Laser filament monitor
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I would also agree, the most important failure modes are:
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out of filament: spool empty
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nozzle jam: no movement at all (at least not forward, retracts do not count)
Detecting under-extrusion or skipped steps would be nice, but I there is no real benefit anyway. With the other two cases one can at least pause and continue after fixing the problem. If a super accurate sensor detects under extrusion of 85% - what would one do? automatically bump up the extrusion multiplier? that sounds far too advanced that I would trust it with a 50 hour print…
Just for reference, what does Prusa use the laser filament sensor for? AFAIK they also only cover the two big (and easier to detect) issues.
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Why not combine the magnet sensor and the laser sensor?
Use a toothed idler, being driven by the filament, with a pattern for the laser to pickup. If you can find the right material and pattern on the idler, once you get it right, every filament will perform identically. It reduces the number of mechanical parts, but gives consistent readings via the laser.
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The prussa monitor has mixed reviews….
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The prussa monitor has mixed reviews….
Have you a link?
I looked at the code that Prusa uses. It checks that when forward extrusion is commanded, forward filament movement is detected. It doesn't attempt to correlate the amount of movement with the amount of extrusion commanded.
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David, to help detect the tricky filaments, what about using a little lens to magnify the image of the filament?
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Yet another idea (sorry)
From the sound of things the magnetic sensor is based on a magnet and hall effect sensor arrangement which suffers from alignment issues.
Have you considered / tried a resolver solution where you have a magnet rotating inside a coil. Alignment is far less critical and you could create a simple movement detector by smply using a voltage sensor to drive a limit input.
If you want something more complex that could be used to measure speed and extrusion distance there are off the shelf chips to interface with them.
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Detecting under-extrusion or skipped steps would be nice, but I there is no real benefit anyway.
Just to highlight another opinion, I want to accurately detect motion so I can write a macro that works through a series of speeds and temperatures to profile a new roll of filament to determine volumetric extrusion limits. Also seems like if you are looking for automatic monitoring to save a 50 hour print, you need a manual solution for out of filament or nozzle jam so why require an automatic response for under extrusion?
From the sound of things the magnetic sensor is based on a magnet and hall effect sensor arrangement which suffers from alignment issues.
Not clear to me that the alignment issues could not be solved by a better housing for the rotating magnet system?
Also seems like Duet3D could just design and sell different option circuit boards with the firmware to hook them up? Another design would be a rotating encoder with LED sensor (like the old computer mice), using a mechanical linkage to the filament like the rotating magnet sensor. There will be pros and cons for all the designs, just depends on what the user is after as to which works best.
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The magnet sensor version worked great until the assembly shifted a small amount and the I got a false trigger. However an injection moulded or machined assembly or a more optimised printed design would solve this problem.
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what about sls nylon to print the enclosure for the magnetic sensor? I know forms for injection molding add a significant cost/risk to the project, and machining is probably even more expensive.
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The magnet sensor version worked great until the assembly shifted a small amount and the I got a false trigger. However an injection moulded or machined assembly or a more optimised printed design would solve this problem.
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I am appealed by the idea of the use of the filament monitor as contactless displacement sensor and the implementation of a Kalman filter to increase accuracy. My Idea is to mount the sensor on the X and Y belts.
My reasoning is that the optical sensor counts could be used as a tachometer to measure velocity. Both the velocity and position information already present on the system can be combined in a Kalman filter to compute the position with higher accuracy. It will be particularly accurate because the sources of noise are unrelated (little noise cross correlations), i.e. the error biasing any one estimate due to position errors will be mitigated by velocity and vice versa. With this technique we could beat the 1.8 or 0.9 degrees per step resolution.
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With this technique we could beat the 1.8 or 0.9 degrees per step resolution.
Isn't this what microstepping is for?
Unless your rotation sensor is geared etc so it can beat 1/16 or more of that step resolution (a direct magnetic rotation sensor isn't nearly that accurate) you won't have any more info than you can already derive from the controller by simply asking for it's current position. You can detect missed steps, but the controller already does that for you because the controller already does some of the feedback sensing you are looking for.
- I'd be more interested in an acceleration sensor in the printhead and feeding back max/min readings from that, then adjusting speeds to keep within boundaries and limits based on this direct observation. Eg Closing the loop with real data, monitoring the belt wont help detect loose belts or sliders snatching/stiction, but an accelerometer would.
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Development of the laser filament monitor has stalled because we are too busy with other things at present. We might be willing to supply one of our prototypes to a user who meets the following conditions, to try to speed up finishing it:
- Must have a functioning 3D printer and a supply of black PLA to print small parts with;
- Must have enough experience of OpenSCAD to modify an existing design and preferably do new designs;
- Preferably either be located in the UK or have experience of programming an attiny microcontroller e.g. with an AVRISP Mk2 or an Arduino running ArduinoISP + 6-pin programing connector.
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
Development of the laser filament monitor has stalled because we are too busy with other things at present. We might be willing to supply one of our prototypes to a user who meets the following conditions, to try to speed up finishing it:
- Must have a functioning 3D printer and a supply of black PLA to print small parts with;
- Must have enough experience of OpenSCAD to modify an existing design and preferably do new designs;
- Preferably either be located in the UK or have experience of programming an attiny microcontroller e.g. with an AVRISP Mk2 or an Arduino running ArduinoISP + 6-pin programing connector.
Having lost yet another piece, this one a 19h print because of a "knot" on the filament roll, I'm highly motivated to get a laser filament monitor.
Is this opportunity still on the table?
Have almost 2 printers (finishing up a HEVO), Duet Wifis and just got an IR probe.
Not an OpenSCAD expert but hey if it's programmable…
Lots of Arduinos and other microcontrollers and programmers.
Portugal based but willing to pay for all expenses. -
Are these still available? to US?
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We are making a batch of prototype laser filament monitors later this month.
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I'm interested to test one of these, with a few folks of our hackerspace, in France (https://www.logre.eu/wiki)... we have all asked skills.
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@dc42
I would be very interested in working on this, I PM'ed you a couple of weeks ago regarding assisting with the laser filament monitor. I am located in the USA with the needed tools to program the attiny. I can even do smd board assembly if needed. -
I am compiling a list big people who have volunteered, thanks! It will be at least 4 weeks before we get the components and I intend to test a large batch to looks for consistency first. Updates to follow.
