Dynamic Modeling And Integrated Control Of Space Continuum Robots

Space robots play a specifically crucial role in complex space tasks,such as refueling and on-orbit assembly.Limited by degrees of freedom and geometric size,the conventional space robots with multilink manipulators are difficult to perform tasks smoothly in the unstructured environment,and are very easy to collide with the target.The space continuum robot(SCR)composed of a base spacecraft,solar arrays,and continuum manipulators,can effectively avoid the above problems.The continuum manipulator can realize compliant operation and is suitable for the unstructured environment.More importantly,the interaction between the continuum manipulator and the astronaut is safer.The remarkable advantages make the SCR show broad application prospects in assisting astronauts’ extra vehicular activities.The SCR is a highly coupled multibody dynamic system,which consists of a rigid-body base spacecraft,flexible solar arrays,and large-deformation continuum manipulators.The elastic vibration of flexible appendages is accompanied by the large overall rigid-body motion of the SCR.In view of the characteristics that the SCR contains many types of components,it is particularly important to derive a dynamic model and analyze the dynamic characteristics of the SCR.The strong nonlinearity and high coupling degree of the dynamic model bring challenges to the control system design of the SCR.In addition,the curvature of a continuum manipulator is a nonlinear function of generalized coordinates,so the reasonable treatment of its input saturation needs to be further studied.The pose maneuver of the SCR will cause the swing of continuum manipulators.To achieve high-precision control,the integrated control of the pose and configuration of the SCR is a key problem that needs to be solved urgently.Therefore,taking the SCR as the research object,this dissertation carries out the dynamic modeling and analysis.On this basis,aiming at the control problems of the base spacecraft pose,the solar array deformation,and the continuum manipulator configuration,an integrated control method is proposed to provide theoretical reference for the development and application of the SCR.The main work of this dissertation is summarized as follows:(1)A modular dynamic model is derived for a SCR composed of rigid,flexible,and largedeformation modules.The base spacecraft is regarded as a rigid body,and the continuum manipulator is equivalent to the large-deformation beam.The elastic deformation of the solar array is calculated by the modal superposition method.The kinetic energy,elastic potential energy,and generalized forces of the SCR are then derived.The constraint equations are used to describe the kinematic constraints between the adjacent modules.The dynamic model of the SCR is derived based on the first kind of the Lagrangian equation.The proposed model can be used to analyze the dynamic response of the base spacecraft pose,the elastic deformation of the solar arrays,and the configuration of the continuum manipulators.The dynamic coupling amonge these components is reflected.The experimental results verify that the derived model can accurately calculate the configuration and responses of the continuum manipulators under the complex actuation forces.(2)The beating phenomenon of a SCR under the certain conditions is found,and its mechanism is analyzed based on the theoretical derivation.The dependent coordinates in the dynamic model of the SCR are first eliminated.Then the dynamic model about independent coordinates is derived and linearized at the equilibrium position by the perturbation method.Based on the linearized dynamic model with only independent coordinates,the mechanism of the beating phenomenon of the SCR is analyzed.The natural frequencies of the flexible components significantly affect energy transfer in the system.When the beating phenomenon of the SCR occurs,the amplitude and the energy of the solar arrays increase significantly,which may cause structural damage.For the above problem,a system parameter design process is further proposed to avoid the beating phenomenon caused by initial disturbances.(3)An energy shaping control method with kinematic constraints is proposed for the pose maneuver and configuration control of a SCR.The derived dynamic model with the Lagrangian form is transformed into the Hamiltonian form.From the perspective of energy,the control design for the pose and configuration of a SCR is carried out.The Hamiltonian function of the SCR is minimized at the desired pose and configuration through energy shaping,and the generalized constraint forces of the system are shaped simultaneously.Damping injection is used to adjust the system damping.A nonlinear disturbance observer is established to estimate external disturbances,and disturbance compensation is designed.The proposed control method can make the SCR maneuver to the desired pose and control the continuum manipulators to the desired configuration.The dynamic performance of the system can be easily adjusted.(4)A solution method based on mixed complementarity theory is proposed for the integrated optimal control problem of the SCR with input saturation constraints.Two observers are used to estimate modal coordinates and external disturbances.Combining the instantaneous optimal control theory and the augmented dynamic model with observers,the integrated control equation of the SCR with input saturation is derived.By introducing parameter variables and a nonlinear complementarity function,an integrated optimal control problem with input saturation is transformed into a mixed complementarity problem to be solved.The proposed method effectively realizes the integrated control of the trajectory-attitude-configuration-vibration of the SCR.When some actuators reach saturation,the required actuation force increment is allocated to the actuators that do not reach saturation,which can realize high-precision control and strictly meet the input saturation constraints.