This paper presents a robust controller design with disturbance decoupling and rejection of a two-degree-of-freedom (2-DOF) Inertially Stabilized Platform (ISP). The objective of these mechanisms is to stabilize the line of sight (LOS) of imaging sensors pointing towards a specific target. There is currently tremendous interest in ISP applications in marine systems. Such a harsh environment subjects the imaging sensors to multiple disturbances, which requires the design of robust control strategies to enhance the performances of ISP systems. The controller designed in this study is a double active controller composed of an inner compensator, and a feedback controller designed based on the H∞ framework. The main advantage of the proposed controller is that it can be implemented in real time, with lower computational complexity and good performance. In this paper, a comparative experimental study was conducted between the designed controller and an integral sliding-mode controller (ISMC). The comparison was achieved through two major tasks of ISP systems: motion tracking and target tracking.

Barge ships are designed to transport and assemble heavy and massive pieces of equipment at sea. Active propulsion systems are not installed in this type of ship, so the desirable motion and positioning of these ships can only be achieved with the assistance of several tugboats. In this study, the dynamical characteristics of barge conveying systems were formulated and robust control systems were designed to ensure efficient barge operation. To achieve these objectives, we first developed a mathematical model of a barge ship, which incorporated a novel conveying system configuration using tugboats. We then designed a robust controller for the tugboats that used the sliding mode law to deliver the desired barge motion performance. Finally, the usefulness of the proposed configuration and controller was verified via simulation studies using another system with an H∞ controller. The proposed sliding mode controller showed superiority, especially in terms of robustness against disturbances.

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