Hi guys,
i’m trying to figure out whether i can adapt my filament diameter sensor ( https://plus.google.com/101189457349966331973/posts/P2PDoQC28Bi ) for use in a 3D printer for diameter feedback to the firmware - the main challenge with that is that filament which has been spooled (especially 3mm on small spools) will tend to curl when run through the sensor and ruin the measurement. So the sensor assembly will have some fairly tight restraining/guiding measures for which i need to know a bit about the filament you’re all using.
Specifically, i need to know a) what the “natural” bending radius of your filament is as it comes off the spool, b) at what bending radius it deforms or breaks and, to make sense of it all, c) your filament diameter and material.
Thanks!
I’ve found that filament wants to relax to a curvature slightly less (larger radius) than where it was coiled on the spool. So, the filament near the end of a spool relaxes to a radius that is smaller than at the beginning. I notice this using Protoparadigm 1.75 ABS. So, anywhere from approximately 75 to 120 mm radius.
The curvature is pretty much in one plane though. Can you do your measurement in the non-curving plane? Or maybe find a way to control the filament such that curvature is not a factor? I’m thinking the filament should be guided within a few mm of either side of the rollers.
@Dale_Dunn The concept i’m sketching out right now has the filament guided before and after the rollers and forces it against the static roller, but i still need to determine how tightly i need to (and can) bend the filament. Quick sketch of the idea here, with the green bearing being the one that is used for measuring and the others static:
Going perpendicular to the bending radius isn’t much of an option, since i can’t guarantee that the filament will always arrive in that orientation. Too loose guidance might result in the filament bowing up and against the measuring roller.
some ideas, you could use a tube in and tube out system to reduce that curl (even if it was like 10 cm), it would insure that the filament entered squarely.
Alternitively you could use the same alignment method a yoyo uses. http://badyoyos.files.wordpress.com/2012/08/wpid-v-shape.jpg%3Fw%3D500
as for the bowing up, you could force the filament down before and after the measurement point, i decided to draw this as i am currently waiting… http://camerinhahn.com/g3825.png - conceptually measuring at the peak of the idler. - http://content.myodesie.com/images/techtransfer.com/wiki/Idler_Pulley_edit.jpg - -
Another simple idea, i dont like this one as much as it relies on the bowden tube remaning exactly the same thickness and flat, but i think better when doing drawings anyway.
@Camerin_hahn i like that “g3825” idea - if the ~90° difference between input and output isn’t too much of an issue. I’ll try it out and determine how much drag it adds.
@Thomas_Sanladerer remember, you need to find a way to deal with retraction. In the g8325 idea (thanks inkscape for giving it an odd name) it would just push the measurement axle up if you do it that way.