Re: [CAD_CAM_EDM_DRO] linear encoder

justjuha wrote:

>I'm going to rebuild old cincinnati cnc milling machine. I think I
>can use the existing servo motor and control them from mach1 (or 2)
>via Rutex's servo drives. These drives require feedback from the
>encoders. One way to get the feedback is to fit the encoders on the
>motor's axle. I'm just thinking now, how would the linear encoders
>work in such construction.
>

If the machine already has linear encoders, you don't need to add shaft
encoders.

> If I want to get 0.01 mm accuracy, would
>0.005 mm resolution be fine enough?
>

Generally, people say you want the encoders to have 10 x the resolution
you want to
be using as your guidepoints. I think there is good sense in this.

> Couple examples of the encoders.
>http://www.elgo.de/e/produkte/laengenmesssystemeinhalte.php?
>produkt=MIX%2FFMIX&id=1&z=4
>http://www.sikoproducts.com/ml/t_mb100.html
>I do not know either, will the linear encoder offer some advatages
>compared to rotating one, considering the backlash issue.
>
>

If you have much backlash, the system will be unstable with a linear
encoder.
But, backlash more than .025 mm is considered quite bad for precision CNC
machining. So, you should really fix the backlash, rather than trying
to work
around it. Worn ballscrews can be rebuilt for a lot less than new
screws and nuts.

Jon