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TECHNICAL PAPERS

Feedback Stability Limits for Active Isolation Systems with Reactive and Inertial Actuators

[+] Author and Article Information
S. J. Elliott, M. Serrand, P. Gardonio

Institute of Sound and Vibration Research, University of Southampton, Southampton SO17 1BJ, England

J. Vib. Acoust 123(2), 250-261 (Oct 01, 2000) (12 pages) doi:10.1115/1.1350822 History: Received October 01, 1999; Revised October 01, 2000
Copyright © 2001 by ASME
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References

Crede, C. E., and Ruzicka, J. E., 1996, “Theory of Vibration Isolation,” Chapter 30, C. M. Harris, ed., Shock and Vibration Handbook, McGraw Hill, New York.
Ungar, E. E., 1992, “Vibration Isolation,” Chapter 11, Noise and Vibration Control Engineering, L. Beranek and I. L. Ver, eds., Wiley, Chichester.
Karnopp,  D., 1995, “Active and Semi-active Vibration Isolation,” ASME J. Mech. Des., 117, pp. 177–185.
Fuller, C. R., Elliott, S. J., and Nelson, P. A., 1996, Active Control of Vibration, Academic Press.
Beard, A. M., von Flotow, A. H., and Schubert, D. W., 1994, “A Practical Product Implementation of an Active/Passive Vibration Isolation System,” Proc. IUTAM Symposium on the Active Control of Vibration, Bath, pp. 101–108.
Franklin, G. F., Powell, J. D., and Emani-Naeini, A., 1994, Feedback Control of Dynamic Systems, Third Edition, Addison-Wesley, Reading, MA.
Blackwood, G. H., and von Flotow, A. H., 1993, “Active Control for Vibration Isolation Despite Resonant Structural Dynamics: A Trade Study of Sensors, Actuators and Configurations,” Proc. 2nd VPI Conference on Recent Advances in the Active Control of Sound and Vibration, pp. 482–494.
Elliott, S. J., Gardonio, P., and Rafaely, B., 1998, “Performance Evaluation of a Feedback Active Isolation System with Inertial Actuators,” ISVR Technical Memorandum No. 832.
Gardonio, P., Elliott, S. J., and Pinnington, R. J., 1996, “User Manual for the ISVR Isolation System with Two Active Mounts for the ASPEN Final Project Experiment,” ISVR Technical Memorandum No. 801.
Serrand, M., 1998, “Active Isolation of Base Vibration,” MSc thesis, University of Southampton.
Serrand,  M., and Elliott,  S. J., 2000, “Multichannel Feedback Control for the Isolation of Base-Excited Vibration,” J. Sound Vib., 234, No. 4, pp. 681–704.

Figures

Grahic Jump Location
A system for the isolation of equipment of mass m from base vibration (a) which has a passive mount, of stiffness k and damping c, and an active system in which the absolute velocity of the equipment is fed back to a secondary force acting on the equipment. The equivalent system, in the case in which the actuator and sensor are perfect, where the feedback system implement a skyhook damper, (b).
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The transmissibility of the system shown in Fig. 1 with no additional damping (bold line) with an increase in the damping of the isolator (dashed line) and an equal level of skyhook damping (faint line)
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Two methods of providing the secondary force on the equipment either by reacting it off the base structure (a) or by using an inertial mass within the actuator (b). In both cases the actuator generates a force fa and the dynamic response of the actuator is assumed to be absorbed into that of the equipment mount for the reactive actuator, (a), or the actuator mounting system for the inertial actuator, (b).
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Block diagram of a negative feedback control system including the response of the plant, G(jω), and the controller H(jω)
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General block diagram for the isolation system in which the unconnected equipment is acted on by a force fe and has a mobility Me, the base is acted upon by a force fb and has an unconnected mobility of Mb. The two systems are connected via the mount which has a mechanical impedance of Zm and the velocity of the equipment and base structure are ve and vb.
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Simulated magnitude, phase and Nyquist plot of Mtotal (solid) and Mee (dashed) for the reactive actuators
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Block diagram of the isolator model with the inertial actuator
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Magnitude and phase of the blocked frequency response of the inertial actuator
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Simulated magnitude, phase and Nyquist plots for the plant response of the active isolation system with an inertial actuator
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(a) Photograph and (b) schematic diagram of the experimental active isolation system with reactive actuation
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Magnitude, phase and Nyquist plots of the measured plant response from secondary shaker input to integrated accelerometer output for the isolation system with the reactive actuators
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Measured (a) and simulated (b) velocity of the equipment per unit primary force with reactive actuators. Results are shown for the passive system (control off, bold line) and for three values of feedback gain (faint line)
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Schematic diagram of the experimental isolator with the inertial actuator
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Magnitude, phase and Nyquist plots of the measured plant response from secondary shaker input to integrated accelerometer output for the isolation system with the inertial actuator
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Measured (a) and simulated (b) velocity of the equipment per unit primary force with inertial actuator. Results are shown for the passive system (control off, bold line) and for two values of feedback gain (dashed and faint line) for which the higher gain, faint line, is close to instability.

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