This paper presents a robust intelligent scheme to control a highly non-linear parallel manipulator. The primary objective is to force the manipulator to track a prescribed Cartesian trajectory accurately when the system is subjected to different types of disturbances in the forms of forced harmonic excitations. In fact, in an environment containing various forms of disturbances, noises, uncertainties, and parametric changes, a robust control approach is pivotal in ensuring the system performance conforms to the desired specifications. A class of computed torque controller (CTC) is designed in cascade form with an active force control (AFC) technique which employs a fuzzy logic (FL) algorithm to control a 3-RRR (revolute-revolute-revolute) planar parallel manipulator. The scheme to be known as CTC-AFCAFL is applied in order to reject the disturbances while at the same time precisely track the prescribed trajectory in the wake of the introduced harmonic disturbances. The FL is specifically used to compute the estimated inertial parameters required in the AFC loop to trigger the compensation effect. The simulation results provide further insight into the superiority of the proposed control scheme in rejecting the disturbances of the 3-RRR manipulator system for the given loading and operating conditions. The results clearly demonstrate that the proposed CTC-AFCAFL scheme provides a much superior trajectory tracking capability compared to the conventional CTC alone.
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