[DrStein99]

Does a spring on the idle pulley serve a purpose, besides easily change the belt?

[steve323]

I am guessing here, but it seems like a spring would help keep the belt tensioned to help reduce backlash.

Steve

[DrStein99]

It is a big guess for me too. I parted out a large office photo copier, and many of the belt drive guides in there had springs on the idle pulley. If someone needed to change a belt, they would have to go through alot more effort to get to it, and putting a spring on it would not reduce a technician's repair time by any reasonable amount.

My best guess is: a controlled weak link. In the unlikely event of a little jam - the spring would cause tension on the spring, instead of causing a borderline weak motor to skip steps. I also do not know what happens when the momentum in the weight of the carriage changes direction immediately, the spring could possibly be a shock absorber. I have also seen springs on carriages themselves, that tether the pulley to the carriage - two springs in both directions.



I saw a few youTube videos with this "CETUS" 3d printer. It's a nice space saving machine using professional linear rails with belt drives. They have gone out of their way to make springs on the idle pullies for their drive-trains:

https://www.cetus3d.com/

The site does not go into detail on their engineering construction, it's setup for basic 3d printer users.

[steve323]

A shock absorber is a good guess also. It could also help keep the belt tight as the belt stretches over time without starting with an overly tight belt.

One basic flaw in my mind is that the belt will be completely tight in one direction, but it will allow backlash in the other direction as the head pulls against the spring. There is some mechanical advantage because a large movement in the spring will only cause a small tightening of the belt. A 1lb spring might resist a 10lb force at the head.

Steve

[DrStein99]

I'm looking at this assembly again. There is just enough spring movement for me to get the belt off easily. It could just be a service factor thing, where the springs automatically provide exact needed tension.