Designing an extruder with integrated magnetic filament monitor

nikscha

Hey all,
I am designing an extruder, and I would like to integrate the magnetic filament sensor directly into the housing. I read that the distance between the sensor and the magnet is important, however so far I found conflicting information on what that distance should be. If someone knows, it would be greatly appreciated!
Greetings!

alankilian

@nikscha Page 34 of the AS5601 datasheet says:

The typical airgap is between 0.5 mm and 3 mm, and it depends
on the selected magnet. A larger and stronger magnet allows a
larger airgap. Using the AGC value as a guide, the optimal airgap
can be found by adjusting the distance between the magnet
and the AS5601 so that the AGC value is in the center of its
range.

So it depends on the magnet you plan on using.

It would be a superb idea to make the gap adjustable.

nikscha

@alankilian I already had a look at that datasheet, thanks a lot for looking it up anyway!

Sadly this range is not precise enough, according to other forum posts, this distance should be right down to a tenth of a millimeter.

alankilian

@nikscha How can the distance be specified to a tenth of a millimeter when the sensor manufacturer does not know the strength of the magnet you choose to use?

Can't you build a prototype, measure the AGC value like the recommendation and then you'll know the precise distance.

At least until your magnet vendor varies something a little and then you'll need to adjust the distance again.

infiniteloop

@nikscha

I would like to integrate the magnetic filament sensor directly into the housing.

Assuming that you use the MFM parts supplied by Duet3D, you can refer to the existing 3D models (from Duet3D and @Lo-Fi), but practice tells that you have to adjust the distance until it "just fits“, either with abrasive methods (e.g. sanding) or by adding material. As you make up your own design, simply provide a separate part for the carrier of the MFM board: in a first approach, you can re-print it with a different height, then, for the last micros, sand it until the AGC readings are within range.

dc42

@infiniteloop @nikscha we are changing to a stronger magnet to make the distance less critical. Unfortunately this means that the magnet rotor assembly will be a little longer than before. So you might want to wait until the new version is available before you finalise your design.

nikscha

@dc42 much appreciated!
Will the pcb also change or just the roller/magnet unit?

T3P3Tony

@nikscha the change is just a slight difference in the length of the magnetic assembly. that combined with the stronger magnet gives a adjustment to the housing in one dimension. The magnet can now be a more reasonable gap from the sensor, and it is more tolerant to variations in the gap. I will update the documentation once we have production assemblies in hand to test with, they are under production now.

nikscha

@T3P3Tony sweet! Do you plan to sell the roller separately so that we don't end up with two boards?

Is there any chance I can get a beta-testing unit?

T3P3Tony

@nikscha drop me a line tony@duet3d.com