"Lloyd E. Sponenburgh" wrote:

"Pete C." fired this volley in news:4c093eef$0
:

I think the issue is encoder "lines" vs. "counts". The encoders on the
machines I worked on were 2,000 line encoders, which as Karl noted
could
provide 8,000 counts per revolution. The US digital site uses counts,
so
presumably the 720 CPR encoder is 180 line?

If, in fact, that's the case, then it's a huge difference.

But still, that only gets you to roughly 11:1 better than the .02
error... and a thou in CNC work is NOT good enough!

The thing about a servo missing up to 256 counts in a full-excursion run
is nuts. My OLD R2E4 doesn't do that sort of thing. Newer, more capable
servo drivers and faster encoders couldn't possibly miss that bad.

LLoyd

+/- 128 counts isn't the same as missing by 256 counts.

Some servo drives will have much tighter tolerance, and that is the
limit under load, not normal. I used +/- 128 in the example since that
is the max error of the popular Gecko servo drives, more than 128 off
and it will generate an alarm to stop the control.