Modeling and Control of Tower Cranes With Elastic Structure

Due to their lightweight construction, large tower cranes are prone to structural vibrations that pose a major challenge for load sway damping control design and are the main reason for the lack of anti-sway systems in most modern tower cranes. Since neglecting the structural elasticity for feedback control design can lead to instability or poor performance, a detailed dynamic model is required that takes the structural elasticity into account. This contribution presents a control-oriented dynamic model of top-slewing tower cranes as a flexible multibody system assuming jib and tower as nonuniform Euler-Bernoulli beams and taking into account the dynamic couplings between steel structure, load motion, system drives, and rope. The distributed deformations are discretized using the Ritz method. For active sway damping, a two-degree-of-freedom control structure is designed consisting of a nonlinear flatness-based feedforward controller and a gain scheduled linear quadratic regulator. Experimental results at a full-scale tower crane validate the model accuracy and demonstrate the effectiveness of the proposed anti-sway control concept.