0% measured minimum

osterac

Hi, I have a DIY filament movement sensor I built from these instructions. It has an optical sensor that monitors a wheel that the filament will spin as it moves through the device. I've tried to calibrate it, but the mm/pulse measurement seems to be fairly random. Not only that, there is a 0% measured minimum - so it's always going to think there is too little movement on the sensor. Despite that, it is getting readings within 2% accuracy. Here's what the calibration message says:

4/17/2022, 5:24:16 PM 	m591 d0
Pulse-type filament monitor on pin e0stop, disabled, sensitivity 1.000mm/pulse, allowed movement 50% to 150%, check every 5.0mm, measured sensitivity 38.186mm/pulse, measured minimum 0%, maximum 19% over 725.5mm

The extruder had pushed out 736.9mm of filament, so it's pretty close. If I set the mm/pulse to what it says, it will just say something different the next time I calibrate it, and always 0% measured minimum.

These are my settings:

M591 D0 P7 C"e0_stop" S0 E5 L1.0 R50:150 A1

Any Idea what's going on here?
Thanks.

osterac

@dc42 figured it out I think. The mounting screws for the sensor were too long so they weren't properly seating the sensor. Now that the sensor is in nice and tight the blinking is consistent. Haven't calibrated yet though.

Phaedrux

Your M591 command looks a bit different than the one recommended by @fractalengineer in the instructions.

M591 D0 P7 C"io6.in" S0 E51 L2.1 R50:150

fractalengineer

@osterac Yep as @Phaedrux said (thank you for the ping) there is a notable discrepancy with your setting

Can you try changing E5 to E51? This helps averaging out the pulses over a whole turn of the wheel; smoothes out printing artifacts of your encoder wheel

L value also depends on which encoder wheel model you chose to go with, you could get a base value by dividing that 51mm perimeter by the amount of slots, but eventually you would replace it with the closest measured value

--> in your case 38mm is abnormally high; I would check that the rubber wheel has a good grip on the filament and nothing is rubbing

osterac

@phaedrux
I set those values and I got this

Pulse-type filament monitor on pin e0stop, disabled, sensitivity 2.100mm/pulse, allowed movement 50% to 150%, check every 51.0mm, measured sensitivity 23.145mm/pulse, measured minimum 7%, maximum 14% over 671.2mm

Better!
RTFM I guess. I'll fool around with it some more.

@fractalengineer
Will do. Thanks so much for your replies.

I think I just printed Axle_A.stl, not 8x, 12x, 24x, or revision 3.

I used 95a tpu for the rubber wheel.

fractalengineer

@osterac hmm that's still way off; ideally you would get as near to 100% on both min/max

You did print the revision 2 right? With the schmitt-trigger sensor?

If so you might want to check if the axle is spinning properly when you're feeding filament through the sensor;

Just take a piece by hand, feed it through the sensor and watch for the axles spinning/sensor blipping.

On V2 you can also pinch the axle while it spins to feel how well does it grips

osterac

@fractalengineer
On Thingiverse it says version 1.2 and various parts have various revision numbers - the parts for the body do not have revision numbers. I found it hard to tell which file to print because there are stl files with no revision numbers and 3mf files that do have revision numbers. I just printed the stl files. I do have the schmitt-trigger that is linked to on thingiverse.
I checked out the grip of the wheel and there is one spot on the wheel that doesn't grip quite as well as the rest. Could be that it is slipping during retraction.
Here's my sensor:

edit I cracked it open and there seems to be a very slight indentation on the rubber wheel. I'll try printing a new one.

fractalengineer

@osterac Ok I just updated the whole files on the thing; there's only one version now for clarity

And yep you really need your seams to be well tuned on that wheel; if they're protruding a bit you can still trim them with flush cutters or a razor blade

osterac

@fractalengineer
Finally got my printer to make a decent wheel. Here's the result of calibration now:

m591 d0
Pulse-type filament monitor on pin e0stop, disabled, sensitivity 25.992mm/pulse, allowed movement 55% to 95%, check every 51.0mm, measured sensitivity 24.010mm/pulse, measured minimum 87%, maximum 177% over 33326.1mm

Look okay? Is 177% too high?

dc42

@osterac you have a very high mm per pulse value (24mm). So you can only measure filament lengths to the nearest multiple of 24mm. This means that in order to get accurate measurements, the length of filament sampled must be many times 24mm. You are using only 51mm, so you can expect to get large variations. If you increase the sampling length to 100mm or more, the variation will reduce.

The instructions on the page you linked to say that the mm per pulse should be 1.2mm, so I don't think you can have built it correctly.

osterac

@dc42

Thanks for explaining that, always helps to know how things work.

I could try re-printing the sensor wheel... Or
maybe my sensor is defective? There are some models of the sensor wheel with fewer teeth but that seems like it would decrease accuracy?
Could it still be a problem with slippage?

Sorry for all the questions... Hope I'm not bothering you...

Phaedrux

It's no bother at all. We're here to try and help people figure it all out.

Can you make a video of your extruder in use?

osterac

@phaedrux

Here's a YouTube link
https://youtu.be/xuf4eaktg_w

dc42

@osterac thanks. It appear s to me that the flashing of the red light in the filament monitor is in frequent (so the 24mm per pulse value is believable) but is also somewhat erratic. Perhaps there isn't a clear path between the opto switch transmitter and receiver through the slots in the wheel?

osterac

@dc42 figured it out I think. The mounting screws for the sensor were too long so they weren't properly seating the sensor. Now that the sensor is in nice and tight the blinking is consistent. Haven't calibrated yet though.

osterac

Yeah, looks good. Here's the calibration:

Pulse-type filament monitor on pin e0stop, disabled, sensitivity 4.141mm/pulse, allowed movement 95% to 103%, check every 51.0mm, measured sensitivity 4.186mm/pulse, measured minimum 97%, maximum 101% over 1837.5mm

I used the 12x sensor wheel rather than the default 24x wheel (fewer teeth), not sure if that helps or not.

Anyway, thanks for your help guys. I appreciate it.