Filament sensor lever-matte finish?
tl:dr: try a matte finish on your filament sensor lever if you find you’re not getting a consistent trigger from the filament sensor?
I bought a MK3 printer early on in production and I had left the filament sensor turned off pretty much all the time to prevent false triggers. Later, I bought a MK3S kit with the MMU2.0 added and the filament detection works great on that printer. So when the MK3S+ upgrade kit came out, I decided to upgrade my older MK3 to the S+ configuration. I self-printed the parts ahead of the kit’s arrival and when I had time, I installed the new parts along with cleaning and lubing all the bearings. I flashed the latest MK3S+ firmware and ran the setup wizard. Everything seemed to go fine, but the new filament sensor kept false triggering. Kept asking for a filament change before every print and I couldn’t kick off a print with the sensor turned on. I could see I wasn’t getting a solid 1 in the sensor screen of the support menu when filament was loaded. So I followed the help page ( https://help.prusa3d.com/en/article/ir-filament-sensor-troubleshooting-mk2-5s-mk3s_112226 ) and I found that my sensor and cable were working fine but it wasn’t being triggered by the filament sensor lever consistently. I thought maybe the “flag” on the lever wasn’t quite long enough so I modded the .stl of the lever to add a couple tenths of a mm. That didn’t work either. In fact, I think it was worse. With the filament sensor connected but unbolted from the extruder, I could carefully insert the flag of the lever into the sensor and it would just flicker from 0 to 1 and back. Odd, right? I’m fully blocking the sensor but it’s not triggering. I could take a short length of filament or a hex key and block the sensor with no problem. I printed the lever in black PETG on the textured sheet so it was fairly shiny. I took a flat needle file and smoothed off the texture, leaving a smooth matte finish on both faces of the flag. Upon reassembly, I get a solid flip from 0 to 1 and back to 0 when filament is inserted and removed in the extruder. I’m cautiously optimistic that the shiny textured surface was causing enough reflection and/or scatter of the IR beam to cause my issue. I turned on autoload and kicked off a small print, it’s an hour into it and hasn’t asked for a filament change yet.
RE: Filament sensor lever-matte finish?
I found this post when I discovered that - after fully executing the ir filament sensor troubleshooting guide - that I was finding that the filament sensor would flip between 0 -1 ONLY FOR MY SILVER SHINY filament. I am still trying to determine whether that is causing my mid-print load faults. After your mod, did you observe that your sensor was sensitive to the filament type as well as the lever material ? Pardon me if this sounds nuts, but at this point, that's the only factor I can clearly isolate.
Prusa is MK4S w/ MMU3 (formerly MK4 / MMU3, MK3S+/MMU2), 2 Prusa MINI+, Octoprint. PETG, PVB, (some) PLA.
RE: Filament sensor lever-matte finish?
I think there is some validity to the scatter effect impacting the IR sensor. On reprint, I monitored the print process from the Support -> Sensor screen and when I saw a flip from 1-0 on the Fil. Sensor, I turned off the (rather bright) light which is usually placed over and to the right of the printer. This immediately caused the bit to flip back from 0 to 1, and through the rest of the print, the Fil. Sensor reading was as steady for my shiny filament as for my standard one.
After the print completed, I checked the MMU fail statistics, and for the first time saw that there were 0 load / unload failures !
In retrospect, the position of the light lined it up perfectly to reach past the lever of the idler door, and hit the filament behind it.
I am testing again now with the same setup, but a longer multi-material print. If I see no further MMU failures, I will count this one solved.
This has been a wild ride tuning this system. Mechanical issues, I expect; electrical issues, I can handle; firmware issues, par for the course; but the physics problem just beat all 😉
Prusa is MK4S w/ MMU3 (formerly MK4 / MMU3, MK3S+/MMU2), 2 Prusa MINI+, Octoprint. PETG, PVB, (some) PLA.
RE: Filament sensor lever-matte finish?
It’s been working good for me since I dulled the finish on the flag.
I have a couple LEDs mounted to the printer that I leave off once the print is running. I could see where a bright light in the wrong spot could cause issues!