Fillament-thickness sensor



  • maybe i am not the first to think about that but this idea just crossed my mind:
    a sensor that measures the thickness of the filament during printing and adjusts the extruder multiplier accordingly.
    Could be incorporated into the already in development filament-sensor



  • Yes it is something that would help a lot, and others - such as I - have thought about it but the difficulty is in the execution rather than idea in this case. Rollers are a start, but the dynamics of the filament motion, and varying hardness is difficult to deal with. likewise as the laser filament monitor illustrates different filaments and colours respond differently to the laser emission.



  • i thought about something like that:
    0_1551186231178_thickness sensor.pdf
    with varying thickness, the lightbeam moves, a reciever similar to the IR probe then detects the diffference.



  • You need to measure in 2 orthogonal directions, as the filament may have the correct section, but not being a circle... In this case, measuring in one direction only will give you a wrong indication.


  • administrators

    It's been done before, using linear CCD sensing elements. As @fma says, you need to measure the diameter in at least 2 directions.

    However, good quality filament has fairly closely controlled diameter these days, so I'm not convinced that monitoring filament diameter is worthwhile. For example, rigidink's 1.75mm PLA is controlled ot +/-0.03mm, which equates to +/-1.7% in diameter or about +/-3.4% in area. Prusament is +/-0.02mm diameter, so even less. Ian (@deckingman) did some tests that indicated that even quite large changes in extrusion rate didn't have much effect on the print.



  • @dc42 said in Fillament-thickness sensor:

    Ian (@deckingman) did some tests that indicated that even quite large changes in extrusion rate didn't have much effect on the print.

    Actually Michael Hackney did it much more scientifically and more in depth that I did - http://www.sublimelayers.com/2017/12/musing-on-under-extrusion-prepare-to.html

    Definitely worth a read but if you are short of time I hope Michael won't mind if I post this extract - quote:

    "The bottom line is, FFF 3D printing is surprisingly robust to non-trivial under-extrusion in the range up to 10% under-extruded, and possibly higher depending on your requirements."

    IMO, over extrusion is very noticeable but I agree with Michael regarding under extrusion. So much so that I simply run 95% extrusion multiplier as my default setting and very rarely change it.



  • I am working on a sensor that measures in more than 2 axes and should eliminate all under and over extrusion issues for good. It even has the benefit of allowing a user to use random diameter filament without having to worry about issues.

    Even good quality filament is far from consistent. It may be '1.75mm', but has an egg shaped cross section or non consistent cross section across the length of the spool.

    This also doubles as a filament run out sensor. 🙂



  • Manufacturers of extrusion products (including filamtent) use for example sensors from sikora, which operate on the principle as shown in the following image

    alt text
    The product creates a shadow on the CCD line sensor. In this case, the number of dark pixels on the line sensor is equivalent to the diameter.

    Decisive for the measuring accuracy is the ccd sensor


 

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