RE: [CAD_CAM_EDM_DRO] stepper-servo system

Hi Graham,

You mention spark gap, reminds me of automotive test work we did. We could
measure and display the spark on any one or all of the plugs in a vehicle.

Do you know if measuring the spark voltage on EDM would tell one something
about its length? Is this info then used to control the advancement of the
electrode?

Probably some sort of simple positional only servo loop?

Alan KM6VV

>
> To get to grips with the programming of the parallax propeller chip
> I'm going to upgrade my RC based sinker EDM. As the chip has 8
> processors it should be possible to have one creating pulses for the
> EDM, one for controlling the stepper on the z-axis and others doing
> the GUI etc.
>
> I will have a DC voltage comming from the spark gap, this will be a
> low pass filtered version of the gap voltage, essentially proportional
> to the gap voltage. It will be digitized and available to the
> processor as feedback for the stepper motor.
>
> I was initially considering just setting the stepper off at a constant
> speed, then using an algorithm to adjust the speed and direction based
> on the amount of time spent in the "machining zone". However some
> form of true servo type system might be preferable.
>
> I hoping someone might know a bit about using a stepper motor within a
> servo loop. Of course the feedback is to be implemented digitally
> which makes things even more tricky for me, I can remember the term z
> transform but not much else.
>
> Graham
>