Vibration gyro

Details Vibration gyro Vibration gyro

2002-09-06

2004-01-13

Moller, Richard A. (Department: 2856)

Measuring and testing

Speed, velocity, or acceleration

Angular rate using gyroscopic or coriolis effect

Reexamination Certificate

active

06675651

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration gyro for detecting an angular velocity.
2. Description of the Prior Art
Conventionally, mechanical rotary gyroscopes have been used as inertial navigation systems of airplanes and ships. The systems have been large in size and expensive. Thus, it has been difficult to build the gyroscopes into small electronic equipment and small conveying machines.
However, in recent years, miniaturization of gyroscopes has been studied to put a vibration gyro into practical use. In the vibration gyro, a vibrator is excited by a piezoelectric element, and voltage generated by vibration resulting from Coriolis force applied to the vibrator when it rotates is detected by another piezoelectric element provided on the vibrator. Such gyroscopes have been used for navigation systems of vehicles, shake detectors of video cameras, and so on.
Particularly, a vibration gyro using a piezoelectric single crystal is promising because the single crystal has a simple configuration, is adjusted with ease, and is excellent in temperature characteristics. As an example using the piezoelectric single crystal, the following will discuss the configuration and function of a tuning-fork vibration gyro using quartz in accordance with
FIGS. 5 and 6
.
The tuning-fork vibration gyro is formed by evaporating driving detecting electrodes onto a vibrator J
10
, on which quartz is integrally worked. The vibrator J
10
is configured such that two tines J
11
and J
12
disposed laterally in parallel are connected to a base J
15
. Driving electrodes J
1
to J
4
are deposited onto the four sides of the left tine J
11
. Detecting electrodes J
5
to J
8
are deposited onto the four sides of the right tine J
12
. The bottom of the base J
15
is used to support the vibration gyro.
Here, the extending direction of the tines J
11
and J
12
is referred to as a Y′-axis direction, the aligning direction of the tines J
11
and J
12
is referred to as an X-axis direction, and a direction orthogonal to X-axis and Y′-axis directions is referred to as Z′-axis direction. As shown in
FIG. 5
, a rectangular Cartesian coordinate of X-Y′-Z′ is formed by rotating the rectangular Cartesian coordinate of X-Y-Z, on which the X-axis and Z-axis conform to crystal axes, by &thgr; around the X-axis.
First, when the first tine J
11
is bent to the second tine J
12
in the X-axis direction, a part around an electrode J
2
expands in the Y′-axis direction, and a part around an electrode J
4
shrinks in the Y′-axis direction. At this moment, in the quartz, an electric field appears on the part around the electrode J
2
in the X-axis direction and an electric field appears on the part around the electrode J
4
in the −X-axis direction due to the piezoelectric effect.
At this moment, in view of the direction of the electric field, the electrodes J
2
and J
4
are equal in potential and are higher in potential than the center of the tines. In the X-axis direction, the electrodes J
1
and J
3
positioned near the center of the tines are relatively lower in potential than the electrodes J
2
and J
4
. Thus, a potential difference appears between the electrodes J
2
and J
4
and the electrodes J
1
and J
3
.
As the piezoelectric effect is reversible, when a potential difference is provided between the electrodes J
2
and J
4
and the electrodes J
1
and J
3
, an electric field appears accordingly in the quartz, and the left tine J
11
is bent in the X-axis direction.
Thus, the potentials of the electrodes J
1
and J
3
are amplified by an amplifier JG according to an amplification factor exceeding the oscillating condition, the phase is regulated by a phase-shift circuit JP so as to satisfy an oscillating condition, and the potentials are returned to the electrodes J
2
and J
4
. Hence, energy is converted between mechanical return force, which is generated by the bending of the left tine J
11
, and electrical force, and the left tine J
11
can be subjected to self-excited oscillation in the X-axis direction.
Entirely on the tuning-fork vibrator J
10
, in order to balance momentum between the left tine J
11
and the right tine J
12
, when the left tine J
11
is moved in the X-axis direction, the right tine J
12
moves in the −X-axis direction, and when the left tine J
11
moves in the −X-axis direction, the right tine J
12
moves in the X-axis direction. The movements of the left and right tines J
11
and J
12
are called in-plane bending vibration, considering the fact that vibration in a single plane is generally regarded ideal for an ordinary tuning-fork. The vibrations of the first tine J
11
caused by the amplifier JG and the phase-shift circuit JP are the same as the in-plane bending vibration. The frequency is substantially equal to a resonance frequency of the in-plane bending vibration of the vibrator J
10
.
In this state, when the vibrator J
10
is entirely rotated around the Y′-axis with an angular velocity &ohgr;, Coriolis force Fc is applied to the left and right tines J
11
and J
12
of the vibrator J
10
in the Z′-axis direction, which intersects in-plane bending vibration. The Coriolis force Fc can be expressed by the equation below.
Fc=
2·
M·&ohgr;·V
In this equation, M represents a mass of the left tine J
11
or the right tine J
12
, and V represents a speed of the left tine J
11
or the right tine J
12
.
The Coriolis force Fc excites bending vibration on the left tine J
11
and the right tine J
12
. The bending vibration is displaced in the Z′-axis direction (orthogonal to the X-axis direction which is the operating direction of the in-plane bending vibration). Hereinafter, the bending vibration will be referred to as out-of-plane bending vibration. Further, Coriolis force does not increase in proportion to the displacement but to the speed. Thus, out-of-plane bending vibration generated by Coriolis force occurs with a phase delayed by 90° from the in-plane bending vibration.
Due to the out-of-plane bending vibration, a part around electrodes J
5
and J
8
of the right tine J
12
expands and shrinks in the Y′-axis direction, and a part around electrodes J
6
and J
7
expands and shrinks in opposite phase from the part around the electrodes J
5
and J
8
.
For example, when the part around the electrodes J
5
and J
8
extends in the Y′-axis direction, an electric field appears in the X-axis direction on the part around the electrodes J
5
and J
8
in the right tine J
12
. At this moment, as the part around the electrodes J
6
and J
7
shrinks in the Y′-axis direction, an electric field appears in the −X-axis direction on the part around the inner electrodes J
6
and J
7
in the right tine
12
. Namely, when the electrode J
5
is higher in potential than the electrode J
8
, the electrode J
7
is higher in potential than the electrode J
6
.
Moreover, when the part around the electrodes J
5
and J
8
shrinks in the Y′-axis direction, an electric field appears in the −X-axis direction on the part around the inner electrodes J
5
and J
8
in the right tine J
12
. At this moment, as the part around the electrodes J
6
and J
7
expands in the Y′-axis direction, an electric field appears in the X-axis direction on the part around the inner electrodes J
6
and J
7
in the right tine
12
. Namely, when the electrode J
5
is lower in potential than the electrode J
8
, the electrode J
7
is lower in potential than the electrode J
6
.
A potential difference between the electrodes J
5
and J
8
and the electrodes J
6
and J
7
is changed according to the direction of the second tine J
12
which vibrates in the Z′-axis direction. From a different point of view, when the electrode J
5
has a high potential, the electrode J
7
also has a high potential. At this moment, the electrodes J
6
and J
8
have low potentials. Meanwhile, when the electrode J
5
has a low potential, the electrode J
7
also has a low potential. At this mome

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