Researches On Micro-vibration Characteristics And Isolation Methods Of Spacecraft Flywheel System

Flywheel systems, such as reaction wheels and control moment gyros, are the key actuators for attitude control of spacecraft in space mission. However, flywheel system brings about micro-vibration disturbances during operation. This kind of disturbance can deteriorate the pointing stability and precision of the spacecraft bus that with high precision requirements. Nowadays, micro-vibration problems induced by flywheel system is generally thought to be one of the major bottleneck issues in the development of high precision spacecraft bus. As the great development of high precision space mission, researches on flywheel micro-vibration become especially imperative in our country. In light of these, this dissertation addresses investigating the micro-vibration with its isolation techniques of onboard flywheel system for spacecraft systematically by ways of theoretical modeling, numeric analysis and ground experiments. The main work of this dissertation can be summarized briefly as follows:1. Micro-vibration disturbance models of reaction wheels and single gimbaled control moment gyro(SGCMG) have been developed; the dynamic and disturbance characteristics of the flywheel systems are examined by numeric methods.(1)A micro-vibration disturbance model of the typical reaction wheel has been developed with considering the nonlinear vibration induced by bearings; the support stiffness of the bearings, dynamic characteristics and disturbance characteristics are obtained by numeric methods. The nonlinearities introduced by bearings in the high-frequency range of disturbance are examined.(2)A micro-vibration disturbance model of the typical SGCMG has been developed; combination support stiffness of the rotor-bearing and gimbal-bearing, coupled dynamics characteristics and disturbance characteristics of the SGCMG are obtained by numeric methods. It is found that the rotating speed of rotor can increase the apparent gimbal inertia due to the coupled dynamics of rotor-bearing and gimbal-bearing.The theoretical results obtained above founded a theory base for micro-vibration isolation design for spacecraft flywheel system.2. Passive isolation methods aiming at both single flywheel system and flywheel system cluster have been proposed, respectively; an optimum design method for passive isolator of flywheel system is put forward.(1)A low stiffness isolator for single reaction wheel has been designed using a set of flexible beams; an analytial model describing the coupled dynamics of reaction wheel and isolator is developed; the dynamic characteristics and isolation performance are analyzed by numeric methods. It is demonstrated that the micro-vibration disturbance can be cut down at an extent of 70% using the proposed isolator.(2)An isolator with six-axial isolation ability for reaction wheel cluster has been designed using a set of flexible struts; an analytical model describing the coupled dynamics of wheel cluster and isolator is developed; the dynamic characteristics and isolation performance are analyzed by numeric methods. It is found that there will be complex dynamic behaviors of modes exchange in resonant zones due to the rotating-related gyroscopic effects.(3)An isolator with six-axial isolation ability for SGCMG cluster has been I designed using a set of flexible struts; an analytical model describing the coupled dynamics of SGCMG cluster and isolator is developed; the dynamic characteristics and isolation performance are analyzed by numeric methods. It is found that varying gimbal angles of SGCMG could induce asymmetric dynamics due to the complex gyroscopic effects and varying inertia.(4)An optimum design method of passive isolation for flywheel system has been put forward; an optimum model of isolated reaction wheel cluster developed, and its sensitivity model is derived accordingly. It is demonstrated that both the isolation performance and dynamic characteristics can be improved greatly using the proposed optimum design method.The theoretical results obtained above provide technical supports for passive isolation design for spacecraft flywheel system.3. Integral passive and active isolation methods aiming at both single flywheel system and flywheel system cluster have been proposed, respectively; the isolation performance of the proposed active methods are analyzed and demonstrated.(1)An integrated passive-active isolator for single reaction wheel has been designed using a set of piezoelectric beams; a dynamic-control model of the coupled wheel-isolator system is developed. It is demonstrated that the proposed control system is controllable at all six degrees of freedom except the axial torsion, and effective in suppressing resonance at critical points and attenuating the disturbance consequently.(2)An integrated passive-active isolator for reaction wheel cluster has been designed using a set of voice-coil actuated struts; a dynamic-control model of the coupled wheel-cluster and isolator system is developed with custom-designed H∞ controller. It is demonstrated that the proposed control system is controllable at all six degrees of freedom and effective in attenuating the disturbance in low rotating speed range.The theoretical results obtained above provide technical supports for intelligent isolation design for spacecraft flywheel system.4. Ground experiments of micro-vibation tests and isolation tests have been conducted for spacecraft flywheel system.(1)Micro-vibration tests have been conducted for a reaction wheel and a SGCMG based on force detection method, respectively. The test results help to understand the disturbance characteristics of flywheel system and validates the proposed micro-vibration disturbance model.(2)An isolator for a single reaction wheel have been designed and fabricated according to the demonstrated isolation method; modal tests and isolation tests have been conducted for the coupled wheel-isolator system. The test results validate the proposed dynamic model and demonstrate the proposed isolation method.The experiments results obtained above provide technical supports for design, manufacture and application of isolator for spacecraft flywheel system.