Fuzzy logic control presents a computationally efficient and robust alternative to conventional controllers for many systems. This paper presents a distributed fuzzy logic controller (FLC) structure for a flexible-link manipulator based on evaluating the importance degrees of the output variables of the system. The two velocity variables, which have higher importance degrees, are grouped together as the inputs of the Velocity FLC. The two displacement variables, which have lower importance degrees, are used as the inputs of the Displacement FLC. The outputs of those two FLCs are summed up to control the joint of the flexible link. The fuzzy rules of the distributed importance-based FLCs are written based on the expert knowledge, and the parameters of the membership functions of the two FLCs are tuned using nonlinear programming. The distributed importance-based FLC structure is further compared with two other commonly used structures: a Linear Quadratic Regulator and a distributed PD-like FLC. The robustness of the three controllers are tested and compared under various conditions.
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