Re: Plasma Voltage Servo

Dale,

A 4016 quad switch could work, but...

You could use an air cylinder to move the whole z in a large move to
provide clearance. This was done on some old multi head machines to
save the cost of drives for additional z axes. (The slide containing
the multiple heads was under computer control, and each spindle had
an air cylinder to "select" it into cutting position).

As you suggest, this air cylinder(clearance move) could be tied to
the on/off of the plasma torch.

Hope this helps.

Ballendo

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