Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2001-03-05
2002-12-10
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C310S370000
Reexamination Certificate
active
06490925
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a vibration gyroscope of a tuning fork type formed of piezoelectric material to be used as a piezoelectric vibration gyroscope, and a method for adjusting resonance frequencies of the same.
BACKGROUND OF THE INVENTION
In general, a vibration gyroscope is known as a device for measuring an angular velocity of a rotating object mounting a vibrating object thereon by making use of a phenomenon that Coriolis force which is vertical to both a vector of the angular velocity and that of the vibration exerts on the vibrating object, and has been used as the device for confirming a position of an aircraft, a vessel or a space orbiter.
Recently, the vibration gyroscope has come to be used for various commercial purposes, such as positioning in a car navigation, control of an attitude of an automobile, or detection of deflection of a camera for a VTR or a still picture.
In the aforementioned vibration gyroscope, a driving voltage is impressed upon this device to excite a driving vibration, and a detecting vibration caused by Coriolis force is detected electrically. The vibration gyroscope of the aforementioned type are classified into a Sperry tuning fork gyroscope, a Watson tuning fork gyroscope, a rectangular metal plate tuning fork gyroscope, a cylindrical vibration gyroscope, etc. as shown in “Elasticwave device hand book” (OHM Co.Ltd) pp.491 to pp.497.
Heretofore, a piezoelectric vibration gyroscope of this kind has been disclosed in Japanese Patent Applications Laid-Open No.8-128830, in which a tuning fork gyroscope with high performance formed of lithium tantalate is made public.
The aforementioned piezoelectric vibration gyroscope will be explained referring to
FIGS. 1A
,
1
B.
As shown in these drawings, a piezoelectric vibration gyroscope
100
is composed of a base
101
having a rectangular major surface
101
a and right and left arms
102
,
103
projecting from both side ends of the base
101
on the same sides thereof, and all these structural elements constitutes a gyroscope of a tuning fork type. The right and left arms
102
,
103
are respectively provided with driving electrodes for exciting a vibration and detecting electrodes for detecting the vibration (both the electrodes are not shown).
Next, the operation of the piezoelectric vibration gyroscope mentioned in the above will be explained referring to
FIGS. 1A
,
1
B.
If a driving voltage is impressed upon the electrodes on the right arm
102
, the arm
102
vibrates from right to left in a plane running in parallel with the major surface
101
a
of the piezoelectric vibration gyroscope
100
. When the right arm
102
vibrates, the vibration is transmitted to the left arm
103
via the base
101
, and the arms
102
,
103
start a tangential vibration. That is to say, these arms repeat such movements that the arms
102
,
103
are close to and remote from each other in a plane running in parallel with the major surface
101
a
of the piezoelectric vibration gyroscope
100
. The tangential vibration is one of characteristic modes of the piezoelectric vibration gyroscope
100
, and functions as a driving vibration mode in this example.
At this time, if the piezoelectric vibration gyroscope
100
is fixed to a rotating object which rotates around the Z axis (a direction of projection of the arms
102
,
103
) shown in
FIG. 1A
at an angular velocity of &OHgr;, Coriolis forces Fc vertical to the major surface
101
a
exert on the arms
102
,
103
.
Accordingly, the vertical vibration is excited in the arms
102
,
103
because of Coriolis forces Fc, and thereby these arms repeat such a movement that they are displaced in the opposite directions vertically to the major surface
101
a.
The vertical vibration is another one of the characteristic vibration modes of the piezoelectric vibration gyroscope
100
also, and functions as a detecting vibration mode in this example.
In order to detect the angular velocity &OHgr; of the rotating object around the Z axis, the vertical vibration of the detecting vibration mode is detected through a difference in a potential between the detecting electrodes formed on the arm
103
.
However, on the conventional piezoelectric vibration gyroscope mentioned in the above, since there is no nodal (unmoved) point of both the driving and detecting vibration modes, not only the vertical vibration (the detecting vibration mode) but also the tangential vibration (the driving vibration mode) are excited in the left arm
103
. Moreover, since both the arms
102
,
103
project on the same side, these arms are situated closely to each other.
As a result, the driving and detecting modes interfere with each other. That is to say, a mechanical coupling occurs between the arms
102
,
103
. Moreover, a voltage impressed upon the driving electrodes interferes with a detecting current flowing through the detecting electrodes, hence an electrostatical coupling occurs between the driving and detecting electrodes. Accordingly, an electromechanical coupling occurs between the driving and detecting electrodes, which causes a noise interfering with the detection, deteriorates a S/N ratio, and lowers a resolution of the angular velocity.
Accordingly, it is an object of the invention to provide a piezoelectric vibration gyroscope and a method for adjusting resonance frequencies of driving and detecting modes of the same, in which an angular velocity of a rotating object is detected under a satisfactory S/N ratio, and a resolution of an angular velocity is heightened.
According to the first feature of the invention, a piezoelectric vibration gyroscope comprises:
a main body shaped into a rectangular plate and provided with obverse and reverse surfaces functioning as major surfaces, and
first and second groups of three arms projecting from the main body in opposite directions and lying on extensions of the major surfaces,
wherein the main body and the first and second groups of the three arms are formed of piezoelectric material,
the first group of the three arms is composed of two excitation driving side arms excited in an opposite phase and a nonexcitation driving side arm inserted between the two excitation driving side arms,
the second group of the three arms is composed of two vibration detecting side arms vibrating in an opposite phase and a nonvibration detecting side arm inserted between the two vibration detecting side arms,
the two excitation driving side arms are respectively provided with driving electrodes for exciting a tangential vibration vibrating in parallel with the major surfaces, and
the two vibration driving side arms are respectively provided with detecting electrodes for detecting a vertical vibration vibrating vertically to the major surfaces.
Accordingly, when the whole gyroscope is situated on a rotating object and a driving voltage is impressed upon the excitation driving side arms to excite a tangential vibration, the vertical vibration is generated in the excitation driving side arms because of Coriolis force, and the vertical vibration is transmitted to the vibration detecting side arms via the main body to excite the vertical vibration therein.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the main body is shaped into the rectangular plate so that a transmission of the tangential vibration from the excitation driving side arms to the vibration detecting side arms can be suppressed.
Accordingly, even when the tangential vibration is excited in the excitation driving side arms, the main body prevents the tangential vibration from being transmitted to the vibration detecting side arms.
In the piezoelectric vibration gyroscope according to another aspect of the invention, the main body and the first and second groups of the three arms are formed into one united body.
The frequency characteristic of the aforementioned piezoelectric vibration gyroscope is more excellent than that of a piezoelectric vibration gyroscope in which the arms are connected with the main body via joints.
In the piezoelec
Inoue Takeshi
Yamamoto Mitsuru
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