It is seen that when the hook mass is larger than the load mass or the load has distributed mass property, the load sway of the crane system presents as double-pendulum effect. In this situation, crane system has two different natural frequencies so that the sway characteristic becomes more complex and greatly increases the difficulty of the dynamic performance analysis and controller design. Moreover, the rope length changes significantly affect the stability and control performance of the crane system. In order to solve the aforementioned problems, the linear dynamics of a two-dimensional overhead crane with double-pendulum effect is derived based on a disturbance observer, and is decoupled for controller design by modal analysis. Next, a state feedback controller is presented to achieve robust control performance for a given range of rope length changes. The controller gains are obtained via linear matrix inequality optimization method. Finally, numerical simulations and experimental results validate that the proposed method has superior control performance.

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Summary The swing characteristics of the load of ship‐mounted rotary cranes is very complicated, due to the rotation of the boom. Especially, when the crane is operating at sea, it is subject to some disturbances caused by waves, which makes the precise control of the load more difficult. We study the control problem of a four degree of freedom ship‐mounted rotary crane with continuous yaw and roll disturbances in this paper. Specifically, we propose an adaptive controller and the adaptive laws can be updated in real‐time depending on the state of the system and the disturbance. This method does not require linearization of the crane dynamic equations, therefore, the crane can get great control performance even if it is far from the equilibrium point. Comparative experiments demonstrate that the proposed method has excellent anti‐disturbance ability.

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