Research On Reconfiguration And Control Technologies Of Modular Robots In Space Applications

Due to reconfigurability in versatile systems of modular robots,they can well adapt to notoriously harsh space environment and thus have broad prospects in their application in space exploration missions.Reconfiguration methodology and control strategy of modular robotic systems are key technologies to fulfill strong adaptability and robustness of the system,also directly related to efficiency and success rate of the reconfiguration,and even the success or failure of the entire space exploration mission.Therefore,it is necessary to carry out research on reconfiguration methodology and control strategy of modular robots.Towards the major demand of application with modular robots in space environment,this thesis aims to tackle specific difficulties in their reconfiguration and control techniques.With the background of space exploration missions,this thesis is dedicated to developing new theories and application methods,studying planning and control techniques in the reconfiguration of modular robots.The main contents of the thesis are as follows.Automatic modelling technique of modular robots is studied.1)Aiming at solving the difficulty in misalignment elimination caused by traditional manner of reconfiguration,a new strategy for reconfiguration of modular robots is proposed,inspired by the art of origami.This strategy can effectively eliminate the misalignment and greatly improve robustness and success rate of the reconfiguration with modular robots;2)Considering time-varying characteristics of the configuration of modular robots,with the aim of achieving systematic autonomy in space environment in real time,the automatic modelling technique of kinematics and dynamics of modular robots is proposed.With this technique,the model of modular robot can be automatically established to meet with different space missions in real-time with high efficiency.3)Considering limited power source in space environment,energy consumption during the reconfiguration process is an important performance index.With the proposed automatic modeling technique,the energy index can be calculated in real time,thus greatly reducing online computational load and improve the efficiency in calculation of energy consumption.Energy-optimized reconfiguration planning method of modular robots is studied.To economize power source of the space system and improve energy utilizing efficiency,planning methodology of energy-optimized reconfiguration with modular robots is studied.For origami-inspired reconfiguration strategy,considering two metrics of energy index,peak torque and energy consumption respectively,planning algorithms are designed correspondingly.Two optimization algorithms for solving energy-optimal reconfiguration schemes are proposed: 1)Optimization algorithm based on automatic modeling technique,which can guarantee the optimality of resultant schemes,but computational load is large and run time is long,casting high demands on computing capability of space robotic systems;2)Optimization based on heuristic algorithm,which decouples each element in the reconfiguration scheme,such as the module of root node,initial configuration and reconfiguration sequence,etc.Heuristic algorithms are designed for these elements correspondingly.Therefore,the computational load and run time of the algorithmic process is greatly reduced,and online planning of space robotic system can be achieved.Optimization methodology of active modules distribution in the configuration of modular robot is studied.Compared with passive module,the composition of active module is relatively complicated,and the manufacture cost is high.To reduce the reconfiguration cost of modular robots in their application,and further reduce energy consumption during the reconfiguration,optimization method of active modules distribution is studied.For two different task scenarios,i.e.,the reconfiguration task for initial planar configuration and target three-dimensional configuration,optimal distribution methods based on graph coloring algorithm and heuristic algorithm are proposed,which generalize the distribution method to general configurations.Both of these methods can generate optimal distribution scheme of active module,so that their number in the configuration is lowest,and target configuration can be formed by actuating the active modules,performing after-transformation motion and implementing related tasks as commanded.Compared with the graph coloring algorithm,the optimal distribution method based on heuristic algorithm greatly reduces complexity and computational time of the algorithmic process.Therefore,the algorithm effectively improves the planning efficiency of space robotic system in real time.Coordinated manipulation and control technique of on-orbit modular manipulators is studied.Considering the space mission of multi-manipulator coordinating the manipulation of flexible components,this task casts high demands on the control system of space robots,aiming not only to ensure trajectory tracking accuracy of the centroid motion of flexible component during the manipulation,but also to minimize the vibration generated by large-range motion of the flexible component.A two-time scale control scheme is proposed based on singular perturbation theory for the coordinated manipulation task to achieve the two control objectives.The composite controller includes a slow subsystem controller based on non-singular terminal sliding mode control,and a fast subsystem controller based on optimal control technique,such that it can simultaneously achieve the two control objectives for the coordinated manipulation task.Simulation results verify the effectiveness of the proposed control scheme.