What is fuzzy logic?

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By fuzzy logic one indicates a series of techniques which can help synthesizing a digital controller even when dealing with a continuous time system. The general framework of these algorithms is the following:

1) Membership sets are defined: if a measurement is within a certain range, then it will belong to a membership set with some degree ranging from 0 to 1.

Example (taken from wikipedia): Fuzzylogic.jpg


2) Rules are defined: to take action according to the membership result or to combine the membership result of several measurements.

Example:

IF temperature==cold THEN heat_room

IF temperature==warm THEN do_not_heat_room

IF temperature==hot THEN cool_room


3) The rules need to be "defuzzified", which means that we need to find a quantitative result to be linked to the rules.

Example:

heat_room: 5%

do_not_heat_room: 60%

cool_room: 35%

They need to be translated to a number and then fed to the controller. There are many techniques to combine and process the results of such rules. If the rules and the defuzzification are properly done, this can be a satisfactory control system.

By Elisa