Research On Underactuated Control Strategy Of 4-DOF Bridge Crane System

With the continuous development of industrial production and the continuous growth of national productivity,more and more industrial under-driven systems are used in production practice and become an indispensable tool for the development of productivity.As a typical under-driven system,the bridge crane system has the advantages of small footprint and high efficiency,so it is used in a variety of places.At present,most of the bridge crane systems rely on manual operation in production,which has low work efficiency and high safety hazards.Therefore,it is of great significance to study the control strategy of modern bridge crane system.The main content of this article is as follows:1.First,a simple analysis of the structure and working status of the bridge crane system is carried out.Considering that the under-actuated characteristics of the bridge crane system are mainly reflected in the horizontal direction,the three-dimensional four-degree-of-freedom bridge crane system is taken as the main part of this article.The research object,based on the second type of Lagrangian equation,conducts dynamic modeling of the three-dimensional fourdegree-of-freedom bridge crane system.2.Aiming at the anti-sway control problem of the four-degree-of-freedom linear bridge crane system model,a linear model predictive control strategy is proposed.Through the determination of the cost function and the setting of constraints,and the introduction of concepts such as robust positive invariant sets,the model predictive control problem is transformed into an online optimization problem.By constraining the input,the Lyapunov stability of the entire system can be guaranteed when the optimization problem is initially solvable.Finally,the effectiveness of the control strategy is verified by simulation.3.Considering a wider range of under-driven control strategies,a nonlinear under-driven sliding mode control strategy is proposed.Through a certain model transformation and compensating force method,the non-holonomic constrained four-degree-of-freedom underactuated nonlinear bridge type traveling crane system model control problem is converted into a general nonlinear control problem,and its steady-state performance is guaranteed by designing a sliding mode surface.The constant velocity approaching law is selected to ensure the dynamic characteristics of the sliding mode arrival stage,and the process of proof of Lyapunov stability is given.Finally,the effectiveness of the control strategy is verified by simulation,and the robustness of the control strategy is verified by changing the rope length.4.Aiming at the four-degree-of-freedom nonlinear bridge crane system model,in order to obtain better control effects,a hierarchical sliding mode control strategy based on global fast terminal sliding mode is proposed.First,set the tracking trajectory as a smooth curve,and then convert the system model into the error state equation form.Two sub-sliding surfaces are designed with crane displacement error and crane swing angle error respectively.Exponential approaching law is selected to ensure the dynamic characteristics of the arrival stage.On this basis,the total sliding surface is designed,and the Lyapunov stability principle is used to give Proof of the stability of the entire system.At the same time,the asymptotic stability of all sliding surfaces is proved according to Barbalat’s lemma,and the stability of all sliding surfaces of the whole system is proved.Finally,the effectiveness of the control strategy is verified by simulation,and the robustness of the control strategy is verified by changing the rope length or adding white noise.