Rockwell Automation RSLogix 5000 Fuzzy Designer - Manual (Page 49)

Publication LOGIX-UM004A-EN-P - March 2007
FuzzyDesigner Component Library 49
FuzzyDesigner also supports this s-norm (fuzzy OR operator):
maximum: S
max
(x, y) = max (x, y)
The evaluation of the Rule Block is completed in three steps.
1. DOFs of all rules are computed from DOFs of the rule premise
by using the selected t-norm.
2. DOFs of all conseqent variables terms are computed for every
rule.
These DOFs are obtained from DOFs computed in step 1,
multiplied by weights of consequent variables.
3. Total DOFs of all consequent variables are computed for the
overall fuzzy system.
Total DOF of one consequent variable is computed as maximum
value of DOFs computed in step 2 for the appropriate
consequent variable.
Assume a simple fuzzy system with these two premise variables
(temperature, pressure) with terms:
• Temperature: (small, large)
• Pressure : (negative, zero, positive)
This system also has two consequent variables: (voltage, current) with
terms:
• Voltage: (small, medium, large)
• Current : (zero, positive)
This system also has a minimum t-norm.
The rule base can be formulated as the following.
If And Then
Temperature is small Oressure is negative Voltage is medium [0.9]
Current is positive [1.0]
Temperature is large Pressure is negative Voltage is small [0.8]
Pressure is positive Voltage is small [1.0]
Current is positive [1.0]