Re: Digest Number 19

<PTENGIN@...> wrote:

> In looking over information from Mitutoyo, they offer BCD and several
>other output cards for the KC and other DRO systems. I have one of these
>(KC) systems and was suspecting the output could be used to inteface to a
>CNC. Also, in the MSC catalog, Mitutoyo used to list a linear spar to digital
>output converter box. Peter

One big problem using the output of the linear encoders of the DRO to
control servos is that *any* backlash between the drive motor and the
workpiece can cause some pretty bad instability (for controls
newbies, the instability I'm talking about is a tendancy for the
motor to oscillate around the target position, buzzing like crazy in
the best case, or slamming back and forth in the worst). There are
ways around it, but none of them are cheap, assuming you are faced
with the normal HSM budget. And no, even zero-backlash ballscrews
won't be enough to eliminate the backlash unless you're running VERY
light loads at low speeds. I had once guessed otherwise, but found
out fast that I was wrong.

If you plan to use steppers, well, you're running open-loop already,
but I guess you could use the linear encoders as feedback to correct
for missed steps. This assumes that you'll be writing a custom
program to run the steppers, unless there's software out there to
take advantage of the encoder feedback. I haven't seen any, but then
again, I haven't looked. :)

-Tom Kulaga