Re: stepper-servo system

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"

> once cutting is established, and the axis has no side to side play,
> and the electrolite is flushing well, then the feed is only a step
> every now and again.

This probably assumes an RC generator but I won't count my chickens in
terms of cutting speed just yet :) FWIW my ballscrews have a 1mm lead
so I'm looking at 2.5um per step at half stepping.

> A better circuit would drop the voltage when a short occurs and do a
> very short wait to see if it was just the odd electrolite/chip
> problem.

This is something I think Agie have done quite a bit on, the idea of
arresting "bad sparks" in their tracks. Because I'm looking at micro
EDM with very short pulse lengths (tens of ns) switched current
regulation is probably out so I'll be using resister banks however I
was thinking a simple trip that could stop a pulse in its tracks if it
became a short and will reduce the average voltage so the head will
still retract.

> a memory of the last good position would great so it could rapid to
> near that, then slowly advance to cutting.

As I mentioned in the previous post you can do that with yet another
comparitor set to say 90% of the open circuit voltage.

Graham