Research On Long Span 4-wire-driven Parallel Mechanism For Space Applications

With the development of space technology,the size of space stations such as space stations and large SAR satellites will be larger and larger.After the spacecraft baseline is increased,on-orbit monitoring and on-orbit accuracy measurements of the spacecraft body are required.The development of actuators with positional accuracy and lightweight features that support the wide range of motion of surveillance cameras and measurement cameras will become new engineering requirements.The traditional space manipulator has a large mass and it is difficult to support the high-speed movement of the observation equipment in a wide range.Therefore,this paper proposes a space-long-span rope traction parallel mechanism for solving the on-orbit monitoring problem of large spacecraft such as space stations.And provide theoretical support and technical reserves for future on-orbit construction and on-orbit services.The article begins with a study of institutional configurations.The on-orbit monitoring tasks of large spacecraft are analyzed to determine the degree of freedom required for the space-long-span rope traction parallel mechanism,and the minimum number of ropes required is determined according to the degree of freedom.Considering the factors such as the installation position of the rope outlet point and the shape of the monitoring component,the number of ropes is determined,and three different configurations are proposed.The working space of the rope traction parallel mechanism and the interference between the ropes are used as indicators,and the configuration of the mechanism is adopted.A comparative analysis was performed to determine the optimal configuration.Aiming at this configuration,vector algebra and Newton-Raphson iterative method are used to analyze the inverse kinematics and kinematics of the large-span rope traction parallel mechanism,which provides an important theoretical basis for the trajectory planning and motion control of the subsequent rope traction parallel mechanism..In order to obtain better positional accuracy and dynamic control performance,a dynamic model study of the mechanism is required.Based on Hooke’s law,the stiffness model of the space-long-span rope traction parallel mechanism is established.The stiffness characteristics of the system actuators(monitoring components)at different positions are analyzed.The established stiffness model is verified by simulation to obtain a large space.The stiffness characteristics of the span rope traction parallel mechanism.Based on the Newton-Eulerian equation,the dynamicmodel of the space-long-span rope traction parallel mechanism is established.Considering the large rope length,the rope quality is increased.Based on the dynamic model of the rope parallel mechanism without considering the rope quality,the dynamic model of the rope parallel mechanism is established.An accurate dynamic model that considers the quality of the rope.Based on the two dynamic models,the tension distribution of the ropes under different motion trajectories of the large-span rope traction parallel mechanism is compared and analyzed,and the necessity of the established system dynamics model considering the rope quality is verified.On the basis of establishing the dynamic model,the research work of control algorithm is carried out.The parabolic interpolation method,the trapezoidal function method and the fifth-order polynomial trajectory planning method are used to plan the point-to-point motion trajectory of the space-long-span rope traction parallel mechanism.The three trajectory planning methods are compared with the speed,acceleration and impact as the indicators.A combined five-order polynomial trajectory planning method with better performance is proposed.The effectiveness of the method is verified by simulation.In view of the characteristics that the rope can only be unidirectionally stressed,two different controllers are designed by dynamic control method.The performance of the two controllers is compared.In order to further improve the control precision and control stability of the mechanism,a kind of mechanism is proposed.The force position hybrid control method is designed,and the corresponding position controller and force controller are designed for the method.The high fidelity model of the space long-span rope traction parallel mechanism is established in the ADAMS environment.The different control methods are simulated based on MATLAB.The simulation results verify the effectiveness and robustness of the force-position hybrid control method.A scaled prototype of a space-long-span rope traction parallel mechanism was developed,and two different trajectories were trajected.The linear feedback control experiment and the force-position hybrid control experiment were completed.The experimental results verified the effectiveness of the two control methods.By comparing the two control methods,the force-position hybrid control method has better control precision and robustness.