Pendulation Reduction on Small Ship-Mounted Telescopic Cranes

Abstract

Small ship-mounted telescopic cranes are used to load and unload cargo of limited size and weight. The wave-induced motions of the crane ship can cause large pendulations of the hoisted payload bringing the transfer operations to a complete halt. The small size of such a crane, combined with its limited maneu-verability, compared to the relatively larger motion of the host ship, poses a serious control challenge. In this work, a nonlinear control system is introduced which reduces pendulations on these cranes to the point where the transfer operations do not pose a dangerous working environment. Delayed position-feedback technique is used to reduce the payload pendulations. The presented control system uses the slewing, luffing, and telescopic degrees of freedom of the crane to drive the horizontal position of the boom tip. The saturation problem arising from the limited speed and motion of the crane actuators is another issue addressed by this control technique. To demonstrate the performance of the developed control system, numerical simulations are performed on a nonlinear three-dimensional mathematical model of the telescopic crane mounted on the USNS WATERS. The crane has four degrees of freedom: hoisting, slewing, luffing, and extension of the telescopic boom. In addition to its limited maneuverability, nonlinear hydraulic actuators are used for the luffing and extensional degrees of freedom.