| Space manipulator has the characteristics of strong operation ability,large working range and high flexibility.It is often used in space to replace or assist astronauts to complete on-orbit operation tasks.Due to the complexity of the space environment,the mission and the structure itself,space manipulator long-term on-orbit service mission is likely to happen joint free-swinging failure,faulty joint cannot receive timely maintenance,seriously affects the original on-orbit operation task execution.Joint freeswinging failure refers to that joints of the manipulator lose the driving torque and are in a free-swinging state.At this time,the movement of the joint depends on the control of the healthy joint.Therefore,the faulty joint is called passive joint,and the faulty joint,base and end do not have autonomous driving ability,which is collectively referred to as the controlled unit.After the joint free-swinging failure occurs,the controlled units of the faulty manipulator increase,the kinematic coupling relationship becomes more complex,the motion ability perturbed,the end trajectory cannot track the expected trajectory,and the original task requirements cannot be met.In more serious cases,the safety of the manipulator or the space station will be threatened.Therefore,the trajectory optimization method of space manipulator with joint freeswinging failure is studied,so as to select the optimal trajectory meeting the requirements of the in-orbit operation task,which is of great practical significance to improve the safety of space manipulator,extend the service life of space manipulator in orbit and promote the further development of space manipulator technology.Based on the national natural science fund projects“space manipulator with joint free-swinging failure movement ability optimization and multi-stage failure-tolerant control"(number:62173044)as the backing,to carry out the research on trajectory optimization of space manipulator with joint free-swinging failure based on redundant characteristics.The concrete content includes:movement characteristics analysis of space manipulator with joint free-swinging failure,reachable space analysis of the end of space manipulator with joint free-swinging failure,research on trajectory optimization of space manipulator with joint free-swinging failure and the experimental study on trajectory optimization of space manipulator with joint free-swinging failure based on redundant characteristics.The concrete research contents are as follows:First of all,the kinematic model of space manipulator with joint freeswinging are established,and the motion characteristics of space manipulator with joint free-swinging are analyzed.Due to the influence of space environment,the space manipulator base is in a floating state.Firstly,the kinematic model of space manipulator with the float base is established,and then the joint free-swinging failure is introduced to establish the kinematic model of space manipulator with joint free-swinging failure;Based on the kinematic model of the faulty manipulator,the velocity mapping relationship between the active joint and the faulty joint,the base and the end is deduced,and the kinematic coupling relationship of space manipulator with joint free-swinging failure is obtained;Analyze the velocity mapping relationship between the active joint and the faulty joint and the end,when the number of degrees of freedom of the active joint is greater than the number of degrees of freedom of the controlled unit,a null space term is introduced into the corresponding mapping relationship.Simulation experiments prove that when the active joint of the faulty manipulator controls the faulty joint and the end,there are not unique active joint trajectories,which proves that the faulty joint has redundant characteristics.It lays a foundation for subsequent trajectory optimization research based on this characteristic.Secondly,based on the kinematic coupling relationship of space manipulator with joint free-swinging failure,the reachable space of the end of space manipulator with joint free-swinging failure is analyzed.The kinematic coupling relationship between the active joint of the faulty manipulator and the base,and the faulty joint and the end,the solution process of the reachability space of the end of the space manipulator is more complicated.By changing the different motion states of the active joint,the influencing factors of the reachability range of the base and the faulty joint are determined,and the reachability range is solved;Based on the reachability range of the base and the fault joint and the solution method of the end reachability space of space manipulator with the float base,the end reachability space of space manipulator with joint free-swinging failure is further solved.The simulation results show that the reachable space radius of the end of the normal manipulator is 13.22m,and the reachable space radius of the end of the faulty manipulator is 12.52m.The reachable space of the end of the faulty manipulator is reduced compared with that of the normal manipulator,which indicates that the reachable space of the end of the faulty manipulator is degraded.The task achievability of the free-swinging joint fault space manipulator can be evaluated based on the degraded workspace.Then,based on the redundant characteristics of space manipulator with joint free-swinging failure,the trajectory optimization is studied.Taking the expected trajectory of the end of the manipulator and the minimum attitude deflection of the base as the optimization objectives,the joint avoidance limit optimization index is constructed,and the joint avoidance limit kinematic equation is obtained to realize the optimization of the joint avoidance limit trajectory of the manipulator.Considering the joint Angle fluctuation and the joint angular velocity is not zero at the beginning and end time,the joint avoidance limit optimization operator is improved to further improve the joint avoidance limit optimization problem.Considering the influence of obstacles in the working space,the threshold distance between the connecting rod and the faulty manipulator is set,the obstacle avoidance point and speed are given.The obstacle avoidance trajectory of the faulty manipulator is optimized by self-motion adjustment of the redundant manipulator.Simulation experiments show that according to the trajectory optimization method proposed in this paper,the fault manipulator can achieve the expected trajectory tracking of the end while avoiding joint limits and obstacles,and the maximum errors are less than 0.02m and 0.06m respectively.Finally,experiments on trajectory optimization of space manipulator with joint free-swinging failure based on redundancy characteristics are carried out.First of all,according to the theoretical method proposed in this paper,the needs of the physical experiment are sorted out,and the existing experimental platform is designed and reformed.According to the experimental purpose,the reasonable and perfect physical experiment is designed,and the joint avoidance limit and obstacle avoidance trajectory optimization experiments of space manipulator with joint free-swinging failure based on redundancy characteristics are carried out.The correctness and effectiveness of the proposed method are verified. |
