Crane operations might be very dangerous in rough sea conditions due to unexpected payload swing induced by ship excitations. In this paper, a novel Cable-Driven Inverted Tetrahedron Mechanism (CDITM) is presented to suppress the payload swing for sake of the workers' safety. The CDITM retrofitting on an offshore crane is simplified as a constrained pendulum with a moving base, and its equations of motion are obtained by Newton Euler Method. Next, three-dimensional dynamic analysis is performed using Matlab/Simulink, and the influence law of ship excitations, tagline tension, crane pose and CDITM configuration on the payload swing are investigated. Finally, through comparative experimental verification, it is found that the simulation tendencies of in-plane swing follows the experiment curves quite well, and the variations between the simulation and experiment results are acceptable. Thus the dynamic modeling and analysis of CDITM are verified. The theoretical and experimental results are fundamental and valuable for the engineering application of CDITM in the offshore industries.

The safety transfer on the sea is threatened by wind, wave and surge loads. An offshore gangway ensures smooth and safe transfer by compensating the ship’s motion. In a mixed offshore gangway system, the transfer gangway is a huge asymmetric load on top of the stable platform, and the displacement of its center of gravity causes it to exert a large dynamic load on the stable platform. A dynamic model of the offshore gangway under dynamic load is established in this work. The Lagrange equation is used to establish the dynamic model of the transfer gangway; the equivalent center of gravity method is used to visualize its dynamic load. The dynamic of the stable platform is modeled by the virtual work principle. Finally, the accuracy of the mathematical model was verified by the joint simulation. Simulation results indicate that under the influence of dynamic load, the tractive force of the second drive support chain is 2–3 times greater than the tractive force of the first and third drive support chains. With the same excitation, the tractive force of the second drive support chain is 2.83 times higher than that under the static load.

Ship derusting has the characteristics of a complex operation environment, high labor intensity and low efficiency. In order to better cope with this situation, a new type of cable-driven parallel derusting robot (CDPDR) is proposed in this article. To improve the positioning accuracy and anti-interference capacity of the motion platform where the end effector is mounted, the system’s dynamic model, considering wave excitation, is established. Further, the controllable workspace and cable tension optimization algorithm are studied. In addition, a fast non-singular terminal sliding-mode controller is designed. Meanwhile, the adaptive technique is used to estimate the disturbance upper bound. Then, the Lyapunov theory is applied to prove the stability of the system. Finally, the performance of the controller is verified by high-fidelity simulations in two different scenarios. The results show that the proposed controller can converge in finite time and maintain small error under multiple external disturbances. The relevant research in this article can provide theoretical guidance for the application of CDPDRs on ships.

The violent swinging motion of a payload imposes significant safety problems for the operation of offshore ship-mounted cranes (offshore cranes). We therefore propose a stable experimental hoisting platform for an offshore crane payload positioning system with a parallel cable-driven method (PP-PCDM), and an adaptive cable-drive anti-swing tension (ACAT) control method based on the PP-PCDM is developed to resolve the problem of swinging of the payload by limiting its spatial position. The PP-PCDM enables synchronous tracking of the movement of the payload when the crane is working. When the payload deviates from a stable state due to an external disturbance, the anti-swing cables are immediately retracted or released based on the feedback signal. The spatial position of the payload is then limited by adjusting the length and tension of the parallel cables until the payload appears stationary from the perspective of the ship’s deck. Operational safety and efficiency is substantially improved, and the proposed PP-PCDM structure and ACAT control method can be applied to a variety of different types of cranes. The results of simulations and physical experiments show that the anti-swing effect exceeds 89.86%. The PP-PCDM enables excellent performance of synchronous tracking and hoisting assistance, and ensures that the rated lifting weight of the offshore crane is not affected.