PD versus fuzzy control of a three-link spatial manipulator with one flexible link

This study addresses the modeling and control problems of a manipulator with rigid and flexible links and a payload at its tip. The model takes into account the coupling between the rigid body motion of the system and the bending deflection of the flexible link. The effect of gravity is also considered. Two different controllers, namely; independent joint PD controller and a fuzzy logic controller (FLC), are applied to the manipulator. The objective of the controllers is to drive the joints of the manipulator toward a desired destination starting from arbitrary initial conditions while reducing the payload vibrations. The fuzzy control action is distributed between two fuzzy controllers; one for joint angles and the other for tip deflections. The outputs of the two controllers are combined and used as the commanded torque to the manipulator. The study shows that the FLC is superior to the PD control in handling rigid as well as flexible manipulators.