Another Modular Focal Plane: Part 2

1
Another Modular Focal PlanePart 2 FP assembly

• Bruce C. Bigelow
• University of Michigan
• Department of Physics
• 5/17/04

2
Modular focal plane assembly

• Motivations
• install/remove single detectors from front of
  FP
• assemble detectors in modules of 3 x 3
• simplify assembly, integration, and test
• reduce part counts, simplify part design
• simplify part fabrication
• individual module thermal control (Vis vs. IR)
• optimize materials for detector packages (CTE)
• local, discrete control of focal plane surface
  height
• minimize mechanical mass
• minimize thermal time constants
• minimize gravity deflections for ground testing
• maximize resonant frequencies

3
Focal Plane Baseplate

• Requirements
• final focal plane flatness /- 25 microns
• detector temperature stability /- 1K
• high stiffness high first resonance
• This talk
• sample base-plate designs
• two materials examined
• base-plate FEA

4
FP Baseplate design and FEA

• Design of baseplate
• consider Al 7075 and Moly MZT materials
• three mounting points to optics bench via
  bipods
• bipods not included in design or FEA
• cut-outs for detector access

5
Focal plane base-plate - front
Note webs in access holes not in FEA models
6
Focal plane base-plate - back
Base-plate rib structure simpler than FEA model
7
Focal plane fully populated
8
FP Baseplate design and FEA

• FEA
• consider Al 7075 and Moly MZT materials
• Moly plate is 50 mm thick 31 Kg
• Al. plate is 75 mm thick 13 Kg
• sub-array loads modeled with point masses
• static and dynamic analyses completed

9
FP Baseplate FEA
rib thickness red - 6 mm purple - 5 mm cyan
- 6 mm blue - 10 mm
10
FP Baseplate FEA
sub-modules as point masses
1.0 kg
0.5 kg
16 Kg total sub- module mass
11
FP Baseplate FEA Al 7075
(meters)
Gy, Y deflections 1.8 microns max
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FP Baseplate FEA Al 7075
(meters)
Gy, Z deflections 2.1 microns PV
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FP Baseplate FEA Al 7075
(meters)
Gz, Z deflections 4.8 microns
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FP Baseplate FEA Al 7075

• Mode/Freq.
• 227 Hz
• 238 Hz
• 261 Hz
• 325 Hz
• 522 Hz

Dynamic analysis first mode
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FP Baseplate FEA MZT
(meters)
Gy, Y deflections 0.8 microns PV
16
FP Baseplate FEA MZT
(meters)
Gy, Z deflections 1.1 microns PV
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FP Baseplate FEA MZT
(meters)
Gz, Z deflections 4.2 microns PV
18
FP Baseplate FEA MZT

• Mode/Freq.
• 249 Hz
• 258 Hz
• 290 Hz
• 491 Hz
• 654 Hz

Dynamic analysis first mode
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Baseplate FEA Summary
Mat. Mass Thick Gy-Uy Gy-Uz Gz-Uz Fn
Al 7075 13 Kg 75 mm 1.8um 2.1um 4.8um 227 Hz
MZT 31 Kg 50 mm 0.8um 1.1um 4.2um 249 Hz
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FP Modular Baseplate

• Conclusions
• sample designs stiff, high resonances
• flatness specs met in two orientations (and
  probably all)
• consider other substrate materials (Ti, CF)?
• refine interfaces
• spectrograph, BITE sources, cryostat mounts
• thermal links, detect. wiring, baffles, shields
• optimize design for loads and material (ribs,
  thicknesses, etc)