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Analysis of TMT primary mirror control-structure interaction

MacMynowski, Douglas G. and Thompson, Peter M. and Sirota, Mark J. (2008) Analysis of TMT primary mirror control-structure interaction. In: Modeling, Systems Engineering, and Project Management for Astronomy III. Proceedings of SPIE. No.7017. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 701715. ISBN 9780819472274. http://resolver.caltech.edu/CaltechAUTHORS:20180802-142536755

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Abstract

The primary mirror control system (M1CS) keeps the 492 segments of the Thirty Meter Telescope primary mirror aligned in the presence of disturbances. A global position control loop uses feedback from inter-segment edge sensors to three actuators behind each segment that control segment piston, tip and tilt. If soft force actuators are used (e.g. voice-coil), then in addition to the global position loop there will be a local servo loop to provide stiffness. While the M1 control system at Keck compensates only for slow disturbances such as gravity and thermal variations, the M1CS for TMT will need to provide some compensation for higher frequency wind disturbances in order to meet stringent error budget targets. An analysis of expected high-wavenumber wind forces on M1 suggests that a 1Hz control bandwidth is required for the global feedback of segment edge-sensorbased position information in order to minimize high spatial frequency segment response for both seeing-limited and adaptive optics performance. A much higher bandwidth is required from the local servo loop to provide adequate stiffness to wind or acoustic disturbances. A related paper presents the control designs for the local actuator servo loops. The disturbance rejection requirements would not be difficult to achieve for a single segment, but the structural coupling between segments mounted on a flexible mirror cell results in controlstructure interaction (CSI) that limits the achievable bandwidth. Using a combination of simplified modeling to build intuition and the full telescope finite element model for verification, we present designs and analysis for both the local servo loop and global loop demonstrating sufficient bandwidth and resulting wind-disturbance rejection despite the presence of CSI.


Item Type:Book Section
Related URLs:
URLURL TypeDescription
https://doi.org/10.1117/12.787003DOIArticle
ORCID:
AuthorORCID
MacMynowski, Douglas G.0000-0003-1987-9417
Additional Information:© 2008 Society of Photo-Optical Instrumentation Engineers (SPIE). The TMT Project gratefully acknowledges the support of the TMT partner institutions. They are the Association of Canadian Universities for Research in Astronomy (ACURA), the California Institute of Technology and the University of California. This work was supported as well by the Gordon and Betty Moore Foundation, the Canada Foundation for Innovation, the Ontario Ministry of Research and Innovation, the National Research Council of Canada, the Natural Sciences and Engineering Research Council of Canada, the British Columbia Knowledge Development Fund, the Association of Universities for Research in Astronomy (AURA) and the U.S. National Science Foundation.
Group:Thirty Meter Telescope
Funders:
Funding AgencyGrant Number
Association of Canadian Universities for Research in Astronomy (ACURA)UNSPECIFIED
CaltechUNSPECIFIED
University of CaliforniaUNSPECIFIED
Gordon and Betty Moore FoundationUNSPECIFIED
Canada Foundation for InnovationUNSPECIFIED
Ontario Ministry of Research and InnovationUNSPECIFIED
National Research Council of CanadaUNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
British Columbia Knowledge Development FundUNSPECIFIED
Association of Universities for Research in Astronomy (AURA)UNSPECIFIED
NSFUNSPECIFIED
Subject Keywords:Extremely Large Telescopes, Control Systems, Control-Structure-Interaction
Record Number:CaltechAUTHORS:20180802-142536755
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180802-142536755
Official Citation:Douglas G. MacMynowski, Peter M. Thompson, Mark J. Sirota, "Analysis of TMT primary mirror control-structure interaction", Proc. SPIE 7017, Modeling, Systems Engineering, and Project Management for Astronomy III, 701715 (9 July 2008); doi: 10.1117/12.787003; https://doi.org/10.1117/12.787003
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:88532
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:02 Aug 2018 21:48
Last Modified:02 Aug 2018 21:48

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