Re: stepper-servo system

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