Stabilization And Tracking Control Of Underactuated Mechanical Systems

The underactuated system refers to a class of nonlinear systems with independent control variables less than the number of degrees of freedom.It is superior to fully actuated system in saving energy,reducing cost,reducing weight and enhancing system flexibility.At the same time,the structure of the underactuated system is relatively simple,so the dynamic analysis and experiment of the whole system are more convenient.Even when some components of some full actuated systems machines fail,the full actuated systems system can be temporarily converted into an under-driven system to work.At the same time,underactuated systems are used more and more widely with the development of industrial engineering and the research of theoretical direction.However,compared with the full actuated systems system,since the degree of freedom of the underactuated system is higher than that of the control input,it makes the design of the controller more difficult.Therefore,the research on underactuated system is of great practical significance both in practical application and in theory.This paper provides several optimized control schemes for several typical underactuated systems.The main work is as follows.(1)The PPB(predictive performance bound)and DSC(dynamic surface control)method is employed to stabilize the bridge crane systems.The controller designed by backstepping optimizes the convergence speed of the crane and improves the transient performance of the crane.(2)The nonlinear adaptive fault-tolerant control strategy is proposed,which makes the whole system still follow a predetermined path when the ship's propeller fails,although there exists unknown system parameters and environmental disturbances caused by waves,wind and ocean currents.The results show that the reference path of the controller proposed in this paper can be globally tracked with any small tracking error.(3)The trajectory tracking problem of underactuated surface ship system under the constraint of input saturation is studied.The multi-input multi-output system is converted into a plurality of single-input single-output systems through finite-time decoupling control,which makes the underactuated ship system becomes two independent single-input single-output subsystems,and since the cascade influence mode of the two systems is unilateral,controllers can be designed for the two subsystems respectively.This kind of method can be applied not only to surface ship systems,but also to the control of other nonlinear constraint systems.Finally,this paper summarizes the work of this paper,discusses the advantages and disadvantages of these control schemes,and on the basis of the summary,looks forward to the follow-up work...