Research On Fault-tolerant Control Method Of Space Manipulator With Joint Failure

With high flexibility,strong operation capacity and large working range,the space manipulator becomes significant equipment in space station on-orbit construction and operation.Dueing to frequently executing heavy tasks in long-term service,the space manipulator is exposed to joint failure.Considering that astronauts repair fault joints on-orbit is accompanied with high-cost and high-risk,we study the fault-tolerant control mothod to solve key problems of modelling,planning and control of the space manipulator with joint failure,to enable the manipulator to keep working on-orbit.The research result posseses high theoretical research and engineering application value for prolonging service life of the space manipulator.Free-swinging faiure and Locked faiure are two typical kinds of joint failure which seriously affect reliable opration of the space manipulator.The space manipulator with free-swinging joint failure loses operating force outputting capacity,so fault joints are usually regulated and locked at certain desired angles to isolate failure.But the locked angles determine subsequent working performance of the manipulator,and there exist complicatied motion/force coupling relationships,which increase the difficulty in regulating fault joints.To process free-swinging joint failure,we need to analyze kinematic/dynamic coupling characteristics,design the reasonable motion planning and control approach,and optimize the locked angle for promoting subsequent working performance.Working performance of the space manipulator with locked joint failure finitely degrades compared with the normal state.To make the space manipulator with locked joint failure execute various space tasks,we need to reevaluate task realizability and replan exectutable task trajectory.In this thesis,aiming at the space manipulator installed on free-floating base,we study the fault-tolerance control method,to decouple complicatied motion/force coupling relationships,design the motion planning and underactuated control strategy,and optimize lock angles of fault joints for the space manipulator with free-swinging joint failure.Then,we contruct task realizability and trajectory planning strategy for the space manipulator with locked joint failure,to make the manipulator execute space tasks reliably.Main research contents are as follows:1 Kinematic and dynamic coupling characteristics analysis of the space manipulator with free-swinging joint failure.Firstly,we derive the motion/force mapping relationships between healthy joints and free-swinging fault joints,free-floating base and end-effector.Then,the kinematic and dynamic coupling relationships are established.With proving the coupling relationships both belong to hybrid-order non-holonomic constraints,motion/force coupling inside the manipulator is decoupled.We point out the space manipulator with free-swinging joint failure is a new kind of underactuated system which contains hybrid-order non-holonomic constraints.Afterwards,the kinematic and dynamic coupling degree indexes are defined,to quantificationally evaluate the ability that healthy joints regulate controlled units.Simulation shows based on motion planning,the space manipulator with free-swinging joint can regulate controlled units with high presicion,so existence of kinematic coupling relationship is proved.Finally,we give the application example for coupling degree indexes.2 Underactuated control method for the space manipulator with free-swinging joint failure.We introduce the conventional terminal sliding underactuated control method which is robust to model uncertainty and joint torque disturbance,and further discuss the problem that control parameters are difficult to be selected under unknown uncertainty and distuebance,and contradiction between chattering elimination and robustness degradation.Then,we introduce the adaptive fuzzy control into the terminal sliding underactuated control.The new control system actively estimates and compensates effects of model uncertainty and torque disturbance according to real-time controlled units states,so that control stability and robustness can break through the limitation of control parameters selection.Simulation verifies the adaptive fuzzy terminal sliding mode control method can accurately compensates effects of uncertainty and disturbance.Compared with the conventional terminal sliding mode control,active joints torque drops down more than 60%,and stable errors of sliding mode manifolds decrease by nearly an order of magnitude.Therefore,the adaptive fuzzy terminal sliding mode control provides an effective control method for regulating free-swinging fault joints.3 Locked angles optimization for free-swinging fault joints of the space manipulator.Aiming at the load carrying task,we define kinematic performance and operation capacity indexes which are relative to joints locked angles and affect task execution reliability,to establish optimization criterions.Then,we utilize gray system relation entropy theory to efficiently construct the comprehensive performance evaluation index.Then,locked angles are expediently optimized for maximizing the comprehensive index.Simuliation shows the calculation efficiency for constructing the comprehensive index based on the gray system relation entropy theory increases by more than 80%compared with the traditional entropy theory.When fault joints are locked at the optimal angles,the degradation of subsequent working performance of the space manipulator is minimal.The correctnesss of the comprehensive index,and the effectiveness of utilizing the comprehensive index to optimize locked angles are verified.4 Task realizability evaluation and trajectory planning for the space manipulator.Considering base disturbance should be limited during task execution,we define the selection criterion of representation variables of the space manipulator.Then,representation space is classified according to three base control modes,including fixed,attitude constrained and free-floating,and the representation space that simultaneously satisfies task requirements and base disturbance limitation is acquired.On this basis,the task realizability criterion and trajectory planning strategy are established.Finally,we apply the representation space analytical method to typical no-load transferring and load carrying tasks,to show the effects that the space manipulator executes these typical tasks.Representation space analytical method establishes the mapping between state change rule and task execution process.It provides the implementation basis for task realizability evaluation and trajectory planning of the space manipulator,which guarantees the space manipulator with locked joint failure to reliably execute on-orbit tasks.5 Experiment research on fault-tolerant control for the space manipulator with joint failure.We design a fault tolerant control experiment platform consisting of air floating system,base,manipulator,simulation software and various kinds of sonsors.Then,experiments are designed and carried out,including motion planning,underactuated control,and trajectory planning based on the representation space analytical method,to verify the feasibility and effectiveness of key theories of fault-tolerant control method.