Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-12-22
2002-04-02
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06366005
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a gyro used for detecting the rotation angular velocity, more particularly, to a tuning fork type vibration gyro having two arms and a base formed in one-piece.
BACKGROUND ART
Gyroscopes have been used as means for identifying the position of moving objects such as airplane, large vessels, space satellites, and the like. Recently, they have been utilized for detecting vibration of apparatus such as a car navigation system and video camera. Among such gyroscopes, research and development of a tuning fork type vibration gyro having a constitution comprising two arms and a base for supporting the two arms, which are formed in one-piece by a piezoelectric monocrystal, have been pursued.
FIG. 1
is, for example, a structural view of a tuning fork type vibration gyro disclosed in Japanese Patent Application Laid-Open (Tokukaihei) No. 9-269228(1997). In
FIG. 1
, numeral
1
denotes a tuning fork type vibrator. The tuning form type vibrator
1
has two arms
2
,
3
and a base
4
for supporting the arms
2
and
3
. The arms
2
,
3
and base
4
are formed in one-piece by processing a piezoelectric monocrystal such as LiTaO
3
, LiNbO
3
, etc. By coupling the base
4
of this tuning fork type vibrator
1
to a supporting substrate
6
mounted on a stem
5
, the tuning fork type vibrator
1
is supported.
Moreover, a horizontal section of a supporting arm
7
having a substantially U-shaped cross section is inserted into a slit of the supporting substrate
6
formed to include the center of rotational motion of the supporting substrate
6
, and attached flexibly to the supporting substrate
6
through an adhesive layer
8
formed of a rubber-like elastic body. Both of the end sections of the supporting arm
7
are provided with a protrusion, and these protrusions are inserted into holes formed in the stem
5
.
Furthermore, in order to cover and protect these members, a cap
9
is provided. The cap
9
and the stem
5
form a case
10
. Besides, a circuit substrate
11
(see
FIG. 5
) including a later-described drive circuit for exciting drive vibration and a detection circuit for processing a detection signal may be provided on the stem
5
and/or the cap
9
so as to be housed in the case
10
.
As shown in FIGS.
2
(
a
) and
2
(
b
), such a tuning fork type vibrator
1
includes fx mode vibration (in-plane vibration) and fy mode vibration (plane-vertical vibration). When drive vibration (in-plane vibration) is exited, if a rotational angular velocity is applied, detection vibration (plane-vertical vibration) occurs, and then an output signal proportional to the magnitude of this vibration is detected so as to find the angular velocity.
By the way, denoting a drive vibration (in-plane vibration) direction, a detection vibration (plane-vertical) vibration direction and a rotation axis direction perpendicular to both of these directions as the X direction, Y direction and Z direction, respectively, when external vibration or impact is applied to the X direction and Y direction particularly, the tuning fork type vibrator
1
produces oscillating motion as shown in FIGS.
3
(
a
) and
3
(
b
) together with the supporting substrate
6
.
In this case, as shown in FIGS.
4
(
a
) and
4
(
b
), the tip of the tuning fork type vibrator
1
(arms
2
and
3
) bumps first against the inner wall of the case
10
, that is, the stem
5
or the cap
9
. Besides, if the circuit substrate
11
is mounted on the inner wall of the case
10
, as shown in FIGS.
5
(
a
) and
5
(
b
), the tip of the tuning fork type vibrator
1
(arms
2
and
3
) bumps first against the circuit substrate
11
. Here, if external vibration or impact is great, the tuning fork type vibrator
1
is destroyed as it is broken at the joint section of the arms
2
and
3
by this impact, causing a problem that the tuning fork type vibrator
1
can not perform the function of a sensor.
Various ideas for protecting the tuning fork type vibrator from external vibration or impact have been proposed (Japanese Patent Application Laid-Open (Tokukaihei) No. 5-18755(1993) (prior art 1) and No. 7-243857(1995) (prior art 2)).
In the prior art 1, a cushioning member and a protecting member are illustrated. This cushioning member is provided between a cover to which a supporting member for supporting the tuning fork type vibrator is secured and a case surrounding the cover, and has the function of absorbing external vibration. Moreover, the protecting member provided in the vicinity of the outside of both of the ends of the supporting member of the tuning fork type vibrator has the function of preventing an excessive displacement of the tuning fork type vibrator, i.e., a large plastic deformation of the supporting member.
However, in this prior art 1, if vibration with a very high accelerating rate is applied, the cushioning member can not absorb this vibration. Consequently, the supporting member has a plastic deformation, and the center axis of the tuning fork type vibrator is displaced from the initial set position, resulting in significant deterioration of gyro characteristics. In addition, there is a possibility that the plastic deformation of the supporting member is further increased by impact, etc. and the tuning fork type vibrator remains contact with the surrounding members. In such a case, since the drive vibration is stopped, the tuning fork type vibrator can not perform the function of a gyro sensor at all.
Meanwhile, the prior art 2 discloses a structure which solves the problem associated with the prior art 1 and is effective to resist external impact. A cushioning member for absorbing external impact is provided between a work plate and a plate to which a supporting member for supporting a tuning fork type vibrator is attached; between a circuit substrate to which the work plate is attached and a case; and between the work cover attached to the work plate and a case. In the structure of this prior art 2, a cushioning member is provided between respective adjacent members among the outermost case, the circuit substrate housed in the case, a shield cover of the circuit substrate, the work cover, the work plate and the tuning fork type vibrator so as to successively absorb external impact by the respective cushioning members.
However, in this prior art 2, since a large number of the cushioning members are provided, there is a problem that the overall structure is not made compact. Moreover, in the event where the tuning fork type vibrator remains contact with the surrounding members, it can not perform the function of a gyro sensor at all like the prior art 1.
Incidentally, in a tuning fork type vibration gyro having a basic structure as shown in
FIG. 1
, when the center axis of rotation of the tuning fork type vibrator
1
and the supporting axis of the supporting arm
7
are perfectly aligned with each other, for example, even if external vibration in the Y direction is applied, the tuning fork type vibrator
1
produces only translation vibration as shown in
FIG. 6
because the upper and lower moments with respect to the line of the supporting axis as the boundary are equal. However, it is difficult to align these axes with each other, and if external vibration in the Y direction is applied when these axes are not aligned with each other, the upper and lower moments with respect to the line of the supporting axis as the boundary are unbalanced, and a rotational motion is produced as shown in FIG.
7
. Thus, there is a problem that, even when a rotational motion is not applied to the tuning fork type vibrator
1
, an unnecessary rotational motion signal is detected.
The principal object of the present invention is to provide a tuning fork type vibration gyro capable of preventing destruction of a tuning fork type vibrator due to external vibration or impact with a compact structure.
Another object of the present invention is to provide a tuning fork type vibration gyro capable of decreasing an unnecessary signal, which is produced when external vibration is applied.
SUMMARY O
Ishikawa Hiroshi
Kikuchi Kazutsugu
Satoh Yoshio
Takahashi Yoshitaka
Yachi Masanori
Addison Karen B
Fujitsu Limited
Greer Burns & Crain Ltd.
Ramirez Nestor
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