Vibration gyro

Details Vibration gyro Vibration gyro

1998-05-08

2001-08-28

Dougherty, Thomas M. (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S311000, C310S360000, C310S366000, C310S367000

Reexamination Certificate

active

06281619

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration gyroscope that detects angular velocity.
2. Description of Related Art
Rotating gyroscopes of the mechanical type have been used in the past as inertial navigation apparatuses for aircraft and vessels, but their large size and high cost make them difficult to build into small electronic equipment and small transport equipment.
In recent years, however, research with regard to making compact gyroscopes has progressed, and progress has been made in the area of a practically usable vibrating gyroscope in which a piezo-electric element resonator is caused to vibrate, another piezo-electric element resonator mounted thereonto rotating, the vibration caused by the resulting Coriolis force being used to detect the voltage that is generated. This is used in car navigation systems and in shake-detection apparatuses for video cameras.
A gyroscope of the past which uses a piezo-electric element will be described below.
FIG. 13
is a perspective view of a tuning fork type of vibrating gyro of the past.
A tuning fork type of vibrating gyro of the past will be described with reference being made to FIG.
13
. The resonator
71
is made of a constant-resiliency metal such as “Elinvar” and has the structure of a compound tuning fork.
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 driving section and drive electrode
76
are attached to the first beam
73
.
While it is not shown in the drawing, in the same manner another piezo-electric element driving section and drive electrode are attached to the first beam
72
.
The piezo-electric element detector and detection electrode
77
are attached to the second beam
75
and in the same type of detection section and detection electrode are attached to the second beam
74
. In this structure, the direction in which a beam extends is taken as the Z-axis direction.
Next, the action of this 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 equation.
Fc=2·M·&ohgr;·V
In the above equation, 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 Fc, a second bending vibration is excited which has displacement in directions that are perpendicular to the intraplane vibration.
This will be called extraplanar vibration.
By detecting the AC voltage that is generated by this extraplanar vibration using the detection electrode
77
or
79
, it is possible to calculate and know the angular velocity &ohgr;.
However, a vibrating gyro of the past had the following problem. When supporting a resonator, to minimize the influence of the support on the resonator, the support is generally made at a position of the resonator that does not move during vibration, which is at a vibration node.
In the tuning fork configuration which is shown in
FIG. 13
, the node of the intraplanar vibration is at the base part and while there is almost no movement in this area, in the case of extraplanar vibration which is excited by Coriolis force, there is no part that does not move in accordance with the vibration. Therefore, regardless of the method of support, the support will influence the resonator.
In general a tuning fork type of resonator is supported in the middle of the base part, and whereas the cases of supporting in this part and not supporting in this part, there is almost no change in the resonant frequency for the intraplanar vibration, in the case of extraplanar vibration the resonant frequency is changed by several percent.
Therefore, the extraplanar vibration will change several percent in accordance with the type of support used. In this case, the alternating Coriolis force that has the intraplanar vibration resonant frequency excites extraplanar vibration, but the excitation efficiency exhibits dependency 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 to achieve sufficient excitation of extraplanar vibration, and a small change in the support can make a large change in the extraplanar vibration resonant frequency, so that the excitation efficiency greatly changes, making detection with good accuracy impossible. For this reason, tuning fork type vibrating gyros did not enjoy sufficiently wide use.
At present, there have been proposed various vibrating gyros having configurations such as a tuning fork configuration or a single-beam configuration, and because a vibrating gyro detects a Coriolis force that acts in a direction that is perpendicular to the vibration direction, it is thought to be advantageous to have a configuration that has symmetry about the center within a plane that is perpendicular to the rotational direction that is to be detected, and at present the single-beam configuration is the chiefly used configuration.
However, the support of a single-beam configuration is difficult, it is difficult to achieve support that does not influence the resonator, and it is not possible to completely prevent leakage of vibration to the outside.
Examples of easy support that has been envisioned long ago are the four-beam tuning fork or the multi-beam tuning fork.
For example, in the Japanese Unexamined Patent Publication (KOKAI)No. 6-258083 there is disclosure of four-beam tuning fork vibrating gyro.
This four-beam tuning fork has a configuration having symmetry about the center within a plane that is perpendicular to the rotational direction that is to be detected, the same as with a single-beam configuration, and additionally, as a characteristic of the tuning fork configuration, because the bottom surface of the base part does not vibrate, it is possible to achieve complete vibrational isolation with the outside.
The four-beam vibrating gyro which is disclosed in the Japanese Unexamined Patent Publication (KOKAI)No. 6-258083 can be used to implement a vibrating gyro with almost no vibration of the base part, by selecting vibrational modes for which the directions of drive and Coriolis force detection are perpendicular from the six existing first-order vibration modes of the four-beam tuning fork and by using first order coupling thereof to detect Coriolis force.
The six first-order vibration modes of a four-beam tuning fork with good symmetry will now be described with reference to relevant accompanying drawings.
FIG. 21
is a front elevation view of a general type of four-beam tuning fork, in which the condition of the bottom surface of the base thereof being semi-fixed is indicated by hatching.
The sizes of various parts of this four-beam tuning fork are: overall length 4.8 mm, base length 1.92 mm, beam length 2.88 mm, base width 1.2 mm, beam width 0.48 mm, and groove 0.24 mm.
FIG.
22
through
FIG. 27
are cross-sectional views of the beams as seen from the ends of the beams of the four-beam tuning fork, the six first-order vibration modes that each of the beams of this four-beam tuning fork having been calculated using the finite element method, verified by experiment, and indicated in sequence of increasing frequency.
Note, however, that the last torsion mode could not b

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