Filament measuring thingy April 24, 2016 01:42PM |
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Re: Filament measuring thingy April 24, 2016 07:20PM |
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Re: Filament measuring thingy April 25, 2016 12:50AM |
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Re: Filament measuring thingy April 25, 2016 05:19AM |
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Re: Filament measuring thingy April 25, 2016 07:19AM |
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Re: Filament measuring thingy April 25, 2016 08:21AM |
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Re: Filament measuring thingy April 25, 2016 08:29AM |
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Re: Filament measuring thingy April 25, 2016 08:51AM |
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leadinglights
As far as audibility goes, I did not have it very loud as I used my signal generator directly and it has an impedance of 50 Ohms, but the sound was a nice melodious note.
Re: Filament measuring thingy August 25, 2020 05:11AM |
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Re: Filament measuring thingy August 25, 2020 09:54PM |
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Re: Filament measuring thingy August 26, 2020 06:01AM |
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Re: Filament measuring thingy August 26, 2020 08:29AM |
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In the case of ABS, the value of dielectric constant was about 3 compared to PLA dielectric constant that reached 2,7 - 2,9 in the case of transparent PLA and 3,1 - 3,2 in the case of white PLA with TiO2. The additive in PLA had a significant influence on the dielectric constant of the sample
Re: Filament measuring thingy August 29, 2020 12:12PM |
Registered: 8 years ago Posts: 65 |
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leadinglights
A possible problem with capacitative sensors is that the dielectric constant of PLA, ABS and other plastics may vary widely. Ways could be found around this,such as having a cell with a sample of the feedstock of a known diameter; but there would remain a quality problem as it would not account for the dielectric constant varying along the length of the roll.
From Google search for "Dielectric properties of PLA" I found this "Study of electrical properties of 3D printed objects Petr Veselý, Eva Horynová, Tomáš Tichý, Ondřej Šef"
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In the case of ABS, the value of dielectric constant was about 3 compared to PLA dielectric constant that reached 2,7 - 2,9 in the case of transparent PLA and 3,1 - 3,2 in the case of white PLA with TiO2. The additive in PLA had a significant influence on the dielectric constant of the sample
So it looks like some work needs to be done on this idea.
Mike
Re: Filament measuring thingy August 30, 2020 01:12PM |
Registered: 13 years ago Posts: 1,465 |
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ECJ
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I believe that moisture absorbed by the material will affect the dielectric constant more than the composition itself.
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Re: Filament measuring thingy September 01, 2020 10:39AM |
Registered: 8 years ago Posts: 65 |
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leadinglights
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ECJ
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I believe that moisture absorbed by the material will affect the dielectric constant more than the composition itself.
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Although there seem to be several strikes against a capacitive sensor for measuring how much plastic is being fed, there may be occasions where it does not matter: One of the original RepRap principles included reuse of plastics such as old prints, plastic bottles etc., In this case, and given reasonable mixing and handling, the dielectric constant and relative humidity should be constant. If the first bit of filament fed through the sensor is a known good diameter and roundness then the capacitive sensor may be a useful way of measuring the effective diameter or cross-sectional area of the filament.
I made a simple sensor to see if I could get some idea of what to expect and this is shown below, the plates of the capacitor are two helixes and the filament goes through the middle of them. This arrangement cancels out any off-center errors.
[attachment 116589 Notaninductor.jpg]
The results are not fantastic at the moment, the capacitance of the sensor is about 2.6pF and all 1.75mm filaments give an increase of about 0.15pF with 2mm nylon strimmer filament giving an increase fluctuating between 0.15pF and 0.2pF (my instrument resolves to 0.05pF)
The electronics for driving this can be very simple and inexpensive as for example in this application note from Microchip [ww1.microchip.com]. This circuit is able to measure changes in the 1fF (1/1000 of a picofarad) region and the MCU can be under £1.00 with very few other components needed.
Mike
Re: Filament measuring thingy September 01, 2020 01:55PM |
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Re: Filament measuring thingy September 02, 2020 05:50PM |
Registered: 8 years ago Posts: 65 |
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leadinglights
@ECJ
I think you are right on all counts although there is still a possible place where the capacitative sensor could be used.
- Humidity will vary between the outer layers of a roll and the inside. The layers most exposed to the most recent humidity will reflect that.
- Filament quality when I made my first printer in 2011 was pretty awful but I don't think I have seen a thickness problem in several years
- New users often try to get all of the "bells and whistles" but it is more likely to confuse them than be helpful
I have pretty much abandoned the sound wave device on points (b) and (c but I think frankvdh's idea has legs in some areas. One is that homemade recycled filament may easily suffer from variation in diameter. Another is that a capacitive sensor would act as a presence/absence indicator to warn of filament breakage and may cost in the same region as an optical sensor - though more expensive than a microswitch sensor. The final one comes from what you have flagged up yourself: Some filaments, notably Nylon, absorb humidity very freely and the print quality of Nylon with absorbed water is very poor. If the change the dielectric constant of these filaments is large enough then the capacitive sensor could give a warning that the filament is damp.
So somewhere in the middle, there may be a reason to keep looking at this.
Mike
Re: Filament measuring thingy September 03, 2020 05:32AM |
Registered: 13 years ago Posts: 1,465 |
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ECJ
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As for the filament presence sensors, I believe that the most useful are those that are also capable of detecting movement, because if something occurs that obstructs the movement, the simplest sensors become useless. I believe that the work of creating a new sensor using capacitance detection would only be justified if it could also detect movement, and not only the absence and presence of the filament.
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Re: Filament measuring thingy September 03, 2020 04:12PM |
Registered: 8 years ago Posts: 65 |
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leadinglights
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ECJ
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As for the filament presence sensors, I believe that the most useful are those that are also capable of detecting movement, because if something occurs that obstructs the movement, the simplest sensors become useless. I believe that the work of creating a new sensor using capacitance detection would only be justified if it could also detect movement, and not only the absence and presence of the filament.
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The most obvious way of measuring feed rate is the obvious one - use a rubber wheel with an optical interrupter to generate distance and direction signals. Using an optical mouse sensor should work except that the optics of the mouse is designed to view a flat surface while the filament is, from the point of view of the mouse, a moving cylinder of much smaller dimension than the mouse sensor looks at.
There was some discussion on using the indentations left by the extruder drive gear to drive a mechanical transducer in this thread [reprap.org]
A few trials with filaments of different hardnesses convinced me that while it worked, some filaments would not take a clear enough impression to give a one to one count from the gear teeth.
One possible thought is that you could combine the optical mouse idea with the indentation detector. The hope here being that the indentations should give an image with a lower requirement for focus. There would be no need to adapt parts from a mouseas a LED and two optical sensors should work although the signal processing would be more complex. The only strike I can see against this is that it needs work - always a fatal flaw.
BTW, the use of two sensors to derive speed from changing features in the return signal is not new, nor does it need much processing power. An early side-scan radar (Ferranti? Marconi?) used much the same technique to measure speed without resorting to Doppler. If memory serves it used valves, mag-amps, and acoustic delay lines.
Mike
Re: Filament measuring thingy September 04, 2020 02:41AM |
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Re: Filament measuring thingy September 04, 2020 09:33AM |
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dc42
I agree that you need to measure movement to detect extrusion issues. However, it's important to measure direction as well as movement. Otherwise, the reverse movements caused by retraction and pressure advance will cause extra movement to be recorded.
Laser filament monitors work great with some types of filament but not at all with other types. We (Duet3D) used to make and sell laser filament monitors, but we switched to using a Hall sensor that monitors a magnet that is rotated by filament movement.
Re: Filament measuring thingy September 04, 2020 10:08AM |
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Re: Filament measuring thingy September 04, 2020 11:51AM |
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Re: Filament measuring thingy September 04, 2020 05:48PM |
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ECJ
@leadinglights
This laser sensor must have a small array of receivers and then the variation in the angle of the received beam to be translated as movement. But I don't think can measure speed and direction.
Re: Filament measuring thingy September 04, 2020 06:43PM |
Registered: 8 years ago Posts: 65 |
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dc42
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ECJ
@leadinglights
This laser sensor must have a small array of receivers and then the variation in the angle of the received beam to be translated as movement. But I don't think can measure speed and direction.
It has a square image sensor that measures amount and direction of movement in two dimensions. Speed can be inferred from the amount of movement over time.
Re: Filament measuring thingy September 05, 2020 02:48AM |
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Re: Filament measuring thingy September 05, 2020 10:31AM |
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Re: Filament measuring thingy April 21, 2021 09:49AM |
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Drill diameter Chamber pressure 1.57mm 3.49mb 1.65mm 4.55mb 1.68mm 4.92mb 1.73mm 6.12mb 1.77mm 7.54mb
Woodfill 1.72mm 5.47mb PET Smooth 1.70mm 5.28mb PLA 1.74mm 5.62mb ABS+ 1.77mm 6.41mb PLA 1.77mm 5.49mb ** This result is odd ABS 1.74mm 5.87mb
Re: Filament measuring thingy April 26, 2021 08:28AM |
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Re: Filament measuring thingy April 26, 2021 02:57PM |
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