Research On Safety Control Methods For Underactuated Nonlinear Overhead Crane

As the typical underactuated system,the bridge crane is widely used in the transportation of all kinds of solid and liquid cargoes.Its main task is to transport the load to the desired position quickly and accurately with full restraint of its residual swing.However,it is liable for the load to swing violently during operation due to the strong nonlinearity and high coupling of the bridge crane.Especially when transporting liquid,the large swing of the load vessel is accompanied by the nonlinear swing of the internal liquid,which brings great challenges to its safe and efficient control.Nowadays,most industrial bridge cranes rely on manual control,which has the defects of low efficiency,high cost and poor safety.Therefore,the automatic control method of bridge cranes with high performance and strong robustness is urgently required.The research of this paper is based on underactuated bridge crane.Comprehensive and thorough theoretical and experimental research has been carried out on a series of essential question which are the its dynamics modeling with solid and fluid load,parameter uncertainties and external disturbances of the adaptive control,the robust control of the operation process,fluid coupling control of load lifting,safe control of high order mode sloshing.The main contents are as follows:(1)Dynamics modeling and operation safety analysis of underactuated bridge crane.In this paper,two types of dynamic models of bridge cranes transporting different loads are established.The first type is to establish the single pendulum and double pendulum bridge crane models respectively for transporting solid load.The second type of the bridge crane is pendulum-radial-spring model and multi-mass-spring-damper model for transporting liquid load.In particular,the sloshing liquid could be divided into the fixed and moving fluid part with the linear potential flow theory.Applied to be equivalent to moving fluid part,the pendulum and multi-order mass block are adopted to avoid complex calculation of the sloshing flow field.Then,the correctness of the above model is verified by simulation and experiment.Finally,after analyzing the safety factors of crane operation,three safety experiments are designed to test the effectiveness of the following control strategies under a series of security control constraints.(2)Robust control method considering parameter uncertainty and external disturbance.Aiming at the problem that the existing control methods of underactuated system are easily affected by the changes of system information,a fast terminal sliding mode control method based on model parameter self-adaptation is proposed.This controller is designed based on partial feedback linearization of the model and newly defined deviation signals.Then,according to the rules of the controller and the model,an adaptive controller is constructed to predict the physical parameters in the controller.At last,compared with the existing methods,simulation and physical experiment show the superior control performance of the proposed method.(3)Robust control methods based on global sliding mode.To overcome the local robustness defects,two nonlinear control methods are designed respectively for variable rope length and two-stage swing bridge crane.In the first method,a global equivalent sliding mode controller is proposed to achieve robust control.The second time-varying sliding mode control method based on exponential approach improves the transient performance of the system by constructing an adaptive gain to dynamically adjust the sliding mode surface,which further ensure that the system performance can maintain excellent state in spite of the off-balance point.In order to verify the actual performance of the above two strategies,detailed simulation and experimental results are provided.(4)Adaptive saftey control method based on enhanced coupling.An adaptive control method based on enhanced coupling for pendulum-spring bridge crane model was proposed to solve the problem of poor robustness and low transient performance caused by inadequate use of the coupling characteristics.Firstly,by analyzing the dynamic coupling relationship among the trolley motion,the container swing and liquid sloshing,the adaptive dynamic gain of sliding mode is introduced to improve the transient performance of the system.Then,In order to compensate for the poor population diversity and weak local search ability of the sparrow search algorithm,the antithesis learning method and normal disturbance are introduced to improve the ability escaping from local convergence and convergence speed of the algorithm.And the improved cuckoo algorithm is applied to the parameter setting of the proposed controller to further optimize the control performance of the system.Finally,the simulation results show that the proposed method has good performance and robustness.(5)Second order time-varying sliding mode method for liquid transportation.Aiming at the problems such as liquid carrying and actuator saturation constraint,a nonlinear safety control method is proposed by considering sloshing characteristics and viscosity effect of fluid.Firstly,a second order sliding mode dynamics is constructed,and a new nonlinear time-varying function is introduced to enhance the system dynamic performance under the condition of satisfying the physical constraints of the actuator.Second,the controller gain setting mechanism based on the improved cuckoo search algorithm is constructed to overcome the defects of high-dimension system parameters and opacity of the selection process.Simulation results show that the proposed control method can achieve safe and efficient transportation of liquid load in various complicated situations.