Equivalent Modelling And Coordinated Compliance Control Of Dual-arm Space Robot

With the rapid development of space activities,the increasing orbital debris brings potential dangers to the normal operation of on-orbit satellites.In order to capture and manipulate the above space debris,dual-arm space robots have attracted extensive attention as an effective tool.However,due to the multiple dynamic couplings between the base and the manipulators,there are still many difficulties in the dynamic modelling and coupling analysis,trajectory planning and control of dual-arm space robots,which bring challenges to practical applications.Therefore,a equivalent modelling method of dual-arm space robotic system is studied in this thesis.Based on the equivalent model,coordinated trajectory planning,trajectory optimization and coordinated compliance control methods are further proposed.In order to simplify the dynamic couplings between the manipulators and the base,a equivalent modelling method for dual-arm space robotic system is proposed.Considering the relative motion between the two arms,the generalized relative Jacobian matrix is derived which can achieve the mapping between the relative velocity of the two arms and the angular velocity of each joint.And it is further extended to a common form for multi-arm space robots and multi-arm terrestrial robots.In order to simplify the multiple dynamic couplings between the base and the manipulators of dual-arm space robot,an equivalent dynamic model is established.The end of one manipulator is defined as a virtual base,and the rest is equivalent to a hyper-redundant virtual manipulator.Therefore,the dual-arm space robot is simplified to a hyper-redundant single-arm space robot.Based on the equivalent model of dual-arm space robot,a multi-priority dual-arm coordinated planning method and a reactionless virtual base motion planning method are proposed.Combining the generalized relative Jacobian matrix with null-space projection,the relative motion planning for the two arms can be realized in the null-space of the master arm,while ensuring the desired trajectories of the two arms' end-effectors in the inertial space.In addition,based on the virtual-base modelling method,the redundant task-space degrees of freedom of the equivalent hyper-redundant single-arm space robot is analyzed.Then the augmented generalized Jacobian and null-space projection generalized Jacobian matrices are derived.The planning and control of redundant degrees of freedom and the desired trajectories of the two arms in the inertial space can be realized simultaneously.In order to save the valuable fuel resources of space robots,a dual-arm coordinated trajectory optimization method with minimum energy consumption is proposed.According to the different dynamic constraints between the two arms and the target,the whole capture process is decomposed into the pre-contact phase and the post-contact phase.For the pre-contact phase,using the arm-angle configuration representation method,the arm-angle trajectory with minimum base disturbance is obtained by particle swarm optimization.Combining arm-angle Jacobian with coordinated planning method,the configuration optimization of dual-arm space robot is realized.For the post-contact phase,it is assumed that the end-effectors of two arms form a stable connection with the target.Considering the kinematic and dynamic closed-chain constraints between two arms and the target,the nonlinear optimization based on the target dynamic equation is proposed to obtain dual-arm coordinated trajectories with minimum base disturbance and capturing time.For the safety problem caused by over-collision during the contact between the manipulators and the target,a dual-arm coordinated compliance control method with online identification of impedance parameters is proposed.According to the relative relationship between the two arms,the relative motion and relative operational force equations are derived.At the same time,the equivalent impedance model is established.By controlling the relative operational force between two arms,the operational force control of each manipulator is realized.Considering that the impedance parameters of traditional methods need to be measured by experiments and given artificially,there are certain risks and difficulties when operating in an unknown environment.Therefore,setting the objective function as the two-norm of relative operational force tracking error,the optimal impedance parameters are generated in real time through quadratic programming.The correctness and effectiveness of the proposed method are verified by dynamic simulation.In order to validate the proposed methods in this thesis,a ground experimental system for dual-arm space robot capturing non-cooperative space target is built,which consists of a dual-arm robot and a target motion simulator.The dual-arm robot is used to simulate the capture motion of dual-arm space robot based on dynamic model and kinematic equivalent principle;the target motion simulator uses a seven degrees-of-freedom redundant manipulator to simulate the initial motion of the space target and the equivalent relative motion resulted from the base disturbance of dual-arm space robot.Based on this ground experimental system,the experiment of dual-arm space robot capturing space target is carried out.The results verify the correctness of the proposed equivalent modelling,trajectory optimization and equivalent experiment methods.