On Sun, 17 Dec 2006, Anders Wallin wrote: > Date: Sun, 17 Dec 2006 11:58:04 +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] duty cycle limiting (was Re: E-stop circuit ?) > >> What we use (in our very limited code space = 1K) for SoftDMC is over-drive >> detection, This is implemented with a 16 bit counter that is incremented by N >> when Drive (PWM etc) is 100 % and decremented by M when Drive is less than >> 100 >> % each sample period. The counter is dead-ended at zero. If the counter ever >> wraps, we do a shutdown on that axis. >> This allows us to program the trip time in sample periods, yet not have false >> triggers when drive is near 100% (a value of M much larger than N will reset >> the count if drive is ever less then full) >> With this simple system (and some reasonable amount of integral term in the >> PID loop) you can pull an encoder connector and have the motor shut down in >> 10 >> mS or so > > this sounds doable in HAL. It would be completely independent of motion > planning, but a safety measure nonetheless. > > The duty cycle limiter would look at the DAC signal and effectively > limit its duty cycle (time integral) to some value. I think you only > need to define two parameters: the time-window, i.e. how much history is > taken into account, and the duty cycle limit. > If the duty cycle ever reaches the limit the component triggers E-stop. > > From looking at the motor specs I can probably figure out what DAC > value corresponds to the rated continuous current. But if the servo amps > are voltage mode, the DAC value will not determine current directly... > > So a question for Jon: are your PWM servo amps voltage or current mode ? > i.e. when I set the DAC to a certain value, does that result in a > constant motor voltage or in a constant motor current ? > > I'm going to test something like this when I get my motors and amps going. > > AW
It should work ok on either voltage or current mode servo Amps. I've only tested it in on voltage mode servo Amps, but the exact current is less important than the behavior of the PID loop when it has no valid feedback. One thing to consider is that its an "open-loop detector" If the PID loop has full DAC value for 100 or so samples, you're not running closed loop, you're in run-away... > > ------------------------------------------------------------------------- > 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
