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Chapter 6
Design Methodology
to as the continuity of a rule base. If neighboring rules have the same or
similar conclusions, the rule base is said to be continuous.
Within large rule bases it is possible to have multiple definitions of the same
rule. This is called redundancy. It has no influence on the inference result
at all if the Max-Min inference method is implemented. But there are other
inference methods, which are not discussed in this manual, such as the
Sum-Product method, in which multiple rules can effect the inference
result.
Operators, Inference Mechanism, and the
Defuzzification Method
In closed-loop control applications that use fuzzy logic, the standard
common operators for the AND- and the OR-operation are the Min- and
Max-operators discussed in the Using IF-THEN Rules in Fuzzy Inference
section of Chapter 5, Overview of Fuzzy Logic. Within certain control
applications in the field of process technology, however, it might be
necessary to use a compensatory AND-operator rather than the pure AND.
The most important compensatory AND-operator is the γ-operator, which
is not discussed in detail here. The γ-operator allows a continuous tuning
between AND, no compensation, and OR, full compensation. In real
situations the word AND is sometimes used to combine two antecedences
meaning as well as, indicating that you can compensate when you have a
little less of one quantity. This is exactly what the γ-operator, also called the
compensatory AND, can model. Refer to the Related Documentation
section of this manual for a list of documents with more information about
this topic.
The standard inference mechanism is the Max-Min method. Other
inference methods have only a marginal influence on the controller
characteristic.
The defuzzification method derives a crisp output value that best represents
the linguistic result obtained from the fuzzy inference process. As
explained in Chapter 4, Overview of Fuzzy Logic, there are generally
two different linguistic meanings of the defuzzification process: calculating
the best compromise, CoM or CoA, and calculating the most plausible
result, MoM.
PID Control Toolkit User Manual
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