Dynamics and control of off-centered crane lifts

When cranes lift heavy payloads off the ground, the payload may slide or swing sideways unexpectedly. This dangerous motion occurs when the payload is not directly beneath the overhead suspension point of the hoist cable. Given that cable suspension points are usually tens of feet, and perhaps hundreds of feet above the payload, it is very difficult for crane operators to know if the hoist cable is perfectly vertical before they start to lift the payload off the ground. Inevitably, some horizontal motion of the payload will occur at lift off. If an offcenter lift creates substantial horizontal motion, then it can create significant hazards for the human operators, the payload, and the surrounding environment. This paper develops dynamic models of off-centered lifts, laying the foundation for determining the unwanted motions that should to be accounted for in a future controller design.