #9 on: April 04, 2011, 12:05:10 PM »
I'll check back for the update, thanks Phil.
Oh, and don't forget to disable the chosen limits in Ports and Pins / Input Signals.
Good luck,
Russ