Research On Coodinated Control Of Dual-arm Space Robots For Target Capturing And Manipulation

With the gradual development of space exploration, the space robotic systemplays an increasingly important role in spacecraft on-orbital assembly, repairing andmaintenance. Comparing with the single-arm space robot, dual-arm space robot hashigher flexibility and reliability, and will be the main force of future on-orbitalservice. However, the dynamics modeling, path planning and control, etc., dual-armspace robot is much more complex than single-arm space robot, especially inclose-chain robotic system. In this paper, taking consideration of the space targeton-orbit for capturing and operation, we do research on modeling of closed-chaindynamics, trajectory planning of dual-arm coordination and compliance controlstrategy for dual-arm space robotic system, etc.When the target grasped by two-arm, a closed-chain dynamic system is formed,the dynamic characteristics of the compounded system are extremely complex. Toprovide a basis for trajectory planning, control and simulation, the closed-chaindynamic model of dual-arm space robot is established, and numerical solutionmethod is proposed based on restricted type constraints. This paper established theopen-chain dynamic equations by the Newton-Euler method, and used cut off thehinge to form the constraint kinematic equations, merged them to form theclosed-chain dynamic equations, this method is suitable for dynamic modeling ofdual-arm coordination operation. The established model laid a foundation for thedynamic characteristics analysis and trajectory planning and control.Due to the dynamic coupling between the manipulator and the base, the motionof manipulator will generate disturbance of the base that will change the basecentroid position and attitude, this changes will further change the pose of theend-effector. The existence of this feature affects the efficiency of space manipulatoron-orbit mission. The dynamic coupling between the manipulator and base can bedecomposed into two parts: the centroid position and attitude, the combination ofthe position-level and velocity-level coupling analysis method have been putforward. The linear velocity of base centroid meet the conservation of linearmomentum equation which belongs to the holonomic constraints, through theestablishment of base centroid virtual manipulator kinematics equation inposition-level, which reflect the relationship between centroid position and eachjoint; however, base angular velocity and joint angular velocity meet the angularmomentum conservation equation which belongs to the nonholonomic constraints,therefore, we can describe the relationship between the base attitude and joint angle in velocity-level. Moreover, this paper also defines the dynamic coupling factor todescribe the degree of dynamic coupling, and draw the base attitude coupled map.Hybrid dynamic coupling modeling and analysis methods can be solving theproblem of traditional method for singular configuration is various, computationalefficiency is not high.Target capturing and operation is the key to realize the on-orbit service, usingdual-arm to perform this task can increase the effectiveness and reliability of thetask. The coordinated trajectory planning algorithm for target pre-capturing andpost-capturing have been put forward. In pre-capturing stage, the goal of measuringdata can be obtained by the hand-eye vision, thus, real-time planning the joint anglemovement of manipulator, until the target is captured by two-arm. After the target iscaptured, we need to adjust the position of target where is suitable for maintenance,this process is mainly through the solution of the closed-chain kinematics equationfor coordinated manipulation. The typical operation processes of the simulationresults verify the validity of the method.When the target is captured by two-arm, a closed-chain robotic system isformed, then, the position control and the internal force distribution is the key to thesuccess of the operation task. Based on the results of the dual-arm coordinatedtrajectory planning, the impedance control method is put forward in the process ofcoordinated manipulation, not only make the target goes the given path movement,but also the internal force of the whole closed-chain system obtain rationaldistribution, and ensure the safety and reliability of the on-orbital task. Theeffectiveness of the proposed control method is verified by typical tasks ofsimulation.