LBT672 opto-electro-mechanical specification overview

Presented by A. Riccardi

A. Riccardi, G. Brusa, R. Biasi, D. Gallieni

FLAO system external review, Florence, 30/31 March 2009

Milestone “Flattened secondary shell” LBTO-INAF contract

Milestone “Ready for optical test” LBTO-Microgate contract

Structure of OEM test

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• Electro-Mechanical acceptance test– Phase I – Safety mechanism test– Phase II – EM performance evaluation test– Phase III – Handling test and Hub-integrated

performance verification

• Optical Acceptance test– Phase IV – Mirror flattening performance and

stability

Successfully passed for LBT672a unit

On progress for LBT672a unit

The LBT672 system and safety mechanism test (Phase I)

FLAO system external review, Florence, 30/31 March 2009 3Spider-arm cabinet

M2 unit in Hub

• Three levels of safety protection– Hardware level

• Hardware over-current protection

• TSS functionality (0.25N/act -> 80km/h wind)

– Firmware level• Check of modal commands, actuator position commands

or force commands (skip command frame in case too large)

• Check of capacitive sensor reading (reset shell in case reading > 120m)

– High-level software• High temperature trapping (power switch-off)

• Dew/freeze-point (power switch-off)

• Broken communication line (self-power-off in case of broken communication with remote switch, shell reset in all the other cases)

Phase II – EM performance evaluation

• Actuator position sensor noise:– Base spec: <10nm rms @ 70kHZ ( 1.2nm rms @ 1 kHz)– Goal spec: <3nm rms @ 70kHz (=P45)

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Noise PatternNoise as a function of local gap

in different elevation angles

All acts in spec93% of acts match goal

Phase II – EM performance evaluation

• Modal step response:– Base spec: <1.5ms (1.0ms≤WFS integ. time), overshoot <10%– Goal spec: <0.7ms, overshoot <10% (=P45)

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All modes in spec50% of modes match goal

Settling time as function of mirror mode Overshoot as function of mirror mode

Phase II – EM performance evaluation

• Turbulence tracking error (0.65as seeing, vwind=20m/s):

– Base spec: <50nm (<delay error w 1.5ms)

– Goal spec: <28nm (≈0.5*delay error w 1.5ms)

– Peak force: < 0.8N (=80% of max force; 20% is allocated for flattening)

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Base spec with 360 modesGoal spec with 600 modes

Residual WFE as function of used modes Peak force as function of used modes

Phase II – EM performance evaluation

• Actuator position sensor stability with temperature

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Temperature of cooling fluidas function of time

Ave force per ring of actsto keep the position

on command

Requirement to temperature stability of telescope cooling:Ripples < 0.2°C/min

1g=0.07N

Phase II – EM performance evaluation• Chopping performance:

– From LBTI requests:• Chop throw: ±2.5 on-sky arcsec with AO capabilities both beams

• Accuracy of throw: 0.1 on-sky arcsec

• Settling time to 95% of step command: 15ms

• Direction: elevation

FLAO system external review, Florence, 30/31 March 2009 8Time history of performed tilt (on-sky arcsec)

In specification

AO step responseswith Settling < 1.5ms

Ex. modal step response for AO operationChopping steps, beam A and B

Phase III - Handling test and Hub-integrated performance verification

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Phase IV – Mirror flattening performance (@Arcetri)

• Shell figuring qualification:– Residual flattening with peak force<0.2N (20% of max force)

• Base spec: <65nm rms WFE (≈fitting error at 0.65as seeing)

• Goal spec: <30nm rms WFE (<1/2 fitting error at 0.65as seeing)

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Goal specification matched:WFE 25nm rmswith <0.2N peak force

Phase IV – Mirror flattening stability

• Flattening command stability with time and temp– F0, F1, F2 flattening commands calibrated using optical

feedback (interferom.)at T0=Tamb, T1=T0-10°C, T2=T0-20°C

– Application of flattening command without optical feedback (supposing no AO, nor active optics):

• Base specification: <200nm rms (=1/3 of atmospheric turbulence WFE with serendipity seeing: 0.23 arcsec, L0=20m)

• Goal specification: <100nm rms

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IN PROGRESS: preliminary results in specification (<150nm rms)

END OF PRESENTATION

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Questions on FLAO_02

• Q: “Inspection of TS#3 magnets gluing”; what are the possible outcome of this test? What is to be checked?

• A: The check is performed in Arcetri after the EM acceptance test in MG-ADS and the transport of shell from MG to Arcetri. The optical side of the shell is not yet coated and it is protected with PreCote film. In Arcetri the protecting film is removed for silver coating and the gluing spots between magnets and glass are visible. We check for glue integrity (no detachment of glue from glass)

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Questions on FLAO_02

• Q: in which simulated seeing condition is the test of power consumption conducted?

• A: median seeing: 0.65as with Vwind=20m/s

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