Re: stepper-servo system

--- 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