Research On Tracking Control For A Space Manipulator On A Floating Base With Flexible Appendages

Booming space exploration portends that some spacecrafts will be large-scale,complex,long-life in the furture.Space manipulator systems play an increasingly significant role in the construction and maintenance of large satellites or space stations.The development of China’s manned space station also promotes extensive and in-depth research on space manipulators in the domestic space field.Large flexible appendages installation,such as satellite antennas,solar panels,etc.,leaves the space manipulator facing with more demanding operational environment.Meanwhile,more and more complex space missions propose higher operation precision and stability requirement for manipulators.Concerning with the space manipulator on a floating-base with flexible appendages,this dissertation studies the dynamic modeling,prescribed performance control,coordination control,and adaptive robust vibration control for the rigid-flexible coupling complex system.This dissertation includes the following several parts:Firstly,the mathematical model and characteristics of the space manipulator on a floating-base with flexible appendages are studied.The structure and basic assumptions of the space manipulator on a floating-base with flexible appendages system are described,and coordinate systems definition and transformation relationship involved in this paper are clarified.We use finite element method to depict the vibration motion of the flexible appendages.The kinematics relationship between the end-effector of the manipulator and the spacecraft base,including flexible appendages vibration,is deduced.After that,we establish the general kinematics model of the system.Considering the mechanical property of the space manipulator working in the free-floating mode and base-attitude-controlled mode,the kinematics equations of the two modes are derived.Then,the general dynamics model of the space manipulator on a floating-base with flexible appendages system is established utilizing Lagrange method to accurately depict the dynamic coupling relationship among the spacecraft base,the manipulator and flexible appendages.Considering the characteristics of the free-floating and base-attitude-controlled space manipulator system,the dynamics model of this two systems was derived,while the characteristics of the dynamic model is analyzed.Secondly,concerning the space manipulator system in base-attitude-controlled mode,we study the prescribed performance control of the manipulator tracking reference trajectory.We propose a prescribeded-time reachable performance function and utilize an error transformation mapping to convert the constrained plant into an unconstrained feedback system.A modified prescribed performance control scheme is designed utilizing the prescribed-time reachable performance function,which is capable of guaranteeing the transient and steady-state performance and prescribed-time stability of the system compared with the traditional prescribed performance control utilizing the exponential decay function.The application of the prescribed-time reachable performance function simplifies the task that rely on the tedious regulation of the controller parameters or an estimation based on the system initial condition to achieve an adequate settling time.Lyapunov theory has been used to prove the prescribed-time convergence and stability of the closed-loop system.Thirdly,Concerning with the problem of coordination control of the spacecraft base and the space manipulator,an integrated coordination controller based on the sliding mode control and immersion and invariant theory is designed,which is capable of guaranteeing that the tracking errors of the manipulator joint angles and angular velocities all asymptotically converge to a small neighborhood of the origin.In the process of designing sliding mode controller for the spacecraft base attitude and manipulator subsystem separately,a lot of unknown disturbanecs and unmodeled dynamics bring difficulty for disturbance estimation.To address the issue,this paper takes full advantage of the coupling between the base attitude and tha manipulator joints.An integrated coordination controller is designed on the basic of the coupling dynamic equations of the spacecraft base attitude and the manipulator,to make the system achieve a better stability and fast responsiveness.Meanwhile,because the plant is a typical second-order dynamic system,a parabolic manifold is designed using the immersion and invariance theory to naturally evolve on a symmetrical parabolic trajectory with respect to the abscissa in the error state phase plane,which overcomes the problem of the chattering phenomenon resulted from the sign function and linear sliding mode surface in sliding mode controller.Lastly,the hybrid control of adaptive tracking and vibration suppression for the space manipulator on a floating-base with flexible appendages system is studied in the presence of external environmental disturbance.In the first place,a tracking differentiator is designed based on a hyperbolic sine function,and the globally uniformly asymptotic stability of the system is proved.Then,on the basic of the tracking differentiator,a nonlinear disturbance observer is designed to estimate the external disturbance,which gets rid of the dependence on the disturbance’s prior information and difficulty in adjusting the design parameters compared with traditional nonlinear disturbance observers.Moreover,utilizing the dynamic coupling among the motion of the space manipulator,the spacecraft base and flexible appendages,an adaptive vibration controller based on immersion and invariance control and energy principle is designed,which simultaneously achieves satisfactory tracking performance and vibration suppression of the flexible appendages.The convergence and stability of the closed-loop system are proved by Lyapunov’s second method.