Sorry, Chris, I get a "Not Found"-Error with your caltech link without
any further comment.
Peter
Am 22.05.2018 um 18:10 schrieb Chris Albertson:
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 <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
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