Dynamics Modelling And Control Of A Six DOF Space Robot

With the rapid development of aerospace technologies,space robots have become one of the research hotspots in the field of on-orbit services on account of its advantages such as the adaption to the harsh space environment,performing long extravehicular activities,lowering the on-orbit service costs,improving the on-orbit service efficiency,and accomplishing the missions of high precision and high reliability that are incompetent for astronauts.Space robot has been applied missions including the construction and maintenance of space station,the assembly and services of satellite,and the explorations of planetary surfaces and space experiments.Considering the strong nonlinear and coupling feature of the dynamic equations of space robot system,and the complex motion of large flexible components(such as panel),there are many unsolved questions about dynamics and capture dynamics of space robots.In addition,since the space robot system generally has a complex structure and works in harsh space environment,the dynamic parameters of the system are difficult to be determined and the actuators may malfunction or even fail completely,enormous challenges are being posed for control system design of the space robot system.This dissertation is funded by the National Natural Science Foundation of China(11772187)and the Natural Science Foundation of Shanghai(14ZR1421000),which presents theoretical and simulation studies of multi-body dynamics and control problem of a 6-DOF space robot with flexible panels.The main research and achievements are as follows:(1)The dynamic modeling of a 6-DOF space robot with flexible panels is studied.Based on the single direction recursive construction method and the Jourdain's velocity variation principle,the equations of kinematics and dynamics of the space robot are established with detailed derivations.The simulation results show that the proposed model can obtain the same results as ADAMS;the panel flexibility has important influence on the dynamic characterstics of the system.(2)A 6-DOF space robot with flexible panels is considered,and the trajectory tracking control problem with system parameters uncertainties is studied.Based on the computed torque method,a robust adaptive controller is designed for the space robot system with uncertain system parameters to perform the track tracking,and the stability of the controller is verified by the Lyapunov stability theory.Finally,the designed controller is validated by numerical simulations.The simulation results show that the controller designed in this paper can drive the joints of the space robot system with uncertain parameters to the desired angles and keep the configuration of spacecraft base unchanged,meanwhile,the elastic vibration of the flexible panels is effectively suppressed.(3)The trajectory tracking control problem of a 6-DOF space robot with flexible panels considering the actuator failure is studied.A sliding mode fault-tolerant adaptive controller for the trajectory track of the space robot in the case of joint failure is designed by the sliding mode theory and the Lyapunov stability theory,and the stability of the closed-loop system is analyzed.Finally,the designed controller is validated by numerical simulations.The simulation results show that whether the actuators fail or not,the fault-tolerant controller designed in this section can achieve a good control effect by adjusting control parameters;Nevertheless,the control effect becomes worse when the failed actuators are not dealt with.Moreover,under the action of the controller,the elastic vibration of the flexible panels can be effectively suppressed.(4)Taking a 6-DOF space robot with flexible panels into consideration,the vibration control of the flexible panels in the trajectory tracking of the space robot system is studied.Firstly,the dynamic equation of the space robot system is decomposed into a slow subsystem of rigid body motion and a fast subsystem of elastic vibration by using the singular perturbation theory;Then,the sub-controllers of two subsystems are designed to obtain the compound controller of the system,which the slow subsystem uses computed torque controller and the fast subsystem uses optimal control.Finally,the compound controller is validated by numerical simulations.The simulation results show that the joints of the space robot system reach the desired angles and the configuration of spacecraft base and the elastic vibration of the flexible panels can be restrained effectively.We can also observe from the simulation results that the sub-controller of fast subsystem in the compound control scheme has a great influence on the control effect of the space robot system.(5)The capture dynamics and control of a 6-DOF space robot with flexible panels is studied.Firstly,the Hertz contact theory is used to describe the interactions between the space robot and the target to be captured,including the calculation of contact impact force and the real-time detection of penetration depth.Then,the dynamic equation of the impact system composed of the space robot and the capture target is obtained by combining the contact impact force with the dynamic equation of the space robot system in Section 2.Finally,in order to ensure the space robot to complete the capture task successfully,an active controller is designed based on the computed torque method.The simulation results show that the flexibility of panels has a great influence on the dynamic characteristics of the space robot system and the eccentric impact can change the attitude of the space robot system.In this paper,the displacement of spacecraft base of the space robot system can be effectively restrained and the elastic vibration of the flexible panels can also be suppressed under the action of the controller.