The Friction Compensation Control Research Of Space Manipulators Under Different Gravity Environment

With the development of modern science and technology, space manipulator in the space community plays an increasingly important role. The motion precision requirement for space manipulator is also more and more high. In almost all mechanical systems, friction is an inevitable phenomenon. Friction will cause the steady-state error and limit the precision of system operation, especially for low speed operation. Kinematic pair is subject to wear after long time running, which will cause the system movement precision and stable performance decline. Friction and wear led to the decrease of the space manipulator performance. Therefore, corresponding measures must be taken to reduce or even eliminate the effects of friction.Friction characteristics in the space microgravity environment have great changed compared with that in ground gravity environment. Whether the space manipulator tuned on the ground can run normally in space has become the hot topic of researchers. In this paper, the dynamic characteristics and friction characteristics under different gravity environments have been studied, as well as the trajectory tracking under different gravity environments. Specific content as follows:Firstly, the dynamic models and friction models of the space manipulators under different gravity environments are established. The specific simulation model provides a theoretical basis for the controller design of subsequent chapters.Secondly, the influence of friction and the different gravity environments to the movement behavior control of space manipulator are researched. This paper considers a two-link planar space manipulator system as the control object and analyzes the influence of friction and the different gravity environments to the joint driving torque of space manipulator in the view of the dynamic characteristics. On this basis, PD control method is adopted to study the influence of friction and the different gravity environments to the trajectory tracking accuracy. This paves the way for the study contents of subsequent chapters.Finally, all space manipulators are debugged on the ground and on-orbit service in space. Their friction characteristics in space microgravity environment have great changed compared with that in ground gravity environment. The ability of manipulators to perform the task of high precision and stability will be a lot of restrictions. For sake of tracking the desired trajectory in both ground and space. A friction compensation control method based on an Active Disturbance Rejection Control(ADRC) is developed in this paper and its effectiveness is validated on a planar 2-DOF free-floating space manipulator. The friction models and the dynamic models under different gravity environments have been derived based on the torque balance, the Kane equation and the Lagrange method. Particle Swarm Optimization(PSO) is put forward to optimize parameters of ADRC so as to improve the efficiency of designing process. Compared with PD controller in tracking simulation under different gravity environments, the results verify the advantage of the proposed improved control method.