Research On Wire-Driven Robot And Virtual-Gravity System

At present, every country in the world, especially the United States, Russia and China, is trying to develop manned spaceflight technology, aiming to take a place within the world's high-tech fields. However, because the space is a high vacuum micro-gravity environment, astronauts in space flight are in a weightless state, which would adversely affect their physiological systems and even badly threaten their lives. Virtual gravity-controlled robot can simulate gravitational field to train astronauts'motor functions, thus avoiding the astronauts in a weightless environment to suffer from space motion sickness. Wire-driven system has many advantages such as good compliance, small occupied space and light weigh, and also as a natural buffer, will not produce the rigid collision with human body that is very suitable for the driven control unit of virtual gravity-controlled robot.The research work comes from a project funded by college doctor disciplines special scientific research foundation, which is "Research on key technology of the muscular-training and enginery-training rehabilitation robot in microgravity environment (20060217024)". The main objective is how to produce a virtual gravity environment by using wire-driven robot to achieve astronauts exercise training techniques. The detailed theoretical analysis and experimental research are carried out including controllable workspace of wire-driven robot, control method of wire-driven robot, virtual gravity control feature of wire-driven virtual gravity robot and force control strategy of wire-driven virtual gravity robot.Mechanism type of wire-driven robot is analyzed from the view of force transmission. Based on vector closure principles, wrench-controllable workspace under the condition of specific force/torque is proposed. The workspace of two completely restrained positioning mechanisms is analyzed. Using vector-algebra theory and three-pyramid methods, the forward and inverse kinematics equations of wire-driven robot are established. The kinematics simulation of wire-driven robot is carried out. Workspace analysis and kinematics study provide a certain theoretical basis for robot structural design and control system design. Using the Newton-Euler method, the dynamic model of wire-driven robot is established and the relationship between wire tension and wire inner force or wire driving force is derived. Two kinds of control methods that are preload-based position control and force/position control are put forward. The control system of wire-driven robot is designed. Using Lyapunov method, stability analysis of robot control system is made. Experimental research on control method of wire-driven robot is carried out in three degrees of freedom experimental platform.Based on the analysis of human pelvic motion, mechanism model of flexible Stewart wire-driven virtual gravity robot is proposed in which six wires substitute the traditional link. Using influence coefficient method and the Newton-Euler method, kinematics model and dynamic model of wire-driven virtual gravity robot are put forward. Considering the moving platform attached to human body, mechanical model is derived by simplifying robot dynamic model. Virtual gravity control feature of wire-driven robot is simulated and analyzed.Based on the analysis of the virtual gravity control principle, a virtual gravity robotic system simulation model is constructed by using MATLAB/Simulink, which is composed of human pelvic simulated mechanism and six wire-driven units. Considering that force signal is easy to fluctuate, the fuzzy sliding controller is applied to force control system of single wire driven unit. Quasi closed loop force control strategy and double closed loop force control strategy of wire-driven virtual gravity robot are proposed. Simulation study on force control strategy of virtual gravity robotic system is carried out.Experimental prototype of wire-driven virtual gravity robot is developed. The components and function of experimental system are described. Based on the dSPACE real-time system, experimental study is completed which mainly include wire-driven unit force closed loop control, quasi closed loop force control strategy, double closed loop force control strategy and so on. The experimental research verifies the rationality of wire-driven virtual gravity robot model, the stability of robot control system, the correctness of virtual gravity control features analysis and the feasibility of virtual gravity control strategy.