design and implementation of a fast-steering secondary mirror system maryfe culiat trex enterprises...
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Design and Implementation of a Fast-Steering Secondary
Mirror System
Maryfe CuliatTrex Enterprises
July 25, 2007
Overview
• Benefits of a fast-steering secondary mirror (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design
Conventional fast-steering mirror technologyis placed downstream from telescope
FSM
• 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
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 pupil2. Simplified adaptive optics system; eliminates need for a pupil relay3. Reduces need for another mirror surface
FSSM
• 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
Goals
Overview
• Benefits of a fast-steering secondary mirror (FSSM)
• FSSM system diagram
• Optical bench set-up
• System parameters
• Implementation of design
• Summary
ActuatorsPosition Sensors
Read camera
Read FSSM position
Offset coordinate transformation
Command actuator
Tracker Camera Fast Steering Secondary Mirror
Computer
Drive Electronics,Position Sensor Module
ActuatorsPosition Sensors
A fast-steering secondary can provide rapid tip/tilt correction for line-of-sight stabilization
3
2
)(2
CBAz
b
CBa
CBA
ActuatorsPosition Sensors
Read camera
Read FSSM position
Offset coordinate transformation
Command actuator
Tracker Camera Fast Steering Secondary Mirror
Computer
Drive electronics,Position Sensor Module
ActuatorsPosition Sensors
A fast steering secondary can provide rapid tip/tilt correction for line-of-sight stabilization
Overview
• Benefits of a fast-steering secondary mirror (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design
Fast steering mirror
Actuators
Position sensors
Drive electronics
Computer
Quad cell
Spare fast-steering mirror allows for better understanding of closed-loop system
• Tilt range of +/- 3mrad
• Small-signal bandwidth: ~ 200-300 Hz
• Full stroke bandwidth: ~ 30-40 Hz
Integration of FSSM components
Overview
• Benefits of a fast-steering secondary mirror (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design
• Piezoelectric actuators
• Voice coil actuators
Two types of actuators are used in fast-steering mirror applications
Source: www.pi.ws, Physik Instrumente Source: www.beikimco.com, BEI Kimco Magnetics
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 HighBased on comparable products from BEI Kimco and Physik Instrumente
Overview
• Benefits of a fast-steering secondary mirror (FSSM)
• FSSM system diagram
• Optical bench set-up
• Actuator analysis
• System parameters and implementation of design
Parameters given: • Mirror tilt range of at least ±2mrad • SiC mirror – allows for reactionless• Tripod drive
Vendor products can be narrowed down given system parameters
Source: www.pi.ws, Physik Instrumente Source: S. Walton
• P-843.60
– 3 actuators = $8,895
Physik Instrumente’s P-843.60 fulfills performance specifications
Source: www.pi.ws, Physik InstrumenteSource: www.pi.ws, Physik Instrumente
• 90 µm stroke• 1.8 nm resolution• Integrated position sensor
• Resistive film bonded to piezo stack
• Sub-nanometer resolution
• Low heat generation
• Indirect metrology
Integrated strain gauge sensors offer high resolution and bandwidth
Source: www.pi.ws, Physik Instrumente
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
Drive electronics are integrated into a single package
Source: www.pi.ws, Physik Instrumente
• Interface between mirror and actuators; mounting details of flexures
Continuation of design includes finite element analysis
• 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
Conclusion
Acknowledgements
• Steve Walton• Rich Holmes• Don Bruns• J.D. Armstrong
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.
Hilary O’Bryan, Scott Seagroves, Lisa Hunter
Riki Maeda, Dennis Douglas, Daron Nishimoto
James Deichmann, Jason Wong
Flexible tips
• M5 threading
• 20mm length
• Tilting angle of +/- 0.5 degrees
• Bending stiffness of 22 nm/rad
• 3 flexures = $459
Raw calculation of actuator stroke
Assuming movement of only one actuator:
Actuator stroke, y
Distance of actuator from center of mirror, x
Θ, maximum tilt angle
mm
ymrad
mmx
mrad
25.30)2tan(
25.30
2
Θ
my 5.60
Calculation of loaded resonant frequency
eff
To m
kf
2
1
eff
effoo m
mff
''
Equations source: www.pi.ws
fo = resonant frequency of unloaded actuator (Hz) fo = 6 kHzkT = piezo actuator stiffness (N/m) kT = 107 N/mmeff = effective mass (kg) meff = 3.5 gm’eff = additional mass M + meff m’eff = 88.5 g
f’o, Loaded resonant frequency ≈ 1293 HzMaximum operating frequency ≈ 431 Hz
Tracker camera
• FLIR SC6000– InGaAs detector (near-IR)
– Resolution: 320 x 256