Research On Halt Strategy For Space Manipulator With Sudden Joint Failure

As a high-end space equipment with large span,high flexibility and strong operation capability,space manipulators have been widely used in the field of space exploration.However,due to the complex joint structure and hostile working environment(high temperature difference,high radiation,etc.),a sudden joint failure(joint locked failure and joint free-swing failure)is prone to occur,which can lead to the degradation of kinematic ability of space manipulator.After the sudden joint failure occurred,it is difficult to plan the motion of the manipulator for the execution of on-orbit operation task.If the manipulator executes the original task without halt,its running parameters(joint velocity,acceleration,torque,etc.)will jump at the failure moment,bringing a deformation or more damage to the manipulator,which can not only lead to the failure of the task but also have an effect on the safe and stable operation of manipulator.Therefore,it is of great research value and application significance to study a halt strategy for space manipulator with the sudden joint failure.The research object of this paper is the seven degree of freedom space manipulator installed on the base which is free-floating.The scientific questions of optimization of halt configuration for space manipulator with the sudden joint failure,optimization of halt motion for space manipulator with joint-locked failure,motion control for safe halt of space manipulator with joint free-swing failure is studied.The main research contents of this paper are as follows:Firstly,the halt configuration optimization method for space manipulator with sudden joint failure.After establishing the kinematic model of space manipulator with joint sudden failure,the mathematical characteristics of the unilateral kinematic ability indexes of the fault space manipulator are analyzed.The kinematic ability indexes of the space manipulator affected by the configuration of the fault manipulator are selected.Considering the kinematic ability of the manipulator and the requirements of the operation tasks on the kinematic ability,the entropy method is combined with the analytic hierarchy process method and then the comprehensive characterization of the kinematic ability can be obtained.Then the halt configuration optimization model of space manipulator with the sudden joint failure is constructed and solved,which can obtain the optimal halt configuration.The simulation shows that the comprehensive kinematic ability of the manipulator is optimal with the optimal halt configuration,which provides guarantee for the execution of subsequent operation tasks,and proves the correctness and effectiveness of the halt configuration optimization method for space manipulator with sudden joint failure.Secondly,the halt motion optimization method for space manipulator with joint locked failure.Considering the characteristics of the halt process for space manipulator with joint-locked failure,the halt motion of the space manipulator is planned with a six-order polynomial interpolation method which contains an optimal coefficient.Considering the characteristics of the base,by taking the limitation of the joint running parameters as constraint conditions,and the minimum disturbance torque of base as the objective,the halt motion optimization model containing the optimal coefficient is constructed and solved,and the halt motion of the faulty manipulator is optimized.The simulation proves the correctness and effectiveness of the halt motion optimization method for space manipulator with joint locked failure.Thirdly,the safe halt method for space manipulator with joint free-swing failure.According to the halt target angle,the motion planning of the space manipulator with joint free-swing failure is carried out,and the motion state of free-swing joint with the optimization coefficient is obtained.Taking the deflection of the base attitude as the optimization objective and the operation parameters of the free-swing joint as the constraint conditions,the halt process of the manipulator is optimized,and the safe halt of the space manipulator with joint free-swing failure is realized.According to the non-holonomic redundancy characteristics,the halt optimization operator is constructed and the halt optimization coefficient matrix is set,considering the base deflection and the variation of joint operation parameters during the halt process.The halt optimization model of the space manipulator with joint free-swing failure is constructed and solved to realize the safe halt.The simulation proves the correctness and effectiveness of the safe halt method for space manipulator with joint free-swing failure.Finally,the research on the physical experiment of the halt strategy for space manipulator with sudden joint failure.Based on the requirements of physical experiment verification,the ground experiment platform is designed and modified,including joint failure manipulator,air flotation system,communication system for experiment.According to the experimental purpose,a reasonable experimental scheme is designed.The physical experiment of halt motion optimization for space manipulator with joint locked failure and the physical experiment of the halt for space manipulator with joint free-swing failure are carried out,which can verify the correctness and effectiveness of the halt strategy for the space manipulator with sudden joint failure.