| Manned space flight can not only expand the scope of human activities,but also play an important role in the development and utilization of space resources.It plays an important role in the economic,technological and political development of a country,so all countries in the world attach great importance to it.However,the microgravity environment on the space station is very different from the gravity environment on the earth.Although the object has no gravity,the inertia force of the object still exists,which will bring some operational risks to the astronauts who are used to living in the gravity environment on the space station.Therefore,it is necessary to train astronauts in microgravity operation on the ground so that they can adapt to the environment on the space station in advance.Astronaut virtual operation training robot is a kind of robot that combines VR equipment with cable driven parallel robot.It provides the astronauts with auditory and visual presence in the space station environment through VR.The cable driven parallel robot provides the astronauts with force presence in the space station environment to train the astronauts in the microgravity environment.The robot can simulate the astronauts’ manipulation of different mass objects in microgravity environment,and bring the same force sense as that of the same mass objects in space station environment.This is of great significance for promoting the technological progress of virtual reality and telepresence,broadening the application fields of robot technology and promoting the development of space science and technology in China.This dissertation is supported by the National Natural Science Foundation of China under grant No.61773007(Research on virtual operation training robot for astronaut and cooperative control technology).Aiming at the problems of complex equipment for simulating microgravity environment,long training preparation time,short training time and small interaction force,etc.This paper explores how to train the force perception of astronauts by simulating objects in microgravity environment with cable driven parallel robot.Four joint technologies,including robot configuration,workspace and cable force allocation,control strategy of cable driven unit and force interaction and control of robot,are analyzed theoretically and experimentally.Firstly,this paper introduces the current status of simulated microgravity environment technology and the technology of virtual operation training robot,the main operation tasks of the astronaut space station are analyzed.Through the analysis of routine operation tasks,the typical operation actions of the arms inside and outside the astronaut space station are determined as pushing objects,retrieving objects,colliding objects and twisting objects.The main design indexes and design requirements of the robot are determined according to the operation indexes.The initial dimensions of the fixed platform and the end effector of the robot are determined by optimization.The space-configuration robot and plane-configuration robot is determined to meet the requirements of operation.The overall control scheme,motor driver and communication scheme of the robot are determined.Secondly,for planar robots,a wrench feasible workspace algorithm considering the interference cables and end effector is proposed.The position of the hinge point of the cable on the end effector of the robot is optimized,and the optimal layout of the robot is determined.A 1 redundantly drive cable tension allocation strategy for planar configuration robot is optimized.The simulation results verify the feasibility of the strategy.A wrench feasible workspace solution algorithm considering the interference between the cable and the cable and the surface of the end effector of the space configuration robot is proposed.The size of the end effector of the robot is optimized,which can maximize the wrench feasible workspace of the robot.The influence of cable layout on the wrench feasible workspace is analyzed,and the cable layout is determined when the workspace is maximum.The maximum attitude angles of the end effectors of the three layout schemes are determined,and the optimal configuration of the robot is determined.In order to improve the real-time control performance of the robot in the wrench feasible workspace,a 2 redundantly drive cable tension allocation algorithm is optimized.Thirdly,the transfer function of the cable driven unit is determined,the method of redundant force reduction is analyzed,and the disturbance observer is designed.The influence of the PI control strategy with or without disturbance observer on the accuracy of active and passive loading of the cable driven unit is analyzed.The simulation and experiment verify that the PI control with disturbance observer improves the loading accuracy of the system.The influence of the composite control with or without disturbance observer on the accuracy of active and passive loading of the cable driven unit is analyzed.The simulation and experiment verify that the composite control with disturbance observer improves the loading accuracy of the system.Comparing the advantages and disadvantages of the two control strategies to improve the loading accuracy of the system,the control strategy using compound control combined with disturbance observer is finally determined.Fourthly,the dynamic models of virtual objects in two-dimensional and three-dimensional microgravity environments are established.The microgravity environment model and the interaction model between human and virtual environment are established.According to the requirement of force sense interaction of robot,the control strategy of robot is established.Good system control strategy can make the astronaut virtual operation training robot simulate the motion and mechanical characteristics of objects in microgravity environment more accurately.The accuracy of free motion model and collision model of planar and spatial robots and the accuracy of interaction force loading are analyzed by simulation.At last,based on the dSPACE semi-physical simulation platform,various training mode experiments are carried out in the micro-gravity environment simulated by linear slide rail,the micro-gravity environment simulated by plane two-cable robot and the micro-gravity environment simulated by plane four-cable.The experiment of planar two-cable robot simulating microgravity environment is carried out.The experimental results are compared with the feeling of arm when manipulating real mass objects in the microgravity environment simulated by linear slide rail.The configuration of cable tension is analyzed,and the validity of the algorithm and control strategy of cable tension configuration is verified.The experiment of planar four-cable robot simulating microgravity environment further verifies the effectiveness of the cable tension allocation algorithm and control strategy,and the rationality of planar configuration of astronaut virtual operation training robot for astronaut virtual operation training. |
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