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Dynamics of a spreader suspended by four flexible cables

Abstract This paper will investigate in detail three-dimensional equations of motion for spreaders. Spreaders, typically suspended by four parallel flexible cables, are widely used in transfer cranes at container terminals. As is well known, owing to the flexibility of the suspension cables, three-dimensional equations of motion of the spreader are hard to express in compact form. The equations of motion are derived through the approximation of the gravitational energy of the spreader and the elastic energy stored in suspension cables. The approximation is shown to be good enough in practical field operation ranges. The characteristics of the derived equations of motion are also investigated. Through computer simulations, the derived equations of motion are verified and some experiments are carried out to show the characteristics of spreader dynamics.