Here are a couple screen shots of the encoder inputs using Halscope. The first is captured at 300 rpm spindle speed. The second is at 2500 rpm. The signals are inconsistent at the higher speed. Not sure if this is normal or an issue?
On Wed, May 6, 2020 at 7:01 AM Dan Henderson <luvtof...@gmail.com> wrote: > A lot of great input here. I’m not sure I fully understand all of the > talking points around kHz and PPR and RPM vs optocoupler speed and parallel > port timing. > > I also have 3 stepper motors in xyz that are being controlled via the same > BOB parallel port combo. They appear to be working okay with the exception > of maxing out at 1” ips jog speed before they lose steps. That seems slow > to me. They are nema 23 425 oz-in with DMQ542 drivers rated up to 80v. I’m > only supplying them 36v. > > But back to the original concern with the spindle motor rpm fluctuation > with encoder feedback. Without the encoder configured in the HAL the > spindle speed is more consistent but not 100% steady. I can drop the PPR on > the encoder from 200 down to 48. I’m not sure if this would significantly > improve the situation at the expense of lower resolution. > > I believe Gene gave me some items to look at in Halscope. I’m going to > attempt to pull this up now and see if I can draw any conclusions as to > where the fluctuation is occurring. > > Thanks for all the input! > > On Wed, May 6, 2020 at 3:44 AM John Dammeyer <jo...@autoartisans.com> > wrote: > >> 1000 PPR encoder turning 300 RPS (18000 RPM) will produce 300,000 Hz >> output. At 10000 RPM it's 167 RPS or 167Khz. >> >> I've been reading through the LinuxCNC source code for the last hour or >> two. If one was just using a parallel port and not sophisticated external >> hardware the hal_parport.c code looks like it reads the input at the >> base_period rate; say 25kHz => 40 uS. >> >> If you figure a standard mill running max 3000 RPM (50 RPS) then a you >> probably need to look at the spindle encoder at least twice per encoder >> period. At 25kHz we're seeing a ParPort task run time of 40 uS. So I'd >> guess the max pulse size from the spindle encoder has to be at least 80 >> uS. >> >> The spindle at 50 RPS uses up 20mS. Divide that by the 80uS implies the >> largest usable encoder is 250 lines. >> >> Have I got that right? I've not found the spindle support code yet. >> Only the HAL install code. >> >> John >> >> >> > -----Original Message----- >> > From: andrew beck [mailto:andrewbeck0...@gmail.com] >> > Sent: May-06-20 12:31 AM >> > To: Enhanced Machine Controller (EMC) >> > Subject: Re: [Emc-users] Fluctuating RPM using CUI ATM 10 encoder >> > >> > John while we are on this subject got a quick question. Just want to >> check >> > my maths. >> > >> > My encoder card on vfd max count rate is 300Khz. Max rpm is 10000rpm >> > >> > So a 1000 ppr encoder should give me 18000 rpm at 300khz. I just need >> > 10000 rpm so that should be well within spec >> > >> > Regards >> > >> > Andrew >> > >> > On Wed, May 6, 2020, 6:45 PM John Dammeyer <jo...@autoartisans.com> >> wrote: >> > >> > > >> > > >> > > > -----Original Message----- >> > > > From: Nicklas Karlsson [mailto:nicklas.karlsso...@gmail.com] >> > > > Sent: May-05-20 9:13 PM >> > > > To: Enhanced Machine Controller (EMC) >> > > > Subject: Re: [Emc-users] Fluctuating RPM using CUI ATM 10 encoder >> > > > >> > > > > Do you have a dual trace 'scope? Spin the spindle and look at the >> > > input >> > > > > and output of the opto-isolator. See if there really is a lag. >> If >> > > you >> > > > > have a new scope would you have it capture the screen and post it. >> > > I'm >> > > > > really skeptical that those isolators are THAT bad. >> > > > > >> > > > > Here is the datasheet for the opto. >> > > > > https://www.mouser.com/datasheet/2/143/EL817-G-26528.pdf >> > > > > They claim an 18 uS rise and fall time. A 1KHz square wave will >> > > have a >> > > > > 1000 uS period and a 500 uS pulse width at 2 KHz the pulse width >> is >> > > still >> > > > > more than 10X the raise time of the opto. But maybe the opto >> is a >> > > fake >> > > > > counterfeit part with very poor performance. >> > > > >> > > > Opto couplers are rather slow. With a high resolution encoder >> frequency >> > > could be maybe up to a few hundred kHz, >> > > > 2000*period/revolution*3600rpm=120000period/second=120kHz, 200PPR >> will >> > > be 12kHz at 3600rpm, 1/(2*18�s) = about 27778Hz = >> > > > about a little bit below 28kHz if mad no misstake. >> > > > >> > > >> > > I think your math is out. Most of the hi res encoders are running >> 2500 >> > > lines per rev. Many are less. But we're only looking at one >> encoder >> > > channel and that works out to twice the number of edges but the actual >> > > frequency is still lines per rev per second. >> > > >> > > So how many revs per second is that? You have to divide RPM by 60 >> to >> > > get revs per second so 3600 RPM is 60 RPS. >> > > >> > > Now you have 60 * 2500 Hz = 150kHz. Still way too high for that >> > > opto-isolator. >> > > >> > > Now if you do like Sam did for his hex milling you update the encoder. >> > > But initially he was milling with about 60 teeth and Linux is more >> than >> > > fine for that when power tapping etc. So 60 * 60 is 3600 Hz and the >> opto >> > > would be fine for that. Even 200 lines at 60 rps (3600 RPM) is >> 12,000 >> > > hz. >> > > >> > > Don't understand how you got 27778Hz >> > > >> > > John >> > > >> > > > >> > > > _______________________________________________ >> > > > Emc-users mailing list >> > > > Emc-users@lists.sourceforge.net >> > > > https://lists.sourceforge.net/lists/listinfo/emc-users >> > > >> > > >> > > >> > > _______________________________________________ >> > > Emc-users mailing list >> > > Emc-users@lists.sourceforge.net >> > > https://lists.sourceforge.net/lists/listinfo/emc-users >> > > >> > >> > _______________________________________________ >> > Emc-users mailing list >> > Emc-users@lists.sourceforge.net >> > https://lists.sourceforge.net/lists/listinfo/emc-users >> >> >> >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> >
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