Multi-Body Dynamics And Capturing Problem Of Space Robot

With the development of human technology and deeper space exploration,space robot is playing an increasingly important role in on-orbit service missions.Compared with the remote controlled and semi-remote controlled space robot,autonomous space robot can avoid the disadvantages of large operation delay and poor adaption to environment,thus the research over autonomous space robot has drawn significant interests and resources from all sides.Considering that the space robot system has strong nonlinear and coupling feature,the complexity of the dynamic problems and operation control are both severer than that of industrial robots on the ground.Evidently the self-controlled on-orbit service operation is a great challenge to the autonomous space robot.This dissertation is funded by the National Natural Science Foundation of China(Grant No.'s 11132001,11272202),the Key Scientific Project of Shanghai Municipal Education Commission(Grant No.'s 14ZZ021)and the Natural Science Foundation of Shanghai(Grant No.'s 14ZR1421000),which presents theoretical and simulation studies of Multi-body dynamics and capturing problem of space robot.The main research and achievements are as follows:(1)The dynamic modeling of rigid space robot and flexible space robot are studied,respectively.Based on the single direction recursive construction method,the equations of kinematics and dynamics of two kinds of space robot are established,and the derivations are given in detailed.The validity of the dynamic models method is verified by comparison of numerical simulations based on ADAMS.(2)The dynamics and control of capturing a floating rigid body by rigid space robot and flexible space robot are studied,respectively.Firstly,the contact testing model and the contact force model between the end-effector of space robot and free-floating object are built by the computer graphics and Hertz theory,respectively.Secondly,the computed torque method and PD active compliance control method are used to design the controller for rigid space robot and flexible space robot,respectively.And then,the dynamics and control of capturing a floating rigid body by space robot are studied by numerical simulations.In the study of rigid space robot capturing a floating body,the influence of central and eccentric impact between the end-effector and the target is considered,on capturing operation and the space system.In the study of flexible space robot capturing a floating body,same direction and opposite direction movement impact are considered besides the central and the eccentric impact.Numerical simulation results show that:the capturing operation can cause some adverse effects on the two kinds of space robot system;during the capturing operation process,the continuous impact can occur between the end-effector and the target;compared with the central impact,the eccentric impact will cause a greater impact because it can bring a larger angular momentum input in the capturing operation process;compared with the same direction movement impact,the opposite direction movement impact will cause a greater impact because it can decrease the system moment of inertia;the controllers designed by two different methods are effective in reducing the impact to the system.(3)The dynamics and control of rigid space robot and flexible space robot considering joint friction is studied,respectively.For the rigid space robot system with joint friction,a dynamics modeling method based on single direction recursive construction method,the Lagrangian equations of the first kind and Newton-Euler method are given.For the flexible space robot system with joint friction,another dynamics modeling method based on single direction recursive construction method and Newton-Euler method is given.The validities of the two modeling methods is verified by comparison of numerical simulation results and results obtained from the software ADAMS.In numerical simulations,the effects of joint friction on the space robot system and the distinctions of different friction model are studied.Numerical simulation results show that:joint friction phenomenon will affect the dynamic characteristic of space robot;under certain conditions,relatively fast speed motion will more easily cause the"stick-slip" phenomenon than low speed motion;compared with Coulomb model and Stribeck model,the LuGre model can describe the low speed friction characteristics better;the parameters(?)0 and(?)1 in LuGre model are vital important to describe the friction force,and the adverse effects of joint friction on the space robot system will be increased with the growth of the two parameters.(4)The kinematics,dynamics and control of variable geometry truss manipulator(VGTM)are studied.Firstly,the structure of the VGTM is simplified,and the system is changed from a close loop system to an open loop system.Secondly,the kinematic and dynamic equations of the system are derived by geometry relations and the single direction recursive construction method.And then,the motion controller of the VGTM is designed by the computed torque method.The validity of the kinematic and dynamic modeling method is verified by comparison of numerical simulation results and results obtained from the software ADAMS.Besides,numerical simulation results show that the controller designed in this paper is effective in controlling the motion of the VGTM.