On Tuesday 22 May 2018 12:10:47 Chris Albertson wrote: > I just got a copy of "Feedback Systems - An Introduction for > Scientists and Engineers, Karl Johan °Aström and Richard M. Murray" > > The book is FREE and pdf format at > http://www.cds.caltech.edu/∼murray/amwiki > I, like others are reporting Chris, am getting a not found error, and I suspect its the character in the little box in front of the "murray" string above. Its reproduced as a small "1/4" symbol here in the browsers (palemoon) font, and I don't think it belongs in a url address. Swag: caltecs way of establishing copyright?
> It is an actual set book that seem to be exactly what anyone working > in this field needs to know. I'd say it is not is mathematically > oriented as a real university control theory book and certainly well > above the hobby level. It assume some know age of Calculus but not a > lot. Pretty much what the title says. But it covers feedback, not > just motion control. so things like op-amps are covered. But you > need to know that to if designing control circuits > > I'm using stepper motors but already have DRO scales. It seems that > I should be able to combine open loop counting with closed loop linear > sensors. > > Suggestion above were good, thanks, because they contain a solution I > had not thought of, drive "I" with different data than "PD" > > On Tue, May 22, 2018 at 6:44 AM, John Kasunich <jmkasun...@fastmail.fm> wrote: > > On Fri, May 11, 2018, at 11:16 PM, Chris Albertson wrote: > >> I looked at the unit. It seems like a good idea. It uses inputs > >> from both the motor's shaft encoders and another encoder on the > >> object that is being moved, like a linear encoder on the table. > >> > >> Question: Let's say I wanted to do this myself. Is there a > >> method that "everyone" in the machine tool industry uses for > >> combining the reading of multiple encoders? If not it seems like > >> the perfect application for a Kalman filter. > >> > >> But maybe you don't combine them but use the linear DRO for > >> position loop and the motor shaft encoders for velocity. > >> > >> This is a common problem I think with robot arms. The joint has an > >> angle sensor but the motor has a shaft encoder. So the control > >> loops might be nested. > >> > >> It reminds my the old saying the "A man with a watch knows what > >> time it is, a man with two watches is never sure of the time." > > > > We did something like this several years ago at Stuart's shop in > > Wichita, on a big Giddings and Lewis boring mill. > > > > We used two PID loops, with their outputs summed. The position > > command went to both loops. The feedback for one loop came from the > > motor encoder, and the feedback for the other loop came from the > > linear scale. > > > > The motor loop was tuned as normal, except that the I-gain was kept > > at zero. The linear scale loop was tuned using ONLY I-gain. So the > > linear scale loop corrected the fairly small steady-state errors due > > to things like the lead screw heating up (10 foot long screw, it > > adds up). It also compensates for backlash in the screw, and if > > there is much of that it leads to disturbances on direction > > reversal. Isn't going to fix a clapped out machine, but can improve > > the accuracy of a tight machine. > > > > > > -- > > John Kasunich > > jmkasun...@fastmail.fm > > > > -------------------------------------------------------------------- > >---------- Check out the vibrant tech community on one of the world's > > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
