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MMU loads filament but doesn’t notice  

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Wc
 Wc
(@wc)
Member
MMU loads filament but doesn’t notice

Hi all,

 

I have a MMU2s with a Prusa mk3s+, and it has been printing fine in both single and multi-material mode for a while. I tried to load ASA to the nozzle, but it loads it, squirts out filament, and then tries to pull it back out, but can’t.

 

The printer loads the filament to the mmu just fine, but when I try to load it to the nozzle, it runs the filament down to the extruder, and starts extruding it. The extruder appears to run continuously, while the mmu appears to be feeding filament in, then stopping, then continuing. The print head occasionally vibrates, and after a few grams of filament have been deposited on the heat bed, the printer attempts to pull the filament out of the print head. It can’t. The mmu spins and makes the loud sound, but the filament appears to stay put. Furthermore, the extruder seems to be still trying to extrude the filament. Eventually, the printer says “mmu needs user attention” and I have to manually pull the filament out of the printer, then restart it. The piece of filament I pull out has several large gouges where the mmu would pull it, and is a bit rough by where the print head would be. After the filament is out, there are large deposits of asa shavings on the bond tech gears in the print head and on the mmu. The loading process doesn’t work with pla either.

 

I have tried firmware updates, checking the filament sensors, and cleaning and greasing the gears. No progress yet.

 

Any help would be appreciated.

This topic was modified 8 months ago by Wc
Posted : 05/07/2023 10:10 pm
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: MMU loads filament but doesn’t notice

The filament sensor on the MMU2 is finnicky... I had so much problem adjusting mine, that I modified the  sensor to have an LED on it. 
there is a sensor display on the LCD, but I find it difficult to use... 


I used a 5 volt LED and soldered it across the pins on the Sensor. Like below


here is a link to ebay for 5volt LED's 
https://www.ebay.co.uk/itm/123200004146?hash=item1caf4ae032:g:lLwAAOSw3EVbKObV&amdata=enc%3AAQAIAAAAwJA5AZvY2mtkfDf%2BFZ4BkcqpCEjqiBjZ7D%2B5Tg%2FvsynWPGxLBO0afxl%2BR0Yl3vLxMWk7Qkf%2BoJSUo3bWY8drutDmOsVr%2FZE%2FSyfUYh5%2FRfmdzo0zD0cqQppuFh8ZGMPUBLK5YN3od3%2BsTk3%2FF%2F9Ww6QuLwNFONscHfHVLBVWTfa3px6A0pNQB74e5g%2BwGSon%2FsDHwWp3Sl0ki2u1q9Oi1eUGSsYydBgu2y3%2BCFVxoXsKcPiCYhGTdSC1yjA6ZtiUGg%3D%3D%7Ctkp%3ABk9SR9jk4oKlYg

Zaribo also  offer a filament sensor with integrated LED. 
https://zaribo.com/sensors/546-5033-zaribo-smart-prusa-filament-sensor-for-3d-printers.html#/177-smart_fs_accessories-none
regards Joan

if the MMU2s does not see the filament sensor activated, it keeps trying to feed filament, this may be the issue you are seeing. unfortunately the extruder and the MMU2S feed filament at different speeds. which leads to the filament being chewed up, if the handover from MMU feed, to Extruder feed, fails. 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 05/07/2023 10:37 pm
Wc
 Wc
(@wc)
Member
Topic starter answered:
RE: MMU loads filament but doesn’t notice

@joantabb

I just checked both of my sensors according to the instructions and both trigger reliably. How did you attach the led to your chimney? Do you have a custom part?

Posted : 05/07/2023 11:19 pm
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: MMU loads filament but doesn’t notice

I simply soldered a 5 volt LED between the +5volts and Out pins on the sensor. 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 05/07/2023 11:34 pm
Hello
(@hello)
Noble Member
RE: MMU loads filament but doesn’t notice

@joantabb i belive @wc ment the plactic 3d printed bit on top of the fillament sensor the one with the led in it see bellow

see above

Please help me out by downloading a model it's free and easy but really helps me out https://www.printables.com/@Hello_474427/models

Posted : 06/07/2023 1:25 am
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: MMU loads filament but doesn’t notice

Ah that, 
I used a standard twist  drill, and made space for the LED to poke through...

Simples...  
🙂

Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 06/07/2023 9:01 am
Wc
 Wc
(@wc)
Member
Topic starter answered:
RE: MMU loads filament but doesn’t notice

I’ll have to try the LED later when I have more recourses, but for now, I tested the ir sensor like in the manual, and it works completely fine. Same goes for the filament sensor in the mmu. I don’t think its a sensor issue.

Posted : 06/07/2023 8:40 pm
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