Save position after AXIS shutdown

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14 Oct 2010 17:56 #4680 by photomankc
I read about the position_file and thought maybe this would be the answer but so far I can not tell that it does anything different than the default. I would like for EMC to remember where it is at from run to run. I don't have home switches yet so it gets a little tedious to jog the mill through sometimes 15" of movement back to my index marks every time I start AXIS again. The description for POSITION_FILE seemed to indicate that it would store machine position between runs and then come back up assuming no movement (safe assumption since I now have no handles) and reload those coordinates instead of returning the machine to 0,0,0

Putting in POSITION_FILE = position.txt doesn't seem to cause that to happen nor does a fully qualified path name. Is that supposed to be how it works and is there any place to see a message that might explain why it didn't if so?

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14 Oct 2010 22:07 #4686 by BigJohnT
Did you put it into the [TRAJ] Section, if not it probably got ignored.

John

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16 Oct 2010 23:24 #4716 by photomankc
Well, it must have been a typo. I just started over on the line and retyped it and it now saves the mills position however it's not much use to me since when I restart it forces me to home each axis again which I can't do perfectly repeatably yet (I use index marks) so I then have to go touch off again anyway. Kinda frustrating.

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17 Oct 2010 09:59 #4719 by Rick G
Take a look here...

EMC V2.4 Integrator Manual Chapter 4. INI File

NO_FORCE_HOMING = 1 The default behavior is for EMC to force the user to home the machine
before any MDI command or a program is run. Normally jogging only is allowed before homing.
Setting NO_FORCE_HOMING = 1 allows the user to make MDI moves and run programs without
homing the machine first. Interfaces without homing ability will need to have this option
set to 1.
Warning: Using this will allow the machine to run past soft limits while in operation and is not
generally desirable to allow this.


In the Traj section of the ini file set NO-FORCE-HOMING = 1 this will llow you to start your machine at the saved location without homing.

Rick G

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18 Oct 2010 03:49 #4732 by photomankc
Thank you. I missed that in reading through the integrators manual. Appreciate the pointer, that's a big help!

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19 Oct 2010 13:49 #4746 by photomankc
Just a curiosity question here. So why does it then allow overrun of the soft-limits when it starts back up. It knows where the old machine coordinate 0 was because the extents lines are still in the correct place. I'm guessing that the extents can only be enforced when the axis is marked as homed in the guts of EMC? Anyway, it's not a big issue I was just wondering about it, I also was looking around to see if there is anyway to force an axis to be marked as homed without changing the axis origin to the current position?

Otherwise it will still help when I have a part that is going to be in the vice over a few nights and shutdowns.

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20 Oct 2010 11:04 #4756 by Rick G
If a axis is not homed EMC does not use soft limits, in theory it does not know where the axis is.

One strategy that I use is to initially start the machine and home all axis. I then jog to the position I want to work, say the lower left side of the work zero height. I then use G92 to set all my axis at 0 (or the position I need). You can then perform your work from this position. When done use G53 G0 x0y0z0 and the machine will return to your original homed position. If you look at the DRO it will show relative numbers for xyz from home to your work position. These positions will be stored in the position file. When you restart EMC these numbers will appear, you can home to them. Then G0 x0y0z0 to the position you left off at. The soft limits will now work. The G53 move has the benefit of verifying that your machine is in the correct machine position on your indexes when you start.

Rick G

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21 Oct 2010 15:23 #4780 by photomankc
Nice tip Rick! Thanks. I'm starting to get better with figuring out the various coordinate systems and offsets but I didn't notice that G53 command to make a single move in machine coordinates. That would be perfect.

Next up I need to map my screw for better accuracy with the acme nuts till I have the equipment to get ball screws installed.

Thanks for all the assistance. I have really been enjoying the machine and you guys have helped greatly in getting me started with EMC. I really appreciate all the tips, suggestions and help.

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