Z-axis calibration after power failure
It would be good if the Z-axis was recalibrated after a power outage. I'll explain the situation. I wanted to resume printing (since I wasn't home), so I plugged the printer (MK4) into the socket and set it to continue printing. Meanwhile, I was doing something near the printer and accidentally bumped into the bed, causing it to shift, and the printer started printing slightly off. So, I unplugged it again and then plugged it back in, and the printer raised by about 3mm and moved very slowly to 0 0 0 and the opposite corner. Then it started printing but slightly higher than it should have. So, I tried turning it off and on again and manually moving the printer up in the meantime, to see if it would return to the original position when I hit "Pause" or "Remove filament." Fortunately, it did not. So, I wanted to suggest that it might be good for the printer to record its position before pausing or changing the filament (in my case before a "power outage") and then return to that position (Z) afterwards (and if a power outage occurred, it would also recalibrate the Z-axis).
RE: Z-axis calibration after power failure
Your idea of having the printer record its position before pausing or filament changes, and recalibrate the Z-axis after a power outage, is a great suggestion for preventing this kind of problem. Maybe this feature could be added in future firmware updates to help avoid the kind of shift you experienced after bumping the bed.
This is a user to user forum, any feature request should be made on Prusa's github...
But I fancy this is a non-starter. The printer has no way of detecting any manual head movements when switched off - so calibrate? er, it also doesn't know where in relation to its current position, the part completed print is - cue new crash. The restart-at-the-next-instruction power panic recovery method has the best chance of succeeding but it can never be 100% certain.
Cheerio,