On Tue, 24 Apr 2012, Eric Johnson wrote: > Date: Tue, 24 Apr 2012 07:14:10 -0400 > From: Eric Johnson <ejohn...@camalytics.com> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: emc-users@lists.sourceforge.net > Subject: [Emc-users] Tuning low resolution axis > > Hi all, > > I have a servo motor axis configured angular with a relatively low > resolution encoder / gear ratio. One revolution of the shaft is 19600 > counts, or 54.4444 counts per degree. I was having a very difficult time > tuning it at 54 counts per degree, so I set the counts per engineering > unit to one revolution, or 19600. I had no problem tuning it in at this > resolution. Positioning error and overshoot were negligible. > > I then started incrementally working my way down to the actual > resolution. Down to about 500 counts per engineering unit, it continued > to work fine without adjusting the PID parameters. For reference, the P > value at this point was about 18. From here on, as I dropped the counts > per engineering unit I also had to reduce P (and eventually D and I) to > keep the motor from humming and otherwise become unstable. By the time I > got down to 54.4444 my P value was down to 0.75. I still had pretty good > lock and hold, however positioning was terrible. On a move, I would get > 20-30 degrees of overshoot before it would settle into position, and > even that was +/- 1.5 degrees from the commanded position, which would > generate following errors and all the rest, except I basically had that > disabled. > > Any insight on what is going on here or how to tune a motor with > relatively low counts per engineering unit would be appreciated. > > Thanks, > Eric
If the input and output units of the PID loop are commensurate you should not have to change any tuning parameters when you change encoder resolution. I think its best to setup PID loops this way so that system/system PID numbers are comparable. If the input and output sunits are _not_ commensurate, you will have to change _all_ tuning parameters if you change encoder resolution. > > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. Discussions > will include endpoint security, mobile security and the latest in malware > threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > 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. ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
