Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-05-25
2001-09-11
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C073S504130, C073S504160, C310S366000, C310S370000
Reexamination Certificate
active
06288474
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gyroscope used in a navigation system or the like and a drive detection device therefor and, more particularly, to a drive detection device for a gyroscope using a piezoelectric vibrator which can be easily manufactured by achieving a reduction of the number of electrodes and simplification of dielectric polarization.
2. Description of the Related Art
FIG. 4
is a perspective view showing a trident-type tuning fork piezoelectric vibrator as an example of a conventional vibratory gyroscope, and is of the same type as that of, e.g., a piezoelectric vibrator disclosed in Japanese Unexamined Patent Publication No. 9-101156.
FIG. 5A
is a front view obtained by viewing the piezoelectric vibrator shown in
FIG. 4
in the direction of arrow V, and
FIG. 5B
is a front view showing a drive state.
In the piezoelectric vibrator shown in
FIG. 4
, three vibrators parallel separated from each other are formed at the distal end of an elastic plate entirely made of a piezoelectric material such as piezoelectric ceramic. In this piezoelectric vibrator, since the vibrators on both the sides vibrate in the same phase, the vibrators on both the sides are indicated by the same reference numeral
1
. Since the middle vibrator vibrates in a phase different from the phases of the vibrators on both the sides, the middle vibrator is indicated by reference numeral
2
which is different from the reference numerals of the vibrators
1
on both the sides.
As shown in
FIGS. 5A and 5B
, electrodes
5
a
,
5
b
, and
5
c
are formed on front surfaces
1
a
of the left and right vibrators
1
on both the sides, and electrodes
6
a
,
6
b
, and
6
c
are formed on rear surfaces
1
b
. Electrodes
7
a
,
7
b
, and
7
c
are formed on a front surface
2
a
of the middle vibrator
2
, and electrodes
8
a
,
8
b
, and
8
c
are formed on a rear surface
2
b
. As shown in
FIG. 4
, the respective electrodes extend along the direction of axis Z throughout the entire lengths of the vibrators
1
and
2
in the longitudinal direction.
The vibratory drive directions of the vibrators
1
and
2
is X directions (first directions). In the vibrators
1
and
2
, when the X directions (first directions) which are vibratory drive directions are set to be directions of width, the electrodes
5
a
,
5
c
,
6
a
,
6
c
,
7
a
,
7
c
,
8
a
, and
8
c
are formed at both the edge portions of the vibrators
1
and
2
in the directions of width. The electrodes
5
b
,
6
b
,
7
b
, and
8
b
are located at the centers of the vibrators
1
and
2
in the directions of width (X directions).
FIG. 5A
shows polarities of an applied electric field when dielectric polarization is performed to a piezoelectric material. DC voltages applied to respective electrodes are represented by + and −, and a ground potential is represented by G. In the vibrators
1
on both the sides, the electrodes
5
b
and
6
b
located at the centers in the directions of width on the front and rear surfaces have ground potentials. On the front surface
1
a
, a negative voltage is applied to the electrodes
5
a
and
5
c
located at both the edge portions in the directions of width. On the rear surface
1
b
, a positive voltage is applied to the electrodes
6
a
and
6
c
located at the edge portions in the directions of width. In the middle vibrator
2
, the electrodes
7
b
and
8
b
located at the centers have ground potentials. On the front surface
2
a
, a negative voltage is applied to the electrodes
7
a
and
7
c
located at both the edge portions in the directions of width. On the rear surface
2
b
, a positive voltage is applied to the electrodes
8
a
and
8
c
located at both the edges in the directions of width. Arrows shown in
FIG. 5A
are directions of electric fields applied across the electrodes at this time, and dielectric polarization is performed along the electric field directions.
In this piezoelectric vibrator, the electrodes
6
b
and
8
b
of the vibrators
1
and
2
are used as detection electrodes. The detection electrodes
6
b
and
8
b
are formed on surfaces (
1
b
,
2
b
) extending the X directions (first directions) on the vibrators
1
and
2
and formed at the central positions in the directions of width of the X directions. In the vibrator
1
, dielectric polarization directions on the left and right of the X directions are symmetrical with respect to the portion of the detection electrode
6
b
. Similarly, in the vibrator
2
, dielectric polarization directions are symmetrical on the left and right of the X directions with respect to a portion where the detection electrode
8
b.
In
FIG. 5B
, the phases of AC drive voltages applied to the respective electrodes are represented by signs + and −. When sign + is expressed on a certain electrode, and sign − is expressed on the other electrode, it means that AC drive voltages having a phase difference of 180° (&pgr;) are applied to both the electrodes. Mark o in
FIG. 5B
represents plus distortion (extension) caused by the piezoelectric effect, and mark x represents minus distortion (contraction).
In the drive method in
FIG. 5B
, the electrodes
5
b
,
6
a
,
6
c
,
7
b
,
8
a
, and
8
c
are grounded. The electrodes
5
a
,
5
c
,
7
a
, and
7
c
are drive electrodes located on the front surfaces
1
a
and
2
a
of the vibrators
1
and
2
, and the electrodes
6
b
and
8
b
located at the centers of the rear surfaces
1
b
and
2
b.
As an AC drive power, voltages which are in-phase are applied to the electrodes
5
c
and
7
a
, and voltages which are in-phase (opposite from the above phase) are applied to the electrodes
5
a
and
7
c
. As a result, on the surfaces
1
a
of the vibrators on the left and right, at a certain point of time, plus distortion o occurs between the electrodes
5
a
and
5
b
, and minus distortion x occurs between the electrodes
5
b
and
5
c
. In the middle vibrator
2
, on the front surface
2
a
, minus distortion x occurs between the electrodes
7
a
and
7
b
, and plus distortion o occurs between the electrodes
7
b
and
7
c
. Therefore, at a certain point of time shown in
FIG. 5B
, bending vibration occurs such that the amplitude directions of the vibrators
1
on both the sides are set to be a +X direction, and the amplitude of the middle vibrator
2
is performed in a −X direction. More specifically, the vibrators
1
on both the sides and the middle vibrator
2
vibrate with phases opposite from each other in the X directions.
When the piezoelectric vibrator is placed in a rotation system rotated about axis Z, force in Y directions (second directions) which are orthogonal to the vibration direction works due to Coriolis force. Since the left and right vibrators
1
and the middle vibrator
2
are vibratorily driven with phases opposite from each other in the X directions, the vibration components generated by Coriolis force are opposite from each other in phase in the vibrators
1
on both the sides and the middle vibrator
2
. For example, when the amplitude direction of the vibrators
1
on both the sides is a +Y direction at a certain point of time, the amplitude direction of the middle vibrator
2
is a −Y direction.
Vibration components generated by the Coriolis force are obtained from the detection electrodes
6
b
and
8
b
formed at the centers of the rear surfaces
1
b
and
2
b
of the vibrators
1
and
2
in the directions of width.
In the vibration component of each vibrator generated by Coriolis force, when the amplitude direction of the vibrators
1
is the +Y direction at a certain point of time, the piezoelectric materials of the portions of the detection electrodes
6
b
“extends”. The amplitude direction of the middle vibrator
2
becomes the −Y direction, and the piezoelectric material of the portion of the detection electrode
8
b
“contracts”. Since all the dielectric polarization directions of the portions where the detection electrodes
6
b
,
8
b
, and
6
b
Hasegawa Kazuo
Ono Yasuichi
Takai Daisuke
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Budd Mark O.
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