Research On Astronaut On-Orbit Multi-mode Exercise Robot

In recent years,with the development of spaceflight technology,human footprint is gradually spreading to the vast space that far from earth.With the advanced space equipment such as space shuttles,rockets and space station,manned spaceflight has already become an important approach of space science exploration.Microgravity remains with astronauts during the entire space trip,it will cause bone loss,muscle atrophy and cardiovascular function decline if astronauts continuous exposure to microgravity.Space exploration missions and space life will be seriously affected,so countermeasures should be taken into space trip.Modern aerospace medical research shows that physical exercise is an effective way to offset and mitigate the adverse effects of microgravity.Therefore,to develop an astronaut on-orbit exercise robot that can be applied for microgravity environment with multiple exercise modes,small volume and light weight has a very crucial research significance.Thus,the space life and work ability of astronauts will be greatly improved.There will be a positive effect on space exploration mission,and a very important practical significance for the development of Chinese space industry and space science exploration.This research work is funded by the National Natural Science Foundation of China:Research on Astronaut Rehabilitation Robotics for Microgravity Environment(61175128),trying to utilize robot technology to maintain astronauts' musculoskeletal and cardiovascular health by the mean of helping astronauts to realize multi-mode physical exercises in space.Indepth theoretical analysis and experimental research have been conducted in robot configuration and control schemes,dimension synthesis and comparative analysis of gait restraint mechanisms,human-machine system dynamic model,biomechanical analysis of bench press and squat exercise,flexible cable tension distribution modeling and safety protection strategies.Firstly,the design requirements of the robot is specified,and the robot structure,configuration and control scheme are proposed.The current physical exercise equipment in the International Space Station and China Space Station,as well as the relevant equipment under research are reviewed.The analysis of these exercise equipment in the criteria such as exercise mode,load force adjustability,user friendly,safety protection,equipment volume,weight,cost and energy efficiency is done.Based on the comparative analysis and aerospace medical theory,considering the special characteristics of the space environment,space station,and the physical exercise needs of astronauts,the design requirements of on-orbit exercise robot is determined.An astronaut on-orbit multi-mode exercise robot based on modular cable driven is proposed.Robot configuration and working space is analyzed.Robot configuration characteristics and working principle is expounded in detail.Overall control system and control flow of the robot are brought forward.Secondly,the optimal gait restraint mechanism and its adjustment scheme are determined,and human-machine system dynamic model is established.First,the human motion capture system is used to collect the walking gait law of healthy individuals,and the ankle trajectories of different heights group are obtained through the human walking model.Secondly,utilizing closed-loop vector method,the end-effector trajectory mathematical models of the 3 kinds of linkage mechanism are established.Third,a dimension synthesis optimization strategy for gait restraint mechanism according to the ankle data is proposed,the optimization objective function and final evaluation criteria are fully introduced.Then the optimization procedure is conducted in Matlab,so the end trajectories of each gait constraint mechanism in 1,2 and 3 adjustable parameters are generated.Fourth,a detailed comparison work is done among the optimization results of the 3 different gait restraint mechanisms in same adjustable parameter number.Thus,the optimal gait constraint mechanism,its adjustment scheme and relevant parameters value are given.Last,the human-machine system dynamic model is established,the joint reaction force,joint moment,the reaction force between human and machine are analyzed.Thirdly,joint reaction force and muscle strength during bench press,deep squat are analyzed,reasonable loading law is determined.First,the simplified rigid body models of bench press and deep squat exercise are proposed.According to Lagrangian method the dynamic models of the 2 exercises are established.Besides,biomechanical models of upper and lower limbs are also acquired.The optimization constrains of bench press and deep squat exercise are given.Second,optimization algorithm based on Radau pseudospectral is introduced.The optimization analysis strategy for joint reaction force and redundant muscle strength is fully described.The optimization objective function has been given.Third,the comparison analysis between exercises conducted under the earth and microgravity environment is carried out in the aspects of joint reaction force and muscle strength.Finally,to improve the efficiency and reduce the risk of injury when astronauts doing exercises,the load law equations for bench press and deep squat are presented.Fourthly,the distribution law of cable tension and the safety protection strategy during exercise assisted by robot are analyzed.First,a flexible cable tension distribution model for the exercises with barbell is proposed,and a flexible cable tension distribution model for the exercises without barbell based on the principle of minimizing the cable tension variance is involved.Second,the ideal and safe working space of loading point in the exercise with and without barbell are proposed respectively.The safety protection strategy is designed to monitor the exercise state of astronaut.Loading point will be adjusted when it deviates from the ideal working space.To reduce the risk of injury during exercise when loading point deviates from the safety working space,a fully protection will be given to astronauts.Finally,the robot system is established in Matlab and simulation work is done to verify the accuracy of the cable tension distribution model and the effectiveness of the safety protection strategy.At last,the prototype of the astronaut on-orbit multi-mode exercise robot is developed and experimental research is carried out.Each components and control system of the robot are introduced.Utilizing the d SPACE hardware in loop simulation system,the rationality of the robot configuration,the accuracy of the cable tension distribution model and the effectiveness of the safety protection strategy are verified through the experimental researches,including load experiments with and without barbell,safety protection strategy experiments with and without barbell,deep squat and running exercise assisted by robot.The experimental results prove that the multi-mode astronaut on-orbit exercise robot can effectively assist the astronauts to carry out physical exercise in space and protect astronaut.