An accurate and cost-effective fuzzy logic controller with a fast searching of moment equilibrium point

This paper proposes a cost-effective architecture of fuzzy logic controller (FLC) that works in an accurate and fast manner. The accuracy of the proposed FLC is obtained by using the center of gravity (COG) defuzzifier that considers both membership values and spans of membership functions in calculating a crisp value. The cost effectiveness of the proposed FLC is obtained by restructuring the conventionally simplified FLC in the following ways. Firstly, the MAX-MIN inference is replaced by a read-modify-write operation that can be implemented economically in the structure of register files. Secondly, the division in the COG defuzzifier is avoided by finding the moment equilibrium point. The proposed COG defuzzifier has two disadvantages, in that it requires additional multipliers and it takes a lot of computation time to find the moment equilibrium point. The first disadvantage is overcome by replacing the multipliers with stochastic AND operations and the second disadvantage is alleviated by using a coarse-to-fine searching algorithm. The hardware complexity of the proposed FLC is analyzed in terms of the number of building blocks. Simulation of the proposed FLC to the truck backer-upper control problem is performed in VHDL, and the control performance of the proposed FLC is compared with that of the conventionally simplified FLC in terms of average tracing distance