Control analysis of the TMT primary segment assembly

Thompson, Peter M.; MacMynowski, Douglas G.; Sirota, Mark J.

doi:10.1117/12.790287

Cited by 11 publications

(14 citation statements)

References 3 publications

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“…3 The shorthand form gives pole and zero frequencies in Hz and the damping ratios of the complex modes. …”

Section: Zernike Methods For Csi Design and Analysismentioning

confidence: 99%

“…The work reported here builds upon previous studies of the M1CS servo control loop [3] and the global control loop. [4] Companion papers describe wind and disturbance models, [5] the prototype PSA built for testing and model verification, [6] ,and the current status of the M1CS global loop.…”

Section: Figure 2: Decision Process For Tmt Psa Actuator Down Selectionmentioning

confidence: 96%

“…This is the approximate model used in earlier work. [3] If the response is fast enough but the material stiffness needs to be included, then the electrical equation can be neglected and the bottom two reduce to f = dkV s + kz. This model suffices for the PZT forcer for all but the CT actuator.…”

Section: Dynamic Model Of Pzt Actuatormentioning

confidence: 99%

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

et al. 2010

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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.

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“…3 The shorthand form gives pole and zero frequencies in Hz and the damping ratios of the complex modes. …”

Section: Zernike Methods For Csi Design and Analysismentioning

confidence: 99%

Section: Figure 2: Decision Process For Tmt Psa Actuator Down Selectionmentioning

confidence: 96%

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

et al. 2010

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“…This algorithm is analogous to the classical feedback control laws that are typically used to actively control large ground telescopes; [24][25][26][27] it is similar to a proportional controller with a logic-driven gain operating on a 2-week timescale rather than continuously. It may seem inefficient or overly simplistic to simply discard six out of seven measurements.…”

Section: Baseline and Averaging Algorithmsmentioning

confidence: 99%

Improving active space telescope wavefront control using predictive thermal modeling

Gersh-Range

Perrin

2014

J. Astron. Telesc. Instrum. Syst

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Abstract. Active control algorithms for space telescopes are less mature than those for large ground telescopes due to differences in the wavefront control problems. Active wavefront control for space telescopes at L2, such as the James Webb Space Telescope (JWST), requires weighing control costs against the benefits of correcting wavefront perturbations that are a predictable byproduct of the observing schedule, which is known and determined in advance. To improve the control algorithms for these telescopes, we have developed a model that calculates the temperature and wavefront evolution during a hypothetical mission, assuming the dominant wavefront perturbations are due to changes in the spacecraft attitude with respect to the sun. Using this model, we show that the wavefront can be controlled passively by introducing scheduling constraints that limit the allowable attitudes for an observation based on the observation duration and the mean telescope temperature. We also describe the implementation of a predictive controller designed to prevent the wavefront error (WFE) from exceeding a desired threshold. This controller outperforms simpler algorithms even with substantial model error, achieving a lower WFE without requiring significantly more corrections. Consequently, predictive wavefront control based on known spacecraft attitude plans is a promising approach for JWST and other future active space observatories. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

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“…3 On the one hand this is caused by the segment assembly itself, due to mutual variations in e.g. segment geometry and mass and manufacturing tolerances in segment supports.…”

Section: Introductionmentioning

confidence: 99%

Primary mirror control for large segmented telescopes: combining high performance with robustness

2016

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Future large telescopes, such as E-ELT and TMT, will need feedback control of the thousands of actuators underneath their segmented primary mirrors (M1). Differences in actuator dynamics and spatially and temporally changing disturbances make it extremely difficult to formulate classical controllers which are both sufficiently robust and highly performing. Therefore, TNO has developed and tested a control approach, in which the actual system response is quickly measured, disturbances are continuously estimated and the controller is adapted in real-time. The algorithm is tested on an actual M1-relevant setup, in which it converges to a sub-nm optimum within a few minutes, keeps track of changing disturbances and shows its reliability over multiple days.

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Control analysis of the TMT primary segment assembly

Cited by 11 publications

References 3 publications

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

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

Improving active space telescope wavefront control using predictive thermal modeling

Primary mirror control for large segmented telescopes: combining high performance with robustness

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