International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 4
Number 3
September 2010
317
1 INTRODUCTION
1.1 Background of the Research
Small vessels have a choice of Gyro compass, mag-
netic compass or GPS compass. They are also using
the GPS for calculating positions.
Even though GPS is very accurate, small and low
cost, it needs signals from satellites. Because GPS is
worked by external signals from satellites, several
weak points have been discussed, for example, jam-
ming, maintenance cost, electromagnetic wave by
the sun and etc. Therefore for the purposes of this
research we studied an autonomous system without
using GPS.
The Inertial Navigation System is an autonomous
and overcome the problems that are caused GPS. In
the recent technological advancements modern iner-
tial systems have removed most of the mechanical
complexity of platform systems by having the sen-
sors attached rigidly to the body of the host vehicle.
It is called the strapdown inertial navigation system.
But to maintain its accuracy, it still needs very accu-
rate systems such as the ring laser gyro (RLG), the
fiber optic gyro (FOG) or more accurate gyro such
as the electro-statically suspended gyroscope (ESG)
and also very complex systems. Those systems are
expensive and uneconomical for small vessels but
new type of MEMS sensors should provide a possi-
ble solution to this problem.
In this research, the basic researches were carried
out for the stated goal that is developing a small and
low cost autonomous system which is affordable for
small vessels.
1.2 The Integrated Compass System
MEMS-ESG is able to detect relative angles which
discussed in this paper. For the compass system, ab-
solute angles are necessary. Therefore integrated
system was being looked at. The considering system
is using INS with MEMS-ESG and sun direction and
altitude detecting system using camera image. The
system diagram is shown in Figure1.
INS using MEMS-ESG is able to navigate for only
2 minutes or less, Gen F. & Shogo H., 2008. One of
the problems is cumulative errors. There for the
camera system update time should be within that
time.
In this thesis, the MEMS-ESG is introduced in
the second paragraph and then the camera system is
introduced in 3
rd
paragraph as basic research for the
integrated compass system.
The Basic Research for the New Compass
System Using Latest MEMS
G. Fukuda
Graduate Student in Tokyo University of Science and Technology, Tokyo, Japan
S. Hayashi
Tokyo University of Science and Technology, Tokyo, Japan
ABSTRACT: This paper demonstrates basic research for a new compass system using latest MEMS (Micro
Electro Mechanical Systems) sensors for small vessels. In 2007, MEMS Electro-statically Gyro (ESG) was
introduced by TOKYO KEIKI which is a Japanese company. This sensor accuracy has dramatically improved
compared to vibration types. For example, instability has been improved 10 times more than the vibration
types. The reproducibility was tested and maximum difference was 0.55 [deg/sec] in the field test. The
MEMS-ESG could detect the relative angles as accurate as GPS compass in short term use. Even though sen-
sor accuracy has been improved, an improvement of another 10 times is needed to detect the earth’s turn rate.
Because of this a second system is required for a complete compass system. A celestial navigation system is
one of the possibilities to complement this. Traditionally the sextant has been used for measuring the altitude,
but it has some human errors and difficult to measure continuously. Therefore, it might be useful to get sun
altitude and direction automatically. In this thesis, the sun altitude and direction detecting system using cam-
era devices are studied. Using 350×288 resolution camera and a radio-controlled clock, the sun movement
was detected 5’14” per pixels and 2’16”. per pixels for the altitude and direction respectively. Although this is
a basic research for an integrated system, the data should have an enormous affect upon future research.
318
Figure 1 Integrated Compass System
2 MEMS ELECTRO SUSPENDED GYRO
SENSOR
2.1 The basic research of MEMS-ESG
The ESG is introduced during the 1950s in the Unit-
ed States. The ESG is very accurate and it has
achieved drifts of the order of 0.0001[deg/h] and
navigation accuracies of the order of 0.1 nautical
miles per hour, David Titterton and John Weston.
2004. Unfortunately, despite being very simple con-
cept, the design is complex and the gyroscope is
large and expensive.
The MEMS-ESG was introduced by a Japanese
company in July 2007. Although the accuracy is not
the same as the previous ESG, its accuracy is greatly
improved as MEMS gyro sensors. Additionally it is
lower price than the previous ESG.
The MEMS-ESG is measuring the turn rate using
the turning sensor rotor which is suspended by elec-
trostatic power. When the turn rate is applied to the
rotor, a slight tilt angle is occurring between sensor
rotor and sensor case. A feedback torque is applied
in order to return the rotor to the normal position.
This feedback torque is proportional to turn rate, so
the sensor can detect the turn rate. In addition, the
sensor detects the 3-dimension accelerations by the
torque which is applied for maintaining the sensor
rotor in the center of the case.
The MEMS-ESG sensor structure has 3 layers that
are glass, silicon and glass. The sensor structure im-
age is shown in Figure2. The sensor size details are
shown in Table1. Picture 1 shows the sensor pack-
age. The package is 4.3[mm] squared and 1[mm]
thickness, Shigeru Nakamura. 2008.
Figure 2 MEMS-ESG Sensor Structure
Picture 1 MEMS-ESG Sensor Package
Table 1 Rotor information
Rotor diameter
1.5[mm]
Thickness
50[μm]
Top and bottom gap
3[μm]
Radial dimension gap
2.5[μm]
2.2 Rate Output
Figure 3 X and Y axes angular velocity output by MEMS-ESG
Figure 3 shows 100 data of the angular velocity
output about X and Y axes by MEMS-ESG. The da-
ta was collected in the laboratory in stable condi-
tions. The vibration type gyro sensor’s output was
collected at the same time. The comparison of the
MEMS-ESG with vibration type is shown in Fig 4.
MESAG-100 Angular Velocity
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0 10 20 30 40 50 60 70 80 90 100
Data Number
Angular Velocity(deg/sec)
X Angular V
Y Angular V
MEMS
INS
Camera
System
Calculation of
the Sun position
Compari-
son &
Altitude & Direction
by image
Filter
Corrections
Direc-
tion
Altitude & Direction
by calculation
Rotor
Common
Electrode
Control Elec-
trode (Thrust Di-
rection)
Control Elec-
trode (Radial
Direction Cal-
culation of the
Sun position)
Rotating
Electrode
1mm
Rotor
319
In this case, the average output of rate sensor by the
MEMS-ESG and a vibration gyro are 2.844×10
-
17
[deg/sec] and 0.131[deg/sec] respectively. Instabil-
ities are 0.260[deg/sec] for MEMS-ESG and
3.125[deg/sec] for a vibration gyro.
Figure 4 Comparing Vibration with ESG type
2.3 Reproducibility Test
Figure 5 Ten times relative angle reproducibility test
Figure 6 The enlarged figure of vibration point
Ten times relative angle reproducibility test was
carried out. The sensor was rotated about 90 degrees
by motor and stopped mechanically by using a relay
switch. Figure 5 shows the test result. The data
shows good reproducibility in short term use. The
biggest difference of this data was 0.550 [deg/s]
around the sensor stopped point which is shown in
Figure 6. It was considered that that difference was
caused by the small vibration caused by the reaction
of the mechanical stop.
2.4 Acceleration Output
It is shown the X-axis acceleration output in the sta-
ble condition in Figure 7. The compared with the vi-
bration type acceleration sensor was shown in Figure
8. In this figure, the average output of acceleration
sensor output by MEMS-ESG and vibration are -
1.215×10
-18
[G/sec] and -0.002[G/sec] respectively.
Instabilities are 0.002[deg/sec] for MEMS-ESG ac-
celeration sensor and 0.053[G/sec] for vibration ac-
celeration sensor.
Figure 7 X-axis acceleration output
Figure 8 Comparing Vibration with ESG type
ESG & Vibration Types Rate Sensor Output
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101
Data Number
Deg/S
Vibration ESG
Test
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
0
0.6
1.19
1.79
2.38
2.98
3.58
4.17
4.77
5.37
5.96
6.56
7.15
7.75
8.35
8.94
9.54
10.1
10.7
Data Number
Rotation Angle( °)
Test1
Test2
Test3
Test4
Test5
Test6
Test7
Test8
Test9
Test10
Test
-90.5
-90
-89.5
-89
-88.5
-88
-87.5
-87
2.42
2.57
2.71
2.86
3.01
3.15
3.3
3.45
3.6
3.74
3.89
4.04
4.19
4.33
4.48
4.63
4.78
4.92
5.07
5.22
5.37
5.51
5.66
5.81
5.96
6.1
6.25
6.4
6.55
Data Number
Rotation Angle( °)
Test1
Test2
Test3
Test4
Test5
Test6
Test7
Test8
Test9
Tes t 10
X Acceleration
0
0.001
0.002
0.003
0.004
0.005
0.006
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Data Number
Acceleration(G)
ESG & Vibration Types Acceleration Sensor Output
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
1 8 15 22 29 36 43 50 57 64 71 78 85 92 99
Data Number
Output(Ｇ)
Vibration ESG
320
2.5 Comparing with GPS compass
Picture 2 GPS compass and MEMS-ESG for the comparing
test
The comparing test was held using GPS compass.
The GPS compass was fixed on the MEMS-ESG
and both equipments are rotated simultaneously by
DC motor. The equipment was shown in Picture 2.
Figure 6 shows the relative angle by the MEMS-
ESG and GPS compass output. The MEMS-ESG is
able to measure the turn rate as accurate as the GPS
compass in short time use. The GPS compass data
has some data blanks since the GPS compass could
not get the signal from the GPS satellite, whereas
MEMS gyro is able to get the data continuously.
This result might suggest that the GPS/INS is very
useful in some areas.
Figure 6 MEMS Gyro and GPS compass Output comparison
2.6 Existing problems with MEMS-ESG
The MEMS accuracy improvement was discussed in
2.2 and 2.4 by comparing the ESG type sensor and
the vibration type. ESG type is very useful concern-
ing its accuracy but it requires some techniques to
provide shock and vibration protection. The vibra-
tion type gyro sensor which discussed in this paper
has 2000 g-powered shock survivability, but ESG
type has got only ±15[G] at 1[kHz]. For example,
when we carried out field test by the car, the sensor
was sometimes stopped because of the light shock
by the brake. This problem is reported not only
MEMS-ESG but also the normal type of ESG gyro
as well. Before considering using the MEMS-ESG
on a ship, this problem must be solved.
Moreover, the sensor box surface temperature is
increased as shown in Figure 10. The test was car-
ried out in the laboratory where the temperature was
27.5[
○
C]. The sensor box surface temperature was
increasing and reached 44.8[
○
C] in 110 minutes.
This was caused mainly by FPGA (Field Program-
mable Gate Array) in the sensor box. This is not di-
rectly caused by sensor itself but concerning afford-
able sensor temperature which is from -20[
○
C] to
55[
○
C], it would be necessary to resolve this prob-
lem in some environments.
Figure 7 Sensor Box Surface Temperature Test
3 SUN DIRECTION AND ALTITUDE
DETECTING SYSTEM USING CAMERA
IMAGE
3.1 The general outline of the system
MEMS-ESG is capable of detecting relative angles.
But it also needs to know the absolute angles for the
compass system. Therefore second system is needed.
Gyro compass has normally been used for that. But
it is expensive and too big for small vessels. The
magnetic compass, the celestial navigation and the
terrestrial navigation are traditionally used on the
ship. The magnetic compass is one of practical solu-
tions but it has got the problem of deviation. The ce-
lestial navigation is also powerful tool but it needs to
detect the altitude using a sextant by hand. This
would cause the human factor errors. It is also diffi-
cult to observe continuously. But considering the ce-
lestial navigation is still using on some ships for a
complement of GPS, it is still useful if it is automat-
ed. There is available radio sextant as an automat-
ed system for this but the equipment cost is too ex-
pensive. Therefore the web camera was considered
to measure the sun altitudes and directions. Accord-
MEMS Gyro and GPS Compass
0
10
20
30
40
50
60
70
80
90
100
0 4.95 9.9 14.85 19.8 24.75 29.7 34.65 39.6 44.55 49.5
Time (s )
Rotation Angle(°)
MESAG100
GPS Compass
Sensor Box Surface Temperature Test
20
25
30
35
40
45
50
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
Minutes
Temperature[℃]
GPS Compass
MEMS-ESG
321
ing to recent development of imaging device, they
are getting cheaper and higher resolutions. There is
the system using CCD cameras, Fabio C. & Erik K.,
1995. But high resolution CCD cameras are still ex-
pensive.
3.2 Direction and altitude calculation
The system needs to calculate the sun position. It
needs very complicated calculation to get the real
sun position. Therefore the calculations have been
completed using a polynomial approximation of
ephemerides, which was invented by Hydrographic
Office of Japan, Japan Coast Guard. 2008. It would
be considered that there are slight differences be-
tween a polynomial approximation and Nautical
Almanac. If using high resolution cameras, those
difference are should be considered.
3.3 Camera device
Picture 3 Camera Device used the evaluation
There is the system using fisheye lens, Matthew C.
D., David W. & Daniel V., 2005. The fisheye lens is
very useful because it could detect the sun only one
camera without any mechanical moving devices. But
there are few fisheye lenses for web cameras. They
also need many calibration works.
Therefore two cameras are used in this system. They
are 352×288 pixels web cameras and put on the sex-
tant for evaluation as shown in Picture 3. Camera1
expected to take sun image and camera 2 is expected
to take horizon. Both cameras are connected with PC
by using USB cables.
3.4 The result
The calculation for the altitude and direction is pro-
duced by Kenji Hasegawa, 1994. The result of sun
altitude by calculation and camera image for 22
minuets are shown in Figure 8. Figure 9 shows 500
data in Figure 8. The sampling time is 0.5[sec]. The
time was given by a radio-controlled watch. There
are two flutters which show in Figure 9 around at
14:53:3 and 14:54:40. This would be caused by the
interlace scan.
The maximum difference and standard deviation
with calculated data and camera image data are
0.0932 degrees and 0.0246 degrees respectively. The
calculated sun altitude is moving uniformly, as you
would see in Figure 9. But the altitude by camera
image is moving like steps. This is caused by the
camera resolution. In this case, it is detected 0.0872
[degree/pixel], which is equivalent to 5’14”.
Figure 8 Calculated Sun Altitude and Altitude by Camera Im-
age
Figure 9 The 500 data in Figure 8
The results of sun direction by calculation and
camera image are shown in Figure 10. Figure 11
shows 500 data in Figure 10. A sampling time is
0.5[sec]. The time was given by a radio-controlled
watch.
The maximum difference and standard deviation
between calculated data and camera image data are
0.0647 degrees and 0.0054 degrees respectively. The
resolution is detected 0.0378 [degree/pixel], which is
equivalent to 2’16”.
Calculated Sun Altitude and Altitude by Camera image
15
15.5
16
16.5
17
17.5
18
18.5
19
14:49:51
14:50:54
14:51:57
14:53:0
14:54:3
14:55:6
14:56:10
14:57:13
14:58:17
14:59:20
15:0:23
15:1:26
15:2:29
15:3:32
15:4:35
15:5:38
15:6:41
15:7:44
15:8:47
15:9:50
15:10:53
15:11:56
15:13:0
Time (h h :mm:s s )
Altitude(degrees)
Calculated
Camera image
Calculated Sun Altitude and Altitude by Camera image
17.8
17.9
18
18.1
18.2
18.3
18.4
18.5
14:52:5
14:52:14
14:52:23
14:52:33
14:52:42
14:52:51
14:53:0
14:53:9
14:53:18
14:53:27
14:53:36
14:53:45
14:53:54
14:54:3
14:54:12
14:54:21
14:54:30
14:54:40
14:54:49
14:54:58
14:55:7
14:55:16
14:55:25
14:55:35
14:55:44
14:55:53
T ime(hh:mm:ss)
Altitude(degrees)
Calculated
Camera image
Camera 1
Camera 2
Sextant
322
Figure 10 Calculated Sun Direction and Direction by Camera
Image
Figure 11 The 500 data in Figure 10
The reason of resolution difference between Alti-
tude and Direction was caused by the initial camera
attitude error. Further more, the camera focus error
is considered as the error term.
4 FUTURE WORKS
A position data is demanded for the calculation of
sun altitude and direction. The MEMS INS is possi-
ble way to calculate the position. The MEMS INS is
demanded to keep its accuracy while the camera sys-
tem is updating the sun position and altitude. Using
the camera system in section 3, more than 2 minuets
updating time is demanded. Therefore the INS using
MEMS-ESG needs more accuracy, Gen F. & Shogo
H, 2008. Many books are published for the INS cal-
culation such as David Titterton and John Weston.
2004. But those calculations are considering more
accurate sensors. Now, the INS program for the
MEMS-ESG is under researching.
There is accuracy difference between the X-axis
and Y-axis. This difference might be caused by the
CMOS sensor in the camera and also initial align-
ment errors. The studies have been undertaking
about it. In addition to that, the research using higher
resolution web camera is also undertaking.
5 CONCLUSION
In this paper, the new type of MEMS sensor,
MEMS-ESG, and the sun altitude and direction de-
tecting system were explained as basic research for
the new compass system using latest MEMS.
An accuracy of MEMS-ESG has much improved
comparing previous vibration type of MEMS sen-
sors. The sensor’s reproducibility was explained.
Furthermore, the relative angle accuracy was shown
comparing with GPS compass. The problem of
MEMS-ESG is explained in 2.5. Especially, some
countermeasures are needed for the shock surviva-
bility on the ship. Although there are still some
problems with MEMS-ESG, it has got much poten-
tial. The vibration type sensors would be difficult to
increase their accuracy because of their structures.
However, ESG type has different structures and eas-
ier to increase its accuracy. For example, inertial
momentum is proportional to the square of rotor’s
diameter and also rotor’s rotation rate. To consider
those and the fact that the company has already
made successfully the bigger diameter rotor sensor,
MEMS-ESG accuracy would be increased in the fu-
ture.
In 3
rd
paragraph, the sun altitude and direction de-
tecting system using camera image was explained.
Using 352×288 resolution web camera, the accuracy
achieved 0.0872 [degree/pixel] for the altitude and
0.0378 [degree/pixel] for the directions.
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Gen F. & Shogo H., 2008. Basic Research of the MEMS Iner-
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Japan Coast Guard. 2008. Celestial Position Calculation.
http://www1.kaiho.mlit.go.jp/KOHO/syoshi/furoku/na09-
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David Titterton & John Weston. 2004. Strapdown Inertial Nav-
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Edition, pp. 103-105
Shigeru Nakamura. 2008. Development and applications of
ESG Gyro
Float
・
Turning type MEMS inertial sensor, 4
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Calculated Sun Direction and Direction by Camera Image
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224
225
226
227
228
229
14:49:51
14:50:54
14:51:57
14:53:0
14:54:3
14:55:6
14:56:10
14:57:13
14:58:17
14:59:20
15:0:23
15:1:26
15:2:29
15:3:32
15:4:35
15:5:38
15:6:41
15:7:44
15:8:47
15:9:50
15:10:53
15:11:56
15:13:0
Time ( hh:mm:s s)
Direction(degrees
Ca lcula tion
Camera Image
Calculated Sun Direction and Direction by Camera Image
224
224.1
224.2
224.3
224.4
224.5
224.6
224.7
224.8
224.9
225
14:52:5
14:52:14
14:52:23
14:52:33
14:52:42
14:52:51
14:53:0
14:53:9
14:53:18
14:53:27
14:53:36
14:53:45
14:53:54
14:54:3
14:54:12
14:54:21
14:54:30
14:54:40
14:54:49
14:54:58
14:55:7
14:55:16
14:55:25
14:55:35
14:55:44
14:55:53
Time(h h :mm:s s )
Direction(degrees)
Calcu lation
Camera Image
