Online trajectory planning for three-dimensional offshore boom cranes

Efficient control of offshore cranes has attracted world-wide attention in recent years. However, due to the persistent ship roll/heave motion disturbances, it is very challenging to guarantee the transient performance for offshore cranes. To solve this problem, this paper proposes an online trajectory planning method for three-dimensional offshore cranes. Specifically, preliminary trajectories are first designed for different crane motions (e.g., boom luffing rotating, rope hoisting motions), following which the cargoes can be delivered to designated sites. After that, some online adjustment terms are integrated with the pre-defined trajectories, which serve to attenuate or eliminate the undesired cargo swing introduced by both the improper crane operations and the ship motion disturbances. Different from traditional off-line planning methods, the proposed method retains satisfactory robustness (in the sense of swing elimination) due to the extra incorporated terms. The proposed control concept can be extended to trajectory planning of similar underactuated systems.