Fuzzy Temperature Control A fuzzy controller adjusts the cold air flow according to the size (V: volume) of the controlled room and its ambient temperature (T). The air flow is adjusted by controlling the angle (F) of a shutter inside the intake pipe that supplies cold air. Partial flow is proportional to the shutter angle. An angle of 90° allows maximum air flow, while an angle of 0° completely closes the shutter and stops the air flow. This is depicted in the following diagram. Intake Pipe Cold Air Flow Input Variables The table to the right shows the input and output variables of the fuzzy controller. The fuzzy knowledge base is shown below. Room Size: V Ambient Temperature: T Angle of Cold Air Flow: F Output Variable Fuzzy Knowledge Base 1 IF (V is low AND T is low) THEN F is low 2 IF (V is low AND T is medium) THEN F is medium 3 IF (V is low AND T is high) THEN F is high 4 IF (V is medium AND T is low) THEN F is medium 5 IF (Vis medium AND T is medium) THEN F is medium 6 IF (V is medium AND T is high) THEN F is high 7 IF (V is high AND T is low) THEN F is medium 8 IF (V is high AND T is medium) THEN F is high 9 IF (V is high AND T is high) THEN F is high The fuzzy sets "low", "medium", and "high" are defined next for each one of the input and output variables. 1) Room Size: V Fuzzy Membership Functions for Controlling Room Temprature 02- 0 80 100 120 60 Room Bize In Cubio Meters 2) Ambient Temperature: T Degree of Membership 0.8- 0.6 40 -low(x) -medium) high 140 160 Fuzzy Membership Functions for The Ambient Temperature 1 08- 06- 04- 02- XXX 10 30 40 50 20 Temperature in Degrees Celdout 3) Angle of Cold Air Flow: F Fuzzy Membership Functions for The Angle of Cold Air Flow 1.2 LEXEXET 0.2 0 20 60 80 100 40 Angle in Degrees low(x) -medium(x) -high(x) medium(K) -high(x) Fuzzy membership functions for the temperature (T) T Low T Medium(T) High (T) 0 1 0 0 2 1 0 0 4 1 0 0 6 1 0 0 8 1 0 0 10 0.75 0.25 0 12 0.5 0.5 0 14 0.25 0.75 0 16 0 1 0 18 0 1 0 20 0 1 0 22 0 1 0 24 0 1 0 26 0 0.75 0.25 28 0 0.5 0.5 30 0 0.25 0.75 32 0 0 1 34 0 0 1 36 0 0 1 38 0 0 1 40 0 0 1 In the above-mentioned fuzzy controller, the room size is 35 cubic meters and the ambient temperature is 28°. 1. Use the MIN/MAX method to find the fuzzy membership function for the shutter angle (F). 2. Use the center of gravity method to find the crisp value of F.
