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Adaptive secondary mirrors for LBT

SPIE conf. Adaptive Optical System Technologies II 22-28 Aug 2002 Waikoloa, Hawaii, USA. Adaptive secondary mirrors for LBT. Presented by A. Riccardi. A. Riccardi 1 , G. Brusa 1,4 , P. Salinari 1 , D. Gallieni 2 , R. Biasi 3 , M. Andrighettoni 3 , H. M. Martin 4.

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Adaptive secondary mirrors for LBT

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  1. SPIE conf. Adaptive Optical System Technologies II22-28 Aug 2002 Waikoloa, Hawaii, USA Adaptive secondary mirrors for LBT 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. Osservatorio di Arcetri 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. See 4837-15, J. Hill Each AdSec: 672 actuators 911mm diam. Adaptive secondary in LBT 2x8.4m mirrors

  5. MMT: Cassegrain336 actuators 642mm 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. Hexapod Interface flange andstructural support 3 cooled electronicsboxes Fixed hexapod Cold-plate andactuator support Astatic levers 50mm thick Zerodurreference-plate 1.6mm thick deformableZerodur shell LBT672 layout

  7. Cooling pipes 0.2W/act 0.5N/W Dt=0.26K Soft gaskets to seal the gapfrom dust contamination LBT672 actuator layout Tested onP1

  8. LBT MMT: cable crowd LBT: cable decoupledfrom the actuator usingdistribution boards asactuato-to-cable interface New cabling MMT: actuator andits cable as one unit (See 4839-90 D. Gallieni)

  9. To the AOsupervisor Diagnostic communication link Gigabit Ethernet Switch 400Mbit/s Daisy chain connection Real timecommlink 2.9 Gbit/s New Control Electronic/Comm. Total computational power: 60 Gmac/s (32bit fp) Real-time reconstructor on-boardWFS: 30x30 => 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. DSP board Reference capacitor(solid state) OUT + 1 Gap Samplehere OUT gap Referencesignal Differentialamplifier 160kHz OUT - Capacitivesensorboard LBT case Samplehere LBT CapSens tested on P1 prototype 90kHz@-3dB New capacitive sensor DSP board ADC 80ksamp/s 80kHz 40kHz Pos at 40kHz MMT case

  11. <12.5ms 80kHz - v(t) v(t) K d/dt K d/dt 80kHz 90kHz @-3dB LBT: damping provided by velocity loop (electronic damping) bandwidth no more dependent on gap (i.e. pos. range) New control implementation DCommand vectorfrom rec. Feed-forward force 56kHz@-3dB FikDck  12.5ms 40kHz CurrentDriverand coil Dci(t) + Delay DAC G + +  + - - e(t) p(t) MirrorShell LIN ADC CapacitiveSensor + + Control loop of i-th actuator 40kHzeffective 27kHz@-3dB n(t) MMT: air trapped in the 50mm gap provides viscous damping it limits the effective positioning range at 25-30mm

  12. Settling time: 0.5ms Preliminary PV control test P36 prototype Test Gap=100mm Settling time: >8ms

  13. Performances

  14. Optical test tower in Arcetri 15m tower Thermalized otical path Test AdSec+AO modulein closed loop (see 4839-20 S. Esposito) Test calibrationprocedures

  15. 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

  16. 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

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