Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-05-09
2002-06-04
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
active
06397676
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric oscillator for use in gyroscopes, and more particularly, relates to a piezoelectric oscillator in which the number of electrodes is reduced, and relates to a signal detection apparatus using the same.
2. Description of the Related Art
FIG. 15A
is a perspective view showing one of the surfaces of a conventional three-pronged tuning-fork-type piezoelectric oscillator.
FIG. 15B
is a perspective view showing the other surface thereof.
FIG. 16
is a front view of a piezoelectric oscillator when the piezoelectric oscillator of
FIG. 15A
is viewed from the direction of arrow
16
.
The whole of an oscillator
1
is formed from a plate-shaped piezoelectric material, such as a piezoelectric ceramic or a quartz crystal; a tip portion thereof is separated by slots
1
A and
1
A, and three vibration legs
1
a
,
1
b
, and
1
c
are integrally formed therewith. The dielectric polarization direction of the piezoelectric material in each of the vibration legs
1
a
,
1
b
, and
1
c
is as indicated by the arrows in FIG.
16
. The dielectric polarization direction is the same for the vibration legs
1
b
and
1
c
on both right and left sides. In the center vibration leg
1
a
, the dielectric polarization direction is laterally and vertically symmetrical with respect to the vibration legs
1
b
and
1
c
on the right and left.
The lower surface of each of the vibration legs
1
a
,
1
b
, and
1
c
is formed with a pair of driving electrodes
2
and
2
, using a conductive material. The driving electrodes
2
,
2
, . . . , extend up to the base end portion
1
B of the oscillator
1
, as shown in FIG.
15
B. These driving electrodes
2
,
2
, . . . , are connected to an AC driving power supply
3
by wiring (not shown), so that a driving voltage of the same electrical potential is supplied to the driving electrodes
2
,
2
, . . . , from the AC driving power supply
3
.
On the upper surface of the oscillator
1
, a pair of ground electrodes
4
and
4
are formed in each of the vibration legs
1
b
and
1
c
on the right and left, and one ground electrode
4
is formed in the center vibration leg
1
a
. The driving electrodes
4
,
4
, . . . , extend to the base end portion
1
B of the oscillator
1
. On the surface of the oscillator
1
shown in
FIG. 15A
, a concentration pattern
4
a
is formed in the base end portion
1
B, and all the ground electrodes
4
are connected to the concentration pattern
4
a
. Each of the ground electrodes
4
is at the ground potential by a wiring path (not shown).
The driving electrodes
2
,
2
, . . . , and the ground electrodes
4
,
4
, . . . , supply a driving voltage to the piezoelectric material which is a driving means. Based on the dielectric polarization structure shown in
FIG. 16
, the vibration legs
1
b
and
1
c
on the right and left are driven to vibrate at the same phase in the X direction, and the vibration leg
1
a
in the center is driven to vibrate 180° out of phase opposite to that of the vibration legs
1
b
and
1
c
on right and left similarly in the X direction. That is, at a particular point in time, the amplitude of the vibration legs
1
b
and
1
c
on the right and left in the X direction and the amplitude of the vibration leg
1
a
in the X direction are opposite.
The surface of the center vibration leg
1
a
is formed with a pair of detection electrodes
5
a
and
5
b
. The detection electrodes
5
a
and
5
b
extend more toward the front than the base end portion
1
B in the back portion of the oscillator
1
, and the detection electrodes
5
a
and
5
b
are formed integrally with land portions
5
a
1
and
5
b
1
, respectively.
In a state in which the vibration legs
1
a
,
1
b
, and
1
c
are driven in the X direction, when the oscillator
1
is placed within a rotating system having an angular velocity &ohgr; about the Z axis, each of the vibration legs
1
a
,
1
b
, and
1
c
has a vibration component in the Y direction due to a Coriolis force. In the vibration legs
1
b
and
1
c
on both sides and the vibration leg
1
a
in the center, since the phases of vibrations by a driving voltage are opposite, the phases of vibrations by a Coriolis force are opposite between the vibration legs
1
b
and
1
c
and the vibration leg
1
a
. That is, at a particular point in time, the directions of the amplitude components, in the Y direction by the Coriolis forces, of the vibration legs
1
b
and
1
c
are the same, and the direction of the amplitude components in the Y direction, of the center vibration leg
1
a
is opposite to the direction of those of the vibration legs
1
b
and
1
c.
The detection electrodes
5
a
and
5
b
are formed on the same plane (the same vibration plane) of the center vibration leg
1
a
, and the piezoelectric material of the center vibration leg
1
a
functions as a Coriolis force detection means. The dielectric polarization directions of the piezoelectric materials in the portions where the detection electrodes
5
a
and
5
b
are formed are opposite to each other. Therefore, when each of the vibration legs
1
a
,
1
b
, and
1
c
is driven to vibrate in the X direction in accordance with a driving signal from the AC driving power supply
3
, and when an angular velocity &ohgr; is given, the Coriolis output component by vibrations in the Y direction by a Coriolis force cause a phase difference &phgr; to occur between a detection output C from the detection electrode
5
a
and a detection output D from the detection electrode
5
b
.
For these detection outputs C and D, a DC voltage corresponding to the phase difference &phgr; is detected by a phase difference detection means (not shown), the angular velocity &ohgr; is determined from this DC voltage, and the angle is determined by numerical integration of this angular velocity &ohgr;.
However, in the signal detection method in the above-described conventional gyroscope, there are problems such as those described below.
First, in the center vibration leg
1
a
, in addition to the detection electrode
5
a
and the detection electrode
5
b
, the ground electrode
4
is provided on the narrow surface thereof, and moreover, this ground electrode
4
must be formed parallel to the detection electrode
5
a
and the detection electrode
5
b
in an area from the tip of the vibration leg
1
a
up to the base end portion
1
B.
However, it is difficult to evenly form the ground electrodes
4
at an equal spacing from both the detection electrodes
5
a
and
5
b
in the area from the tip of the vibration leg up to the base end portion
1
B. Therefore, if the creeping distance Wa between the ground electrode
4
and the detection electrode
5
a
differs from the creeping distance Wb between the ground electrode
4
and the detection electrode
5
b
, there is a problem in that insulation breakdown is likely to occur between the ground electrode
4
and the detection electrode
5
a
or between the ground electrode
4
and the detection electrode
5
b.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above-described conventional problems. An object of the present invention is to provide a piezoelectric oscillator in which the number of ground electrodes, which are required conventionally, can be reduced, simplifying a manufacturing process.
Another object of the present invention is to provide a piezoelectric oscillator in which electrodes are arranged appropriately in vibration legs so that a phase difference can be reliably detected, and to provide a signal detection apparatus using this piezoelectric oscillator.
To achieve the above-mentioned objects, according to the present invention, there is provided a piezoelectric oscillator for outputting an angular velocity proportional to a Coriolis force in a rotating system, the piezoelectric oscillator comprising: a vibration leg having a rectangular or square cross section; a pair of driving electrodes extending with a spacing therebetween in a direction in which the vibration leg is d
Hasegawa Kazuo
Ono Yasuichi
Takai Daisuke
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
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