Nonlinear Sliding Mode Tracking Control of Underactuated Tower Cranes
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ISSN:1598-6446 eISSN:2005-4092 http://www.springer.com/12555
Nonlinear Sliding Mode Tracking Control of Underactuated Tower Cranes Zhuoqing Liu, Ning Sun*, Yiming Wu, Xin Xin, and Yongchun Fang 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. Keywords: Sliding mode control, swing suppression, tower cranes, underactuated systems.
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INTRODUCTION
Presently, demands keep growing in the fields of construction industry and real estate industry. As a kind of essential hoisting apparatus in building sites, tower cranes have advantages in many aspects, including high operation efficiency and large working space, which play important roles and are widely applied in practice. However, nowadays, tower crane systems still mostly depend on manual manipulations, which not only consume manpower and material resources, but also make the positioning accuracy and work efficiency difficult to be ensured. In addition, since operators usually work under complicated environment such as high altitude, uncertain weather, etc., safety accidents occur frequently, which are caused mainly by misoperations, especially when operators are fatigued by doing repeated works. Hence, to avoid potential safety risks and further improve control performance and ac-
curacy, it is important to design effective controllers for tower cranes to achieve automatic control. However, it is not easy to realize satisfactory control of tower cranes. On one hand, tower cranes usually work in harsh environments (high altitude, strong interference, etc.), and hence, it is difficult to realize accurate positioning with negligible payload swing. On the other hand, tower crane systems exhibit high nonlinearity and strong state coupling, making their dynamics particularly complicated. Compared with widely used overhead crane
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