This seems like a firmware bug to me, but recently whenever I reach near the end of a spool, instead of printing through all the residual filaments, my AMS would start to try to roll back. However the filament has already detached from the tape, so now it’s basically hanging free. The AMS trys to roll the spool back to unload the filament but never trys to load it back again because the retraction/unload process cannot be done (because it thinks the filament hasn’t been unloaded, as there’s no connection between the spool and the filament, so rewinding the spool would not do anything to the filament, and the filament would not create an restriction on the spool movement, which I think triggers the unload sucess/retraction success signal).
I’m not entirely sure if it’s only related to the new firmware, but I didn’t notice it with previous ones.
My assumption is that:
Filament reached end of spool stage 2. Tape or end of spool hook (to hook the filament on the spool) caused some restriction on spool movement
AMS detected that so it tries to go back and retract, rewind the spool
AMS tries to retract the filament, but now the filament has been detached from the spool & tape end, so it’s basically just rewinding the empty spool.
AMS finds out it cannot retract the filament, so it gives up.
reports an extrusion error (on my printer it thinks that the nozzle has been cloged, but that’s not true)
I think the main issue is between step 4 and step 5. It should try to reload the filament if one or two retries failed. So it should be an Unload → Load → Unload → Load → Unload → report error process. And a failed unload should result in a new load, not endless unload then error out.
Is the filament passing the feeder? If it doesn’t pass the feeder then it still thinks it can retract. Has your print ended with that couple inches of filament sticking out of the feeder but not on the spool anymore?
It’s paused, probably because a tangle detection/untangle operation was triggered by that extra pulling power from tape. However during the untangle process the spool got detached from the filament strand, so the untangle process could not be done because its retraction would never work.
This happened to me, had another spool ready to take over since I knew it would run out. Come the next morning print is paused, filament was loose around the spool, seemed to have pulled itself off the tape as expected but think you are right it felt the resistance and did a retract and then got stuck trying to feed again since the pool was free sunning with the filament disconnected.
I can imagine a scenario where the filament has already been pulled off the spool and the end has already passed the AMS feeding system, and then a material change has been triggered. Rewinding is not possible anymore because there is no filament in the AMS feeder.
I never realized that this is a scenario that could happen and cause an issue.
In case it would have been pulled off the spool and the filament is still in the feeding system of the AMS, it is able to pull the filament back into the AMS but it will not be rolled onto the spool anymore. That can cause an issue also and could even interfere with the movement of other spools.
I make it a habit to dig up the end of the filament when its close to the end and snip it. Ive had issues with bambu tape but also generic filament with a too stiff of a fold that would jam the AMS.
This just started happening to me back to back on 3 spools in a row with Sunlu filament. I previously ran through about 80 of the same Sunlu spools with no issues and now all of a sudden this starts happening.
It’s been some time now since you posted this, any fixes?