Adaptive Extrusion Feed

Greetings,

I would like to be able to vary the extrusion feed rate based on the diameter of the filament in real time. It would allow some compensation for uneven filament.

I vaguely recall reading about the idea some time ago but I can't remember where.

How hard would this be to add to say Marlin? Seems like it wouldn't be too difficult to feed in an analog signal from a measurement device and vary the extruder stepper in response. Thinner than what it is set for and it will add step(s), thicker and it will omit step(s)...


Cheers,

Jeshua Lacock
Founder/Engineer
3DTOPO Incorporated
[3DTOPO.com]

The problem is that filament that varies much in diameter tends to be low quality and oval-shaped. So you would need to measure the diameter of the filament in different directions. Also, filament that's low quality, oval-shaped, and has a variable diameter tends to have fillers and contaminants in it, making it less than ideal for printing for a number of reasons.

However, if you were producing your own filament with a Filastruder or something, then with a system like you propose the filament production wouldn't have to be nearly as accurate. Again though you would want to be able to measure for ovalness.

Here's one thread where someone did some experimenting with real-time filament diameter measuring: [forums.reprap.org]
He mentions integrating the variability into Marlin, but does not provide code or how he did it. He also only has one post on the forums, and doesn't appear to have posted again since.

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Sensing the diameter would be the biggest challenge, the rest is just software..

The capacitive approch seems to be the way to go, as this would give you volumetric measurements.

Edited 1 time(s). Last edit at 03/12/2014 12:01PM by Ralf.

Quote
Ralf
Sensing the diameter would be the biggest challenge, the rest is just software..

Yep. If you have a known distance between the measuring device and the melt-zone of the hot end, real-time adjusting of extruder feed rate based on the detected diameter and known distance (adding a delay to the adjustment) should be fairly trivial.

Quote
Ralf
The capacitive approch seems to be the way to go, as this would give you volumetric measurements.

Getting a true volumetric (or cross-sectional area) measurement would make the software side of things easy, as I mentioned.

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you could measure the thickness with a pair of of pinch wheel that measure the diameter. I am sure you could use some cheap digital calipers to build the design and then send the data to the board. Honestly for all the work you are going to put into it, you will be better off using good filament.

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