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 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 <[email protected]> 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 > [email protected] > > ------------------------------------------------------------------------------ > 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 > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
