Fuzzy Control


Subject: Fuzzy Control
From: Gregory L. Hansen (glhansen@steel.ucs.indiana.edu)
Date: Wed Oct 11 2000 - 01:19:57 MET DST


Is this the right place to ask about fuzzy logic in control systems? It's
the only fuzzy logic newsgroup I could find.

I'm trying to understand fuzzy logic control systems compared to more
traditional systems like the PID controllers. The examples go through
decision matrices and elaborate logic and calculation to do what seems to
be the moral equivalent of "if sensor moves away from setpoint, adjust
parameter in a direction that will bring the system back", which seems
equivalent to the integral term in a PID controller. What does fuzzy gain
you?

It's been said that fuzzy logic lets you use simple English rules and
focus on what you want the system to do rather than trying to model the
system, and that it easily handles non-linear systems, in contrast to
control theory. And I suppose that's true to a point. But even a simple
PID can handle systems that are non-linear to a degree, because all it
does is produce an output related to the deviation of the system from the
ideal, which is pretty much focusing on what you want the system to do,
and there are simple and even automated methods to calibrate the run
parameters. And in a fuzzy system you still need to define control
regions -- number, locations, widths, overlaps. You still need to
defuzzify the output, you need to tweak parameters. It seems like those
simple English statements are just code words for the modeling and
mathematics that must eventually be done. And I'd be surprised if fuzzy
controllers never suffer instabilities.

I like fuzzy logic. It looks fun and interesting, and probably very
useful in things like expert systems. But I feel a little cheated in how
I've seen fuzzy control systems explained. The popular media seems to
pretend that all non-fuzzy systems are stupid on/off affairs and that
control theory doesn't exist. They bemoan the fact that the U.S. hasn't
been putting many resources into fuzzy logic, but don't mention if that
might be because U.S. industry is satisfied with traditional controllers.
The more technical articles compare traditional controllers in fuzzy logic
terms, like the numerous if...then statements a PID controller must have
rather than just giving a discretized formula that it follows relentlessly
with no decision element whatsoever; a formula, I might add, that seems
simpler than determining the membership of an input to various sets,
cutting out sections of an output set, and finding the centroid. I feel
like a lot of hype surrounds the field.

-- 
"A good plan executed right now is far better than a perfect plan
executed next week."
                       -Gen. George S. Patton

############################################################################ This message was posted through the fuzzy mailing list. (1) To subscribe to this mailing list, send a message body of "SUB FUZZY-MAIL myFirstName mySurname" to listproc@dbai.tuwien.ac.at (2) To unsubscribe from this mailing list, send a message body of "UNSUB FUZZY-MAIL" or "UNSUB FUZZY-MAIL yoursubscription@email.address.com" to listproc@dbai.tuwien.ac.at (3) To reach the human who maintains the list, send mail to fuzzy-owner@dbai.tuwien.ac.at (4) WWW access and other information on Fuzzy Sets and Logic see http://www.dbai.tuwien.ac.at/ftp/mlowner/fuzzy-mail.info (5) WWW archive: http://www.dbai.tuwien.ac.at/marchives/fuzzy-mail/index.html



This archive was generated by hypermail 2b25 : Wed Oct 11 2000 - 01:22:48 MET DST