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Feedback stability limits for active isolation systems with reactive and inertial actuators

Feedback stability limits for active isolation systems with reactive and inertial actuators
Feedback stability limits for active isolation systems with reactive and inertial actuators
Some of the compromises inherent in using a passive system to isolate delicate equipment from base vibration can be avoided using fully active skyhook damping. Ideally, a secondary force, which is made proportional to the absolute equipment velocity by a feedback controller, acts only on the equipment and so the response of the system under control, between the secondary force input and the collocated velocity output, i.e., the plant response, is proportional to the driving point mobility of the mounted equipment. The frequency response of the plant is guaranteed to have a positive real part under these ideal conditions, and so the feedback system is unconditionally stable for any positive real feedback gain. In practice, the actuator generating the secondary force must either react off the base structure or an inertial mass. In both of these cases the plant response is no longer guaranteed to be positive real and so the control system may become unstable at high gains. Expressions for the overall plant responses are derived for both of these arrangements, in terms of the dynamic response of the individual parts of the isolation system. When using a soft mount, the stability of the reactive system is found to be surprisingly tolerant of the additional contributions to the plant response from the reactive force. In order for the inertial system to be stable with a high feedback gain, however, the natural frequency of the actuator must be well below the natural frequency of the equipment on the mounts. Experimentally measured plant responses are compared with those predicted from theory for both types of actuator and the performance of practically implemented feedback controllers is discussed.
1048-9002
250-261
Elliott, S.J.M.
721dc55c-8c3e-4895-b9c4-82f62abd3567
Serrand, M.
3f1731d8-4c05-4ddf-b5d6-a86cae54034d
Gardonio, P.
bae5bf72-ea81-43a6-a756-d7153d2de77a
Elliott, S.J.M.
721dc55c-8c3e-4895-b9c4-82f62abd3567
Serrand, M.
3f1731d8-4c05-4ddf-b5d6-a86cae54034d
Gardonio, P.
bae5bf72-ea81-43a6-a756-d7153d2de77a

Elliott, S.J.M., Serrand, M. and Gardonio, P. (2001) Feedback stability limits for active isolation systems with reactive and inertial actuators. Journal of Vibration and Acoustics, 123 (2), 250-261. (doi:10.1115/1.1350822).

Record type: Article

Abstract

Some of the compromises inherent in using a passive system to isolate delicate equipment from base vibration can be avoided using fully active skyhook damping. Ideally, a secondary force, which is made proportional to the absolute equipment velocity by a feedback controller, acts only on the equipment and so the response of the system under control, between the secondary force input and the collocated velocity output, i.e., the plant response, is proportional to the driving point mobility of the mounted equipment. The frequency response of the plant is guaranteed to have a positive real part under these ideal conditions, and so the feedback system is unconditionally stable for any positive real feedback gain. In practice, the actuator generating the secondary force must either react off the base structure or an inertial mass. In both of these cases the plant response is no longer guaranteed to be positive real and so the control system may become unstable at high gains. Expressions for the overall plant responses are derived for both of these arrangements, in terms of the dynamic response of the individual parts of the isolation system. When using a soft mount, the stability of the reactive system is found to be surprisingly tolerant of the additional contributions to the plant response from the reactive force. In order for the inertial system to be stable with a high feedback gain, however, the natural frequency of the actuator must be well below the natural frequency of the equipment on the mounts. Experimentally measured plant responses are compared with those predicted from theory for both types of actuator and the performance of practically implemented feedback controllers is discussed.

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Published date: April 2001

Identifiers

Local EPrints ID: 10838
URI: http://eprints.soton.ac.uk/id/eprint/10838
ISSN: 1048-9002
PURE UUID: 1a353307-2b73-400b-a91f-82d299048532

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Date deposited: 13 Feb 2006
Last modified: 15 Mar 2024 05:01

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Contributors

Author: S.J.M. Elliott
Author: M. Serrand
Author: P. Gardonio

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