Fuzzy logic: An application

Operation of a fuzzy controller

Source: Hitachi Micro System Asia Pte Ltd

Operation of fuzzy controllerBegin

Crisp input

Fuzzification

Fuzzy input

Rule Evaluation

Fuzzy output

Defuzzification

End

Crisp output

Step 1

Step 2

Step 3

Step 1

• Input membership function– E.g.

Cold Cool Normal Warm Hot

0-16 8-25 16-33 25-42 33-500-16 8-25 16-33 25-42 33-50

So, if crisp input = 20°C

We will get, 0.8 truth value of Cool, 0.15 truth value of Normal

Step 2• Create Rule

– If antecedent 1 and antecedent 2 Then consequent 1, etc.

• Determine antecedent truth values– Determine the degree of truth

• Find rule strengths– Find the strength of the entire rule– Which is equivalent to minimum of antecedent degree of

truth

• Determine fuzzy outputs for each consequent label– Derive fuzzy output which is equal to maximum rule

strength

Step 3

• Defuzzification

• Methods:– Centre of gravity (COG)– Maxdot Centroid

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