Defuzzification Methods (PID and Fuzzy Logic Toolkit)

LabVIEW 2012 PID and Fuzzy Logic Toolkit Help

Edition Date: June 2012

Part Number: 370401J-01

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Defuzzification is the process of converting the degrees of membership of output linguistic variables within their linguistic terms into crisp numerical values. Consider the following rules:

(1) IF Vehicle Position x is Center
(degree of membership = 0.8)
AND (Minimum) Vehicle Orientation β is Left Up
(degree of membership = 1.0) = 0.8
THEN Steering Angle φ is Negative Small
(2) IF Vehicle Position x is Right Center
(degree of membership = 0.1)
AND (Minimum) Vehicle Orientation β is Left Up
(degree of membership = 1.0) = 0.1
THEN Steering Angle φ is Negative Medium

These two rules specify two non-zero values for the Steering Angle φ output linguistic variable:

Negative Medium
Negative Small
to a degree of
to a degree of
 0.1
 0.8
Note   Fuzzy controllers use an implication method to scale the membership functions of output linguistic variables before performing defuzzification.

A fuzzy controller can use one of several mathematical methods to perform defuzzification: Center of Area (CoA), modified Center of Area (CoA), Center of Sums (CoS), Center of Maximum (CoM), or Mean of Maximum (MoM). Selecting a defuzzification method depends on the context of the design you want to calculate with the fuzzy controller.

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