Research On Dynamics Modeling And Capture Control Of Space Flexible Manipulator

As the space exploration and development deepens, spacecraft in the future will tend to be large-scale, complicated, high-precision and long-life. Therefore, the application of space manipulator becomes widespread as well as significant. With large radius, low structural stiffness, a wide range of load mass change and distinct flexibility features of joints and links, space manipulator shows complex nonlinearity. Studies on key issues, including the dynamic modeling of space flexible manipulator system, dynamic analysis and the on-orbit operation control of capture target, lay the foundation of mechanism design and on-orbit service.The space manipulator is a typical chain rootless multibody system which shows apparent rigid-flexible coupling characteristics affected by link flexibility. Based on the recursive algorithm, a space rigid model has been established with high efficiency. The inertia matrix and Jacobian given in this paper are able to be used in control system. What’s more, according to the Lagrange method and the modal synthesis method, the dynamic model of space flexible manipulators is obtained to achieve dynamic analysis and calculation of floating flexible manipulator system. Ultimately, the correctness and efficiency of the model could be verified by comparison with results from commercial software.Joint flexibility is necessary to be considered for dynamic analysis of space flexible manipulator. Nonlinear factors, such as joint mesh stiffness, clearance and friction are main factors for motion accuracy and stability of manipulator system. Since an accurate dynamic model of flexible joint is the foundation of manipulator system design, dynamic analysis and controller design, the joint dynamic model considering all nonlinearities above is proposed in this paper. Dynamic modeling method that is available to consider all these factors is obtained in this paper. And then, effect of nonlinear and flexible factors on the joint dynamics has been analyzed.Successful capture of the target load is the key to on–orbit service. For rope end effector with large tolerance and soft capture characteristics, the discrete finite segment method is used to establish the dynamic model of flexible rope. The principle of parameter selection is analyzed for the rope discrete model and a nonlinear model of contact force and friction is provided for the capture dynamic model of the end effector. Besides, the impact experiment is designed to verify the correctness of the model which fully takes the space motion state of the rope and the impact process between the rope and the target into consideration. It is inevitable for manipulator to be in contact with the target when capture occurs. The excessive impact force may not only results in attitude deviation of the base but also lead to target escape. Accordingly, the fast approach-slow contact-velocity tracking (FA-SC-VT) end capture strategy has been put forward for procedure of the target capturing. Based on the capture dynamic model, the simulation analysis has been carried out. The result shows that compared with traditional uniform capture strategy the FA-SC-VT capture strategy reduces impact force generated at the end of manipulator significantly and solves the escape problem efficiently for light weight target. Furthermore, the joint damping and impedance controller of the manipulator have been designed to achieve flexible capture control respectively for cooperative and non-cooperative target, the result shows that compared with the hard capture of position maintain,the impedance control capture can reduces impact force generated at the end of manipulator significantly and the deviation of base Attitude.