Distributed Vibration Control For Large Space Structure During On-orbit Assembly

With the continuous deepening of space mission and rapid development of space technology,lightweight and modular large space structure(LSS)has a wide range of application requirements.Subject to the single launch capability of the vehicle,on-orbit assembly is one of the most promising construction methods of LSS.Along with the continuous development of space robot technology,on-orbit assembly technology will play a greater potential role in the future to construct super LSS.Successful on-orbit assembly is the basic premise for LSS to on-orbit operate.The whole on-orbit assembly task includes a huge amount of work,and takes a long time to complete.Many kinds of space perturbations,especially the assembly collisions,will cause the vibration of whole LSS during on-orbit assembly.Especially in the late assembly,the structural vibration becomes more and more prominent,which will seriously affect the assembly task.In order to achieve high-precision,efficient,and safe on-orbit assembly,related technologies of structural dynamic modelling and analysis,the assembly planning,and vibration control are the core that require prioritize breakthroughs.However,the overall size of LSS in this stage gradually and discretely increases.Resultly,the breakthroughs in the above-mentioned technologies have problems,such as cumbersome modeling work,insufficient consideration of structural vibration,and inapplicability of centralized active control strategies.Therefore,this paper studies the dynamic modelling,the assembly sequence planning and the distributed adaptive vibration control for modular LSS during on-orbit assembly,taking the large plate space structure and the large truss space structure as the specific objects.The contents of the dissertation are given as follows.(1)Dynamic modeling and analysis of modular LSS during on-orbit assembly.Making full use of the modular characteristics of LSS and the repeatability of the on-orbit assembly task,a modeling method is developed,through calling the basic model base(BMA)by the adjacency relationship vector of the modules and loading it according to the "node degree of freedom".The structure dynamics model of modular LSS with complex configurations and diverse assembly schemes can be quickly established,and the model's update process during on-orbit assembly doesn't need much tedious work.Based on this method,the dynamic characteristics of LSS during on-orbit assembly are analyzed,and the dynamic analysis is carried out considering the modular assembly impact.Numerical simulation results show that the established model is suitable to describe the discretely and gradually changing dynamic characteristics of LSS which is related to the assembly sequence,and the assembly impact has great influence on the structural vibration of LSS during on-orbit assembly.(2)Multi-constrained assembly sequence planning to reduce structural vibration of LSS.Considering the structural vibration of LSS during on-orbit assembly,the entire assembly sequence planning problem is decomposed into the optimal position problem at each module assembly.Based on the proposed modeling method,maximizing the first-order natural structual frequency at each assembly is chosen as the optimization index.Using the modules' position relationship matrix to describe the continuity and feasibility of the assembly operation and other constraints,a multi-constrained assembly sequence planning algorithm to reduce vibration of LSS is proposed with the genetic algorithm.In the numerical simulation,the algorithm is applied to optimize the assembly sequence of the large plate and truss space structures,and the dynamic analysis during on-orbit assembly is carried out.The results show that assembling modules in the sequence that maximizing the first-order natural frequency,compared with other optimization index such as assembly efficiency,can effectively reduce the vibration amplitude of LSS during on-orbit assembly.(3)Dynamic modeling oriented to distributed control and distributed adaptive cooperative control.Fully considering the incremental characteristics of LSS during on-orbit assembly,the distributed control strategy is adopted for active vibration control.The modular intelligent components(IC),which can be changing along with assembly,is introduced as the distributed control unit.The dynamic model of the IC oriented to distributed control is established through the proposed modeling method.Then the cooperative controller of IC and the adaptive updating strategy during on-orbit assembly are proposed.After that,the stability of the closed-loop control system is analyzed through Lyapunov stability theory.Finally,considering the assembly impact and the failure of some controllers,the dynamic anlysis and active vibration control are carried out for the large plate space structure during on-orbit assembly.The numerical simulations illuatrate the feasibility and good robustness of the proposed distributed adaptive cooperative control system.It also shows that the cooperative part in the distributed controller can further enhance the vibration suppression effect of the control system.(4)Distributed adaptive fast model predictive control(DAFMPC)for improving the computational efficiency of the control system.In order to further improve the adaptive updating efficiency of the distributed control system during on-orbit assembly,the DAFMPC system is designed,through deducing the discrete explicit expression form of IC's state based on Newmark-? method and combining with the fast calculation strategy.Under different cases that considering the uncertainty of assembly impact and the failure of some controllers,the active vibration control for the large plate space structure during on-orbit assembly are carried out.Numerical simulations show the feasibility and the robustness of the proposed DAFMPC system,and the comparison results of different control systems also verify its obvious advantages in adaptive update efficiency.(5)Experimental verification of distributed active vibration control.The flexible cantilever plate structure is used as the controlled structure,piezoelectric fiber MFC actuators and noncontact laser displacement sensors are used to build an experimental platform,to carry out experimental verification of modeling methods and distributed control methods.Using the proposed modeling method of modular LSS and the load comparison method,the BMA is firstly formed.Through calling and loading BMA,the dynamic model of the piezoelectricdriven cantilever plate is established.After verifying the validity of the theoretical model with modal analysis and static deformation experiments,the active vibration control experiment of the cantilever plate structure are carried out under the cases with initial deformation and partial failure of active components.The experimental results show that the distributed control system can obviously suppress the structural vibration,and has good robustness to the failure conditions of some active components.It also verifies that the cooperative part in the IC's controller has an enhanced suppression effect on structural vibration.