Re: Homebrew STG card - 8254

[Ray Henry <rehenry-at-up.net>]

At 03:37 PM 3/2/2000 -0500, Jon E. wrote:
>
>Also, with a DC tach in an analog computing loop, the velocity
>bandwidth can be GREATER than the computer can provide, giving very
>smooth velocity, down to rediculously slow motion, like .01 IPM.
>If the encoder resolution is coarse, it can't give good velocity info near
>zero.  Again, a bandwidth vs. resolution problem.  My analog loop servos
>don't jitter, AT ALL!  A servo based on the encoder would likely jitter
>badly, unless the encoder had VERY high resolution.

These kinds of problems must be why some machine tool companies are moving
from 125k ppr to as high as 1m ppr.

I did read about some kind of velocity from encoder system that switched
over from computing velocity from pulses per unit time to time between
pulses to get a little better resolution of velocity at very low speed.
But such a system would still be dealing in digital rather than analog.  

Ray