The Study On Optimization Strategies During The Contact Process For Space Flexible Manipulators

With the development of space exploration,the failed/retired spacecraft are increasing year by year,and the number of space debris is growing.The space orbits are occupied and getting crowded,and the safety of other spacecraft in service are threatened.Therefore,the mission needs for failed/retired spacecraft targeting and space debris removal are growing more urgent.It is a trend in the future space exploration to use space manipulators to replace the astronauts to perform operations in terms of safety,energy consumption and efficiency.When the space flexible manipulator performs the tasks such as spacecraft targeting and debris recycling,the end-effector will contact with the target,producing the contact force and disturbance.The contact force will aggravate the wear of the end-effector and the target,while influencing the stability of the system and causing tasks fail.Meanwhile,the nature of space operation tasks(large operation span and wide variation range of load mass)requires the space manipulators consist of slender arms and have low structural stiffness,which makes the structural flexibility obvious,which aggravates the negative effects of collision on the manipulator and the target.Therefore,aiming to the contact between the space flexible manipulator and the target,the space flexible manipulator needs to have the ability to optimize the contact force and disturbance.Taking the space flexible manipulator as the research object,this paper aims at the problems of contact force and disturbance when performing the contact missions,and studies on optimizations strategies during the contact process.They consist of the contact force minimization strategy,vibration suppression strategy of flexible arms and attitude optimization strategy of the float base.And the effectiveness of the proposed strategies will be verified through the MATLAB.Main work of this paper is:Firstly,aiming to the contact process between the space flexible manipulator and the target,the method to establish the contact dynamical model is studied.Considering the rigid-flexible coupling character of the space flexible manipulator,the kinematic relationship among the base,joints,flexible links and the end-effector is analyzed,and the dynamic model is established.Based on the hertz theory,the contact dynamical model between the space flexible manipulator and the target is established.Then combining the dynamic model and the contact dynamical model,the dynamical responses of the space flexible manipulator and the target in the contact process are obtained respectively,which is of benefit to design the optimization strategies during the contact process.Next,aiming to the contact force producing by the contact tasks,the contact force minimization strategy is designed.Based on the dynamical equation of space flexible manipulator,its effective character in the operating space is analyzed.Combining the effective character and the contact dynamical model,the change rule of the contact force with the contact configuration and contact direction is obtained.Then the contact force minimization strategy is designed.The best contact configuration and contact direction of the space flexible manipulator is solved by the designed strategy,which can minimize the contact force and reduce the contact influence on the manipulator system and the target.Then considering that the vibration of flexible arms would be intensified and the stability of the system would be influenced in the contact process,the vibration suppression strategy of flexible arms is designed.Based on the dynamical model and the contact dynamical model of the space flexible manipulator,the vibration law of flexible arms with/without external force is analyzed.The vibration of arm is suppressed when the manipulator is in free motion based on the singular perturbation algorithm,which can guarantee the manipulator achieve the target configuration simultaneously.The vibration of arm is suppressed under the contact force based on the optimal control method,which can reduce the detriment on the flexible manipulator system.Finally,considering that the base attitude would change and the stability of the system would be influenced in the contact process,the attitude optimization strategy of the float base is designed to reduce the negative effect.Based on the dynamical response of the space flexible manipulator,the movement of the base in the contact process is solved.By taking into account the coupling relationship among the base movement and the joints movement and the flexible deformation,the optimization function of the base attitude is set.The objective function is solved based on the particle swarm optimization method,and the optimization of the base attitude under the contact force is achieved,improving the reliability of in-orbit contact operation.