13/24/05 Bruce C. Bigelow -- UM Physics
Hexapod Detector MountsHexapod Detector Mounts
B. C. Bigelow, UM Physics
3/24/05
23/24/05 Bruce C. Bigelow -- UM Physics
Hexapod Detector MountsHexapod Detector Mounts
Motivations:
1. Provide a common mount design for Vis and IR detectors
2. Minimize detector package SS thermal stresses
3. Minimize detector package SS temperature gradients
4. Accommodate various detector package materials (Invar, TZM)
5. Accommodate various FPA baseplate materials (TZM, SiC, ?)
6. Accommodate local detector PCBs, connectors, heaters, etc.
7. Minimize weight, maximize first resonance
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Hexapod Detector MountsHexapod Detector Mounts
Detector space frame! – but fabrication unfriendly…
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Hexapod Detector MountsHexapod Detector Mounts
A fabrication-friendly version…
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Hexapod Detector MountsHexapod Detector Mounts
Fabrication options for hexapod:
1. Fabrication method may depend on hexapod material choice
2. Powder metallurgy methods (HIP, laser sintering)
3. Abrasive water-jet cutting
4. Laser cutting
5. Plunging and/or wire EDM
6. Stress-relieve rough blanks prior to cutting
7. Polish blanks flat and parallel prior to cutting
8. Final grind/polish mounting pads to spec. after cutting
9. Other?
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Hexapod Detector MountsHexapod Detector Mounts
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Hexapod Detector MountsHexapod Detector Mounts
Arbitrary mount height of 12mm – can be lower
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Hexapod Detector MountsHexapod Detector Mounts
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Hexapod Detector MountsHexapod Detector Mounts
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Hexapod Detector MountsHexapod Detector Mounts
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Finite Element AnalysesFinite Element Analyses
Quantify performance via FE analyses :
1. Hexapod flexures are 1mm wide x 3mm high (all cases)
2. Hexapod material is TZM (Invar another option)
3. Static analyses: 100g deflections and stresses
4. Dynamic analyses: first 10 frequencies and mode shapes
5. Steady-state thermal: stress for -150K temp excursions
6. Steady-state thermal: heat flow and temperature gradients
7. Summary follows individual results
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Focal Plane Material PropertiesFocal Plane Material Properties
Material
Properties
TZM (Moly)
Invar 36 SiC (CVD)
E (GPa) 325.0 147.0 466.0
Yield (MPa) 415.0 300.0 470.0
Density (kg/m^3) 10160 8050 3210
CTE (PPM/K) 4.90 1.26 2.20
K (W/mK) 138 11.1 300
Room temp. material properties
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FEA - staticFEA - static
Static FEA:
1. 100g accelerations, Gx, Gy, Gz
2. Det. package base models only, no AlN, MCT, epoxy, etc.
3. Two material combinations – Invar/TZM, and TZM/TZM
4. Simplified model of hexapod mount (no “pads”)
5. Max deflections: 1.5 - 1.9 microns
6. Max stresses: 20 - 26 MPa (Invar/TZM)
• Invar yield = 300 MPa
• TZM yield = 860 Mpa
7. Low stress in package material - max. 20 Mpa (point load)
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FEA - staticFEA - static
Gz, Z-axis deflections – 1.4 microns max
Deflections in meters, 1.4 microns max.
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FEA - staticFEA - static
Gz, Z-axis deflections – 1.4 microns max
Stress in Pa, 26 MPa max., (point loads)
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FEA - dynamicFEA - dynamic
Dynamic FEA:
1. Det. package base models only, no AlN, Si, MCT, epoxy, etc.
2. Two material combinations – Invar/TZM, and TZM/TZM
3. Simplified model of TZM hexapod mount
4. First resonances:
• TZM/invar – 3000 Hz
• TZM/TZM – 3053 Hz
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FEA - dynamicFEA - dynamic
Gz, Z-axis deflections – 1.4 microns max
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FEA – steady state thermalFEA – steady state thermal
Steady-state thermal stress:
1. Minus 150 K temperature excursion
2. Baseplate, hexapod mount, and package base
3. Four material combinations for baseplate and package:
• TZM/Invar, TZM/TZM, SiC/TZM, SiC/Invar
4. Simplified model of hexapod mount (no “pads”)
5. Deflections: 6.9 – 8.7 microns (TZM/TZM, TZM/Invar)
6. Deflections: 7.9 - 9.7 microns (SiC/Invar, SiC/TZM)
7. Pkg stresses: 2.3 Mpa (TZM/Invar)
8. Pkg stresses: 1.1 - 1.7 Mpa (SiC/TZM, SiC/Invar)
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FEA – steady state thermalFEA – steady state thermal
Gz, Z-axis deflections – 1.4 microns max
Elements
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FEA – steady state thermalFEA – steady state thermal
Stress in Pa, 14.8 MPa max.
(point loads)
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FEA – steady state thermalFEA – steady state thermal
Steady-state heat flow:
1. Baseplate, hexapod mount, and package base
2. 200 mW heat load imposed on top surface of package
3. Baseplate – back side sunk to a cold source at 140 K
4. Four material combinations for baseplate and package:
• TZM/Invar, TZM/TZM, SiC/TZM, SiC/Invar
5. Simplified model of TZM hexapod mount (no “pads”)
6. Max. temp variation: 0.56 K (TZM/Invar)
7. Min. temp variation: 0.05 K (SiC/TZM and TZM/TZM)
8. Min final temp: 142.3 K (SiC/TZM)
9. Max final temp: 144.6 K (TZM/Invar)
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FEA – steady state thermalFEA – steady state thermal
Boundary cond.
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FEA – steady state thermalFEA – steady state thermal
Temp variations (K) – SiC/TZM
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FEA summaryFEA summary
Materials Pkg, 100g, X,Y,Z Fn -150K hex pkg D T Tf
Base Pkg ux uy uz s,MPa Hz uz s,Mpa s,MPa K K
TZM Inv. 1.9 1.9 1.5 20.8 3000 8.7 20.3 2.3 0.56 144.6
TZM TZM 1.9 1.9 1.4 26.1 3053 6.9 -- -- 0.05 142.4
SiC Inv. -- -- -- -- -- 9.7 28 1.7 0.56 144.5
SiC TZM -- -- -- -- -- 7.9 14.8 1.1 0.05 142.3
deflections, u, in microns
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Detector mount taxonomyDetector mount taxonomy
Yale flex LBL flex
UM flex UM hexapod
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Detector mount comparisonDetector mount comparison
Pkg thermal stress, -150K
Pkg temp gradient
First resonance
Design: MPa K Hz
Yale flex 41 0.2 1508
LBL flex 31 0.1 988
UM flex 5.6 0.1 3216
UM hexapod 21 0.05 3000
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Hexapod Detector MountsHexapod Detector Mounts
Conclusions:
1. Hexapod mount kinematically connects detectors to focal plane:• Low thermal stress for -150 K temperature change
• Large conduction cross-section minimizes thermal gradients
• Common mount design works for both NIR and VIS detector packages
• Very low thermal stresses in base plate, mount, and packages
2. Hexapod provides “optimal” support for detectors:• Minimum mass, maximum stiffness solution
• Very high first resonance – 3000 Hz or higher
3. Hexapod mount is readily fabricable by standard methods
4. Hexapod performance demonstrated via FE analysis