State Observer Based Dynamic Surface Control Of Free-floating Space Robot

Space robot is an important participant in space exploration activities,and research on space robot motion control has been a hot research topic for domestic and foreign researchers.Due to the uncertainties of space robots in the service phase,such as system quality change,friction,external interference,etc.,it is almost impossible to obtain accurate dynamic model of space robot.At the same time,Considering the speed signal is often susceptible to noise pollution at the time of detection,the free-floating space robot system with external disturbance and modeling errors was studied in this paper,and the trajectory tracking problem of three free-floating space robots(free-floating rigid-arm space robot,free-floating flexible joint space robot,free-floating elastic base space robot)was discussed,the observer based dynamic surface controllers were designed.Firstly,the trajectory tracking problem of free-floating rigid-arm space robot system with external disturbance and modeling errors,carrier position uncontrolled and attitude controlled was discussed.The observer was designed to observe the velocity term and the observer based dynamic surface controller was designed.Secondly,the trajectory tracking problem of the floating base rigid arm space robot when the actuator had saturation characteristic was discussed.The saturation function of the actuator was described by using the saturation function.The compensation of the actuator saturation characteristic was realized by RBF neural network,and the adaptive updating law was designed for the neural network weight.An observer-based dynamic surface controller was designed combined with RBF neural network.In addition,considering the saturation characteristics of the actuator,the problem of trajectory tracking and flexible vibration suppression when the joints of the space robot were flexible was discussed.For free-floating flexible joints space robot with external disturbance and modeling errors,both carrier position and attitude uncontrolled,the speed difference feedback controller was designed to suppress the flexible vibration of the system.An observer-based dynamic surface controller was designed for the slow change subsystem to realize the trajectory tracking of the system.Finally,the problem of trajectory tracking and elastic vibration of free-floating elastic base space robot was discussed.Dynamic surface controllers were designed for two cases(without active suppression and active suppression)for the free-floating elastic base space robot with external disturbance and modeling errors,carrier position uncontrolled and attitude controlled.Firstly,a dynamic surface controller based on observer was designed combined with the augmented variable method.Then,a composite control method was proposed to carry out motion control.A linear quadratic optimal controller was designed to dynamically suppress the elastic vibration of the system,and a dynamic surface controller based on the observer was designed for the slow sub-system.The controller was used to track the trajectory of the system.The stability of the closed-loop systems was proved by Lyapunov method,and the tracking errors and convergence of the system were analyzed.The above control schemes were verified by Matlab numerical simulation.The simulation results showed that the designed controllers coulde achieve the accurate tracking of the desired motion,and the convergence speed was fast,and it had some robustness to the external disturbance.