Force feedback versus acceleration feedback in active vibration isolation

This paper compares the force feedback and acceleration feedback implementation of the sky-hook damper when it is used to isolate a flexible structure from a disturbance source. It is shown that the use of a force sensor produces always alternating poles and zeros in the open-loop transfer function between the force actuator and the force sensor, which guarantees the stability of the closed loop. On the contrary. the acceleration feedback produces alternating poles and zeros only when the flexible structure is stiff compared to the isolation system; this property is lost when the flexible modes of the sensitive payload interfere with the isolation system. (C) 2002 Elsevier Science Ltd. All rights reserved.