CABLE STRETCH ASYMMETRIES IN MULTI-CABLE SPREADER SUSPENSION SYSTEMS UNDERGOING COMBINED TRANSLATIONS AND ROTATIONS

The work presented in this paper proposes that for widely spaced cable reeving configurations in container-handling cranes there is an inter esting, and unexpectedly useful, phenomenon defined henceforth as geom etrical extension which gives rise to unevenly distributed cable stret ch and, hence, uneven tensions across the system. Geometrical extensio n is entirely caused by the reluctance of the trolley, spreader and ca ble system to conform, as a whole, to certain overall shapes. Such sha pes are developed because of the various translational and rotational motions which can be experienced at the trolley (that is at the attach ment point of the cables running down to the spreader). Other cables s tretch effects, such as those due to static and dynamic (inertia) load s, are additional to the geometrical extension (which can, in some cir cumstances, manifest as a compression instead). The net effect of cabl e stretch asymmetries is to stiffen up the suspension for certain case s of translation and rotation. This has a direct, and useful, influenc e for anti-sway control.