High bandwidth fast steering mirror

Transcription

1 High bandwidth fast steering mirror Presenter Francisc M. Tapos Authors:Francisc M. Tapos a, Derek J. Edinger a, Timothy R. Hilby a, Melvin S. Ni a, Buck C. Holmes b, David M. Stubbs a a Lockheed Martin Space Systems Company, 3251 Hanover Street, Palo Alto, CA, ; b Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA,

2 Application and Requirements Fixed mirror From source FSM Beamsplitter The FSM is the optical path-length adjustment mirror in a Michelson interferometer setup. To detector DOF Requirements tip, tilt, piston Steady state piston error Steady state tip/tilt error Settling time Maximum range Optic diameter Closed-loop bandwidth Surface distortion Ambient pressure Ambient temperature 25ºC 0.1 nm 4 e-9 rad ~1 ms 10 micron 50.8 mm ~1 khz < 1 nm 760 Torr 2

3 Design features Mirror size: 50.8mm O.D., 12.7mm THK. Mirror CA: 25.4mm Mirror surface quality: λ/100 Mirror mount: monolithic, stress free bonding Manual coarse adjustment Closed-loop fine adjustment: PZT actuators Gimbaled tip/tilt motion about the mirror surface center Kinematic mount of the moving mass Moving mass CG on the gimbal point Moving mass preloading: helical extension springs Adjustable preloading Sturdy mounting structure 3

4 Moving parts Manual adjuster tip Manual adjuster Mirror Mirror mount Mirror reflecting surface 4

5 Monolithic mirror mount Ring shaped mount body Bipods Bonding pad knife-like edge Tack bond hole Manual adjuster bushing inset 5

6 Manual coarse adjuster Mirror mount Locking screw.25-80tpi Adjustment screw Ball tip Adjustment screw bushing 6

7 Fixed parts Actuator mounting boss Actuator Actuator mounting screw Bracket Gusset Mounting screw clearance hole Bracket Potting hole Actuator with custom vee groove attachment Boss 7

8 Off the shelf actuator specifications Open-loop 0 to 100V Closed-loop travel * Integrated feedback sensor Closed-loop / open-loop ** resolution < ** Static Large-signal stiffness* Push/pull force capacity Torque limit (at tip) Electrical capacitance Dynamic operating current coefficient (DOCC) Unloaded resonant frequency (f 0 ) Standard operating temperature range Voltage connection Sensor connection Weight without cables Material case / end pieces Length L Recommended Amplifier/Controller (codes explained p.6-46 Closed- Loop P to +80 N-S C, D, G, H * Closed-loop models are supplied with calibration data sheets; **Resolution of PZT actuators is not limited by friction or stiction. Noise equivalent motion with E-503 amplifier; ***Dynamic small-signal stiffness 30% higher SGS 0.3 / / VL L Units µm ±20% µm nm N/µm ±20% N Nm µf ±20% µa/ (Hz x µm) khz ±20% C G ±5% Mm ±0.3 8

9 Interface parts Jam nuts Spring hook Extension spring Dowel pin Vee grooves (actuators) Mirror assembly Bracket assembly Balls (adjusters) 9

10 Analysis Requirements 100g static design load (should conservatively envelope loads from random vibration). Minimum 1000 Hz piston and tip/tilt modes required. Minimum 2000 Hz piston and tip/tilt modes goal. Mirror surface distortions should be much less than 0.84 nm RMS. 38 lb preload per spring required to prevent gapping. +/- 5 F temperature variation. Safety factor of 2.0 for qualification by analysis. 10

11 Finite Element Model Bipods Fused silica optic Pre and Post Processed in I-DEAS 9 Solved in NX/NASTRAN Total Elastic Elements: 99 Beam Elements (for bipods) 1279 Shell Elements (for bipod pads and data recovery on mirror surface) Solid Elements Nodes 6AL-4V Titanium ring 11

12 Modal analysis Effective Mass Mode Frequency (Hz) ux uy uz rx ry rz Description % 71% 0% 5% 0% 0% Decenter % 5% 0% 0% 5% 0% Decenter % 0% 64% 0% 0% 0% Piston % 0% 0% 14% 13% 0% Tip/Tilt I-DEAS Visualizer Display 1 Fem1 SUB ID=1,MODE=1,F= HZ, ->MODE SHAP TITLE = NATURAL FEQUENCY DISPLACEMENT Magnitude Unaveraged Top shell Min: 2.63E-01 in Max: 5.18E+01 in SUB ID=1,MODE=1,F= HZ, ->MODE SHAP TITLE = NATURAL FEQUENCY DISPLACEMENT XYZ Magnitude Min: 2.63E-01 in Max: 5.18E+01 in Part Coordinate System Frequency: 1.58E+03 Hz in 5.18E E E E E+01 I-DEAS Visualizer Display 1 Fem1 SUB ID=1,MODE=3,F= HZ, ->MODE SHAP TITLE = NATURAL FEQUENCY DISPLACEMENT Magnitude Unaveraged Top shell Min: 1.55E-00 in Max: 5.57E+01 in SUB ID=1,MODE=3,F= HZ, ->MODE SHAP TITLE = NATURAL FEQUENCY DISPLACEMENT XYZ Magnitude Min: 1.55E-00 in Max: 5.57E+01 in Part CoordinateSystem Frequency: 2.45E+03 Hz in 5.57E E E E E+01 I-DEAS Visualizer Display 1 Fem1 SUB ID=1,MODE=4,F= HZ, ->MODE SHAP TITLE = NATURAL FEQUENCY DISPLACEMENT Magnitude Unaveraged Top shell Min: 3.93E-03 in Max: 1.10E+02in SUB ID=1,MODE=4,F= HZ, ->MODE SHAP TITLE = NATURAL FEQUENCY DISPLACEMENT XYZ Magnitude Min: 3.93E-03 in Max: 1.10E+02in Part Coordinate Sys tem Frequency: 3.90E+03 Hz in 1.10E E E E E E E E E E E E E E E E E E E E E E E-03 Mode 1 (1580 Hz) - Decenter Mode 3 (2450 Hz) - Piston Mode 4 (3900 Hz) Tip/Tilt 12

13 Surface distortion I-DEAS Visualizer Display 1 Fem1 IMPORTED DISPLACEMENT DATA Filename DISPLACEMENT Z Unaveraged Top shell Min: -4.95E-11 in Max: 5.07E-11 in CS3 5.07E E E E E-11 in I-DEAS Visualizer Display 1 Fem1 3 - IMPORTED DISPLACEMENT DATA Filename DISPLACEMENT Z Unaveraged Top shell Min: -2.59E-10 in Max: 1.74E-10 in CS3 in 1.74E E E E E-13 Load Case Surface Distortion (nm RMS) 5.88E E E E-11 1g sag in X E E E E E E-10 1g sag in Y E E-10 Clear Aperture Surface Distortion (nm) 1g X Clear Aperture Surface Distortion (nm) 1g Z 1g sag in Z 0.11 I-DEAS Visualizer Display 1 Fem1 5 IMPORTED DISPLACEMENT DATA Filename DISPLACEMENT Z Unaveraged Top shell Min: -2.42E-10 in Max: 1.97E+10 in CS3 in 1.97E E E E E-11 I-DEAS Visualizer Display 1 Fem1 4 - IMPORTED DISPLACEMENT DATA Filename DISPLACEMENT Z Unaveraged Top shell Min: -1.78E-10 in Max: 8.08E-11 in CS3 in 8.08E E E E E lb preload at each spring E E E E E E E E-10 5F temperature delta E E E E-10 Clear Aperture Surface Distortion (nm) - 38 lb Preload Clear Aperture Surface Distortion (nm) 5 deg F Temperature Delta 13

14 Stress Analysis lbf/in 2 I- DEAS Visualizer Display E+04 Fem1 SUB ID=5,LOAD ID=1, ->STRESS TITLE = 1G INERTIAL LOAD 1.10E+04 STRESS Von Mises Unaveraged Top shell Beam stress: Von Mises, maximum point Min: 3.08E+01 lbf/in 2 Max: 1.23E+01 lbf/in E+03 CS3 8.59E E E E E E E+03 Margin of Safety = [ Allowable Load / (Safety Factor x Working Load) ] 1 Margin of safety > 0 required. Margin of safety summary: 3.08E+01 Component Material Failure Mode Allowable Working Load Safety Factor Margin of Safety Bipod 6-AL-4V Titanium Compression 120 ksi 2 ksi Bipod 6-AL-4V Titanium Buckling 483 lbf 6 lb Bond Pad Epoxy Adhesive Shear 2 ksi 0.3 ksi Mirror Fused Silica Tensile Fracture 7800 ksi TBD 10 TBD Ring 6-AL-4V Titanium Tension 120 ksi 55 ksi

15 Manufacturing and assembly FSM Assembled and Mounted in the Test Setup Bracket: stainless steel Mirror mount: titanium 6-AL-4V Mirror: fused silica Spring hook: stainless steel Vee groove attachment: stainless steel Adjuster bushing: brass 15

16 Testing setup FSM Beamsplitter Source Detectors Polarizer 16

17 Summary The design features implemented made possible to meet all requirements Successfully manufactured all necessary parts and built the FSM Good results in partial testing Testing in progress 17