How to Store Efficiently a Linguistic Rule Set in a Fuzzy Controller

Abstract

A fuzzy controller can determine its output values either by evaluating a fuzzy look-up table or by interpreting directly its linguistic rule set. Sometimes the second way has advantages. In this case a method has to be derived to store the rule set in the actual runtime environment such that the controller can interprete it sufficiently fast at run-time.

In this article a fundamental solution of this task is presented. The original rule set is transformed by replacing rules with an identical conclusion by one single rule. If necessary, the premise of such an integrated rule is reformulated such that each rule premise has a standard structure — an OR-connection of AND-connections of linguistic values. A standard structure premise is coded as a matrix with integer-valued elements. It is shown in detail how to code a premise and what are the storage requirements of this method.

It is demonstrated how the controller calculates its output values during run-time. For each sample point it determines the truth value of each linguistic rule premise by evaluating its corresponding premise matrix.

Fuzzy control was implemented with the help of standard functional units of an automatization language. This approach integrate the novel technique of fuzzy control into an automatization environment. As an application of the introduced storing method, it is shown how one can realize the presented approach by additional functional units.