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'Re[4]: FuzzyTech MP'
1996\04\08@095253
by
Mike Riendeau

>Mike: fuzzy logic doesn't "know" anything; it would be more useful to
>the debate to limit that sort of personification.
I think I implied that in the second half of the paragraph.
>For that matter, the closed form math doesn't "know" where the poles
>& zeros are, either, no matter what algorithm you choose to
>express it.
Your right, the engineer who analyzed the plant response knows
where the poles and zeros are, and his closed form algorithm
provides the gain and phase compensation.
>And, most importantly, physical processes don't have poles & zeros,
>anyway. The poles & zeros are a feature of your mathematical model of
>the process.
I don't know where you studied control theory, but If you are using
a linear timeinvariant system to control a physical process, It
had better have a response in the frequency domain.
>There is no reason that I know of to believe that there
>are no other valid models of physical processes, or to
>believe that other models might not be as good.
I didn't say there were no other valid models. I said if you have
a model which in closed form, you know what compensation will
provide stability for all time.
Regards,
Mike
1996\04\08@122728
by
John Payson

> Your right, the engineer who analyzed the plant response knows
> where the poles and zeros are, and his closed form algorithm
> provides the gain and phase compensation.
>
> >And, most importantly, physical processes don't have poles & zeros,
> >anyway. The poles & zeros are a feature of your mathematical model of
> >the process.
>
> I don't know where you studied control theory, but If you are using
> a linear timeinvariant system to control a physical process, It
> had better have a response in the frequency domain.
>
> >There is no reason that I know of to believe that there
> >are no other valid models of physical processes, or to
> >believe that other models might not be as good.
>
> I didn't say there were no other valid models. I said if you have
> a model which in closed form, you know what compensation will
> provide stability for all time.
I think one of the issues with fuzzy systems is that reallife systems
seldom exhibit ideal linear behavior; PID systems can be unstable or
conditionallystable on such systems and changing system behavior can
change controller response. While fuzzy systems will seldom have closed
loop behavior as good as a perfectlytuned PID system, they can often be
made less sensitive to system characteristics.
As a (very) rough analogy, a camera lens which is designed to focus perfectly
at a certain distance will be very sensitive to changes in that distance;
objects at other distances will be out of focus. By contrast, a lens which
is focuses less well at is focusing distance may blur less at other distances.
The extreme example of this is a pinhole camera which blurs objects at all
distances roughly uniformly.
1996\04\09@101831
by
terogers
John Payson wrote:
> I think one of the issues with fuzzy systems is that reallife systems
> seldom exhibit ideal linear behavior; PID systems can be unstable or
> conditionallystable on such systems and changing system behavior can
> change controller response. While fuzzy systems will seldom have closed
> loop behavior as good as a perfectlytuned PID system, they can often be
> made less sensitive to system characteristics.
John: you make a good point. But is it true that a fuzzy control system
will seldom have as good a loop behavior as a tight pid system? I
haven't ever seen any theoretical treatment of this.
 Tom
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