**Subject: **Fuzzy Control

**From: **Gregory L. Hansen (*glhansen@steel.ucs.indiana.edu*)

**Date: **Wed Oct 11 2000 - 01:19:57 MET DST

**sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Next message:**robert_wilhelm_land: "Re: Grid-partitioning Fuzzy Systems"**Previous message:**Jerry Avins: "OT Re: Visual computation using aliasing and interference"**Next in thread:**james.becker.b@bayer.com: "re: Fuzzy Control"**Reply:**james.becker.b@bayer.com: "re: Fuzzy Control"**Reply:**P. Sarma: "Re: Fuzzy Control"

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

**Next message:**robert_wilhelm_land: "Re: Grid-partitioning Fuzzy Systems"**Previous message:**Jerry Avins: "OT Re: Visual computation using aliasing and interference"**Next in thread:**james.becker.b@bayer.com: "re: Fuzzy Control"**Reply:**james.becker.b@bayer.com: "re: Fuzzy Control"**Reply:**P. Sarma: "Re: Fuzzy Control"

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