On Wed, 2 Feb 2011, Jon Elson wrote: > Date: Wed, 02 Feb 2011 22:27:17 -0600 > From: Jon Elson <el...@pico-systems.com> > Reply-To: EMC developers <emc-developers@lists.sourceforge.net> > To: EMC developers <emc-developers@lists.sourceforge.net> > Subject: Re: [Emc-developers] pid bug > > Peter C. Wallace wrote: >> It looks like the integral term has some funny problems in the pid comp. >> >> The symptom is that when the integral term causes the output to saturate, and >> there is no integral limit or the integral limit is > MaxOutput/Igain it >> never recovers, and ends up driving in one direction regardless of the error, >> This seems to be broken in the part of the code that prevents integral >> wind-up >> this code prevents integral wind-up but also prevents recovery if the output >> saturates (because its stops calculating the integral term in when >> in saturation an therefor the integral term that cause the saturation is >> "latched") >> >> > Good detective work! I have never liked the way EMC's I term worked, > form the very beginning. > The original one had no "horizon" so error from hours ago could still > influence the output. > The new one was supposed to work, but I think your discovery exactly > matches what I have seen. > > Jon >
It was pretty surprising. I was using Matt Shavers velocity mode test hal file with halrun, so the effect was not masked by a FE as it would be under EMC. If we had any integral gain and put enough load on the motor that it could not match the requested velocity, and therefore saturated the PID output, as soon as we removed the load, instead of a velocty overshoot and recovery, the PID loop locked up with a saturated output resulting in a runaway. Peter Wallace Mesa Electronics ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
