Re: Plasma voltage servo : Mariss?

Hi,

OK, sorry about that. I haven't been following this thread until I
saw my name pop up.

I dashed off this circuit at someone's request some time ago. It was
designed according to what was asked at the time as far as deadband
and thresholds go.

The problem is without the equipment here I could put a scope on and
puzzle out what is needed, I am working with one hand tied behind my
back. I will give it a go though.

Increasing both 470 ohm resistors increases deadband. Increasing the
the 470K resistor or the .01 uF cap decreases the step frequency. The
270K and series combo of 10K resistor and 10K pot provides input
scaling. The 1uF cap was a guess on what would provide enough low
pass filtering while keeping the frequency response high enough to
servo the motor to within the deadband.

Also keep in mind plasma is nasty stuff regarding RFI, so the circuit
should have .1uF ceramic and 10uF 'lytic cap bypass on the +5VDC
supply. The +5VDC should ideally come from a linear (7805) regulator
for best noise suppression. Place a .1uF cap from the two 470 ohm/10K
resistor nodes to ground as well as well; I think they may be exposed
to noise. Put the whole mess in a metal box for shielding.

What I am asking for is for someone equipped with a scope that can
take data of what voltages are required and the rate at which they
change in a typical working enviroment.

Also, anyone that has built this circuit; it would be helpful to know
what is the nature of the problems experienced. This would help me to
know if it is a scale/offset situation or a noise related one. Both
are solvable.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "aspaguy" <spaguy@l...> wrote:
> Mariss, are our needs here just to far outside of the parameters
of
> the comparitors, or can this be adjusted with different values of
the
> other components.
> Thanks in advance,
>
Dale
>

>

> -- In CAD_CAM_EDM_DRO@y..., "morgtod" <todmorg@h...> wrote:
> > Hey there Dale-
> > I am in the same boat as you, I am looking for the best
voltages,
> > dead bands and almost everything else about "voltage servo". I
> have
> > not hooked the circuit to my table yet, I tested the operation on
> the
> > bench with a scope and found out I was stuck. When building the
> > circuit I installed an extra 14 pin socket with the dead band
> > resistors and the step oscillator capacitor wired through it,
this
> > way I can vary the dead band and step rate easily by plugging in
> > components instead of soldering. ( in other words I'm sure I'll
be
> > adjusting these ). I am using a hypertherm powermax 900 and I
plan
> on
> > letting the software raise the torch after a cut and on a call
for
> > torch I'll have a relay switch control from the computer to the
> servo
> > circuit. Hypertherm calls for 1/16", but they call for at least
> > twice that on pierce, so we are going to have to work that in
> > somehow. At present I am using a floating head with Z retraction
> > between cuts, this works suprisingly well except for on light
metal
> > wich tends to get dragged by the torch. I'm sure Mariss can help
> us
> > blindfolded, but I just hate to bug the guy :)
> > Happy cuttin'
> > Todd
> >
> >
> > --- In CAD_CAM_EDM_DRO@y..., "aspaguy" <spaguy@l...> wrote:
> > > Hi Todd, As you can see from the note in the files section,
this
> > > circuit was designed by Mariss, of Geckodrive fame. It was
> designed
> > > due to a thread in which I started when I asked why a stepper
> > > couldn't be controlled by voltage variations. Mariss asked
what
> > the
> > > voltage parameters were an the best I could do with my limited
> > > knowledge is give him the info from my hypertherm manual. If
> anyone
> > > can correct or fine tune the circuit it would be Mariss. I'm
sure
> > > your added information on what is required will be helpful.
What
> > type
> > > and model of plasma are you using? how are you conducting the
> > test?,
> > > by hooking the unit to a complete machine, or by varying the
unit
> > by
> > > hand? My hypertherm manual reccomends a 1/16" distance from the
> > torch
> > > to the material. this may be difficult to maintain with a hand
> > test.
> > > A 1/16" varience may fall inside the5%. What are the voltages
you
> > are
> > > dealing with? What seems to be the optimum voltage for
the "dead
> > > band"? how far outside the band do the voltages go? Does the
> > voltage
> > > increase when the arc distance increases or when it decreases?
> > > Sorry about so many questions, some of them will no doubt help
> > > Mariss, and some will help myself and others when implementing
> the
> > > circuit. I have built the circuit, but have not yet gotten my
> > drives
> > > far enough along to test it.
> > > Thanks,
> > >
> >
>
Dale
> > > P.S. the original thread was about a month ago and could be
> found
> > > easily with a search of "plasma torch height controll". Also,
the
> > > design was purely theoretical,and probably a great starting
> place.
> > > With your help, I imagine we can turn it into something really
> > cool!
> > > thanks
> > >
> >
>
again.
> >
>
>
> >
> > > --- In CAD_CAM_EDM_DRO@y..., "morgtod" <todmorg@h...> wrote:
> > > > Hi-
> > > > Has anyone tried building the plasma voltage servo circuit
> > > listed
> > > > in the files section? I just built one and it only steps
when
> > the
> > > > voltage is between the 5% comparator. For plasma control I
> need
> > > the
> > > > steps to happen outside the 5% going towards center, with a
+/-
> > 5%
> > > (
> > > > or less )dead band. Any ideas on how to get there from here?
> > > > Thanks
> > > > Todd