Adaptive Optics Deformable Mirror Electronics Simulation

Pearl Yamaguchi

Subaru TelescopeNational Astronomical

Observatory of Japan

Mentor: Stephen Colley

Outline

• Project Scope

• Adaptive Optics

• Deformable Mirror

• Protecting the Deformable Mirror

• Determinations

Project Scope

• Investigate ways of protecting the Deformable Mirror– From sharp changes in

voltage– Slew rate limit

• Concern– Possible damage due to

rapid changes in drive signals

Adaptive Optics

• Primary Components of AO System

– Wavefront Sensor

– Control Computer

– Deformable MirrorImage without AO Image with AO

Bimorph Deformable Mirror

• Two piezoelectric wafers• Oppositely polarized• Array of electrodes• Dynamically compensates

for aberrations• Expanding or contracting

with stimulus

Deformable Mirror Actuators

• Current AO System

36 actuators• Second Generation AO

188 Actuators

Electrode pattern– Inner and Outer segments

– Load on electronics appears as pure capacitance

Project Objective

• Manufacturer suggested slew rate limit100 Volts/ms

• Full scale range+/- 400 Volts

• Ramping

insures limit100V

200V

1ms 2 ms time

V

Protection from Voltage Jumps

• Control Computer

• Digital to Analog Converters

• High Voltage Amplifiers

ControlComputer

D/AConverter

HVAmplifier

DM

Ideal safety feature here

High Voltage Amplifiers

• Current Limiting to limit charging of segment

• Capacitive Load• Non-Linear

operation of amplifiers

Electronics Simulation for Deformable Mirror

• Implemented and expanded circuit• Using PSpice• Models behavior of circuit elements• Time and frequency response• Test validity of design considerations

Current Limiting High Voltage Amplifiers

Significant Results• Oscillates• Unstable• Eliminated as a

solution

Digital to Analog Converters

• Determine if digital logic implemented slew rate limit is feasible

• Continue simulation of D/A Converters

• Test step limited slew rate

ControlComputer

D/AConverter

HVAmplifier

DM

Stepping Approximation

• Approximate ramp with Stepping

• Implement in digital logic

• D/A Converters

100V

200V

1ms 2 ms time

V

Summary

• Protect the mirror

• Created PSpice model

• Ruled out High Voltage Amplifiers

• Investigated

D/A

Converters 100V

200V

1ms 2 ms time

V

Acknowledgements

• Stephen Colley, AO Project Engineer• Hideki Takami, AO Project Manager• Subaru Telescope, NAOJ• Center for Adaptive Optics• University of Hawaii, Manoa

This project is 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