|Nonlinear Sliding Mode Tracking Control of Underactuated Tower Cranes
Zhuoqing Liu, Ning Sun*, Yiming Wu, Xin Xin, and Yongchun Fang
International Journal of Control, Automation, and Systems, vol. 19, no. 2, pp.1065-1077, 2021
Abstract : As representative underactuated systems, tower cranes exhibit high nonlinearity and strong state coupling, which makes their controller design (analysis) challenging and of great research values. In addition, since tower cranes are widely applied in outdoor environment with inevitable external disturbances, (the state variables tend to go far away from the equilibrium point), how to ensure the control performance in this case is particularly important; moreover, most existing control methods can only ensure closed loop stability, but cannot theoretically ensure the system states convergence time. Considering the above factors, this paper proposes a nonlinear sliding mode tracking controller, which can realize satisfactory tracking performance and effective swing suppression. To our knowledge, for tower cranes, this is the first tracking method designed based upon the nonlinear dynamics without any linearization, which can eliminate the tracking errors rapidly in finite time by introducing the elaborately constructed sliding mode surface and simultaneously suppress the swing. Furthermore, through rigorous analysis, the system closed loop stability is proven theoretically. Finally, hardware experiments imply that the proposed controller is effective and exhibits satisfactory robustness.
Sliding mode control, swing suppression, tower cranes, underactuated systems.