Laser filament monitor
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I'm sure that the prototypes will be subjected to rigorous testing, so if detection needs to be improved the necessary steps will be taken.
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I like the simplistic idea of the laser. I have one of the magnetic sensors and had to take it off because it drove me nuts when the magnet would slide away from the sensor. Although when it work properly it worked well. Its going on my delta as soon as I finish it.
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Hi folks, very interested in this when/if it reaches production. I was just wondering though about the possibility of using some sort of ultrasonic sensor which could detect density and hence be more accurate?
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I don't think you could detect filament motion using ultrasound because the filament surface s too smooth. Also you would need to use high frequency ultrasound to get the wavelength shorter than the filament diameter.
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What about using OpenCV? This is similar to the laser sensor, but it would allow to measure the diameter. It would need a decent GPU-based board (like NVidia's ones). Who said overkill?
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hi David,
would it be an issue if laser versus transparent filaments? i mean even a tiny light can trigger the sensor even if the light is refracted by a clear transparent filament. just a thought. -
I tested with a transparent PETG filament and the laser had no trouble tacking it. Black filament was more of a problem.
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interesting. so the darker the color there would be a higher inconsistency?
would like to get my hands on one to tinker with. -
Currently i have some spools of black PLA filament which tends to clog. Perfect time for betatesting if you need someone running it under "real user conditions".
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Apparently pet-g is the hardest filament to detect. So, if you get that one done, you are golden.
I wonder if putting the sensor past the extruded on a bowden setup makes it read better (since now it has tooth marks that might make it easier to see)
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Yes that occurred to me too. However, the optical sensor would need to be protected from filament dust produced when the hobbed shaft grinds the filament.
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what about a laser before the reader to etch little lines into the filament?
nvm, you’d need quite the laser to make that work….
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Yes that occurred to me too. However, the optical sensor would need to be protected from filament dust produced when the hobbed shaft grinds the filament.
And it wouldn't work after a RDD like the Nimble or Flex3drive so it has to go before them
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You could create something secondary to create the notches, then clean the filament but that likely just creates other issues and failure modes.
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Anything new about this apparatus?
Will it be prefered against the old version? and when will we normal (actually maby not so normal) humans be abel to get hold on these things? -
At present the laser sensor is not as reliable as the rotating magnet one. We have some more work to do to see whether we can improve it.
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Since the laser approach seems to be causing problems the suggestion of using ultrasound may not be as impractical as you think.
It is commonly used for highly accurate non-invasive flow measurement of gasses and liquids which you have to admit are pretty smooth. Sensing is based around doppler effects of minor differences in internal density.
The main advantage if it could be made to work is that it would work through the feed tube - just clamp on and measure.
I don’t know how well it would handle highly homogenous filaments but I suspect there would be suffucient internal structure to make it work.
You’d also have to source a suitable transducer / sensor system.
I don’t know if you can get transducers small enough, the pipes in a domestic gas meter are around 25mm so our sensor would need a field of operation 10 times smaller though they may be made for lab equipment.
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Why do we want/need a filament sensor?
Me personally, to stop the print if the flow of filament stops for any reason, e.g. due to a clocked nozzle.
If the sensor can measure the exact length of filament extruded, that would be totally cool and open the door for dynamically maxing out the feeder speed for any filament. That would be a dream come true…
But, how about making that a requirement for filament sensor v2?
For starters, detection of that blocked nozzle can probably be accomplished with less fancy measures, and likely cover the immediate needs of most users. How about adding a timer? If no movement is detected within 1-2 seconds of the stepper engaging, then something might be wrong. This should greatly reduce the sensitivity requirement for any type of sensor. Due to the normal pressure between extruder and nozzle, a short period of time should have no significant impact on the ongoing print, as filament will still be flowing.
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The ultrasound idea from Markdnd is interesting, but isn't it so that ultrasound transducers have problems with linear movement? They detect rotation (not possible in this scenario) and radial movement, but an object passing by in a straight line is not so good.
I might be wrong, but believe that an ultrasound solution would require a mechanism to "wobble" the filament on its way past the transducer. If that is accomplished, then a disc type transducer might work. These are used in many applications, e.g. string music instruments, and are available in diameters down to about 10mm. They are also very thin and cheap.
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The primary reason I want filament monitors is to detect inadequate filament feeding, whether from partially blocked nozzles, clogged hobbed wheels, tangles or some other cause. I have never yet had filament break, and I generally know if there is enough on a reel for the print at hand.
I designed and built a filament sensor that worked very well on the Zesty Nimble and e3d Chimera equipped cartesian printer I upgraded from RAMPS to Duet. These used multiple tiny (1mm diameter) magnets and hall effect sensors to provide 12 pulses per revolution (about 7mm filament feed). It was fully reliable and detected filament feed issues of all types and worked with PLA, ABS and PETG filament without issue.
Photo shows a dual mount with the right hand sensor installed. The tiny magnets are just visible.Unfortunately these were not compatible with the Duet and I simply don't have the skills to write the necessary code to do this so am keenly awaiting the Duet version.
(edited to add) Although I never implemented the second sensor, the boards I used are rotary encoders so can detect forwards or backwards movement and could thus measure retracts and normal feed. I'd be very happy to share the designs if anyone wishes to do the software to enable them to work with the Duet.
Richard
