Dynamic Model for Improved Controller Design in Tower Crane Disassembly

When a crane lifts a payload, there are complex dynamic effects that occur as the payload transitions from being supported underneath by its original support surface to being supported above by the overhead rigging. For example, when payloads are lifted off the ground, the payload may unexpectedly swing sideways. This occurs when the payload is not directly beneath the hoist and the hoist cables are at an angle relative to vertical. The dynamics become even more complicated when a payload is held in a jig or structure that applies forces to the sides of the payload during lift, rather than simply resting on a ground surface. Such lift-off effects occur during the dangerous activity of tower crane disassembly when the various parts of the tower crane are removed one-by-one by a mobile telescopic boom crane. The assisting boom crane must attempt to maneuver its endpoint directly over top of the rigging connection point before it can remove each section without inducing complex lift-off dynamic effects. This paper presents a model to predict the lift-off dynamic effects when the assist crane is not positioned perfectly overhead. The model can be used to assess what range of offset angles are relatively innocuous and also to identify conditions that would lead to increased challenges in a lift-off process. The model can be integrated into a control system that performs autonomouscentering solutions to mitigate the detrimental effects of offcentered lifts during tower crane disassembly.