Backoff when limit switch is hit

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08 Oct 2021 22:22 #222593 by hwe
Hi,
how can I set a backoff distance when the limit switch is hit ?
Currently the axis hits the limit switch and gets stuck - no way to move the table, unless I unpower the CNC and manually move the table until the switch is deactivated.

Nothing found in pncconf to set it.
Nothing found by searching the forum/google for 1h.

I assume I can set it in the .ini file, but how ?


 

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08 Oct 2021 22:37 #222598 by tommylight
Put a - in front of the home_latch_velocity or remove it if it is already there.

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09 Oct 2021 14:07 - 09 Oct 2021 14:36 #222641 by hwe
Nothing like this found in .hal not .ini.

I want to use "Limit-All" on Pin4 of my Mesa 7i92 with DIY breakoutboard.
I want the machine to detect the limit and then backoff by 5mm to release the switch.
I do not want to detect any HOME position. I am homing manually.

The function "Limit All" works and detects the switch, but does not backoff.

After playing with pncconf settings:
- Function "Limit+Home All" did not at all detect (or react) on the switch.

I think I need a little bit more explanation about how to setup the limit+backoff - if this is possible at all.
I did not find any meaningful setting in pncconf.
The documentation also did not enlight me very much.

Can you explain in greater detail if its possible to use "Limit-All" and have a backoff on all axis ?

Edit:  I found the checkbox in AXIS to deactivate limits - this at least lets me move the table back from the limit switch !
I think this is the function I was looking for - its manual, but it enables to release the switch and not get stuck at the limit.
:-)
 
Last edit: 09 Oct 2021 14:36 by hwe.

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10 Oct 2021 09:56 #222727 by rodw
Remember that limit switches should never be hit and are just there for safety.
So having a manual process is the correct way so you can resolve whatever went wrong....

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10 Oct 2021 11:34 #222735 by phillc54
Limit + backoff is not possible.
Combined Home/Limit + backoff is possible during homing:
linuxcnc.org/docs/2.8/html/config/ini-ho...witch_example_layout
Soft limits (the ini file MAX_LIMIT & MIN_LIMIT) should be set inside physical limit switches so the limit switch will not normally be hit unless something goes wrong.

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10 Oct 2021 11:37 - 10 Oct 2021 11:38 #222736 by hwe
Hi
thanks for the clarification and I feel I have to better understand the usage of a HOME position.
So far I was thinking abut limit switches as you describe - never try to hit them.

The HOME position is basically the position where the machine rests when not in use.
But it rarely is the (0,0,0) position of my work-piece at the same time, right ?

I could combine HOME+LIMIT positions and I think this is what I will do.

What I see in my AXIS GUI is only a "Referenzfahrt" (german for reference run) for each axis and this searches for the HOME position by acitvating limits/home switches.

But how can I set the (0,0,0) position on the workpiece ?
This position is different from the HOME position, but I find no button how to set the coordinate system to (0,0,0).
Last edit: 10 Oct 2021 11:38 by hwe.

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10 Oct 2021 11:48 #222740 by hwe
Thanks phillc54 for the link - I will work myself thru this.
When working in the wood-shop I was not able to load those doc-pages, so thought they were offline. But now from the living-area WLNA I cann access it - seem a network issue in the shop.

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10 Oct 2021 12:03 #222742 by phillc54
After homing use the "Touch Off" button to set the work coordinates.

linuxcnc.org/docs/2.8/html/gui/axis.html#cha:axis-gui 

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