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Distance along a line

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I want to determine the volume of yarn on a bobbin.  If it's filled evenly I could use a low cost time of flight sensor on the center point and calculate this.  However in the attached image the bobbin isn't filled evenly.  Do you have any suggestions on a low cost (<$5 in 1K qty) that can do this?  The bobbin will be rotating at around 2000 rpms if that matters.

One option is to move the time of flight sensor to about 64 positions and sample, but I don't want another moving piece like that.  The only other thing I could think of is use a low cost 640x480 camera with an IR filter ($2) and some IR LEDs to light up the bobbin.  Then in most environments the edges of the bobbin's yarn could be detected and with correct calibration the volume calculated.  I have some experience with low level graphics and could handle the algorithms of this system, but I suspect it would take a lot of time to get it working robustly.

Oh, I did think of using the weight and that would kind of work, but the density of yarn can vary, but it would require some end user calibration and is thus not ideal.

Do you guys have any other ideas for sensors that could do this?

I think the camera idea is your best bet.
But why can't you fill the bobbin evenly?

Thanks for the feedback!

Bobbins are typically filled by the user manually moving some sliding hooks and some users just don't fill the bobbin evenly.  I do have a way on this future project to automatically fill the bobbins with a level winding system and will see how evenly the bobbins get filled.  That said the mechanical system to do this is kind of difficult because the whole center piece holding the hooks is spinning and most solutions to move these spinning hooks either makes it bigger or adds a lot of weight (both are bad).  Here I'm trying to plan for options if the mechanical level wind system doesn't work as well as I'd like.

For the time of flight distance sensor I'm looking at VL6180.  If you have better ideas for this let me know.  It only needs to work to a max distance of 15 cm.

Conrad Hoffman:
I think the camera is your best bet, looking at a backlit edge. You should be able to determine the area under the curve and get a pretty good measurement.


--- Quote from: Conrad Hoffman on December 02, 2021, 12:20:12 am ---I think the camera is your best bet, looking at a backlit edge. You should be able to determine the area under the curve and get a pretty good measurement.

--- End quote ---

Sounds like a good idea to me.

Speaking of IR, most cameras have IR filters, they filter out the IR.  If you want to see IR, you'd want a camera without IR filter.

If you just want a cheap camera, ignore IR, it probably doesn't matter if you have it or not.

If you use LEDs, use visible spectrum. IR LEDs can be a safety hazard, they can be strong enough to damage eyes without being very noticeable.  They are also a pain to work with because its hard to tell if they are working or not.  I made a trail camera once and had to keep using my phone's camera to see if the LEDs were on or not.


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