Save Axis state (including homing info)

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15 Dec 2014 16:50 #54013 by gaeldk
Hello,

I work on some things that take hours and sometimes in the middle of some cnc operations I would like to shutdown the PC and the machine and to start again later.

The problem is that after I start again I need to home again against my home switches which are ok but will probably induce a bit or errors...

I'd rather be able to restart in the exact same state as I left the machine since nothing has moved...

How can I do this so that Axis would start already homed and in the state as I left it ?

Thanks

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15 Dec 2014 19:57 - 15 Dec 2014 19:58 #54017 by emcPT
Hello,
What hardware do you have?
The only safe method to do that, as far I know, is to use hardware that pass though the encoder position to linuxcnc (for example mesa 7i77) where linuxcnc knows the encoder position and therefor the machine position. At the same time you will still need to leave the PC on and the encoders under power, but not need to leave the motors under power.

Any other solution can result in bad things, because when you power of the machine the machine will move. Maybe in your case only a small amount, but still problematic.
Last edit: 15 Dec 2014 19:58 by emcPT.

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15 Dec 2014 22:33 #54023 by BigJohnT
The only way is to leave it running. With power off you might bump something and move an axis... so accurate home switches are needed to power down and back up and resume a program.

JT
The following user(s) said Thank You: gaeldk

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20 Dec 2014 00:59 #54166 by gaeldk
Ok no miracles then...

Will test the accuracy of my home switches with a comparator...

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25 Jan 2022 08:29 #233041 by mahdi2001h
hi i read this topic and  read "emcPT" answer .
but i checked some cnc machine that not have absolute encoder and powering down and starting up and not homing every time.
if i want to save homing , what i should to do ?
is any config in linuxcnc or i should edit source code?
 

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12 May 2022 08:43 #242761 by Trihwangyudi1990
No miracle.. I have same issue with that ,my machine have no limit switch no encoder
so i tricked with stop the machine.... Write last position number, then i switch to MDI run home comands "G0 X0 Y0"
i have touch probe.. So i dont need to tell my machine where Z 0
Beware to safe your Z axis before run this home comands
When the machine setup to home position i shut down my machine,pc 
when i turn on my machine i just clik home axis for X and Y then go to number  then "start from here" 

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13 May 2022 01:30 #242841 by cakeslob
This guy has some sweet stuff
github.com/yur7aev?tab=repositories
yurtaev.com/

From what I recall, he has a no homing linuxcnc but because his servos pass information back to linuxcnc. I think theres also a soft limit issue when doing a no homing thing. I think another no homing required application would be motors with brakes on them, so you know the axis didnt move. Im fairly sure some non absolute servos use a battery backup and still count when powered down, and the information is passed on startup

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