Vibration gyroscope

Details Vibration gyroscope Vibration gyroscope

2000-03-22

2002-08-20

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

Reexamination Certificate

active

06437490

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a vibration gyro that detects angular velocity.
BACKGROUND TECHNOLOGY
A variety of vibration gyros, having tuning forks or tines of various shapes have been devised.
While mechanical type rotating gyros have been used as inertial navigation devices in aircraft and ships, the large size of these gyros made it difficult to use them in compact electronic equipment and transportation machinery.
In recent years, however, progress has been made in research in the development of practical compact vibration gyroscopes, in which a piezo-electric vibrating element is caused to vibrate an angular velocity current that is generated by the vibration caused by Coriolis force received because of the rotation of the vibrating element being detected by another piezo-electric element provided in the vibrating element, and such gyros are used car navigation systems and as detector for shaking in video cameras.
A vibration gyro of the past using a piezo-electric device is described below with reference to drawings.
FIG. 29
is a perspective view showing a tuning fork type vibration gyro of the past.
This tuning fork type vibration gyro of the past is described below, with reference to
FIG. 29. A
resonator
71
made of a constant-resiliency metal such as Elinvar has a compound tuning fork structure. That is, the resonator
71
has joined onto the top part of the first beams
72
and
73
the second beams
74
and
75
.
The piezo-electric element or the piezo-electric material driving section and drive electrode
76
are attached to the second beam
73
.
While it is not shown in the drawing, in the same manner another similar driving section and drive electrode are attached to the first beam
72
.
The piezo-electric element or the piezo-electric material driving section and drive electrode
77
are attached to the second beam
75
.
While it is not shown in the drawing, in the same manner another similar driving section and drive electrode are attached to the first beam
74
.
In this structure, the direction in which a beam extends is taken as the Z-axis direction.
The action of the above-noted structure will be described. As a result of an AC voltage that is applied to the drive electrode
76
, the first beams
72
and
73
exhibit a first bending vibration which displaces them to the left and to the right. In the description which follows, this will be called “intraplane vibration,” since it is normally customary to consider the vibration of a tuning fork in a single plane to be the ideal case.
In response to this intraplane vibration, the second beams
74
and
75
that are joined to the first beams
72
and
73
exhibit intraplane vibration. If the overall tuning fork is caused to rotate about the Z axis at an angular velocity of &ohgr;, a Coriolis force Fc acts in a direction that is perpendicular to the intraplane vibration.
This Coriolis force Fc can be expressed by the following relationship.
Fc=M·&ohgr;·V
In the above relationship, M is the mass of the first beams
72
and
73
, or of the second beams
74
and
75
, and V is the velocity of the vibration.
In accordance with the Coriolis force Fc, a second bending vibration is excited which has a displacement in directions that are perpendicular to the intraplane vibration.
This will be called hereinafter extraplanar vibration. By detecting the AC voltage that is generated by this extraplanar vibration using the detection electrode
77
, it is possible to calculate and know the angular velocity &ohgr;.
However, a vibration gyro of the past had the following problem. In general when supporting a vibrating element, to minimize the effect of the support on the vibration, support is made at a node at which the vibrating element does not move when vibrating.
In the case of the tuning fork having the configuration shown in
FIG. 29
, the intraplanar vibration node is at the furcated part, and while this part almost exhibits no movement, with extraplanar vibration excited by Coriolis force, there is no part that does not move due to vibration. Therefore, regardless of the location and method of support, there support will affect the vibrating element.
In general a tuning fork is supported near the center of the furcated part, and in contrast to intraplanar vibration of the vibrating element
71
, which changes hardly at all whether supported at this location or not, with extraplanar vibration there is a change in the resonant frequency which can be as much as several percent.
Therefore, the resonant frequency for extraplanar vibration can change several percent, depending upon the method of support.
Extraplanar vibration is excited by Coriolis force with a frequency of the intraplanar vibration, the excitation efficiency being dependent upon the extraplanar vibration resonant frequency.
If there is distance between the intraplanar vibration resonant frequency and the extraplanar vibration resonant frequency, it is not possible cause sufficient excitation in the extraplanar vibration mode, and if there are large changes in the extraplanar vibration resonant frequency caused by a slight change in the support, the excitation efficiency will change greatly, making highly accurate detection impossible, this problem hindering a sufficient application of vibration gyros of the tuning fork type.
Because a vibration gyro detects a Coriolis force that acts in a direction that is perpendicular to the excitation direction, an element having a shape that is symmetrical about a center of a plane that is perpendicular to rotation direction to be detected is used, and at present a beam type is most commonly used.
However, such a beam-type element is difficult to support and difficult to support without affecting the vibrating element, and makes it impossible to completely prevent leakage of vibration to the outside. Easy-to-supports examples devised in the past include a four-beam tuning fork and a multiple beam tuning fork.
For example, there is the four-beam tuning fork vibration gyro disclosed in the Japanese Unexamined Patent Publication (KOKAI)No. 6-258083.
This four-beam tuning fork has a center symmetry within a plane that is perpendicular to the rotation direction to be detected, the same as with a single-beam type, and has a further feature of not vibrating at the bottom surface of its base part, thereby enabling complete isolation of the vibration with the outside.
In the four-beam tuning fork type vibration gyro disclosed in the Japanese Unexamined Patent Publication (KOKAI)No. 6-258083, of the 6 existing primary vibration modes of the four-beam tuning fork, vibration modes for which the drive and Coriolis force are perpendicular are selected, primary couplings between these modes being used to detect the Coriolis force, thereby achieving a vibration gyro that has almost no vibration at its base part.
The 6 primary vibration modes of a four-beam tuning fork having good symmetry are described below, with reference to the drawings.
FIG. 1
to
FIG. 3
show front views of a general four-beam tuning fork, in which hatching is used to show the fixed condition of the bottom surface of the base part thereof.
The sizes of the various parts of this four-beam tuning fork are a total length of 4.8 mm, a base part length of 1.92 mm, a beam length of 2.88 mm, a base part width of 1.2 mm, a beam width of 0.48 mm and a groove width of 0.24 mm.
FIG.
17
through
FIG. 22
are cross-section view showing this four-beam tuning fork as seen from the ends of the beams, the 6 primary vibration modes that each of these beams of the four-beam tuning fork has, the sequence of the drawings being that of increasing frequency as calculated using finite element analysis and verified later by experiment. The last torsional mode was not verifiable by experiment, however.
FIG.
23
through
FIG. 28
show cross-section views of the beams of the four-beam tuning fork as seen from the ends of the beams, in the same manner, with the overall width of the tuning fork reduced by 1% but the thickness remaining the same.
In con

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