When I look at it again: there is no problem with low speed, only at higher speeds your fast loop needs to be fast enough to track it! You have 0.625 micrometer resolution, so the maximum speed is limited to (1 resolution step size)/(fast loop time - jitter) in units/second (~30mm/s in your case and good computer with 20000ns fast loop)
Output to the motors is ALSO from the fast loop! So the PID is only the control mechanism that sets speed of the motor, not the one that performs the control, that is a separate module (see your *.ini and *.hal files) But PID tuning with all those feedbacks and feedforwards is the most important thing always... It has to be fast, appropriate and not overschoot too much to prevent oscillation. On 12/28/06, Peter C. Wallace <[EMAIL PROTECTED]> wrote: > 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 > ------------------------------------------------------------------------- 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
