Laser filament monitor away from direct drive extruder



  • I'm running a direct drive hemera extruder, and I don't think I have the space on my print carriage/drag chain for an indirect laser filament monitor w/o significant rework of the carriage/drag chain spacers, plus the added mass (however negligible next to the hemera itself) is a concern.

    How viable is it to have, say 500mm of PTFE tubing (capricorn or otherwise) between the sensor on a fixed monitor and the extruder? Expected E/R values?


  • Moderator

    It's going to be problematic because the retractions won't be captured as well since they will be masked by the flex in the PTFE tube. Definitely not recommended.



  • I seemed to have it "working" w/ M591 D0 P5 C"e0_stop" R120:350 E4.0 S, although it seems to have problems tracking anything at all when ironing large areas where it'll underreport the amount of flowed filament. Wonder if it's the bearings slipping, the laser sensor not being able to pick up low flow rates, or the bowden tube (I don't think much retraction is happening for this part of the print).


  • Moderator

    @jhnphm said in Laser filament monitor away from direct drive extruder:

    the laser sensor not being able to pick up low flow rates,

    That would be my guess



  • What can be done about this, other than perhaps switching sensors entirely to maybe something encoder based? Unfortunately the magnetic sensor is out of stock.


  • Moderator

    There are mods that let you convert it into an indirect sensor, which removes the filament color/transparency from the equation. A pinch roller is used to rotate against the filament which is then detected by the sensor.

    Such as this one: https://forum.duet3d.com/topic/10042/indirect-bearing-laser-filament-monitor-concept?_=1605579445029



  • I'm actually using the indirect monitor by crash69 from that thread. It looks like it works fine until it reaches the ironing portion of the print where the filament feed rate goes down to about 0.1mm every 10 seconds or so. Might need to figure out how to gear it up to 10:1 unless there's a way to increase the low speed sensitivity of the sensor, or try out the bigtreetech encoder. Or just go without ironing.


  • Moderator

    @jhnphm said in Laser filament monitor away from direct drive extruder:

    Or just go without ironing.

    Could you maybe use the gcode at layer height function to send a gcode to change the configuration of the sensor at the ironing layer to be more sensitive or even disable temporarily? Though that wouldn't be ideal since ironing is prone to jamming due to the slow feed rate.



  • That's possible. I think I'm giving up on ironing for the time being though due to the actual jamming and filament grinding that seems to be happening with my Hemera+Proto pasta (turned off the sensor and it seemed to jam for real eventually).


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