Re: stepper-servo system

--- In CAD_CAM_EDM_DRO@yahoogroups.com, John Dammeyer <johnd@...> wrote:

>
> Hi all,
>
> As I recall, measuring the arc voltage is described in several DIY EDM
> projects. As Dave says, run that into a comparator and the digital

output

> could be fed into an Electronic Leadscrew Module with slightly different
> software.

Yes it is and I know how it is done in several DIY EDM projects but
that doesn't mean I have to just ape those methods, having done quite
a lot of reading on the subject I want to implement something closer
to a true servo system or at least discuss how.

A servo system does not mean it has to resemble something you screw to
a mill, yes the feedback is taken from the gap conditions (doesn't
have to be voltage) but it is still a control trying to maintain some
system parameter. I don't see why this cannot be implemented in a
similar way to any other controller with at least P and I terms.

> The real question is how quickly does a system like this need to
>respond?

You need to average over several machining pulses so not overly
quickly however a faster retract than feed for short conditions would
be advantageous. In one implementation I have read about they use a
rapid feed for getting out of trouble and also for getting back into
the action, the general feedrate is then tweaked according to a gap
conditions (I think they were using the ratio of time spent in maching
zone to time retracting or something).

Graham