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