Impact oscillator based suspension system for a reaction wheel

Abstract eng:
The working of most passive systems for vibration isolation can be reconducted to the dynamics of a single degree of freedom system (mass on a spring and damper) excited by the motion of the support. The damping controls the response at resonance, although the negative effect of viscous damping is to increase the transmissibility at high frequency. An alternative method to control the amplitude of the response of the system at resonance is to include mechanical hard stops that physically limit the amplitude of the oscillation. When the system is excited by a broad band random vibration of the support, if the intensity of the input is relatively low and the mass does not hit the hard stops, the system filters out the high frequency vibrations. However, increasing the amplitude of the input the mass starts to hit the hard stops and mechanical shocks are produced. This type of system, better known as an impact oscillator has been studied by various authors and various mathematical models are available. This paper examines a practical application of this type of system for a reaction wheel to be used on board satellites. Typically in these cases the rotor of the wheel is fixed on a shaft which is rigidly supported by bearings fitted in the supporting structure of the wheel case. The design presented here uses an alternative approach where the rotor/shaft/motor assembly is supported by a soft suspension that when the system is subjected to harsh random vibrations (i.e. the mechanical environment produced by the launch vehicle) allows the suspended mass to clash with the internal walls of the case. A trade off is carried out showing the influence of the various design parameter, e.g. the gap between the oscillating mass and the enclosure, on the loads experienced by the bearings and the motor.

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