Research On Multi-Dimensional Compliant Docking Joint And Stabilization Strategy For On-Orbit Operation

The continuous and in-depth exploration of space by humans has led to the increasing number of spacecrafts that have failed in orbit.Space missions have shown a complex and diverse development trend.The on-orbit service technology based on space robots is an important ability expansion for humans to continue to carry out in-depth space exploration activities.It is a necessary condition to complete the "on-orbit service" to use the service spacecraft to capture the failed target spacecraft in orbit.The space targets taken over by the service spacecraft are often out-of-control non-cooperative targets.They lack part or all of the necessary state information.There is often a certain position error and relative speed between the end of the actuator and the captured point of the target,which makes them inevitably collide during the docking process.Then,it may cause actuator failure,spacecraft damage,target spacecraft being ejected or rolled over and other adverse consequences due to excessive contact force.Therefore,how to ensure the successful docking of two spacecraft and ensure the structural safety as well as attitude stability of spacecraft is the key link of the in-orbit acquisition of space non-cooperative targets.To solve this problem,the flexible docking with the target spacecraft is realized by adding a flexible link with buffering and unloading capability in the service spacecraft.To solve this problem,a flexible link with buffering and unloading capability is added to the service spacecraft to achieve compliant docking with the target spacecraft.The specific work is as follows:First of all,in order to avoid the risks brought by rigid operation,based on the analysis of existing passive compliance strategies and mechanisms,an omni-directional compliant docking joint with omni-directional compliance capability is proposed,which can realize the rigid/flexible dual-mode conversion operation according to the different stages of the capture task.At the same time,four sets of spring-damping buffer components can be used to realize the space omni-directional six-dimensional contact force buffer and momentum unloading,It also has the function of motion state perception and displacement compensation.According to the design requirements and functional requirements of the omni-directional compliant docking joint proposed,the three-dimensional structure of the omni-directional compliant butt joint is designed using SolidWorks.Secondly,the omni-directional compliant docking joint is combined with the traditional rigid service spacecraft to form the omni-directional compliant composite spacecraft system,and its dynamic model is established using the Lagrange’s equation containing dissipation function to comprehensively analyze the dynamic characteristics of the system.The correctness of the theoretical model is verified by the joint comparative simulation of two platforms based on Matlab and Adams,which provides a theoretical basis for subsequent research.The effectiveness of the omni-directional compliant docking mechanism and damping stabilization mechanism of the compliant docking joint is verified by the simulation experiment of the space omni-directional contact force.Then,in order to research the docking process between the service spacecraft with the non-spin non-cooperative target spacecraft,and verify the rationality and effectiveness of the omni-directional compliant docking joint applied to the non-cooperative target docking process.A non-cooperative target docking model consisting of target spacecraft and service spacecraft is established in the Adams dynamic simulation environment based on the docking strategy of taking the spacecraft engine nozzle as the capture point.The simulation of the space non-cooperative target docking model under different errors of distance and angle is carried out,and the compliance performance of the compliant docking joint is fully verified by the results of the rigid-flexible comparison experiment.In addition,in order to study the stabilization control problem of the service spacecraft after capturing the spinning non-cooperative target,an inversion control strategy based on the ultra-local model of the compound system is proposed,and the disturbance term and unmodeled dynamics of the system are estimated online in real time through the time delay estimation method.Aiming at the modeling error caused by time delay estimation,an adaptive compensation strategy based on RBF neural network is adopted for real-time compensation.Based on the principle of the minimum momentum of the base,the parameters in the controller are globally optimized based on genetic algorithm to achieve the optimal performance of the controller.Based on the joint simulation platform of Matlab and Adams,the effectiveness of the control strategy is verified at first,and then the compliance effect and buffering and unloading performance of the omni-directional compliant docking joint in solving the compound system attitude disturbance control problem are analyzed through the rigid-flexible comparison simulation.Finally,the structural design,theoretical research and simulation verification of the omni-directional compliant docking joint have been completed in the previous paper.Then,a physical prototype of the two-degree-of-freedom omni-directional compliant docking joint is designed and developed,and the ground verification system of the multi-dimensional compliant docking mechanism was developed based on the laboratory air flotation test platform and the multi-DOF satellite simulator.Through a reasonable soft docking experimental scheme,further experimental verification of the compliant docking joint is carried out to test the weak impact performance of the joint under the simulated actual working conditions.