Dynamic Modeling And Simulation Of Extravehicular Spacesuit-Astronaut Lower Limbs System

With the development of manned space technology and deep space exploration technology,extravehicular activities such as resources exploration,base construction,and scientific experiments on the surface of Moon,Mars and other celestial bodies are important part of manned space exploration.Pressurized spacesuit can provide life safety assurance for astronauts’ extravehicular activities.However,it will increase the astronauts’ workload and reduce their work efficiency because of the existence of joint damping moment.Therefore,the mobility of spacesuit is one of the important factors during the design of spacesuit.In the previous design of the spacesuit,much consideration is given to the mobility of the spacesuit joint system associated with upper limbs,while litter attention is put on the activity of the spacesuit lower limbs system.Extravehicular activities with long time and far distance will impose more requirements on the performance of the spacesuit lower limbs system.Hence,studies on the dynamics of the extravehicular spacesuit-astronaut lower limbs system are carried out to provide theoretical guidance for designing joints to improve the activity of spacesuit.Firstly,the degree of freedom for each joint of the spacesuit lower limb is configured based on the human gait analysis and physiological structure of human body.Considering the diversity of limb movements during the planetary exploration,the degrees of freedom for lower limbs joint system are optimized to 12.Moreover,the concept model of each joint is proposed to give reference for the design and performance analysis of the spacesuit lower limbs joint system.Secondly,on the basis of establishing the physical model of the extravehicular spacesuit-astronaut lower limbs system,the D-H(Denavit-Hartenberg)parameter method is used to analyze the forward and inverse kinematics of the lower limbs system,the inverse solution method for the single leg joint angle of the lower limbs system is given,and corresponding verification is carried out.Then,based on the established physical model and moving target curve,the dynamics of unsuited astronaut lower limbs system is analyzed via the Lagrange equation method.The associated torque of each lower limb joint is obtained.Taking extravehicular mobility unit as example,the dynamic model of the suited astronaut lower limbs system is established with consideration of mass,moment of inertia and resistant torque with hysteresis characteristics of pressurized spacesuit.The influence of the spacesuit on the joint torque during the gait walking of the astronaut is analyzed.Finally,on the ADAMS(Automatic Dynamic Analysis of Mechanical Systems)simulation platform,a 3D model of the lower limb system of the unsuited and suited astronaut is created respectively.The corresponding dynamic simulation is conducted to determine the torque of each joint of lower limbs.The agreement of the simulation results and the theoretical results verifies the accuracy of the theoretical model.During a gait cycle,the work done by the hip,knee and ankle joints of the suited astronaut has respectively increased 205%,134% and 95% compared with the work done by joints of the unsuited astronaut.It is indicated that pressured spacesuit has impact on the astronaut mobility.