Filament monitor using HC-020K encoder

dc42

Strill P7.

Are you saying that 26mm filament movement give 20 pulses? If so that's 1.3mm per pulse.

I've put a new firmware binary with more sensible default values at https://www.dropbox.com/s/iq9pzfaugyfei7x/Duet2CombinedFirmware.bin?dl=0.

paboman

Diameter of the encoder wheel is 26mm so the circumference is 26 x 3.1416 = 81.7 mm
So 81.7mm of extruded filament is one full turn of the encoder wheel which gives 20 pulses
81.7 / 20 = 4
if so 4mm per pulse

upgraded to: 1.21RC5+ (2018-03-18 build 1)

with this config.g:
[c]; Filament Monitor HC-020K
M591 D0 P7 C3 S0 R70:130 L4.1 E50 ; D= sensor for extruder drive 0, C= E0 endstop input, P=Sensor type, S1= Enable, R=70% to 130% tolerance, L= mm/pulse, E= detection length
M591 D0 ; display filament sensor parameters for extruder drive 0[/c]

i get this response:
[c]10:16:26M591 D0
Pulse-type filament monitor on endstop input 3, disabled, sensitivity 4.10mm/pulse, allowed movement 70% to 130%, check every 50.0mm, current position 0.0, measured sensitivity 12778.21mm/pulse, measured minimum 0%, maximum 33% over 1763392.6mm
10:14:15M591 D0
Pulse-type filament monitor on endstop input 3, disabled, sensitivity 4.10mm/pulse, allowed movement 70% to 130%, check every 50.0mm, current position 0.0, measured sensitivity 12296.81mm/pulse, measured minimum 0%, maximum 25% over 479575.5mm[/c]

If I enable the monitor with S1 i get "Extruder 0 reports too little movement":
[c]10:18:18Printing paused
10:18:17Resume-after-power-fail state saved
10:18:16M591 D0
Pulse-type filament monitor on endstop input 3, enabled, sensitivity 4.10mm/pulse, allowed movement 70% to 130%, check every 50.0mm, current position 0.0, measured sensitivity 25.00mm/pulse, measured minimum 16%, maximum 16% over 50.0mm[/c]

The strange thing is the measured sensitivity of 12778.21mm/pulse while monitor is disabled

dc42

So the filament runs on the outside of the 26mm diameter encoder wheel?

The measured sensitivity is clearly absurd, as is the recorded extrusion amount (1.76km in the first report). I'll take another look at the code.

paboman

yes, the filament runs on the outside diameter of the 26mm encoder wheel for now. later I will change that to a smaller diameter

dc42

I found a likely explanation for the absurd values. Please pick up a new binary from https://www.dropbox.com/s/iq9pzfaugyfei7x/Duet2CombinedFirmware.bin?dl=0.

paboman

ok, upgraded the firmware, now im getting "Extruder 0 reports too much movement"
also reducing the E Value from 50 to 10 gives the same result
[c]11:18:53M591 D0
Pulse-type filament monitor on endstop input 3, enabled, sensitivity 4.10mm/pulse, allowed movement 70% to 130%, check every 10.0mm, current position 0.0, measured sensitivity 0.66mm/pulse, measured minimum 439%, maximum 801% over 22.5mm[/c]

dc42

Are you certain that he pulse rate of your encoder is 4.10mm of filament per pulse? What happens if you set it to 0.66mm as reported by the calibration?

I'll have the calibration value reported to 3 decimal places in the next build.

paboman

Correct me if I am wrong, the 4.1mm per pulse is given by this calculation:
Diameter of the encoder wheel is 26mm so the circumference is 26 x 3.1416 = 81.7 mm
So 81.7mm of extruded filament is one full turn of the encoder wheel which gives 20 pulses (the wheel have 20 slots thru light can pass)
81.7 / 20 = 4.085
I rounded it to 4.1

As you said with L= 0.66 I get "Extruder 0 reports too much movement"
[c]
Pulse-type filament monitor on endstop input 3, enabled, sensitivity 0.66mm/pulse, allowed movement 70% to 130%, check every 10.0mm, current position 0.0, measured sensitivity 0.59mm/pulse, measured minimum 60%, maximum 168% over 21.3mm[/c]

so I changed L= 0.59 but I get "Extruder 0 reports too little movement"

[c]
Pulse-type filament monitor on endstop input 3, enabled, sensitivity 0.59mm/pulse, allowed movement 70% to 130%, check every 10.0mm, current position 0.0, measured sensitivity 0.80mm/pulse, measured minimum 39%, maximum 111% over 42.6mm[/c]

then I changed L= 0.80 but I get "Extruder 0 reports too much movement"

[c]Pulse-type filament monitor on endstop input 3, enabled, sensitivity 0.80mm/pulse, allowed movement 70% to 130%, check every 10.0mm, current position 0.0, measured sensitivity 0.94mm/pulse, measured minimum 83%, maximum 86% over 20.7mm
[/c]

dc42

Can you post a photo of how you are using that encoder to measure filament movement?

The calibration data indicates that there is quite a large variation in the amount of extrusion commander per revolution of the wheel. One possible reason for that may be that when filament is retracted, it doesn't force the wheel to rotate backwards because you haven't constrained the filament path sufficiently; so that when forward extrusion is commanded after a retraction, initially the wheel doesn't rotate because there is slack filament to take up.

Unless you can make it more reproducible, you will need to increase the allowed tolerance. For example, when you had the sensitivity set to 0.66 it reported:

measured minimum 60%, maximum 168%

which means that in order to avoid spurious alarms you would need to use R60:168 or wider, not the R70:130 that you are currently using.

paboman

In the youtube link you can see my test setup: https://youtu.be/0md1yE183kc

The encoder wheel is directly connected to the stepper shaft, that way the encoder is reading the real revolution of the extruder and no slippage may occur as no filament is being pulled.
This setup is simulating the filament being pulled by the extruder gear and consequently rotating the encoder wheel with a perfect ratio of 1:1. This way im taking out of the equation any filament slippage, dont you think so?
Secondly the Gcode I am running is without retraction.

dc42

I suspect that you are not getting clean edges from that sensor because of a fundamental flaw in its design. This would also account for the average mm/pulse being lower than you expect. See https://androminarobot.blogspot.co.uk/2016/04/tutorial-sobre-el-encoder-fotoelectrico.html. That design needs a resistor added between pins 1 and 3 of the LM393 to make it stable. A value of 47K should be about right.

paboman

ok, I can try !

two questions:
1. right now I have 15k resistors, can I add 3 in series to have 45k ?
2. Is Pin 1 of LM393 marked with a circle near the corner ?

paboman

EUREKA!
adding 45k (15x3) resistor between pin 1 and 3 of LM393 solved the issue

[c]Pulse-type filament monitor on endstop input 3, enabled, sensitivity 1.89mm/pulse, allowed movement 70% to 130%, check every 10.0mm, current position 0.0, measured sensitivity 1.88mm/pulse, measured minimum 100%, maximum 101% over 373.1mm
[/c]

holding the extruder wheel from turning trigger the pause as it should

now the last question is: why the sensitivity calculated is 1.89 instead of the 4.1 that mathematical model gives us ?

thank you David!

dc42

Perhaps your extruder steps/mm is wrong? Please explain how you arrived at 1166. From your video, I think you don't have an extruder connected to the extruder drive yet, only the encoder wheel - is that correct?

I guess it's also possible that you are still getting more than one edge at each transition. If that's the case, reducing the value of the resistor will help, for example try 15K. If you make the value too low then it won't produce any pulses at all. However, as your variation during calibrarion seems to be very low now, that's probably not the cause.

paboman

The motor have 200 full steps per revolution (1.8 deg per full step)
The gear ratio is 1:13.76 so the number of full step per revolution is 13.76 x 200=2752 full steps
The hobbed gear diameter is 12mm so the Circumference is 3.14 x 12=37.68mm
with full step than the steps/mm is 2752/37.68=73.03 step/mm
Driver works at 1/16 step so 16x73.03=1168 steps/mm

The extruder motor is connected to E0 but instead of the hobbed gear i mounted the encoder wheel (only for testing)

dc42

So instead of a 12mm diameter hobbed gear you have a 26mm extruder wheel. So the amount of extruded filament will be 12/26 of the amount you have assumed in the encoder wheel calculations. (12/26) * 4.1 = 1.89.

paboman

That is right! Definitely something I have overlooked.
thanks again

Monster Delta

Does the resistor go between A0 and GND OR VCC AND D0?

dc42

@monster-delta said in Filament monitor using HC-020K encoder:

Does the resistor go between A0 and GND OR VCC AND D0?

Which resistor are you referring to? If you mean the one to clean up the output of the encoder, it's neither, it's between pins 1 and 3 of the LM393 chip.

Monster Delta

@dc42 thank you for clearing that up