Comparison of Distributed PD-like and Importancebased Fuzzy Logic Controllers for a Two-link Rigid-flexible Manipulator

Abstract

Fuzzy logic control presents a computationally efficient and robust alternative to conventional controllers. While experts can easily design fuzzy logic controllers (FLCs) for many applications, some systems such as multilink flexible manipulators, which have many variables and complex behavior, offer challenges to fuzzy logic control. In this paper we present two distributed controllers for a two-link rigid-flexible manipulator that moves in a vertical plane where the gravity field is active. The first distributed controller, which is based on observing the performance of the manipulator, uses three PD-like FLCs: the first two FLCs control joint angles and joint angular velocities while the third controls the tip vibration. The second distributed controller is based on evaluating the importance degrees of the output variables of the system. Variables with the same rank of high importance degrees are grouped together, while variables with low importance degrees may be deleted to simplify the design of the controller. The fuzzy rules in the two proposed structures are selected to mimic the performance of comparable linear controllers. The parameters in both FLCs are tuned using nonlinear programming to obtain better performance. The two distributed FLCs are simulated and compared. The robustness of both tuned distributed FLCs is tested by varying the joint trajectories and angular velocities. The effect of changing the payload on the robustness of the two controllers is also considered.