On Tue, 7 Nov 2017, Gene Heskett wrote:
Date: Tue, 7 Nov 2017 17:40:40 -0500
From: Gene Heskett <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: [email protected]
Subject: Re: [Emc-users] PID refresher for Gene?
On Tuesday 07 November 2017 12:48:36 Peter C. Wallace wrote:
On Tue, 7 Nov 2017, Gene Heskett wrote:
Date: Tue, 7 Nov 2017 12:28:31 -0500
From: Gene Heskett <[email protected]>
Reply-To: "Enhanced Machine Controller (EMC)"
<[email protected]>
To: [email protected]
Subject: Re: [Emc-users] PID refresher for Gene?
On Tuesday 07 November 2017 10:08:33 Peter C. Wallace wrote:
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
Not too likely Peter, there is a 74ls04 used to clean up, square up,
the waveforms from the photointerrupters. about 3" of cable away
from them. Because of the limited space under the cover, and the
longer lines to the electronics box I had to make it in two pieces.
The square waves are nice and clean at the bob inputs on a 100 mhz
dual trace scope, and at the encoder a/b inputs on the halscope.
Limited there of coarse by the bandwidth of the halscope which shows
a clean ramp. The little monster, with only 4 feet of cable between
the same photointerrupter and the bob inputs. And it has the same
problem, in fact it was on TLM that I first made this fifo based
averager. And I incorporated it in the hal file in the pi version on
the Sheldon, which has ATS667's watching the 60 tooth bull gear. It
however has a vfd, which doesn't need the feedback to maintain
within a couple percent of the requested speed.
Can you plot the encoder velocity signal via halscope at a known
constant speed and post a screen shot?
What spindle speed would give you the most info?
300 or 600 RPM should be fine
I asked about EMI because I dont know of any other customers with this
kind of issue with velocity estimation.
Thanks Peter.
Peter Wallace
Mesa Electronics
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
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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