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Active Vibration Control – Where is it absolutely necessary ?
- Active Vibration Control (AVC) was first introduced in a group of Space Structures – generally known as Large Space Structure (LSS)
- Consider, for example, the International Space Station (ISS)
Figure 22.1: International Space Station
Need of AVC for ISS
- The fundamental modal frequency of the ISS is around 8 Hz and the corresponding structural damping is only about 0.358%. A classic case of Flexible Body System with very low inherent damping!
- This poor damping in the absence of air can cause continuous vibration of the structure which may finally result in Fatigue Failure.
- Use of Passive Dampers accrues with large weight penalty – hence, active control of vibration is the only feasible solution in such cases.
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AVC needed to mitigate the Control-Structure Interaction (CSI) in Flexible Body Systems
- Often space structures are required to maintain high pointing accuracy – for example, Hubble Telescope.
- Now, during maneuvering of these highly flexible structures the actuators inadvertently excite structural modes of vibration.
- A small 10 micro-radian of filtering motion is equivalent to 50 m shift in the field of view for an imager at a distance of 500 km.
- The problem is traditionally known as control-structure interaction problem (CSI). Similar CSI problems occur in flexible robotic manipulators, rockets and missiles. Active Control of Vibration using an array of actuators and sensors is again the only feasible solution in such cases.
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