Research On Fault-Tolerant Control Strategy For Space Manipulator With Multi-Joint Multi-Type Failure

It is invaluable for national security protection and economic development to explore the space.During space exploration,space manipulators have been widely used because of its advantages of large span,high flexibility and strong load capacity,and occupied an irreplaceable important position.Due to the hazardous space environment and heavy on-orbit operation tasks,single joint failure is likely to occur to space manipulators with long-term on-orbit service.On the premise that the quality requirement for the completion of on-orbit operation tasks remains unchanged,single joint failure space manipulator will greatly increase the possibility of other joint faults with continuing on-orbit operation tasks,that is,it may lead to multi-joint multi-type(locking and free swing)failure occur to space manipulators with long-term on-orbit service.After the failure occurs,kinematics performances in both joint space and operation space will degrade greatly if not effectively control the space manipulator for tolerating fault,which seriously restricts smooth implementation of subsequent on-orbit operation tasks and impacts the on-time implementation of the space exploration program.Therefore,it is of great theoretical value and practical significance to study a fault-tolerant control strategy for space manipulator with multi-joint multi-type failure.The research content of this paper comes from the National Natural Science Foundation of China "Research on Motion Performance Evaluation and Fault Tolerant Path Planning of Space Manipulator with Failed Joints" under grant 61403038.The research object is space manipulator,and the scientific questions of construction of comprehensive kinematics performance index for space manipulator with joint failure,structure of coping strategy for space manipulator with multi-joint multi-type failure with optimizing kinematics performance,and fault-tolerant path planning with optimal running time is studied.The main research work is as follows.Considering that the meaning of the current kinematics performance indexes is unilateral,study the construction of comprehensive kinematics performance index(CKPI)for space manipulator.Analyze the mathematical expression and meaning of kinematics performance indices,and determine the kinematics performance indices affected by joint angle.In order to get the comprehensive characterization of kinematics performance both in joint space and operation space,select multiple kinematics performance indices,where the local kinematics performance indices are globalized and analyzed at the overall levels to determine the sub-indices for constructing CKPI.Analyze the influences of sub-indices on CKPI,and determine the weight of each sub-index to construct CKPI.Then the comprehensive evaluation of kinematics performance indices both in joint space and operation space is achieved.Aiming at that space manipulator with multi-joint multi-type failure can continue to carry out on-orbit operation task,study the coping strategy for space manipulator with multi-joint multi-type failure.For the space manipulator with joint locked failure,utilize the Newton-Raphson method to solve the artificial joint limits,and make joints rotate only in the limits to complete the structure of prevention strategy for serious kinematics performance degradation.For the space manipulator with joint free swinging failure,evaluate CKPI value to obtain the optimal locked angle of fault joint,and adjust the free swinging fault joint to the optimal locked angle,then a treatment strategy for joint free swinging failure is built.Considering the random characteristic of joint failure and the requirements for space manipulator degree of freedom(DOF)of on-orbit operation tasks,the above prevention strategy and treatment strategy are synthesized to complete the structure of coping strategy for space manipulator with multi-joint multi-type failure,which can let the CKPI meet the requirements of on-orbit operation tasks after coping multi-j oint multi-type failure.In order to raise the actual operating efficiency,study the fault-tolerant path planning for space manipulator.After reconstructing the kinematics model of space manipulator when the fault joints are locked,utilize the probabilistic roadmaps(PRM)method to collect path nodes and connect them,and delete the ones where space manipulator kinematics performance cannot meet the requirements of on-orbit operation tasks,then the roadmap that makes space manipulator meet the requirements of the tasks is constructed.Regard the actual running time as target,optimize the number of path nodes and complete the improvement of the method(A*algorithm)used to search path in traditional PRM method,then the path with the shortest actual running time for space manipulator with multi-joint failure is obtained.The experimental research on fault-tolerant control strategy for space manipulator with multi-joint multi-type failure is carried out.Reconstruct the space manipulator air floating microgravity ground experimental platform,and design experimental program for coping strategy for space manipulator with multi-joint multi-type failure and fault-tolerant path planning.Analyze contrastively physical experiment results and theoretical research results,then the correctness and effectiveness of the proposed fault-tolerant control strategy for space manipulator with multi-joint multi-type failure is verified.