Design and tuning of a distributed fuzzy logic controller for flexible-Link manipulators

Fuzzy logic control is already in use due to its computational efficiency and robustness. If a person is sufficiently familiar with a system, intuition can be used as a basis to design a fuzzy controller for it. It may be difficult to accurately describe the behavior for flexible manipulators as their variables are strongly coupled. This paper reviews existing fuzzy logic controllers for flexible manipulators and discusses some of their limitations. It presents an alternative structure using a distributed fuzzy logic controller that controls angle and link vibrations of flexible manipulators independently. While the rules and structure of the proposed distributed controller offers significant advantages compared to those available in literature, its performance still depends on the membership functions for its input and output. variables. Wrong choices of these membership functions may lead to sluggish response, excessive vibration, or instability. The paper presents a novel algorithm, Low Dimensionality Tuning Algorithm (LDTA), for tuning a fuzzy controller by changing the membership functions of its variables using nonlinear programming. LDTA uses only two variables to describe each fuzzy variable to avoid dimensionality problems associated with searching for a solution to problems with large number of variables. The paper also discusses possibilities of simplifying the tuned fuzzy controller.