Design and Implementation of a Fast-Steering Secondary Mirror System

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Design and Implementation of a Fast-Steering
Secondary Mirror System

• Maryfe Culiat
• Trex Enterprises
• July 25, 2007

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(No Transcript)
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Overview

• Benefits of a fast-steering secondary mirror
  (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design

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Conventional fast-steering mirror technologyis
placed downstream from telescope

• Atmospheric turbulence and mechanical jitter
  results in the loss of resolution in imagery
• Adaptive optics needed for correction
• Microscopic Deformable mirror
• Macroscopic Fast-steering mirror
• Tip-tilt easiest to correct, yet provides
  substantial return in image quality

FSM
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Why use fast-steering mirrors at the secondary
mirror position?

• Advanced technologies such as ultra
  light-weighted SiC allow for FSSM
• Benefits of having a fast-steering secondary
  mirror
• 1. Tilt correction at the secondary keeps FSM
  close-coupled to the pupil
• 2. Simplified adaptive optics system eliminates
  need for a pupil relay
• 3. Reduces need for another mirror surface

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Goals

• Understand closed-loop FSSM system
• Hands-on hardware integration
• Actuator trade study
• Obtain product information from vendors
• Using system parameters, down-select from vendor
  products

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Overview

• Benefits of a fast-steering secondary mirror
  (FSSM)
• FSSM system diagram
• Optical bench set-up
• System parameters
• Implementation of design
• Summary

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A fast-steering secondary can provide rapid
tip/tilt correction for line-of-sight
stabilization
Fast Steering Secondary Mirror
Tracker Camera
Position Sensors
Actuators
Drive Electronics, Position Sensor Module
Computer
Read camera
Read FSSM position
Offset coordinate transformation
Command actuator
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A fast steering secondary can provide rapid
tip/tilt correction for line-of-sight
stabilization
Fast Steering Secondary Mirror
Tracker Camera
Position Sensors
Actuators
Drive electronics, Position Sensor Module
Computer
Read camera
Read FSSM position
Offset coordinate transformation
Command actuator
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Overview

• Benefits of a fast-steering secondary mirror
  (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design

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Spare fast-steering mirror allows for better
understanding of closed-loop system
Fast steering mirror Actuators Position sensors
Quad cell
Computer
Drive electronics
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Integration of FSSM components

• Tilt range of /- 3mrad
• Small-signal bandwidth 200-300 Hz
• Full stroke bandwidth 30-40 Hz

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Overview

• Benefits of a fast-steering secondary mirror
  (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design

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Two types of actuators are used in fast-steering
mirror applications

• Piezoelectric actuators
• Voice coil actuators

Source www.pi.ws, Physik Instrumente
Source www.beikimco.com, BEI Kimco Magnetics
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Piezoelectric actuators are preferred over voice
coil actuators for this application
Voice coil Piezoelectric
Stroke High Low
Bandwidth Low High
Resolution Low High
Repeatability Low High
Thermal dissipation High Low
Cost Low High
Based on comparable products from BEI Kimco and
Physik Instrumente
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Overview

• Benefits of a fast-steering secondary mirror
  (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design

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Vendor products can be narrowed down given
system parameters

• Parameters given
• Mirror tilt range of at least 2mrad
• SiC mirror allows for reactionless
• Tripod drive

Source www.pi.ws, Physik Instrumente
Source S. Walton
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Physik Instrumentes P-843.60 fulfills
performance specifications

• P-843.60
• 3 actuators 8,895

Source www.pi.ws, Physik Instrumente
Source www.pi.ws, Physik Instrumente

• 90 µm stroke
• 1.8 nm resolution
• Integrated position sensor

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Integrated strain gauge sensors offer high
resolution and bandwidth

• Resistive film bonded to piezo stack
• Sub-nanometer resolution
• Low heat generation
• Indirect metrology

Source www.pi.ws, Physik Instrumente
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Drive electronics are integrated into a single
package

• Drive electronics 16,025
• E-500, chassis w/ voltage supply 2,327
• E-505, amplifier 6,687
• E-509.S3, SGS module 3,075
• E-516.I3, display module 3,936

Source www.pi.ws, Physik Instrumente
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Continuation of design includes finite element
analysis

• Interface between mirror and actuators mounting
  details of flexures

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Conclusion

• Fast-steering secondary mirror technology allows
  for simplified adaptive optics system
• Piezoelectric actuators fulfill requirements for
  this application
• Continued analysis of system includes interface
  between mirror and actuators

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Acknowledgements
Riki Maeda, Dennis Douglas, Daron Nishimoto
Hilary OBryan, Scott Seagroves, Lisa Hunter

• Steve Walton
• Rich Holmes
• Don Bruns
• J.D. Armstrong

James Deichmann, Jason Wong
This work has been supported by the National
Science Foundation Science and Technology Center
for Adaptive Optics, managed by the University of
California at Santa Cruz under cooperative
agreement No. AST - 9876783.
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Flexible tips

• M5 threading
• 20mm length
• Tilting angle of /- 0.5 degrees
• Bending stiffness of 22 nm/rad
• 3 flexures 459

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Raw calculation of actuator stroke

• Assuming movement of only one actuator

Distance of actuator from center of mirror, x
T
Actuator stroke, y
T, maximum tilt angle
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Calculation of loaded resonant frequency
fo resonant frequency of unloaded actuator
(Hz) fo 6 kHz kT piezo actuator stiffness
(N/m) kT 107 N/m meff effective mass
(kg) meff 3.5 g meff additional mass M
meff meff 88.5 g fo, Loaded resonant
frequency 1293 Hz Maximum operating frequency
431 Hz
Equations source www.pi.ws
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Tracker camera

• FLIR SC6000
• InGaAs detector (near-IR)
• Resolution 320 x 256