An adaptive tracking control method for offshore cranes with unknown gravity parameters

Abstract

The offshore crane system is a typical underactuated system which is installed on the ship and carried out the payload transportation in the offshore environment. The payload transportation for offshore cranes is extremely sensitive to the influence of the ship motion. High couplings also exist between the offshore crane state variables. These factors may lead to large payload swing, and the offshore crane control problem is very difficult. In addition, since some physical parameters of the offshore crane system are difficult to be measured, there usually exist parameter uncertainties, which may lead to positioning errors. In order to tackle the above problems, a new adaptive tracking control method for offshore crane system is proposed, which brings satisfactory tracking performance of the reference trajectories and realizes the control objectives of the payload accurate and fast transportation, the payload swing elimination, and the accurate gravity compensation. Unlike the traditional adaptive control method, an elaborately designed adaptive estimation update law is proposed, which is used to ensure the accurate online estimation for gravity-related parameters. By using Lyapunov stability theory, it is proved that the proposed adaptive tracking controller is effective. Simulations are included to further show the performance of the proposed method.