ABSTRACT
This era belongs to modern computer technology . The field of artificial intelligence is showing a definite utility in all spectrum of life .In the field of control , there is always a need of optimality ,with improved with improved controller performance . In this paper, the feasibility of fuzzy logic as an effective control tool for dc motors .
This fuzzy logic controller (FLC) is showing better performance than the conventionalcontrollers in the form of increased robustness .
In this paper , the role of fuzzy logic as controller and its implementation is studied .
INTRODUCTION:
· Fuzzy logic is a powerful problem solving methodology introduced by lotfi zadeh in 1960’s .
· It provides tool for dealing imprecision due to uncertainty and vagueness , which is intrinsic to many engineering problems.
· It is a superset of Boolean or crisp logic .
· It emerged into mainstream of information technology in late 1980’s and early 1990’s .
· If feedback controller is programmed to accept noisy, imprecise input they would be much more effective and perhaps easier to implement.
What is fuzzy logic ?
· Fuzzy logic resembles human decision making with its ability to work from approximate data and find precise solutions .
· Classical logic or boolean logic has two set of values (true or false). It requires deep understanding of a system ,exact equations ,and precise numeric values.
· Fuzzy logic is continuous form of logic ,(eg: bad , very bad ,poor , average), it allowes modeling complex system using a higher level of abstraction originating from our knowledge and experience .
WORKING OF FUZZY LOGIC :
· The working of fuzzy logic can be understood by considering simplified example of thermostat controlling a heater fan.
· The room temperature detected through a sensor is input to a controller , which outputs a control force to adjust heater fan speed.
· The first step in designing such a fuzzy controller is to characterize the range of values for input and output variables of the controller.
· Labels such as cool for the temperature and high for fan speed are assigned and a set of simple English-like rules to control the system are writtern.
· Inside the controller all temperature regulating actions will be based on how current room temperatures falls into these ranges and the rules describing the system behavior .
· The controller output will vary continuously to adjust the fan speed. The temperature controller described above can be defined in four simple rules:
1. If temperature is cold then fan_speed is high.
2. If temperature is cool then fan_speed is medium.
3. If temperature is warm then fan_speed is low.
4. If temperature is hot then fan_speed is zero.
Fuzzy controller accepts an input value, performs calculations and generate an output value. This process is called fuzzy inference process.
Thermostat works in three steps:
1. fuzzification
2. rule evaluation
3. defuzzification
FUZZY LOGIC