Steve,
When I first started looking at spindle control I had a brief look at
PWM to DC conversion but could't come up with a way of doing it
without a lot of circuitry.
The easy way is to use a PIC but I didn't feel the application
warranted that much effort.
I agree with the conclusions from the referenced article. My
thoughts are that, provided the PWM base frequency is stable, the
useful information is the ON period, this can be used to charge an
integrator and would be linear, this voltage could be then transfered
to a sample & hold circuit, triggered by the falling edge of the
waveform.
I never took it beyond the initial thoughts because it seemed the
FtoV solution seemed so much simpler. It would be interesting to see
how Servo's circuit works.
Bernard
--- In mach1mach2cnc@..., Steve Blackmore <steve@p...>
wrote:
On Sun, 10 Aug 2003 15:16:03 -0000, you wrote:
If you need a linear frequency response from an RC network look up
op-
amp integrators.
Hi again Bernard - I altered my circuit, without too much sucess.
The
response is still slightly curved. I've posted a file called
pwmv.pdf
with a couple of graphs of voltage output versus speed selection. As
you can see altering the pwm rate makes no difference, increasing
the
voltage gives a more linear top end, but its still not quite there.
It
would appear that from browsing various articles that it is a commom
phenomina and in a lot of commercial systems the top and bottom and
of
the scale is discarded.
It would also appear that maybe my assumption of PWM and Art's
implementation is flawed? I incorrectly assumed that RMS values are
proportional to duty on/off cycles, until I read this article
Comments?
--
Steve Blackmore
