Re: stepper-servo system

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet" <thom@...> wrote:

> Actually it's pretty easy. Your define a target voltage. You compare
> that with the scaled gap voltage. If it's higher you set the
> processor to flip the DIR pin the correct dir and then output a

ramped STEP rate from another pin.

But if it were a dc servo system there would be some gain factor to
take the error voltage and determine the rate of that pulse train.

>The gap voltage becomes the feedback. The coupling is loose rather
>than like in a postional loop.

The coupling is based on the gap voltage of course but this should
respond quite quickly to electrode position. I don't care at all
about the actual servo position just maintaining the gap. In terms of
a dead band, the steady state should have the head moving forwards
slowly with the feedrate adjusted to acheive this rather than a
bang-bang approach which will always cause oscillation or a pulsing
forward motion with a deadband.

Graham