On Thu, 28 Dec 2006, Anders Wallin wrote: > Date: Thu, 28 Dec 2006 18:00:56 +0200 > From: Anders Wallin <[EMAIL PROTECTED]> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Subject: [Emc-users] Lowest speed with servo system ? > > > Hi all, > > With a servo system using quadrature encoder feedback, what is the > slowest speed that can reliably be used ? > > I would imagine that there is a problem if there are no counts between > successive calls to the PID loop ? resulting in jerky instead of smooth > slow motion ?
Well since you are in a feedback loop, a position error is needed for drive, so the best you can do is about +- 1 encoder count. At very low speeds you will get behavior that looks like a stepper, every time the desired position moves a count, the servo will follow with a 1 count move and then stop, so it sounds like a slow stepper :tic,tic,tic... At higher speeds where the motor/mechanics inertia comes into play, there are tricks with PLLs and encoder period measurement that can give you sub count resolution. > > any way to improve on this using some smart HAL code ? > > The setup I'm planning would use a 1000 line encoder (4000counts/rev) > motor directly coupled to a 2.5mm/rev ballscrew. If I require one count > for each call to the PID loop (1 kHz count rate) then that works out to > 0.25rev/s or 15 rpm or a feedrate of 37.5mm/min which does not seem that > low ?? > > comments appreciated ! > > Anders > > ------------------------------------------------------------------------- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to share your > opinions on IT & business topics through brief surveys - and earn cash > http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > 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. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
