Research On Micro / Low Gravity Simulation Technology For Astronaut Ground Training

There is a micro / low gravity environment in the earth’s orbit and on the surface of alien planets.In this environment,astronauts will feel different body sensations and motion states than in the earth’s gravity environment,which will make astronauts uncomfortable during the mission.It takes longer and reduces reliability.Therefore,it is necessary to develop ground micro / low gravity simulation equipment to conduct operation training for astronauts in a simulated environment.Traditional methods such as parabolic flight,water flotation and air flotation have limitations such as short simulation time,high cost,and large additional resistance and inertial force.Therefore,active suspension,active lift,and exoskeleton are currently used.The existing systems cannot meet the micro / low gravity simulation training requirements of 1-2 astronauts involved in the construction of my country’s space station at the current stage and future manned moon landing missions in terms of simulation speed,simulation freedom,number of simulation objects and simulation accuracy.Therefore,this paper carries out theoretical research,key technology research,experimental platform construction and experimental research on astronaut micro / low gravity simulation.For the micro / low gravity simulation of astronauts in the three-dimensional translation direction,the simulation conditions and simulation requirements are firstly analyzed,and then the overall configuration of the system combining suspension type and lift type is selected for the need to support the simulation training of two astronauts.A 3D translational micro / low gravity simulation subsystem configuration based on serial elastic drive is proposed,and the relationship between serial elastic drive,disturbance frequency,equivalent stiffness and simulation accuracy is deduced and analyzed in detail.In the vertical constant-force system,a design method of a rotary low-stiffness mechanism is proposed based on the principle of minimum energy.Based on this,a lightweight,highload,low-stiffness mechanism with a axial torsion bar and radial compressed springs is designed.In the horizontal lift two-dimensional position follow-up system,a plane low stiffness mechanism with the same stiffness and inertia in all directions is adopted.Active control of the motor and passive buffering of the low-stiffness mechanism ensure high simulation accuracy in the full frequency domain.Aiming at the micro / low gravity simulation in the astronaut’s three-dimensional rotation direction,the motion state of the astronaut is firstly analyzed,the main motion type and motion range are obtained,and the magnitude and characteristics of the gravitational moment are analyzed.A simplified unified static model is established,and a purely passive gravity moment compensation configuration is proposed based on the principle of quasi-static equilibrium.Based on this configuration and the parallelogram equivalent translation principle,the exoskeleton human-machine backframe is designed,the pitch and roll gravity moment compensation is simplified and integrated,and factors such as human interference and safety are considered.In order to adapt to the uncertainties such as different human body sizes,different gravity compensation levels and manufacturing errors,the research on the load and size adjustability of the human-machine backframe was carried out.The micro / low gravity simulation control strategy for the three-dimensional translational direction of astronauts is studied.Firstly,the simulation conditions,astronaut force and control objectives are analyzed,and a unified simplified dynamic model suitable for each translational DOF is established.Based on this,the unified control strategy is studied.Low-gravity simulation mainly focuses on the instantaneous simulation accuracy and disturbance suppression characteristics,and has low requirements on the cumulative error,so the proportional-integral-acceleration feedforward control algorithm is adopted.Microgravity simulation mainly focuses on the accuracy of floating speed,and has low requirements on disturbance suppression characteristics.Therefore,two control algorithms,dual proportional-integral and model prediction-proportional-integral,are used.The applicability of the control algorithms under different working conditions and degrees of freedom and the influence of the introduction of the human-machine backframe on the performance of the control strategy are analyzed.The effectiveness of the strategy is verified by simulation analysis.An astronaut micro / low gravity simulation experimental platform is built and related experimental research is carried out.Firstly,the experimental verification of the control strategy is carried out for each translational degree of freedom,and on this basis,the composite experimental verification of multiple degrees of freedom is carried out.For the human-machine backframe,the experimental verification of the gravity moment compensation effect of each rotational degree of freedom is carried out.Finally,the combination of the suspension system and the human-machine backframe is used to verify the astronaut’s 6-DOF simulation experiment,and the combination of the suspension and the lifting systems is used to verify the collaborative operation of the two astronauts.