Fundamental questions (long)

Adrian Cheok (cheok@ita.melco.co.jp)
Sat, 5 Jul 1997 19:28:45 +0200


Hello everybody,

I am new to this list, so excuse me if I am asking a question which
has already been dealt with.

My background is that I am finishing the writing up of my Ph.D thesis
on the subject of fuzzy logic based sensorless control of motor
drives. The thesis is mainly about power electronics and motor
drives, with the application of fuzzy logic, and therefore I come
from a more applied rather than theoretical fuzzy logic background.

Anyway, I have a some questions which I hope someone can help with or
point me to some references. I have literally hundreds of papers on
fuzzy logic, and also receive the IEEE trans. on fuzzy systems, but I
still feel I do not have a concrete answer. I think I would feel
safer with regards to my thesis is I can have a concrete defense of
fuzzy logic techniques.

My first question is what can fuzzy logic do UNIQUELY - i.e that no
other method can do. For example you often hear about the application
in complex model free systems, and so we can use linguistic knowledge
- but what about modeling the system using neural networks or even
*conventional* mathematical numerical based models? Under what
circumstances will the linguistic knowledge be the ONLY knowledge,
and why? Is there ANY theoretical PROOF of the uniqueness of
advantage of fuzzy techniques in controlling complex systems?

Also what is the advantage in using fuzzy logic when it is being
trained with numerical data. I don't mean to cause offense but I
often read papers that use fuzzy logic trained with numerical data
*only* and wonder what was the actual advantage in doing that?

Lastly but just as importantly, I perceived the main benefit in my
application was that the system could cope very well with noisy input
data. I have the experimental results to prove it, and I believe it
is fundamentally due to the fuzzification of the data, so that noisy
data may still trigger the same input sets and thus rules as clean
data. However I would like more solid proof of this, does anyone have
a reference to a theoretical proof of the ability of fuzzy systems to
cope with input noise?

Sorry for the length of this letter, I hope you can help me, an I
thank you for your time.

Adrian

+++++++++++++++++++++++++++++++++++++++
+ Adrian Cheok
+ DENTETSU SYSTEM BU
+ Product Development Dept.
+ MITSUBISHI ELECTRIC
+ 1-1 Tsukaguchi Honmachi 8 Chome
+ Amagasaki City 661 JAPAN

+ cheok@ita.melco.co.jp
+++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++
+ Adrian Cheok
+ DENTETSU SYSTEM BU
+ Product Development Dept.
+ MITSUBISHI ELECTRIC
+ 1-1 Tsukaguchi Honmachi 8 Chome
+ Amagasaki City 661 JAPAN

+ cheok@ita.melco.co.jp
+++++++++++++++++++++++++++++++++++++++