Inconsistent results with optical encoder wheel filament sensor

[JohnOCFII]

Just a quick update.

The sensor continues to work well:

Pulse-type filament monitor on pin e1stop, enabled, sensitivity 1.710mm/pulse, allowed movement 30% to 900%, check every 6.0mm, measured sensitivity 1.748mm/pulse, measured minimum 95%, maximum 102% over 255.9mm

I hadn't been printing on this printer for a few weeks, and had left some PLA mounted. I started a print today, and on the first layer, I heard the print pause, and the print carriage start to move out of the way. My first thought was, "Oh oh -- a false alarm." Looking more closely, I saw it had triggered on a real filament failure. The filament in the feed tube had broken after the filament sensor, so the filament wasn't moving!

Filament swapped, and print continues!

And as @fractalengineer and I started to think about how to put the ST in the sensor package, he found a board on Ali Express that already had the ST as part of the optical sensor! He and I each ordered a few, and some day -- they will arrive.

I'll report back when that happens.

John

[fractalengineer]

@JohnOCFII wow very nice and did that leave a mark on the print?

or does it resume from the beginning of the layer/layer before?

I'm thinking that with such tight measured error we could reduce the measurement distance to improve the reactivity

[JohnOCFII]

@fractalengineer said in Inconsistent results with optical encoder wheel filament sensor:

@JohnOCFII wow very nice and did that leave a mark on the print?

or does it resume from the beginning of the layer/layer before?

It resumes from where it senses the error, so with my configuration, that could be up to 6mm after the break. I don't know that I'd want to get any shorter than that, for fear of false alarms. I think I'd have to test with something like a vase-mode print to see what the possible imperfection could be.

Many times you'll get lucky, and a failure will happen on infill, and not an exterior perimeter. In that case, you shouldn't see anything. In this case, it was on a first layer and there was a tiny hole, but not something I'd be likely to see.

John

[JohnOCFII]

FYI -- still loving the results!

Pulse-type filament monitor on pin e1stop, enabled, sensitivity 1.710mm/pulse, allowed movement 30% to 900%, check every 6.0mm, measured sensitivity 1.727mm/pulse, measured minimum 87%, maximum 111% over 3654.4mm

@fractalengineer has received his new optical sensor with ST. Mine are still enroute.

[JohnOCFII]

Yes, maybe I am bragging a bit, but this was a team effort after all:

Longest print to date with the filament sensor:

M591 D0
Pulse-type filament monitor on pin e1stop, enabled, sensitivity 1.710mm/pulse, allowed movement 30% to 900%,
check every 6.0mm, measured sensitivity 1.753mm/pulse, measured minimum 46%, maximum 140% over 52885.0mm

The new optical sensor with Schmitt Trigger has arrived -- now just waiting on the stars to align before I can test it.

John

[dc42]

This thread may be of interest https://forum.duet3d.com/topic/4498/filament-monitor-using-hc-020k-encoder. The issue was that the HC-020K optical sensor used a comparator with no hysteresis. That is an elementary design mistake, that causes the output to bounce between high and low many times whenever the output transitions, instead of providing a clean edge. Adding a resistor to the comparator circuit to provide positive feedback solved that.

[JohnOCFII]

I've got the new optical sensor with the integrated Schmitt Trigger installed and operating. Seems to be working fine, and showing clean signals.

Pulse-type filament monitor on pin e1stop, disabled, sensitivity 2.000mm/pulse, allowed movement 30% to 900%, check every 6.0mm, measured sensitivity 2.002mm/pulse, measured minimum 88%, maximum 123% over 758.9mm

Full Saleae log available on request.

John

[arhi]

@JohnOCFII that is nice, obviously the encoder input is not having Schmitt trigger input so simple analog devices will not work. Not sure why 'cause if I remember correctly these inputs can have ST input turned on in port configuration. One hint - what logic analyzer sees and what duet sees are not identical!!! It is similar as you have a similar input port on the CY in the logic analyzer as is on the SAM in duet but they are not the same.