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Medientyp:
E-Artikel
Titel:
Active Vibration Isolation by Cancelling Bending Waves
Beteiligte:
McKinnell, R. J.
Erschienen:
The Royal Society, 1989
Erschienen in:Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences
Sprache:
Englisch
ISSN:
0080-4630
Entstehung:
Anmerkungen:
Beschreibung:
<p>Active forces applied to a vibrating beam structure may be driven to cancel propagating and evanescent waves entering the region beyond their point of application, thereby preventing those waves from carrying the effects of an external disturbance into that region. The application of this concept to the problem of vibration isolation has great potential; a system designed to detect bending waves as they pass a sensor and then inject an antidote further downstream can achieve total isolation of the entire structure beyond the point of application of just two point forces. The feedforward configuration ensures that the effectiveness of active isolation is limited only by the accuracy of implementation of the control system. Synthesis of the controller in terms of flexural waves suggests that the compensation required would contain irrational terms resulting from the dispersive nature of the waves; the inaccessibility of individual wave components to any measurement system in a finite structure, where vibrations are the superposition of waves in both directions, would complicate implementation and make accurate identification of the system impractical. These difficulties were removed by including the effects of waves generated by the active forces and detected at the controller input in the control system synthesis, and a simple, stable, active isolation system emerged. We show that the compensation required may be expressed in a rational polynomial form, and that identification of the optimal compensation in a noisy environment may be made using input-output response measurements on the structure to be isolated. The same response data can be used to predict limits imposed on the achievable isolation by inaccuracies in implementation. This work culminated in the application of these techniques to the problem of isolating a cantilever beam from vibrations caused by a random, broadband disturbing force near the fixed end. Although component inaccuracies in the particular apparatus used in the experiment allowed only 6 dB of attenuation to be achieved over a bandwidth of 200 Hz, good agreement between predicted and experimental results was shown.</p>