On Thu, 5 Jul 2012, Jon Elson wrote: > Date: Thu, 05 Jul 2012 22:17:04 -0500 > From: Jon Elson <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: "Enhanced Machine Controller (EMC)" <[email protected]> > Subject: Re: [Emc-users] linear motor tuning questions > > Ralph Stirling wrote: >> That did it! D=0.12 gives me much smoother f-error at >> higher accelerations. I had always assumed that derivative >> term would make oscillations worse, so didn't play with it >> much. At D=0.14 new oscillations appear, but at D=0.08 to >> 0.12 the 10Hz resonance disappears. >> > That's what the D is FOR! But, too much amplifies the unavoidable sampling > granularity of the encoder counts being turned into velocity, and so adds > a disturbance noise to the system. If you are lucky, you can get enough > damping > before that noise starts to make it worse. > > Jon > A couple other tricks with D
1. Use the velocity estimation (encoder velocity) feed into the PID component (pid.N.feedback-deriv) so the the PID component does not use the D/DT of position for the D term calculation (which suffers from the granularity problem so is much noiser) 2. For torque mode drives or simple Hbridges, higher servo thread rates (say up to 4KHz or so) help with stability. This allows higher P and D terms than would be possible at 1 KHz 3. As Jon mentioned, 10 Hz is a very low resonant frequency especially for a linear motor. You probably need much more P and D to get decent acceleration 4. For a simple three phase bridge, you will need a substantial amount FF1 to compensate for back EMF Peter Wallace Mesa Electronics ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
