Research On Multi-objective Trajectory Planning Of 7-DOF Redundant Space Manipulator

As an important subsystem of space station,space manipulator system plays an important role in the process of human exploration of space.In this paper,the space manipulator with redundant degree of freedom is taken as the research object.On the basis of kinematic and dynamic analysis,the research on multi-objective trajectory planning and task planning is carried out:Firstly,kinematics and dynamics analysis of space manipulator with redundant degree of freedom is studied.The improved D-H method is used to establish the kinematics model of the space manipulator,and the vector matrix is used to compute the Jacobi matrix of the manipulator.The inverse kinematics of the redundant degree of freedom manipulator is solved by the damping least square method,and the advantages of the redundant degree of freedom manipulator can be brought into play by the gradient projection method.The improved Newton-Euler method is used to solve the inverse dynamics of manipulator.The positive dynamics of the manipulator is calculated based on the general equation of dynamic model,and the calculation process is mainly divided into two steps,which is to obtain the angular acceleration of the joints and to calculate the numerical integration.The kinematics simulation and dynamics simulation of the space manipulator with redundant degree of freedom are realized by building the Simulink model and the Sim Mechanics model in the Matlab respectively.Then,the multi-objective trajectory planning of space manipulator is studied.Three uniform B spline curves are used to construct the joint trajectories of space manipulator with continuous velocity and acceleration.With the shortest moving time,the least energy consumption and the minimum trajectory impact as the three independent optimization targets,the mathematical model of the trajectory planning of the space manipulator is established by the constraints of the joint displacement,velocity,acceleration and joint torque of the manipulator.The simulation results show that using the genetic algorithm to solve the mathematical model,the desired trajectories of the manipulator joints can be obtained,and the constraints of the trajectory planning of the space manipulator can be satisfied.After that,the task planning of the space manipulator is studied.A unified task model is established for the complicated space manipulator operation tasks in orbit,and the process of the space manipulator to perform a certain operation task is divided into 5 task stages.Combined with the characteristics of each stage,the corresponding indicators of optimization objectives are given.In view of the conflicting optimization objectives in some stages,the NSGA-II algorithm is used to solve the multi-objective comprehensive optimization problem of the space manipulator,and a good set of Pareto optimal solutions can be obtained.The simulation results show that the manipulator can achieve a comprehensive optimal performance of the multiple performance indicators at the same time.Finally,the ground experiment system based on semi-physical simulation is built for experimental research.Firstly,the Cartesian space trajectory planning of redundant manipulator is studied.Then,several groups of manipulator configurations are selected in the joint space trajectory sequence of the manipulator,which are used as the data points of each joint trajectory for multi-target trajectory planning of the space manipulator.Finally,the task planning experiment of space manipulator is carried out.The experimental results prove that the multi-objective trajectory planning algorithm and task planning algorithm of the space manipulator studied in this paper have good correctness and practicability.