On Tue, Nov 7, 2017 at 4:35 PM, Gene Heskett <[email protected]> wrote: > 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 tried to explain this before. Ideally you want quiet a few pulses per servo cycle. One way to go is slow down the servo cycle. But there is nothing better then just getting a better sensor. On another list I saw a spindle encoder on a mini lathe that was geared up with a cog belt so the encoder spun about 3X faster then the spindle and had about 3,000 pulses per spindle revolution. With this step even at 60 RPM should be 3,000 lines or counting up and down edges on both A and B phases 12,000 edges per second at 60RPM. That is enough. Good quality 1000 or 600 line optical encoders are under $20 on eBay I'd place the encoder on the motor no the spindle as typically the motor spins faster. >> >> 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 > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ 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
