Past, present and future of fuzzy control: a case for application of fuzzy logic in hierarchical control

Fuzzy logic control emerged in the mid 1970s as a paradigm for rule based control of dynamic systems, primarily in process type control situations. In the past two decades, and specially in the mid 80s to mid 90s, fuzzy logic control, has been successfully deployed in a broad spectrum of application areas ranging from automatic train operation to flight systems. None the less there remains a great deal of scepticism within the control community as to what the real merits of this paradigm are. We focus on the positive aspect of fuzzy logic control, as well as some significant controversial issues that surround this paradigm. In particular, we contend that while the semantic transparency offered by fuzzy logic enables control engineers to efficiently develop control strategies in application areas marked by low order dynamics with weak nonlinearities, the broader impact of fuzzy logic should be in hierarchically structured systems, perhaps in combination with conventional control techniques. We offer examples of application of fuzzy logic in hierarchical setting and discuss a number of theoretical issues that arise in these settings.