Study On Anti-disturbance And Robust Control Method Of Flexible Manipulator

Flexible manipulator is widely used in advanced manufacturing,medical device and on orbit service spacecraft due to its light weight,large working radius,high flexibility,high load ratio and low energy consumption.Compared with the rigid manipulator,its dynamic characteristics are more complex.This complexity is not only reflected in the number of system states,but also in the “flexibility”.During the movement of flexible manipulator,obvious vibration will occur,which will affect the positioning and tracking accuracy.In order to meet the increasing demand of flexible manipulator positioning and trajectory tracking performance,anti-disturbance and robust control methods are studied in this paper.The main contents and innovations are as follows:Aiming at the position control problem of multi degree of freedom flexible joint manipulator with external disturbance,combined with hierarchical sliding mode control method,a hierarchical sliding mode controller with double power reaching law is designed to suppress the influence of external disturbance on the system,reduce the residual vibration,and ensure that the joint angle can reach the desired position quickly and stably.Furthermore,an adaptive hierarchical sliding mode controller is designed without knowing the bound of the disturbance,realizing accurate positioning of joint angle and suppression of unknown disturbance.Theoretical analysis and simulation results verify the effectiveness of the proposed control strategy.A robust adaptive dynamic surface control strategy is proposed for a multi degree of freedom flexible joint manipulator system to ensure that the joint angle can track the desired trajectory with high accuracy,facing external disturbance,stiffness uncertainty and input saturation.Two adaptive laws are designed to estimate the upper bound of the disturbance and the stiffness coefficient respectively,which can effectively deal with the uncertainty of the stiffness and suppress the influence of the disturbance on the system.In order to reduce the influence of control input saturation,an auxiliary system is designed to compensate it.The stability of the closed-loop system is proved by Lyapunov stability theory and the simulation results verify the effectiveness of the proposed method.Aiming at the multi degree of freedom flexible link manipulator system with external disturbance,in order to suppress flexible vibration and ensure that the link angle can track the desired trajectory with high accuracy,combined with barrier Lyapunov function and prescribed performance control,a composite robust control method considering flexible state constraint is proposed.Firstly,the singular perturbation method is used to decouple the original system into two subsystems: rigid subsystem and flexible subsystem.Then,an adaptive robust controller is designed for the rigid subsystem to realize disturbance rejection and ensure the accurate tracking of the link angle.For the flexible subsystem,a control scheme based on a barrier Lyapunov function with dynamic constraint is designed.Through a dynamic boundary function,the transient process and steady-state performance of the flexible state are constrained,thus the flexible vibration can be suppressed.The stability of the two subsystems is proved via Lyapunov stability theory,and then the stability of the original system is also guaranteed.Simulation results verify the effectiveness of the proposed control method.Working in outer space,flexible link manipulator will be affected by various complex disturbances,such as the matching disturbance like the friction torque at the motor,and the unmatched disturbance like the solar pressure and the gravitational gradient moment.The base of the free floating flexible space manipulator is not controllable.In order to ensure that the end-point of the manipulator can track the desired trajectory with high accuracy under matched and mismatched disturbance,a composite robust control method based on disturbance observer is proposed.The original system is decoupled into rigid subsystem and flexible subsystem using the singular perturbation method,and the influence of two kinds of disturbances is analysed.Furthermore,according to the Jacobian relationship between the joint and the end-point,the dynamic equation of the rigid subsystem is extended to the end-point task space,which lays the foundation for the design of the end-point trajectory tracking controller.Then,a disturbance observer is designed to estimate the disturbance.Finally,a computed torque controller with disturbance compensation is designed for the rigid subsystem to realize the end-point trajectory tracking;for the flexible subsystem,the influence of two kinds of disturbance on quasi-static manifold is analysed,and a sliding mode controller is designed to realize the fast stabilization of the flexible state.Simulation results show that the proposed control method can effectively resist disturbance and ensure the flexible space manipulator endpoint tracking the desired trajectory accurately.