Research On Fault Tolerant Control Method Of Space Manipulator With Joint Effectiveness Partial Loss Failure

With strong load capacity,large workspace and flexible operation,space manipulator is often used to assist or replace astronauts to complete on-orbit tasks efficiently,economically and safely,such as on-orbit assembly,on-orbit capture.However,the space environment has high temperature difference,strong radiation and microgravity,which will lead to severe challenges to the reliable operation of the space manipulator.And long-term implementation of heavy and complex tasks in this environment will make each component of the space manipulator often in a heavy state.As the key unit of the manipulator,any abnormal state of its components may lead to the joint failure,and the faulty joint can not be repaired in time in space.Under the influence of multiple factors,such as special environment,heavy tasks and complex joint structure,the longterm reliable operation of joints is seriously threatened,and joint failure is inevitable.Joint failure mainly include locked failure,free-swing failure and effectiveness partial loss failure.Joint locked failure and free-swing failure correspond to the joint velocity and torque being zero,respectively.Once the output of joint is perturbing,and cannot reach the expected value,that is,the joint effectiveness partial loss failure occurs.So,it is the most common kind of joint failure.After joint effectiveness partial loss failure occurs,the motion model of the manipulator changes.If the effective fault-tolerant control method is not carried out,the motion capability of the manipulator will be perturbed and the trajectory will deviate from the expected trajectory.Therefore,it is very important to study the fault-tolerant control method of space manipulator with joint effectiveness partial loss failure.Based on the support of National Natural Science Foundation of China "Motion Capability Optimization and Multi-stage Fault-tolerant Control of space manipulator with free-swing joint failure"(No.62173044),this paper carries out research on fault-tolerant control methods of space manipulator with joint effectiveness partial loss failure,including:Motion model establishment,motion capacity influence analysis,fault-tolerant control method research,and physical experiment of fault-tolerant control method for space manipulator with joint effectiveness partial loss failure.Firstly,considering the characteristics of joint effectiveness partial loss failure,the kinematic model construction method of the faulty manipulator is studied.Aiming at the problem that only torque partial loss failure is considered in the existing methods,the mathematical representation of velocity and torque partial loss failure are constructed respectively,and the universal failure model was constructed.The motion model of the faulty manipulator is established,and a universal fault model was introduced to analyze the mapping relationships between the joint expected output velocity(control velocity)and the base/EEF velocity,as well as the torque(control torque)and the base/EEF acceleration.So as to the decoupling of the motion model is realized.This method can be applied to any type of joint failure(including joint locked failure and free-swing failure)and any failure form(including velocity and torque partial loss failure),which has strong universality and practicability.Meanwhile,this method can lay theoretical foundations for the motion capacity influence analysis and fault-tolerant control.Secondly,considering the actual requirements of on-orbit tasks,a method was proposed to analyze the motion capability influence of the manipulator with joint effectiveness partial loss failure.Aiming at the precise representation of the motion capability,the requirements of typical on-orbit tasks are sorted out.Then,the motion capability indexes affected by joint failure are analyzed,and the mathematical representation method of them are constructed based on the motion model.The mapping relationship between failure characteristics(location and degree)and motion capability was established.The influence rule of failure degree on motion capability is analyzed.The proposed method can be used to characterize the motion capability of space manipulator with any location and degree joint failure,which can be used to evaluate the task performance and provide theoretical guidance for motion capability optimization.Thirdly,based on the motion model and the redundancy characteristics,the fault-tolerant control method of the space manipulator with joint effectiveness partial loss failure is studied.After the joint failure,the EEF could not move along the desired trajectory,and the orientation of the floating base is deflected.Meanwhile,the motion capacity of the manipulator could not meet the task requirements.For the problem of EEF trajectory deviation and the base orientation deflection,the EEF trajectory and base orientation error are taken as control variables,and the system state space equation are designed.Considering the model uncertainty,the fault-tolerant controller are designed based on sliding mode control method,respectively.And the EEF trajectory tracking and base orientation disturbance attenuation are realized at the same time.Aiming at the motion capability degradation problem,a motion capability optimization model was designed based on the redundant characteristics of the faulty manipulator.Then,the optimization model is introduced into the fault-tolerant controller,and the fault-tolerant control system with optimal motion capability is obtained.Simulation results show that the fault-tolerant control method proposed in this paper can make the EEF trajectory and the base orientation converge rapidly to the expected value,and the steady-state error is less than 2 × 10-4.The motion capability optimization control method can improve the dexterity at every moment in the task execution process.And the dynamic load capacity of the faulty manipulator is improved that the improvement rate is as high as 68%.Finally,a physical experiment of fault-tolerant control method for space manipulator with joint effectiveness partial loss failure was carried out.Combined with theoretical methods,the demand for physical experiments was sorted out,and the existing experimental platform was reformed.A reasonable experimental scheme is designed,and the faulttolerant control method physical experiment of the faulty manipulator in the case of under the base disturbance and the optimal motion capacity are carried out respectively,which further verified the correctness and effectiveness of the theoretical methods proposed in this paper.