146 Chapter 5 Fuzzy LogiC
it. The process of designing a fuzzy control system can be described using fol-
Step 1: Identify the principal input, output, and process tasks.
Step 2: Identify linguistic variables used, and deﬁne fuzzy sets and mem-
Step 3: Use these fuzzy sets and linguistic variables to form procedural
Step 4: Determine the defuzziﬁcation method.
Step 5: Test the system and modify if necessary.
The components of a typical control system are shown in Figure 5.15.
Mamdani and Assilian (1975) designed a fuzzy control system for a
steam engine. The purpose was to maintain a constant speed by control-
ling the pressure on pistons by adjusting the heat supplied to a boiler. After
that, fuzzy controllers were developed for air conditioners, video cameras,
washing machines, and so on. The fuzzy control system can be considered a
nonlinear static function that maps controller inputs on controller outputs.
Fuzzy controllers are used for systems where a preferred response must be
maintained based on whatever inputs are received. Naturally, inputs to the
system can alter the state of the system, which causes a change in response.
Thus, the duty of the controller is to take appropriate action by providing a
set of inputs to ensure the preferred response.
A fuzzy controller consists of four main components:
Fuzzy knowledge base: The knowledge base consists of fuzzy rules for 1.
the system that represent the knowledge and experience of a human
expert. For example, “If the temperature is fairly high and the pressure is
very low, then the output is medium.”
A fuzzy controller
Fuzzy sets and
Fuzzy values for
Crisp values for
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