Re: Controlling VFDs from your PC?

Hi Sean,

in the old days, we would put a voltage divider to get the voltages
for each step, (or use a pot to adjust it) then use a relay to
determine which circuit to use.

it would work like this, you set your tool path and in that part of
the code when you need to speed up or slow down the motor, you signal
a relay. instant new speed. two outputs could offer 4 speed
settings and each pot/relay would be adjustable.

Of course it does not follow that your code can control the speed in
real time nor can it change speed, only change circuits forcing you
to have set the speed correctly.

I'm sure there is a simple serial circuit that would receive a serial
data set and adjust the output accordingly. I have a cohort that
does such electriconical stuff.

A note on VFD's; they have an internal ramp up circuit allowing a
speed change to ramp from 2 hz to 20 hz in so many seconds. speed
change is not instant. The time may be a fraction of a second, or
over a minute. This is a setting you make when you set it up. ditto
for slowing from high to lower speed, different setting so you can
speed up quickly, an slow slowly. Braking is also a separate
adjustment.

As a note to the group, how many speed changes would you make with
one tool in the same operation ?

Dave




--- In CAD_CAM_EDM_DRO@y..., "stevenson_engineers" <machines@n...>
wrote:

> >--- In CAD_CAM_EDM_DRO@y..., "audiomaker2000" <audiomaker@s...>
> wrote:
> > Thanks guys.
> >
> > That makes me ask....
> >
> > How do you produce an analog signal of varying voltage from one

of

> > your computer's ports? I don't know much about this, but from

what

> > I've read, most pins produce either a "high" or "low" condition
> >which
> > I can see triggering a relay, but not a variable "pot".
> > I suppose this is normally taken care of by the complex

electronics

> > of a CNC machine, but I am retrofitting with a system that

appears

> >to
> > only produce step and direction signals.
> > So how do you turn your computer into a "dimmer" instead of
> > a "switch"?
> >
> >
> > Any ideas?
>
> Sean,
> What system are you using?
> I ask because AHHA is able to output an analog signal 0 - 10V on

it's

> card to control a VFD. You just take two wires from the port to the
> VFD and whatever you program in is then sent to the VFD as a
> referance voltage.
>
> John S.