On Tuesday 07 November 2017 17:53:19 Peter C. Wallace wrote:
> 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
Actually I took 2 snapshots. one at nominally 600 revs, and a 2nd one at
about 105 revs to demo how much worse it is when the speeds get down to
a crawl like Nicklas has mentioned. This is when the velocity update
rate is playing with the 1 edge per servo cycle thing. I played with
the photointerrupters to change the quad phase and managed to reduce it
to about 1/2 at the slower speed. By 2200 revs, its only a single,
slightly fat line, one that would work well. however the snapshots bring
this msg to a about 900k. I hope it comes through.
> >> 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>
> >
> > --------------------------------------------------------------------
> >---------- Check out the vibrant tech community on one of the world's
> > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> > _______________________________________________
> > Emc-users mailing list
> > [email protected]
> > https://lists.sourceforge.net/lists/listinfo/emc-users
>
> Peter Wallace
> Mesa Electronics
>
> (\__/)
> (='.'=) This is Bunny. Copy and paste bunny into your
> (")_(") signature to help him gain world domination.
>
>
> ----------------------------------------------------------------------
>-------- Check out the vibrant tech community on one of the world's
> most engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> Emc-users mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/emc-users
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>
------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
