Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1997-02-20
2001-07-03
Kwok, Helen C. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06253613
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention generally relates to tuning-fork type vibratory gyros, and more particularly to a tuning-fork type vibratory gyro having a piezoelectric substance.
A gyroscope has been used to identify the current position of a vehicle such as an airplane, a ship or a satellite. Recently, a gyroscope has been applied to devices for personal use, such as car navigation and vibration detection in video cameras and still cameras.
A conventional coma gyro detects an angular velocity by utilizing a principle in which a rotating coma (disk) continues to rotate without any change of the attitude thereof while keeping the rotation axis even when a device equipped with the coma gyro is tilted. Recently, an optical type gyro and a piezoelectric type gyro have been developed and reduced to practical use. The principles of the piezoelectric type gyro were proposed around 1950. Various piezoelectric type gyros having, for example, a tuning fork, a cylinder or a semi-spherical member have been proposed. Recently, a vibratory gyro having a piezoelectric member has been in practical use. Such a vibratory gyro has less measurement sensitivity and precision than those of the coma gyro and the optical gyro, but has advantages in terms of size, weight and cost.
FIG. 1
shows a tune fork type vibratory gyro utilizing a piezoelectric single crystal, as disclosed in U.S. Pat. No. 5,329,816. The vibratory gyro shown in
FIG. 1
(which is also referred to as a gyro element) includes a piezoelectric single crystal having two arms
10
and
12
and a base
14
supporting the arms
10
and
12
. The arms
10
and
12
and the base are integrally formed. A drive electrode
18
for driving a tuning-fork vibration is provided on the arm
12
, while a detection electrode
16
for detecting the angular velocity is provided on the arm
10
. In the following description, the surface of the gyro appearing in
FIG. 1
is referred to as a front surface, while the surface opposite to the front surface is referred to as a back surface. The drive electrode
18
has two electrode portions provided on the front surface of the gyro.
FIG. 2
shows a tune fork type vibratory gyro having a different electrode arrangement from that of the gyro shown in FIG.
1
. Such a gyro is disclosed in, for example, U.S. Pat. No. 5,251,483. In
FIG. 2
, the arm
10
has the detection electrode
16
and the drive electrode
18
, and similarly the arm
12
has the detection electrode
16
and the drive electrode
18
. The detection electrodes
16
are located closer to the free ends of the arms
10
and
12
than the base
14
. In an electrode arrangement shown in
FIG. 3
, the detection electrodes
16
are located closer to the base
14
than the free ends of the arms
10
and
12
.
The capacitance ratios of the gyros shown in
FIGS. 1
,
2
, and
3
are provided in these figures.
However, the gyros shown in
FIGS. 1
,
2
and
3
have the following respective disadvantages.
The gyro shown in
FIG. 1
has the electrode arrangement in which the detection electrode
16
is provided symmetrically with the drive electrode
18
. Hence, the capacitance ratios with respect to the drive electrode
18
and the detection electrode
16
are small. However, an unwanted vibration such as a curvature movement is output.
This disadvantage will now be described in detail with reference to
FIGS. 4A through 4D
.
FIG. 4A
is a perspective view of the gyro shown in
FIG. 1
in which an unwanted vibration is illustrated.
FIG. 4B
is a side view of the gyro shown in
FIG. 4A
,
FIG. 4C
illustrates the unwanted vibration.
FIG. 4D
shows the electric field caused in the arms
10
and
12
by the unwanted vibration. The electrodes are omitted in
FIGS. 4A through 4C
. In
FIG. 4D
, the electrodes with no hatching are at an identical potential, and the electrodes with hatching are at another identical potential. Since the detection electrode
16
is provided on the arm
10
only, the potential difference generated by the electric field shown in
FIG. 4D
develops. The above potential difference serves as noise, which degrades the detection accuracy. Further, the unwanted vibration may include a torsional vibration, which is a factor causing a temperature drift. Furthermore, a leakage output may occur due to a mechanical coupling and/or electrostatic coupling between the detection-side arm and the drive-side arm.
In the electrode arrangement shown in
FIG. 2
, a reduction in the drive voltage can be realized because the capacitance ratio with respect to the drive electrodes
18
is small. Further, the detection electrodes
16
are provided on the arms
10
and
12
, so that the unwanted vibration can be canceled and the leakage output is small. However, the capacitance ratios obtained at the free ends of the arms
10
and
12
are as large as approximately twenty times those obtained at the root portions thereof, and the sensitivity is thus small. Furthermore, the wiring lines extending from the detection electrodes
16
and the drive electrodes
18
are complex and the productivity is not high because the detection electrodes
16
and the drive electrodes
18
are provided on the arms
10
and
12
.
The electrode arrangement shown in
FIG. 3
enables high sensitivity because the capacitance ratio with respect to the detection electrodes
16
is small. However, a high drive voltage is required because the capacitance ratio with respect to the drive electrodes
18
is high. Furthermore, the wiring lines extending from the detection electrodes
16
and the drive electrodes
18
are complex and the productivity is not high because the detection electrodes
16
and the drive electrodes
18
are provided on the arms
10
and
12
.
SUMMARY OF THE INVENTION
It is a general object of the present invention to eliminate the above disadvantages.
A more specific object of the present invention is to provide a tuning-fork vibratory gyro which is highly sensitive and accurate and is suitable for mass production.
The above objects of the present invention are achieved by a tuning-fork vibratory gyro having first and second arms and a base integrally connected to the first and second arms, the tuning-fork vibratory gyro comprising: drive electrodes used to generate tuning-fork vibrations due to a piezoelectric transversal effect; and detection electrodes provided on the first and second arms and used to output a detection voltage due to an angular velocity.
The tuning-fork vibratory gyro may be configured so that the detection electrodes are respectively provided on opposite surfaces of the base.
The tuning-fork vibratory gyro may be configured so that the detection electrodes have first portions provided on inner portions of first and second surfaces of each of the first and second arms opposite to each other and second portions provided on first and second surfaces of the base opposite to each other, the first and second portions being integrally formed.
The tuning-fork vibratory gyro may be configured so that the detection electrodes have first portions provided on outer portions of first and second surfaces of each of the first and second arms opposite to each other and second portions provided on first and second surfaces of the base opposite to each other, the first and second portions being integrally formed.
The tuning-fork vibratory gyro may be configured so that the detection electrodes are provided on at least three surfaces of each of the first and second arms.
The tuning-fork vibratory gyro may be configured so that the detection electrodes are connected so as to form first and second groups, the detection voltage corresponding to a difference between potentials of the first and second groups.
The tuning-fork vibratory gyro may be configured so that the detection electrodes are connected so as to form first, second and third groups, the detection voltage corresponding to a potential difference between a potential of the first group and a potential of the second group as well as a potential difference betw
Fujiwara Yoshiro
Ishikawa Hiroshi
Ono Masaaki
Satoh Yoshio
Yachi Masanori
Fujitsu Limited
Kintner Arent Fox
Kwok Helen C.
Plotkin & Kahn PLLC
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