Re: [CAD_CAM_EDM_DRO] encoders and table position

On Friday 06 June 2003 01:47 am, Jon Elson spake:

> >Well, for a few reasons as I understand (or not).
> >First is that no one seems to be able to tell me with certainty what the
> > wires do, and as far as I've found in my searches, there isn't any
> > standard to the color coding of the wires.
>
> You got that right, as I found out a while ago.

:)
You'd think they'd at least have a _standard_...

> >Exactly my feelings...
> >I am considering heavily the option of ballscrews and nuts at this point,
> > but I'm still thinking I want my positioning done by table, not screw
> > position.
>
> But, a good ballscrew and encoder can have MUCH higher resolution that
> a high resolution linear encoder of considerable length. The most basic
> (roughly .0005" but metric) linear encoders in 30" length run $350 at
> least, new. That is really insufficient for smooth motion and decent
> precision work. I am using actual resolution of .00005" on my system, with
> ballscrews and shaft encoders. (Yes, that's 50 micro-inches.) I was lucky
> enough to get
> high accuracy ground screws off a scrapped machine. But, in a small
> area, most ballscrews with shaft encoders can do better than a bottom
> of the line linear encoder. Over the full length, the basic accuracy of
> the linear scale will be better than a rolled screw and shaft encoder, of
> course,
> but these errors can be compensated for.

I was asking in an earlier post about what options people had used.
I _do_ have the QEDS units, and could mount and use them somehow, but
the linear encoder idea seemed better to me. I'm open to suggestion, though.

> >For that matter, is it possible that I might be able to simply buy
> >the reader heads and use them with the scales I've already got?
> >At $25.00 each from US Digital, it makes
> >a very reasonable solution to this problem.
>
> Not likely. The US digital read head is designed for a 7-mil thick plastic
> scale with 360 line/inch (I think). The glass scale will be a lot
> thicker, and
> the stripes will be roughly 500/inch (.002"). So, the US digital read head
> would not work without extensive modification.

Ahhh... I see. Kewl, thanks for the heads-up.
I wonder how hard it would be to make mounts for the linear strips...?
Even with some length (like 24") it's still a relatively affordable solution.
($48 for the strip and $25 for the head = $73 + labor) (not *TOO* bad...)

Still, the QEDS are _here_ and already work with the K&M DRO board...
I could take the money saved and apply that to the ballscrew conversion.
I suppose I could figure out a way to drive these things. (they're tiny)
HP QEDS-7099

What about the backlash, though?
Is EMC handling that?

Thanks,

Weyland