RE: [CAD_CAM_EDM_DRO] Re: stepper-servo system

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. One could even program how deep it's supposed to go.

Cool. Yet another possible project for ELS hardware. <GRIN> I already use
a comparator now, to test the threshold for the spindle encoder. I'll have
to dig deeper and see if that same circuit couldn't be used for testing the
'gap height'.

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

John Dammeyer

> Subject: [CAD_CAM_EDM_DRO] Re: stepper-servo system
>
>
>
> >
> > So if voltage of the gap = height (or depth or whatever you call it)
> > and the wire cuts the "servo" (reading the voltage would force the
> > motor to move down to correct. You are not talking about
> inches here
> > but fractions. Things like acceleration, move rate etc
> would be close
> > to meaningless. The target voltage would determine the
> speed at which
> > it cut and it would move in the correct direction to maintain the
> > balance.
>
> I think you've got it.
>
> it is dead simple.
>
> one can do it with a pulse generator from a 555 and an op-amp.
>
> 10 volts will jump the gap of some 5 thenths or so, (I have a chart
> somewehre) and there is the sweet spot of +/- 5 volts or so where no
> action is needed.
>
> movement is in thousandts of a mm so the leadscrew has to be really
> fine, or the stepper driver has a high multiplier.
>
> one step can often change the voltage into the 'too close' range, so
> sitting there, it will cut, open the gap, let the voltage increase,
> and then hit the 'too far' limit.
>
> Screw feed per step and accuracy of the axis are the two super
> cirtical things. too coarse and it will dither itself to death and if
> the axis has any movement, when you do reverse the screw, you can have
> the electrode move sideways, short, and require the whole thing to
> back out and approach with the backlash on the feed-in side.
>
> Dave
>
>
>
>
>
>
>
>
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