Autonomous offshore container crane system using a Fuzzy-PD logic controller

A Fuzzy-PD control strategy for an offshore container crane is investigated in this study. The offshore crane is used to handle containers between a mega container ship (called the "mother ship") and a smaller ship (called the "mobile harbor"), which is equipped with container crane. The concept of the mobile harbor is a floating form that has the capability of transferring cargo to the local harbor from a large ship that is anchored in a nearby sea, thereby minimizing the port congestion and also eliminating the need of expanding outwards. The control objective during the loading and unloading process is to keep the payload in the desired region in the presence of ship motions. A new control strategy which is a combination of a Fuzzy controller, PD controller and compensation mechanism, is proposed as well. A Fuzzy controller plays a main role in creating the appropriate voltage, based on the dynamics and knowledge of an experienced designer, for guarantees not only prompt suppression of load swing but also accurate control of container crane position. In addition, a classical PD controller is used to tune the value of state variables into suitable range before becoming the inputs of the fuzzification process. This control scheme guarantees the stability of the closed-loop system. Simulation and experimental results are provided to verify the effectiveness of the proposed control system for offshore container cranes.