Study On Dynamic Characteristics Of Space Flexible Manipulator

With the continuous development of space technology and the further development of human exploration of space,space manipulator will play an important role.Especially,when assisting astronauts in extravehicular activity,flexible use of space manipulator will provide sufficient convenience and safety.Due to the light weight and large working range of space manipulator,it is inevitable to introduce some flexibility.Therefore,space manipulator is a time-varying dynamic system with strong coupling and nonlinear properties.It is the basic research to improve the position control precision of space flexible manipulator to analyze the dynamics modeling and corresponding dynamics characteristics.Firstly,the kinematics and dynamics models of the 7 degree of freedom(7-DOF)manipulator are established.The kinematics model uses the forward kinematics description of Euler Angle to express the position and attitude of the end of a given manipulator.Considering the flexibility brought by the harmonic reducer and sensor at the joint,the dynamics model of the 7-DOF spatial flexible manipulator was established.The dynamics model of rigid and flexible manipulator with single degree of freedom was established and the spatial flexible manipulator with 7 degrees of freedom was deduced.Secondly,the in-orbit stiffness of the space manipulator is calculated,analyzed and verified according to the dynamics model and flexibility matrix theory of the flexible manipulator.Because space manipulator has different configurations when performing space tasks,it is difficult to use finite element to analyze the fundamental frequency of space manipulator in different configurations.Therefore,a calculation method based on flexibility matrix theory modeling is proposed and verified.Based on the kinematic and dynamic models of space flexible manipulator,a theoretical modeling method of flexibility matrix was proposed.Then the theory is verified by finite element analysis of the manipulator in two typical configurations.Finally,the ground deployable fundamental frequency experiment is carried out to verify the manipulator.Then,according to the flexibility matrix theory algorithm,the manipulator model is simplified to analyze the jitter of the end of the manipulator during emergency braking.The finite element model of the manipulator was simplified by using the finite element software Patran and the flexibility matrix theory.The two typical configurations of the manipulator were analyzed when the terminal load was no load,astronaut and 3T,and the results of the theoretical model were compared with the results of the finite element calculation.The braking distance at the end of the manipulator is calculated when emergency braking occurs under different circumstances.Finally,in order to simulate the jitter of space manipulator subjected to impact of different duration,the model was first imported into Dynamics simulation software to set relevant parameters,and then the impact jitter was analyzed according to the force generated by the astronaut’s foot pedal on the end of the manipulator under different duration.At the same time,the comparison test between the rigid manipulator and the flexible joint manipulator shows that when the manipulator is rigid,the end of the manipulator will not jitter when the manipulator is impacted by different lengths of time,because there are pretightening torques at each joint of the manipulator.When the manipulator is a flexible joint manipulator,the end of the manipulator will jitter around a displacement when it receives impact of different lengths.