How does the MMU know the filament has broken/run out?
I have a question. How does the MMU know the filament has broken/run out? When it thinks the filament is broken it slides the selector to the side and ejects the filament forward about 2 inches into the open. The screen says to pull the filament out and then push more filament up to do a load. I have had this happen a couple times when some old/brittle filament broke in the buffer or supply tube so somehow the MMU realized it had a break before it reached the MMU.
I reworked my buffer set up. I replaced all the supply tubing with 4mm OD / 3mm ID tube with Festo fittings at both ends. I added the new parts to the buffer for the fittings to screw into and to the back of the MMU. With the reduced friction in the wider tubing and better angles in the buffer the filamen glides through the system with very little resistance. Yesterday I tried a two color print to see how it was working. At about 7mm and after several color changes the printer started beeping. It had ejected some filament forward and the screen says to pull the filament out and then push more filament up to do a load. I checked d all the way back to the roll and there was no break so I clipped the tip and pulled the filament back into the MMU, pressed the middle button to let it load and then the right button to continue. It asked me if the color was correct, I said OK and then it printed the rest of that color. When it tried to change color the same exact thing happened only with the other filament. This went on for about 7 layers with the same failure on each color change. In the mean time I tried adjusting the idler screw tension, blowing air in all the openings in case of bits of filament jamming something, opening the idler, etc. Finally after about 7 layers of this it started working perfectly and went on for 10 more hours and completed the print with no more stoppages.
Hence my question about how it senses breakage. Have I lowered the friction to the point there is not enough tension and it thinks the filament is broken?