Servo design and analysis for the Thirty Meter Telescope primary mirror actuators

Creators: Thompson, Peter M.; MacMynowski, Douglas G.; Regehr, Martin W.; Colavita, M. Mark; Sirota, Mark J.

Others:: Stepp, Larry M.; Gilmozzi, Roberto; Hall, Helen J.

Abstract

The Thirty Meter Telescope has 492 primary mirror segments, each incorporated into a Primary Segment Assembly (PSA), each of which in turn has three actuators that control piston, tip, and tilt, for a total of 1476 actuators. Each actuator has a servo loop that controls small motions (nanometers) and large motions (millimeters). Candidate actuators were designed and tested that fall into the categories of "hard" and "soft," depending on the offload spring stiffness relative to the PSA structural stiffness. Dynamics models for each type of actuator are presented, which respectively use piezo-electric transducers and voice coils. Servo design and analysis are presented that include assessments of stability, performance, robustness, and control structure interaction. The analysis is presented for a single PSA on a rigid base, and then using Zernike approximations the analysis is repeated for 492 mirror segments on a flexible mirror cell. Servo requirements include low-frequency stiffness, needed for wind rejection; reduced control structure interaction, specified by a bound on the sensitivity function; and mid-frequency damping, needed to reduce vibration transmission. The last of these requirements, vibration reduction, was found to be an important distinguishing characteristic for actuator selection. Hard actuators have little inherent damping, which is improved using PZT shunt circuits and force feedback, but still these improvements were found to result in less damping than is provided by the soft actuator. Results of the servo analysis were used for an actuator down-select study.

Additional Information

© 2010 SPIE The International Society for Optical Engineering. The TMT Project gratefully acknowledges the contribution of the following actuator manufactures: The Pilot Group for the Piezo Pump Actuator (inquiries@the-pilot-group.com), Marjan Research (mvjean@marjanresearch.com) for the voice-coil soft actuators, and the Jet Propulsion Laboratory (www.jpl.nasa.gov) for the CT actuator. The work described in this paper was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The authors wish to thank the Thirty Meter Telescope Observatory Corporation for funding this work. 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.

Attached Files

Published - 77332F_1.pdf

Files

77332F_1.pdf

Files (1.2 MB)

Name	Size	Download all
77332F_1.pdf md5:61ab4b08783107afb21f5f66a7b233d3	1.2 MB	Preview Download

Additional details

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes