Modeling And Trajectory Tracking Control Of Ultra-low-orbit Manipulator Considering Environmental Torque

The space manipulator is a very important operation tool for on-orbit space robots. On the ultra-low-orbit, the environmental torque, especially the atmospheric-drag torque, will have an effect on the operation accuracy of the manipulator. This paper will study on modeling of environmental torque and space manipulator and achieving trajectory tracking control of space manipulator.First of all, this paper introduces the rarefied gas dynamics development situation, gives development plan of the currently space manipulator research, analyses and discusses on manipulator trajectory tracking control in the world.Secondly, this paper studies in modeling method of environmental torque on ultra-low orbit. For gravity gradient torque, this paper uses the method of dividing the research object, and calculates the objects separately. And the number of gravity gradient torque the system is obtained is about 410 N m-× by simulation. For atmospheric-drag torque, this paper introduces micro division theory on the basis of general engineering application model, and proposes a new method for calculating the effective wind area accurately. With simulation, the accuracy of the result is more than 99.9%. Use this algorithm, the magnitude of atmospheric-drag torque reaches 210 N m-×. Compared with gravity gradient torque, atmospheric-drag torque is the main influence torque.Thirdly, the definition of the manipulator joint coordinate system and the conversion in the joint coordinate systems is presented, and the dynamic normal solution of the manipulator is deduced. The paper focuses on the rigid dynamic modeling method of manipulator. Firstly, this paper establishes a dynamic model of manipulator based on Newton Euler method, because of the large calculation, a method for dynamic modeling is proposed, and the dynamic equations are obtained. By simulating with the environment torque model which is obtained by the second chapter and analyzing the movement of the manipulator, and result is the environmental torque has a large influence on joint movement and terminal position of the manipulator when the joints are not controlled. And at the same time, it verifies the correctness of the dynamic model.Finally, the paper discusses the trajectory tracking control of the space manipulator. To the dynamic model that established in last chapter, it is simplified according to the characteristics of the manipulator system. Based on computational torque control method, a joint trajectory tracking controller is designed. In the simulation, the environmental torque is used as the disturbance to the joint control torque, and the control effect of the manipulator system is good. At the same time, the effect of environmental torque on the tracking is also analyzed.