| For the increasingly complex space operations in orbit such as faulty satellite recovery,spacecraft fueling,and formation of large spacecraft,the space robotic arm needs to have the ability to capture space noncooperative targets in a soft way.All those capture tasks require the robot to interact or docking with capture target where big contact force can be exerted,if the contact force cannot be buffered and offset in time,it will cause large disturbance to the system attitude,thus affecting the completion of the on-orbit operation mission.This article is based on National Natural Science Foundation of China general project "Multi-dimensional Soft Docking Mechanism Dynamics and Cluster Sedation Strategy for In-orbit Capture(No.51875046)".This paper is oriented to the on-orbit compliant capture task of non-cooperative targets in space.In order to solve the problem of rapid stability after the complex is disturbed during the capture process,the space compliant capture manipulator with multi-dimensional controllable damping is taken as the research subject,and its buffer absorption can realize the unloading of the six-dimensional impulse in space,and design a compliant and cooperative control strategy to achieve smooth soft contact during the capture and rapid stabilization of the complex after capture.Four key technologies are investigated in this paper,namely,flexible joint structure with multi-dimensional controllable damping and key parameter analysis,the contact dynamics of the capture process,the identification of space target parameters,and the cooperative stabilization control of the complex system.The main research contents and results are as follows:(1)The compliant capture form of the space manipulator with mul-tidimensional controllable damping joints is constructed,and its omnidirectional compliant capture principle is analyzed to realize the omnidirectional cushioning of six-dimensional impulse in space.The key parameters of the compliant joint with multi-stage spring-controllable damping are analyzed in depth.The space manipulator with compliant joint at the end can be regarded as a compliant manipulator.Because its dynamic be-havior presents complex rigid-flexible coupling characteristics,the Kane equation Recursively deduce the rigid-flexible coupling dynamic equation of the space manipulator with multi-dimensional controllable damping joints,and analyze the soft contact mechanism of the space capture ma-nipulator under the multi-dimensional collision force,and further study the impact of different damping and different stiffnesses on the space ma-nipulator during the capture process.The internal influence of the state response,through simulation and experiments,summarizes the dynamic response law of the space manipulator under different damping and stiff-ness after being impacted.(2)A mixed contact force model in the process of capturing the target by the space compliant manipulator is constructed,and the dynamic tracking of the dynamic characteristics of the complex contact force is realized.Analyze the contact dynamics characteristics in the capture,vector synthesis the improved Hertz model and the LuGre modified friction model,build a physical contact model including normal positive pressure and tangential friction force,and introduce the necessary friction force in the contact collision In the collision model,the sliding-stick state transition criterion is designed.Among them,the LuGre friction model parameters are identified by genetic algorithm,so that the friction model can adapt to more contact and collision scenarios.Furthermore,combined with the radial basis function(RBF)neural network,a data-driven hybrid contact collision model is obtained.The hybrid contact model can correct errors that cannot be modeled in the physical model.Compared with the physical model,the contact force peak of the hybrid model error is reduced from 17.7%to 1.4%,and the collision impulse error is reduced from 8.8%to 2.4%.It has better dynamic performance in the tracking process of complex contact collision characteristics in the capture process..(3)A parameter identification algorithm for space non-cooperative targets and a stiffness estimation algorithm for compliant capture manipulators are proposed,and the effective identification of unknown parameters of the complex system is realized.The rigid-flexible coupling dynamic model of the manipulator is captured in space,and the parameters to be identified of the space target are separated,and the identification correction model is obtained based on the contact force information.This model can significantly reduce the accumulation of sensor measurement errors in the joints of the manipulator.The steady-state error of identification is 1.09%～1.54%.Aiming at the time-varying characteristics of the flexible elements in the controllable damping joint,a stiffness estimation algorithm based on the unknown input observer(UIO)is proposed,combined with the neural network algorithm to update the variable parameter matrix of the observer,to effectively estimate the flexible force in the joint And stiffness,the steady-state error range is 2.12%～2.67%,and the stiffness value is used as the input of the modified model to optimize the collaborative control strategy,providing more reliable model parameters for improving the stability control accuracy of the complex.(4)A backstepping non-singular integral terminal sliding mode cooperative control method integrating controllable damping,joint driving force and reaction flywheel torque is proposed to achieve rapid stabilization of the post-capture complex system.Taking the angular momentum migration in the complex as the constraint condition,and aiming at the minimum disturbance of the base,based on the identification of the target dynamic parameters,the cooperative control of the controllable damping force,joint active torque and base reaction flywheel torque is realized,the steady-state error is less than 0.2%,and the average amplitude of torque buffeting is reduced by 75.6%compared with the classical sliding mode control,which solves the problem of limited unloading kinetic energy of the base reaction flywheel and realizes the cooperative stabilization control of the complex after capture..(5)The verification experiment of the compliant capture mechanism,target dynamic parameter identification and base stabilization control strategy on the ground micro-gravity platform was carried out.A ground verification system including physical prototypes of compliant joints,air-floating satellite simulators,drive devices and sensor components was developed.The principle of compliant capture by compliant joints is verified by comparative experiments,the effectiveness of the parameter identification method is verified by the designed target dynamic parameter identification experiment,and the effectiveness of the complex cooperative stabilization control method is verified by the base stabilization experiment.The experimental results prove that The space compliant capture manipulator can adapt to a variety of on-orbit capture scenarios,which fully demonstrates that the multi-dimensional controllable damping joint improves the compliant capture ability of the space manipulator to the target. |
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