U.S. patent application number 12/789170 was filed with the patent office on 2010-09-16 for angular velocity sensor and method for fabricating the same.
This patent application is currently assigned to FUJITSU MEDIA DEVICES LIMITED. Invention is credited to Kazutaka Araya, Yuki Endo, Hiroshi Tanaka, Yoshinori Uwano, Masanori Yachi.
Application Number | 20100229647 12/789170 |
Document ID | / |
Family ID | 39495283 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100229647 |
Kind Code |
A1 |
Tanaka; Hiroshi ; et
al. |
September 16, 2010 |
ANGULAR VELOCITY SENSOR AND METHOD FOR FABRICATING THE SAME
Abstract
An angular velocity sensor includes a tuning-fork vibrator
having a base and multiple arms extending from the base. Two arms
out of the multiple arms driven to vibrate have first end parts
opposite to second end parts connected to the base. The first end
parts being wider than the second end parts.
Inventors: |
Tanaka; Hiroshi; (Yokohama,
JP) ; Endo; Yuki; (Yokohama, JP) ; Yachi;
Masanori; (Yokohama, JP) ; Araya; Kazutaka;
(Yokohama, JP) ; Uwano; Yoshinori; (Yokohama,
JP) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W., SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
FUJITSU MEDIA DEVICES
LIMITED
Yokohama
JP
|
Family ID: |
39495283 |
Appl. No.: |
12/789170 |
Filed: |
May 27, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12036585 |
Feb 25, 2008 |
|
|
|
12789170 |
|
|
|
|
Current U.S.
Class: |
73/504.16 |
Current CPC
Class: |
Y10T 29/49789 20150115;
Y10T 29/49002 20150115; Y10T 29/49995 20150115; G01C 19/5607
20130101; Y10T 29/49798 20150115; Y10T 29/42 20150115 |
Class at
Publication: |
73/504.16 |
International
Class: |
G01C 19/56 20060101
G01C019/56 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2007 |
JP |
2007-043363 |
Claims
1. An angular velocity sensor comprising: a tuning-fork vibrator
having a base and multiple arms extending from the base, two arms
out of the multiple arms driven to vibrate having first end parts
opposite to second end parts connected to the base, the first end
parts being wider than the second end parts.
2. The angular velocity sensor as claimed in claim 1, wherein the
first end parts protrude from first side surfaces of the multiple
arms opposite to second side surfaces facing each other.
3. The angular velocity sensor as claimed in claim 1, wherein the
first end parts have steps so that the first end parts are wider
than the second end parts.
4. The angular velocity sensor as claimed in claim 1, wherein the
two arms have driving electrodes that extend from front and back
surfaces of the two arms to side surfaces thereof.
5. The angular velocity sensor as claimed in claim 1, wherein the
base and the multiple arms are made of LiNbO.sub.3 or
LiTaO.sub.3.
6. The angular velocity sensor as claimed in claim 1, wherein the
angular velocity sensor senses an angular velocity about an axis in
a longitudinal direction of the multiple arms.
7. The angular velocity sensor as claimed in claim 1, wherein the
angular velocity sensor senses an angular velocity about an axis in
a thickness direction of the multiple arms.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Divisional Application which claims the benefit of
pending U.S. patent application Ser. No. 12/036,585, filed on Feb.
25, 2008, and claims priority of Japanese Patent Application No.
2007-043363, filed on Feb. 23, 2007. The disclosures of the prior
applications are hereby incorporated herein in their entirety by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to an angular
velocity sensor and a method for fabricating the same, and more
particularly, to an angular velocity sensor having a tuning-fork
vibrator and a method for fabricating the same.
[0004] 2. Description of the Related Art
[0005] An angular velocity sensor is a sensor that senses an
angular velocity in rotation, and is used in systems for image
stabilization of camera, for automotive navigation, for stability
control of vehicles or postures of robots, and the like. Japanese
Patent Application Publication No. 2001-165664 discloses an angular
velocity sensor having a tuning-fork vibrator and a technique to
improve drive efficiency by a composition of electrodes provided on
the tuning-fork vibrator which is made by putting together two
tuning-fork vibrators directly so that each of generated electric
charges of the tuning-fork vibrators is opposite each other.
Japanese Patent Application Publication No. 2004-301510 discloses
an angular velocity sensor having a tuning-fork vibrator and a
technique to sense angular velocities about a plurality of axes. In
order to realize this technique, it needs to put some weight on
upper parts of arms of the tuning-fork vibrator in order to
increase inertial force.
[0006] Tuning-fork vibrators make a progress in downsizing in
accordance with downsizing of angular velocity sensors. However,
downsized tuning-fork vibrators have a problem to decrease drive
efficiency and thus amplitude in driving vibration is small. In
this case, amplitude in detecting vibration generated by Coriolis
force is relatively small when an angular velocity is applied, and
it is thus difficult to sense angular velocity.
SUMMARY OF THE INVENTION
[0007] The present invention has been made in view of the
above-mentioned circumstances and provides an angular velocity
sensor, which is suitable for mass-production being made of high
electromechanical coupling coefficient piezoelectric single crystal
and have high sensitivity and high drive efficiency, and a method
for fabricating the same thereof.
[0008] According to an aspect of the present invention, there is
provided an angular velocity sensor including: a tuning-fork
vibrator having a base and multiple arms extending from the base,
two arms out of the multiple arms driven to vibrate having first
end parts opposite to second end parts connected to the base, the
first end parts being wider than the second end parts. According to
another aspect of the present invention, there is provided a method
for fabricating an angular velocity sensor including: cutting a
substrate made of one of LiNbO.sub.3 and LiTaO.sub.3 into a piece;
forming grooves extending from opposite sides of the piece
alternately, the grooves having a length equal to or greater than
half of a distance connecting the opposite sides; and dividing the
piece into parts in the grooves extending from either one of the
opposite sides so as to form dividing grooves narrower than the
grooves.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1A shows a driving vibration of two arms, and FIG. 1B
shows a detecting vibration when an angular velocity about a Y axis
is applied to;
[0010] FIGS. 2A and 2B are perspective views of a front surface and
a back surface of a tuning-fork vibrator of an angular velocity
sensor in accordance with a first comparative example;
[0011] FIGS. 3A and 3B are perspective views of a front surface and
a back surface of a tuning-fork vibrator of an angular velocity
sensor in accordance with a first embodiment;
[0012] FIGS. 4A and 4B are perspective views of a front surface and
a back surface of a tuning-fork vibrator of an angular velocity
sensor in accordance with a first variation of the first
embodiment;
[0013] FIGS. 5A through 5D are perspective views that respectively
show a method of fabricating the tuning-fork vibrator of the
angular velocity sensor in accordance with the first
embodiment;
[0014] FIG. 6 is a cross-sectional view taken along a line A shown
in FIG. 3A, in which the tuning-fork vibrator of the angular
velocity sensor is connected to a drive power source in accordance
with the first embodiment;
[0015] FIG. 7 shows results of simulating effects on a driving
resonance frequency by a width t1 of free-end parts of arms;
[0016] FIG. 8 shows results of simulating a sensitivity change
ratio as a function of change of temperature;
[0017] FIG. 9 shows results of simulating effects on a
sensitivity-temperature change ratio affected by the width t1 of
the free-end parts of the arms when the temperature changes from
room temperature (+25.degree. C.) to high temperature (+85.degree.
C.) and from room temperature to low temperature (-40.degree.
C.);
[0018] FIG. 10A shows a driving vibration of the tuning-fork
vibrator of the angular velocity sensor in accordance with the
first embodiment, and FIG. 10B shows a detecting vibration when an
angular velocity about Y axis is applied to;
[0019] FIGS. 11A and 11B are perspective views of a front and a
back surface of a tuning-fork vibrator of an angular velocity
sensor in accordance with a second embodiment;
[0020] FIG. 12 is a cross-sectional view taken along a line A shown
in FIG. 11A, in which the tuning-fork vibrator of the angular
velocity sensor is connected to a drive power supply in accordance
with the second embodiment;
[0021] FIG. 13A shows a driving vibration by two arms, and FIG. 13B
shows a detecting vibration when an angular velocity about Z axis
is applied to;
[0022] FIG. 14 is a cross-sectional view of a tuning-fork vibrator
of an angular velocity sensor connected to a drive power supply in
accordance with a third embodiment;
[0023] FIG. 15 is a cross-sectional view of the tuning-fork
vibrator of the angular velocity sensor when another electrode
arrangement is employed;
[0024] FIGS. 16A and 16B are perspective views of a front and a
back surface of a tuning-fork vibrator of an angular velocity in
accordance with a fourth embodiment;
[0025] FIGS. 17A through 17C are perspective views that
respectively show a method of fabricating the tuning-fork vibrator
of the angular velocity sensor in accordance with the fourth
embodiment;
[0026] FIG. 18A shows driving vibrations of four arms, and FIG. 18B
shows detecting vibrations of the four arms when an angular
velocity about a Y axis is applied to;
[0027] FIG. 19 shows effect of driving vibrations by four arms;
[0028] FIG. 20A and 20B are perspective views of a front and a back
surface of the tuning-fork vibrator of the angular velocity sensor
when another electrode arrangement is employed; and
[0029] FIG. 21A shows driving vibrations of four arms, and FIG. 21B
shows detecting vibrations of the four arms when an angular
velocity about a Z axis is applied to.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] A description will now be given of embodiments of the
present invention with reference to the accompanying drawings.
First Embodiment
[0031] A first embodiment is an angular velocity sensor having a
tuning-fork vibrator composed of two arms and a base. The
tuning-fork vibrator senses an angular velocity about Y axis of the
tuning-fork vibrator, which is a longitudinal direction of the arms
12. A description is now given, with reference to FIGS. 1A and 1B,
of a driving vibration of the tuning-fork vibrator and a detecting
vibration that is caused when an angular velocity about Y axis is
applied. It is assumed that the longitudinal direction of the arms
12 of the tuning-fork vibrator is Y axis, the width direction is X
axis, and the thickness direction is Z axis. Referring to FIG. 1A,
the arms 12 vibrates so as to become close to and away from each
other in turn when a drive signal is applied to driving electrodes
(not shown) of the tuning-fork vibrator. This vibration is parallel
to the X axis and is referred to as driving vibration. When an
angular velocity is applied to the Y axis, each of the arms 12
vibrates in opposite directions due to Coriolis force as shown in
FIG. 1 B. This vibration is parallel to the Z axis and is referred
to as detecting vibration. It is possible to sense an angular
velocity about the Y axis when detecting electrodes (not shown)
sense the detecting vibration.
[0032] FIGS. 2A and 2B are respectively perspective views of a
front and a back surface of a tuning-fork vibrator of an angular
velocity sensor in accordance with a first comparative example.
FIGS. 3A and 3B are respectively perspective views of a front and a
back surface of the tuning-fork vibrator of the angular velocity
sensor in accordance with the first embodiment. FIGS. 4A and 4B are
respectively perspective views of a front and a back surface of a
tuning-fork vibrator of an angular velocity sensor in accordance
with a first variation of the first embodiment. It is assumed that
the front surface of a tuning-fork vibrator is an X-Y plane, the
back surface of a tuning-fork vibrator is another X-Y plane
opposite to the front surface, and the side surfaces of a
tuning-fork vibrator are Y-Z planes.
[0033] Referring to FIGS. 2A and 2B, the tuning-fork vibrator of
the angular velocity sensor in accordance with the first
comparative example is composed of a base 10 and two arms 12
extended from the base 10. The arms 12 are caused to have driving
vibration. Detecting electrodes 14 are provided on the front, back
and side surfaces of the arms 12. The detecting electrodes 14
provided on the front and back surfaces of the arms 12 are
connected together via electrodes 16, and those of provided on the
front and side surfaces are connected to extraction electrodes 18.
Driving electrodes 20 are provided on the front and back surfaces
of the base 10 and arms 12 and are connected to the extraction
electrodes 18. The base 10 and the arms 12 are formed of a
piezoelectric material of LiNbO.sub.3 (lithium niobate), and the
detecting electrodes 14 and the driving electrodes 20 are formed
with metal films of Au (gold) with an underlying layer formed by an
alloyed film of Ni (nickel) and Cr (chromium).
[0034] FIGS. 3A and 3B show the tuning-fork vibrator of the angular
velocity sensor in accordance with the first embodiment. A free-end
part 22 of each of the arms 12 away from the base 10 has a width t1
in the X-axis direction, which is twice as much as a width t2 of a
fixed-end part of the arm 12 close to the base 10. The free-end
parts 22 protrude from side surfaces of the arms 12 opposite to
side surfaces that face each other via a space so that the arms 12
have steps in the free-end parts 22. The length of the free-end
parts 22 in the Y-axis direction is half of that of the arm 12 in
the Y-axis direction. The other structure of the first embodiment
is the same as that of the first comparative example shown in FIGS.
2A and 2B.
[0035] FIGS. 4A and 4B show a tuning-fork vibrator of an angular
velocity sensor in accordance with a first variation of the first
embodiment. The width t1 of the free-end parts of the arms 12 away
from the base 10 has a length equal to 1.5 times the width t2 of
the fixed-end parts of the arms 12 close to the base 10. The other
structure of the first variation of the first embodiment is the
same as that of the first embodiment shown in FIGS. 3A and 3B.
[0036] A method of fabricating the angular velocity sensor in
accordance with the first embodiment is explained with reference to
FIGS. 5A through 5D. Referring to FIG. 5A, a substrate 24 formed of
LiNbO.sub.3 is cut into rectangular pieces 26 by dicing with a
dicing saw.
[0037] Referring to FIG. 5B, grooves 28 are formed by dicing with a
dicing saw having a blade width of 400 .mu.m from the sides A and B
of the rectangular piece 26 opposite to each other in the
short-side direction of the rectangular piece 26. The grooves 28
are formed so as to have lengths H1 and H2 from the sides A and B,
in which the lengths H1 and H2 are two-thirds of a length L1 of the
short sides of the rectangular piece 26. The grooves 28 extending
from sides A and B are arranged alternatively in the longitudinal
direction at fixed intervals of 150 .mu.m. More specifically, a
distance P1 from the short-side edge of the rectangular piece 26 to
the closest groove 28 on the side A in the longitudinal direction
is 500 .mu.m longer than a distance P2 from the above short-side
edge of the rectangular piece 26 to the closest groove on the side
B. Further, a pitch L2 between two adjacent grooves 28 on the side
A and a pitch L3 between two adjacent grooves 28 on the side B are
both equal to 1100 .mu.m. Furthermore, two adjacent grooves 28 on
the side B are arranged symmetrically about the groove 28 on the
side A interposed therebetween. That is, the center of the groove
28 on the side A is overlapped with the center of the space between
the two adjacent grooves 28 on the side B.
[0038] Referring to FIG. 5C, electrode patterns 29 such as driving
electrodes and detecting electrodes are formed on the rectangular
piece 26 by the exposure technique. The electrode patterns 29 shown
in FIG. 5C are only parts of the electrode patterns formed on the
arms 12. With reference to FIG. 5D, the rectangular piece 26 is
divided into pieces on the centers of the widths t3 of the grooves
28 on the side B by dicing with a dicing saw having a blade width
of 100 .mu.m. The pieces are the tuning-fork vibrators of the
angular velocity sensors in accordance with the first embodiment
shown in FIGS. 3A and 3B.
[0039] FIG. 6 schematically shows the tuning-fork vibrator of the
angular velocity sensor in accordance with the first embodiment to
which a drive power supply 30 is connected. FIG. 6 shows an X-Z
cross-sectional view of the tuning-fork vibrator that is taken
along a line A in FIG. 3A and is viewed from the side of the
vibrator opposite to the side on which the base 10 is provided.
Referring to FIG. 6, the driving electrodes 20 provided on the
front and back surfaces of the arm 12 are connected to the drive
power supply 30. The detecting electrodes 14 provided on the front
and back surfaces of one of the arms 12 are connected to detection
2, and the detecting electrodes 14 on the side surfaces thereof are
connected to detection 1. The detecting electrodes 14 located on
the front and back surfaces of the other arm 12 are connected to
detection 1, and the detecting electrodes 14 on the side surface of
the arm 12 are connected to detection 2. When a drive signal, which
may be an alternating signal, is applied to the driving electrodes
20, electric fields E1 are generated in the arms 12 in the same
direction between the driving electrodes 20 of the front and back
surfaces of the arms 12. Thus, the arms 12 are caused to have
driving vibration. When an angular velocity is applied to the Y
axis, detecting vibration is generated. The detecting vibration
results in electric fields E3 in the arms 12. The electric fields
E3 have a direction from the electrodes 14 connected to detection 2
to those connected to detection 1. Detecting electrodes 14 sense
charges generated by the electric fields E3. It is thus possible to
detect an angular velocity about the Y axis. The sense signals that
appear at detection 1 and detection 2 are opposite phase
signals.
[0040] FIG. 7 shows results of simulating effects on the driving
vibration frequency by the width t1 of the free-end parts 22 of the
arms 12. The horizontal axis of FIG. 7 denotes the width t1 of the
free-end parts 22 of the arms 12 normalized by the width t2 of the
parts of the arms 12 connected to the base 10. The vertical axis of
FIG. 7 denotes the driving vibration frequency normalized by the
drive resonance frequency of the first comparative example
(relative drive resonance frequency). Referring to FIG. 7, it is
clear that the first variation of the first embodiment has a lower
drive resonance frequency than that of the first comparative
example. Further, the drive resonance frequency of the first
embodiment is lower than that of the first embodiment. The widths
t1 and t2 of the first comparative example are the same. The width
t1 of the first variation of the first embodiment is 1.5 times as
much as the width t2, and the width t1 of the first embodiment is
twice the width t2. This explains that the drive resonance
frequency is decreased by setting the width t1 of the free-end
parts 22 of the arms 12 greater than the width t2 of the fixed-end
parts of the arms 12. The following Formula 1 describes the
sensitivity of the angular velocity sensor. A .omega..sub.drive in
the Formula 1 denotes the drive resonance frequency. It can be seen
from Formula 1 that the sensitivity of angular velocity is
inversely proportional to the drive resonance frequency. FIG. 7
shows that the drive resonance frequency of the first embodiment
can be made lower than that of the comparative example. Thus, the
first embodiment has improved sensitivity of angular velocity, as
compared to the first comparative example.
FM
(sensitivity).ident.V.sub.detect/.OMEGA..sub.0.apprxeq.j2*A.sub.drive-
*A.sub.detect*Q.sub.detect*{1/(Cd.sub.detect*SO.sub.detect)}*Q.sub.drive/.-
omega..sub.drive*V.sub.drive [Formula 1]
[0041] A.sub.drive and A.sub.detect denote electromechanical
coupling coefficients involved in drive and detect, respectively.
Q.sub.drive and Q.sub.detect denote resonance Q values involved in
drive and sense, respectively. Cd.sub.detect denotes the
electrostatic capacitance on the detect side. SO.sub.detect denotes
the equivalent stiffness on the detect side, and V.sub.drive
denotes the drive voltage.
[0042] FIG. 8 shows results of simulating the sensitivity change
ratio as a function of change of temperature. The horizontal axis
denotes temperature and the vertical axis denotes the sensitivity
change ratio normalized by the sensitivity at a temperature of
25.degree. C. A broken line represents the first comparative
example, a bold solid line represents the first embodiment, and a
thin solid line represents the first variation of the first
embodiment. It can be seen from FIG. 8 that the sensitivity change
ratio of the first comparative example is most influenced by the
temperature, and that the sensitivity change ratios of the first
variation of the first embodiment and the first variation become
smaller in this order. That is, the sensitivity change ratio by
temperature change decreases as the width t1 of the free-end parts
22 of the arms 12 that is greater than the width t2 of the
fixed-end parts of the arms 12 connected to the base 10
increases.
[0043] The above simulation results may be explained as follows.
The drive resonance frequency decreases as the width t1 greater
than the width t2 increases, as shown in FIG. 7. The change ratio
of the drive resonance frequency as a function of the change of
temperature is constant, so that the change ratio of the
sensitivity of the angular velocity sensor inversely proportional
to the drive resonance frequency is also constant to the change of
temperature as shown by Formula 1. The sensitivity of the angular
velocity sensor of the first embodiment is the highest, since the
drive resonance frequency is the smallest. The sensitivity of the
angular velocity sensor also depends on the difference between the
drive resonance frequency and the detect resonance frequency
(hereinafter, the difference is referred to as a frequency
difference). When the frequency difference increases, the
sensitivity of the angular velocity sensor decreases. The detect
resonance frequency is the resonance frequency in the detecting
vibration mode in FIG. 1B. When the angular velocity sensors of the
first embodiment, the first variation of the first embodiment, and
the first comparative example are adjusted so as to have an
identical sensitivity, the first embodiment has the greatest
frequency difference. Since the frequency difference changes
constantly along with temperature, the first embodiment having a
great frequency difference has a small ratio of change of the
frequency difference caused by temperature change with reference to
the frequency difference at a temperature of 25.degree. C. When the
angular velocity sensor of the first embodiment, the first
variation of the first embodiment, and the first comparative
example are adjusted so as to have an identical sensitivity of
angular velocity, the first embodiment has the smallest ratio of
change in sensitivity. In contrast, the first comparative example
having the smallest sensitivity of angular velocity has a small
frequency difference, and thus, has a large ratio of change of the
frequency difference caused by temperature change with reference to
the frequency difference at a temperature of 25.degree. C. Thus,
the first comparative example has a large change ratio of
sensitivity of angular velocity.
[0044] FIG. 9 shows results of simulating effects on the
sensitivity-temperature change ratio affected by the width t1 of
the free-end parts 22 of the arms 12 when the temperature changes
from room temperature (+25.degree. C.) to high temperature
(+85.degree. C.) and from room temperature to low temperature
(-40.degree. C.). The horizontal axis of the graph is the width t1
of the free-end parts 22 of the arms 12 normalized by the width t2
of the fixed-end parts of the arms 12 connected to the base 10, and
the vertical axis is a difference in the sensitivity-temperature
change ratio obtained when the temperature changes from room
temperature to high temperature and that obtained when the
temperature changes from room temperature to low temperature with
reference to the sensitivity-temperature change ratio of the first
comparative example (difference in the relative
sensitivity-temperature change ratio). The difference in the
sensitivity-temperature change ratio has a minus sign when it has a
smaller change ratio than that of the first comparative example,
and has a plus sign when it has a greater change ratio than that of
the first comparative example. A broken line denotes the
sensitivity-temperature change ratio when the temperature changes
from room temperature to low temperature, and a solid line denotes
when the temperature changes from room temperature to high
temperature. That is, the greater the width t1 than the width t2
is, the smaller the sensitivity change is. This means that the
difference in the sensitivity-temperature change ratio obtained
when the temperature changes from room temperature to high
temperature and that obtained when the temperature changes from
room temperature to low temperature are both minus. The reason for
the above simulation results is similar to that of in FIG. 8.
[0045] In accordance with the first embodiment, as shown in FIGS.
3A and 3B, the arms 12 driven to vibrate have free-end parts 22
having the width t1 greater than the width t2 of the fixed-end
parts connected to the base 10. Thus, the free-end parts 22 of the
arms 12 have a respective increased mass, and increased inertia
force is available in driving vibration shown in FIG. 10A. It is
thus possible to improve the efficiency of driving vibration to the
drive signal, that is, drive efficiency. The improved drive
efficiency increases detecting vibration generated when an angular
velocity about the Y axis as shown in FIG. 10B, that is, the
longitudinal direction of the arms 12. Accordingly, it is possible
to improve detection sensitivity of angular velocity about the Y
axis.
[0046] The above-mentioned exemplary structure of the first
embodiment has free-end parts 22 that protrude from the outer side
surfaces of the arms 12 opposite to the inner side surfaces that
face each other via a space, as shown in FIGS. 3A and 3B. There are
other exemplary structures. For example, the free-end parts 22 may
protrude inwards from the inner side surfaces of the arms 12 so as
to face each other or may protrude from the front or back surfaces
of the arms 12. In these structures, the width t1 is greater than
the width t2, so that the inertia force in driving vibration can be
increased and drive efficiency can be improved.
[0047] Furthermore, as shown in FIGS. 3A and 3B, each of the arms
12 has the step in the respective free-end parts 22. Thus, the
width t1 is greater than the width t2 and the free-end parts 22
have an increased mass, so that the inertia force in driving
vibration can be increased and the drive efficiency can be
improved.
[0048] As shown in FIGS. 5A through 5D, the substrate 24 of
LiNbO.sub.3 is cut into the rectangular pieces 26. The grooves 28
are formed by dicing. The grooves 28 have a length equal to
two-thirds of the length L1 in the short-side direction of the
rectangular piece 26, and are formed on the opposite sides A and B
by turns at the given intervals. The rectangular piece 26 is
divided by dicing with a dicing blade narrower than the grooves 28
at the center of the width t3 of the grooves 28 on the side B. It
is thus possible to easily produce the tuning-fork vibrator having
the free-end parts 22 of the arms 12 having the width t1 greater
than the width t2 with excellent mass productivity even for LiNbO3,
which is high electromechanical coupling coefficient piezoelectric
single crystal that has difficulty in process by chemical
etching.
[0049] FIG. 5B exemplarily shows that the grooves 28 having a
length of two-thirds of the length L1 of the rectangular piece 26
in the short-side direction alternately extend from the sides A and
B of the rectangular piece 26 opposite to each other in the
short-side direction. The present invention is not limited to the
above, but may include an arrangement in which the sum of the
heights H1 and H2 of the grooves 28 is equal to or more than half
of the length L1 of the rectangular piece 26 in the short-side
direction. That is, the sum of the height H1 and H2 should be
greater than the length L1 of the rectangular piece 26 in the
short-side direction. It is thus possible to obtain the tuning-fork
vibrator having the width t1 of the free-end parts of the arms 12
that is greater than the width t2 of the fixed-end parts thereof.
It is possible to employ another arrangement in which the grooves
28 having a length greater than half of the length in the long-side
direction of the rectangular piece 26 alternately extend from the
two sides opposite to each other in the long-side direction. That
is, the grooves may be formed on one of pairs of the opposite sides
of the rectangular piece 26 so as to have, a length equal to or
greater than half of the distance between the pair of opposite
sides.
[0050] FIG. 5B exemplarily shows that the grooves 28 that
alternately extend from the opposite sides A and B in the
short-side direction of the rectangular piece 26 are arranged at
the predetermined constant pitches in the long-side direction. It
is to be noted that the alternative arrangement of the grooves 28
is not limited to the constant pitches. However, in view of mass
productivity, it is preferable to arrange the interleaving grooves
28 at the predetermined constant pitches.
[0051] FIG. 5B exemplarily shows that the two adjacent grooves 28
on the side A of the rectangular piece 26 are arranged
symmetrically about the groove 28 on the side A interposed between
the two adjacent grooves 28. It is to be noted that the present
invention is not limited to the above arrangement. However, it is
preferable to employ the above arrangement because the two arms 12
having the driving vibration have an identical width and
well-balanced amplitudes in vibration.
[0052] FIG. 5D exemplarily shows that the rectangular piece 26 are
divided in the center of the width t3 of the grooves 28. The
present invention is not limited to the above but may include
another arrangement in which the rectangular piece 26 is divided so
that the free-end parts 22 of the two arms 12 having the driving
vibration have an identical width t1. Even in this arrangement, the
tuning-fork vibrator vibrates with well-balanced amplitudes.
However, it is preferable to divide the rectangular piece 26 in the
center of the width t3 of the grooves 28 in order to manufacture
the tuning-form vibrators having well-balanced amplitudes without
degrading the mass productivity.
[0053] FIGS. 5B and 5D exemplarily show the grooves 28 formed by
the dicing saw having a width of 400 .mu.m and the rectangular
piece 26 is divided by the dicing saw having a width of 100 .mu.m.
The present invention is not limited to the above. The width of the
dicing saw used to divide the rectangular piece 26 is required to
be less than that of the dicing saw used to form the grooves 28.
The dicing process using the dicing saws may be replaced by another
dicing process using wire saws or a laser process.
[0054] FIG. 5B exemplarily shows that the grooves 28 formed from
the two opposite sides A and B of the rectangular piece 26 in the
short-side direction have an identical width. The present invention
is not limited to the above, but may be another arrangement in
which the width t3 (see FIG. 5D) of the grooves 28 on the side B is
greater than that of the grooves 28 on the side A. Even in this
arrangement, it is possible to obtain the tuning-fork vibrator
having the free-end parts of the arms 12 having a comparatively
great width t1.
[0055] The present invention is not limited to the base 10 and the
arms 12 made of LiNbO.sub.3 but may use LiTaO.sub.3. Preferably, a
material having a great electromechanical coupling coefficient is
used because such a material improves the sensitivity of angular
velocity sensor as described in Formula 1.
Second Embodiment
[0056] A second embodiment has an exemplary structure having the
driving electrodes having an arrangement different from that of the
driving electrodes of the angular velocity sensor of the first
embodiment. FIG. 11A is a perspective view of a front surface of an
angular velocity sensor of the second embodiment, and FIG. 11B is a
perspective view of a back surface thereof. Referring to FIGS. 11A
and 11B, driving electrodes 20 are provided so as to extend from
the front and back surfaces of the two arms 12 driven to vibrate to
the side surfaces that face each other. The other structure of the
second embodiment is the same as that of the first embodiment.
[0057] FIG. 12 schematically shows the tuning-fork vibrator of the
angular velocity sensor in accordance with the second embodiment to
which the drive power supply 30 is connected. FIG. 12 shows an X-Z
cross-sectional view of the tuning-fork vibrator that is taken
along a line A in FIG. 11A and is viewed from the side of the
vibrator opposite to the side on which the base 10 is provided.
Referring to FIG. 12, the driving electrodes 20 are provided so as
to extend from the front and back surfaces of the two arms 12
driven to vibrate to the side surfaces that face each other. Thus,
when the drive signal, which may be an alternative signal, is
applied to the driving electrodes 20, electric fields E2 generated
from the side surfaces of the arms 12 are added to the electric
fields E1 generated between the driving electrodes 20 on the front
and back surfaces of the arms 12. The other structure of the second
embodiment is the same as that of the first embodiment.
[0058] According to the second embodiment, as shown in FIG. 12, the
electric fields E2 generated from the side surfaces of the arms 12
are added to the electric fields E1 generated between the driving
electrodes 20 on the front and back surfaces of the arms 12. It is
thus possible to obtain an increased densities of the electric
fields between the driving electrodes 20 of the arms 12, as
compared to the first embodiment. Thus, the second embodiment has a
higher drive efficiency than the first embodiment.
[0059] The present invention is not limited to the above-mentioned
arrangement of the driving electrodes 20 but may be arranged so
that the driving electrodes 20 extend from the front and back
surfaces of the arms 12 driven to vibrate to any of the side
surfaces of the arms. Even with this arrangement, the densities of
the electric fields generated between the driving electrodes 20 of
the arms 12 can be enlarged and the drive efficiency can be
improved. It is possible to employ yet another arrangement in which
the driving electrodes 20 extend from the front and back surfaces
of at least one of the two arms 12 to any of the side surfaces
thereof. However, in order to realize excellent balanced
amplitudes, it is preferable to employ the arrangement in which the
driving electrodes 20 extend from the front and back surfaces of
each of the two arms 12 to any of the side surfaces thereof.
Third Embodiment
[0060] A third embodiment is an angular velocity sensor capable of
detecting an angular velocity about the axis in the thickness
direction of the arms 21, that is, the Z axis of the tuning-fork
vibrator of the angular velocity sensor of the first embodiment.
FIG. 13A shows driving vibration and FIG. 13B shows detecting
vibration caused when an angular velocity about the Z axis.
[0061] Referring to FIG. 13A, driving vibration parallel to the X
axis is generated so that the two arms 12 alternately become close
to and away from each other. Referring to FIG. 13B, an angular
velocity about the Z axis is applied, the arms 12 have detecting
vibration in which the arms 12 vibrate in an identical direction in
parallel with the X axis. The detecting electrodes (not shown)
sense the detecting vibration, so that the angular velocity about
the Z axis can be detected.
[0062] FIG. 14 schematically shows the tuning-fork vibrator of the
angular velocity sensor in accordance with the third embodiment to
which the drive power supply 30 is connected. The driving
electrodes 20 provided on the front and back surfaces of the arms
12 are connected to the drive power supply 30. The detection
electrode 14 provided on the front surface of one of the arms 12 is
connected to detection 2, and the detection electrode 14 provided
on the back surface thereof is connected to detection 1. The
detection electrode 14 provided on the front surface of the other
arm 12 is connected to detection 1, and the detection electrode 14
provided on the back surface thereof is connected to detection 2.
When the drive signal is applied to the driving electrodes 20, the
electric fields E1 are generated between the driving electrodes 20
on the front and back surfaces of the arms 12, so that the arms 12
are caused to vibrate. When an angular velocity is applied about
the Z axis, detecting vibration is generated and results in
electric fields E3 in the arms 12 oriented from the detecting
electrodes 14 connected to detection 2 to the detecting electrodes
14 connected to detection 1. The resultant charges are sensed via
the detecting electrodes 14, so that the angular velocity about the
Z axis can be detected. The sense signals obtained via the
detections 1 and 2 are opposite phase signals.
[0063] According to the third embodiment, the increased width t1 of
the free-end parts of the arms 12 increases the mass and inertia
force, and improves the sensitivity of angular velocity about the
axis in the thickness direction of the arms 12. Since the angular
velocity sensor of the third embodiment is capable of sensing the
angular velocity about the Z axis, the tuning-fork vibrator can be
horizontally housed in a package of the angular velocity sensor. It
is thus possible to realize a reduced height of the angular
velocity sensor, as compared to the first embodiment capable of
sensing angular velocity about the Y axis
[0064] Even in the third embodiment, as shown in FIG. 15, the
densities of the electric fields generated in the arms 12 between
the driving electrodes 20 can be increased by arranging the driving
electrodes 20 so as to extend from the front and back surfaces of
the arms 12 to the side surfaces that face each other as in the
case of the second embodiment. Thus, the drive efficiency can be
improved. Further, the densities of the electric fields E3
generated between the detecting electrodes 14 due to detecting
vibration can be enhanced by arranging the detecting electrodes 14
so as to extend from the front and back surfaces of the arms 12 to
outer side surfaces opposite to the inner side surfaces that face
each other. It is thus possible to further improve sensing of
angular velocity about the Z axis.
Fourth Embodiment
[0065] A fourth embodiment is an exemplary angular velocity sensor
with a tuning-fork vibrator that is equipped with four arms 12 and
is capable of sensing angular velocity about the Y axis, that is,
the axis in the longitudinal direction of the arms 12. FIG. 16A is
a perspective view of a front surface of a tuning-fork vibrator
employed in the fourth embodiment, and FIG. 16B is a perspective
view of a back surface thereof.
[0066] Referring to FIGS. 16A and 16B, two outer arms 12 out of the
four arms 12 and the base 10 are substantially the same as those of
the tuning-fork vibrator of the first embodiment, as shown in FIGS.
3A and 3B.
[0067] A description will now be given, with reference to FIGS. 17A
through 17C, of a method for fabricating the angular velocity
sensor in accordance with the forth embodiment. The substrate 24 of
LiNbO.sub.3 is cut into the rectangular piece 26 in the same manner
as that of the first embodiment, and a description thereof will be
omitted here.
[0068] Referring to FIG. 17A, the grooves 28 are formed so that
three grooves 28 are provided on the side A between two adjacent
grooves 28 on the side B opposite to the side A in the short-side
direction of the rectangular piece 26. The grooves 28 may be formed
by using a dicing saw having a blade width of 400 .mu.m. The three
grooves 28 on the side A are arranged symmetrically about the
center of the distance between the two adjacent grooves 28 on the
side B. The length H1 of the grooves 28 on the side A and the
length H2 of the grooves 28 on the side B are formed so as to
become equal to two-thirds of the length L1 of the rectangular
piece 26 in the short-side direction. A distance P1 from an end of
the rectangular piece 26 to the groove 28 on the side A closest to
the above end in the long-side direction is 550 .mu.m longer than a
distance P2 from the above end to the groove 28 on the side B
closest to the above end in the long-side direction. The grooves 28
may be formed so that the intervals L2a and L2b related to the
grooves 28 on the side A are, for example, 550 .mu.m and 1100
.mu.m, respectively, and the intervals L3 related to the grooves 28
on the side B are, for example, 2200 .mu.m.
[0069] Referring to FIG. 17B, the electrode patterns 29 for the
driving electrodes and the detecting electrodes are formed on the
rectangular piece 26 by using the exposure technique. In FIG. 17B,
only some electrode patterns 29 formed on portions of the
rectangular piece 26 corresponding to the arms 12 are illustrated
for the sake of simplicity. Referring to FIG. 17C, the rectangular
piece 26 is divided by a dicing process using a dicing saw having a
blade width of 100 .mu.m in the center of the width t3 of the
grooves 28 formed on the side B. Thus, the tuning-fork vibrator for
the angular velocity sensor of the fourth embodiment can be
obtained, as shown in FIGS. 16A and 16B.
[0070] FIG. 18A shows driving vibration, and FIG. 18B shows
detecting vibration generated when an angular velocity about the
longitudinal direction of the arms 12 is applied. Referring to FIG.
18A, the drive signal is applied to the driving electrodes (not
shown) formed on the two outer arms 12, which are thus driven to
vibrate in parallel with the X axis. The two inner arms 12 are
driven to vibrate in parallel with the X axis so as to be
counter-balanced with the two outer arms 12. That is, the two outer
arms 12 and the two inner arms 12 are driven to vibrate in opposite
phases. Referring to FIG. 18B, when an angular velocity about the Y
axis is applied, detecting vibration is generated in the two outer
arms, which vibrate in parallel with the Z axis so that one of the
two outer arms moves forward and simultaneously the other moves
backward. Similarly, the two inner arms 12 vibrate in parallel with
the Z axis so that one of the two inner arms moves forward and
simultaneously the other moves backward. The detecting vibration is
sensed via detecting electrodes (not shown), so that the angular
velocity about the Y axis can be detected.
[0071] According to the fourth embodiment, the four arms 12 are
driven to vibrate so that the two outer arms 12 and the two inner
arms 12 are counter-balanced with each other in opposite phases.
Thus, as shown in FIG. 19, torque generated in the two outer arms
12 and torque generated in the two inner arms 12 act in opposite
directions, so that these torques can be canceled. It is thus
possible to more effectively restrain twist displacement of the
base 10 and that of a support member 32, which is connected to the
base 10 and is used to support the tuning-fork vibrator. Further,
it is possible to obtain a wider supportable region on the base 10
to which the support member 32 can be attached since twist
displacement of the base 10 is well restrained.
[0072] According to the fourth embodiment, as in the case of the
second embodiment, the driving electrodes 20 are provided so as to
extend from the front and back surfaces of the arms 12 driven to
vibrate to the side surfaces that face each other. It is thus
possible to increase the densities of the electric fields between
the driving electrodes 20 generated in the arms 12 and to improve
the drive efficiency. According to the fourth embodiment, the four
arms 12 are involved in driving vibration. Thus, it is possible to
arrange the driving electrodes 20 so as to extend from the front
and back surfaces of the two outer arms 12 to the side surfaces
that face each other and the other side surfaces opposite to the
above side surfaces and to arrange the driving electrode 20 on the
front, back and side surfaces of the two arms 12. It is thus
possible to further enhance the densities of the electric fields in
the arms 12 between the driving electrodes 20 and to further
improve the driving efficiency. In FIG. 20, only the driving
electrodes 20 and the detecting electrodes 14 provided on the arms
12 are illustrated for the sake of simplicity.
[0073] The above-mentioned structure of the fourth embodiment
employs the driving electrodes 20 provided on the two outer arms
12. Similar effects can be obtained in another arrangement in which
the driving electrodes 20 are provided on the two inner arms
12.
Fifth Embodiment
[0074] A fifth embodiment has an exemplary structure directed to
sensing angular velocity about the Z axis of the tuning-fork
vibrator of the angular velocity of the fourth embodiment, that is,
the thickness direction of the arms 12. FIG. 21A shows driving
vibration, and FIG. 21B shows detecting vibration when an angular
velocity about the Z axis is applied. The driving vibration shown
in FIG. 21A is the same as that of the fourth embodiment, and a
description thereof will be omitted here. Referring to FIG. 21 B,
when an angular velocity about the Z axis is applied, the two outer
arms 12 vibrate in parallel with the X axis in the same direction.
Similarly, the two inner arms 12 vibrate in parallel with the X
axis in the same direction. The detecting vibration of the two
outer arms 12 and that of the two inner arms 12 are 180 degrees out
of phase. Detecting electrodes (not shown) sense the detecting
vibrations so that the angular velocity about the X axis can be
detected.
[0075] The above-mentioned first through fifth embodiments have the
tuning-fork vibrators having two or four arms. However, the present
invention is not limited to the above but may employ a tuning-fork
vibrator having another number of arms.
[0076] The present invention is not limited to the specifically
disclosed embodiments, but other embodiments and variations may be
made without departing from the scope of the present invention.
[0077] The present application is based on Japanese Patent
Application No. 2007-043363 filed Feb. 23, 2007, the entire
disclosure of which is hereby incorporated by reference.
* * * * *