Tom wrote: > Jon Elson <el...@...> writes: > > - I just kind of feel my way and eventually get a > >> response I can live with, but I know it would be better with a bit more >> damping. But, if I turn D up any higher, it becomes unstable. There >> obviously is a phase shift somewhere in the system, I have a good idea >> it is from electrical through the motor to mechanical, and then back >> from the encoder. But, I don't really have a tool to quantify it. >> >> > > So an electro-mechanical resonant loop... > > Have you tried any sort of mechanical damping directly on the encoder shaft- > kind of like a stepper motor damper? > These are probably fairly sharp resonances, so you'd have to tune the damper to the specific frequency of the resonance. I kiow that I can grab a handle and damp out some modest resonances, but that really is a poor approach. Much better to REMOVE the resonance than try to "mask" it with a damper.
Yes, there is an inductance in the motor and some added in the servo amp output filter, this adds some delay or phase shift. The motor has finite resistance and rotational inertia, so another lag. The belt can stretch, and the leadscrew has mass, so there's another lag. So, this puts several poles into the transfer fuction, and the servo loop needs to set so it never has more than unity gain at any frequency where one of these poles exists. If the servo loop adds another millisecond of delay, it can get real tricky. Maybe that is the REAL clue to why turning up the servo rate helps, is that it cuts down the delay in the servo loop. Hmmmm.... Jon Jon ------------------------------------------------------------------------------ This SF.net email is sponsored by: High Quality Requirements in a Collaborative Environment. Download a free trial of Rational Requirements Composer Now! http://p.sf.net/sfu/www-ibm-com _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
