1 3/24/05bruce c. bigelow -- um physics hexapod detector mounts b. c. bigelow, um physics 3/24/05

13/24/05 Bruce C. Bigelow -- UM Physics

Hexapod Detector MountsHexapod Detector Mounts

B. C. Bigelow, UM Physics

3/24/05

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

Detector space frame! – but fabrication unfriendly…

A fabrication-friendly version…

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?

Arbitrary mount height of 12mm – can be lower

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

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

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)

Gz, Z-axis deflections – 1.4 microns max

Deflections in meters, 1.4 microns max.

Stress in Pa, 26 MPa max., (point loads)

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

FEA - dynamicFEA - dynamic

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)

Elements

Stress in Pa, 14.8 MPa max.

(point loads)

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)

Boundary cond.

Temp variations (K) – SiC/TZM

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

Detector mount taxonomyDetector mount taxonomy

Yale flex LBL flex

UM flex UM hexapod

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

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

1 3/24/05bruce c. bigelow -- um physics hexapod detector mounts b. c. bigelow, um physics 3/24/05

um physics32405bruce

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