Vibration Characteristic Analysis And Optimal Control Of Space Manipulator For On-orbit Assembly

Space manipulator is the main executing mechanism of on-orbit assembly task.In the process of large-scale space structure assembly,the dynamic performance of the end is highly demanded.In the process of operation,the end is prone to vibration due to start-stop,change of mass characteristics,impact effect and other factors.Due to the particularity of the space environment,it is difficult to simulate and verify the on-orbit operation of space manipulator system.To solve this problem,the vibration characteristics of the end of the manipulator under different structural parameters and working conditions during start-stop and interaction are analyzed,and the corresponding control algorithm is designed to realize the vibration suppression and trajectory tracking control of the space manipulator.The specific research content is as follows:Firstly,considering the influence of solid lubrication on the dynamic characteristics of clearance joints,based on the clearance joint model and introducing the joint axial size,the detailed calculation methods of the joint non-linear normal contact force and tangential friction force under the action of solid lubricant are given,and the mechanical arm dynamic model is established by Newton-Euler method.Secondly,considering that the space gravity release will not only affect the motion behavior of the manipulator,but also affect the friction characteristics of the joint.In order to achieve accurate dynamic modeling of the manipulator system,a semi-physical simulation test platform with solid lubricated manipulator joints as its own actuator was designed and built by integrating physical objects into mathematical simulation.The hardware-in-the-loop simulation experiment was used to solve the problem of difficulty in ground test.According to the test results,the joint contact force is modified,and then the joint contact force model applied to different gravity environments is obtained.Furthermore,the radial vibration characteristics of the manipulator under different structural parameters and working conditions are studied based on the model of the manipulator under different gravity environments.In order to meet the requirement of frequent start-stop operation in on-orbit assembly process,the vibration characteristics of variable load start-stop are analyzed,and the optimal control method is given to improve the dynamic performance.Finally,considering the impact effect in the interaction process,the influence of the change of base and load mass characteristics on the non-linear dynamics of the manipulator system is analyzed.A state-extended adaptive passivity control method is designed to extend the state of the system without changing the structure and parameters of the controller.The estimation of mechanical environment changes within the system is realized,and the vibration suppression at the end of the space manipulator system under different working conditions is realized.