Hexapod Detector Mounts

1. Hexapod Detector Mounts B. C. Bigelow, UM Physics 3/24/05 Bruce C. Bigelow -- UM Physics

2. Hexapod Detector Mounts Motivations: • Provide a common mount design for Vis and IR detectors • Minimize detector package SS thermal stresses • Minimize detector package SS temperature gradients • Accommodate various detector package materials (Invar, TZM) • Accommodate various FPA baseplate materials (TZM, SiC, ?) • Accommodate local detector PCBs, connectors, heaters, etc. • Minimize weight, maximize first resonance Bruce C. Bigelow -- UM Physics

3. Hexapod Detector Mounts Detector space frame! – but fabrication unfriendly… Bruce C. Bigelow -- UM Physics

4. Hexapod Detector Mounts A fabrication-friendly version… Bruce C. Bigelow -- UM Physics

5. Hexapod Detector Mounts Fabrication options for hexapod: • Fabrication method may depend on hexapod material choice • Powder metallurgy methods (HIP, laser sintering) • Abrasive water-jet cutting • Laser cutting • Plunging and/or wire EDM • Stress-relieve rough blanks prior to cutting • Polish blanks flat and parallel prior to cutting • Final grind/polish mounting pads to spec. after cutting • Other? Bruce C. Bigelow -- UM Physics

6. Hexapod Detector Mounts Bruce C. Bigelow -- UM Physics

7. Hexapod Detector Mounts Arbitrary mount height of 12mm – can be lower Bruce C. Bigelow -- UM Physics

8. Hexapod Detector Mounts Bruce C. Bigelow -- UM Physics

9. Hexapod Detector Mounts Bruce C. Bigelow -- UM Physics

10. Hexapod Detector Mounts Bruce C. Bigelow -- UM Physics

11. Finite Element Analyses Quantify performance via FE analyses : • Hexapod flexures are 1mm wide x 3mm high (all cases) • Hexapod material is TZM (Invar another option) • Static analyses: 100g deflections and stresses • Dynamic analyses: first 10 frequencies and mode shapes • Steady-state thermal: stress for -150K temp excursions • Steady-state thermal: heat flow and temperature gradients • Summary follows individual results Bruce C. Bigelow -- UM Physics

12. Focal Plane Material Properties Room temp. material properties Bruce C. Bigelow -- UM Physics

13. FEA - static Static FEA: • 100g accelerations, Gx, Gy, Gz • Det. package base models only, no AlN, MCT, epoxy, etc. • Two material combinations – Invar/TZM, and TZM/TZM • Simplified model of hexapod mount (no “pads”) • Max deflections: 1.5 - 1.9 microns • Max stresses: 20 - 26 MPa (Invar/TZM) • Invar yield = 300 MPa • TZM yield = 860 Mpa • Low stress in package material - max. 20 Mpa (point load) Bruce C. Bigelow -- UM Physics

14. FEA - static Deflections in meters, 1.4 microns max. Gz, Z-axis deflections – 1.4 microns max Bruce C. Bigelow -- UM Physics

15. FEA - static Stress in Pa, 26 MPa max., (point loads) Gz, Z-axis deflections – 1.4 microns max Bruce C. Bigelow -- UM Physics

16. FEA - dynamic Dynamic FEA: • Det. package base models only, no AlN, Si, MCT, epoxy, etc. • Two material combinations – Invar/TZM, and TZM/TZM • Simplified model of TZM hexapod mount • First resonances: • TZM/invar – 3000 Hz • TZM/TZM – 3053 Hz Bruce C. Bigelow -- UM Physics

17. FEA - dynamic Gz, Z-axis deflections – 1.4 microns max Bruce C. Bigelow -- UM Physics

18. FEA – steady state thermal Steady-state thermal stress: • Minus 150 K temperature excursion • Baseplate, hexapod mount, and package base • Four material combinations for baseplate and package: • TZM/Invar, TZM/TZM, SiC/TZM, SiC/Invar • Simplified model of hexapod mount (no “pads”) • Deflections: 6.9 – 8.7 microns (TZM/TZM, TZM/Invar) • Deflections: 7.9 - 9.7 microns (SiC/Invar, SiC/TZM) • Pkg stresses: 2.3 Mpa (TZM/Invar) • Pkg stresses: 1.1 - 1.7 Mpa (SiC/TZM, SiC/Invar) Bruce C. Bigelow -- UM Physics

19. FEA – steady state thermal Elements Gz, Z-axis deflections – 1.4 microns max Bruce C. Bigelow -- UM Physics

20. FEA – steady state thermal Stress in Pa, 14.8 MPa max. (point loads) Bruce C. Bigelow -- UM Physics

21. FEA – steady state thermal Steady-state heat flow: • Baseplate, hexapod mount, and package base • 200 mW heat load imposed on top surface of package • Baseplate – back side sunk to a cold source at 140 K • Four material combinations for baseplate and package: • TZM/Invar, TZM/TZM, SiC/TZM, SiC/Invar • Simplified model of TZM hexapod mount (no “pads”) • Max. temp variation: 0.56 K (TZM/Invar) • Min. temp variation: 0.05 K (SiC/TZM and TZM/TZM) • Min final temp: 142.3 K (SiC/TZM) • Max final temp: 144.6 K (TZM/Invar) Bruce C. Bigelow -- UM Physics

22. FEA – steady state thermal Boundary cond. Bruce C. Bigelow -- UM Physics

23. FEA – steady state thermal Temp variations (K) – SiC/TZM Bruce C. Bigelow -- UM Physics

24. FEA summary deflections, u, in microns Bruce C. Bigelow -- UM Physics

25. Detector mount taxonomy Yale flex LBL flex UM flex UM hexapod Bruce C. Bigelow -- UM Physics

26. Detector mount comparison Bruce C. Bigelow -- UM Physics

27. Hexapod Detector Mounts Conclusions: • 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 • Hexapod provides “optimal” support for detectors: • Minimum mass, maximum stiffness solution • Very high first resonance – 3000 Hz or higher • Hexapod mount is readily fabricable by standard methods • Hexapod performance demonstrated via FE analysis Bruce C. Bigelow -- UM Physics