On Tue, 18 Nov 2008, Jon Elson wrote: > Date: Tue, 18 Nov 2008 11:25:41 -0600 > From: Jon Elson <[EMAIL PROTECTED]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] How can I reduce the DAC noise > > 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
We have a simple velocity low-pass filter in our SoftDMC motion controller. It can eliminate about 80% of the D term whine at the encoder count frequency, and all the weird swishy samplerate/encoder rate beats you hear when ramping velocity. There are disadvantages of course, mainly too much filtering leads to too much phase delay and instability, and just the fact that its yet another dimension to the PID tuning space. > > ------------------------------------------------------------------------- > 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 > [email protected] > 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. ------------------------------------------------------------------------- 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
