Fuzzy logic output defuzzification

Abstract

A microcontroller-based fuzzy logic processing module for generating control signal values in response to variable input signal values in accordance with constraints imposed by propositions or 'rules' stored in memory in a standardized format. Each rule consists of one or more input conditions and an output directive. The input conditions and the output directive for a given rule are 'fuzzified' by determining the degree of membership of each in fuzzy sets defined by membership functions. Fuzzy logic processing is accomplished by determining the extent to which the input conditions are satisfied by the current values of the input signals in order to develop a rule strength value, and then performing a 'center-of-gravity' determination based on the rule strength values assigned to the output membership functions. The center-of-gravity determination performed by representing each output membership function by a discrete value whose magnitude is adjusted to reflect the non-linear relationship between a rule's strength and its influence on the command output value. Using the discrete values weighted in accordance with their pre-calculated area centers, with an adjustment for overlap between adjacent output functions, the center-of-gravity is accurately approximated without requiring piece-wise integration of the output centroid.