Modelling and control of an elastic ship-mounted crane using variable-gain model-based controller

摘要

This article deals with mathematical modelling and control of elastic ship-mounted cranes that have the Maryland Rigging. The model contains three inputs to control the vibrations in the plane of the boom; the luff angle is proposed to control the elastic vibration in the boom; and the total length of the upper cable in conjunction with the position of its lower suspension point is proposed to control the pendulation of the payload. The disturbance acting on the ship due to sea motions is represented by the rolling displacement of the ship about its centre of gravity. The dynamics of the crane is described by a variable-model problem. Accordingly, a variable-gain observer and a variable-gain controller are designed to cover the operation of the crane for all possible equilibrium points in the working space. The switching action between these gains takes place automatically according to the output of a region finder, which uses the measurements of the luff angle and the length of the upper cable to detect the current operating region. A proportional - integral observer is used to estimate the states and the unknown disturbance force acting directly on the payload; the observer guarantees that the estimated states converge to their real values even though a non-zero disturbance force acts on the payload. The controller uses the estimated states and the measured roll angle to create the required damping and, therefore, to compensate for the rolling effects. Stability and performance robustness are ensured for the total working space and also for the expected range of the payload mass. Simulation results show that the observer can estimate the states and the unknown disturbance acting on the payload very well and that the controller can reduce the payload pendulations significantly.