Study On Planning Of Cellular Space Robot For On-orbit Truss-climbing

As a new type of space robot for on orbit tasks,cellular space robot(CSR)is more flexible and functional compared with the traditional modular robot,and it can realize multi-level reconstruction to cope with the trend of large-scale and complex on orbit service objects in the future.Space truss is an important support and expansion platform for spacecraft.In order to assemble and maintain spacecraft on orbit,CSR must climb and carry on the truss.But the space truss is a complex system with multiple nodes and rods,which is easy to collide when the robot climbs on orbit,so the climbing path needs to be planned.Therefore,the paper will study the problem of planning of cellular space robot for on orbit climbing truss.Firstly,this paper expounds the concept of cellular space robot.Three elementary cells(junctional cell,rotational cell and end-effector cell)are proposed.In addition,in order to intuitively and accurately express the arbitrary configuration and tissue migration process of CSR,the cell migration matrix is obtained by improving the incidence matrix and using graph theory and topology.Then,the kinematics model is established by exponential product formula based on screw theory.Newton-Euler is used for dynamic modeling.Further,three generalized two-bar climbing conditions are summarized by considering application environment of the truss and the characteristics of CSR,it can meet the needs of most climbing tasks on truss.And the climbing gaits are proposed for each climbing condition by employing the principles of consistency,repeatability and non-interference.Finally,the joint torque,energy consumption and the workspace occupied by the end trajectory of CSR with different gait are analyzed and compared by numerical simulation.The simulation results can be used for reference in the selection of climbing gait of space robot.In view of the specific climbing environment,the climbing optimization is carried out with energy consumption as the optimization objective,the robot configuration and climbing time as the decision variables.The configuration decision variables are quantified as the length of the rod by the configuration constraints.Finally,the optimal model of energy consumption is established considering kinematic and dynamic constraints.In this paper,DE algorithm is introduced,and two different optimization processes are used to simulate.The optimal results and the required operation time of the two optimization strategies are compared,so as to select the appropriate optimization strategy.It provides a reference for the configuration and climbing time selection of the robot in the space task.The robot climbing joint simulation control system is established based on PID algorithm,and the climbing simulation experiments are carried out.The results show that the virtual prototype system can meet the robot climbing control requirements.The prototype models of three elementary cells are processed,and the three-dimensional truss experiment platform is built.Then,the corresponding climbing configuration is reconstructed for the actual climbing experiment.Experiments are carried out to verify the correctness and rationality of the proposed climbing gait.According to the climbing optimization results,the transition climbing operation between poles is carried out.And the actual joint trajectory of the robot in the climbing process is measured,then compared with the simulation planning(expected trajectory)results.The results show that CSR has excellent climbing performance,and the choice of control system will affect the trajectory error.The experimental results have important engineering value for the optimization of CSR prototype and the selection of control mode.