Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
2002-03-12
2004-11-02
Ngheim, Michael (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
Reexamination Certificate
active
06813584
ABSTRACT:
FIELD OF THE INVENTION
This present invention is generally subject to the field of instrument & measurement technology based on Micro Electro-mechanical Systems (MEMS), especially relates to a novel design of micro navigation system.
BACKGROUND OF THE INVENTION
Navigation is actually to determine position and attitude for a vehicle by using kinds of sensors. The conventional navigation schemes can be cataloged as: (1) Inertial navigation system, uses gyroscopes and accelerometers to measure rate of rotation and acceleration respectively. However gyroscope is always expensive, has relative big size, slow start-up and long-term drift. (2) Imaging navigation system is composed of camera, units for processing and recognizing, etc. But the imaging processing is complicated and difficult to be implemented in real time. (3) Global position system (GPS), comprises 24 satellites, receiver and signal-processor. It highly depends on the outside information from satellites.
Compared with the conventional methods, the burgeoning MEMS navigation equipments on the basis of micro silicon-based sensors can put miniaturization, practicability and intelligence together. The MEMS-based navigation systems take advantages of low cost, small size, lightweight and adequate performances with respect to the conventional systems.
MEMS is based on integration of micro-electron technology and micro-mechanics technology. A main representative of MEMS-based attitude system is Honeywell Digital Compass HMR3000. It is a tilt compensated compass that uses tilt sensor for enhanced performance up to ±40° tilt range. Its composing and block diagram is shown in FIG.
1
: liquid filled tilt sensors
11
determine inclination angles, the heading (or azimuth) is calculated
13
from the tilt information and the three magnetic field components detected by triaxial magnetometers
12
, the angles then can be communicated with PC
15
through RS-232
14
. HMR3000 measures 0°~360° heading within ±40° tilt, and the heading accuracy is ±1° for level, but ±2° for incline. The tilt range is only ±40°, and the tilt accuracy is ±0.4° for 0°~20°, and ±0.6° when exceed ±20°.
The disadvantages of HMR3000 are:
(1) The tilt range is small, only covers ±40°.
(2) The measurement accuracy will decline with bevel rising.
SUMMARY OF THE INVENTION
The present invention has a novel structure and attitude calculation algorithm to avoid the foregoing disadvantages.
The object of the present invention is to design a novel MEMS attitude system with nonrestrictive tilt range and excellent performance. The inventer designs architecture, composing of three-axis orthogonal accelerometers and three-axis orthogonal magnetometers, and schemes out the optimum attitude calculation algorithm for getting higher accuracy and higher reliability.
During sensors assembly, the directions of the tilt sensor (accelerometers) must be carefully aligned with the corresponding magnetic axes, and the three axes in the same orthogonal placement must be mutually orthogonalized strictly. It is critical for determining the measurement accuracy. Aiming at this assembling problem, the present invention constructs an optical alignment approach against the misalignment.
The present integrative system can attain overall attitude (−90°~90° for pitch, −180°~180° for roll, 0°~360° for heading) with high accuracy in any tilt, and possesses characteristics as solid-state structure, high accuracy, small size, lightweight, low consumption, fast start-up and low cost.
The invention is about a novel micro azimuth-level detector based on MEMS, which comprises multi-sensors, A/D converter for converting the analog signals of the sensors to the digital signals, microprocessor for calculation of the digital signals, RS-232 for connecting the microprocessor with PC, and further comprises signal-processing in the microprocessor and Operation-Display software in PC, wherein multi-sensors are triaxial silicon accelerometers with the processing circuit and triaxial silicon magnetometers with the processing circuit.
The foregoing the signal-processing and the Operation-Display software include signal-syncretizing, attitude computation and graphical Operation-Display interface.
For overcoming the misalignment in assembling, a micro-cube with three micro-mirrors in orthogonal directions using for optical alignment is added to the system structure.
The signal-syncretizing is combination of signal-filter and electric/physical (E/P) signal conversion.
For signal-filter, 2nd-order FIR filter is employed:
y
(
n
)=
h
0
x
(
n
)+
h
1
x
(
n−
1)
where x(n),x(n−1) are the output of sensor (input of the filter) and its backward shift, h
0
, h
1
are constant coefficients, y(n) is the output of the filter.
For E/P signal-conversion, that is actually conversion from electrical voltage v(n) to corresponding physical signal u(n):
u
(
n
)=(
v
(
n
)−
v
0
)/
k
v
where v
0
is zero-point, and k
v
is scale factor. v
0
and k
v
are obtained in advance by calibration.
The attitude computation is as following:
Establish two reference coordinate systems: the geographic coordinate system (GCS) shown in FIG.
2
(
a
) and the vehicle coordinate system (VCS) shown in FIG.
2
(
b
). Defining the three orthogonal axes of the GCS as North21-East22-Ground23 (N-E-G), and the three orthogonal axes of the VCS as X-Y-Z (X
31
refers to the forward direction of the vehicle, Y
32
refers to the left-right direction of the vehicle, and Z
33
refers to downward direction of the vehicle).
The rotations of the VCS relative to the GCS represent the attitude status of the vehicle. The terms ROLL (&ggr;), PITCH (&thgr;) and HEADING (&psgr;) are commonly used in aviation to represent attitude: ROLL refers to the rotation round the X-axis, PITCH refers to the rotation around the Y-axis, and HEADING refers to the rotation round the G-axis. The two representations of the same vector in GCS and VCS can be transformed each other through the Orientation Cosine Matrix C
n
b
.
C
n
b
=
[
cos
(
N
,
X
)
cos
(
E
,
X
)
cos
(
G
,
X
)
cos
(
N
,
Y
)
cos
(
E
,
Y
)
cos
(
G
,
Y
)
cos
(
N
,
Z
)
cos
(
E
,
Z
)
cos
(
G
,
Z
)
]
=
[
T
ij
]
3
×
3
The element T
ij
of C
n
b
is composed of pitch, roll and heading. The three magnetometers are assembled along the X-Y-Z axes to form an orthogonal placement. And the assembling placement is also for the three accelerometers. The independent X, Y, and Z magnetic and gravity readings [x
M
,y
M
,z
M
]
T
and [x
g
,y
g
,z
g
]
T
, which figure the independent X, Y, Z components of the earth's magnetic and gravity field, can be transformed back to the geographic coordinates by applying the Cosine Matrix C
n
b
. Further considering about errors [e
Mx
e
My
e
Mz
]
T
and [e
gx
e
gy
e
gz
]
T
, the following equations are attained (where H is magnetic hall effect, &bgr; is magnetic dip angle, f
g
is gravity acceleration):
[
x
M
y
M
z
M
]
=
HC
n
b
[
cos
β
0
sin
β
]
+
[
e
Mx
e
My
e
Mz
]
⇒
{
H
×
(
T
11
cos
β
+
T
13
sin
β
)
+
e
Mx
=
x
M
H
×
(
T
21
cos
β
+
T
23
sin
β
)
+
e
My
=
y
M
H
×
(
T
31
cos
β
+
T
33
sin
β
)
+
e
Mz
=
z
M
[
x
g
y
g
z
g
]
=
C
n
b
[
0
0
f
g
]
+
[
e
gx
e
gy
e
gz
]
⇒
{
x
g
=
T
13
f
g
+
e
gx
y
g
=
T
23
f
g
+
e
gy
z
g
=
T
33
f
g
+
e
gz
In the equations above, the errors can be eliminated through signal filter and error compensation.
From the foregoing equations, the three attitude angles are figured out via inverse tangent. The procedures of computation are:
Step one: calculating roll &ggr; according to Table 1 and value of &ggr;
ref
&ggr;
ref
=arctg(
y
g
/z
g
),
TABLE 1
z
g
y
g
&ggr;
Quadrant
→0
+
9
Sun Xuefeng
Wang Guanglong
Wang Xiaohao
Wei Qiang
Xiong Shenshu
Li Man
Ngheim Michael
Tsinghua University
Venable LLP
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