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?
> 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
