Re: stepper-servo system

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@...>
wrote:

>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Thomas J Powderly
> <tomp-tag@> wrote:
> >
> > Â How many cycles to 'normal' instructions?
> > Â This determines the max oscillator freq.
> > Â But you may want 2 cpu's clocking each other ( one for on, one

for

> off )
>
> I think Ballendo has already answered that one. The nice thing is
> that there is a system clock that can be accessed for timing, you

take

> a note of its value and wait for it to become that value plus a

bit.

> Quite simple code but it will be interesting to see the min pulse
> widths possible.
>
> > Â Or you may be looking at a dynamic offtime based on gap
> >condition.. Â Something like Iso-energetic pulses
>
> I wasn't until last night, there are a few papers on iso-energetic
> generators for micro EDM, apparently fixed rate generators don't

work

> so well but these an produce fairly massive speed advantages when
> roughing it may be that a pure hardware approach will be better

suited

> though because of the short pulse durations.
>
> > Now for your 'stepper in a servo loop',
> > I think you mean to control a stepper motor by the process, not a
> velocity of position loop.
>
> That's correct.
>
> > Open conditions allowed forward pulses ( changed state of
> >amplifier's DIR signal, and enable the Step input )
> > Â The 'velocity' was proportional to the difference between a
> desired target voltage ( say 30V )
> > Â and the actual average gap voltage ( say 28V ) , this gives a

+2

> error.
> > Â The proportion is determined by (Err / Range) * Gain
> >
> > Good conditions were a null point in the control system.
> > The Step line is disabled ( or just not en-abled).
> > No motion is desired when the cut has no error.
> > Â Just wait a few pulses and it'll shift off this nullpunkt :-)
> >
> > Bad conditions changed the sense of the amplifier's DIR line.
> > Â A separate gain can be used for 'running away'
> >
>
> I suspect that because the EDM process is generally quite slow this
> sort of sensible multi zone approach is probably going to work,

have a

> feed rate that can be modified, a get-away speed for shorts and a
> deadzone.
>
> Thanks for the input, I'll try and get something up and running,

the

> sooner I do that the sooner I can find out exactly how good/complex
> the thing needs to be.
>
> Graham
>

Graham: As a mfg of digital THC units and power control products we
have often discussed the EDM market. Plasma and TIG (for which we
are working on a controller as we speak) uses a constant DC
current. The "gap" is controlled by reading the gap voltage and
through a "servo" type feedback to MACH3 the Z is adjusted to give a
constant height as it cuts.

We know a lot about plasma (and learning a lot about TIG) but know
virtually nothing about EDM other than the obvious. We have
discussed offering a power unit but don't know if the best approach
is a pulsed output or constant DC (regulated by the gap?). The
voltages and currents involved are in question as well.

Since our THC uses embedded processors its easy to deal with
different parameters....if we knew what they were.

If you have an EDM or there is soemone here that has built one and
knows the deep technical aspect of the process we are willing to
work with you to develop a control for home EDM.

Contact me if anyone is interested. You get your control unit for
free for helping in the quest.

Tom Caudle
www.CandCNC.com