Power off resume

Developers
1

General goal: implement a progress save every layer change to allow print resuming after a short black out, brown out and also a software crash.

Many have said that a power resume won’t work well since the pi won’t know the actual location of the printhead. I’ve come up with this method which I think is balanced between easy to implement and also effective:

On every layer change, save layer z

On power back up:

  1. Check if the max layer Z of last print is not equals to save file layer z
  2. If different, immediately raise bed temp to normal printing temperature
  3. Raise Z by something small like 5mm
  4. Wait for user to confirm resume
  5. Home XY (Z should automatically move up with the XY home)
  6. if printer has both Z max and min endstop, home to Z max, otherwise decrease Z motor current and move up by Z max height, and then set current Z pos to max height before resetting Z motor current.
  7. Move Z back down to where unfinished layer started
  8. Find nozzle temp and fan value of last print and set it to that
  9. Get the gcode automatically after the layer z and execute from there

Currently this is what I’m working on with the part that executes every layer. I’ve written it with what I mostly learnt from going through existing klipper extras scripts.

class SaveZHelper:
    def __init__(self, config):
        self.printer = config.get_printer()
        self.printer.register_event_handler("klippy:connect", self.handle_connect)
    
    def handle_connect(self):
       kin = self.printer.lookup_object('toolhead').get_kinematics()
    
    def do_save_z(self):
        toolhead = self.printer.lookup_object("toolhead")
        curpos = toolhead.get_position()
        cur_z = curpos[2]

        # todo read from cfg
        with open("/home/user/progsafe.txt", "w") as save_file:
            save_file.write(str(cur_z))


class SaveZ:
    def __init__(self, config):
        self.printer = config.get_printer()
        self.SaveZHelper = SaveZHelper(config)
        gcode = self.printer.lookup_object('gcode')


        gcode.register_command("SAVE_Z_PROGRESS", self.cmd_SAVE_Z_PROGRESS, self.cmd_SAVE_Z_PROGRESS_help)


    cmd_SAVE_Z_PROGRESS_help = "save current z progress"
    def cmd_SAVE_Z_PROGRESS(self, gcmd):
        self.SaveZHelper.do_save_z()
    
def load_config(config):
    return SaveZ(config)

Does anyone have a good idea where I should start with the resume part? I’m quite new with python so could someone experienced outline what happens codewise when the printer starts? Thanks for any help in advance.

2

You may have a look:

3

Yeah that seems quite possible but I’m trying to find a process of automating more of it. Is there an easy way to do anything on startup automatically such as my suggestion of auto heating the bed though?

4

Hello,

It could be possible to get your klippy log, and recover the stored Z that way. That seems possible, but idk.

Hope this helps,
Blake

5

You can fairly easily implement this using macros and some minimal slicer support. Basically, you can do something along the lines of

[save_variables]
filename: /home/user/progsafe.txt # your filename

[gcode_macro DUMP_Z]
gcode:
    SAVE_VARIABLE VARIABLE=saved_z VALUE={params.Z}

Then in the slicer layer change gcode you can add DUMP_Z Z=... command with the next layer Z height (there should be a placeholder for that in your slicer). Then the file /home/user/progsafe.txt will contain a human-readable value of the last saved Z height.

1 Like