Research On Pointing And Stabilization Technology Of Optical Space Payload For Parallel Integration Of Coarse And Fine Actuators

With the continuous development of space technology,the requirements for pointing control of optical payloads have become increasingly diverse.Small optical payloads on large spacecraft require independent and large-scale pointing adjustment capabilities so that they can aim at targets without changing the spacecraft’s attitude.At the same time,they also need to have a good dynamic performance to maintain a precise and stable Line-Of-Sight(LOS)when subjected to disturbances.To meet the control requirements of a large motion range and high dynamic performance,this paper studies a new payload pointing and control technology.The technology provides a large range of motion for the payload through coarse actuators and fast dynamic response capability through fine actuators.Furthermore,the technology integrates coarse and fine actuators in parallel to achieve a compact design.The research is beneficial in reducing the size of the optical mechanism,payload mass,and launch costs while combining multiple functions,thus it has significant value in the development of high-performance small optical space payloads.Firstly,the kinematic characteristics of the pointing and stabilizing mechanism integrating coarse and fine actuators in parallel were analyzed,and the geometric conditions for the coarse and fine actuators to completely control the LOS were given,ensuring that the additional constraints caused by the difference in stroke and response speed between the two when they are integrated into the same parallel mechanism will not affect the control of LOS,thereby guaranteeing that the proposed parallel integration scheme can achieve coarse and fine division of labor.A kinematic algorithm for coarse actuators independently controlling the LOS and a simple static stiffness modeling method for parallel mechanisms were proposed,and the effectiveness of the proposed methods was verified through simulation and experiment,respectively.Secondly,a dynamic modeling method of a double-mobile platform system was proposed,which is used to study the dynamic response characteristics of the pointing and stabilizing mechanism to floor disturbance,and the effect of the "mobile base" effect of the double-mobile platform system on the controlling characteristics of the mechanism.On this basis,a feed-forward active vibration isolation algorithm and a decoupling method based on parameterized models were proposed,and the effects of the "mobile base" effect,delay,and other factors on the robust stability and performance of the optimal controller were analyzed.The effectiveness and robustness of the feed-forward algorithm were verified by simulation,and the compensation for dynamic disturbance was realized.Thirdly,a novel adaptive feed-forward vibration isolation algorithm was further proposed to improve the robustness of the feed-forward vibration isolation method.The algorithm consists of parameter update algorithms and a feed-forward error system.Firstly,parameter updating algorithms for Multiple-Input-Multiple-Output(MIMO)systems were designed,and a theoretical method for analyzing the algorithm convergence was also proposed.In particular,the adverse effect of unbalanced excitation of multichannel input signals on the convergence of the adaptive algorithm was pointed out.On this basis,an improved feed-forward error system construction was proposed to ensure that the algorithm keeps good convergence characteristics under complex excitation conditions.Finally,a prototype of the pointing and stabilizing mechanism integrating coarse and fine actuators in parallel was designed and manufactured,and the tests on the motion range and stabilizing performance of the prototype were conducted.The results show that the range of roll angle,pitch angle,and yaw angle both reached more than 7 degrees,a maximum of 20dB attenuation to the floor disturbance of 2-20Hz was achieved,and the suppression ratio of the Root-Mean-Square(RMS)level of angular acceleration was at least 50%.Therefore,the feasibility of the proposed parallel integration scheme of coarse and fine actuators could be accepted.