Filament Sensor  

RE: Filament Sensor

Just received MK4 last Friday. I've had this issue since Wednesday, now on hold with support who have told me to recalibrate the filament sensor, which I have already done with no resolution.

RE:

tldr; it's probably something in the firmware or interference in the daughterboard.

Background: was trying to use up some spare filament and thus tried to print the Prusa-supplied Robo Alpaca on the Prusa-supplied USB stick. 6.5 hours went by, filament ran out, asked my nephew to swap to the new spool. He runs a MK3S+ every day so I trust him with the task. He says the UI is stuck on "change filament" despite the filament having been unloaded. He is unable to proceed because the screen is hung. Clicking the wheel makes an audible beep but there's nothing else happening, despite pushing the filament in and out of the printer. So I had to abandon the print.

I come back, remove the failed print, load new PLA into it, cut it near the extruder to simulate a runout. Reprint. It seems to work. I leave it running. Another 7 hours go past, but this time the nozzle is a good 2mm above the print. Filament sensor failed to detect that filament had run out.

Support says to calibrate the filament sensor. I do it.

Third attempt, now with a full spool. Robo Alpaca completes so it's definitely not the Gcode or the USB stick. Remove the print, cut the filament again. Again, MK4 continues to behave like nothing's wrong when clearly filament has run out and there's nothing coming out of the nozzle. 

Reset the printer, and try again. Again, MK4 behaves like there's filament when there isn't any. I go into Sensor info>Filament sensor. I open the idler door. I see that no matter what I do, it says "INS/[some large number]". Once in a while, it will flash "NINS/[some small number]"

Reset the printer once more, calibrate the filament sensor. I go into Sensor info>Filament sensor. With the idler door open, I insert filament. Now, I see it says "INS", and when I remove it, it says "NINS".

So there it is. The current workaround I suppose is to just turn off the filament sensor and make sure you have a full spool.

RE: Filament Sensor

Before the filament sensor can do its job properly,

you need to do a few steps.

Which can be found in the MK4's manual starting on page 22.

RE: Filament Sensor

Any of you guys using the Beta PrusaSlicer software by any chance?

Dont think it should matter, but still…..

RE: Filament Sensor

Please, read the post. It is the pre-sliced Robo Alpaca Gcode from Prusa Research, on the Prusa Research-supplied USB stick. The print completed successfully on a full spool, so that pretty much rules out any slicer problems.

RE: Filament Sensor

I generally always slice myself rather then use any pre-sliced files that come from factory. 

RE: Filament Sensor

My exact situation in the middle of a long print. In the past all I’ve been able to do is reset the printer as there’s no way past the ‘remove filament’ screen.

I’ll be disabling the run out sensor going forward. Not impressed losing 20 hrs of printing.

RE: Filament Sensor

Ouch, that would really frustrate me! 20 hours in and the filament sensor plays up!!

So not even fixed with the latest firmware yet??

Posted by: @matthew-oliver

My exact situation in the middle of a long print. In the past all I’ve been able to do is reset the printer as there’s no way past the ‘remove filament’ screen.

I’ll be disabling the run out sensor going forward. Not impressed losing 20 hrs of printing.

RE: Filament Sensor

Hi all,

Just to add to the pile: my filament sensor does not detects anything anymore. Not sure how long it kept working after the initial self check since I never ran out of the very first spool I used. Then when I tryed to use the "change filament" from the menu, things did not look too good as the printer did not seam to dtect either new filament inserted or old being removed. Now I retried both calibrating the sensor, or doing full self check, both fail, ending in having the sensor disabled.

I was hopping to enjoy this kind of fail-safe feature after switching from very old printer to mk4. I hope someone comes up with a simple fix.

Thank you all for all the infos above.

RE: Filament Sensor

I’m going to test the sensor early on in a print by cutting the filament as it goes through and simulating the end of a roll. I’d hate to be through a time consuming print only to find I can’t change the filament!

RE: Filament Sensor

My sensor is currently working from my kit assembly but it only has under 24 hours of print time on it so it is likely too soon to tell, I saw something about someone blowing air in the little whole near the filament path whole with compressed air and that ended up getting it to work again.

RE: Filament Sensor

If the filament sensor stops responding during a filament change, the fix is to place a magnet near the filament inlet. There is a Hall sensor there that reacts to changes in the magnetic field. It is advisable to calibrate the filament sensor afterwards. In general, Prusa needs to address this in the next firmware update.

RE: Filament Sensor

my today when trying to print it keep triggering and changing filament like every 30 secs. i turned it off so we will see 

RE: Filament Sensor

It's switched off just via the printers menu system?

RE: Filament Sensor

Yes that can be done through the printer's menu.

RE: Filament Sensor

Very true, but I would ask why you (@kevsurp) are having a problem.  I have rebuilt many filament sensors on the MK3S because they did not trigger properly.  You will figure it out.  

I got my sensor working when I assembled it, but it is easy to get it wrong.  This is especially true with 3D-printed parts.  

Posted by: @rene-3

Yes that can be done through the printer's menu.

Posted by: @kevsurp

my today when trying to print it keep triggering and changing filament like every 30 secs. i turned it off so we will see 

 

RE:

Just chiming in to say that my filament sensor on the MK4 seems to be on the fritz as well.  When doing a filament change yesterday, halfway through the print it detected it had run out of filament.  I removed the last remaining bit during the changeout.  It never detected that it was removed and there was no way to manually tell it that the filament was gone.  Locked on the "please remove the filament" screen.  Had to reset the printer and lost my print.

Today, during a reprint, I ran out half way through and it never detected it was empty.  Lost the print again.  Went to try to recalibrate and got to the "insert the filament until the sensor detects it" but it never did. 

I've been running the newest firmware a few days now.  Reset it back to 4.6.4 and filament sensor still didn't work.  Went to calibrate the sensor again and same problem.  Decided to "unload" the filament that was not in it.  It made some noise but nothing came out (because it was empty).  However, when I went back to calibrate again, this time the sensor functioned properly.

Tried the magnet suggestion to no avail as well.  

Not sure what's going on here but hopefully they address this issue quickly.

Mine was pre-assembled FYI.

RE: Filament Sensor

Hey, I had issues with my MK4 (built from kit) that, at some point, it asked me to change the filament every minute or so even though it was inserted. Eventually, it stopped detecting it whatsoever. After some digging, I figured out that "the tubular spacer" in Nextruder was a bit longer than it should be imho. Thus, the Nextruder didn't close fully, and eventually, it caused the filament sensor ball holder to pop out from the heatsink (I'm referring to Step 4).

I don't think I made any mistake building it, considering I reviewed everything twice, so I just used a bit of glue to hold the ball holder assembly in place. It's been working smoothly so far. 

RE: Filament Sensor

Well, i've had no issues at all.  Changing filament etc etc, Today, I let it run out, it noticed kicked out the filament asked if it was successful unloading and is now seemingly not there anymore. magnets, calibration never sees anything come in, it simply does nothing.  I think they have a bad hardware issue.