K-D-PR-1100-009
Fabrication and testing of KGMT Fabrication and testing of KGMT FSM prototypeFSM prototype
Oct. 4. 2010
Ho-Soon Yang, Hak-Yong Kihm, Il-Kwon Moon, Jae-Bong Song, Yun-Woo Lee
Korea Research Institute of Standards and Science, Korea
Young-Soo KimKorea Astronomy & Space Science Institute, Korea
Contents
Objective of project Recent experiences in KRISS Manufacturing flow diagram Optical testing Working cell design Future works
2
Objective
3
Technology development related to manufacturing of FSM for
GMT project in advance
For FSMP
Use a model very close to FSM FSM prototype in KGMT project
Fabrication of FSMP with its own working cell designed by KRISS
Optical testing of FSMP after assembly with a cell (very close to real
FSM cell)
4
Recent experiences @ KRISS
800 mm lightweighted mirror for space application (1/2)
Gravity
Quilting (30 g/cm2)
And other environmental effects …
5
Recent experiences @ KRISS
800 mm lightweighted mirror for space application (2/2) - Measurement of wavefront error with two different methods : CGH (computer generated hologram) and conventional null lenses
CGHConventional null lens
/30 rms
6
1 m off-axis paraboloid for collimator (1/2) - Focal length = 6 m - Distance between the center of OAP and optical axis = 700 mm
Recent experiences @ KRISS
Flat mirror
Interferometer
OAP
7
1 m off-axis paraboloid for collimator (2/2)
Reference flat Interferometer
OAP mirror
Alignment telescope
Recent experiences @ KRISS
8
Fabrication facilities in KRISS
Rotating table with aspheric surface under test
Measuring tower with null interferometer
2 m CNC machine
1 m polishing machine
2 m coating chamberAssembly room
0.6 m polishing machine & testing tower
2 m polishing machine
9
Manufacturing flow diagram
Curve Curve generationgeneration
Curve Curve generationgeneration
Chemical Chemical EtchingEtching
Chemical Chemical EtchingEtching
Assembly Assembly with cellwith cell
Assembly Assembly with cellwith cell FATFATFATFAT
10% larger size 10% larger size Mirror blank Mirror blank procurementprocurement
10% larger size 10% larger size Mirror blank Mirror blank procurementprocurement
LightweightingLightweightingLightweightingLightweighting
PolishingPolishingPolishingPolishing GrindingGrindingGrindingGrinding InspectionInspectionInspectionInspection
InspectionInspectionInspectionInspection
Figuring Figuring (98%)(98%)
Figuring Figuring (98%)(98%)
InspectionInspectionInspectionInspection
Rounding to Rounding to target target
dimension dimension
Rounding to Rounding to target target
dimension dimension
Final Final figuring figuring
Final Final figuring figuring
10
SpherometerProfilometer
~ mm
Grinding
ProfilometerInterferometer
~ μm
Polishing
Interferometer with CGH
~ nm
Figuring
Scheme of Optical testing
Efficient testing process is a key for successful fabrication of mirror
11
KRISS profilometer
Measurement accuracy ~ 1 um Compensation of measurement errors of probe system using a high quality reference mirror
Reference mirror
150 mm
CGH layout :(Line spacing : ~ 20 um)
Adjustment between interferometer and CGH
Test configuration of FSMP off-axis segment (off-axis type CGH )
Interferometric testing using CGH
12
3
4
Adjustment I between CGH and FSMP segment
Adjustment II between CGH and FSMP segment
CGH alignment
12
3
4
15
Optical testing during fabrication Optical testing after assembly with FSMP cell
Testing configuration
Concept for working cell design
Minimization of print through Load cell on the back plate of the mirror 24 axial support location Polishing pressure at the pocket of mirror with 0.1 psi
FE Model of M2
Thin shell elements Material : Zerodur Diameter : 1064 mm Thickness : 140 mm Hole size : 100 mm Mass : 94 kg Face sheet : 20 mm Back plate : 14 mm Rib : 5 mm Web : 10 mm
Top view
bottom view
Axial support
x
y
support Radius (mm) Force (N)
Ring 1 157.5 21
Ring 2 242.5 33
Ring 3 367.5 42
Ring 4 424.4 58
Support locations
Print through
Gravity z
Displacement PV 165 nm
Surface error Without correction
PV 166 nmRMS 48 nm
Surface error With correction
PV 50 nmRMS 9 nm
Print through
Gravity z
10-2
10-1
100
101
102
101
102
103
separation (cm)
rms
wav
efro
nt e
rror
(nm
)
Structure function of M2
M2 structure function
Surface error
Quilting effect from polishing pressure of 0.1 psi
Surface error Without correction
PV 110 nmRMS 31 nm
Surface error With correction
PV 35 nmRMS 6 nm
Displacement PV 110 nm
Surface error
Polishing pressure 0.1 psi
10-2
10-1
100
101
102
101
102
103
separation (cm)
rms
wav
efro
nt e
rror
(nm
)
Structure function of M2
M2 structure function
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