Resume after power fail guidance required.

[deckingman]

I'm starting to think about what I need to do to resume a print after my DC UPS batteries become depleted and I have to cancel a print. Assuming that the part is still attached to the build plate (the batteries will keep the printer running for about an hour but not the mains powered bed which will cool), that is.

Re-homing Z is problematic because I use the nozzle as a probe/Zmin switch. But because it's highly unlikely that the Z axis could physically move (it needs some effort to turn the lead screw screws by hand) then the only movement is likely to come from the motor power being cycled. I read that this could be up to 4 full steps but with 2mm lead screws and 1.8 degree motors, that's 100 full steps per mm so 4 full steps would only lead to an error of 0.04mm - more that good enough for resume printing purposes I'd have thought.

So I reckon I could use G92 to set the Z position. The question is, how do I do that? i.e how do I extract the position from resurrect.g and use G92 Znn to set that? Can I use conditional gcode to do that or is it a question of reading the file and manually taking note of the value?

[jay_s_uk]

@deckingman

Note: recent firmware versions write a G92 command containing the coordinates at the time of failure into resurrect.g

This is from https://docs.duet3d.com/en/User_manual/Tuning/Resume#setting-up-the-sysresurrect-prologueg-file

[deckingman]

@jay_s_uk Ahh - cool.