Quang Hieu Ngo

Sliding-Mode Antisway Control of an Offshore Container Crane

In this paper, a sliding-mode control for an offshore container crane is discussed. The offshore container crane is used to load/unload containers between a huge container ship (called the “mother ship”) and a smaller ship (called the “mobile harbor”), on which the crane is installed. The purpose of the mobile harbor is to load/unload containers in the open sea and transport them to shallower water where they can be offloaded at existing conventional ports, thereby obviating the need for expansive and expensive new facilities. The load/unload control objective is to suppress the pendulum motion (i.e., “sway”) of the load in the presence of the wave- and wind-induced movements (heave, roll, and pitch) of the mobile harbor. A new mechanism for lateral sway control, therefore, is proposed as well. A sliding surface is designed in such a way that the longitudinal sway of the load is incorporated with the trolley dynamics. The asymptotic stability of the closed-loop system is guaranteed by a control law derived for the purpose. The proposed new mechanism can suppress lateral sway, which functionality is not possible with conventional cranes. Simulation results are provided.

Active control of an offshore container crane

Open sea loading/unloading cargos provides a potential solution to tack the problem related with port construction, expansion and congestion. This process involves a crane attached to a mobile harbor (MH) which can dynamically handle container from a large container anchored in deep water. The control objective during the operation is to maintain the payload in the desired position in the presence of ocean waves. This paper presents a robust control strategy for trajectory tracking and sway suppression of an offshore container crane. A fuzzy sliding mode control law is proposed for that. Experimental results are provided to indicate the efficiency of the proposed control strategy.

Skew control of a container crane

This article describes the mathematical model of the 3-dimensional motions of a container crane used in the dockside of a container terminal. The container is suspended by four cables via a spreader. When the container is accelerated or affected by wind, the container will oscillate around horizontal axis (sway) or vertical axis (skew). And an accurate position control of the container is difficult to realize because of uncertain weight, inertial sway, and winds. This paper proposes a simple PID control of the skew motion based on the analysis of 3-dimensional dynamics of the container. This system uses four cylinders to increase and decrease forces in the individual cables so that the container can be affected by yaw torque to reduce the skew error. The simulation results show the effectiveness of the PID controller in controlling the skew motion in the presence of winds.

Sway suppression of an offshore container crane

In this paper, a method to suppress the sway motion of an offshore container crane is discussed. The offshore container crane is used to load/unload containers between a huge container ship (called the “mother ship”) and a smaller ship (called the “mobile harbor”), on which the crane is installed. The load/unload control objective is to suppress the pendulum motion (i.e., “sway”) of the load in the presence of the mobile harbor (heave, roll, and pitch) induced by wave and to compensate for the ship motions to keep the spreader at the desire position. Experiment results are provided to demonstrate the ability of the proposed control law.

Transverse vibration control of axially moving web systems by regulation of axial tension

In this paper, an active control scheme that suppresses transverse vibrations and regulates axial speed so as to track a desired profile for an axially moving web system is investigated. The spatially varying tension and the time-varying axial speed of the axially moving web are considered. The system dynamics includes the equations of motion of the moving web and the velocity dynamics of the drive rollers at boundaries of the web span. The two roller motors provide control torque inputs for the control system. The principle of the vibration control strategy is the regulation of the axial tension by a designed profile according to which the vibration energy of the moving web decays. The designed profile for the axial tension is generated by using vibration analysis based on the total mechanical energy of the axially moving web system. Lyapunov method is employed to derive the model-based torque control laws ensuring that the transverse vibration and the speed tracking error converge to zero exponentially. The effectiveness of the proposed control scheme is demonstrated via numerical simulations.

Adaptive boundary control of an axially moving string system: Application to container cranes

An axially moving system of a string with time - varying length and a mass attached at the lower end is considered to be a fundamental model of a container crane in a dockside. The objective of this paper is to move a load hanging under a very long rope from one place to another and suppressing the transverse vibrations of the load at the end of movement by adaptive control. The Lyapunov function taking the form of the total mechanical energy of the system is adopted to ensure the uniform stability of the closed-loop system. Through experiments, the effectiveness of the proposed control law is demonstrated.