Design of a prototype primary mirror segment positioning actuator for the Thirty Meter Telescope

Lorell, Kenneth R.; Aubrun, Jean-Noel; Clappier, R.; Miller, Scott W.; Sirota, Mark J.

doi:10.1117/12.672917

Cited by 8 publications

(8 citation statements)

References 3 publications

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“…As seen, wind spectrum is recreated in the lower frequency regime which is the main frequency region of our interest. which aimed to perform reasonably well to the science programs requiring very high spatial resolution by the aid of extreme AO (Lorell et al, 2006;MacMynowski et al, 2011). This happens mainly because they have got the ability to reject structural vibration which is nothing but high-frequency, lowamplitude disturbances.…”

Section: Discussionmentioning

confidence: 99%

“…All these telescopes use rigid segment support actuators which have extremely high axial sti®ness and hence, the wind does not have a major e®ect on maintaining the shape of the primary mirror. Since the next generation telescopes are getting bigger and bigger, the vibration becomes a concern (Lorell et al, 2006) as the natural frequency of structure shifts towards the low-frequency region. Therefore, to overcome the problem of structural vibration, which will degrade the image quality, upcoming extremely large telescopes such as TMT (Lorell et al, 2006) and E-ELT (Dimmler et al, 2008) have planned to use the soft actuators (however the baseline for E-ELT is the hard actuator).…”

Section: Introductionmentioning

confidence: 99%

“…Since the next generation telescopes are getting bigger and bigger, the vibration becomes a concern (Lorell et al, 2006) as the natural frequency of structure shifts towards the low-frequency region. Therefore, to overcome the problem of structural vibration, which will degrade the image quality, upcoming extremely large telescopes such as TMT (Lorell et al, 2006) and E-ELT (Dimmler et al, 2008) have planned to use the soft actuators (however the baseline for E-ELT is the hard actuator). The soft actuator technology is favorable for high-frequency vibration attenuation, but little poor in suppressing wind disturbances due to low dynamic sti®ness.…”

Section: Introductionmentioning

confidence: 99%

“…Soft actuator performance requirement comparison. Data is adopted fromfor TMT (Lorell et al, 2006), for EELT (Jim enez et al, 2010) (Witvoet et al, 2014) (Kamphues et al, 2008) (Vernet et al, 2013) and for PSMT (Viera et al, 2008) developed for E-ELT telescope, which is a seven segment telescope with all the control subsystems of a complete segmented mirror telescope. Though such experiment can be a best possible attempt to understand the wind effect on SMT actuators, however, such experiments are extremely costly and designed to serve several other objectives.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic Loading Assembly for Testing Actuators of Segmented Mirror Telescope

Deshmukh

Parihar

Balasubramaniam

et al. 2017

J. Astron. Instrum.

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Upcoming large telescopes are based on Segmented Mirror Telescope (SMT) technology which uses small hexagonal mirror segments placed side by side to form the large monolithic surface. The segments alignment needs to be maintained against external disturbances like wind, gravity, temperature and structural vibration. This is achieved by using three position actuators per segment working at few-nanometer scale range along with a local closed loop controller. The actuator along with a controller is required to meet very stringent performance requirements, such as track rates up to 300 nm/s (90 mN/s) with tracking errors less than 5 nm, dynamical forces of up to AE40 N, ability to reject disturbances introduced by the wind as well as by mechanical vibration generated in the mirror cell, etc. To conduct these performance tests in more realistic manner, we have designed and developed a Dynamic Loading Assembly (DLA) at Indian Institute of Astrophysics (IIA), Bangalore. DLA is a computer controlled force-inducing device, designed in a modular fashion to generate di®erent types of user-de¯ned disturbances in extremely precise and controlled manner. Before realizing the device, using a simple spring-mass-damper-based mathematical model, we ensured that the concept would indeed work. Subsequently, simple concept was converted into a detailed mechanical design and parts were manufactured and assembled. DLA has static and dynamic loading capabilities up to 250 N and 18 N respectively, with a bandwidth su±cient to generate wind disturbances. In this paper, we present various performance requirements of SMT actuators as well as our e®ort to develop a dynamic loading device which can be used to test these actuators. Well before using DLA for meaningful testing of the actuator, the DLA itself have gone through various tests and improvements phases. We have successfully demonstrated that DLA can be used to check the extreme performance of two di®erent SMT actuators, which are expected to track the position/force with a few nanometer accuracy.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dynamic Loading Assembly for Testing Actuators of Segmented Mirror Telescope

Deshmukh

Parihar

Balasubramaniam

et al. 2017

J. Astron. Instrum.

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“…Whereas, the soft actuator uses a voice coil motor that gives high bandwidth actuation. The soft-actuator is relatively simple to implement, relatively inexpensive, lightweight and compact, has very few moving parts, capable of producing large forces, can move through a large mechanical range, and does not require lubrication [6]. The Thirty Meter Telescope (TMT) mirror segment actuator is a soft actuator designed by Jet Propulsion Laboratory (JPL), Pasadena USA [7] [8].…”

Section: Introductionmentioning

confidence: 99%

Precision controller for segmented mirror telescope actuator: Control and tuning

Deshmukh

Parihar

2016

2016 Indian Control Conference (ICC)

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The segmented mirror telescopes are built using small hexagonal mirrors positioned and aligned by the three actuators and six edge sensors per segment to maintain the shape of the primary mirror. The global loop controller does this by sending commands to the actuators to move within few nanometers. These commands are executed at individual actuator locally by a precision controller. The paper describes our effort to develop a precision actuator controller at India TMT Coordination Centre (ITCC) laboratory, Indian Institute of Astrophysics, Bangalore. The actuator controller is implemented around a single board computer called SBC6845. We have also designed and developed a customized actuator drive board which comprises power electronics to handle the voice coil motor (VCM), off-loader as well as snubber stepper motors. In addition to this, drive board also contains a decoder, current sensor and related circuitry to get the position and other feedbacks. The closed loop proportional-integralderivative controller (PID controller) is implemented for position loop using the feedback from linear optical encoder. Another closed loop is introduced around off-loader with the feedback from current sensor. The tuning of position loop is done by two different methods based on Relay Auto tuning and System Identification. By making use of above controller and the optimum gain, several experiments have been conducted to test the performance of prototype soft actuator. The Actuator along with its best tuned controller gives the steady state position error around 2.44nm RMS. At the tracking rate of 300nm/s, we could achieve RMS position error of 4.04nm, which is better than what is required. These results and other details of controller and its tuning are presented.

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