On Sun, 2012-12-09 at 20:26 -0500, Gene Heskett wrote: > On Sunday 09 December 2012 20:19:59 andy pugh did opine: > > > On 10 December 2012 00:40, Gene Heskett <[email protected]> wrote: > > > I can't make Pgain cause more than about a 10% of that range cyclic > > > wibble, not near enough to hear it with the spindle at say 6 rps > > > commanded. At least at Pgains up to 150 or so, with FF0 = 100, FF1 = > > > 20 and FF2 = 10. > > > > What makes you think that you need FF1 and FF2? This s your spindle > > that we are talking about here, I think? > > > Yes. In my playing this afternoon, it seemed to have the effect of > speeding up the corrections when I loaded it, or when I changed the speed > from axis. It seems much 'stiffer' with the higher order FF's applied. > > > > Should I be able to induce a rail to rail oscillation with Pgain? > > > > Not always. In the case of your spindle I think the physical > > time-constant and the servo period might be so far apart that it might > > never happen. > > > > > pid.N.feedback-deriv float in > > > > > > I hadn't noticed this before, so encoder.0.velocity only feeds the > > > > > > pid.N.feedback pin. > > > > > > It sounds as if I should feed both pins with encoder.0.velocity. > > > Done, but not tested yet. > > > > Not in your case, as encoder velocity is the controlled quantity, not > > the derivative thereof. > > > > encoder.velocity is only an appropriate feedback-deriv term in a > > position loop. > > But this is not a position loop per sei, its a velocity loop, working in > the rps domain. Does that not change things, and if not, why? > > Thanks Andy. > > Cheers, Gene ZN was thinking about process control but also works for position. The original statement was increase gain until you 'just' get sustained oscillation, i.e. it should not dampen out over time.
I should think that a spindle should look a lot like a cruise control ... back to you Andy et al. ;-) Dave ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
