On Thursday 07 April 2016 13:45:14 Peter C. Wallace wrote: > On Thu, 7 Apr 2016, Gene Heskett wrote: > > Date: Thu, 7 Apr 2016 13:21:35 -0400 > > From: Gene Heskett <ghesk...@wdtv.com> > > Reply-To: "Enhanced Machine Controller (EMC)" > > <emc-users@lists.sourceforge.net> > > To: emc-users@lists.sourceforge.net > > Subject: Re: [Emc-users] Servos and Drives PID Values > > > > On Thursday 07 April 2016 12:43:41 sam sokolik wrote: > >> I have tried the at_pid.. I have not had it work for me (create > >> workable PID numbers) Even with velocity mode amps. > >> > >> sam > > > > Coming from you Sam, I am surprised. Which makes me want to see > > what it can, or cannot, do for me, starting with my most difficult > > axis, Z, which is both slow and quite heavy for a 16mmx5 screw to > > move up even with a 1600 oz/in motor doing the screw twisting. But > > its a low current, very high inductance motor, so the torque falloff > > is a huge problem above 25 ipm. > > > > Do you recall how it failed at this late date? > > > > Thanks Sam. > > Unless this is a servo system, AT-PID is pretty useless. Tuning the > stepper PID loop is trivial since its an almost perfect first order > loop and can have values plugged in:
The only "servo's" in my locale are the spindle controls, both the toy lathe, and the newer mill. > FF1 = 1.00 My new machines steppers are set to that, seems to work. I'll have to check the X,Z on the lathe. > P = 1/servo period With a 4khz servo loop, 4000 seems to be ok. I'll have to check the lathe though as I don't recall its that high. > FF2 = seconds from position read to velocity write (only if you need > uinch following errors ) In at least a decade of LCNC useage, this is the first cogent, believeable explanation I have ever seen for FF2. Thanks Peter. But it makes me ask the question: If its that simple, why the heck is it not in the manpage(s)? Also, should any additional cycles in the feedback path be added? I ask because I wrote a couple paragraphs in hal, used on the lathe and the new mill, that interposes a 4 stage shift register, followed by 3 sum2's in a tree that have the net result of averaging the error generated by the optical disk's irregularities as it averages the velocity over the last 4 edges of the encoders A/B signals. This reduced the encoders noise output to 1/4 what it would be if used raw. This in turn lets me up the PID stuff to stiffen the speed control achieved by a quite noticeable amount. Thats all addf'd in the order so it all takes place on one execution of the servo loop, but for quick reversals, where quick reversals can be done (forget it on the lathe, the chuck is way to heavy), it would seem to affect the FF2 ideal value given the above clarity of explanation. Does it, or is it so quickly settled its a never mind? I have no clue how much time is elapsing between the read, and the subsequent write. Only that on the mill, a 4khz servo loop is running well, and IIRC its 2khz on the lathe. And using halscope, I do not believe that is a way to measure it since the halscope is synchronous to the reads I have been led to believe. Is there a way to measure that via hal's showconfig? Thank you very much Peter. > AT-PID might work on velocity mode servo drives if FF1 was set first > (it certainly will just be a waste of time if FF1 is not set) > > > [...] > > > > 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> > > > > -------------------------------------------------------------------- > >---------- _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > 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. > > > ---------------------------------------------------------------------- >-------- _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > 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> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
