Camera Protection using Sun Sensor-Shutter Device

22-July 2008Jay Jiaquan Zheng

Mentor: Dennis Douglas

Overview of Sun Sensor – Shutter Device

• Analogy: Human Eye & Camera – Purpose Of Sun Sensor – Shutter Device

• Introduction of Sun Sensor – Shutter Device– System Diagram– Overall Preliminary Design

• Detailed Design of System– Sun Sensor– Electrical Components – Solar Shutter

• Summary & Path Forward

– Has design met specification– Future goals

The Human Eye Provides A Conceptual Basis For A Solar Sun Sensor

……There’s a reason they tell you not to look into the sun!

• Brain – Sun Sensor

• Eyelid – Solar Shutter

• Eye – Camera

Camera

Sun Sensor

Solar Shutter

• SS boresighted to telescope

• Shutter mounted on back of telescope

• Can be apply to ALL telescopes

Sun Sensor

SS Design:Extend/RetractableRay-Box, pinhole in front, optical detector in the back.

Shutter Design: Slider-Crank usingRack & Pinion assembly driven by a Micromotor.

Shutter

Preliminary Design Locates Sun Sensor & Shutter Device On A Telescope

TelescopeHousing

front

back

ADC (Analog Digital Converter)

Microprocessor

2

Overall System Diagram Links Functionalities Of COTS And Custom Components

Slider –Crank Mechanism

Motor

Convert to Mechanical Power (Torque)

Lid3

OPM Convert toElectrical Power (voltage)

OPD

Pinhole

1

Detector Optical Power Input (sun light)

COTS = Commercial Off The Shelf Components

SolidWorks Modeling Suggests Sun Sensor (Ray-Box) Design Meets Specifications

• Housing

– Adjustable : Threshold: 10o – 60o

– Determine by: Distance: Detector – Pinhole

• Complete CAD Assembly Constructed in SolidWorks

Back Mount

Detector Housing

Pinhole Extender

Thread pattern

Ray-Box Geometry Allows For Multiple Solar Exclusion Angles To Be Set

L

θ

R

r

a b ( )tan

R rL θ

θ+

=

Geometric Relationship:

θ

Sun Position 1

Sun Position 2

L

R

r

detector

pinhole

Adjusting Length Of Sun Sensor Corresponds To Specific Solar Threshold Angle

6.702 / (tan )L θ=

Detector Radius,

R : 5.207 mm

Pinhole Radius,

r : 1.500 mm

θ (o) l (mm) θ (o) l (mm)

10 76.581 36 20.620

12 63.746 38 19.458

14 54.567 40 18.408

16 47.673 42 17.454

18 42.302 44 16.583

20 37.998 46 15.784

22 34.469 48 15.048

24 31.521 50 14.368

26 29.021 52 13.737

28 26.872 54 13.149

30 25.005 56 12.601

32 23.366 58 12.087

34 21.915 60 11.605

Threshold Angle- Given by Optical Straylight Analysis -Cameras can be damage when reached

Detecting Threshold Angle Using Voltage

Curve Generated By Optical Power Meter Red area represents •Threshold Angle = Solar Exclusion Zone

OPM

detector

Vo

ltag

e re

adin

g

Sun Positions

30o

0

25mm

Optical Power Meter outputs voltage depends on incident light

summer

winter

Computing Unit Analysis Signal From Sun Sensor Effectively Controls Shutter Device

• Analog to Digital Converter (ADC)– OPM outputs analog signals,

Microprocessor could only read digital signals.

• Microprocessor – Controls motion of motor in

Shutter device

SolidWorks Modeling Of Shutter Provides Spatial Tolerances & Structural Properties

Lid

Ball Slide

Motor

Rack & Pinion

Slider-Crank

If it takes 10 seconds for your eyelid to close when looking directly at the Sun…

Slider-Crank Mechanism

Synthesized based on Position, Velocity & Force/Stress Analysis.

Rack & Pinion Assembly

Designed using Dynamic Analysis.

Motor

Selected based on Max Torque.

Superimposing All Major Components Allows For Analysis Of Effective Shutter Design

Ball Slide

Selected based on sliding distance.

Position Analysis & Motion Of Slider-Crank Modeled Using Matlab Programming

Lid

slider

Velocity Analysis Of Slider-Crank Generates Relationship Between Lid And Slider Velocity

c sv v=r r

bcvr

o

b

c

bvr

1θφ

a

a lv v=r r

abvr

svr

fix

lvr

O

A

B

C

1/222

1 1 11

2sin sin sin sin cos( )

sin( )s

lAB AB

BC BC

vv θ φ θ φ φ θπ φ θ

⎡ ⎤⎛ ⎞= ⋅ + ⋅ − ⋅ ⋅ ⋅ +⎢ ⎥⎜ ⎟− − ⎝ ⎠⎢ ⎥⎣ ⎦

Note: All terms defined in Position Analysis except slider velocity , or vs .

( )lid slider f positionv v= ⋅

Velocity Polygon

Lid

Slider

Dynamic Analysis Performed On Rack & Pinion System Based On Kinetic Energy Theory

T – motor torque x – rack displacementR – gear radius I – gear inertia m – rack mass

•Equivalence Inertia

•Dynamics Model

2eI mR I= + R

I

x, vs

T

m2

2s

TRv x

mR I= ⋅

+

Customer Specification Designer Input

Calculation OutputPurchase Parts

LinkageFactor Safety

Response Time

MaximumAllowable Pressure

Slider Acceleration

Slider Velocity

Lid Velocity

Motor

Slide

Gears

Dimension

Position

Materialn Lg

P

T

R,I

a

dvs

(x,y,z)

vl

Customer

$

Block Diagram Demonstrates Design Process And Components Specifications of Shutter Device

GUI Interface Allows User Input To Optimize Design Based On System Parameters and Variables

Summary and Path Forward

• Effective Sun Sensor-Shutter Device can be constructed using Commercial Off The Shelf and custom components.

• Modeling suggests this device will have a time response of 0.4 seconds and perform safely.

• Future goal is to determine costs of COTS and custom equipments and integration plan...

Acknowledgement Dennis Douglas,

Daron Nishimoto, Riki Maeda, Chet Jonston

Lani LeBron, Scott Seagroves,

Lynne Raschke, Lisa Hunter

The Akamai Internship Program is funded by the Center for Adaptive Optics through its National Science Foundation Science and Technology Center grant (#AST-987683) and by grants to the Akamai Workforce Initiative from the National Science Foundation and Air Force Office of Scientific Research (both administered by NSF, #AST-0710699) and from the University of Hawaii.