Adaptive secondary mirrors for LBT

1
Adaptive secondary mirrors for LBT
SPIE conf. Adaptive Optical System Technologies
II22-28 Aug 2002 Waikoloa, Hawaii, USA
Presented by A. Riccardi
A. Riccardi1, G. Brusa1,4, P. Salinari1 , D.
Gallieni2, R. Biasi3, M. Andrighettoni3, H. M.
Martin4
1 INAF - Osservatorio Astrofisico di Arcetri,
Firenze, Italy 2 ADS, Lecco, Italy 3
Microgate, Bolzano, Italy 4 Steward
Observatory, Tucson, AZ, U.S.A.
2
Overview

• LBT AS units layout
• New features wrt MMT AS
• Actuators and cabling
• Control electronics and communication
• Capacitive sensor
• Control strategy
• Optical test tower
• Schedule
• Conclusions

3
Involved partners
INAF-Osservatorio Astrofisico di Arcetri
(Italy) Conceptual design. Optical and
Electronic testing, calibration and diagnostic
software development
ADS (Italy) mechanical engineering,mechanical
drawings and assembly
Microgate (Italy) electronics development
and production. DSP software development.
Mirror Lab-Steward Observatory (USA) Optical
components production (aspheric shell and
reference plate)
4
Adaptive secondary in LBT
2x8.4m mirrors
5
From MMT336 to LBT672
LBT Gregorian672 actuators
The LBT672 design is based on the experience
gained during the extensive tests in lab and at
the telescope of MMT336.
Both mechanics and electronics has been revised
improving performances, stability, reliability,
maintenance with respect to MMT336. (see posters
4839-90 D. Gallieni, 4839-91 R. Biasi)
See 4839-19 F. Wildi 4839-85 G. Brusa
911mm
6
LBT672 layout
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LBT672 actuator layout
Tested onP1
8
New cabling
MMT actuator andits cable as one unit
(See 4839-90 D. Gallieni)
9
New Control Electronic/Comm.
Total computational power 60 Gmac/s (32bit
fp) Real-time reconstructor on-boardWFS 30x30
gt 34-47ms (z-m) Slope comm time 20ms
Communication Board
Communication Board



Communication Board

Communication Board

Communication Board

Communication Board
(1x backplane)
(1x backplane)
(1x backplane)
(1x backplane)
(1x backplane)
(1x backplane)
Reference Signal
Reference Signal
Reference Signal
Reference Signal
Reference Signal
Reference Signal
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
DSP control Board (14x backplane)
48V, 35 A
Power
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
Liquid cooled crates,
each comprehending 2 backplanes (3x)
3 cooled electronics boxes2 crates/box 84 custom
DSP boards 4 DSP/board - 8 acts/board 32-bit
floating-point 180Mmac/s (MMT 16-bit integer
40Mmac/s)
Distribution boards
Actuators
Coil
Gap
Thin mirror
Reference signal
(See 4839-91 R. Biasi)
10
New capacitive sensor
DSP board
ADC
80kHz
80ksamp/s
40kHz
Pos at 40kHz
MMT case
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New control implementation
DCommand vectorfrom rec.
Feed-forward force
56kHz_at_-3dB
?FikDck
?
12.5ms
40kHz
CurrentDriverand coil
Dci(t)

G
Delay
DAC


?

-
-
e(t)
p(t)
MirrorShell
ADC
LIN
CapacitiveSensor


Control loop of i-th actuator
27kHz_at_-3dB
40kHzeffective
n(t)
MMT air trapped in the 50mm gap provides viscous
damping it limits the effective
positioning range at 25-30mm
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Preliminary PV control test
P36 prototype Test Gap100mm
Settling time gt8ms
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Performances
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Optical test tower in Arcetri
15m tower Thermalized otical path Test AdSecAO
modulein closed loop (see 4839-20 S.
Esposito) Test calibrationprocedures
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Schedule

• Late 2002 P45 prototype
• Spring 2003 starting of LBT672 assembly
• Late 2003-Spring 2004 tests on LBT672
  with AO module
• Mid 2004 LBT672 packed and sent to the
  telescope

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Conclusions

• Both mechanics and electronics has been revised
  improving performances, stability, reliability,
  maintenance with respect to MMT336.
• The improvement in computational power of the
  control electronics allows to implement the real
  time reconstructor on-board.
• The introduction of the electronic damping allows
  to use the voice-coil large stroke without
  bandwidth reduction (100mm with 0.5ms settling
  time)
• The solar tower in Arcetri will host the optical
  test facility for AS calibration and test of CL
  operations with the 1st light AO module.
• Part of the electronics and mechanics has been
  already tested on P1 prototype
• P45 prototype will be operative late 2002