On Monday 30 October 2017 19:52:00 Chris Albertson wrote: > I think I see a reason why advice about PIDs used an axis and a > spindle might differ. The axis servo will have a huge about of > gearing so the motor will run fast and the controller will see a lot > of edges per PID loop interval. > > If Gene is using a gear tooth sensor on an 80 tooth gear and running > at 1000 RPM then he is only seeing 1333 gear teeth per second.
On the Sheldon, its ats667's on the bull gear which is 60 teeth, so I am seeing 240 edges per revolution. However, there is no servo pid, and the only thing the encoder is really doing is feeding its position into motion for rigid tapping. Works well even at 25 rpm in backgear. At that speed, the vfd can reverse the chuck in under a revolution. Brutal reversal but it works. The chuck has clamp rings fitted to keep it from unscrewing itself. I've cut air at 500 rpms doing a rigid tap, but there the biggest problem is the nearly 6 turns of overshoot at the bottom of the hole as it reverses. Since I don't own stock in Hanson, I don't do that. :) On this mill, there are 278 edges per spindle revolution. And the quantization noise will excite too much Pgain pretty fast. > I > hope he is not running the PID loop at 1KHz or he sees either 1 or 2 > teeth per interval. We call this an extreme case of quantization > error. In this case needs to be measuring microseconds per tooth or > a MUCH higher resolution sensor. Encoder sampling is running at 50 megahertz in either case. At that speed, waiting for the next edge is as bad as watching paint dry. > > For a spindle I think a longer control loop period is in order. > Unless you are doing rigid tapping all you car about is speed > stability. > > On Mon, Oct 30, 2017 at 4:29 PM, Peter C. Wallace <[email protected]> wrote: > > On Mon, 30 Oct 2017, Gene Heskett wrote: > > > > Date: Mon, 30 Oct 2017 18:44:49 -0400 > > > >> From: Gene Heskett <[email protected]> > >> Reply-To: "Enhanced Machine Controller (EMC)" > >> <[email protected]> > >> To: [email protected] > >> Subject: Re: [Emc-users] Spindle pid problems > >> > >> > >> On Monday 30 October 2017 15:20:35 andy pugh wrote: > >> > >> On 30 October 2017 at 17:49, Gene Heskett <[email protected]> wrote: > >>>> Which is computationally less cpu usage 1, a 6 pack of mux2's, or > >>>> another pid with separate settings and just one mux2 to select > >>>> which pid gets sent to the spindle servo? > >>> > >>> PID is not very CPU intensive, neither is mux2. I wouldn't really > >>> worry about either. > >>> > >>> You can see how much CPU time each module uses in HAL. > >>> > >>> The "lincurve" component was intended specifically for this type > >>> of situation, which is why it has outputs of the r/w style that > >>> can be connected directly to the pre-2014 PID gain pins (which for > >>> no good reason were bidirectional) > >>> > >>> But in this case mux2 seems more appropriate if it is a simple > >>> switch between states. > >>> > >>> Between pid.sh.output and pid.sl.output. When I get everything > >>> else > >> > >> working again. Probably not yet tonight as I had to come and do > >> something about an empty skillet for dinner. > >> > >>> However, I suspect that your problem is that you are trying to use > >>> P on a controller that only really needs FF0 and I. > >> > >> A dc powered spindle is a velocity servo I think, so I been trying > >> to follow John Thorntons wiki article from 2012 where he describes > >> tuning a axis servo in the velocity mode. Is this the wrong > >> approach for a spindle that needs to have quite stiff control? > >> > >> And I just found his other description of spindle tuning, where its > >> all FF0 and Igain. That one however doesn't describe the hardware > >> setup at all, nor does it have any halscope pictures. I suspect > >> that the spindle John was calibrating was being driven by a vfd, > >> which is inherently a pretty stiff drive. > >> > >> But when I get it back to where I can run it (I'm in the middle of > >> moving the spindle power control sequencer from the 5i25 P3 to the > >> same on P2, which feeds a different bob in a different box. And > >> reconnecting it to where I can use an A axis with those pins, and > >> while I am up on the ladder, I'll get the individual boxes bolted > >> together to prevent another short that blew a chain of 5i25's). > >> > >> I really ought to build another, even bigger box, at least another > >> 3" deeper, and 4 or 5" taller so the A driver could fit inside it. > >> Unforch that would take another half a sheet of 1/8" alu plate to > >> go with the close to half a sheet I have on hand. > >> > >> So many projects, so little 'extra' time. :) > >> > >> 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 > > > > As Andy mentioned, Spindle tuning is normally done with mostly FF0 > > and then some I > > > > Johns tutorial is for tuning a position mode loop with velocity > > PID output, but your spindle is a velocity mode loop with velocity > > PID output > > > > > > > > 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
