G92 messing up the coordinate

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14 Feb 2012 07:30 #17643 by KenC
Hi,
I have no idea where to post this but here is my problem.
Open EMC, home X,Y,Z axis manually ( I run the machine without limit switches)
run one button auto Zero touch off, & execute the G code & everything runs like clock work.
The problem come when I the Z-touch off again & it shows the "exceed joint limit" in red letter bar at the bottom right corner of AXIS screen.

My idiot solution to that is to re-start a fresh session of EMC2 without incident.

I eventually isolated the problem to the use of G92. The X Y & Z coordinates will have a mind of its own & disregard what I type in the MDI command bar.

I tried everything to my ability, the problem started with V2.3.4 on 8.04LTS, now updated to 10.04LTS & 2.4.3, tear the Z-touch off hal apart & even unplug the par-port but the issue persist...

##Other info I use Atom board with 2G Ram on board & a 8Gig pendrive as hard drive...

Any help is highly appreciated.

Regards

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14 Feb 2012 10:07 #17647 by ArcEye
Hi

As this wiki

linuxcnc.org/docs/2.4/html/gcode_coordin...html#sec:G92-Offsets

explains,

They can give rise to big errors and confusion, especially on machines without consistent mechanical homing or where no cancellation G92.1 command was used before quitting

( In the latter basically the increment is applied to the values pre-existing in the var file and results in excessive offsets which were unintended and could be the cause of your "exceed joint limit" error )

regards

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14 Feb 2012 11:17 #17651 by Rick G

I eventually isolated the problem to the use of G92. The X Y & Z coordinates will have a mind of its own & disregard what I type in the MDI command bar.

I tried everything to my ability, the problem started with V2.3.4 on 8.04LTS, now updated to 10.04LTS & 2.4.3,


Can you explain how you are using G92, and are you saying that there was not a problem with it before 2.3.4?

Rick G

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14 Feb 2012 11:53 #17654 by KenC
Thanks for the response.

Rick,
1) I do have the same issue with 2.3.4
2) I use G92 for Z-axisZero touch-off 99% of the time..

Arceye,
Thanks for the link, but I just don't understand how its affecting...

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14 Feb 2012 12:08 - 14 Feb 2012 12:09 #17655 by BigJohnT
Do you issue a G92.1 after using G92?

linuxcnc.org/docview/2.5/html/gcode/gcod...id_sec_g92_1_g92_2_a

I use G92 to set the Z of my plasma torch with no issues.

Can you attach your G code file to a message?

John
Last edit: 14 Feb 2012 12:09 by BigJohnT.

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14 Feb 2012 13:33 #17662 by KenC
Hi John,

The same problem persisted in any situation when ever I click on the Z-zeto touch-off the second time when I open up EMC2. & its not G-code file related.

:woohoo: I think I'd cracked the problem after digging deep into the links BigJohnT & Arceye posted earlier.

Before this, I never knew G92.1 & G92 existed :blush:
Always sometime new to learn :)

Its a mystery that this started only about 10 days ago after 2 years of operating with G92 without G92.1....

My solution
Issue a G92.1 command before every G92 command, this will reset the axis value that you worked on earlier. Than G92 what ever value to which ever axis I fancy. Not as convenient as before but at least I get it back to normal.

Maybe there is a better way, I'm all ears. :cheer:


Thousand thank!


#PS, adding MDI-COMMAND G92.1 at the begining of the Auto Z-touch-off code line doesn't help.

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14 Feb 2012 13:59 - 14 Feb 2012 14:01 #17663 by BigJohnT
KenC wrote:

Hi John,

The same problem persisted in any situation when ever I click on the Z-zeto touch-off the second time when I open up EMC2. & its not G-code file related.


Are you saying that you jog the Z axis down to a point then with the Z axis radio button selected you click on the "Touch Off" button, then select "Tool Table" then click on the "Ok" button? If this is the case then you are adding the current G54 offset to your tool offset. In 2.4 always issue a G59.3 or similar (I used to use G55) to select a coordinate system that does not have any offsets before touching off the tool table or clear any G54 offsets before touching off the tool table.

John
Last edit: 14 Feb 2012 14:01 by BigJohnT.

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25 Feb 2012 08:54 #18071 by KenC
Hi,
I would like to report that my G92 is still messing up my machine co-ordinate...

G92.1 does reset the coordinates, but when I proceed with a new G92 issue, the coordinates mess us again...

Any help is highly appreciated.

Regards

Ken

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25 Feb 2012 10:39 #18073 by Rick G
Are you using tool table offsets? Do you cancel them after use? Do the offsets in the tool table relate to your errors?
Can you try G10 L20 instead of G92 to set the coordinate system?

Rick G

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25 Feb 2012 14:33 #18080 by BigJohnT
Ken,

Your going to have to give us more information than "it's messing up" to get past your learning curve. Please tell us exactly what your doing, what you expected, and what you got along with a sample of the code that gives you the unexpected result.

John

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