Research On Microvibration Isolation Method For Control Moment Gyroscope Onboard Spacecraft

High precision spacecraft is of great value to remote sensing,laser communication and deep space observation etc.Control moment gyroscope(CMG)can provide high torque without consuming any fuel,thus is suitable for attitude control system of high precision spacecraft.However,since a CMG consists of a rotor with high rotating speed,when outputs attitude control torque,it also brings about microvibration due to rotor imbalance and other factors,affecting attitude stability of the spacecraft.Therefore,study on the microvibration characteristics and isolation technique of the CMG is of great importance.In this work,systemic research on microvibration dynamic modeling and analysis,passive and active microvibration isolation of the CMG is conducted by means of theoretical analysis,numeric simulation and experimentation.The detailed work is as follows:1?Microvibration dynamic model of the CMG is developed and dynamic characteristics of the CMG is analyze d.(1)Microvibration dynamic model of a CMG is established.Microvibration characteristics of the CMG is analyzed and the relation of natural frequencies of the CMG to gimbal angle and rotating speed of the rotor is acquired.The characteristics of disturbance caused by the CMG as well as the swaying locus of axes of the gimbal and the rotor are investigated when the gimbal is locked or actuated.Differences and similarities of ideal output torque and actual output torque corrupted by microvibrat ion of the CMG are analyzed.The relation between the output disturbance and gimbal angle is also acquired.(2)Dynamic model of the coupled system of CMG cluster and spacecraft is developed.The influence of microvibration caused by CMG on attitude stability of spacecraft and dynamics of flexible appendages is analyzed when the spacecraft is stabilized or manoeuvred.Simulation results show that the disturbance caused by CMG will cause high-frequency microvibration of the spacecraft and flexible appendages.2 ? Passive microvibration isolation method for the CMG is developed.Vibration isolation apparatus for CMG is designed and analyzed.(1)Research on passive microvibration isolation method for CMG is conducted.Means to isolate microvibration passively based on constrained layer damping is proposed and a set of vibration isolation apparatus for CMG is designed by using several parallel installed isolation units.Dynamic model of the vibration isolation apparatus is established.The influence of the shape a nd configuration of the isolation units on the distribution of the natural frequencies for the vibration isolation system is analyzed.(2)Dynamic model for the coupled system of CMG and the vibration isolation apparatus is established.The dependence of the system transmissibility on the disturbance frequency is studied.Results show that the designed apparatus can ensure that high-frequency vibration isolation performance of the system will not be affected by high order modes.(3)The microvibration isolation performance of the vibration isolation apparatus is simulated and analyzed under the conditions of the gimbal is locked or actuated.Results show that when the gimbal is locked,the vibration isolation apparatus can reduce disturbance caused by rotor imbalance of the CMG by 87.27% minimally and 99.57% maximally.When the gimbal is actuated,the vibration isolation apparatus can isolate parasitical high frequency disturbance while normal attitude control torque is not affected.3?Active-passive hybrid microvibration isolation method for the CMG is developed.(1)Active microvibration isolation method for CMG is studied.Means to isolate microvibration actively is proposed by appending piezoelectric material to passive isolation units.Three kinds of control method are investigated.They're active vibration isolation control method based on overall state variable feedback,control method based on output disturbance feedback and control method based on local vibration information feedback respectively.The influence of position of the piezoelectric material on performance of the vibration isolation system is also analyzed.(2)Output disturbance characteristics of the passive and active vibration isolation system are analyzed and compared when flywheel rotor of the CMG is spinned up.Simulation results show that in the passive vibration isolation system,there exists vibration amplification zone when the rotor spins at low frequency while in the active vibration isolation system,the output disturbance keeps at very low level all the time when the rotor is spinned up.(3)The influence of parameters of the vibration isolation apparatus for CMG on the stability of attitude control system of spacecraft is investigated.Integrated dynamic model of “CMG cluster + vibration isolation platform + spacecraft” coupled system is established.Attitude stability of spacecraft and dynamics of flexible appe ndages is analyzed and compared with or without the existence of the vibration isolation apparatus.Results show that the vibration isolation apparatus can effectively reduce microvibration of three-axis attitude angular speed of spacecraft and high freque ncy microvibration of flexible appendages.4?Experime ntal research on microvibration isolation of CMG is conducted.(1)A prototype of passive microvibration isolation apparatus for CMG is developed and manufactured.Direct microvibration disturbance measurement system for CMG and indirect microvibration disturbance measurement system based on beam pointing measurement of an optical payload is built.(2)Output disturbance of CMG is measured under the conditions that gimbal of the CMG is locked or steered.Test results show that the microvibration isolation apparatus can effectively reduce the level of microvibration in CMG's all operational mode.When gimbal of the CMG is locked,the root mean square value of disturbance caused by the CMG can be reduced by the microvibration isolation apparatus by 93.58% minimally.The influence of microvibration caused by CMG on beam pointing of optical payload is measured and results show that the microvibration isolation apparatus can reduce jitter amplitude of the beam pointing.The work of this thesis provides theoretical and technical support for analysis of microvibration problem of CMG as well as development and application of microvibration isolation apparatus for CMG.