Research On Dynamic Characteristics Of Space Manipulator With Active Stiffness Control

With the rapid development of space technology,space manipulator needs to meet the requirements of lightweight,high precision and high performance.The characteristics of space manipulator with the lightweight,large working radius and high load can lead to structural deformation and elastic vibration due to the arm flexibility in the movement process of manipulator,which seriously affects the motion stability and the positioning accuracy of the end.In order to solve the dynamic problems caused by the flexibility of the arm,the dynamic modeling,experimental study and simulation analysis of the space manipulator based on the active control of arm stiffness is systematically studied in this paper.These studies provide the theoretical basis for dynamics modeling and vibration suppression of space manipulator.The active control method of arm stiffness of the manipulator is put forward,and the arm stiffness model is established in this paper.The influence of the radial bending deformation of the arm on the axial deformation during the movement of the manipulator is studied by the deformation coupling method,and the flexible manipulator is described by the assumed mode method.Then the dynamic equations are established by the Lagrange method.The numerical simulation results show that the radial bending deformation of the arm end is gradually reduced and the stiffness of the arm is gradually increased as the increase of the rope preload,which indicates the active control method of arm stiffness can effectively suppress the elastic vibration in the movement of the manipulator.An experiment rig of plane single degree of freedom with the active control method of arm stiffness is designed in this paper,whose arm stiffness can be adjusting by changing the rope preload.The vibration characteristics of manipulator under different stress conditions and speed are studied experimentally.The results show that the active control method of arm stiffness can lead to stiffness effect,by which the elastic vibration can be suppressed,and the manipulator arm generates the softening effect with the increase of the speed,which leads to more intense vibration.Based on the experiment rig of plane single degree of freedom with the active control method of arm stiffness,the coupling dynamic characteristics of the joint and the manipulator arm under different speed are studied.The results show that the dynamic response of the joint and the arm is rooted in the nonlinear friction from the transmission process of the motor and harmonic reducer,the hysteresis of the harmonic transmission as well as the torque from manipulator arm.Besides that,the dynamic response of the arm is also influced by the arm stiffness and damping.By the study,the law of the manipulator arm vibration with the rope preload and speed is obtained,and the optimal value of the rope preload is analyzed for the arm stiffness adjustment.The varying stiffness model of the manipulator arm is analyzed by the ADAMS virtual prototype technology.By changing the simulation parameters,the influence of the material parameters and structural parameters of the manipulator on the vibration response is studied.The results indicate that the material parameters and structural parameters have a great influence on the dynamic response of the manipulator,and the reasonable choice of material parameters and structural parameters can reduce the dynamic response,which provides a method to improve the performance of the manipulator.Also,the dynamic model of the free-floating space manipulator is derived,and the numeiical simulation results demonstrate the coupling the dynamic behavior between the manipulator carrier and the arm.