Correcting for pulley imperfections in software

Does anyone know if work has been done on measuring and correcting for imperfect and/or off-center pulleys? This would mainly be a concern with printed pulleys, but I'm thinking it could really improve the print quality on machines with printed pulleys, given that moving to GT2 belts and machined pulleys make such a big difference.

Edit: I don't mean backlash, but pulleys that aren't perfectly round or perfectly centered.

Edited 1 time(s). Last edit at 09/22/2012 06:48PM by ketil.

My opinion: you'll have a hard time actually quantifying the shape of the outer surface.
If you say the hole center is off, you'll also have to consider egg shapes, pear shapes, etc.

This community could have solved z-wobble by coding a warble action to counteract the imperfect all thread.
they chose higher quality parts or to decouple the wobble from the axis (let the all-thread float and not affect)


the coding would have to be perfectly tuned the current position of the pulley.
If you lost the clocking of the mechanism to the firmware, you'd be off badly/twice as much.
Also, all that code would have to edited into every firmware release. not hard to do though.

I'd just add quality where it's needed. pulleys are cheap.

You could also put it into a drill press and fashion a tool post, then true up the outer pulley surface.
The teeth are less important than the circular outer running surface, as long as they are deep grooves.
this idea only works to true up a very small amount. I'd say like .25mm or .010in. just a guess.

optical encoders, used in industry for over 30 years. there must be a reason.
mark references on side of rod, then add an optical encoder setup, if there is more counts than should be it will compensate, if there are less counts it will compensate.

[en.wikipedia.org]

IMHO, this is a case where trying to correct substandard hardware with software tweaks is going to be futile. The pulleys are so important to the motion that it's really worth it to just splurge on some manufactured ones, at least until you have your machine dialed in so well that you can print ones with the accuracy required.

Hey people,

While I firmly agree that buying properly machined pulleys would be a much easier way to get better results, I figured that it would be in the spirit of RepRap to improve prints using printed and imperfect pulleys. Also, it might make RepRap more useful in less accessible locations, where machined pulleys perhaps aren't available.