Advantages of active over passive systems:
small size, inherently stiff, rapid recovery from shock (1-10 ms), no air required, no set up time, and a performance
better than the best passive system. |
Passive damping systems work well at relatively high frequencies (>50Hz) but fail at low frequencies where
building vibrations occur. Passive systems have their resonance frequency there and amplify the vibrations instead of
damping it in that region.
Active vibration isolation systems employ inertial velocity in a feedback loop. A signal proportional to inertial
velocity is very similar to a viscous damping force, but with the very important difference that the damping is relative
to an inertial plane. So in contrast to the passive system, by increasing the damping as in curve [C] and [D], the
system becomes 'glued' to the inertial plane which by definition means the system is isolated from the environment.
[more details in chapter "ACTIVE vs. PASSIVE"].
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