Prusa-firmware-buddy: [FEATURE REQUEST] Power panic

[hawwwran]

Printer type - [MINI]

I thought power panic is MINI's feature already. Found the hard way it probably isn't.

I expect the same behavior as MK3s has. Rise the print head and continue once the power is restored.

[np22-jpg]

I'm not a dev, however I doubt that in the case of a blackout there would be enough residual power remaining in the (small) PSU that the mini uses.

[derenma]

@npgoalkeeper It's listed as a future software upgrade here: https://www.prusa3d.com/original-prusa-mini/

[yonie1]

I looked at the schematic an the pin 'BED_MON" could be used to detect a falling supply voltage and cut heater power immediately if detected an save the position. But I think this will sadly never be as good as the mk3 that can detect a power outage on the primary side and therefore has a larger Power reserve to work with because the primary side caps are still charged

[d0ugak]

Considering the power supply that is supplied with the mini doesn't have the same hardware as the power supplies in the i3. The caps that can keep enough power stored to safe the printer and store its last status before the power is cut. There is probably no way to implement this exactly as it is on the i3's. If they did implement such a feature it would probably be something along the lines of constantly writing either to eeprom on the buddy board or a "status file" on the thumbdrive which file it is reading from and which line in the file it last processed. (lots of wear and tear for flash memory) That way if power was cut, it could read from this eeprom or "status file" to resume where it left of. My guess is it would not result in the most seamless of resumes depending on where in the tool movement power was lost after the last line read of the gcode file. There is also the issue of the still hot print head just sitting on the part as it cools causing imperfections in the print. Perhaps it might be possible to detect power loss on the power supply as the voltage rail starts to sag and immediately cut power to the heaters to use the little residual power left in the power supply caps to jerk the print head up off the piece being printed. But then there is the issue of truly knowing where the print head is once power is restored. You could program it in that jerk movement to jerk the print head up 1cm, but if there was only enough residual power that the print head only moved up 0.5cm and then on power resume the printer just assumes to move the print head down 1cm and resume printing, it will slam into the piece being printed.

Probably the best way to implement power panic on the hardware that the mini has, is build in support to the firmware to read the status of a USB connected UPS that powers the printer or more advanced ethernet connected UPSs do periodic SNMP queries to the UPS to find out it's status. On powerloss the firmware would be able to detect the UPS is in offline mode, safe the printer, write status out to eeprom or a "status file" on the thumbdrive then pause the print, waiting for either the UPS to go back online and resume. or to be freshly powered back up after power is restored from an extended outage and then resume.