On Mon, 03 Oct 2005 18:48:46 GMT, xray
wrote:

On Mon, 03 Oct 2005 11:06:12 -0700, Eric R Snow
wrote:

On Mon, 03 Oct 2005 17:56:08 GMT, xray
wrote:
What encoder are you using, and what is it connected to?

A US Digital H6S-2500-I. And I realize I made a bunch of errors in my
first post. I am using the ED3 display from US Digital too. I need to
eliminate the encoder as a source of error before I continue. I don't
think it's the problem but so far it seems like the culprit.
Eric

H6S-2500-I? That's 2500 CPR (Counts Per Revolution). For a shaft with 1"
circumference, that gives a resolution of .0004". I'm thinking you've
got an uncertainty in the +- 1 count range, which is pretty close to
what you are seeing.

Had to go look to refresh my memory. As I recall the best A2 encoders,
which I have used, are spec'd to 12 bits output although they give 16
bits. 12 bits is 4096, or 2.4 tenths in your application.

I think you need a smaller shaft.
Actually, since the encoder is being read in quatrature the resoultion
is 10,000 pulses per rev. When moving the carriage one direction it
counts right along with a 1/10000" .500" travel indicator. When the
direction is reversed the carriage must move .0009" before the display
shows a change. After the .0009" movement is satisfied everything
works OK. The problem occurs no matter where in the .500" of the
indicator I use. It also happens if the indicator is moved anywhere in
the 8" travel of the carriage. If the problem still shows with the
laser measure then I'll try it with 1X counting instead of 4X. But
that should not make any difference. I think.
Eric