Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2001-08-16
2003-11-18
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S497000
Reexamination Certificate
active
06647786
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a tuning-fork type vibration gyro and an electrode trimming method therefor and more particularly a tuning-fork type vibration gyro and an electrode trimming method therefor which enable to reduce pyroelectric noise produced by temperature change and to obtain sensor output having high signal-to-noise ratio.
BACKGROUND OF THE INVENTION
In recent years, a tuning-fork type vibration gyro has been developed aiming to provide a miniaturized gyroscope. The gyro of this type typically includes two arms and a base to support the arms integrally formed of ferroelectric material. The gyro is used for detecting angular rate in a car navigation system, unintentional hand movement in a video camera, and so forth.
In
FIG. 15
, there is shown a schematic configuration diagram of an example of the tuning-fork type vibration gyro disclosed in the official gazette of Japanese Unexamined Patent Publication No. 2000-9476 by the present applicants. The tuning-fork type vibration gyro includes a tuning-fork type vibration body
51
constituted by two arms
52
,
53
, and a base
54
for supporting the arms. This tuning-fork type vibration body
51
is formed integrally with ferroelectric material of lithium tantalate (LiTaO
3
), lithium niobate (LiNbO
3
) or the like.
The bottom plane of base
54
of tuning-fork type vibration body
51
is fixed to a support substrate
56
having a slit in the center portion thereof. At this slit, support substrate
56
is connected to a support arm
57
through a bonding layer
58
formed of rubbery elastic body. Both ends of support arm
57
are bent perpendicularly to secure to a stem
55
.
Stem
55
secures a circuit board
60
on which a driving circuit for vibrating arms
52
,
53
, a sensor circuit for detecting a signal output from tuning-fork-type vibration body
51
, etc. is mounted. These members are covered with a cap
59
to protect against externally applied impulse. Using such tuning-fork type vibration gyro, angular rate of rotation around z-axis, which is parallel with arms
52
,
53
can be detected.
Two arms
52
,
53
of tuning-fork type vibration body
51
are driven by a non-illustrated driving circuit so that each end of two arms
52
,
53
vibrates in the x-axis direction. This vibration is referred to as fx mode vibration, or in-plane vibration. During this state, when tuning-fork type vibration gyro rotates around z-axis, Coriolis force is generated to two arms
52
,
53
in the y-axis direction, perpendicular to x-axis, in proportion to the angular rate of rotation.
For this reason, each end of two arms
52
,
53
starts fy mode vibration in the y-axis direction having magnitude proportional to the Coriolis force. The fy mode vibration is referred to as plane-vertical vibration. Coriolis force is proportional to angular rate of rotation. Therefore the angular rate of rotation can be detected by detecting the magnitude of fy mode vibration.
Next, an electrode configuration of the tuning-fork type vibration gyro is illustrated hereafter.
FIG. 16A
shows a perspective view of tuning-fork type vibration body
51
, while
FIG. 16B
shows a plan view of tuning-fork type vibration body
51
viewed from the upper side.
As shown in
FIG. 16B
, driving electrodes
61
,
62
are provided on arm
52
, and driving electrodes
63
,
64
are provided on arm
53
. These driving electrodes are aimed to produce fx mode vibration. Also, as electrodes for detecting fy mode vibration, detecting electrodes
71
,
72
and
73
are provided on arm
52
, and also detecting electrodes
74
,
75
and
76
are provided on arm
53
.
In
FIGS. 17A and 17B
, a chart is shown for illustrating fx mode vibration. As shown in
FIG. 17A
, when driving voltage generated by an oscillator
81
is applied between driving electrodes
61
and
62
, and also between electrodes
63
and
64
, an electric field E is produced in arms
52
,
53
to expand and contract the side faces of arms
52
,
53
as a consequence of piezoelectric effect. This expansion and contraction causes fx mode vibration on the ends of arms
52
,
53
in a direction shown with arrows
82
,
83
in
FIGS. 17A and 17B
.
During this condition, when rotation around z-axis is produced as shown in
FIG. 18A
, Coriolis force is generated in the y-axis direction perpendicular to the vibration direction. As a result the ends of arms
52
,
53
starts fy mode vibration having the magnitude proportional to the Coriolis force in the y-axis direction. Each direction of fy mode vibration is shown with arrows
84
,
85
.
In this case, as shown in
FIG. 18B
, an electric field E proportional to angular rate of rotation is produced in arms
52
,
53
which are vibrating mutually in opposite directions on receiving the Coriolis force. For this reason, by detecting voltage of sensor terminals
86
,
87
connected to detecting electrodes
71
,
72
,
73
,
74
,
75
and
76
, angular rate of rotation can be identified.
In
FIG. 19
, there is shown a schematic configuration diagram of a sensor circuit for detecting the voltage proportional to fy mode vibration. This sensor circuit includes input terminals
88
,
89
connected to sensor terminals
86
,
87
of tuning-fork type vibration body
51
; terminating resistors
21
,
22
connected to input terminals
88
,
89
; and a differential amplifier
90
to output a signal proportional to the difference of sensor signals being input to terminals
88
,
89
. The sensor circuit further includes a synchronous detector
91
provided for the synchronous detection of the signal output from differential amplifier
90
; an oscillator
82
for feeding a reference clock signal to synchronous detector
91
; a low-pass filter (LPF)
92
having a predetermined cutoff frequency fc to cut off high frequency component included in the sensor signal; a direct-current amplifier
93
for amplifying the output of LPF
92
; and output terminals
94
,
95
to output detecting voltage proportional to angular rate of rotation.
As explained above, in a tuning-fork type vibration gyro, fx mode vibration is produced in arms
52
,
53
. Angular rate of rotation can be obtained by detecting the voltage proportional to fy mode vibration from detecting electrodes
71
,
72
,
73
,
74
,
75
and
76
.
However, because tuning-fork type vibration body
51
formed of ferroelectric body is integrally configured, pyroelectric effect appears in the sensor signal as an inherent nature of ferroelectric body. This pyroelectric effect is a characteristic of electric charge generation caused by temperature change.
Namely, in the tuning-fork type vibration gyro, a superposed voltage of the following is detected as detecting voltage; a voltage generated by stress change based on the vibration; and the other voltage (pyroelectric noise) resulting from the pyroelectric effect. Accordingly, in order to detect angular rate of rotation accurately, it is necessary to reduce this pyroelectric noise as much as possible.
In
FIGS. 20A and 20B
, an explanatory drawing illustrating the pyroelectric noise generation mechanism is shown, as well as a conventional measure therefor. As shown in FIG.
20
A(
a
), ferroelectric body
96
remains in a stable state at a certain temperature with spontaneous polarization P
1
produced according to the current temperature. When temperature changes, different spontaneous polarization P
2
is produced, to set ferroelectric body
96
to a stable state.
On the surface of ferroelectric body
96
, charges corresponding to the spontaneous polarization P
1
, P
2
are stored. Therefore, when temperature changes, the charges staying on the surface of the ferroelectric body either migrate to other ferroelectric body
96
or disappear after combined with other charges having reverse polarity, as shown in
FIG. 20
A(
b
). In this case, when charges of reverse polarity are combined abruptly, pyroelectric noise is produced resulting in signal-to-noise ratio deterioration of the tuning-fork type vibration gyro.
To cope with the above-mentioned problem, t
Kikuchi Kazutsugu
Ohta Kazuhiro
Saito Keiji
Takahashi Yoshitaka
Yachi Masanori
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Media Devices Limited
Moller Richard A.
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