[BFW-5545] [BUG] MK4 keeps requesting filament path to be cleared upon empty spool change

[bolsoncerrado]

Please, before you create a new bug report, please make sure you searched in open and closed issues and couldn't find anything that matches.

Printer type -

MK4

Printer firmware version - [e.g. 4.0.5, ...]

Any

Original or Custom firmware - [Original/Custom]

Original

Optional upgrades - [e.g. Filament Runout Sensor]

Stock Factory Assembled MK4

USB drive or USB/Octoprint

USB

Describe the bug

1. Start a print
2. Spool runs out of filament
3. Filament sensor kicks in
4. Filament is removed BUT
5. even if you reply YES to the "was filament removed ok?" the printer KEEPS asking you to remove filament. Nothing helps, the dial, the clicky, nothing. Only a RESET, ruining the print.
6. Upon rebooting filament sensor works as intended, so there's no debris no filament messing the sensor, no nothing.

How to reproduce

Read above.

Expected behavior

Since it has happened to me already TWICE and non correlative, I asume this is a firmware glitch. I already opened the idler door and removed any filament (first time none was there, second time a section was there, I chose NO to the question, but apparently it didnt detect I removed it), blowed air, moved filament on the port hole, nothing helps when the bug is present. ONLY Reset button fix the issue and once the printer reboots, everything works as intended.

G-code

No particular gcode.

Video

Next time it happens I'll tape it.

[marcelismus]

+1

But after the last time the restart didn't help, sensor calibration also shows always "NO". I need to push the filament to the left, but after that the calibration failed. After a little test print I retried with success. ¯_(ツ)_/¯ I'm wondering if it's a firmware bug or a hardware problem or both...

[bolsoncerrado]

@marcelismus what fw version did u have issues with? mine is 4.6.1 -- i'll install alpha3 now.

[unclej84]

I am having the same issue with 4.7.1 firmware - goes to park position, unloads and shows confirm screen (selected "yes") but still shows to clear the path

[unclej84]

Made a test with colorchange today and there the filament change worked - don't know what the difference between both cases (color change <-> filament runout) internally is

[bolsoncerrado]

Idk either but I lost another print today again, pretty frustrating.

[unclej84]

@bolsoncerrado are you on alpha3 now or still on 4.6.1?

[bolsoncerrado]

Now on 4.7

[arcenik86]

Confirmed issue on 4.7.1, however I did get it to clear after inserting and removing filament quickly a few times. Before doing so, verified there was no filament in the idler area. New MK4 build, third print.

[bolsoncerrado]

I tried that technique and it didnt work for me :(

[IftiBashir]

I would consider this a rather serious issue. Have Prusa responded?

[bolsoncerrado]

No :(

[zhiyao]

It happened to me as well twice.

I realized the filament sensor is not calibrated for me and will always register as a detected filament.

Temp Fix: The only way to fix this is to do a control > filament sensor calibration.

Proposed Fix: There should have been a way to overwrite the sensor during such an issue.

[unclej84]

Firmware 4.7.2 got released. Has anyone already tested, if it is fixed? Release note does not mention anything related.

[bolsoncerrado]

Why would they? No one from Prusa ever commented here :(

[MilleniumDawn]

Same issue on v5.0.0-alpha4. Stuck on requesting filament path to be cleared.

[derthomers]

same here on 5.0.0-alpha4. pushing in and pulling out a piece of filament multiple times worked in some cases. had it 8 times in 2 weeks. also on 5.0.0-alpha1..3. that really tends to ruin your print if you want to empty a spool completely before switching to a new one.

[bolsoncerrado]

Happens also if you plan to leave and don't trust enough on the filament sensor stopping the print while away if spool dries out, hence if you manually opt to change filament manually, sensor may ruin the print awaiting you remove the filament you've already acknowledged to have removed correctly.

Pretty absurd altogheter.

[arcenik86]

Just wanted to comment that this is easily duplicated with a filament change from the printer menu as well. Even after you confirm the filament is removed (yes on the prompt), you have to toggle the filament in and out for the printer to recognize nothing is loaded.

[bolsoncerrado]

What I just said yep.

[micro17]

Had the same odd behaviour today. Would be nice if Prusa can response if this is a software or hardware bug.

For me it cleared after putting the filament in and out multiple times

[bolsoncerrado]

SOunds to me they have a severe hardware design issue with this filament sensor placement :(

This radio silence is nothing but worrysome!

I also wonder if XL people is having the same issue...

EDIT: Apparently, they're:

https://www.facebook.com/groups/Prusai3users/posts/2417025891815211/

[marcelismus]

I think the problem is that the sensor is blocked by fine strings of unloaded filament. It often works if you put filament in and out many times or print a little longer. Whether design flaw (and as far as I know, the sensor cannot be reached "just like that") or just too sensitive, no idea. But a "No filament loaded" button is necessary.

[bolsoncerrado]

Well it's quite absurd the screen asks you "was the filament removed correctly?" just to ask you again to please remove the filament from the sensor path when you can't clearly reach it AND no other option (specially mid print) left than pray that wiggling multiple times the new filament will trigger the sensor :(

So I think it's both a hardware design flaw (like having a hole that gravity will end up filling with dust and such anyway) and a firmware issue...

[FliesWithWind]

+1 on this. It just happened to me when I runed out of filament. Wasted 24h of print....

[HaWiWe]

I had this happen a few times and could fix it by sticking the filament in and pulling out again a few times. It seems the hall sensor does not spring back, you can notice that there is no resistance when doing the above. At least that's what I think is happening.

[unclej84]

In the Podcast they just mentioned that new final firmware with input shaping will be released (around) Friday - let's see if this included

[Shushuda]

I just had this issue on 5.0.0-RC. The ball didn't spring back, there was no resistance. Inserting and pulling out a looot of times very rapidly finally made it spring back, resistance was there and the printer started detecting filament correctly.

[bolsoncerrado]

I think all these posts prove they have a serious hw design issue...

[Nulifier]

Something that worked for me to prevent the print from failing is to bypass the filament sensor when it gets into this stuck state.

What I did after receiving the remove the filament from the filament sensor message:

1. Remove the LoveBoard-cover-right using the M3 screw on the right side of the extruder. (Link)
2. Unplug the filament sensor cable from the lower connector. I found a pair of tweezers helpful. (Link)
3. The message should clear and you should be left with the normal load filament message
4. Install the filament sensor cable again
5. Reinstall the LoveBoard-cover-right (Its important to do it now as once you load the filament the extruder will start zipping around)
6. Load the filament

Obviously this involves some delicate work in the middle of a print and take your own precautions but it did allow me to resume a 6 hour print after hour 4. But definitely needs to be fixed on a hardware or software level.

[bolsoncerrado]

Perhaps a cleaner, less risky way would be to add some small reset button somewhere to cut the power just enough for the message to clear....

[bolsoncerrado]

Perhaps a savaged mechanical endstop? 😂

[bolsoncerrado]

If anyone has links or names or part numbers to the male and female connectors may be I can order some and test a bypass system for this until a solution comes out. Granted this issue was opened on July 7th and no one from Prusa has chimmed in & granted we have had 2 firmware revisions in between i think it will still take a while for us to see a feasible solution and not just a temp fw patch...

[Nulifier]

If anyone has links or names or part numbers to the male and female connectors

Pretty sure this is a Molex 5025850370

[bolsoncerrado]

Cool, what about the male One? :)

[bolsoncerrado]

This? https://www.digikey.es/en/products/detail/molex/5025780300/2818999

[Prusa-Support]

Thanks for reaching out to us.

This seems to be a duplicate of https://github.com/prusa3d/Prusa-Firmware-Buddy/issues/3056. I'd rather close the first issue in favor of this one, as this duplicate grew in popularity.

We acknowledge the possible presence of a problem based on the number of reports on this issue. However unfortunately we have not been able to confirm the presence of a bug so far.

We are working on this. If you encounter this issue again though, please follow these steps before reporting.

• Re-inserting the filament several times may knock off debris from the filament sensor mechanism.
• Find the cleaning hole on the top of the Nextruder, in the middle of it, next to the brass ring, and blow canned air through it.
• As the last resort, you can remove the "Nextruder sandwich" (brass ring + plastic parts, so you don't need to repeat the PG alignment) and remove the filament sensor spring for deeper inspection and cleaning.

Also, make sure you have tested the most recent firmware version. Consider testing the non-final versions available on GitHub if you don't mind (could be unstable).

Please refrain from disconnecting components or touching electronic components while the printer is powered on as this may cause damages.

Michele Moramarco Prusa Research

[bolsoncerrado]

Wiggling constantly is the only thing that worked for me so far, as long as I have patience and I don't move the print head accidentally during the process.... ::

[bolsoncerrado]

And btw I think the "bug" is actually a hw design flaw as one of my 2 mk4 started failing almost "next day", so no many prints on it... :/

[mataksik]

5.0.0RC same problem. Helped only disconecting filament sensor. 7h print was ruined

[bolsoncerrado]

5.0.0 FINAL IS version:

Not only I keep having the same old issue that now I have a NEW one too:

Printer requests to change filament when filament is still present and printing!! :( :/ :(

[marcelismus]

Very rare bug since the 1st 5.0 alpha...

[enerbe]

I can reproduce it. Made a video. https://youtu.be/0cFO8x1V8tU

It is not even needed to be in the middle of a print. The video contains the process to reproduce.

[bolsoncerrado]

Not the same last issue I reported here but yeah, pretty much no way out.... Unless you violently start moving up, down and dragging the filament on the sides until the sensor realizes you're moving it....

But having to reload filament midprint because the printer feels so is just meeeeh

[ladislav37]

We have new MK4 (with 5.0.0 fw ver.) and have the same issue.. It looks like this is not a fw/sw problem but hardware... Most probably spring force is too low and it will not push the ball to correct place for filament detection. But this is only my assumption, because I can't find online any schematics or models for MK4 and I don't want to disassemble printer extruder right now.. :-)

[bolsoncerrado]

Wdy mean schematics or models? To do what?

I guess you can take this as reference and perhaps source a stronger spring hmmm

https://help.prusa3d.com/guide/5-nextruder-assembly_434014

[ladislav37]

Och, now I can see from zoomed picture, that filament sensor is hall sensor, so it is clear. When you remove filament form the printer, the metallic ball will not move back on the place in front of the sensor and sensor will not detect it presence.. Therefore printer "thinks" that filament is in... So, i think the simplest for now it is order some springs from AliExpress (outer diameter 3mm) with length more than 9mm and try to exchange it to provide more pushing force towards hall sensor...

[bolsoncerrado]

Plus the fact there's an opening on the extruder housing and any dust or buildup or even filament particles when pulling out the filament may collapse the system... IMHO the whole thing is flawed.

You may have issues if you put more pressure thru a new spring and the actual issue is ball does not pull back.

[JonasFischer1]

I currently have the same issues on the MK4. During printing the filament sensor stops the print at random times and only allows printing again after a reset.

The only thing that worked for me was to turn off the filament sensor in the settings menu.

[eklynx]

I just ran in to this as well, changing filament mid-print due to spool running out, but it wouldn't recognize the filament was removed and i had to reset/abort.

[bolsoncerrado]

Next time instead of reset try inserting and removing and wiggling the filament quickly until sensor triggers...