Re: [CAD_CAM_EDM_DRO] Encoder location

ccs@... wrote:

> When driving a leadscrew via a timing belt and closed loop servo,
> should the encoder go on the motor or on the screw?
>
> I feel like it would be more accurate on the screw, since belt stretch
> would be factored out.

You are correct. Also, sprockets may not be totally perfect, belt pitch
may not be perfect, and so cyclical errors are introduced. With the
encoder on the screw, these errors are eliminated. (I had some sprockets
that were not concentric with the hole. I held them in a 3-jaw chuck
while reboring the hole, which I needed to do anyway, but I have no
idea how concentric they are now.

> However any stretch present might lead to instability, and it would
> be easier to mount it on the motor than on the leadscrew.

If you have the belts tight enough, there won't be any slip, and the
stretch is a long-term event, so it will not cause servo instability.
It's up to you - but you can't argue that a direct drive with a precision
helical-slit coupler has to be more accurate than putting belts and
sprockets in between.

Jon