Development Of Fault-tolerant Motion Control System For Space Manipulator With Joint Failure

Space manipulator is an important tool for on-orbit maintenance and construction,which plays a key role in place of astronauts in extravehicular operations,cabin transfer and docking.Considering the abominability of the working environment of the space manipulator and the structural complexity of the joint,the joint failure is likely to occur during its long-term service.Once the space manipulator is failed,it cannot be repaired in time,which will result in the delay of the space task,thus affecting the implementation of the whole space program.In order to make sure the space manipulator still can continue to complete the following tasks when joint failure occurred,the fault-tolerant requirements for the space manipulator are put forward.In this paper,the joint failure of the 7-DOF space manipulator is studied,and the development of the fault-tolerant control system of the space manipulator is carried out.The research contents include online adjustment,kinematics model reconstruction,fault-tolerant path planning and system development and physical experiment.Firstly,in view of the problem of the joint swing type failure of the space manipulator,the on-line adjustment strategy of the fault joint is put forward.Through the comprehensive analysis of the motion performance of the manipulator,the optimal locking angle of the fault joint is determined.In order for the fault joint to be adjusted to the optimal locking angle,the dynamic coupling relationship between the passive joint and the active joint is established,and the adjustment of the passive joint to the desired angle is solved by PD control.The motion performance analysis method proposed in this paper considers the motion performance of manipulator in joint space and the operation space;coupling relationship analysis method can solve the adjustment of 7-DOF manipulator with arbitrary joint failure occurred.Secondly,in view of the problem that the kinematics model is no longer applicable after the joint locked of the space manipulator,the reconstruction of the kinematics model is carried out.In this paper,based on the DH parameter modeling method and the spinor theory modeling method,we reconstruct the kinematics model of the 7-DOF space manipulator with single joint failure,and get the reconstructed kinematic parameters.On this basis,a general kinematic model reconstruction method is proposed,which can adapt to the kinematic model reconstruction of manipulator with different degrees of freedom and different configurations when any joint fails.Then,in order to make sure manipulator can carry out subsequent tasks after single joint failure,the fault-tolerant path planning of single joint failure space manipulator is studied in this paper.Through the establishment of comprehensive motion performance index,a workspace analysis method for comprehensive performance of space manipulator is proposed,which can solve the performance characterization of the workspace of the fault manipulator.On the basis of traditional A*algorithm,an improved comprehensive motion performance index is added to solve the fault-tolerant path planning considering the comprehensive motion performance,and a path planning algorithm suitable for the fault manipulator is established.Finally,the fault-tolerant control system of the single joint failure space manipulator is built and the physical verification is carried out.The system can not only verify the theoretical results,but also can display the simulation tasks in a visual way.On this basis,based on the laboratory ground experiment platform,we carried out a physical experiment,and further verified the practical application of the proposed method.