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@mail.
Multiplexing image detector based
digital sun sensors for high precision
and large field of view
Minsong Wei, Fei Xing, Geng Wang, Zheng You
Department of Precision Instrument, Tsinghua University, Beijing, China
June 10,2014
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Tsinghua University
Outline
1 Introduction
2 Multiplexing image detector method
3 The digital sun sensor with high performance
4 The wireless digital sun sensor
5 Summary
2
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Tsinghua University
1 Introduction
2 Multiplexing image detector method
3 The digital sun sensor with high performance
4 The wireless digital sun sensor
5 Summary
3
Outline
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Tsinghua University
Introduction
4
hy
z
txo
ty
Incident
sunray
Mask
Image detector
x
Sun spot
XO
Y
β
α
l
h
y
h
x
t
t
arctan
arctan
Sun
sensor
The sun sensors
Typical application of the sun sensors
Bentum M J, Leijtens J, Verhoeven C, et al. Measurements on an
autonomous wireless payload at 635 km distance using a sensitive radio
telescope//The 33rd ESA Antenna Workshop on Challenges for Space
Antenna Systems 2011
Principle of the Digital Sun Sensor(DSS)
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Tsinghua University 5
Development of the sun sensors in Tsinghua Univ.
Feature FOV Accuracy Size/ mm3 MassPower
consumption
Analogue Sun Sensors
Wireless
(2013) 120°×120° 0.12°(1σ) 30×30×15 21g Self-powered
Digital Sun Sensors
Multiple
pinholes
(2009)
128°×128° 0.02°(3σ) not available 350g 2.5W
N-slit mask
(2011)120°×120° 0.06°(3σ) 80×60×30 130g 300mW
Introduction
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FOV
Res
Tsinghua University
Introduction
6
Accuracy VS FOVh
y
z
o
Mask
Image detector
x
XO
Y
xs
ys
FOVx
FOVy
2cos ( )Res ( )dd l
h
2arctan2
sx
xFOV
h
2arctan2
sy
yFOV
h
h
d2arctan2
lFOV
h
Trade off between FOV and Resolution
Smaller FOV
Better Resolution
Larger FOV
Worse Resolution
h
2cos ( )( )dd d l
h
2cos ( )( )dd d l
h
Field of View(FOV)Accuracy ∝ Resolution(Res)
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Tsinghua University
Outline
1 Introduction
2 Multiplexing image detector method
3 The digital sun sensor with high performance
4 The wireless digital sun sensor
5 Summary
7
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Tsinghua University 8
Principle
Multiplexing image detector method
• Each pattern determines acorresponding sub-FOV
• The whole FOV is composedof all sub-FOVs
Advantages:
Extend the system FOV without decrease in resolution
Application of planar mask, no optical lens needed
Mask pattern is fabricated by MEMS procedures with high machining accuracy
Image detector
Mask
Sub-FOV1 Sub-FOV2Sub-FOV3
Image detector
Mask
FOV FOV
Conventional design – single pattern Multiplexing image detector method
hh
ldld
#3 #1 #2Pattern
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Tsinghua University 9
Modeling
Multiplexing image detector method
0
- -arctan ,arctan
2 2
d m d ml l l lFOV
h h
:
1
2 + - - +2arctan ,arctan
2 2
m m d d m md l l l l dFOV
h h
:
2 + - - +2arctan ,arctan
2 2
m m d d m mn
nd l l l l ndFOV
h h
:
+ -- +2=2arctan =2arctan
2 2
d pattern md m ml l ll l nd
FOVh h
- +2( 1) 2 + -arctan arctan
2 2
d m m m m dl l n d nd l l
h h
The whole FOV
Continuous coverage requirement
m m dd l l
At least one pattern completely imaged on the detector at any incident angle
No gap between sub-FOVs
Image detector
Pattern
FOV0
FOV1
h
ld
lpattern
lm
dmlmlm lmlm
FOV-n
FOV-1
FOVn
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Tsinghua University
Outline
1 Introduction
2 Multiplexing image detector method
3 The digital sun sensor with high performance
4 The wireless digital sun sensor
5 Summary
10
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Tsinghua University
DSS with high performance
11
Implementation of multiplexing image detector
Resolution simulation result
Mask patternNs:the clearance between two adjacent apertures
N: the pixel size
1 0N
s
LLx N 2 0
Ns
LLy N
Group distinction
h=17.2mm is required to achieve arc-sec level resolution
h=17.2mm results in a FOV of 20°× 20°, approximately
CMOS image detector
1.3 million (1280×1024) pixels,
5.3 μm square pixels
FOV is broaden by multiplexing image detector method
A group of positioning apertures contains
three identical apertures
Every group is distinguished from each
other through the unique set of (Lx, Ly)
定位孔
L1 L2
lmx
dmx
dmy
Positioning apertures
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Tsinghua University
DSS with high performance
12
Optimization design
Aperture size
169.6μm× 169.6μm
Incident angle θ =0°
Illustrated pixel number /number of pixels
Aperture size /×5.3um15 20 25 30 35
300
350
100
150
450
200
250
400
d=20pixels d=25pixels
d=30pixels d=35pixels
100μm 定位孔
L1 L2
lmx
Positioning apertures
d
d
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Tsinghua University
DSS with high performance
13
Optimization design定位孔
L1 L2
lmx
Positioning apertures
≥Ns ≥Ns
Position/ ×5.3μm
1
0.9
0.4
0.2
0
Inte
nsi
ty
0.3
0.5
7550250-75 -50 -25
0 10 20 30 40 50 600.002
0.004
0.006
0.008
0.01
0.012
0.014
data1
data2
0.1
0.7
0.6
0.8
y directionx direction
Incident angle θ =50°
Clearance
Ns=100pixels
θ=0°
100μm
θ=20°
θ=35° θ=50°
d=169.6μm
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Tsinghua University
DSS with high performance
14
Pattern parameters
Mapping code of (Lx, Ly)
1 0N
s
LLx N 2 0
Ns
LLy N
Group mapping design
Pattern size
lx×ly = 47.5 mm × 48.8 mm
Distance between adjacent groups
dmx×dmy = 3.392mm×3.816mm
Groups arrangement
13 × 13 groups
Mask pattern
定位孔
L1 L2
lmx
dmx
dmy
Positioning apertures
ly
lx
Groups in the same line are coded
with the same Lx and disparate Ly
Groups in the same column are coded
with the same Ly and disparate Lx
Each group has a unique (Lx, Ly)
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Tsinghua University
DSS with high performance
15
Lab tests
Random error Measurement error
Performance
Accuracy--6.1″(3σ)
NO gapbetween sub-FOVs
Characteristics Performance
FOV 105° × 105°
Resolution 0.72″
Size 96×80×41.5mm3
Mass 182 g
Power consumption
500 mW
0 10 20 30 40 50 60 70 80 90 100-4
-3
-2
-1
0
1
2
3
4Error/″
Test #
0 20 40 60 80 100
0
2
-3
-4
3
4
-2
10 30 50 70 90
1
-1
0 10 20 30 40 50-8
-6
-4
-2
0
2
4
6
8
10
Yerror
Xerror
Error/″
Incident angle/°
0 10 20 30 40 50
0
4
2
-4
-8
β
-6
8
6
10
-2
α
0 10 20 30 40 50-8
-6
-4
-2
0
2
4
6
8
10
Yerror
Xerror
DSS prototype
Sun Simulator
Rotary table
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Tsinghua University
Outline
1 Introduction
2 Multiplexing image detector method
3 The digital sun sensor with high performance
4 The wireless digital sun sensor
5 Summary
16
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Tsinghua University
Wireless DSS
17
Multiplexing image detector method for profile sensor
Mask pattern
Lx, Ly:the clearance between two adjacent groups
256×256 pixels,
projection data output
A group of positioning apertures contains two identical apertures
The two apertures in one group arrange diagonally
Every group is distinguished from each other through the unique parameter Sx (Sy)
Sx
Sy
Lx
Ly
CMOS profile sensor
Sx Sy S 1i iS S
Safe distance limit — in case of misjudgment of groups
min max2Lx S min max2Ly S
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Tsinghua University 18
Apertures locating
Wireless DSS
p2 p4
p1
p5
p6
p7
p3
Lxmin
Lymin
S4
S4
Aperture size 46.8μm×46.8μm
Group parameter S
S1=156μm Si+1= (Si+7.8)μm
Safe distance limit
Lxmin=686.4μm > 2Smax=405.6μm
Lymin=686.4μm > 2Smax=405.6μm
1. Get multiple peaks from X/Y direction output
Mask pattern
2. Pack the peaks by the safe distance limit
3. Group the packed peaks through the same S
4. Determine the group# and the location info.
Pixel number in X direction
0
Inte
nsi
ty
50 100 150 200 2500
50
100
150
200
250
Pix
el n
um
be
r in Y
dire
ctio
n0
Intensity
50
10
01
50
20
02
50
0 50
10
0
15
0
20
0
25
0
?
Pixel number in X direction
0
Inte
nsi
ty
50 100 150 200 2500
50
100
150
200
250
Pix
el n
um
be
r in Y
dire
ctio
n0
Intensity
50
100
150
200
250
0 50
100
150
200
250
Safe distance
Safe distance?
Pixel number in X direction
0
Inte
nsi
ty
50 100 150 200 2500
50
100
150
200
250
Pix
el n
um
be
r in Y
dire
ctio
n0
Intensity
50
100
150
200
250
0 50
100
150
200
250
Sx
Sy
Sx=Sy=S5
Safe distance
Safe distance
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Tsinghua University
Wireless DSS
19
Electrical and mechanical design
Electrics
sketch map
Wireless DSS prototype
PCB board
with profile sensor
PCB board
with RF MCU
Mask
Bottom cover
Connecting partPCB board
with profile sensor
PCB board
with RF MCU
HousingSize 45×40×20mm3
Mass 38 g
Solar
cell
Power
management
AntennaRF MCU
Profile
DataSPI
S9132
3.3V
5V
3.3V
2.6V
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Tsinghua University 20
Lab tests
Wireless DSS
Random error Measurement error
Prototype of the wireless DSS has an accuracy of 0.07°(3σ) within the whole FOV
System FOV is 100°×100° and there is no gap between sub-FOVs
Function of self-power is achieved during the whole FOV
under a sun simulator with the
brightness of 1 sun constant
Performance test
Results
Self-power test
0 10 20 30 40 50 60 70 80 90 100-0.06
-0.04
-0.02
0
0.02
0.04
0.06Error/°
Test #
0 20 40 60 80 100
0
0.02
-0.04
-0.06
0.04
0.06
-0.02
10 30 50 70 90 -50 -40 -30 -20 -10 0 10 20 30 40 50-0.025
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
Error/°
Incident angle/°
0 10 20 30 40 50
-0.005
0.005
0
-0.015
-0.025
-0.02
0.015
0.01
0.02
-0.01
-50 -40 -30 -20 -10
0 10 20 30 40 50-8
-6
-4
-2
0
2
4
6
8
10
Yerror
Xerrorβ α
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Tsinghua University
Outline
1 Introduction
2 Multiplexing image detector method
3 The digital sun sensor with high performance
4 The wireless digital sun sensor
5 Summary
21
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Tsinghua University
Summary
22
10 times more precise than traditional
DSS
FOV is increased by 25 times with the
employment of the multiplexing
image detector method
self-powered wireless DSS
5 times lower in size and weight
than traditional DSS
FOV and accuracy are improved by
the multiplexing image detector
method
Multiplexing image detector method can be applied
for FOV and accuracy improvement of DSS
FOV 105° × 105°
Accuracy 6.1″(3σ)
Size 96×80×41.5mm3
Mass 182 g
Power consumption
500 mW
FOV 100° × 100°
Accuracy 0.07°(3σ)
Size 45×40×20mm3
Mass 38 g
Power consumption
Self-powered
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Thank you!Contact information:
Minsong Wei
Room 1306 Building 9003, Department of Precision Instrument, Tsinghua University
Beijing, China 100084
Email: [email protected]