Design Of Soft-docking Wrist And Research On The Compound Stabilization Control For On-orbit Acquisition

The space docking device is the core component of the on-orbit acquisition mission,and is one of the core technologies of the space strategic development of the major countries in the world.For noncooperative targets such as failed spacecraft,the space docking device should not only achieve in-orbit capture and locking,but also be able to reduce and buffer the impact impulse of docking,prevent hard collision,and achieve soft-docking of non-cooperative targets,which is of great significance for completing the in-orbit acquisition task.At the same time,if the dynamic parameters of non-cooperative targets cannot be accurately obtained,it will seriously affect the stability of the post-acquisition complex and the accuracy of subsequent operation control;In addition,the impulse carried by non-cooperative targets after acquisition can easily lead to the instability of the floating base.Minimizing the disturbance of the free-floating base is still a challenging task for in-orbit acquisition.The topic is derived from the general project of the National Natural Science Foundation of China:"Dynamic Mechanism and Cluster Stabilization Strategy for Multidimensional Soft-docking Mechanisms for On-Orbit Capture"(Project No.:51875046).Taking the space capture mechanism as the research object,the paper designs an omnidirectional compliant soft-docking wrist with the ability to buffer and unload the impact impulse in space.And a rigid-flexible coupling dynamic model of the soft-docking wrist is constructed,and a stiffness optimization strategy is proposed for the soft-docking wrist based on the principle of conservation of momentum after collision.Furthermore,the parameter identification methods for non-cooperative targets after soft-docking is it studied,providing the key parameters for the compound cooperativestabilization control.Finally,the cooperative-stabilization control of the compound after the on-orbit soft-docking is realized.The results of the paper have a positive role in promoting basic theoretical research and key technological breakthroughs in the field of space on-orbit acquisition and rendezvous-docking.The main work of this paper is as follows:(1)A soft-docking wrist for on-orbit capture is designed,which can realize the buffering and unloading of collision impulses in space sixdimensional docking,i.e.,omnidirectional compliance.Aiming at capturing non-cooperative target tasks on orbit and the functional requirements of omnidirectional compliance,the design indicators of the soft-docking wrist is proposed.And the overall configuration design,key flexible component design,and modular parameter analysis of the softdocking wrist are carried out,providing the key parameters for the simulation and verification of the rigid flexible coupling dynamic model of the soft-docking wrist.Further,the omnidirectional compliance mechanism of the soft-docking wrist is analyzed.And the simulation experiments to verify the omnidirectional compliance mechanism is conducted,under the conditions of single dimensional limit collision and six-dimensional limit collision respectively.The results indicate the effectiveness of the buffer unloading spatially six-dimensional dockingcollision impulse for the soft-docking wrist.(2)A rigid-flexible coupling dynamic model of a soft-docking wrist is constructed,and global optimization of multiple stiffness parameters of the soft-docking wrist is achieved.The Kane equation is used to analyze the kinematics and dynamics of the topology model of the rigid-flexible coupling links of the soft-docking wrist,and the dynamic model is constructed.According to the principle of conservation of momentum,a global optimization strategy for multi-stiffness parameters of the softdocking wrist is proposed to solve the problem of exceeding the limit of each joint of the soft-docking wrist,under the limit collision conditions.Under limit collision conditions,the omnidirectional compliance mechanism optimization simulation experiments for the stiffness parameters of the soft-docking wrist is carried out,and obtain the mapping relationship between multi-dimensional stiffness and peak vibration displacement,then the initial value of particle swarm optimization algorithm for soft-docking wrist stiffness parameters is determined by analyzing.Further,a multi-stiffness optimization objective function is constructed.Under spatially six-dimensional limit-collision conditions,the particle swarm optimization algorithm simulation is conduct,and the optimal stiffness of each joint of the soft-docking wrist is obtained.The overrun problem of each joint of the soft-docking wrist under the limit collision conditions is solved.(3)A non-excitation parameter identification method for the noncooperative target after soft-docking is proposed.Taking the compound after capturing non-cooperative targets by a space capture mechanism equipped with the soft-docking wrist as the research object,a binocularvision identification model for the kinematic parameters of the noncooperative target is established,and the kinematic parameters of the non-cooperative targets were solved by singular value decomposition(SVD)and rotational quaternion(QTN)methods.Then,the noise resistance and distance experiment are conducted to verify the effectiveness of the binocular-vision identification method for the kinematic parameters of the non-cooperative target,which provide a foundation for the state perception of the floating base in the process of non-excitation identification of dynamic parameters after soft-docking of the non-cooperative target.Further a compound momentum increment equation is established,which contains only dynamic parameters of the non-cooperative target,without the rigid and flexible attributes,kinematic states and internal and external active excitation.Realize least-squares solution to avoid singularity by continuously increasing the dimension of the coefficient matrix of the momentum increment equation,and solve the matrix condition number to achieve measurement of termination conditions.Finally,through simulation experiments on accuracy,delay characteristics,and sampling characteristics,the effectiveness of the nonexcitation identification method for dynamic parameters of the noncooperative target after soft-docking is verified,which lays the foundation for achieving cooperative stabilization of the compound after on-orbit soft-docking.(4)A cooperative stabilization control method for the compound system after on-orbit soft-docking is proposed.Aiming at the problem of the compound cooperative stabilization after on-orbit soft-docking,firstly,the research on the stabilization control of base attitudes after on-orbit soft-docking is carried out.By deriving the state-space equation and control objective function of base attitudes,and using the sliding mode controller and terminal sliding mode controller to obtain the reaction flywheel output torque,the base attitude stability control with softdocking wrist vibration,vibration suppression,and no excitation stages is achieved.Further,a multi-priority objective function for compound cooperative-stabilization control is constructed with the control objectives of floating base attitude stabilization,accurate identification of the noncooperative target dynamic parameters,and coordination of soft-docking wrist vibration suppression,and the limits by the joint output of the softdocking wrist,controllable damping output,and the reaction flywheel output.Through simulation experiments of GA and PSO algorithm guided by objective function,the controllable damping optimization of each joint of the soft-docking wrist is achieved.Through the simulation experiments of the compound cooperative stabilization control under the conditions of the truth parameters and identification parameters of the non-cooperative target,the effectiveness of the compound cooperative stabilization after the on-orbit soft-docking is fully verified.(5)Experimental research on the mechanism of soft-docking and the compound stabilization on the ground micro-weight air-floating platform is carried out.A principle prototype of the soft-docking wrist is developed,equipped with multiple heterogeneous sensors to complete multi-source experimental data collection.On the ground micro-weight air-floating platform,the two-dimensional planar motion simulation of a floating base,a prototype of a soft-docking wrist principle,and the non-cooperative target was realized.Three experimental verifications are completed,including thle mechanism of the soft-docking wrist,the non-excitation dynamic parameter identification method for the non-cooperative target after soft-docking,and the compound stabilization control strategy after on-orbit soft-docking.