On Tue, 2008-11-18 at 11:25 -0600, Jon Elson wrote: > Jeff Epler wrote: > > On Mon, Nov 17, 2008 at 10:50:32PM +0800, Howard Chan wrote: > > > >> http://myweb.polyu.edu.hk/~icwfchan/P1.png > >> > > > > This graph does not show measured noise in the DAC output. To measure > > that you would have to hook a scope or other diagnostic equipment to the > > physical DAC output pin on the mesa servo daugher card. > > > > This graph shows DAC output commanded by emc2, which is presumably the > > output of the pid algorithm mentioned by seb. He is correct that it's a > > tuning issue. In addition to the P, I, D, and FF parameters you may > > wish to adjust deadband. deadband can be used to get a PID output of > > exactly 0 when within a specified range of the commanded position. > > (However, if there is an uncompensated voltage offset in the DAC or > > amplifier, this may not fix the problem entirely) > > > I wonder if Mr. Chan is having problems with the D term magnifying the > quantizing error in the encoder count. > I find I have to use very small amounts of D or the quantized noise > dominates the system and causes horrible squealing of the servo. > Sometime I want to see if I can splice a simple digital filter into the > D term to taper off the frequency response of the D term. > Possibly a filter could just be applied between the PID output and the > DAC, PWM or other output device. > > Jon
I think Howard is using an external controller, which may have its own PID. Could this be part of the problem? Kirk http://www.wallacecompany.com/machine_shop/ ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
