Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1999-12-28
2002-04-30
Chapman, John E. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504120
Reexamination Certificate
active
06378369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an angular velocity sensor, and more particularly to a micromachined angular velocity sensor, which can be used for a hand shake compensating camera, a car navigation device or the like.
2. Description of the Related Art
As a conventional angular velocity sensor using a micromachining technique, an angular velocity sensor
80
disclosed in Japanese Unexamined Patent Publication No. 6-174739 is described referring to
FIGS. 18 and 19
. A reference numeral
81
denotes a frame formed by machining a silicon substrate, and beams
82
a
-
82
d
respectively extending orthogonal to an inner wall of the frame
81
are coupled with each other at a center part of the frame
81
. A vibrating weight
83
is formed on a lower part of this center part. These beams
82
a
-
82
d
and the vibrating weight
83
are integrally formed with each other through the same silicon substrate as the frame
81
using semi-conductor micromachining technology such as photo-etching.
Piezoelectric elements
84
a
,
84
c
for drive are formed on an upper surface side of the beams
82
a
,
82
c
opposite to each other, while piezoelectric elements
84
b
,
84
d
for detection are formed on an upper surface side of the beams
82
b
,
82
d
opposite to each other. The piezoelectric elements
84
a
,
84
b
for drive and the piezoelectric elements
84
b
,
84
d
for detection are of the structure in which a zinc oxide film
87
is interposed between an upper electrode
86
a
and a lower electrode
86
b.
When drive signals which differ in phase by 180° are respectively added to piezoelectric elements
84
a
and
84
c
for drive, the beams
82
a
and
82
c
vibrate in the vertical direction with a base point
85
as a node as illustrated by the broken line and the two-dot-chain line due to the reversed phase, and a lower tip of the vibrating weight
83
vibrates in the X-axis direction.
When the rotation is thus added about the Z-axis passing through the center of the vibrating weight
83
when the vibrating weight
83
vibrates, the lower tip of the vibrating weight
83
is also vibrated in the Y-axis direction due to the Coriolis force. This vibration is detected as the voltage by the piezoelectric elements
84
b
,
84
d
for detection, and the angular velocity of the rotation is obtained by achieving the differential amplification thereof.
In this conventional angular velocity sensor
80
, however, internal stress is left behind in the beams
82
a
-
82
d
due to shrinkage during the crystallization of zinc oxide when the zinc oxide film is formed on silicon to constitute the beams
82
a
-
82
d
. When the excitation frequency is changed, the excitation amplitude shows a hysteresis characteristic and the excitation vibration becomes unstable.
Further, in the conventional angular velocity sensor
80
, the stress in the beams
82
a
-
82
d
is changed by temperature due to the difference in the coefficient of thermal expansion between silicon and zinc oxide which constitute the beams
82
a
-
82
d
. The resonance frequencies of the beams
82
a
,
82
c
for drive and the beams
82
b
,
82
d
for detection are separately changed, and the temperature drift of the angular velocity detection sensitivity is increased thereby.
Also, in the conventional angular velocity sensor
80
, no correct symmetry can be obtained due to the error in manufacturing the beams
82
a
-
82
d
, and the vibration in the X-axis direction escapes in the Y-axis direction, and the lower tip of the vibrating weight
83
effects the elliptic motion with the axis having a certain declination relative to the line X
2
—X
2
as the major axis as illustrated by a broken line in FIG.
18
. Thus, an offset voltage is generated in the piezoelectric elements
84
b
,
84
d
in a stationary condition, and the angular velocity detection sensitivity and the angular velocity detection resolution are degraded.
SUMMARY OF THE INVENTION
The present invention can provide an angular velocity sensor in which the above-described conventional disadvantages are solved, the angular velocity detection sensitivity is stabilized, and the angular velocity detection resolution is improved.
An angular velocity sensor in accordance with the present invention comprises a support body, a plurality of beams individually supported by the support body, and a coupling part with which a plurality of the beams are commonly coupled, and a vibrating weight formed on the coupling part, in which the each beam comprises a wide beam part and a narrow beam part narrower than the wide beam part.
According to this structure, since a beam is constituted as a coupling part of wide beam parts and narrow beam parts, the internal stress generated in manufacturing the beams, the coupling parts and the support body can be absorbed by the narrow beam parts. Therefore, the angular velocity sensor can be stably operated in a condition where no stress is present, and the detection sensitivity can be stable.
When the vibrating weight vibrates in the extending direction of the beam, or the direction to divide a space between beams into two by exciting the beam, and the narrow beam parts are between the wide beam parts and the coupling part, the vibration of the vibrating weight is absorbed by the narrow beam parts of the beam in the direction where the Coriolis force is generated, and not propagated to the wide beam parts of the beam, and thus, the offset or the noise caused by the escape of the excitation vibration contained in the detected signal to detect the Coriolis force can be reduced. The detection resolution of the angular velocity sensor can be improved thereby. In detecting the Coriolis force, the narrow beam parts of the beam to excitation-vibrate the vibrating weight are deformed, and do not suppress the vibration of the beam to detect the Coriolis force, and the detection sensitivity of the Coriolis force can be improved. When the narrow beam parts are between the wide beam parts and the support body, the coupling body of the wide beam parts with the coupling part is detached from the support body, the vibration energy of the vibrating weight is accumulated in the coupling body, and the coupling body can vibrate in a condition of high mechanical Q, and thus, the detection output by the Coriolis force can be increased.
The narrow beam part of the each beam may be coupled with the coupling part, and the wide beam part may be coupled with the support body.
According to this structure, the internal stress in the beam part is absorbed between the wide beam parts and the vibrating weight. Thus, the excitation vibration by the wide beam parts of the specified beam can be effected without suppression by other beams, and when the Coriolis force is applied to the vibrating weight, the vibration of the beam to detect the Coriolis force can be effected without suppression of the beam to be excitation-vibrated. The vibration in the exciting direction and the vibration in the direction where the Coriolis force is generated are performed without interference with each other in each beam.
Alternatively, the narrow beam part of the each beam is coupled with the support body, and the wide beam part is coupled with the coupling part.
According to this structure, the internal stress in the beam part is absorbed between the wide beam parts and the support body. As a result, the coupling body of the wide beam parts with the coupling part can vibrate like a free vibrating body with the narrow beam parts as end parts. Thus, the coupling body can vibrate in a condition where high mechanical Q is maintained by minimizing the escape of the vibration energy from the coupling body to the support body, and the detection sensitivity of the angular velocity sensor can be improved.
When the specified beam is excited, all beams vibrate together with the vibration of the vibrating weight, and the stress along with the vibration is absorbed by the narrow beam parts, and the excitation vibration is little suppressed by the support body. This also
Kobayashi Shinji
Konaka Yoshihiro
Takata Eiichi
Chapman John E.
Murata Manufacturing Co. LTD
Ostrolenk Faber Gerb & Soffen, LLP
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