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. 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. 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 > -- 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
