Research On Trajectory Planning And Control Of Space Robot For Autonomous Capturing Target

The number of launched spacecraft has progressively increased year by year asthe ability to exploit and apply technology in outer space has developed, therefore,great advantages and enormous economic benefits can be gained by on-orbitservices through space robots. The key points of on-orbit services are the trajectoryplanning and control of autonomous capturing. This dissertation is prepared inaccordance with a project sponsored by the National High-Tech R&D Program ofChina (863Program). The research problem include modeling of the space robot,the autonomous capturing of target spacecraft, the attitude adjustment and pathplanning of the target after capturing, the trajectory tracking control after capturingand the development of semi-physical experiment. The main contributions of thisdissertation are as follows.Firstly, general kinematics equations and dynamic equations of space robot areestablished based on Lagrangian methods. The features of non-holonomic constraintare analyzed and utilized as the foundation of nonholonomic path planning andtrajectory tracking control design. In addition, in order to satisfy the requirements ofreal-time performance, calculation accuracy and stability for the space robot groundsemi-physical simulation system, the R-W method, proposed by Robertson andWitten Berg, is used to established the associated matrix and path matrices whichdescribed the topology relationship of the system. The relative motion equation ofthe adjacent rigid body are derived, and the dynamics equations of the space robotsystem are then established on the basis of the Virtual Power equation.Secondly, the visual servo method is studied for autonomous target capturingby a space robot. The workspace of the space robot is obtained by Monte-Carlomethod. Then, in order to avoid the possibility that the target moves out of thecamera’s FOV and the planned joint angle exceeds the limits, a visual servotrajectory planning method with multi-constraints is proposed. The camera FOVconstraint equation and the joint movement limits repulsive equation are established.The planned trajectory is generated in the image space on the basis of the artificialpotential field method, and then the trajectory in the image space is mapped to themovement of the end effector according to the image jacobian matrix. In order toreduce the disturbance aroused by the dynamic coupling of the manipulator and thebase, coordinated control is introduced into visual servo operation.Thirdly, path planning for the attitude adjustment of the composite body andthe target transfer are studied. A non-holonomic cartesian space path planningmethod based on quantum particle swarm optimization is proposed based on the nonholonomic redundancy features of a free-floating space robotic system. Thetrajectory of the manipulator joints is parameterized, and the target function isestablished by the control accuracy of the end effector and the base attitude. Thetrajectory-planning problem of a free-floating space robot converted into anoptimization problem of nonlinear system. The optimization problem of nonlinearsystem is then solved by quantum particle swarm algorithm. The solved parametersare substituted into the trajectory equation of the robotic arm to realized the goal ofnonholonomic trajectory planning. The effectiveness of the proposed method isverified by simulation.Fourthly, when the target is captured by a space robot, trajectory trackingcontrol problems with the uncertainty parameters of the kinematic and kineticequations are researched. The control law is designed based on back-stepping andadaptive control theory for free-flying space robot system. The relationship betweenthe control parameters and system transient performance is obtained. For a free-floating space robot system, in order to make the system’s tracking error meet theresponse constraints in time domain, one method that transforms the constrainedoutput to unconstrained control parameter is designed, then the back-steppingadaptive neural network control is designed to realize unconstrained variablestability control. Not only can the tracking error with global asymptotic stability ofthe system in the task space can be ensured according to this method, but also thetracking error of the closed loop system in a predetermined time domain response,which significantly improves the tracking performance of the system.Finally, in order to reduce the risk of research, ensure on-orbit mission success,and verify the method proposed in this paper, the real-time semi-physical simulationsystem whose electric interface is identical to a real system is established to meetthe mission requirements in space robot area.