Research On Variable Stiffness Joint And Compliance Control Of Space Manipulator

Space manipulators are taking on more and more on-orbit missions,and therefore will contact with other spacecrafts or capture targets frequently.During the contact process and the target capture operations,the space manipulator will be inevitably impacted.At this time,the variation of the dynamics parameters of the free-floating space manipulator will degrade the stability of the base attitude.In order to solve this problem,this paper presents a new compliance control algorithm based on variable stiffness technique.The variable stiffness joint is introduced into the space manipulator,and the dynamics model of the variable stiffness joint space manipulator is established according to the Lagrange dynamic equation.Moreover,we designe a soft-capturing control algorithm to reduce the angular momentum of the base.Specific works are as follows:Firstly,a virtual prototype of variable stiffness joint,of which,the position and stiffness are controlled by different motors,is established.Secondly,the designed joint with variable stiffness is introduced into the space manipulator,and the kinematics and dynamics model of the variable stiffness joint free-floating space manipulator with base position and attitude uncontrolled are established.The simulation is carried out based on Matlab software platform.The results verify the correctness of the model.At the same time,the kinetics of the pre-impact and post-impact phases of the variable stiffness joint free-floating space manipulator are analyzed,which lays the foundation for the research of the soft-capturing control strategy.Then,based on the derivation of the dynamic equations of the variable stiffness joint free-floating space manipulator system,a compliance control strategy of multi-degree-of-freedom joint free-floating space manipulator is designed based on the cellular automaton differential evolution algorithm.Due to the coupling between base and joints,the objective function is designed based on the minimum angular velocity of base and all joints.Cellular automata differential evolution algorithm is used to solve the desired joint stiffness value and then buffer to reduce the base angular momentum.The simulation of a planar two-DOF space manipulator system verifies the effectiveness of the proposed control strategy.Finally,since the stiffness of the joint is nonlinearly related to the angle of the stiffness adjustment motor,the problem of controlling the stiffness of the joint is converted to control the angle of the stiffness adjustment motor.Considering the disturbance and the change of system parameters,an adaptive backstepping sliding mode control method is proposed for the stiffness adjustment motor so that the actual joint stiffness value can track the desired joint stiffness value.The simulation based on Simulink software platform verifies the effectiveness of the control method.In the end,summarize the research results and make a forecast.