The Study Of Space Manipulator Trajectort Tracking Control Considering The Joint Clearance And Gravity

With the development of space exploration, the requirement for the precision of the space manipulator was higher and higher, and the dynamic nonlinear characteristics of the space mechanism caused by the joint space was gradually becoming the focus of attention.As is known to all, all space agency service on orbit in the space microgravity environment, but were designed and debugged in the ground gravity environment. From the ground to space, due to the existence of clearance, the dynamics model and the kinematics model of space agencies were changed resulting in that the controller debugged under the ground was difficult to achieve the expected control precision in space.In this paper, A two degree-of-freedom(DOF) manipulator was studied considering different gravity environment. Through the establishment of dynamic model of the mechanism with joint clearance, the clearance compensation controller was designed to achieve the desired trajectory tracking accuracy of the space manipulator under different gravity environment. The main contents are as follows:Firstly, the main factors affecting the formation of the clearance under different gravity environment were analyzed. By analyzing the dynamic characteristics, the dynamic model of the space manipulator with clearance under different gravity environment was established using the model of the equivalent joint about massless link method. Simulation experiments were carried out about effect of joint clearance and gravity on the control precision of trajectory tracking control. On the basis of this, the clearance compensation controller was designed according to the model uncertainty and disturbance caused by the clearance equivalent model, and the effectiveness of the clearance compensation controller was verified by simulation.Secondly, by analysing the joint space motion characteristics of mechanism with clearance under different gravity environment, approximate joint equivalent model of alignment on the ground and in the space were established based on Kelvin-voigt linear spring damping assumption. Taking a two-DOF manipulator as an example, the dynamics analytical solution of space manipulator with joint clearance in the gravity and gravityrelease condition were derived by Newton Euler, and the clearance compensation was isolated. On this basis, through the simulation of trajectory tracking control, the differences between dynamic behavior of space manipulator under different gravity environment was explored and the effectiveness of the joint compensation controller was demonstrated.Finally, by using the Newton Euler method and moment balance principle, the dynamic model of the mechanism with joint clearance was studied during ground alignment and space application. What’s more, based on that the controller designed on the ground can not achieve the control precision in space because of the change of the gravity and the joint clearance, the ADRC was designed which does not depend on the model of the controlled object. In this method we treated the changes of gravity and joint clearance as interference in the system, by using the extended state observer for its estimation, then through the nonlinear feedback control for compensation to improve the control precision of system.