Configuring "resume a print after a power failure"

[anraf1001]

Hi, I want to configure "resume a print after a power failure" option on my Duet but I have one problem with understanding documentation. It says that I need to use G92 command in sys/resurrect-prologue.g to tell the printer Z coordinate. But what parameters should I use?

[wilriker]

@anraf1001 If the machine lost power the position of the motors is no longer known so usually you need to home the printer again in sys/resurrect-prologue.g. On many printer types homing X and Y is not a problem even if a partial print is already in the build-plate but homing Z can be problematic as some part of the printer could collide with the partial print.

There are several ways around this problem

1. Your printer has layout that makes regular homing possible even with a partial print of arbitrary size on your build plate
   -> just put G28 in your sys/resurrect-prologue.g and you're done
2. You have a way of reliably determining the Z position of your printer
   -> use G28 XY to only home X and Y and G92 Znnn where nnn is the current position of Z to tell the printer the current Z height without the need of the homing process for Z

[dragonn]

@wilriker In second scenario you need to update the position every time you use power-recovery?
Not really user friendly.

[anraf1001]

@wilriker said in Configuring "resume a print after a power failure":

2. You have a way of reliably determining the Z position of your printer
   -> use G28 XY to only home X and Y and G92 Znnn where nnn is the current position of Z to tell the printer the current Z height without the need of the homing process for Z

Yup But I asked what parameters should I use. I need to know what Z coordinate was beore power loss.

[wilriker]

@anraf1001 This is basically under discussion in this thread. Look at my (currently) last post in this thread, there I explain where you can find this information.

@dragonn Yes, you are right, this is currently a rather tedious and manual process in case you cannot home your printer with something on the build plate. I am in the lucky position that by coincidence I can home my printer in Z if Y is at max unless that print would basically cover the whole build plate (it probably never will). So in my case I have

G28 XY             ; Home X and Y regularly
G0 Y216            ; Move Y to the front maximum
G28 Z              ; Home Z now where the head has least chance to hit something

in my resurrect-prologue.g. But as I said, I am lucky here.

[dc42]

Another option is to add a Z-max homing switch to use for homing Z only after power recovery.

I could add a G92 command in resurrect.g to set the head coordinates to the location at which power failure occurred. This won't take account of any Z-raise that your your power fail script attempts to do.

[wilriker]

@dc42 said in Configuring "resume a print after a power failure":

I could add a G92 command in resurrect.g to set the head coordinates to the location at which power failure occurred. This won't take account of any Z-raise that your your power fail script attempts to do.

I have a feeling that this should then be configurable or happen before resurrect-prologue.g is called so that the user has means to override/prevent this. Other than that I like the idea.

[dc42]

@wilriker said in Configuring "resume a print after a power failure":

@dc42 said in Configuring "resume a print after a power failure":

I could add a G92 command in resurrect.g to set the head coordinates to the location at which power failure occurred. This won't take account of any Z-raise that your your power fail script attempts to do.

I have a feeling that this should then be configurable or happen before resurrect-prologue.g is called so that the user has means to override/prevent this. Other than that I like the idea.

I'll write that command immediately before the call to resurrect-prologue.g.

[Knaudler]

hi

is it possible to use an break on Z ?
so with power or start print, the break ist open (magnet ?/Solenoid)
and when power fail, duet activates the break (magnet off) and saves the position ?

[Phaedrux]

@knaudler if your brake can be triggered by the duet you could modify the commands to run on power loss to trigger it.