Development of Motion Reduction Device for Ship Using Underactuated Parallel Link Mechanism

Transferring between a ship and an offshore platform is potentially dangerous owing to excessive motion caused by rough conditions. In this paper, we focus on a small vessel with consideration of three degrees of freedom of motion: heaving, rolling, and surging. To stabilize these motions using a relatively small device, we propose an underactuated mechanism including two linear actuators and a two-degree-of-freedom gangway connected to the transfer platform. First, we clarify the degrees of freedom and range of the mechanism. Next, we derive a model and design a controller to stabilize the system. Finally, the effectiveness of the mechanism and its controller are tested by numerical simulation as well as by an actual experiment on a small-scale model of the mechanism.