Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
1997-03-11
2001-05-15
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06230562
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a gyro for detecting angular velocity, and more particularly to a tuning-fork type vibratory gyro using a piezoelectric substance and a detection circuit (sensor) which processes an output signal of the vibratory gyro.
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 piezoelectric vibratory gyro utilizes the effect in which when an angular velocity is applied to the gyro which is being vibrated, a Coriolis force is produced in a direction perpendicular to the direction in which the gyro is vibrated. Various types of piezoelectric vibratory gyro have been proposed. Recently, a tuning-fork type vibratory gyro has been attracted because it has relatively high cost performance. Particularly, there have been considerable activities in the development of a tuning-fork type vibratory gyro utilizing a piezoelectric single crystal.
Such tuning-fork type vibratory gyros utilizing a piezoelectric single crystal are proposed in, for example, U.S. Pat. Nos. 5,329,816 and 5,251,483. The U.S. Pat. No. 5,329,816 discloses a tuning-fork type vibratory gyro (gyro element) utilizing a piezoelectric single crystal shaped so that two arms and a base supporting the arms are integrally formed. Drive electrodes for driving a tuning-fork vibration are provided to one of the two arms, and detection electrodes are provided to the other arm in order to detect a voltage based on the angular velocity applied to the gyro.
FIGS. 1A and 1B
show a tuning-fork type vibratory gyro having an electrode arrangement as described above. The gyro includes a tuning fork made of a piezoelectric single crystal, such as LiTaO
3
or LiNbO
3
. The tuning fork has two arms
11
and
12
, and a base
13
which integrally connects the arms
11
and
12
together. As shown in
FIG. 1B
, drive electrodes
14
-
17
are attached to the arm
11
, and detection electrodes
18
and
19
are attached to the arm
12
. A drive source
20
, which generates a rectangular wave signal, is connected to the electrodes
14
-
17
. A detection signal (voltage) depending on the angular velocity is output across the detection electrodes
18
and
19
.
U.S. Pat. No. 5,251,483 has a piezoelectric tuning-fork type vibratory gyro having an electrode arrangement different from that of the gyro shown in
FIGS. 1A and 1B
. The gyro disclosed in U.S. Pat. No. 5,251,483 has detection electrodes attached to two arms. Generally, such an electrode arrangement is called a differential-type structure. The detection electrodes disclosed in U.S. Pat. No. 5,251,483 are provided to four or three surfaces of each of the two arms.
A vibratory gyro having the electrode arrangement as described above is shown in
FIGS. 2A and 2B
. Electrodes
14
-
17
and
25
are provided to the arm
11
, and electrodes
21
-
24
and
26
are provided to the arm
12
. The electrodes
15
,
17
,
21
and
23
function as drive electrodes, and electrodes
14
,
16
,
22
,
24
,
25
and
26
function as detection electrodes. As shown in
FIG. 2B
, two detection signals DET
1
and DET
2
are obtained, and the potential difference between the detection signals DET
1
and DET
2
corresponds to the angular velocity applied to the gyro.
FIG. 3
shows an operation of the gyros shown in
FIGS. 1A
,
1
B,
2
A and
2
B. When the drive signal (voltage) generated by the drive source is applied to the drive electrodes, the two arms
11
and
12
are vibrated in the X directions. When the vibratory gyro is rotated about the Z axis, the two arms
11
and
12
are vibrated in the Y directions perpendicular to the X directions. The magnitude of the vibrations of the arms
11
and
12
in the Y directions is proportional to the Coriolis force, which is proportional to the angular velocity. Hence, a signal (a detection signal) proportional to the vibrations of the arms
11
and
12
in the Y directions reflect the value of the angular velocity applied to the gyro.
A detection circuit is provided which senses the detection signal. A detection circuit
27
shown in
FIG. 4
is used for the vibratory gyro in which the drive electrodes are attached to one of the two arms
11
and
12
and the detection electrodes are provided to the other one of the arms
11
and
12
. The detection signal from the vibratory gyro is applied to a synchronous detection circuit
31
via a phase adjustment circuit (not shown). The synchronous detection circuit
31
performs a synchronous detection in which a drive signal output by a drive circuit
30
is used as a reference signal for synchronous detection. A resultant signal derived from the synchronous detection circuit
31
is applied to a differential amplifier
32
via a smoothing circuit (not shown). The differential amplifier
32
performs a differential amplifying operation between the synchronous detection output and an offset voltage produced by an offset adjustment circuit
29
supplied with a power supply voltage
28
. The above differential amplifying operation results in first and second output signals OUT
1
and OUT
2
. The value of the voltage difference between the first output signal OUT
1
and the second output signal OUT
2
indicates the value of the angular velocity applied to the gyro, and the sign of the voltage difference indicates the direction of the rotation.
FIG. 5
shows a detection circuit
33
for use in the gyro having the electrode arrangement shown in
FIGS. 2A and 2B
. The detection signals DET
1
and DET
2
are applied to a differential amplifier
34
, which performs a differential amplifying operation thereon. An output signal of the differential amplifier
34
is compared with the offset voltage by the differential amplifier circuit
32
used in the structure shown in FIG.
4
. The differential amplifier
32
results in first and second output signals OUT
1
and OUT
2
.
The detection signals DET
1
and DET
2
are subjected to the differential amplifying operation, so that leakage voltage which may be included in the detection signals DET
1
and DET
2
can be canceled. It should be noted that the gyro produces no detection signals if the gyro does not receive any angular velocity. However, the gyro may slightly produce detection signals irrespective of the gyro does not receive any angular velocity. Such detection signals are leakage voltages or signals.
FIG. 6
shows factors which cause the leakage voltage. The factors can be categorized in three groups. The first group of factors is called an electro-magnetic coupling leakage and is due to a surplus component of force coefficients caused by an unbalanced situation of the electrodes (errors in the size of electrodes and/or positions thereof). The electro-magnetic coupling leakage includes a leakage on the drive side and a leakage on the detection side. The second group of factors is called an electrostatic coupling leakage and is due to an electrostatic coupling capacitance between the input and output sides, that is, between the drive-side electrodes and the detection-side electrodes. The third group of factors is called a mechanical coupling leakage and is due to a mechanical coupling between the drive-side vibration and the detection-side vibration.
It may be possible to reduce the leakage voltages due to any of the first through third groups of factors by means of complex and troublesome works. For example, the electrodes are finely formed and finely positioned. If a positional error of an electrode happens, the electrode is cut off, for example. Alternatively or additionally, as shown in
FIGS. 7A and 7B
, a corner portion
35
of one or both of the arms
11
and
12
is cut off in order to change the moment of at least one of the arms
11
and
12
and thus reduce an unwanted vibration.
However, in practice, it is very difficult to greatly reduce the leakage, preferably t
Ishikawa Hiroshi
Satoh Yoshio
Takahashi Yoshitaka
Yachi Masanori
Yamada Sumio
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
Moller Richard A.
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