Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-12-02
2001-09-25
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504120
Reexamination Certificate
active
06293148
ABSTRACT:
BACKGROUND OF THE INVENTION
Gyroscopes or gyro rate sensors are widely used for navigation, stabilization, general rate control, pointing, autopilot systems, missile guidance control, etc. A typical example is the application of yaw rate sensors to automobiles to provide input to the control systems for suspension, braking and steering. During recent years there have been attempts to develop low cost gyroscopes suitable for mass production. A promising concept of such a device is the vibratory gyroscope which can be fabricated using surface-micromachining technology.
The basis operating principle of a vibratory gyroscope
10
is illustrated in FIG.
1
. The purpose of the gyroscope
10
is to measure the angular velocity &OHgr;. To achieve this, it is first necessary to cause the particle
12
to vibrate with constant amplitude along the axis Ox. This motion is referred to as primary motion (or driven motion). When the gyroscope
10
rotates, the particle
12
experience a Coriolis inertia force. This force has a magnitude proportional to &OHgr; and a direction along the axis Oy. In the absence of further control on the motion of the particle
12
, the Coriolis force will cause the particle
12
to vibrate along the axis Oy. This motion is referred to as secondary motion (or sensing motion) and a measurement of its amplitude will provide an estimate of the angular velocity &OHgr;.
The sensitivity of such a vibratory gyroscope can be determined by:
S
=
Y
o
Ω
=
2
ω
x
X
o
ω
y
2
[
(
1
-
r
2
)
2
+
(
r
/
Q
)
2
]
1
/
2
Where:
Yo is the magnitude of the sensing motion;
&OHgr; is the angular rate applied to the gyroscope;
&ohgr;
x
is the excitation frequency of the driven motion in the axis Ox;
&ohgr;
y
is the resonant frequency of the sensing motion in the axis Oy;
r=&ohgr;
x
/&ohgr;
y
; and
Q is the mechanical quality factor for the sensing motion.
It can be seen from the foregoing equation that, when r=&ohgr;
x
/&ohgr;
y
=1, the sensitivity can reach its maximum value, i.e.,
S
=
Y
o
Ω
=
2
QX
o
ω
y
Assuming that X
o
=1 &mgr;m, &ohgr;
y
={square root over (K
y
+L /m)}=6879 Hz and the gyro is vacuum packaged so that Q≈10000. One can get the sensitivity,
S
=
Y
0
Ω
=
0.4627
×
10
-
6
For the input of unit angular rate, &OHgr;=1
0
/s=0.0174 rad/s the amplitude of the sensing motion is:
Y
o
=8.07×10
−9
m=8.07 nm
It can be thus understood that the sensing motion is the secondary effect of the Coriolis force. Note that the above estimate is based on various idealizations and assumptions. In practice, the real magnitude of the sensing motion could be far below this value, e.g., a few angstroms. Such a tiny magnitude of the sensing motion presents a major difficulty in measurement, especially if the motion is detected capacitively. It is therefore necessary to seek a proper structural design so that the sensitivity of the vibratory gyroscope can be improved.
SUMMARY OF THE INVENTION
The present invention is a motion sensor apparatus for use as a general mechanical amplifier a gyroscope, or other resonant sensor such as an accelerometer. In accordance with the invention, the motion sensor apparatus includes a primary mass and a primary flexure structure. The primary flexure structure supports the primary mass to experience driven motion against a bias of the primary flexure structure. The apparatus further includes a secondary mass which is less massive than the primary mass. A secondary flexure structure interconnects the secondary mass with the primary mass, and supports the secondary mass to experience sensing motion relative to the primary mass against a bias of the secondary flexure structure. The stiffness ratio between the primary and secondary flexure structures is equal to the mass ratio between the primary and secondary masses.
REFERENCES:
patent: 5392650 (1995-02-01), O'Brien et al.
patent: 5780740 (1998-07-01), Lee et al.
patent: 5895850 (1999-04-01), Buestgens
patent: 5979246 (1999-11-01), VanCleve et al.
patent: 6067858 (2000-05-01), Clark et al.
patent: WO915323A1 (1999-05-01), None
patent: WO96/24652 (1995-09-01), None
patent: WO95/34798 (1995-12-01), None
patent: WO96/05480 (1996-02-01), None
patent: WO97/45699 (1997-12-01), None
Park, et al., Laterally Oscillated and Force-Balanced Micro Vibratory Rate Gyroscope Supported by Fish-Hook-shaped Springs, Sensors and Actuators, A-64 (1998) 69-75.
Oh, et al., A Tunable Vibratory Microgyroscope, Sensors and Actuators A64 (1998) 51-55.
Clark, et al., Surface Micromachined Z-Axis Vibratory Rate Gyroscope, Solid State Sensor and Actuator Workshop, Hilton Head, South Carolina, Jun. 2-6, 1996.
Lim Mong King
Lin Rong Ming
Sridhar Uppili
Wang Zhe
Institute of Microelectronics
Jones Day Reavis & Pogue
Kwok Helen
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