Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-06-21
2004-06-08
Budd, Mark (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06747393
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibrator used for an angular rate sensor used for detecting a turning angular rate in a turning system and a vibratory gyroscope using the same vibrator, and particularly to a vibrator using a piezoelectric member and a vibratory gyroscope using the same vibrator.
2. Description of the Related Art
Up to now, as an angular rate sensor used for detecting a turning angular rate in a turning system, a vibratory gyroscope using a piezoelectric member has been used for detecting position of an aircraft, a ship, a space satellite, or the like. Recently, it is used in a car-navigation system, a movement detecting mechanism of a VTR or a still camera, and the like in the field of public livelihood.
Such a vibratory gyroscope utilizes the phenomenon that when an angular speed is applied to a vibrating object, a Coriolis force is generated in the direction perpendicular to the vibratory direction. Its mechanism is analyzed by using a dynamic model (for example, “Handbook of Elastic Wave Device Technologies” (Danseiha-Sosi Gijutsu Handbook) issued by Ohm, Inc., pp.491 to 497). Various kinds of piezoelectric vibratory gyroscopes have been proposed up to now. For example, a Sperry tuning-fork gyroscope, a Watson tuning-fork gyroscope, a regular-triangle prism-shaped tuning-piece gyroscope, a cylindrical tuning-piece gyroscope, and the like are known as a piezoelectric vibratory gyroscope.
The inventors are studying various applications of vibratory gyroscopes, and have studied using a vibratory gyroscope as a turning rate sensor used in a car control method of an automobile body turning rate feedback system, for example. Such a system detects the direction of a steering wheel itself by a turning angle of the steering wheel. At the same time as this, the system detects the actual turning rate of the car body by means of a vibratory gyroscope. The system finds a difference between the direction of the steering wheel and the actual body turning rate by comparing them with each other, and attains a stable body control by compensating a wheel torque and a steering angle on the basis of this difference.
However, any example of the above-mentioned former piezoelectric vibratory gyroscopes can detect a turning angular rate only by arranging a vibrator in parallel with the axis of turning (what is called a vertical arrangement). The turning axis of a turning system to be measured is usually perpendicular to the gyroscope mounting part. Accordingly, in mounting such a piezoelectric vibratory gyroscope it has been impossible to shorten the piezoelectric vibratory gyroscope in height, namely, to reduce the piezoelectric vibratory gyroscope in size in the direction of the turning axis.
In recent years, a piezoelectric vibratory gyroscope capable of detecting a turning angular rate even when arranging a vibrator perpendicularly to the turning axis (what is called a horizontal arrangement) has been proposed in a Japanese laid-open publication Tokkaihei No.8-128833. In this example, as shown as an example in
FIG. 1
, a vibrator extends in the directions X and Y, namely, extends perpendicularly to the turning axis Z. Each of three elastic members
51
a
,
51
b
and
51
c
is provided with a weight
53
at one end thereof. The elastic members
51
a
,
51
b
and
51
c
are vibrated by piezoelectric devices
54
and
55
in the X-Y plane in phase inverse to one another. A Coriolis force in the Y direction generated by a turning angular rate &ohgr; around the Z axis is applied to the center of gravity of the weight
53
. Since the plane of the elastic members
51
a
,
51
b
and
51
c
and the center of gravity of the weight
53
are slightly distant in the Z direction from each other, the ends of the elastic members
51
a
,
51
b
and
51
c
are bent reversely to one another in the Z direction by the Coriolis forces each of which is applied to the center of gravity of the weight
53
. A turning angular rate &ohgr; around the Z axis is obtained by detecting this bending vibration by means of piezoelectric devices
56
and
57
.
And up to now, various configurations have been known as a vibratory gyroscope using a vibrator which is composed of plural arms and a base part joining the plural arms, gives a drive vibration in a specified plane to each of the arms, and obtains a turning angular rate on the basis of a detection vibration which is perpendicular to this drive vibration and corresponds to the applied turning angular rate. For example, a Japanese laid-open publication Tokkaihei No. 7-83671 has disclosed a vibratory gyroscope using a tuning-fork vibrator made by joining three arms composed of a middle drive arm and two detection arms at both sides of the middle drive arm in one body at the base part.
FIG. 2
shows a configuration of such a former vibratory gyroscope. In the example shown in
FIG. 2
, a vibrator
102
forming a vibratory gyroscope is composed of three arms which are composed of a middle drive arm
104
and two detection arms
103
and
105
arranged at both sides of it nearly in parallel with it, and a base
106
at which the drive arm
104
and the detection arms
103
and
105
are joined in one body with one another.
In the above-mentioned tuning-fork vibrator
102
, the drive arm
104
is vibrated in the X-Z plane by an unillustrated driving means provided on the drive arm. And the left and right detection arms
103
and
105
are resonated in the same X-Z plane. When a turning angular rate &ohgr; acts around the axis Z of symmetry of the tuning-fork vibrator
102
, a Coriolis force f acts on each of the detection arms
103
and
105
. Since the detection arms
103
and
105
are vibrating in the X-Z plane, vibration in the Y-Z plane is induced in the detection arms
103
and
105
. A turning angular rate is measured by detecting this vibration by means of an unillustrated detecting means provided on each of the detection arms
103
and
105
.
A piezoelectric vibratory gyroscope disclosed in the above-mentioned Japanese laid-open publication Tokkaihei No. 8-128833 can certainly detect a turning angular rate using the Coriolis principle even when the vibrator is arranged horizontally. However, necessity of providing the weight
53
makes it insufficient to shorten the gyroscope in height. And when the weight
53
is made thin in thickness in order to sufficiently shorten it in height, moment by a Coriolis force is made small and a bending vibration is made very small, and there is a problem that a measurement sensitivity is lowered.
And in a vibrator of a piezoelectric vibratory gyroscope having the above-mentioned configuration, the drive vibration and the detection vibration are different in the vibrating direction from each other due to configuration of the vibrator. That is to say, that vibrator needs such vibrations in two directions that the elastic members
51
a
,
51
b
and
51
c
which are vibrating in the X-Y plane need to vibrate also in the Z direction. Generally in a piezoelectric vibratory gyroscope, it is required to keep always a constant relation between a vibration frequency for driving and a vibration frequency for detection in order to keep a good measurement sensitivity. Now, considering a single crystal as a material for a vibrator, since a single crystal is anisotropic, variation in vibration frequency caused by a temperature change varies with the direction of vibration. Therefore, attempting to form a vibrator having the above-mentioned configuration out of a single crystal causes a problem that even in case of setting a constant relation between a drive vibration frequency and a detecting vibration frequency at a certain temperature, when the temperature is changed the relation cannot be kept and the measurement sensitivity is liable to vary with temperature.
In a former vibratory gyroscope of the above-mentioned composition shown in
FIG. 2
, in case of forming the vibratory gyroscope by supporting the tuning-fork vibrator
102
, the vibrator
102
is supported by fixing
Gouji Shosaku
Kikuchi Takayuki
Osugi Yukihisa
Soma Takao
Budd Mark
Burr & Brown
NGK Insulators Ltd.
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