Driving Force Analysis And Trajectory Tracking Control Of Space Manipulator Considering Gravity Effects

Manipulators are used in space to assist or replace astronauts to complete some complex,fine or repetitive operations,and plays an irreplaceable role in the space station construction and maintenance.In the design of space manipulator system,energy consumption and control precision are very important performances.However,due to lack of long-time effective microgravity simulation method,system performances can't be assured.In order to solve this problem,a method is proposed to conduct ground simulation test by changing the joint axis orientations,the driving torque and model differences under different gravity environments are analyzed,and trajectory tracking controllers for rigid and flexible manipulators are designed for trajectory tracking under different gravity environment.Then the contradiction between ground assemble and space application and high frequency resonance brought by flexibility of flexible joint are solved.Firstly,driving torque simulation of 4-DOF humanoid manipulator is conducted considering joint friction.And the driving torque difference and key effecting factors under different gravity environments are analyzed by changing friction,joint angular velocity and load.After this the ground simulation test is carried out by changing the orientation of joint axis,and the test results show that this method is feasible.Also the actual friction model was obtained by friction characteristic curve fitting based on the experimental data.The results show that friction is a key factor affecting its spatial driving force for small inertia arm system.And due to the change of the gravity and friction coefficient,the variation law of the driving force in the space microgravity environment is very different from that of the ground.Secondly,the adaptive back-stepping sliding mode controller is designed to control the rigid free-floating space manipulator.The gravity and system modeling error are regarded as the total disturbance,and the adaptive law is used to estimate it online.The sliding mode controller is used to compensate the system uncertainty,thus the robustness of the system is ensured.Then the stability of the system is proved using the Lyapunov theory.Simulation is carried out by using the designed controller and compared with the simulation results under PD control law,and the simulation results verified the effectiveness and superiority of the controller.Finally,the Active Disturbance Rejection Controller based on singular perturbation theory is designed for the control of the flexible joint space manipulator to realize the trajectory tracking and buffeting suppression under different gravity environments.Based on the singular perturbation theory,a linear active disturbance rejection controller with feedforward compensation is designed for the slow-variable subsystem.In which the state observer is used to estimate the gravity,modeling error,system disturbance and so on,and the total disturbance is compensated in the control law,also the feedforward compensation is introduced to reduce the observer bandwidth.Then the stability of system is proved by Lyapunov theory,and the simulation results show the effectiveness and robustness of the controller by using different linear feedback control law and compared with the singular perturbation PD control.