U.S. patent application number 09/753098 was filed with the patent office on 2001-05-31 for vibrators, vibratory gyroscopes, devices for measuring a linear acceleration and a method of measuring a turning angular rate.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Gouji, Shosaku, Kikuchi, Takayuki, Osugi, Yukihisa, Soma, Takao.
Application Number | 20010001928 09/753098 |
Document ID | / |
Family ID | 27287651 |
Filed Date | 2001-05-31 |
United States Patent
Application |
20010001928 |
Kind Code |
A1 |
Kikuchi, Takayuki ; et
al. |
May 31, 2001 |
Vibrators, vibratory gyroscopes, devices for measuring a linear
acceleration and a method of measuring a turning angular rate
Abstract
A vibratory gyroscope for detecting a turning angular rate in a
turning system is provided. The gyroscope comprises a vibrator, an
exciting means for exciting driving vibration in the vibrator, and
a detecting means for detecting vibration induced in the vibrator.
The vibrator comprises a plurality of vibration systems 1A, 1B, 2A
and 2B, which are formed within a specified plane intersecting the
turning axis Z. Vibration systems comprises first vibration systems
1A and 1B whose vibrations include radial vibration components, in
which the center of gravity of first vibration system vibrates in a
radial direction in the specified plane with respect to the center
of gravity GO of the vibrator. The vibration systems also comprises
second vibration systems 2A and 2B whose vibrations include
circumferential vibration components, in which the center of
gravity of vibration of the second vibration system vibrates in the
specified plane along a circle with the center of gravity GO as its
center.
Inventors: |
Kikuchi, Takayuki; (Nagoya,
JP) ; Gouji, Shosaku; (Ama-Gun, JP) ; Osugi,
Yukihisa; (Nagoya, JP) ; Soma, Takao;
(Nishikamo-Gun, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
|
Family ID: |
27287651 |
Appl. No.: |
09/753098 |
Filed: |
January 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09753098 |
Jan 2, 2001 |
|
|
|
09181554 |
Oct 29, 1998 |
|
|
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Current U.S.
Class: |
73/504.12 |
Current CPC
Class: |
G01C 19/5642 20130101;
G01C 19/5607 20130101 |
Class at
Publication: |
73/504.12 |
International
Class: |
G01P 003/44 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 4, 1997 |
JP |
9-316,634 |
Jan 30, 1998 |
JP |
10-032,297 |
Oct 14, 1998 |
JP |
10-306,434 |
Claims
1. A vibrator to be turned around a turning axis and having a
center of gravity (GO), comprising: a first vibration system whose
vibration includes a radial vibration component with respect to an
imaginary circle whose center is coincident with said center of
gravity of said vibrator; a second vibration system whose vibration
includes a circumferential vibration component with respect to an
imaginary circle whose center is coincident with said center of
gravity of said vibrator; and a base portion; wherein said first
vibration system, said second vibration system and said base
portion are formed along a specified plane intersecting said
turning axis, and wherein said first vibration system and said
second vibration system are connected through said base
portion.
2. The vibrator of claim 1, wherein said first and second vibration
systems are connected only through said base portion without any
other connection.
3. The vibrator of claim 1, wherein a ratio between amplitudes of
said radial vibration component and a circumferential vibration
component, with respect to an imaginary circle whose center is
coincident with said center of gravity of said vibrator, in said
first vibration system is 1:0 to 3.
4. The vibrator of claim 3, wherein said ratio is 1:0 to 1.
5. The vibrator of claim 1, wherein a ratio between amplitudes of a
radial vibration component, with respect to an imaginary circle
whose center is coincident with said center of gravity of said
vibrator, and said circumferential vibration component in said
second vibration system is 0 to 1:5.
6. The vibrator of claim 5, wherein said ratio is 0 to 1:10.
7. The vibrator of claim 1, wherein said vibrator has a plurality
of said first vibration systems, and a ratio between amplitudes of
said radial vibration component and a circumferential vibration
component, with respect to an imaginary circle whose center is
coincident with said center of gravity of said vibrator, in said
first vibration systems is 5:0 to 1, provided that said first
vibration systems vibrate in vibration modes containing vibration
components having inverse phases with each other and said
amplitudes are measured after canceling said vibration components
having inverse phases.
8. The vibrator of claim 7, wherein said ratio is 10:0 to 1.
9. The vibrator of claim 1, wherein said first vibration system and
said second vibration system vibrate in substantially independent
vibration modes.
10. The vibrator of claim 1, wherein said base portion does not
substantially vibrate in bending vibration mode.
11. The vibrator of claim 1, wherein said base portion does not
constitute a part of a bending vibration piece.
12. The vibrator of claim 1, wherein said center of gravity of said
vibrator is located in or near said base portion.
13. The vibrator of claim 1, wherein said base portion has a
peripheral part, and wherein said first vibration system and said
second vibration system extend from said peripheral part.
14. The vibrator of claim 13, wherein adjacent vibration systems
extend from said peripheral part in directions intersecting at an
angle not smaller than 30.degree. with respect to said center of
gravity of said vibrator.
15. The vibrator of claim 1, wherein a plurality of said first
vibration systems are provided in positions which are substantially
identical after turning said positions around said center of
gravity of said vibrator.
16. The vibrator of claim 15, wherein said first vibration systems
are provided in positions which are diad-symmetrical,
triad-symmetrical or tetrad-symmetrical with each other with
respect to said center of gravity of said vibrator.
17. The vibrator of claim 1, wherein a plurality of said second
vibration systems are provided in positions which are substantially
identical after turning said positions around said center of
gravity of said vibrator.
18. The vibrator of claim 17, wherein said second vibration systems
are provided in positions which are diad-symmetrical,
triad-symmetrical or tetrad-symmetrical with each other with
respect to said center of gravity of said vibrator.
19. The vibrator of claim 1, wherein each of said first vibration
systems and said second vibration systems has a bending vibration
piece connected with said base portion, and wherein said bending
vibration piece vibrates in bending motion around the root of said
piece to said base portion.
20. The vibrator of claim 1, wherein said base portion is a frame
having an inner peripheral part and an outer peripheral part.
21. The vibrator of claim 20, wherein at least one of said first
vibration system and second vibration system extend from said inner
peripheral part.
22. The vibrator of claim 1, wherein said first vibration system
comprises first bending-vibration piece or pieces whose vibration
includes at least said radial vibration component and a supporting
portion extending from said base portion, and wherein said first
bending-vibration piece extends in a direction intersecting the
longitudinal direction of said supporting portion.
23. The vibrator of claim 1, wherein said second vibration system
comprises a bending-vibration piece whose vibration includes at
least said circumferential vibration component and said
bending-vibration piece is connected with said base portion.
24. A vibratory gyroscope for detecting a turning angular rate
around a turning axis comprising: a vibrator to be turned around
said turning axis and having a center of gravity (GO), said
vibrator comprising: a first vibration system whose vibration
includes a radial vibration component with respect to an imaginary
circle whose center is coincident with said center of gravity of
said vibrator, a second vibration system whose vibration includes a
circumferential vibration component with respect to an imaginary
circle whose center is coincident with said center of gravity of
said vibrator, and a base portion, wherein said first vibration
system, said second vibration system and said base portion are
formed along a specified plane intersecting said turning axis, and
wherein said first vibration system and said second vibration
system are connected through said base portion; exciting means
provided in one of said first vibration system and said second
vibration system for exciting a driving vibration in said vibrator;
and detecting means provided in the other of said first vibration
system and second vibration system for detecting a detecting
vibration that occurs due to Coriolis force in said vibrator when
said vibrator is turned around said turning axis.
25. The vibratory gyroscope of claim 24, wherein said first and
second vibration systems are connected only through said base
portion without any other connection.
26. The vibratory gyroscope of claim 24, wherein a ratio between
amplitudes of said radial vibration component and a circumferential
vibration component, with respect to an imaginary circle whose
center is coincident with said center of gravity of said vibrator,
in said first vibration system is 1:0 to 3.
27. The vibratory gyroscope of claim 26, wherein said ratio is 1:0
to 1.
28. The vibratory gyroscope of claim 24, wherein a ratio between
amplitudes of a radial vibration component, with respect to an
imaginary circle whose center is coincident with said center of
gravity of said vibrator, and said circumferential vibration
component in said second vibration system is 0 to 1:5.
29. The vibratory gyroscope of claim 28, wherein said ratio is 0 to
1:10.
30. The vibratory gyroscope of claim 24, wherein said vibrator has
a plurality of said first vibration systems, and a ratio between
amplitudes of said radial vibration component and a circumferential
vibration component, with respect to an imaginary circle whose
center is coincident with said center of gravity of said vibrator,
in said first vibration systems is 5:0 to 1, provided that said
first vibration systems vibrate in vibration modes containing
vibration components having inverse phases with each other and said
amplitudes are measured after canceling said vibration components
having inverse phases.
31. The vibratory gyroscope of claim 30, wherein said ratio is 10:0
to 1.
32. The vibratory gyroscope of claim 24, wherein said first
vibration system and said second vibration system vibrate in
substantially independent vibration modes.
33. The vibratory gyroscope of claim 24, wherein said base portion
does not substantially vibrate in bending vibration mode.
34. The vibratory gyroscope of claim 24, wherein said base portion
does not constitute a part of a bending vibration piece.
35. The vibratory gyroscope of claim 24, wherein said center of
gravity of said vibrator is located in or near said base
portion.
36. The vibratory gyroscope of claim 24, wherein said base portion
has a peripheral part, and wherein said first vibration system and
said second vibration system extend from said peripheral part.
37. The vibratory gyroscope of claim 36, wherein adjacent vibration
systems extend from said peripheral part in directions intersecting
at an angle not smaller than 30.degree. with respect to said center
of gravity of said vibrator.
38. The vibratory gyroscope of claim 24, wherein a plurality of
said first vibration systems are provided in positions which are
substantially identical after turning said positions around said
center of gravity of said vibrator.
39. The vibratory gyroscope of claim 38, wherein said first
vibration systems are provided in positions which are
diad-symmetrical, triad-symmetrical or tetrad-symmetrical with each
other with respect to said center of gravity of said vibrator.
40. The vibratory gyroscope of claim 24, wherein a plurality of
said second vibration systems are provided in positions which are
substantially identical after turning said positions around said
center of gravity of said vibrator.
41. The vibratory gyroscope of claim 40, wherein said first
vibration systems are provided in positions which are
diad-symmetrical, triad-symmetrical or tetrad-symmetrical with each
other with respect to said center of gravity of said vibrator.
42. The vibratory gyroscope of claim 24, wherein each of said first
vibration systems and said second vibration systems has a bending
vibration piece connected with said base portion, and wherein said
bending vibration piece vibrates in bending motion around the root
of said piece to said base portion.
43. The vibratory gyroscope of claim 24, wherein said base portion
is a frame having an inner peripheral part and an outer peripheral
part.
44. The vibratory gyroscope of claim 43, wherein at least one of
said first vibration system and second vibration system extend from
said inner peripheral part.
45. The vibratory gyroscope of claim 24, wherein said first
vibration system comprises first bending-vibration piece or pieces
whose vibration includes at least said radial vibration component
and a supporting portion extending from said base portion, and
wherein said first bending-vibration piece extends in a direction
intersecting the longitudinal direction of said supporting
portion.
46. The vibratory gyroscope of claim 24, wherein said second
vibration system comprises a bending-vibration piece whose
vibration includes at least said circumferential vibration
component and said bending-vibration piece is connected with said
base portion.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a vibrator and a vibratory
gyroscope used for an angular rate sensor measuring a turning
angular rate in a turning system, a device for measuring a linear
acceleration and a method of measuring a turning angular rate.
[0002] 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 material has been used for detecting position
of an aircraft, a ship and a space satellite. Recently, the
gyroscope is used in a car-navigation system, a movement detecting
mechanism in a VTR or a still camera in the field of public
livelihood.
[0003] Such a vibratory gyroscope utilizes a Coriolis force, which
is generated, when an angular movement is applied to a vibrating
object, in a direction perpendicular to the vibratory direction.
Its mechanism may be understood by using a dynamic model (For
example, "Handbook of Elastic Wave Device Technologies"
(Danseiha-Sosi Gijutsu Handbook) published by Ohm, Inc., pp. 491 to
497). Various kinds of piezoelectric vibratory gyroscopes have been
proposed. 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 are known.
SUMMARY OF THE INVENTION
[0004] The inventors have studied various applications of vibratory
gyroscopes, and have tried to use a vibratory gyroscope as a
turning rate sensor in a car control system of an automobile body
turning rate feedback system. Such a system detects the direction
of a steering wheel itself by a turning angle of the wheel. At the
same time, the system detects a turning rate of the actually
turning car body by means of the vibratory gyroscope. Then 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.
[0005] However, any example of the above-mentioned former
piezoelectric vibratory gyroscopes can detect a turning angular
rate only when arranging its vibrator in parallel with the axis of
turning (what is so called "vertical arrangement"). The turning
axis of a turning system to be measured is usually perpendicular to
the gyroscope mounting part. Accordingly, when 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.
[0006] Recently, a piezoelectric vibratory gyroscope, capable of
detecting a turning angular rate even when arranging a vibrator
perpendicularly to the turning axis (what is called "horizontal
arrangement"), was proposed in a Japanese laid-open publication
Tokkaihei No. 8-128833. However, even such a vibratory gyroscope
has a limit to reduce the vibratory gyroscope in size in the
direction of the turning axis.
[0007] An object of the invention is to provide a novel vibratory
gyroscope comprising a vibrator extending in a given plane, and
when the vibrator is subjected to a turning in the plane, the
gyroscope being capable of detecting an angular velocity of the
turning.
[0008] The invention provides a vibrator to be turned around a
predetermined turning axis, the vibrator comprising at least
plurality of vibration systems which are formed within a specified
plane intersecting the turning axis, the plurality of vibration
systems comprising first vibration system whose vibration includes
a radial vibration component, in which the center of gravity of
first vibration system vibrates in a radial direction in the
specified plane with respect to the center of gravity of the
vibrator, and a second vibration system whose vibration includes a
circumferential vibration component, in which the center of gravity
of vibration of the second vibration system vibrates in the
specified plane circumferantially, that is, along a circle with the
center of gravity of the vibrator as its center.
[0009] The invention also provides a vibrator comprising a base
portion and a plurality of vibration systems, each vibration system
extends radially from the edge of the base portion, the base
portion and the vibration systems extend in a specified plane.
[0010] The invention also provides a vibratory gyroscope for
detecting a turning angular rate in a turning system, comprising
said vibrator, an exciting means provided in one of first vibration
system and second vibration system for exciting a driving vibration
in the vibrator, and an detecting means provided in the other of
first vibration system and second vibration system for detecting a
detecting vibration occurred in the vibrator when the vibrator is
turned.
[0011] The invention also provides a vibratory gyroscope comprising
a vibrator, an exciting means for exciting a driving vibration in
the vibrator and an detecting means for detecting a detecting
vibration occurred in the vibrator when the vibrator is turned,
wherein the vibrator comprises a plurality of vibration systems
extending in a specified plane intersecting a turning axis, the
exciting means being provided in at least one of the vibration
systems, and the detecting means being provided in at least one of
the vibration systems in which the exciting means is not
provided.
[0012] The invention also provides a vibratory gyroscope comprising
a vibrator, an exciting means for exciting a driving vibration in
the vibrator and an detecting means for detecting a detecting
vibration occurred in the vibrator when the vibrator is turned, the
vibrator extending in a specified plane and comprising a plurality
of vibration systems, the exciting means and the detecting means
being provided in the different vibration systems, the center of
gravity of the whole driving vibration in the vibrator being
positioned within a domain near the center of gravity of the
vibrator.
[0013] The invention also provides a vibratory gyroscope for
detecting a turning angular rate in a turning system, the vibratory
gyroscope comprising a vibrator to be subjected to a turning around
a specified turning axis, a exciting means for exciting a driving
vibration in the vibrator and a detecting means for detecting a
detecting vibration occurred in the vibrator when turning the
vibrator, the vibrator extending in a specified plane and
comprising a plurality of vibration systems, the exciting means and
the detecting means being provided in the different vibration
systems, the center of gravity of the vibrator being located within
a domain in which displacements caused by the driving vibration are
small when exciting the driving vibration in the vibrator.
[0014] The invention also provides a vibratory gyroscope for
detecting a turning angular rate in a turning system, the vibratory
gyroscope comprising a vibrator to be subjected to a turning around
a specified turning axis, a exciting means for exciting a driving
vibration in the vibrator and a detecting means for detecting a
detecting vibration occurred in the vibrator according the turning
of the vibrator, the vibrator extending in a specified plane and
comprising a plurality of vibration systems, the exciting means and
the detecting means being provided in the different vibration
systems, and the center of gravity of the vibrator being located
within a domain in which displacements caused by the detecting
vibration are small when the detecting vibration is induced in the
vibrator.
[0015] The invention also provides a method of detecting a turning
angular rate around a turning axis in a turning system comprising a
vibrator, the vibrator comprising a plurality of driving vibration
systems and at least one detecting vibration system extending in a
specified plane intersecting the turning axis, the method
comprising:
[0016] turning the vibrator around the turning axis and exciting
driving vibrations in the driving vibration systems at the same
time to cancel at least parts of the excited driving vibrations
with each other; and
[0017] detecting a detecting vibration induced in the detecting
vibration system.
[0018] The invention also provides a method of detecting a turning
angular rate around a turning axis in a turning system comprising a
vibrator, the vibrator comprising a plurality of vibration systems
extending in a specified plane intersecting the turning axis, the
method comprising:
[0019] exciting at least radial vibration component in at least one
of the vibration systems, the radial vibration component being a
vibration in a radial direction in the specified plane with respect
to the center of gravity of the vibrator;
[0020] exciting a Coriolis force in the circumferential direction
based on the radial vibration component when turning the vibrator;
and;
[0021] detecting a detecting vibration, occurred in the vibrator
according to the Coriolis force, within the other vibration
system.
[0022] The invention also provides a method of detecting a turning
angular rate around a turning axis in a turning system comprising a
vibrator, the vibrator comprising a plurality of vibration systems
extending in a specified plane intersecting the turning axis, the
method comprising;
[0023] exciting at least circumferential vibration component in at
least one of the vibration systems, the circumferential vibration
component being a vibration in the specified plane along a circle
with the center of gravity of the vibrator as its center;
[0024] exciting a Coriolis force in the radial direction based on
the circumferential vibration component when turning the vibrator;
and;
[0025] detecting a detecting vibration, occurred in the vibrator
according to the Coriolis force, within the other vibration
system.
BRIEF EXPLANATION OF THE DRAWINGS
[0026] FIG. 1 is a diagram for explaining the principles of the
inventive gyroscopes;
[0027] FIG. 2(a) and 2(b) are diagrams schematically showing
examples of vibration modes in first vibration systems;
[0028] FIG. 3 is a diagram schematically showing examples of
vibration modes in first vibration systems;
[0029] FIG. 4(a) and 4(b) are diagrams schematically showing
examples of vibration modes in second vibration systems;
[0030] FIG. 5(a) and 5(b) are diagrams schematically showing
another examples of vibration modes in second vibration
systems;
[0031] FIG. 6 is a diagram for explaining the position of the
center of gravity GD of driving vibrations induced in a
vibrator;
[0032] FIG. 7 is a diagram schematically showing a vibratory
gyroscope according to one embodiment in which vibration systems
protrude radially from a base portion;
[0033] FIG. 8 is a diagram schematically showing a vibrator in
which first vibration systems protrude from a base portion and
second vibration systems protrude inwardly from a frame
portion;
[0034] FIG. 9 is a diagram schematically showing a vibrator in
which second vibration systems protrude from a base portion and
first vibration systems protrude inwardly from a frame portion;
[0035] FIG. 10 is a diagram schematically showing a vibrator in
which first and second vibration systems together protrude inwardly
from a frame portion;
[0036] FIG. 11 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0037] FIG. 12 shows a relative ratio of an amplitude of vibration
at each point in a vibrator to the maximum vibration amplitude in
the driving vibration mode;
[0038] FIG. 13 shows a relative ratio of an amplitude of vibration
at each point in the vibrator of FIG. 11 to the maximum vibration
amplitude in the detecting vibration mode;
[0039] FIG. 14 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0040] FIG. 15 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0041] FIG. 16 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0042] FIG. 17 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0043] FIG. 18 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0044] FIG. 19(a) is a line diagram schematically showing the
driving vibration mode of the vibrator of FIG. 18;
[0045] FIG. 19(b) is a line diagram schematically showing the
detecting vibration mode thereof;
[0046] FIG. 20 is a plan view of a vibratory gyroscope using a
vibrator formed by means of a silicon semiconductor processing;
[0047] FIG. 21 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0048] FIG. 22 shows a relative ratio of an amplitude of vibration
at each point in the vibrator of FIG. 21 to the maximum vibration
amplitude in the driving vibration mode;
[0049] FIG. 23 shows a relative ratio of an amplitude of vibration
at each point in the vibrator of FIG. 21 to the maximum vibration
amplitude in the detecting vibration mode;
[0050] FIG. 24 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0051] FIG. 25 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0052] FIG. 26 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0053] FIG. 27 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0054] FIG. 28 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0055] FIG. 29 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0056] FIG. 30 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0057] FIG. 31 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0058] FIG. 32 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0059] FIG. 33 shows a relative ratio of an amplitude of vibration
at each point in the vibrator of FIG. 32 to the maximum vibration
amplitude in the driving vibration mode;
[0060] FIG. 34 shows a relative ratio of an amplitude of vibration
at each point in the vibrator of FIG. 32 to the maximum vibration
amplitude in the detecting vibration mode;
[0061] FIG. 35 is a plan view schematically showing a vibrator
according to another embodiment of the invention;
[0062] FIG. 36 is a perspective view showing a vibrator embodying
the vibrator of FIG. 24;
[0063] FIGS. 37(a) and 37(b) are cross-sectional views each showing
electrodes for driving or detecting provided in each
bending-vibration piece in the vibrator of FIG. 36;
[0064] FIG. 38 is a perspective view showing a vibrator embodying
the vibrator of FIG. 24;
[0065] FIGS. 39(a) and 39(b) are cross-sectional views each showing
electrodes for driving or detecting provided in each
bending-vibration piece in the vibrator of FIG. 38;
[0066] FIG. 40 is a perspective view showing a vibrator embodying
the vibrator of FIG. 24;
[0067] FIGS. 41(a) and 41(b) are cross-sectional views each showing
electrodes for driving or detecting provided in each
bending-vibration piece in the vibrator of FIG. 40;
[0068] FIG. 42 is a block diagram showing an example of a
phase-difference detecting means 62 used in measuring a turning
angular rate;
[0069] FIG. 43 is a perspective view schematically showing a
gyroscope of another example of the invention, in which a through
hole is formed in each supporting portion;
[0070] FIG. 44 is a perspective view schematically showing a
gyroscope of another example of the invention, in which a
bending-vibration piece for driving is curved;
[0071] FIG. 45 is a perspective view of a gyroscope of another
example of the invention;
[0072] FIG. 46 is a perspective view of a gyroscope of another
example of the invention, comprising a vibrating loop system
71C;
[0073] FIG. 47 is a perspective view of a gyroscope of another
example of the invention;
[0074] FIG. 48 is a graph showing the difference, between maximum
and minimum values during -30.degree. C. to +80.degree. C. of the
differences of natural resonance frequencies in driving and
detecting vibration, with respect to lengths of bending-vibration
pieces, and ratios of heights of protrusions to thicknesses of the
pieces;
[0075] FIG. 49 is a plan view showing a gyroscope of another
examples of the invention, in which protrusions are provided on the
side of a vibrator;
[0076] FIG. 50 is a plan view showing a gyroscope of another
examples of the invention, in which through holes are formed in end
portions of bending-vibration pieces;
[0077] FIG. 51 is a schematic diagram explaining an etching process
proceeding in a bending-vibration piece; and
[0078] FIG. 52 is a plan view showing a gyroscope of another
example of the invention, in which enlarged portions with through
hole formed are provided in ends of bending-vibration pieces.
DETAILED DESCRIPTION OF THE INVENTION
[0079] The inventors have studied concerning basic principles of
vibrators used in vibratory gyroscopes, and successfully developed
a vibrator and a vibratory gyroscope based on totally novel
principle, which will be described referring to FIGS. 1 to 10.
[0080] "O" is a crossing point of a turning axis "Z" and a
specified plane of a vibrator, or the center of the turning. "GO"
is the center of gravity of the vibrator as a whole when the
vibrator is not vibrated. "GD" is the center of gravity of a
driving vibration. A plurality of vibration systems are provided
around the centers of gravity "GD" and "GO". The embodiments
described referring to FIGS. 1 to 10 comprise four vibration
systems, however, whose number may be varied.
[0081] As shown in FIG. 1, first and second vibration systems 1A
and 1B are provided around the center of gravity GO and GD and in
positions identical with each other after turning the positions
around the center of gravity GO. The vibrations of the systems 1A
and 1B comprises radial vibration components 5A and 5B with respect
to the center of gravity GO. Second vibration systems 2A and 2B are
further provided around the center GO. The vibrations of the
systems comprise circumferential vibration components 6A and 6B
with respect to the center GO.
[0082] The circumferential vibration component is a vibration
component within the specified plane in the circumferential
direction, that is, along a circle with the center of gravity GO as
its center. The radial vibration component is a vibration component
in the radial direction with respect to the center GO of gravity
within the specified plane, that is, a vibration component
approaching and withdrawing from the center GO in turn.
[0083] All the above first and second vibration systems are
connected with each other by means of any connecting portion to
form a vibrator extending within the specified plane. Such vibrator
is subjected to turning around the turning axis "Z" as an arrow
".omega." to detect the turning angular rate.
[0084] For example, when subvibrators 3A and 3B in first vibration
systems 1A and 1B are used as driving subvibrators, the radial
vibration components 5A and 5B are used as the driving vibration
and the vibrator is subjected to turning, Coriolis force 7A exerts
on the vibrator to cause circumferential vibration components 6A
and 6B within the subvibrator 4A and 4B in second vibration system
2A and 2B. The vibration components 6A and 6B may be detected to
obtain its indication, from which a turning angular rate may be
calculated.
[0085] When subvibrators 4A and 4B in second vibration systems are
used as driving subvibrators and the circumferential vibration
components 6A and 6B are used as the driving vibration, Coriolis
force 7B exerts on the vibrator to induce radial vibration
components 5A and 5B within the subvibrator 3A and 3B in first
vibration system 1A and 1B. The vibration components 5A and 5B may
be detected to obtain its indication, from which a turning angular
rate may be calculated.
[0086] According to the vibrator and gyroscope of the invention, a
driving vibration and a detection vibration are generated in a
specified plane, and the invention can detect a turning angular
rate at a sufficiently high sensitivity without providing a
projection of a certain weight projecting from the vibrator in the
direction of the axis of turning, in case of setting up the
vibrator so that bending-vibration pieces of the vibrator extend
perpendicularly to the axis of turning.
[0087] Moreover, in prior vibratory gyroscopes, a driving vibration
generated in a driving vibration arm may induce some influences on
a detecting arm as its deformation to generate noises in a
detecting signal excited in the detection arm. However, the
vibrator of the invention comprises a driving and detecting
vibration systems both extending radially from the center of
gravity of the vibrator so that the driving vibration induced in
the vibrator hardly influences the detecting vibration system. That
is, the driving vibration is buffered or cancelled to reduce the
influence of the driving vibration on the detecting vibration
system, so that noises has been inevitably induced in the detection
signal may be prohibited or prevented. These inevitable and
inherent problems in vibratory gyroscopes may be solved by the
invention.
[0088] Further, as shown in vibrators of FIG. 1 or 6, for example,
radial vibration components 5A and 5B induced within first
vibration systems 1A and 1B are utilized as the driving vibrations,
first vibration systems are provided in positions being identical
with each other when turning the positions around the center of
gravity GO of the vibrator, so that each driving vibration induced
in each driving vibration system cancel with each other. The
influence of the driving vibration exerted on second vibration
systems for detecting may be reduced.
[0089] Thus, the vibrator of the invention may comprises a
plurality of first vibration systems, whose positions are
substantially identical after turning them around the center of
gravity GO. For example, as shown in FIGS. 1 and 6, first vibration
systems 1A and 1B are provided in positions being dyad-symmetrical
around the center of gravity GO.
[0090] Moreover, a plurality of second vibration systems may be
preferably provided, whose positions are substantially identical
after turning them around the center of gravity GO. For example, as
shown in FIGS. 1 and 6, second vibration systems 2A and 2B are
provided in positions being dyad-symmetrical around the center of
gravity GO.
[0091] "Vibration systems are provided in positions substantially
identical after turning them around the center of gravity GO" means
that the adjacent vibration systems are located at a predetermined
angle around the center of gravity GO in the specified plane.
Therefore, when one vibration system is turned a predetermined
angle around the center of gravity in the specified plane, the
turned system is located in a position in which the adjacent
vibration system is provided. For example, in FIGS. 1 and 6, first
vibration systems 1A is provided in a position distant 180.degree.
from a position of the system 1B and identical after turning
180.degree. the position of the system 1B.
[0092] The vibration systems preferably be provided in positions
being dyad-, triad, or quad-symmetrical with respect to the center
of gravity GO. When driving systems comprise either of first or
second vibration systems, a plurality of the driving vibration
systems may be in positions, which are substantially identical with
each other after turning them around the center of gravity GO, to
reduce the influence on relatively small detecting vibration,
thereby improving the effects of the invention.
[0093] Especially, the center of gravity GD of whole vibration in
the driving vibration systems (for example, first vibration
systems) may preferably be located within a domain near the center
of gravity GO, so as to reduce the influence on the detecting
vibration systems (for example, second vibration systems). That is,
as schematically shown in FIG. 6, when vibrations in subvibrators
3A and 3B in vibration systems 1A and 1B comprise a radially
vibrating components 5A and 5B, the components are in inverse
phases to cancel the components 5A and 5B with each other.
[0094] "The center of gravity GD is located within a domain near
the center of gravity GO of the vibrator" includes that the center
of gravity GD may substantially exist on the center GO, or located
within a circle having GO as its center and a diameter of 1 mm.
[0095] In the vibratory gyroscope of the invention, when one of
first and second vibration systems is a driving vibration system,
the other is a detecting vibration system. Especially, the
inventive vibrator may comprise a plurality of driving vibration
systems, in which one driving vibration system is located in a
position 90.degree. distant from the adjacent driving vibration
system, and a detecting vibration system or systems may preferably
be provided between the adjacent driving vibration systems. The
driving vibrations in the driving vibration systems cancel with
each other to reduce the influence on the detecting vibration
system.
[0096] While the inventive vibrator comprises a plurality of
vibration systems extending in a specified plane, the plurality of
the vibration systems may actually be provided within a
plate-shaped space of thickness of 1 mm including the specified
plane. Moreover, the portions other than the plurality of vibration
systems of the vibrator may be protruded form the specified plane
or the above space, although the whole of the vibrator may
preferably be formed in a specified plane.
[0097] An angle at a specified plane and a turning axis may
preferably be 60 to 120.degree., more preferably be 85 to
95.degree., and most preferably right angle.
[0098] In the invention, actual shapes or forms or components of
first and second vibration systems are not limited. In preferred
embodiments, each vibration system comprises a bending-vibration
piece or pieces within. Referring to FIGS. 2 to 5, embodiments
mainly using such pieces will be described.
[0099] In FIG. 2(a), bending-vibration pieces 13A and 13B are
provided in first vibration systems 1A and 1B as the subvibrators
3A and 3B, respectively (refer to FIG. 1). The bending-vibration
piece of the present embodiment comprises a fixing portion 8 in its
central portion and open ends 9 on both side thereof. Consequently,
the open ends of each piece 13A or 13B vibrate around the fixing
portion 8. Among the vibrations of the pieces 13A and 13B, radial
vibration components 5A and 5B are utilized.
[0100] In FIG. 2(b), bending-vibration pieces 23A and 23B are
provided in first vibration systems 1A and 1B. The
bending-vibration pieces of this embodiment comprise both end
portions connected and fixed with fixing portions 8. Consequently,
the central portions of each piece 23A or 23B mainly vibrates.
[0101] In FIG. 3, bending-vibration pieces 33A and 33B are provided
in first vibration systems 11A and 1B, respectively. The vibrator
of the present embodiment comprises one end fixed and the other end
not fixed. Consequently, the other ends of the pieces 33A and 33B
vibrate mainly. The phases and amplitudes of the vibrations in the
pieces 33A and 33B, and positions of the open ends are designed so
that the vibrations in the pieces 33A and 33B cancel with each
other.
[0102] In FIG. 4(a), while first vibration systems 1A and 1B are
described in FIG. 1, bending-vibration pieces 14A and 14B are
provided in second vibration systems 2A and 2B, respectively. The
bending-vibration pieces of the embodiment comprises a fixing
portion 8 in a position near the center of gravity GO of the
vibrator, and the end distant from the center GO is not fixed.
Consequently, the end of each piece 14A or 14B distant from the
center of gravity GO vibrates in the circumferential direction
around the center.
[0103] In FIG. 4(b), while first vibration systems 1A and 1B are
described in FIG. 1, bending-vibration pieces 24A and 24B are
provided in second vibration systems 2A and 2B, respectively. Each
bending-vibration piece comprises a fixing portion 8 in one end
distant from the center of gravity GO and the other end near the
center GO not fixed. Consequently, the end of each piece 24A or 24B
near the center GO mainly vibrates. While the vibrations comprise
substantially circumferential vibration components 6A and 6B, they
also comprise radial-vibration components.
[0104] In FIG. 5(a), bending-vibration pieces 34A and 34B are
provided in second vibration systems 2A and 2B, respectively. The
bending-vibration piece of the embodiment comprises a fixing
portion 8 in its central portion and both ends not fixed.
Consequently, both ends of the bending-vibration piece 34A and 34B
vibrate as arrows 6A, 6B, 6C and 6D.
[0105] In FIG. 5(b), second vibration systems 2A and 2B comprise
bending-vibration pieces 44A and 44B, respectively. The
bending-vibration piece of the embodiment comprises both ends fixed
with fixing portions 8. Consequently, each piece 44A or 44B mainly
vibrates in the central portion.
[0106] While, in FIG. 1, the center of turning O (a crossing point
of a turning axis and a specified plane) is on a position identical
with that of the center of gravity GO of the vibrator and center of
gravity GD of the whole driving vibration, the center of turning O
is not shown in the vibrators of FIGS. 2 to 6. The reason is
described below. When the center of turning O is not on a position
of the center of gravity GO of the vibrator, and even when the
center of turning O is outside the vibrator itself, the inventive
vibrator may also be used for vibratory gyroscopes of the
invention. Because, when turning the vibrator, a displacement of
each portion of the vibrator, where the center of turning O is not
identical with the center of gravity GO, is a vector sum of a
displacement of each portion of the vibrator, where the center of
turning O is identical with the center of gravity GO (the
displacement is due to the turning), and a displacement due to
transnational movement of each portion thereof. Coriolis force does
not apply on the displacement due to the transnational movement and
does not induce any effects on the detection of a turning angular
rate by the vibratory gyroscope.
[0107] One embodiment of the invention provides a vibrator
comprising a base portion and a plurality of vibration systems
separated with each other, each system extending radially from the
peripheral portion of the base portion, wherein the base portion
and the vibration systems extend in a specified plane. Alternately,
the center of gravity GO of the vibrator is located in a base
portion and preferably, one of first vibration system and second
vibration system extends from the base portion, in which case,
first and second vibration systems may extend radially from the
base portion.
[0108] These embodiments will be described below referring to FIG.
7, in which 11 is a base portion and first vibration systems 1A and
1B and second vibration systems 2A and 2B protrude radially from
the peripheral part 11a of the base portion 11.
[0109] In the embodiment, vibration systems extend from the
peripheral part of the base portion. However, the vibration systems
does not necessarily extends radially with respect to the center of
the base portion, and may extend from the peripheral part of the
base portion away from the center of gravity GO.
[0110] For example, first vibration system comprises a supporting
portion protruding radially from the peripheral part of the base
portion and a bending-vibration piece or pieces extending in a
direction intersecting the supporting portion. Second vibration
system comprises a bending-vibration piece or pieces protruding
radially from the peripheral part of the base portion. A weight may
be provided in the bending-vibration piece to reduce a whole length
of the piece.
[0111] Moreover, the inventive vibrator may comprises a frame
portion in which a hollow portion formed and at least one of a
driving vibration system or a detecting vibration system extends
from the inner surface of the hollow portion. FIGS. 8 to 10 relate
to the embodiments.
[0112] In FIG. 8, a base portion 11 is provided within a hollow
portion 70 inside a frame portion 19. Second vibration systems 2A
and 2B protrude from the frame portion 19 towards the base portion
11 and first vibration systems 1A and 1B extend from the peripheral
part of the base portion 11 away from the center of gravity GO.
[0113] In FIG. 9, a base portion 11 is provided within a hollow
portion 70 inside a frame portion 19. First vibration systems 1A
and 1B protrude from the frame portion 19 towards the base portion
11 and second vibration systems 2A and 2B extend from the
peripheral part of the base portion 11 away from the center of
gravity GO.
[0114] In FIG. 10, the base portion 11 is not provided within the
hollow portion 70 inside the frame portion 19. First vibration
systems 1A and 1B and second vibration systems 2A and 2B protrude
towards the center of gravity GO inside the frame portion 19.
[0115] Preferably, a ratio, between each of radial vibration
component and circumferential vibration component of the vibration
induced in each vibration system, is as follows.
[0116] (A) A ratio between amplitudes of the radial vibration
component and circumferential vibration component in first
vibration system may preferably be 1:0 to 3, and more preferably be
1:0 to 1, and a ratio between amplitudes of the radial vibration
component and circumferential vibration component in second
vibration system may preferably be 0 to 1:5, and more preferably be
0 to 1:10, provided that each amplitude of the radial vibration
component or circumferential vibration component in each vibration
system is measured without canceling the vibration components
having inverse phases existing in each vibration component.
[0117] (B) A ratio between amplitudes of the radial vibration
component and circumferential vibration component in first
vibration system may preferably be 5:0 to 1, and more preferably be
10:0 to 1, and a ratio between amplitudes of the radial vibration
component and circumferential vibration component in second
vibration system may preferably be 0 to 1:5, and more preferably be
0 to 1:10, provided that each amplitude of the radial vibration
component or circumferential vibration component in each vibration
system is measured after canceling the vibration components having
inverse phases existing in each vibration component.
[0118] The specific examples of the invention will be explained
below.
[0119] Since displacement of the vibrator of the invention occurs
in the specified plane, the whole vibrator may be made of the same
piezoelectric single crystal. In this case, the whole vibrator can
be made by making a single crystal thin plate and processing this
plate by means of etching or grinding. Each portion of the vibrator
may be the different part joined together to form it, although the
whole vibrator may preferably be an integral body.
[0120] When forming the vibrator by an etching process from a thin
plate, for example a thin plate made of a piezoelectric single
crystal such as quartz, a projection of a particular shape, such as
an elongated projection, may be formed on the surface of each
constituent piece, such as a bending vibration piece, of the
vibrator. Such projection might change the symmetrical shape of the
design of the vibrator. However, such projection may be present in
the vibrator. The height of the projection may preferably lower,
for example not higher than 1/5 of the width of the constituent
piece with the projection formed, generally causing substantially
no adverse effects. This may be true when the other portion
changing the symmetrical design other than the projection exists
within the vibrator, which portion may be produced during processes
other than etching.
[0121] When the portions such as projections exist within a
vibrator, a part of the projection may be deleted or the other
portions of the vibrator may be deleted by means of a laser
processing so that the shape of the vibrator may be adjusted and
the center of gravity of the whole driving vibration piece is
located within a domain near the center of gravity of the
vibrator.
[0122] Although a material for the vibrator is not limited in
particular, it is preferable to use a single crystal of quartz,
LiNbO.sub.3, LiTaO.sub.3, a solid solution of lithium
niobate-lithium tantalate (Li(Nb, Ta)O.sub.3, langasite and lithium
tetraborate.
[0123] Among the above-mentioned single crystals, single crystals
of LiNbO.sub.3, LiTaO.sub.3 and a solid solution of lithium
niobate-lithium tantalate have particularly large electromechanical
coupling coefficients. Comparing single crystals of LiNbO.sub.3 and
LiTaO.sub.3 with each other, the single crystal of LiTaO.sub.3 has
a better thermal stability than that of LiNbO.sub.3.
[0124] The sensitivity may be improved and the detection noise may
be reduced by using such a piezoelectric single crystal. And since
a single crystal is particularly insensitive to a temperature
change, it is suitable for a sensor used in a car which sensor
needs thermal stability. The reason will be further described.
[0125] As an angular rate sensor using a tuning-fork vibrator,
there is for example a piezoelectric vibratory gyroscope disclosed
in the above-mentioned Japanese laid-open publication Tokkaihei No.
8-128833. In such a vibrator, however, the vibrator vibrates in two
directions. Therefore, particularly in case of forming the vibrator
out of such a single crystal as described above, it is necessary to
match the characteristics of the single crystal in the two
directions with each other. In practice, however, a piezoelectric
single crystal is anisotropic.
[0126] Generally in a piezoelectric vibratory gyroscope, in order
to keep a good sensitivity, it is required to keep a constant
vibration frequency difference between natural resonance
frequencies of a drive vibration mode and of a detection vibration
mode. However, a single crystal is anisotropic and a degree of
variation in vibration frequency caused by a temperature change
varies with the crystal face. For example, although variation in
vibration frequency caused by a temperature change is very little
in case of cutting a single crystal along a specific crystal face,
variation in vibration frequency is very sensitive to a temperature
change in case of cutting the single crystal along another crystal
face. Thus, in case that a vibrator vibrates in two directions, at
least one of the two vibrating faces is a crystal face having a
large variation in vibration frequency caused by a temperature
change.
[0127] On the other hand, as shown in the invention, by making the
whole of a vibrator vibrate in a specified plane and forming the
vibrator out of a piezoelectric single crystal, it is possible to
prevent the vibrator from being influenced by anisotropy of a
single crystal as described above and use only the best crystal
face in characteristics of the single crystal in the vibrator.
[0128] Concretely, since every vibration of a vibrator takes place
in a single plane, it is possible to manufacture a vibrator using
only a crystal face having little variation in vibration frequency
caused by a temperature change of a single crystal. Therefore, it
is possible to provide a vibratory gyroscope having very high
thermal stability.
[0129] When the vibrator of the invention is formed by a
piezoelectric material, a driving electrode and a detecting
electrode is formed within the vibrator. Such material includes a
piezoelectric ceramics such as lead zirconate titanate (PZT),
relaxer compounds (general expression: Pb(A1/3B2/3)O.sub.3 where A
is Cd, Zn, Mg or the like, and B is Nb, Ta, W or the like), other
than the piezoelectric single crystal.
[0130] The vibrator of the invention may be formed by an invariable
elasticity metal such as elinvar. In this case, piezoelectric
bodies are provided on predetermined positions of the vibrator.
[0131] FIG. 11 is a plan view roughly showing a vibratory gyroscope
provided with a vibrator made of a piezoelectric single crystal
according to this embodiment. A base portion 11A is in the shape of
a tetrad-symmetric square with the center of gravity GO of the
vibrator as the center. Two driving vibration systems 1A, 1B (first
vibration system in this example) and two detecting vibration
systems 2A, 2B (the second vibration system in this example)
project from the peripheral part 11a of the base portion 11A
radially in four directions, and the respective vibration systems
are separated from one another. The driving vibration systems 1A
and 1B are dyad-symmetric with the center of gravity GO as the
center, and the detecting vibration systems 2A and 2B are
dyad-symmetric with the center of gravity GO as the center.
[0132] The systems 1A and 1B are provided with supporting portions
12A and 12B projecting from the peripheral part 11a of the base
portion 11A and first bending-vibration pieces 13C and 13D
extending from the top ends 12b of the supporting portions 12A and
12B perpendicularly to the supporting portions. The
bending-vibration pieces 13C and 13D are, as shown in FIG. 2(a),
bound in the centers and released in both ends. The first-vibration
pieces are respectively composed of bending-vibration pieces 16A
and 16B, and 16C and 16D. Each bending-vibration pieces is provided
with driving electrodes 15A and 15B. The detecting vibration
systems 2A and 2B comprise long and narrow circumferential
bending-vibration pieces 14C and 14D (see: FIG. 4(a)), and these
bending-vibration pieces are respectively provided with detecting
electrodes 89A and 89B.
[0133] FIG. 12 shows a driving mode of driving vibration in this
vibrator. The respective bending-vibration pieces bending-vibrate
around the vicinities of the top ends 12b of the supporting
portions 12A and 12B.
[0134] FIG. 13 shows a mode of detecting vibration in this
vibrator. The supporting portions 12A and 12B bending-vibrate
circumferentially around the fixing portions 12a, and the
bending-vibration pieces 14C and 14D of the detecting vibration
system bending-vibrate correspondingly to this.
[0135] The inventors applied a natural mode analysis by a finite
element method to the vibrator of FIG. 11 in order to examine an
influence of the driving vibration mode and the detecting vibration
mode on the whole vibrator. And they made the vibrator of quartz
and obtained distribution of the ratios of the amplitudes of
vibration of respective points of the vibrator to the maximum
vibration amplitude thereof.
[0136] FIG. 12 shows a relative ratio of the amplitude of vibration
at each point in the vibrator to the maximum vibration amplitude in
a driving vibration mode, and FIG. 13 shows a relative ratio of the
amplitude of vibration of each point in the vibrator to the maximum
vibration amplitude in a detecting vibration mode. In FIGS. 12 and
13, the respective domains different in color from one another show
domains each of whose colors represents the above ratio at a
domain. Orange indicates a domain being smallest in amplitude.
[0137] According to FIG. 12, a tensile stress is applied in the
vicinity of the fixing portion 12a of each of the supporting
portions 12A and 12B to the base portion 11A with vibration of each
driving vibration system, and transformation is seen. But since the
driving vibration systems 1A and 1B are arranged at dyad-symmetric
positions, influences of this transformation cancel each other in
the base portion. Therefore, no influence by the driving vibration
is seen near the center of the base portion and in the detecting
vibration systems 2A and 2B located between the driving vibration
systems.
[0138] According to FIG. 13, influences exerted by the driving
vibration systems 1A and 1B on the base portion cancel each other.
Furthermore, since the detecting vibration systems are located at
dyad-symmetric positions, influences exerted by the detecting
vibration systems 2A and 2B on the base portion cancel each other,
also. As the result, no influence by the detecting vibration is
seen in the vicinity of the center 21A of the base portion (see
FIGS. 11 and 13).
[0139] In the vibratory gyroscope according to the invention,
therefore, the vibrator is supported and fixed in the domain where
the detecting vibration of the driving vibration is smallest in
amplitude. Thereby, the detecting vibration generated by Coriolis
forces effectively occurs without reduction thereof, and then Q
value of the detecting vibration becomes higher and the sensitivity
of the vibrator becomes higher. Since the detecting vibration
generated by Coriolis forces is small in the amplitude, the
vibrator is particularly effective to be supported in the domain
where the amplitude of detecting vibration is smallest, for the
purpose of increasing the sensitivity.
[0140] Further, in this example, the domains where the amplitudes
of both the driving vibration and the detecting vibration are
smallest are located at the center portion of the base portion like
21A shown in FIG. 11, as shown in FIGS. 12 and 13. For this reason,
this domain 21A is supported and fixed. In this case, a concrete
method of supporting the vibrator is not particularly limited and
any supporting and fixing means usable therefor may be adopted.
[0141] For instance, as a method of adhering a piezoelectric
member, any known adhering method may be used. As its example, the
vibrator may be fixed by forming a predetermined hole 20A in the
domain 21A and inserting a supporting member into the supporting
hole 20A. For example, the supporting member is projected from a
jig for supporting the vibrator, and inserted into the supporting
hole 20A, and thereby the vibrator may be fixed. When the
supporting member is inserted into the supporting hole and fixed, a
metallized layer is formed on a surface of the supporting member
and a further metallized layer is, if necessary, formed on an inner
peripheral surface, and then soldering or brazing is applied
between the supporting member and the surface of the supporting
hole. Alternatively, resin is applied therebetween.
[0142] In that case, the supporting hole 20A may penetrate or not
penetrate through the vibrator. When the supporting hole 20A is a
penetrating hole through the vibrator, the supporting member can
penetrate through the supporting hole 20A, but the supporting
member may not penetrate therethrough.
[0143] If the supporting hole is not formed in the vibrator, the
supporting member may be soldered or adhered by resin on the front
or back surface of the domain 21A of the vibrator.
[0144] Further, in the vibrator and the vibratory gyroscope
according to this example, as shown in FIGS. 11 and 12, the center
of gravity GO of the vibrator is located in a domain where the
amplitude of the vibrator is small in driving vibration. The term
"domain where the amplitude of the vibrator is small in driving
vibration" means a region where an amplitude is {fraction (1/1000)}
or less of a maximum amplitude in driving vibration.
[0145] Further, in the vibrator and the vibratory gyroscope
according to this example, as shown in FIGS. 11 and 13, the center
of gravity GO of the vibrator is located in a domain where the
amplitude of the vibrator is small in detecting vibration. The term
"a domain where the amplitude of the vibrator is small in detecting
vibration" means a region where an amplitude is {fraction (1/1000)}
or less of a maximum amplitude in detecting vibration.
[0146] In first vibration systems, the longitudinal direction of
the supporting portion is preferably perpendicular to a
longitudinal direction of each bending-vibration piece, although
the longitudinal direction is not necessarily perpendicular to a
longitudinal direction of each bending-vibration piece.
[0147] FIGS. 14-18 are plane views roughly showing vibrators and
vibratory gyroscopes in the embodiments according to the invention,
in which each vibration system is projected from base portions. In
each of these embodiments, known driving and detecting means in
addition to the above-mentioned driving electrodes and detecting
electrodes may be applied as a vibration-exciting means and
detecting means (not shown).
[0148] The vibrator of the vibratory gyroscope as shown in FIG. 14
has a circular base portion 11B. Four driving systems 1A, 1B, 1C,
and 1D, and two detecting systems 2A and 2B are projected radially
from the peripheral part 11a of the base portion 11B. Each
vibration system is separated from each other. The driving systems
1A, 1B, 1C, and 1D are tetrad-symmetric around the center of
gravity GO as the center, and the detecting systems 2A and 2B are
dyad-symmetric around the center of gravity GO as the center.
[0149] Each driving vibration system is provided with supporting
portion 12A, 12B, 12C, and 12D projecting from the peripheral part
11a of the base portion 11B in the radial direction, and the
bending-vibration pieces 13C, 13D, 13E, and 13F extending from the
top side 12b of each supporting portion in the direction
perpendicular to the supporting portion. These bending-vibration
pieces are bound at the centers as shown in FIG. 2 (a), and
released at both ends. Each bending-vibration piece is composed of
binding-vibration pieces 16A, 16B, 16C, 16D, 16E, 16F, 16G, and
16H. The detecting vibration systems 2A and 2B are fine and long
circumferential direction bending-vibration pieces 14C and 14D.
[0150] In vibration mode of driving vibration of the vibrator, each
bending-vibration piece vibrates mainly in the radial direction
around the end portion 12b of each supporting portion. In vibration
mode of detecting vibration of the vibrator, each of the supporting
portions 12A, 12B, 12C, and 12D bending-vibrates in the
circumferential direction as shown with an arrow C around the
fixing portion 12a, in correspondence to this, the detecting
vibration systems 2A and 2B bending-vibrate as shown with arrows 6A
and 6B, respectively. Besides, in FIG. 14, movement of each portion
is indicated with a fine line.
[0151] In this case, in FIG. 14, 21B indicates a region where a
minimum amplitude domain in the driving vibration overlaps a
minimum amplitude domain in detecting vibration, and particularly
it is preferable that the region 21B is supported and fixed in the
above-mentioned way.
[0152] In the vibrator of the vibratory gyroscope in FIG. 15, a
base portion 11C is composed of a regular triangle central portion
11d and square projecting portions 11a, 11b, and 11c respectively
connecting to each piece of the central portion 11d. The base
portion 11C is a triad-symmetric shape around the center of gravity
GO of the vibrator. Three driving vibration systems 1A, 1B, and 1C
and three detecting vibration systems 2A, 2B, and 2C are projected
radially from peripheral portions 11e of projecting portions 11a,
11b, and 11c of the base portion 11C. Each vibration system is
separated with each other.
[0153] The driving vibration systems 1A, 1B, and 1C are
triad-symmetric around a point O, and the detecting vibration
systems 2A, 2B, and 2C are triad-symmetric around the center of
gravity GO. In the embodiment, each detecting vibration system does
not extend from the center of gravity GO in a regularly radial
direction, but extends away from the peripheral portion 11e almost
radially.
[0154] In driving vibration mode of the vibrator, each of the
bending vibration pieces 13C, 13D, and 13E bending-vibrates mainly
in the radial direction as shown an arrow 5A around the vicinity of
the top portion 12b of each supporting portion. In detecting
vibration mode of the vibrator, each of the supporting portions
12A, 12B, and 12C bending-vibrates around the fixing portion 12a
circumferentially, and in responsive to this, each of the
bending-vibration pieces 14C, 14D, and 14E of each detecting
vibration system bending-vibrate as shown an arrow F.
[0155] In the central portion of the base portion 11C, there is a
region 21C where a minimum amplitude region in driving vibration
overlaps a minimum amplitude region in detecting domain.
Particularly, it is preferable that the region 21C is supported and
fixed in the above-mentioned way. For example, a supporting hole
20B is formed in the region 21C, and the vibrator is supported by
means of the supporting hole 20B like the previously mentioned
way.
[0156] A base portion 11D of a vibrator in FIG. 16 is a
tetrad-symmetric square, and two driving vibration systems 1A and
1B, and two detecting vibration systems 2A and 2B are projected
radially from a peripheral part 11a of the base portion. Each
vibration system is separated from each other.
[0157] Four supporting holes 20C are formed in the base portion
11D, and connecting portions 22 are formed between four supporting
holes. Vibration mode of each of driving and detecting vibration
systems is as described above.
[0158] A vibrator in FIG. 17 has the same conformation as in the
vibrator in FIG. 11 except that a frame 19 is formed to surrounds a
base portion of the vibrator, driving vibration systems and
detecting vibration systems of the vibrator. The inner peripheral
surface of the frame 19 is connected with four corners of a base
portion 11A through connecting portions 25. The vibratory gyroscope
according to the invention may preferably be supported within a
portion 21A or the frame 19.
[0159] In a vibrator in FIG. 18, two driving vibration systems 1A
and 1B and two detecting vibration systems 2A and 2B are projected
from a peripheral part 11a of a base portion 11A towards four
directions radially, and vibration systems are separated with each
other. The driving vibration systems 1A and 1B are dyad-symmetric
around a point O, and the detecting vibration systems 2A and 2B are
dyad-symmetric around the center of gravity GO of the vibrator.
[0160] The driving vibration systems 1A and 1B are provided with
supporting portion 12A and 12B projecting from the peripheral part
11a of the base portion 11A, and bending-vibration pieces 13I and
13J extending from the top side 12b of supporting portions in the
direction perpendicular to the supporting portions. These
bending-vibration pieces 13I and 13J are bound at the centers as
shown in FIG. 2 (a). Each bending-vibration piece is composed of
bending-vibration pieces 16I, 16J, 16K, and 16L. Each driving
vibration system is provided with bending-vibration pieces 27A and
27B, or 27C and 27D each extending in the direction perpendicular
to each radial-direction bending-vibration pieces.
[0161] The detecting vibration systems 2A and 2B are respectively
composed of fine and long circumferential-direction
bending-vibration pieces 14E and 14F (see: FIG. 4 (a)), and each of
the circumferential-direction bending-vibration pieces 14A and 14B
is provided with weight portions 26A and 26B.
[0162] Mode of the driving vibration of the vibrator is shown in
FIG. 19 (a). Each of the bending-vibration pieces 16I, 16J, 16K,
and 16L bending-vibrates as shown with an arrow 5A or 5B around the
vicinity of a top portion 12b, and at the same time, each of the
bending-vibration pieces 27A, 27B, 27C, and 27D vending-vibrates as
shown with an arrow H.
[0163] The driving vibration mode of this vibrator is shown in FIG.
19. The supporting portions 12A and 12B vibrate in bending movement
in the circumferential direction around the fixing portion 12a.
Responsive to this vibration, bending-vibration pieces 14E and 14F
vibrate in bending motion as arrows 6C and 6D. A projection 28 is
provided as an adjusting part which may be subjected to laser
processing to adjust the frequency of the driving vibration.
[0164] The vibrator constituting the vibratory gyroscope of the
invention may be produced by a silicon semiconductor process as
used in a micromachine made of silicon, other than the above
described piezoelectric materials and invariable elasticity metals.
In such gyroscopes, electrostatic force may be used for driving the
vibrator.
[0165] The vibrator shown in FIG. 20 is produced by a silicon
semiconductor process and by forming elongated spaces in a silicon
plate. The shape of the vibrator itself is substantially same as
that shown in FIG. 11. A base portion 11E of the vibrator has a
square shape being tetrad-symmetrical around the center of gravity
GO. Two driving vibration systems 1A, 1B and detecting vibration
systems 2A, 2B project radially in four directions from the
peripheral part 11a of the base portion 11E and are separated with
each other.
[0166] The driving vibration systems 11A and 1B comprise supporting
portions 12A and 12B, projected from the peripheral part 11a of the
base portion, and bending vibration pieces 13K and 13L each
extending from the top edge 12b of the supporting portion in a
direction perpendicular to the supporting portion. Each bending
vibration piece 13G or 13L comprises a bending-vibration piece 16M,
16N, 16P or 16Q. Each detecting vibration system 2A or 2B comprises
each circumferential-bending-vibration piece 14G or 14H.
[0167] Each electrostatic driving electrode 30A, 30C, 30E or 30G
are provided on the side of each bending-vibration piece 16M, 16N,
16P and 16Q. Each electrostatic driving electrode 30B, 30D, 30F or
30H is provided on the side of a frame 29 opposing to each
radial-bending-vibration piece. The above electrodes
electrostatically drive each bending-vibration piece.
[0168] Each electrostatic detecting electrode 31A or 31C are
provided on the side of each circumferential-bending-vibration
piece 14G or 14H. Each electrostatic detecting electrode 31B or 31D
is provided r the side of the frame 29 opposing each
circumferential-bending vibration piece.
[0169] A doped-semiconductor domain doped with a specific metal may
be provided in the vibrator, instead of the above electrostatic
detecting electrode. This doped-semiconductor domain forms a
piezoelectric resistance device. A change in resistance caused by a
stress applied to each of the piezoelectric resistance devices in
each circumferential-bending vibration piece is measured and
detected as an index of a turning angular velocity, when the
vibrator is turned. 12a is a fixing portion of the supporting
portion 12.
[0170] FIG. 21 is a plan view roughly showing a vibrator according
to another embodiment. Driving vibration systems 1A, 1B and
detecting vibration systems 2A, 2B and operation of them are
similar to those shown in FIG. 11. Frame portions 32A and 32B
extend from two peripheral parts 58a at the detecting vibration
system sides of the base portion 58, and each detecting vibration
system is surrounded by each frame portion. Each frame portion is
provided with connecting portions 32a extending in parallel with
each detecting vibration system and a supporting frame 32b for
supporting and fixing the vibrator. A domain having the smallest
amplitude in a driving vibration and a detecting vibration in each
of the frame portions 32A, 32B is supported and fixed.
[0171] FIG. 22 shows a relative ratio of the amplitude of vibration
of each point in the vibrator of FIG. 21 to the maximum vibration
amplitude in a driving vibration mode, and FIG. 23 shows a relative
ratio of the amplitude of vibration of each point in the vibrator
to the maximum vibration amplitude in a detecting vibration
mode.
[0172] According to FIG. 22, a tensile stress is applied in the
vicinity of the fixing portion 12a of each of the supporting
portions 12A and 12B to the base portion 58 with vibration of each
driving vibration system, and transformation is seen. This
influence is slightly seen in the connecting portion 32a of the
frame portion. Since these influences cancel each other, however,
no influence by the driving vibration is seen near the center of
the base portion and in each bending-vibration piece 14C, 14D and
in each supporting frame 32b of the frame portion.
[0173] According to FIG. 23, influences exerted by the driving
vibration systems and the detecting vibration systems on the base
portion 58 cancel each other, and as the result, no influence by
the detecting vibration is seen in the vicinity 21A of the center
of the base portion 58. In addition to this, however, since a
domain 21D in the supporting frame 32b is also smallest in
amplitude, this domain 21D also can be supported and fixed.
[0174] In the vibrator and vibratory gyroscope according to this
example, as shown in FIGS. 21 and 22, the center of gravity GO of
the vibrator is located within a domain having the smallest
amplitude in driving vibration. And as shown in FIGS. 21 and 23,
the center of gravity GO of the vibrator is located within a domain
having the smallest amplitude in detecting vibration.
[0175] FIG. 24 is a perspective view schematically showing a
vibratory gyroscope with a vibrator of an embodiment of the
invention. A base part 11E has a rectangular shape. Two driving
vibration systems 1A, 1B (first vibration system in this
embodiment) and detecting vibration systems 2A, 2B (second
vibration system) project radially from the peripheral part 11a of
the base portion 11E and are separated with each other. The systems
1A and 1B, or the systems 1A and 2B are dyad-symmetric around the
center of gravity GO of the vibrator, respectively.
[0176] The driving vibration systems 1A and 1B comprise supporting
portions 35, projected from the peripheral part of the base
portion, and first bending-vibration pieces 23C and 23D each
extending in a direction perpendicular to the supporting portion.
As shown in FIG. 2(b), each bending-vibration piece 23C or 23D has
both ends fixed respectively to a frame and a central portion
vibrating in a relatively large amplitude. Preferably, the
bending-vibration pieces are vibrated so that the center of gravity
of the whole vibration of the vibration pieces 23C and 23D is
located on or within the domain near the center of gravity GO of
the vibrator.
[0177] In a vibrator shown in FIG. 25, two driving vibration
systems 1A, 1B and two detecting vibration systems 2A, 2B project
from the peripheral part of the base portion 11A and separated with
each other. The systems 1A and 1B, or, the systems 2A and 2B are
dyad-symmetric around the center of gravity GO of the vibrator.
[0178] The systems 1A and 1B comprise supporting portions 12A and
12B, projected from the peripheral part of the base portion, and
first bending-vibration pieces 13C and 13D each extending in a
direction perpendicular to the supporting portion from the end
thereof (refer to FIG. 2). Each bending vibration piece 13C or 13D
comprises bending-vibration pieces 16A and 16B, or 16C and 16D.
First bending-vibration pieces 23C and 23D are further provided
outside the above bending vibration pieces (refer to FIG. 2). The
bending vibration pieces 13C and 13D are connected with 23C and
23D, respectively, to form frames with spaces 36 formed. The
central portions of the pieces 23C and 23D vibrate in a relatively
large amplitudes as arrows 5A, 5B. In this case, the
bending-vibration pieces are vibrated so that the center of gravity
GD of the whole vibration of the vibration pieces 13C, 13D, 23C and
23D is located on or within a domain near the center of gravity GO
of the vibrator.
[0179] In the vibrator shown in FIG. 26, two driving vibration
systems 1A, 1B and one detecting vibration system 2A project from
the peripheral part of the base portion 11A and separated with each
other. The systems 1A and 1B are dyad-symmetric around GO. The
systems 1A and 1B comprise supporting portions 12A and 12B,
projected from the peripheral part of the base portion, and first
bending-vibration pieces 13C and 13D each extending from the edge
of each supporting portion in a direction perpendicular to the
supporting portion (refer to FIG. 2(a)).
[0180] On the other hand, the system 2A is as described above,
except that a weight portion 37 and a fixing piece 38 are provided
on the opposing side to the system 2A. In this case, when the
center of gravity of the whole driving vibration in the driving
systems is located within a domain near GO, the influence on the
detecting vibration system may be reduced to allow relatively
accurate measurement with only one detecting vibration system 2A.
The vibrator may preferably be held in a predetermined position in
the side of the base portion opposing to the detecting vibration
system, or, in a predetermined position being identical with the
position of the detecting driving system when turning it around GO,
or the vibrator may be held on the elongated line of the above
position.
[0181] In a vibrator of FIG. 27, the driving vibration systems 1A
and 1B are same as the above. The vibrator falls within the
category of FIG. 8. The detecting vibration systems 2A and 2B
comprise frame portions 19A and 19B, respectively, projecting from
the base portion 11A, and second bending-vibration pieces 24C and
24D, respectively, projecting towards the center of gravity GO from
the frame portions 19A and 19B. As shown in FIG. 4(b), each bending
vibration piece 24C or 24D comprises a fixing portion 8 distant
from GO and an open end near GO, and vibrates as an arrow 6A or
6B.
[0182] In a vibrator shown in FIG. 28, two first vibration systems
and two second vibration systems are formed within a frame portion
19C so that the open ends extend towards the center of gravity GO.
The vibrator falls within the category shown in FIG. 10.
[0183] Each driving vibration system comprises a supporting portion
12C or 12D extending towards the center of gravity GO from a frame
portion 19C, and first bending-vibration piece 13M or 13N extending
from the open end of each supporting portion in a direction
perpendicular to the supporting portion (refer to FIG. 2(a)). Each
bending-vibration piece 13M or 13N comprises pieces 16R and 16S, or
16T and 16U.
[0184] Each detection vibration system comprises second
bending-vibration piece 24C or 24D extending linearly from the
frame portion 19C towards the center of gravity GO. Each bending
vibration piece 24C or 24D has a shape shown in FIG. 4(b).
[0185] In the invention, a plurality of first vibration systems may
be connected with connecting portions extending in a
circumferential direction around the center of gravity of the
vibrator to form a vibrating loop system surrounding the center
with the first vibration systems and the connecting portions.
[0186] For example, in a vibrator of FIG. 29, two driving systems
1A, 1B and detection vibration systems 2A, 2B project radially from
the peripheral part of the base portion 11A. The systems 1A and 1B
are dyad-symmetrical and the systems 2A and 2B are also
dyad-symmetrical with the center of gravity GO as the center.
[0187] The systems 1A and 1B comprise supporting portions 12A, 12B,
projecting from the peripheral part of the base portion, and first
bending vibration pieces 13P and 13Q (refer to FIG. 2(a)) each
extending in a direction perpendicular to the supporting portion
from the edge thereof. The bending-vibration pieces 13P and 13Q are
connected with connecting portions 39A, 39B, 39C and 39D. The
connecting portions and the pieces 13P and 13Q together form a
vibrating loop system 71A with GO as its center.
[0188] In the vibration mode shown in FIG. 29, the
bending-vibration pieces 16A, 16B, 16C and 16D vibrate as arrows 6A
and 6B, and responsive to these vibrations, the connecting portions
vibrate as arrows I. When the vibrator is turned, a detecting
vibration mode shown in FIG. 30 is induced, in which the driving
vibration systems vibrate as arrows A and B in the circumferential
direction, and responsive to this, the whole vibrating loop system
deforms. To compensate this deformation, the pieces 14C and 14D in
the detecting vibration systems vibrate as arrows 6A and 6B. 40 is
a weight portion provided within each pieces 14C or 14D.
[0189] Vibrators shown in FIGS. 31 to 35 comprise a small base
portions whose widths are substantially same as those of bending
vibration pieces.
[0190] In vibrators of FIGS. 31 and 32, the supporting portions
12A, 12B and bending vibration pieces 13R, 13S, 14C and 14D, within
the driving and detecting vibration systems, are substantially same
as described above. However, the vibrators comprise base portions
11F which are located at the cross points of the supporting
portions 12A, 12B and the pieces 14C, 14D and whose width are
substantially same as those of the portions 12A, 12B and the pieces
14C, 14D.
[0191] In FIG. 31, a linear elongated portions 41 are provided from
the end portions of the supporting portions 12A, 12B in the
longitudinal direction of the supporting portions. Each elongated
portion is connected with a fixing piece portion 42. The driving
vibration systems 1A, 1B vibrate between a pair of the fixing piece
portions 42 as described above. In FIG. 32, such fixing piece
portions and elongated portions are not provided in the
vibrator.
[0192] FIG. 33 shows a relative ratio of the amplitude of vibration
at each point in the vibrator of FIG. 32 to the maximum vibration
amplitude in a driving vibration mode, and FIG. 34 shows a relative
ratio of the amplitude of the vibration of each point to the
maximum vibration amplitude in a detecting vibration mode. The
FIGS. 32 and 33 can be understood substantially same as FIGS. 12
and 13.
[0193] According to FIG. 33, deformations induced by the driving
vibration are hardly observed in the detecting vibration systems
and the supporting portions. According to FIG. 34, since the
detecting portions are located at dyad-symmetric positions around
the center of gravity of the vibrator, influence exerted by the
detecting vibration on the base portion 11F is hardly observed.
Consequently, the vibrator may preferably be held within the base
portion 11F.
[0194] In the vibrator and gyroscope of this example, as shown in
FIGS. 32 and 33, the center of gravity GO of the vibrator is
located within a domain where the driving vibration is smallest,
and as shown in FIGS. 32 and 34, the center of gravity GO is
located within a domain where the detecting vibration is
smallest.
[0195] A vibrator of FIG. 35 comprises two detecting vibrating
systems 2A and 2B extending from the base part 11F. The detecting
vibration systems comprise bending-vibration pieces 44C and 44D,
respectively. The end portions of the pieces 44C and 44D are
connected through connecting portions 46 to bending-vibration
pieces 23C and 23D, respectively. The bending-vibration pieces 23C
and 23D constitute the driving vibration systems 1A and 1B,
respectively, and extend in a direction substantially parallel to
the pieces 44C and 44D. The pieces 23C, 23D and the connecting
portions 46 together form a vibrating loop system 71B vibrating as
a whole around the center GO of gravity.
[0196] The both ends of the bending-vibration pieces 23C and 23D
are fixed as shown in FIG. 2(b), and these central parts vibrate as
arrows 5A and 5B. The vibration pieces 44C and 44D vibrate as shown
in FIG. 5(b). Besides, the vibrator of the present example may
comprises a projection 45 provided near the base portion, as a
fixing piece portion, which may be held.
[0197] Then, a process for driving bending-vibration pieces and for
detecting vibrations induced in bending vibration pieces is further
described below. The operation of a vibrator of FIG. 36 is same as
that of the vibrator shown in FIG. 24. However, the vibrator is
formed of a piezoelectric single crystal having "a" axises
extending within the specified plane and "c" axis extending in a
direction perpendicular to the vibrator. Such combination of the
"a" axises and "c" axis is seen, for example, in quartz.
[0198] The vibrator of FIG. 36 comprises bending vibration pieces
for driving 23C and 23D having driving electrodes 15A and 15B. FIG.
37(a) shows its cross-sectional view. Further, the vibrator
comprises bending vibration pieces for detecting 14C and 14D having
detecting electrodes 16A and 16B. FIG. 37(b) shows its
cross-sectional view.
[0199] The vibrator according to the invention may comprise
vibration systems each having a subvibrator, especially
bending-vibration piece, provided with a through hole or a hollow
or a groove extending in the longitudinal direction of the
subvibrator or the piece. As a result, the natural resonance
frequency of vibration of the bending-vibration piece may be
reduced to further improve "Q" value of the driving vibration or
detecting vibration. FIGS. 38 to 41 show gyroscopes according to
this embodiment of the invention.
[0200] The vibrator of FIG. 38 comprises bending-vibration pieces
23C, 23D, 14C and 14D, in which through holes 47, 48 are provided,
extending in the longitudinal direction of the respective
bending-vibration piece. As shown in FIG. 39(a), each piece 23C or
23D comprises driving electrodes 49A and 49D on the outer side
surface of the piece, and driving electrodes 49B and 49C on the
inner side surface facing the through hole 47. As shown in FIG.
39(b), each piece 14C or 14D comprises detecting electrodes 50A and
50D on the outer side surfaces of the piece, and detecting
electrodes 50B and 50C on the inner side surfaces facing the
through hole 48.
[0201] In this embodiment, it is used a plate made of a
piezoelectric single crystal, such as quartz, having "a" axises,
which are triad-symmetrical axises.
[0202] In each bending-vibration piece shown in FIG. 39(a), the
driving electrodes 49A and 49D on the outer side surfaces are
connected to a alternating current supply, and the driving
electrodes 49B and 49C on the inner side surfaces are grounded.
Consequently, the directions of the electric fields by the applied
voltages between the driving electrodes 49A and 49B and between the
electrodes 49C and 49D are reversed to induce bending movement in
the bending vibration piece.
[0203] Further, the directions of the electric fields, induced by
the bending movement of the detecting bending-vibration piece
between the detecting electrodes 50A and 50B and between the
electrodes 50C and 50D, are reversed.
[0204] According to the present embodiment, since a pair of driving
electrodes are provided on the outer and inner side surfaces,
respectively, of both sides of the through hole in each
bending-vibration piece, bending motion may be induced in the
bending-vibration piece. The similar principle also applies to each
detecting bending-vibration piece. Therefore, the bending vibration
piece may be driven or its vibration may be detected by applying a
voltage in a direction of "a" axis, which has the largest
electromechanical coupling coefficient.
[0205] In the above-mentioned embodiments, the vibration pieces or
arms are driven by applying a voltage in the a-axis direction of
the piezoelectric single crystal. On the other hand, for example,
in case of a single crystal of lithium niobate, lithium tantalate,
or a single crystal of a solid solution of lithium niobate-lithium
tantalate, as shown in FIG. 40 for example, it is most advantageous
from a viewpoint of thermal stability to orient the a-axis in
parallel with the paper face and direct the c-axis at an angle of
50.degree. to the paper face. In this case, the bending-vibration
pieces are bending-vibrated by applying a voltage in the direction
perpendicular to the paper face.
[0206] In FIG. 40, a 130.degree. Y-plate made of lithium tantalate
whose "c" axis is oriented at an angle of 50.degree. with respect
to the specified plane of the vibrator is used, so that the thermal
stability of the vibrator is most improved. Bending-vibration
pieces 23C and 23D for driving comprise through holes 47, each
extending in the longitudinal direction of the piece, respectively.
Bending-vibration pieces 14C and 14D for detecting comprise through
holes 48, each extending in the longitudinal direction of the
piece, respectively.
[0207] As shown in FIG. 41(a), elongated driving electrodes 99A,
99B, 99C and 99D are provided on both outer sides of the hole 47.
The directions of the electric fields by the applied voltages
between the driving electrodes 99A and 99B and between the
electrodes 99C and 99D are reversed to induce bending movement in
the bending vibration piece. As shown in FIG. 41(b), elongated
detecting electrodes 51A, 51B, 51C and 51D are provided on both
outer sides of the hole 48 in each piece for detection. The
directions of the electric fields, induced by the bending movement
between the detecting electrodes 51A and 51B and between the
electrodes 51C and 51D, are reversed.
[0208] In the above described embodiments, instead of providing the
through holes 17 and 48, grooves or hollow portions, having
substantially same shapes as those of the through holes, may be
provided. That is, a thin wall may be provided so as not to make
each hole 47 and 48 go through or penetrate the bending vibration
piece.
[0209] In the preferred embodiment of the detecting method of an
angular turning rate, an electrical signal for generating a drive
vibration is assumed as a reference signal, an output signal is
obtained by detecting another electrical signal by a detecting
means from a vibration having a vibration mode which is caused by
the drive vibration and is different from the drive vibration mode,
and a phase difference between the reference signal and the output
signal is detected to measure the angular turning rate based on the
detected phase difference.
[0210] FIG. 42 is a block diagram showing an example of a phase
difference detecting means used in this embodiment.
[0211] In the phase difference detecting means 62 shown in FIG. 42,
an output signal is amplified through an alternating-current
amplifier 61 and then supplied to a phase different detecting
circuit 63. A reference signal is preprocessed for waveform-shaping
or the like by a reference signal preprocessing circuit 64, and
then is supplied to a phase different detecting circuit 63, which
detects a phase difference between the preprocessed reference
signal and the output signal which have been supplied. The detected
phase difference is supplied to a low-pass filter 65 and a
direct-current amplifier 66 to convert it to a direct-current
signal whose amplitude varies according to the phase difference.
The direct-current signal obtained by the above-mentioned phase
difference detecting means 62 is supplied to a turning angular rate
detecting circuit 67, which calculates a turning angular rate on
the basis of a predetermined relation between the magnitude of a
direct current and a turning angular rate.
[0212] Since the above-mentioned circuit 62 cannot directly
calculate a phase difference between an output signal and a
reference signal as a numerical value, it calculates a turning
angular rate from the magnitude of the direct-current signal
varying according to the phase difference. However, the phase
difference may be obtained as a numerical value and then a turning
angular rate may be obtained on the basis of a predetermined
relation between a phase difference and a turning angular rate.
[0213] The vibratory gyroscope of the invention proves to be
particularly effective for the above method for detecting the phase
difference to provide high linearity between the phase difference
and the turning angular rate. The linearity between the phase
difference and the turning angular rate may be especially improved
when a ratio of a gyroscopic signal to a leakage signal is 1 to not
lower than 7. A too large leakage signal exceeds the detection
limit of the vibrator, even if it is made of a piezoelectric single
crystal. Therefore, the upper limit of a leakage signal is
determined according to the sensitivity of the vibratory
gyroscope.
[0214] Thus, in a range where a leakage signal is larger than a
gyroscopic signal, especially in a range where the ratio of a
gyroscope signal to a leakage signal is 1 to not lower than 7, the
detection sensitivity is low but the linearity of a phase
difference to a turning angular rate is improved.
[0215] Further, the vibrator of the invention may be produced by
laminating 2 or more piezoelectric layers with each other. In the
vibrator of this embodiment, axial directions of polarization of
the respective layer may preferably different from one another, and
especially, may be in a direction perpendicular to main faces of
the vibrator.
[0216] According to a linear accelerometer using a vibrator of the
invention, since a noise signal, caused by an extending-contracting
vibration taking place in the base portion when a driving vibration
is given to the vibrator, may be remarkably reduced, it is possible
to prevent an error caused by variation of a noise signal with a
temperature change.
[0217] A sensor for measuring a turning velocity and a linear
acceleration at the same time can be made by using the vibrator of
the invention. In the vibrator of the present invention, in case
that a turning rate and a linear acceleration are applied to the
vibrator at the same time, detection signals corresponding to the
turning rate and corresponding to the linear acceleration are
generated. Among the detection signals at this time, a change in
amplitude of a signal component having the same frequency as that
of the drive signal is proportional to the turning rate, and a
change in a direct-current voltage signal component is proportional
to the linear acceleration.
[0218] FIGS. 43 to 47 are perspective views showing gyroscopes
according to another examples of the invention. A vibrator of FIG.
43 is substantially same as that shown in FIG. 11. However, a
through hole 72 is formed in each supporting portion 12E or 12F of
each driving vibration system 1A or 1B, and extends in the
longitudinal direction thereof, thereby reducing the mechanical
strength of each supporting portion. Hollow portions or grooves may
be formed instead of the through holes 72.
[0219] A vibrator shown in FIG. 44 is also substantially same as
that of FIG. 11. However, the vibrator is made of a piezoelectric
single crystal whose "a" axis is oriented in "x" axis and "c" axis
is oriented at an angle of 50.degree. with respect to the specified
plane. Therefore, the driving vibration electrodes 99A to 99D and
detecting electrodes 51A to 51D are substantially same as those
shown in FIG. 40. Further, each bending-vibration piece 16V, 16W,
16X and 16Y of the driving vibration systems 1A and 1B has an shape
of an arc.
[0220] A gyroscope shown in FIG. 45 is substantially same as that
shown in FIG. 35, except that projections 78A, 78B extend outwardly
from the junctions of connecting portions 46 and bending-vibration
pieces 44C and 44D. However, the projections may be omitted. Each
bending-vibration piece 44C or 44D are connected with a base
portion 11H, which comprises a frame portion 74 with a
substantially rectangular shape. A pair of bridges 76A and 76B
extend from the inner surface of the frame portion 74 and support a
central base portion 97 between the bridges. The centers GD, GB and
GO is located within the central base portion 97. Projections 77A
and 77B extend from the central base portion 97 towards spaces 75A
and 75B. 72A and 72B are spaces and 73 is a radius portion.
[0221] The vibrator of this example may be supported within the
projections 78A and 78B, or within the central base portion 97, or
within the projections 77A and 77B, to reduce the influences on the
sensitivity of the detecting vibration induced by the
supporting.
[0222] The gyroscope of FIG. 46 comprises driving vibration systems
each having bending-vibration piece 23C or 23D, which is connected
through a pair of connecting portions 80 to bending-vibration
pieces 44C and 44D, to form a vibrating loop system 71C. Each
connecting portion 80 comprises subconnecting portions 80a and 80c,
extending in a direction of "X" axis, and a subconnecting portion
80b extending in a direction of "Y" axis and connecting the
subconnecting portions 80a and 80c. Bending-vibration pieces 44C
and 44D are connected to a base portion 11A, respectively. 72A and
72B are hollow portions.
[0223] A gyroscope of FIG. 47 comprises the driving vibration
pieces 1A and 1B, detecting vibration pieces 2A and 2B, and the
base portion 11A, which are substantially same as those described
in FIG. 11. Further, driving vibration systems 1E and 1F are
provided outside of the systems 1A and 1B. The systems 1E and 1F
comprise bending-vibration pieces 23A and 23D, respectively, each
having both ends connected through a connecting portion 100 to the
end of each bending-vibration piece 44C, 44D.
[0224] The sensitivity of a gyroscope varies according to the
difference of natural resonance frequencies of its driving
vibration and detecting vibration. However, when ambient
temperature changes, the natural resonance frequencies and
therefore the differences change. In actual experiments conducted
by the present inventors, the differences varies about 10% in a
temperature range of -30.degree. C.-+80.degree. C. Therefore, it is
desired to maintain the differences to a constant with smaller
deviations in a temperature range of -30.degree. C.-+80.degree.
C.
[0225] To solve this problem, when the vibrator comprises a pair of
main surfaces, which are parallel to the specified plane, and
sides, a projection or projections may preferably be provided on
the side or sides, the projection or projections having a height,
from the side on which it is provided, of 1/3 to {fraction (1/7)}
(preferably 1/4 to 1/5) of a thickness of the vibrator. Moreover,
when the projection or projections may be provided in a
bending-vibration piece or pieces, whose length may preferably be
not more than 7 mm, most preferably not more than 6 mm.
[0226] The inventors actually measured natural resonance
frequencies of the driving and detecting vibrations in the
bending-vibration piece according to the invention in a temperature
range of -30.degree. C.-+80.degree. C. and presented a graph in
FIG. 48, showing the difference between maximum and minimum values
of the differences in the same temperature range, in which the
bending-vibration piece has a length of 6, 8, or 10 mm, a thickness
of 0.3 mm, a width of 10 mm and is made of quartz.
[0227] As can be seen from the results of FIG. 48, the difference
of maximum and minimum values of the differences of the resonance
frequencies in a temperature range of -30.degree. C. to +80.degree.
C. may be reduced to not more than 2.5 Hz, especially 2.0 Hz to
control the fractuation of the sensitivities of the gyroscope in a
range of not more than 5%, by reducing a length of the
bending-vibration piece to not more than 6 mm and controlling the
height of the projection as described above.
[0228] Further, a projection or projections may preferably be
provided on a side or sides of a base portion, the projection or
projections extending in the longitudinal direction of the side, to
further reduce the influences on the detecting vibration induced by
the driving vibration. In this case, projections may preferably be
provided, in positions symmetrical with respect to the center of
gravity of the base portion, to reduce the noise induced in the
detecting vibration.
[0229] Further, when each driving or detecting vibration system
comprises a bending-vibration piece or pieces and its supporting
portion, a projection or projections may preferably be formed on at
least one side, more preferably on both sides, of the supporting
portion, the projection or projections extending in the
longitudinal direction of the side. The influences on the base
portion induced by the vibration of the bending-vibration pieces
may be thereby reduced. Moreover, a projection or projections may
be provided on at least one side of the detecting vibration piece
so that the influence on the detecting vibration piece induced by
the driving vibration, and therefore the noise may be reduced, when
the vibrator is not turned.
[0230] FIG. 49 shows a gyroscope according to this embodiment,
comprising a vibrator having projections 90G, 90I, 90H and 90J
provided on sides of a base portion 11A. The projections are in
positions symmetrical with respect to the center of gravity of the
base portion 11A. Further, a projection 90A, 90B, 90C or 90D are
formed on both sides of each supporting portion 12A, 12B in each
driving vibration system 1A, 1B. Each projection 90E or 90F is
formed on one side of each bending-vibration piece 14C or 14D in
each detecting vibration system 2A or 2B.
[0231] When producing vibrators by means of an etching process,
fluctuations may occur in a time duration for the etching process
or concentrations of etching solution depending on a manufacturing
rot to which the vibrator belongs. Such fluctuations may induce
fluctuations in the differences between the natural resonance
frequencies of the driving and detecting vibrations of the vibrator
and fluctuations in the sensitivities of the produced vibrators. To
prevent such fluctuations, a through hole or holes, or a hollow
portion or portions, or a groove or grooves may be formed in a
bending-vibrating piece in a position or positions closer to the
end of the piece than a driving or detecting vibration means and
with such means not provided.
[0232] FIG. 50 is a plan view schematically showing a gyroscope
according to this embodiment. The gyroscope is substantially same
as that of FIG. 11, except that through holes 91A, 91B, 91C and 91D
are formed in bending-vibration pieces 16A, 16B, 16C, 16D, 14C and
14D, in positions closer to the ends of the pieces than driving or
detecting vibration electrodes and with such electrodes not
provided. The through holes or the hollow portions or grooves may
preferably be formed in positions 0.3 mm distant form the
electrodes.
[0233] The effects of such through hole or hollow portion or groove
will be described below. As shown in FIG. 51, when producing a
bending-vibration piece by etching a material, such material may be
further etched as shown in broken lines with respect to a
predetermined design shown by a solid line. In this case, the edge
surface 101 of the piece is etched after the material has been
already etched to the solid line, a mass of the bending-vibration
piece is decreased to increase its resonance frequency. On the
other hand, when the material is further etched in its sides as
shown in broken lines, a width of the bending-vibration piece is
decreased to reduce its resonance frequency. Consequently, the
effects of the overetching on the sides 102 exceeds the effects of
that of the end surface 101.
[0234] However, by providing through holes 91A to 91D in the piece,
when the sides are overetched as shown by broken lines, the through
holes 91A to 91D are also etched as shown by the broken lines to
reduce a mass of the piece after the etching.
[0235] For example, when forming the bending-vibration piece made
of quartz and with a length of 6 mm, a width of 1.0 mm and a
thickness of 0.3 mm, and if the sides 102 are overetched 1 .mu.m
deeper than the designed length, the difference between the
resonance frequencies of the driving and detecting vibrations is
made about 2.85 Hz different from the predetermined value. On the
other hand, when through holes 91A to 91D each having a length of
0.4 mm and a width of 0.3 mm in the piece of the above design, the
difference is only 0.08 Hz different from the predetermined
value.
[0236] Moreover, an enlarged portion may be preferably provided at
the end of each bending-vibration piece, and such portion having a
through hole or holes, or a hollow portion or portions, or a groove
or grooves formed within. Such enlarged portion may improve the
above effects of the through hole or the hollow portion, or in
other words, even smaller through hole or hollow portion or groove
may provide the above effects.
[0237] FIG. 52 shows a gyroscope according to this embodiment. Each
bending-vibration piece 16A, 16B, 16C, 16D, 14C or 14D comprises
each end with an enlarged portion 95 or 96 formed, each enlarged
portion having a width lager than that of the corresponding
bending-vibration piece. Within each enlarged portion, through
holes 91A and 91B, or 91C and 91D are formed.
[0238] As described above, the present invention provides a novel
vibratory gyroscope comprising a vibrator, especially extending in
a specified plane, and the gyroscope being capable of detecting an
angular turning rate of a turning when subjecting the vibrator to
the turning.
* * * * *