Re: Plasma Voltage Servo

--- In CAD_CAM_EDM_DRO@y..., "aspaguy" <spaguy@l...> wrote:

> Mariss and Tom, In the "real world" the theory has been being used
> for some time in commercial applications, it just controls the
> direction of a dc moter by reversing polarity rather than using a
> stepper.
> Also Mariss, I wonder how hard it would be to add a feature of

the

> axis being raised all the way up when the voltage drops to zero,

then

> lowers again to the previous height when the plasma is activated
> again. this would be to give more safety room between cuts to avoid
> tip ups, etc. from damaging the plasma cutter. I would assume this
> would need to be handled in the software. What would happen if I

were

> to wire up both this circuit and a computer output to the same

gecko

> drive? In theory, they would be not be sending commands at the same
> time.
> Thanks,
>

Dale

>

Mariss, or others,
It occurred to me after posting the above message that I could
probably use a software command such as one normally designated to
turning on and off a spindle to Activate or deactivate a DPDT relay
in order to toggle back and forth between computer control and torch
voltage control. The two poles of the relay would switch the step and
direction inputs. What do you think? Is this even neccesary?
Thanks, Dale

>

>

> --- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...>
> wrote:
> > Hi,
> >
> > The circuit I drew up has a 30Hz bandwidth; any signal frequency
> > component above that value will average to its DC value. The
> trimpot
> > would allow you to adjust the torch to any height between 70 and
> 140V.
> >
> > It would be useful for me to see a 'scope picture of what the
> actual
> > voltage looks like in operation. You mention a sawtooth waveform.
> > What is the amplitude and frequency? What is desirable to servo

to?

> > Since I lack any practical knowledge on this subject, I would

need

> > this info to make a sensible comment.
> >
> > Mariss
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "ths992001" <thscarince@h...> wrote:
> > > WRT plasma arc voltage vs torch to work distance:
> > >
> > > Once I read an Amercan Welding Society paper on this subject.
> > > According to this article, the arc voltage wavform is something
> of
> > a
> > > sawtooth. At the beginning of the cycle the arch starts at the
> top
> > > of the material at a certain voltage. As it rapidly burns its
> way
> > > down the face of the cut, the voltage ramps up to some peak at
> the
> > > bottom surface of the material. At this point, the arc jumps
> back
> > to
> > > the top surface and the cycle begins again.
> > >
> > > This means that the average arc voltage may not be an ideal
> > > indication of the torch height in all conditions (material,
> > > thickness, feed rate, amps, target height...). The author
> proposed
> > > using the "peak low" (the base of the sawtooth) voltage as this
> > best
> > > represents the actual height under varying conditions.
> > >
> > > Got an extra op amp for an averaging peak (or valley, in this
> case)
> > > detector Mariss? Seriously, his design will probably do the
> trick
> > > just fine in the real world.
> > >
> > > Tom Scarince