Custom Filament Pulse Sensor and PA weirdness...
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Hi All,
I'm getting filament sensor behaviour that I don't understand, I'm using the automated meta gcode for generating a PA calibration print. I've attached the gcode and some log files. The log file contains a readout of the filament sensor status triggered at each layer change.Inspecting the print optimal PA seems to be at about 25mm, Pressure advance: 0.25
The sensor is tripping out at about 40mm (3 times now), but the measured sensitivity seems to start gradually reducing at about 20mm (0.2 PA).
Not sure if this data is useful, seems to me that the brim prints OK at slower speeds with measured calibration there being in line with settings. So IMO that seems correct, albeit there is somthing wierd right at the start that results in the initial measured minimum 96%, maximum 126% which I also don't understand.
The speeds don't vary after the first layers so the only thing that's changing is the PA as we go up the tower. And the first 20mm of Z seems OK in terms of measured filament usage. But starts to decrease after that. But then warns of too much movement?
As I said it doesn't make sense to me.
It's a custom pulse sensor based on one of the output channels of a 600ppr (2400cpr) encoder and an old extruder gear system.
The measured values are consistent with the settings. It works well most of the time, but appears to glitch out every now and then. This is the first time I've been able to measure anything potentially useful to characterise the problem.
Best regards
Barry M -
@cncmodeller as your encoder and the "extruder" that is coupling it to the filament movement should be fairly accurate - and you are seeing the "more movement" increase I wonder if this is todo with a difference in the way retractions/ reverse movement is handled. @dc42 will need to confirm.
This is not a "typical" pulse style filament monitor which often just show "is moving" with long gaps between pulses. Ideally such an encoder would be interfaced to give direction as well, but we don't currently support doing so.
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Thanks @T3P3Tony, that might be part of it too.
I did wonder if I could use the second encoder phase to give direction data to the duet, sounds like it'd require a firmware update. Fair enough.
I have also wondered if the level of precision available for the distance per pulse setting is letting rounding errors build up in this case. But that being said it would be a continuous build up of error rather than one that comes and goes during the print.
I've disabled the sensor again for now so I can get on with printing some larger parts. However I'd really like to get this working as I want to use a layer by layer readout of filament status as a metric for print quality.
The plan is to eventually merge the data with the lower error threshold data logged from closed loop stepper motors to give an overall print quality metric, and indication of where any remedial action might be necessary.
As always really appreciate the level of support from the duet team.
Many thanks
Barry M
