https://www.youtube.com/watch?v=r4B-MksNBJQ
On Mon, Sep 19, 2022 at 3:34 PM Sam Sokolik <samco...@gmail.com> wrote: > The blue is encoder position.. white in encoder position interpolated.. > > > https://electronicsam.com/images/emco/Screenshot%20from%202022-09-19%2015-28-44.png > > On Mon, Sep 19, 2022 at 2:05 PM John Dammeyer <jo...@autoartisans.com> > wrote: > >> And is correct. For RPM measurement a count of 6 is still required. >> Here's my math for this. Perhaps you can explain what position >> interpolated means. >> >> So we have a spindle turning 6000 RPM or 50 RPS. That means if we didn't >> have the longer slot we'd see an edge every 0.0033333333333333333333 >> seconds. >> >> Now assume our counter (parallel port for example) is running 20kHz. >> That's a tick every 50 uS so divide that into 0.00333333 seconds and you >> get 66.6666666666 counts before the next hole on the disk. >> >> In reality you would see 66 counts and then 67 counts and then 66 counts >> etc. and then 133.333333 counts for the index slot. >> >> Anyway, assume we test and can tell the difference between the slot and >> the holes we get 66. Multiply that by 0.000050 (50uS) and we get the time >> for one hole edge to hole edge which is 0.0033 seconds or inverted 303. >> Scale it by 10 to get RPM which is 3030 RPM; out by 30 RPM. >> >> Next time we count 67 which works out to 2985 RPM; out by 15 RPM. >> >> Or we could accumulate 5 readings of 66,67,66,67,66 which gives us 66.4 a >> bit closer at 3012 RPM but really not the 3000 we're actually turning. And >> if it's the other way around 67,66,67,66,67 it's 66.6 average and is 3003 >> RPM. Closer. >> >> Increasing to 60 holes improves things but there will still be a certain >> amount of jitter since we have repeating decimals in the math. With 20kHz >> we're still able to count 5 or 6 ticks but above that encoder count the >> 20kHz tick clock has to be much faster. >> >> Anyway, that's how I'd calculate RPM. What's the position interpolated. >> And is there a better way to get more accurate RPM? >> John >> >> >> >> > -----Original Message----- >> > From: Sam Sokolik [mailto:samco...@gmail.com] >> > Sent: September-19-22 10:20 AM >> > To: Enhanced Machine Controller (EMC) >> > Subject: Re: [Emc-users] missing tooth index questions.. >> > >> > That was my plan - use position-interpolated.. 100 counts is barely >> enough >> > for smooth motion. >> > >> > sam >> > >> > On Mon, Sep 19, 2022 at 11:51 AM andy pugh <bodge...@gmail.com> wrote: >> > >> > > On Mon, 19 Sept 2022 at 17:06, John Dammeyer <jo...@autoartisans.com> >> > > wrote: >> > > >> > > > No. >> > > > A slot is still a hole. So if you are counting, say falling >> edges, you >> > > > will get 5 of them. If you count rising edges you will get 5 of >> them. >> > > >> > > >> > > Actually, the missing-tooth scheme takes a different opinion. Each >> hole >> > > corresponds to 1/6 of a revolution, so the correct scale is 6. But it >> only >> > > responds to actual edges seen, so does not create a synthetic count >> in the >> > > middle of the gap, instead it recognises the approximately double >> period >> > > and adds two (or more) counts when it sees the gap. >> > > >> > > Using position-interpolated will smooth through this jitter. >> > > >> > > -- >> > > atp >> > > "A motorcycle is a bicycle with a pandemonium attachment and is >> designed >> > > for the especial use of mechanical geniuses, daredevils and lunatics." >> > > � George Fitch, Atlanta Constitution Newspaper, 1912 >> > > >> > > _______________________________________________ >> > > 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
