RE: [CAD_CAM_EDM_DRO] Spindle RPM control

My idea on the same lines was use the step and direction of an axis to
drive an up/down counter. The output of that counter could be made into
PWM, or drive a DAC. You could set the axis in the control program so
that the step size is proportional to whatever you're driving. For
instance, 1volt out from a DAC equals 1000 rpm, and a count of 100 on
the counter makes 1 volt. Set the steps/inch of that axis to 100 and you
could:
G00 W1.000
To get a count of 100, giving a voltage of 1 volt, and 1000 rpm.

If you then said:
G00 W0.500
The counter would count down to 50, making 500 rpm.

(Think my math is right, it's early yet, but you get the idea)

Regards,
JJ

Be Kind, Be Careful, Be Yourself

> -----Original Message-----
> From: RichD [mailto:cmsteam@...]
> Sent: Thursday, September 26, 2002 10:21 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Spindle RPM control
>
>
> Jon,
> You are so right. Oh well.
> RichD
>
>
> Jon Elson wrote:
> >
> > RichD wrote:
> >
> > > CNC Idea!
> > > RPM control of a spindle motor (controller) with a
> frequency to voltage
> > > converter by using a spare axis CNC control program step output.
> > > The rate is set in any block with the F word as needed.
> > > The direction bit can control on/off/disable if wanted.
> > > The FVC output will substitute for the pot in a typical
> PWM full wave
> > > rectifier controller such as used in the Sherline machines.
> > > The KBE controllers can be used in this manner.
> > > This idea sort of is a poor mans constant velocity
> control or speed change
> > > for various reasons in special cases.
> > >
> > > Is this viable, plausible or practical?
> >
> > The problem is that most CNC programs do coordinated motion
> on all axes
> > simultaneously, so the spindle would stop every time the
> other axes stopped,
> > and would be ramping up and down with every feedrate change
> as the axes
> > accelerated and slowed.
> >
> > > I have not identified a VFC chip as yet. Do they exist?
> >
> > Yes, but for this purpose, simple circuits might do just as
> good a job.
> > A pulse stretcher, made from a one-shot, followed by an integrating
> > op-amp to smooth out the pulses would do it.
> >
> > Jon
> >
>
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