Modelling and control of offshore crane systems

University of Technology Sydney. Faculty of Engineering and Information Technology.Cranes are widely used in transportation, construction and manufacturing. Suspended payloads in crane system are caused to swing due to actuator movement, external disturbance such as wind flows, and motion of the crane base in the case of portable cranes. Recently, offshore cranes have become a new trend in stevedoring and in offshore construction as they can help to avoid port congestion and also to exploit ocean engineering applications. For crane operations, it is important to satisfy rigorous requirements in terms of safety, accuracy and efficiency. One of the main challenges in crane operations has been identified as the sway motion control, which is subject to underactuation of crane drive systems and external disturbances. Particularly in offshore cranes, the harsh conditions can produce exogenous disturbances during the load transfer at various scenarios of offshore crane operations in practice. Therefore, it is interesting as to how to design robust controllers to guarantee high performance in the face of disturbances and parameter variations in offshore cranes. The motivation for this thesis is based on recent growing research interest in the derivation of dynamic models and development of control techniques for offshore cranes in the presence of, for example, the rope length variation, sway, ocean waves and strong winds in offshore crane systems. Accordingly, the work for this thesis has been conducted in the two main themes, namely analytical modelling and control design, for which new results represent its contributions. Dynamic models of two types of offshore crane systems, namely the offshore gantry crane and offshore boom crane, are derived in the presence of vessel’s ocean wave-induced motion. The effect of wind disturbances on the payload sway is also considered in the modelling. In the control context, sliding mode control techniques for a generic form of underactuated mechanical Lagrangian systems are presented, including the conventional first-order, second-order and adaptive fuzzy sliding mode controllers. The major component in this part of the thesis is the design of sliding mode control laws based on the developed offshore crane models for trajectory tracking problems, in the presence of persistent disturbances in severe open-sea conditions. Extensive simulation results are presented to demonstrate the efficacy of the models and robustness of the designed controllers

Second-order sliding mode control for offshore container cranes

Open-sea stevedores of containers provide an alternative way to avoid port congestion. This process involves a mobile harbour equipped with a crane which loads/unloads containers from a large cargo ship. However, the presence of ocean waves and gusty winds can produce an excessive sway to the hoisting ropes of the crane system. This paper presents a second-order sliding mode controller for trajectory tracking and sway suppression of an offshore container crane. From the proposed control law, the asymptotic stability of the closed-loop system is guaranteed in the Lyapunov sense. Simulation results indicate that the developed control system can achieve high performance in trajectory tracking and swing angle suppression despite the presence of parameter variations and external disturbances as in the case of offshore cranes

Adaptive fuzzy sliding mode control for uncertain nonlinear underactuated mechanical systems

Sliding mode control has been shown to be a robust and effective control approach for stabilization of nonlinear systems. However the dynamic performance of the controller is a complex function of the system parameters, which is often uncertain or partially known. This paper presents an adaptive fuzzy sliding mode control for a class of underactuated nonlinear mechanical systems. An adaptive fuzzy system is used to approximate the uncertain parts of the underactuated system. The adaptive law is designed based on the Lyapunov method. The proof for the stability and the convergence of the system is presented. Robust performance of the adaptive fuzzy sliding mode control is illustrated using a gantry crane system. Simulation results demonstrate that the system output can track the reference signal in the presence of modelling uncertainties, external disturbances and parameter variation. © 2013 IEEE

Modelling and robust trajectory following for offshore container crane systems

© 2015 Elsevier B.V. In stevedoring operations, the ship-to-ship transfer of containers in open-sea is becoming an alternative way to avoid port congestion and subsequently can increase port efficiency. This process involves a large container ship or a barge, equipped with a crane, and a smaller vessel which transports containers between the ship and the harbour. However, the harsh open-sea conditions can produce exogenous disturbances to the crane system during the load transfer. Besides, the uncertainties and disturbances in the crane system may degrade the control performance. Hence, one of the requirements of offshore container cranes is to enhance robustness of the crane control system. This paper addresses the problem of robust sliding mode control for offshore container crane systems subject to bounded disturbances and uncertainties. The mathematical model of the control plant is first derived whereas the effects of ocean waves and strong winds are taken into account. Then, a robust sliding mode controller is proposed to track an optimal trajectory of the crane system during load transfer. Extensive simulation results are given to show that the proposed controller can significantly suppress the effects of disturbances from the vessel's wave- and wind-induced motion

Observer-based trajectory tracking for a class of underactuated Lagrangian systems using higher-order sliding modes

Trajectory tracking control of an underactuated mechanical system is a challenging task when tracking errors of all the system coordinates need to be minimized, while the number of control inputs is limited. This paper addresses the observer-based multivariable control of a class of nonlinear, underactuated Lagrangian systems with application to trajectory tracking and sway control of a 3D overhead gantry crane subject to Coulomb friction. A second-order sliding mode observer is proposed for the estimation of velocities. Based on robust estimates, the sliding function of a second-order sliding mode controller for trajectory tracking and anti-swing control is proposed. The simulation results indicate that the proposed observer-based controller can achieve high performance in following a pre-specified trajectory with minimum tracking errors and swing angle suppression, despite the presence of model uncertainties and disturbances. © 2012 IEEE