On Tue, 7 Nov 2017, Gene Heskett wrote:
I fail to see why a 2 or 3 percent error in duty cycle and or quadrature
results in so much noise. There simply is no way in hell that spindle
can be moving at 200 rpms on one servo-thread sample, and 600 rpms on
the next sample one millisecond later while its filtered display on a
pyvcp tach dial says 400 rpms. Thats physically impossible due to the
mass of spinning material involved. One could expand the size of the
fifo, but eventually the lag in seeing a real change in the velocity due
to a tap starting to actually cut will become a factor in the Nyquist
response causing even more instability since thats a direct Pgain input
in any feedback calculations. That of course is self defeating.
It may be that you have a EMI issue, false counts will play havoc with the
velocity estimation so impulse noise generated edges should be eliminated by
quadrature input filtering
To set the input filtering, you set the encoder filter hal pin (set means 15
counts to recognize an input) and then set the encoder sampling frequency
(also a hal pin) so that at you highest spindle speed you have about twice as
many filter counts (30) as needed to respond to the input square wave high and
low states
The man page says I might be able to use some FF1, but 0.05 makes the
whole thing oscillate at about 3 Hz. And I'm talking stopped to 500
revs, 3 times a second when 300 is requested.
So, how does one get a velocity signal out of an encoder with perhaps a
5% peak to peak noise component for a 5% error in input signal timing?
Good question, that... And I certainly have not found an answer.
Cheers, Gene Heskett
--
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soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>
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Peter Wallace
Mesa Electronics
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