Research On Dynamic Modeling And Vibration Control For The Flywheel Of Spacecraft

Reaction wheel assembly and momentum wheel assembly (named flywheel in thisdissertation) are widely used on high accuracy spacecraft to provide attitude controltorque or maintain stability. However, the microvibrations produced by the flywheel canaffect the pointing accuracy and stability of the spacecraft, and even degrade theperformance of high sensitive instruments. Thus, the vibration control of the flywheel isimperative. This dissertation focuses on investigating the issue of dynamic modelingand vibration control of the flywheel through theoretical analysis, numerical simulationand experimental research. The methods of passive and active vibration control for theflywheel are proposed and verified by experiment; the main research efforts in thisdissertation are summarized as follows.1. A linear and a nonlinear dynamic model of the flywheel for spacecraft areestablished; the dynamic characteristic of the flywheel is analyzed; and theprinciple that the soft suspension flywheel can increase the rotational speed anddecrease the disturbance is studied.(1) The dynamic models of the flywheel and the disturbance sources areestablished; the dynamical equation of the flywheel based on transfer matrix isdeveloped; the influence of the vibration sources on the disturbance force and momentproduced by the flywheel is analyzed.(2) Considering the nonlinear effect of the bearing stiffness, the flywheel issimplified as a Jeffcott rotor model, and the basic principle is analyzed that the softsuspension can effectively increase the maximum rotational speed and decrease thedisturbance force.2. The passive vibration isolation model and active vibration control modelare established; method and technique of the passive vibration isolation and activevibration control for the flywheel are proposed and analyzed.(1) A soft suspension flywheel based on folded beams is proposed; the dynamicmodel of the flywheel is established; the dynamic equation of the flywheel is developed,the passive vibration isolation performance of the soft suspension flywheel is analyzed.The analysis results show that the soft suspension structure can effectively isolate thedisturbance force and moment produced by the mass imbalance when the flywheeloperates above the critical speed.(2) A passive vibration isolation platform for the flywheel (momentum wheelassembly) is proposed; the dynamic model of the flywheel and the platform isestablished; the dynamic equation of the system is developed, which includes thegyroscopic effect term; the influence of the gyroscopic term on the performance ofvibration isolation of the platform is analyzed. The analysis results show that the critical speed of the system consisting of flywheel and platform is affected by the mass propertyof the flywheel; the critical speed occurs before the natural frequencies of the system atrest if the axial moment of inertia of the rotor is larger than the radial moment of inertiaof the flywheel; else, the critical speed occurs after the natural frequencies at rest. Theplatform can effectively isolate the disturbance force and moment produced by massimbalance.(3) An active vibration control structure for the soft suspension flywheel isproposed; the dynamic model of the active control for the soft suspension flywheel isestablished; the dynamic equation of the active vibration control based on velocityfeedback is developed; the performance of active vibration control for the flywheel isanalyzed. The results show that the active control structure can suppress the vibrationsat all the six degrees of freedom except the axial rotation, and the active vibrationcontrol can effectively suppress the dynamic amplification at critical speed,3. An experimental system for the vibration control of the flywheel ofspacecraft is established; the effectiveness of the vibration control method for theflywheel is verified.(1) A high accuracy and broad frequency range microvibration measurementexperimental system for the flywheel is constructed, which can measure themili-Newton force at the frequency range of3-300Hz.(2) The disturbance produced by the flywheel is tested; the test results areconsistent with the theoretical results, which demonstrates the correctness andeffectiveness of the dynamic model and disturbance sources model of the flywheel.(3) The natural frequencies and nonrotating damping coefficients of the softsuspension flywheel and the passive vibration isolation platform are studied. The resultsshow that both of the designed natural frequencies are consistent with the experimentalvalues, which verifies the validity of the design method and mathematical model of thesoft suspension flywheel and the platform.(4) The performance of the soft suspension flywheel is researched by experimentaltest. The results show that the flywheel implements the relatively high rotational speedbut low disturbance force, which verifies that it is correct and valid to isolate thevibration from the flywheel using soft suspension design.(5) The performance of the passive vibration isolation platform is researched byexperimental test. The results show that the critical speed occurs at2600rev/min, whichis larger than the sixth natural frequency of the system (26.29Hz), which demonstratesthat the gyroscopic effect affects the performance of the platform; the platform caneffectively isolate the high frequency disturbance, which verifies the effectiveness of thepassive vibration isolation of the platform.(6) An integrated passive and active vibration control strategy for the flywheel isresearched by experimental test. The test results show that the active vibration control strategy can effectively suppress the disturbance force at critical speed, which verifiesthe correctness and effectiveness of the integrated passive and active control strategy.