Research On Dynamic Modeling And Vibration Control For Flexible Space Robot

With the rapid development of space technology,the space robots have attracted more and more attention.The space robots can adapt to the harsh space environments,such as large temperature difference between day and night,ultra-vacuum,space microgravity,atomic oxygen and space radiation,complete the high-precision and highreliability space operations instead of the astronauts.Thus,the space robots are widely used in space missions,such as component replacement,space debris remove,carrying payload,failed satellite maintenance,fuel refueling,and assistance in docking and transposition of the space station cabins and orbital spacecraft.However,due to the influence of flexible components on the space robots,such as the flexible solar panels and space manipulators,the flexible components motion and base motion are coupled complexly.The space robots exhibit complex dynamic characteristics and the controller design of the space robots becomes very difficult.The flexibility of solar panels and manipulators is considered in this paper.The dynamic characteristics and vibration control methods of the space robots are studied.The main research contents and results are as follows:For the space robot system with flexible solar panels and flexible manipulators,the system dynamic model is established based on the recursive construction method and the velocity variation principle.The solution method and calculation process of the dynamic equations are given.The simulation results of the proposed model are compared with the multi-body dynamics calculation software ADAMS in order to verify the accuracy and effectiveness of the model.The simulation results show that the results of the proposed model are basically consistent with those of the ADAMS software.Based on the dynamic model of the flexible space robot,the influence of the movement law of the flexible body on the vibration of the flexible body is analyzed.The influence law of the different stages' movement time on the vibration of the flexible body is obtained.The frequency characteristic analysis method of the flexible body is established by Fourier transform.The influence law of flexible body motion on spectrum amplitude is obtained.The dynamic coupling factor model of the flexible space robot system is established.The dynamic coupling degree among the manipulator joints motion,the manipulator flexible vibration,the solar panel flexible vibration,the central rigid body motion and the manipulator end motion is analyzed.The influence of the central rigid body mass and the rotation angle of the manipulator joint on the system coupling factor is analyzed.The cloud map of the dynamic coupling factor in the manipulator joint space is obtained,which provides theoretical guidance for reducing the dynamic coupling effect of the flexible space robot system.The multi-impulse robust shaper(MIR shaper)is proposed in this paper to control the flexible system vibration.The MIR shaper has flexible design parameters to adjust the number of shaper pulses and the pulse length.Compared with the traditional input shaper,The MIR shaper is more robust to the system natural frequency and damping ratio.The numerical simulation results show that the MIR shaper can suppress the residual vibration more effectively than the traditional shaper when the system parameter errors are large.In the high-frequency area,the MIR shaper can suppress vibration in a wider frequency range.When the system parameter error is large or the flexible vibration is in a wide frequency range,the system vibration can be regarded as high frequency vibration and then the MIR shaper can be designed according to its characteristics of suppressing vibration in the high frequency range in order to suppress the system vibration more effectively.A control strategy combining the MIR shaper with the optimal control is proposed in this paper.The simulation analysis is carried out.The results show that the proposed control strategy can suppress vibration more effectively compared with the control strategies combining other input shapers with the optimal control.Considering the flexibility of the solar panels and the manipulators,a free flight controller and a free-floating controller are proposed according to the space robot working state on the basis of the flexible space robot dynamic equations.Based on the characteristics of the MIR shaper in suppressing high-frequency vibration components,a shaper is designed to shape the desired input and control the flexible space robot with combination of the free space controller and the free-floating controller.The numerical results show that the designed controller can effectively suppress the vibration of the flexible components.The operation control of the space robot can be realized using the free flight controller and the free-floating controller.The free flight controller can simultaneously control the movement of the base,while the free-floating controller can not control the base posture.The flexible space robot system is easily susceptible to the external interference in space.The dynamic model of the flexible space robot is decomposed into a slow-variable subsystem and a fast-variable subsystem using the singular perturbation principle.The sliding mode control method is used to control the systems with external interference and the RBF neural network is used to estimate the boundary of external interference force.Then an anti-interference controller for flexible space robots is proposed.The simulation results show that the proposed anti-interference controller can accurately control the flexible space robot and reduce the vibration response of the flexible components for the system with external interference.