re: Fuzzy Control

From: kfitzger@foxboro.co.nz
Date: Wed Jan 03 2001 - 02:51:49 MET

  • Next message: William Gray: "AI Software"

    A convenient text that covers this is "Fuzzy Logic & NeuroFuzzy
    Applications Explained" by Constantin von Altrock. This includes a demo of
    FuzzyTECH software and is a good introductory text for industrial
    applications of fuzzy logic.
    Regards,
    Kevin FitzGerrell
    Systems Engineer
    Foxboro New Zealand

    ----------original message-----------
    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
    

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