U.S. patent application number 13/410736 was filed with the patent office on 2012-06-28 for vibration gyro sensor, control circuit, and electronic apparatus.
This patent application is currently assigned to SONY CORPORATION. Invention is credited to Kazuo Kurihara.
Application Number | 20120160028 13/410736 |
Document ID | / |
Family ID | 39593139 |
Filed Date | 2012-06-28 |
United States Patent
Application |
20120160028 |
Kind Code |
A1 |
Kurihara; Kazuo |
June 28, 2012 |
VIBRATION GYRO SENSOR, CONTROL CIRCUIT, AND ELECTRONIC
APPARATUS
Abstract
Provided is a vibration gyro sensor including: a vibration
element including a piezoelectric element group which has a first
side provided with a drive electrode and a detection electrode and
a second side opposed to the first side and provided with a common
electrode, which vibrates by a drive signal input between the drive
electrode and the common electrode and generates an output signal
containing a detection signal corresponding to Coriolis force from
the detection electrode; a bias section applying a bias voltage to
the detection electrode; an oscillation circuit outputting the
signal for causing vibration of the vibration element to the drive
electrode as the drive signal based on the output signal generated
by the detection electrode; and a phase inversion circuit
outputting an inversion signal obtained by inverting a phase of the
drive signal output from the oscillation circuit to the common
electrode.
Inventors: |
Kurihara; Kazuo; (Miyagi,
JP) |
Assignee: |
SONY CORPORATION
Tokyo
JP
|
Family ID: |
39593139 |
Appl. No.: |
13/410736 |
Filed: |
March 2, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11970027 |
Jan 7, 2008 |
8136398 |
|
|
13410736 |
|
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Current U.S.
Class: |
73/504.12 |
Current CPC
Class: |
G01C 19/5649
20130101 |
Class at
Publication: |
73/504.12 |
International
Class: |
G01C 19/56 20120101
G01C019/56 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 9, 2007 |
JP |
2007-001031 |
Claims
1. A vibration gyro sensor, comprising: a vibration element
including a piezoelectric element group which has a first side
provided with a drive electrode and a detection electrode and a
second side opposed to the first side and provided with a common
electrode, which vibrates by a drive signal input between the drive
electrode and the common electrode and generates an output signal
containing a detection signal corresponding to Coriolis force from
the detection electrode; bias means applying a bias voltage to the
detection electrode; an oscillation circuit outputting the signal
for causing vibration of the vibration element to the drive
electrode as the drive signal based on the output signal generated
by the detection electrode; a phase inversion circuit outputting an
inversion signal obtained by inverting a phase of the drive signal
output from the oscillation circuit to the common electrode; an
addition circuit that adds the first signal obtained from the first
detection electrode and the second signal obtained from the second
detection electrode, wherein, the detection electrode includes a
first detection electrode generating a first signal and a second
detection electrode generating a second signal for obtaining the
detection signal based on a difference between the first signal and
the second signal, the vibration element includes a vibration arm
to which the piezoelectric element is mounted, and a base body
having a lead electrode group for external connection of the drive
electrode and the detection electrodes and which supports the
vibration arm, and the vibration element includes an insulation
body having a conductive film serving as the common electrode of
the piezoelectric element group.
Description
RELATED APPLICATION DATA
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/970,027, filed Jan. 7, 2008, the entirety
of which is incorporated herein by reference to the extent
permitted by law. This application claims the benefit of priority
to Japanese Patent Application No. JP 2007-001031 filed in the
Japanese Patent Office on Jan. 9, 2007, the entirely of which is
incorporated herein by reference to the extent permitted by
law.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a vibration gyro sensor for
detecting an angular velocity of an object, a control circuit
therefor, and an electronic apparatus mounted with the vibration
gyro sensor.
[0004] 2. Description of the Related Art
[0005] Up to now, so-called vibration gyro sensors have been widely
used as angular velocity sensors for consumer use. The vibration
gyro sensors are sensors that detect angular velocities by allowing
a cantilever vibrator to vibrate at a predetermined resonance
frequency and detecting Coriolis force generated due to an
influence of the angular velocity by a piezoelectric element or the
like.
[0006] The vibration gyro sensors have advantages in that the
sensors have a simple mechanism, requires short time to activate,
and can be manufactured at low costs. The vibration gyro sensors
are mounted to, for example, electronic apparatuses such as a video
camera, a virtual reality apparatus, and a car navigation system,
and are used as sensors in shake detection, movement detection, and
direction detection, respectively.
[0007] In recent years, the vibration gyro sensors are required to
be downsized and improved in performance due to the downsizing and
improvement in performance of the electronic apparatuses to which
the vibration gyro sensors are mounted. For example, because of
multi-functionalization of the electronic apparatuses, demands are
made to mount the vibration gyro sensor to a substrate in
combination with various sensors for other purposes, thereby
reducing a size thereof. A generally-used technique for realizing
such reduction in size is called MEMS (Micro Electro Mechanical
System) which involves using an Si substrate and forming a
structural body using a thin-film process and a photolithography
technique used in forming semiconductors.
[0008] Incidentally, a vibration system becomes light along with
the downsizing of the vibration gyro sensor. However, because the
Coriolis force is proportional to the weight of the vibration
system, detection sensitivity deteriorates that much. Further,
because an amplitude of the vibrator becomes small when a power
supply voltage is decreased due to the downsizing of the vibration
gyro sensor, the detection sensitivity also deteriorates thereby.
An S/N of a detection output signal is degraded by the
deterioration of the detection sensitivity.
[0009] Thus, to solve the problems as described above, there is
disclosed a technique in which drive signals having the same phase
and amplitude and output from two detection electrodes are added in
an addition circuit and the signal whose phase has been inverted in
an inversion circuit is input to the two detection electrodes (see,
for example, Japanese Patent Application Laid-open No. 2000-205861
(paragraphs (0005) and (0016), and FIG. 1)).
SUMMARY OF THE INVENTION
[0010] However, recently, further downsizing and reduction in
voltage of a vibration gyro sensor are required. Therefore, there
is a need to further improve sensor detection sensitivity and a
need for a higher S/N than ever before.
[0011] In view of the above-mentioned circumstances, there is a
need for a vibration gyro sensor capable of improving detection
sensitivity and realizing a high S/N, a control circuit therefor,
and an electronic apparatus mounted with the vibration gyro
sensor.
[0012] According to an embodiment of the present invention, there
is provided a vibration gyro sensor including a vibration element,
bias means, an oscillation circuit, and a phase inversion circuit.
The vibration element includes a piezoelectric element group which
has a first side provided with a drive electrode and a detection
electrode and a second side opposed to the first side and provided
with a common electrode, vibrates by a drive signal input between
the drive electrode and the common electrode, and can generate an
output signal containing a detection signal corresponding to
Coriolis force from the detection electrode. The bias means applies
a bias voltage to the detection electrode. The oscillation circuit
outputs the signal for causing vibration of the vibration element
to the drive electrode as the drive signal based on the output
signal generated by the detection electrode. The phase inversion
circuit outputs an inversion signal obtained by inverting a phase
of the drive signal output from the oscillation circuit to the
common electrode.
[0013] In the embodiment of the present invention, a bias voltage
is applied to the detection electrode provided on the first side,
and the drive signal can be input between the drive electrode
provided on the first side and the common electrode provided on the
second side in that state. Accordingly, the vibration element
operates so that the drive signal corresponding to the bias voltage
is input between the common electrode and the detection electrode.
In other words, the detection electrode also functions as the drive
electrode. As a result, the detection sensitivity of the detection
electrode can be further enhanced to realize a high S/N.
[0014] The piezoelectric element group is an element constituted by
a plurality of piezoelectric elements. A piezoelectric element is
provided for each electrode of the drive electrode and the
detection electrode. The vibration element vibrates by the driving
of the piezoelectric element provided with the drive electrode
among those piezoelectric elements.
[0015] According to the embodiment of the present invention, the
detection electrode includes a first detection electrode generating
a first signal and a second detection electrode generating a second
signal for obtaining the detection signal based on a difference
between the first signal and the second signal, and the vibration
gyro sensor further includes an addition circuit adding the first
signal obtained from the first detection electrode and the second
signal obtained from the second detection electrode. In other
words, the vibration gyro sensor according to the embodiment of the
present invention causes self-excited oscillation by the
oscillation circuit using the addition signal obtained by the
addition in the addition circuit.
[0016] According to the embodiment of the present invention, the
vibration element includes an insulation body having a conductive
film serving as the common electrode of the piezoelectric element
group. In other words, the insulation body to which the conductive
film has been formed becomes a base vibration body of the vibration
element. For example, the vibration element is produced such that
the piezoelectric element group is mounted on the conductive film
of the insulation body to which the conductive film has been
formed.
[0017] According to another embodiment of the present invention,
there is provided a vibration gyro sensor including a vibration
element, bias means, an oscillation circuit, and a phase inversion
circuit. The vibration element includes a piezoelectric element
which has a first side provided with a drive electrode and
detection electrodes and a second side opposed to the first side
and provided with a common electrode, vibrates by a drive signal
input between the drive electrode and the common electrode, and can
generate output signals containing detection signals corresponding
to Coriolis force from the detection electrodes. The bias means
applies a bias voltage to the detection electrodes. The oscillation
circuit outputs the signal for causing vibration of the vibration
element to the drive electrode as the drive signal based on the
output signals generated by the detection electrodes. The phase
inversion circuit outputs an inversion signal obtained by inverting
a phase of the drive signal output from the oscillation circuit to
the common electrode.
[0018] According to the embodiments of the present invention,
regarding the piezoelectric element included in the vibration
element, the drive electrode and the detection electrodes are
formed of the same piezoelectric material.
[0019] According to the another embodiment of the present
invention, the vibration element includes a vibration arm to which
the piezoelectric element is mounted, and a base body having a lead
electrode group for external connection of the drive electrode and
the detection electrodes and which supports the vibration arm.
Accordingly, a plurality of vibration elements can be produced on a
single substrate by an MEMS method, for example.
[0020] According to still another embodiment of the present
invention, there is provided a control circuit including bias
means, an oscillation circuit, and a phase inversion circuit. The
bias means applies a bias voltage to a detection electrode of a
vibration element including a piezoelectric element group which has
a first side provided with a drive electrode and the detection
electrode and a second side opposed to the first side and provided
with a common electrode, which vibrates by a drive signal input
between the drive electrode and the common electrode and can
generate an output signal containing a detection signal
corresponding to Coriolis force from the detection electrode. The
oscillation circuit outputs the signal for causing vibration of the
vibration element to the drive electrode as the drive signal based
on the output signal generated by the detection electrode. The
phase inversion circuit outputs an inversion signal obtained by
inverting a phase of the drive signal output from the oscillation
circuit to the common electrode.
[0021] According to yet another embodiment of the present
invention, there is provided a control circuit including bias
means, an oscillation circuit, and a phase inversion circuit. The
bias means applies a bias voltage to detection electrodes of a
vibration element including a piezoelectric element which has a
first side provided with a drive electrode and the detection
electrodes and a second side opposed to the first side and provided
with a common electrode, which vibrates by a drive signal input
between the drive electrode and the common electrode and can
generate output signals containing detection signals corresponding
to Coriolis force from the detection electrodes. The oscillation
circuit outputs the signal for causing vibration of the vibration
element to the drive electrode as the drive signal based on the
output signals generated by the detection electrodes. The phase
inversion circuit outputs an inversion signal obtained by inverting
a phase of the drive signal output from the oscillation circuit to
the common electrode.
[0022] According to yet still another embodiment of the present
invention, there is provided an electronic apparatus including a
vibration gyro sensor and a main body to which the vibration gyro
sensor is mounted. The vibration gyro sensor includes: a vibration
element including a piezoelectric element group which has a first
side provided with a drive electrode and a detection electrode and
a second side opposed to the first side and provided with a common
electrode, which vibrates by a drive signal input between the drive
electrode and the common electrode and can generate an output
signal containing a detection signal corresponding to Coriolis
force from the detection electrode; bias means applying a bias
voltage to the detection electrode; an oscillation circuit
outputting the signal for causing vibration of the vibration
element to the drive electrode as the drive signal based on the
output signal generated by the detection electrode; and a phase
inversion circuit outputting an inversion signal obtained by
inverting a phase of the drive signal output from the oscillation
circuit to the common electrode.
[0023] As described above, according to the embodiments of the
present invention, it is possible to improve detection sensitivity
of the vibration gyro sensor and to realize a high S/N.
[0024] These and other objects, features and advantages of the
present invention will become more apparent in light of the
following detailed description of best mode embodiments thereof, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0025] FIG. 1A is a perspective view of a vibration gyro element,
and FIG. 1B is a sectional view of a surface perpendicular to an
axis in a longitudinal direction in the vibration gyro element;
[0026] FIG. 2 is a circuit block diagram of a gyro sensor including
the vibration gyro element shown in FIG. 1;
[0027] FIG. 3 is a graph showing impedance characteristics of the
vibration gyro element;
[0028] FIG. 4 is a diagram showing an equivalence circuit of the
gyro sensor shown in FIG. 2;
[0029] FIG. 5 is a circuit block diagram showing a structure of a
gyro sensor provided with a phase inversion circuit;
[0030] FIG. 6 is a diagram showing an equivalence circuit of the
gyro sensor shown in FIG. 5;
[0031] FIG. 7A is a view of a vibration element of a vibration gyro
sensor according to an embodiment of the present invention, and
FIG. 7B is a sectional view thereof;
[0032] FIG. 8 is a circuit block diagram showing a structure of the
vibration gyro sensor including the vibration element shown in FIG.
7;
[0033] FIG. 9 is a diagram showing an equivalence circuit of the
vibration gyro sensor shown in FIG. 8;
[0034] FIG. 10 is a block diagram showing a vibration gyro sensor
that is not provided with a phase inversion circuit in FIG. 9;
[0035] FIG. 11 is a diagram showing an equivalence circuit of the
vibration gyro sensor shown in FIG. 10;
[0036] FIG. 12 is a diagram showing an equivalence circuit of
another exemplary vibration gyro sensor;
[0037] FIG. 13 is a diagram showing a time chart of voltage
waveforms of detection electrodes in the circuits shown in FIGS. 9,
11, and 12;
[0038] FIG. 14A is a perspective view showing a vibration element
according to another embodiment of the present invention, and FIG.
14B is a sectional view of a surface perpendicular to a
longitudinal axis of a vibration arm;
[0039] FIG. 15 is a block diagram showing a structure of a
vibration gyro sensor including the vibration element shown in
FIGS. 14A and 14B;
[0040] FIG. 16A is a schematic diagram showing a vibration element
according to further another embodiment of the present invention,
and FIG. 16B is a sectional view taken along the line A-A in FIG.
16A;
[0041] FIG. 17 is a block diagram showing a structure of a
vibration gyro sensor including the vibration element shown in
FIGS. 16A and 16B;
[0042] FIG. 18 is a schematic perspective view showing a digital
camera as an example of an electronic apparatus mounted with the
vibration gyro sensor; and
[0043] FIG. 19 is a block diagram showing a structure of the
digital camera.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0044] Prior to giving descriptions on a vibration gyro sensor
according to embodiments of the present invention, a principle of
the vibration gyro sensor will first be described with reference to
the drawings.
[0045] FIG. 1A is a perspective view of a vibration gyro element,
and FIG. 1B is a sectional view of a surface perpendicular to an
axis in a longitudinal direction in the vibration gyro element.
[0046] A vibration gyro element 1 includes a base vibration body 2
of a quadrangular prism shape, whose surface is conductively
plated, a piezoelectric element 3a, and a piezoelectric element 3b.
The piezoelectric elements 3a and 3b are formed so as to be aligned
on a first side surface 2a of the base vibration body 2. The
piezoelectric element 3a includes a piezoelectric body 54a and an
electrode 55a formed on a surface of the piezoelectric body 54a. In
a similar manner, the piezoelectric element 3b includes a
piezoelectric body 54b and an electrode 55b formed on a surface of
the piezoelectric body 54b. A conductive plating 4 serves as a
common electrode of the piezoelectric elements 3a and 3b.
[0047] FIG. 2 is a circuit block diagram of the gyro sensor
including the vibration gyro element 1 shown in FIG. 1. An output
of an oscillation circuit 7 is input as a drive signal to a second
side surface 2b opposed to the first side surface 2a of the base
vibration body 2 (see FIG. 1B). The drive signal passes through the
common electrode (reference electrode) 4 of the base vibration body
2 and is input to side surfaces 56a and 56b of the piezoelectric
elements 3a and 3b that are in contact with the common electrode 4.
The drive signal is the same in phase and magnitude in the
piezoelectric elements 3a and 3b. Signals output from the
electrodes 55a and 55b of the piezoelectric elements 3a and 3b are
respectively input to resistors 5a and 5b and to an addition
circuit 6. The resistors 5a and 5b are resistors for applying a
bias voltage Vref to the output signals of the piezoelectric
elements 3a and 3b. An output of the addition circuit 6 is input to
the oscillation circuit 7. The outputs of the piezoelectric
elements 3a and 3b are input to a differential amplifier circuit
9.
[0048] The vibration gyro element 1, the addition circuit 6, and
the oscillation circuit 7 constitute a self-excited oscillation
circuit. The vibration gyro element 1 oscillates by the
self-excited oscillation circuit and bends and vibrates in a
direction perpendicular to the first side surface 2a and the second
side surface 2b of the base vibration body 2 (Y-axis direction).
The entire vibration gyro element 1 bends and vibrates along with
the bending vibration of the piezoelectric elements 3a and 3b. When
the vibration gyro element 1 rotates in this state with an axis in
the longitudinal direction (Z-axis) (hereinafter, referred to as
longitudinal axis) as a center, Coriolis force is generated in the
vibration gyro element 1 and a direction of the bending vibration
changes. Thus, an output difference is generated between the
piezoelectric elements 3a and 3b, thereby obtaining an output from
the differential amplifier circuit 9. As described above, the drive
signals for driving the vibration gyro element 1 are signals that
are the same in phase and magnitude in the piezoelectric elements
3a and 3b. Accordingly, the drive signals are canceled out in the
differential amplifier circuit 9 and a signal corresponding to a
level of angular velocity is output from the differential amplifier
circuit 9.
[0049] As described above, the piezoelectric elements 3a and 3b are
used as a drive piece for causing bending vibration of the base
vibration body 2 and also as a detection piece for obtaining a
signal corresponding to the angular velocity.
[0050] FIG. 3 is a graph showing impedance characteristics of the
vibration gyro element 1. The abscissa axis represents a resonance
frequency and the ordinate axes represent an impedance Z and phase
.theta. of the piezoelectric element 3a or 3b, respectively. The
impedance becomes a minimum value Zs and the phase becomes 0 (deg)
at a frequency fs. The frequency fs is a series resonance point.
Further, the impedance becomes maximum and the phase becomes 0
(deg) at a frequency fp. The frequency fp is a parallel resonance
point. The gyro sensor shown in FIG. 2 is caused to oscillate at
the series resonance point by the self-excited oscillation circuit
constituted by the vibration gyro element 1, the addition circuit
6, and the oscillation circuit 7.
[0051] FIG. 4 is a diagram showing an equivalence circuit of the
gyro sensor shown in FIG. 2. An operation principle of the gyro
sensor shown in FIG. 2 will be described more specifically with
reference to FIG. 4. An output of an oscillator 7a is input as a
drive signal to the second side surface 2b of the base vibration
body 2. The drive signal passes through the common electrode 4 of
the base vibration body 2 and is input to the side surfaces of the
piezoelectric elements 3a and 3b that are in contact with the
common electrode 4. Signals output from the electrodes 55a and 55b
of the piezoelectric elements 3a and 3b are respectively input to
the resistors 5a and 5b and also to the differential amplifier
circuit 9a.
[0052] The vibration gyro element 1 is caused of separately-excited
oscillation by an alternating voltage signal Vd input by the
oscillator 7a. At this time, an impedance Zsa of the piezoelectric
element 3a and an impedance Zsb of the piezoelectric element 3b of
the vibration gyro element 1 become minimum. In addition, an
alternating voltage signal Vra across both ends of the resistor 5a
and an alternating voltage signal Vrb across both ends of the
resistor 5b become maximum.
[0053] When an angular velocity .omega.o of the vibration gyro
element 1 with the longitudinal axis as the center is not imparted,
the impedance Zsa and the impedance Zsb become the same level Zs,
and the Vra and Vrb also become the same signal. Therefore, the
output of the differential amplifier circuit 9a becomes 0. The
amplitude of the alternating voltage signal across both ends of
each of the piezoelectric elements 3a and 3b at this time is
represented by Ag.
[0054] When the angular velocity .omega.o with the longitudinal
axis as the center is imparted to the vibration gyro element 1, a
detection signal corresponding to the Coriolis force appears in the
output of the differential amplifier circuit 9a. When a mass of the
vibration gyro element is represented by m, the magnitude Vo of the
detection signal can be expressed by Expression (1).
Vo.varies.m*Ag*.omega.o (1)
[0055] A resistance Rb of the resistors 5a and 5b is smaller the
better in view of drive efficiency. This is because, since the
alternating voltage signal Vd is divided by the impedance Zs (Zsa,
Zsb) and the resistance Rb, the amplitude Ag increases when the
resistance Rb becomes smaller. However, the resistance Rb is larger
the better in view of detection efficiency. Specifically, this is
because a difference between the impedance Zsa and the impedance
Zsb generated by the angular velocity .omega.o appears as a
difference in voltage across both ends between the resistors 5a and
5b.
[0056] In view of the above, the value of the resistors 5a and 5b
with which the detection signal becomes maximum can be obtained
when Rb=Zs. This is because as described above, the piezoelectric
elements 3a and 3b both function as the drive piece and the
detection piece.
[0057] In a case where the values of the resistors 5a and 5b are
selected to be Rb=Zs, to increase the magnitude of the detection
signal with respect to a certain angular velocity .omega.o, as is
apparent from Expression (1), it is only necessary to increase the
mass m of the vibration gyro element 1 or increase the amplitude Ag
of the alternating voltage signal across both ends of the
piezoelectric elements 3a and 3b. However, it may be difficult to
increase the mass m in a gyro sensor that is required to be
downsized. Thus, attempts are made to increase the amplitude Ag.
For increasing the amplitude Ag, it is only necessary to increase
the amplitude of the alternating voltage signal Vd input by the
oscillator 7a. However, the maximum amplitude of the signal Vd is
determined by the level of the power supply voltage of the gyro
sensor, whereby it may be difficult to increase the power supply
voltage under the circumstance that low power consumption is
required.
[0058] Thus, as shown in FIG. 5, there is proposed a gyro sensor
provided with a phase inversion circuit 8. The output of the
oscillation circuit 7 is input to the common electrode 4 of the
base vibration body 2 and to the phase inversion circuit 8. The
output of the phase inversion circuit 8 passes through the
resistors 5a and 5b to be input to the surfaces of the
piezoelectric elements 3a and 3b opposed to the side surface in
contact with the base vibration body 2, that is, the electrodes 55a
and 55b.
[0059] FIG. 6 is a diagram showing an equivalence circuit of the
gyro sensor shown in FIG. 5. The diagram of FIG. 6 is different
from the circuit block diagram of FIG. 4 in that an output of an
oscillator 8a is input to the resistors 5a and 5b. The alternating
voltage signal -Vd input by the oscillator 8a is a signal of the
same magnitude as the alternating voltage signal Vd input by the
oscillator 7a but with an inverse phase.
[0060] The vibration gyro element 1 is caused of the
separately-excited oscillation by the alternating voltage signals
Vd and -Vd input by the oscillators 7a and 8a. Upon the
separately-excited oscillation, the impedance Zsa of the
piezoelectric element 3a and the impedance Zsb of the piezoelectric
element 3b of the vibration gyro element 1 become minimum. When the
angular velocity .omega.o with the longitudinal axis of the
vibration gyro element 1 as the center is not imparted, the
impedance Zsa and the impedance Zsb become the same level Zs. The
amplitude of the alternating voltage signal across both ends of the
piezoelectric elements 3a and 3b is determined by a difference 2*Vd
between the alternating voltage signals Vd and -Vd being divided by
the impedance Zs and the resistance Rb, which is 2*Ag. Further, the
alternating voltage signal across both ends of the resistor 5a
becomes 2*Vra and the alternating voltage signal across both ends
of the resistor 5b becomes 2*Vrb, which are the same signal.
[0061] When the angular velocity .omega.o with the longitudinal
axis as the center is imparted to the vibration gyro element 1, the
impedance Zsa and the impedance Zsb are changed in level. As a
result, there is caused a difference between the alternating
voltage signal 2*Vra across both ends of the resistor 5a and the
alternating voltage signal 2*Vrb across both ends of the resistor
5b, whereby a detection signal corresponding to the Coriolis force
appears in the output of the differential amplifier circuit 9a. The
magnitude of the detection signal is represented by Expression (2),
which is twice as that represented by Expression (1).
2*Vo.varies.2*m*Ag*.omega.o (2)
[0062] Therefore, by providing two oscillators and driving the
vibration gyro element 1 by the differential, the detection signal
can be doubled without increasing the amplitude of the alternating
voltage signals of the oscillators 7a and 8a.
[0063] FIG. 7A shows a vibration element of a vibration gyro sensor
according to an embodiment of the present invention, and FIG. 7B is
a sectional view thereof.
[0064] The vibration element includes a base vibration body 22 and
a piezoelectric element group 23 provided to the base vibration
body 22. The base vibration body 22 is an insulation body or a
piezoelectric body having a common electrode 4 that has been
conductively plated, for example. Examples of the method of plating
include electroplating, electroless plating, deposition, and
sputtering. Examples of the insulation body include quartz, glass,
crystal, and ceramics, or other insulation bodies. Examples of the
piezoelectric body include barium titanate, lead zirconate
titanate, lithium niobate, and lithium tantalate, or other
piezoelectric bodies. It is only necessary that a piezoelectric
material similar in the case of the base vibration body 22 be used
as a piezoelectric material of the piezoelectric element group 23.
Alternatively, the base vibration body 22 may be a semiconductor or
a conductor. In the case of the conductor, nickel, iron, chromium,
titanium, or an alloy thereof is used, for example. As the alloy,
elinvar or nickel-iron alloy is used, for example. When the base
vibration body 22 is formed by a conductor, the entire base
vibration body 22 serves as the common electrode (reference
electrode) having a common reference potential.
[0065] The piezoelectric element group 23 is constituted by a first
piezoelectric element 23a, a second piezoelectric element 23b, and
a third piezoelectric element 23c. The first piezoelectric element
23a is a piezoelectric element for driving the vibration element 21
and has a drive electrode 65a provided on a first side thereof. In
the piezoelectric element group 23, the first side refers to a side
opposed to the side of the base vibration body 22. Hereinafter, the
side opposed to the side on which the base vibration body 22 is
provided will be referred to as first side also with respect to the
second piezoelectric element 23b and the third piezoelectric
element 23c.
[0066] The second piezoelectric element 23b and the third
piezoelectric element 23c are provided so as to sandwich the first
piezoelectric element 23a. The second piezoelectric element 23b and
the third piezoelectric element 23c are piezoelectric elements for
detecting the angular velocity and respectively have detection
electrodes 65b and 65c on the first side thereof.
[0067] A second side of the piezoelectric element group 23 opposed
to the first side is in contact with the common electrode 4. In
other words, the second side of each of the first piezoelectric
element 23a, the second piezoelectric element 23b, and the third
piezoelectric element 23c (bottom surfaces 66a, 66b, and 66c of the
piezoelectric element group 23) is in contact with the common
electrode 4.
[0068] FIG. 8 is a circuit block diagram showing a structure of a
vibration gyro sensor including the vibration element 21 shown in
FIG. 7. A vibration gyro sensor 100 includes an addition circuit
26, an oscillation circuit 27, a phase inversion circuit 28, a
differential amplifier circuit 29, and resistors 25 (25a and 25b)
as bias means. The addition circuit 26, the oscillation circuit 27,
the phase inversion circuit 28, the differential amplifier circuit
29, and the resistors 25 constitute a control circuit of the
vibration gyro sensor 100.
[0069] An output signal of the oscillation circuit 27 is input to
the drive electrode 65a of the first piezoelectric element 23a and
to the phase inversion circuit 28 as a drive signal. The output
signal of the phase inversion circuit 28 is input to the common
electrode 4. The output signal of the phase inversion circuit 28 is
input to the surfaces 66a, 66b, and 66c of the first, second, and
third piezoelectric elements 23a, 23b, and 23c that are in contact
with the common electrode 4. Outputs from the detection electrodes
65b and 65c of the second and third piezoelectric elements 23b and
23c are respectively input to the resistors 25a and 25b and also to
the addition circuit 26. The resistors 25a and 25b are resistors
for applying a bias voltage Vref to the output signals. In
addition, the outputs of the second and third piezoelectric
elements 23b and 23c are input to the differential amplifier
circuit 29. Further, the output of the addition circuit 26 is input
to the oscillation circuit 27.
[0070] Based on the output signal containing the detection signals
generated by the detection electrodes 65b and 65c of the second and
third piezoelectric elements 23b and 23c, the oscillation circuit
27 outputs a signal for causing self-excited oscillation of the
vibration element 21 to the drive electrode 65a of the first
piezoelectric element 23a as the drive signal. Specifically, the
vibration element 21 oscillates by the self-excited oscillation
circuit constituted by the vibration element 21, the addition
circuit 26, the oscillation circuit 27, and the phase inversion
circuit 28. Accordingly, the vibration element 21 is caused of the
bending vibration in a direction perpendicular to a first side
surface 22a and a second side surface 22b of the base vibration
body 22.
[0071] When the vibration element 21 rotates with the longitudinal
axis (Z-axis) as the center in this state, Coriolis force is
generated in the vibration element 21 and the direction of the
bending vibration changes. Thus, an output difference is generated
between the second and third piezoelectric elements 23b and 23c,
whereby an output can be obtained from the differential amplifier
circuit 29. The signals input to the second and third piezoelectric
elements 23b and 23c at the time of driving by the self-excited
oscillation of the vibration element 21 are the same in phase and
magnitude. Therefore, the signals input to the second and third
piezoelectric elements 23b and 23c are canceled out in the
differential amplifier circuit 29. Specifically, a signal
corresponding to the level of the angular velocity .omega.o is
output from the differential amplifier circuit 29.
[0072] In the vibration gyro sensor 100 according to this
embodiment, the output of the phase inversion circuit 28 is input
to the second side of the piezoelectric element group 23 (bottom
surfaces 66a, 66b, and 66c) via the common electrode 4. The first
piezoelectric element 23a is used as the drive piece for causing
bending vibration of the base vibration body 22. Because a bias
voltage is applied by the resistors 25a and 25b regarding the
second and third piezoelectric elements 23b and 23c, by inputting
the output of the phase inversion circuit 28 to the common
electrode 4, the second and third piezoelectric elements 23b and
23c are not only used as the detection piece but also as the drive
piece.
[0073] FIG. 9 is a diagram showing an equivalence circuit of the
vibration gyro sensor 100 shown in FIG. 8. Outputs of the
oscillators 27a and 28a are input to the vibration element 21. The
base vibration body 22 is caused of the bending vibration in the
direction perpendicular to the first side surface 22a and the
second side surface 22b of the base vibration body 22 by the
alternating voltage signal Vd output by the oscillator 27a being
input between the first side and the second side of the first
piezoelectric element 23a. An output difference between the signals
from the second and third piezoelectric elements 23b and 23c is
obtained in the differential amplifier 29a. A signal of the
difference is Vs=Va-Vb.
[0074] Here, FIG. 10 is a block diagram showing the vibration gyro
sensor that is not provided with the phase inversion circuit in
FIG. 9. The second side surface 22b of the base vibration body 22
is connected to the reference potential Vref. In this example, the
first piezoelectric element 23a is used as the drive piece for
causing bending vibration of the base vibration body 22, and the
second and third piezoelectric elements 23b and 23c are used as the
detection piece for obtaining a signal corresponding to the angular
velocity.
[0075] FIG. 11 is a diagram showing an equivalence circuit of the
vibration gyro sensor shown in FIG. 10. The second side surface 22b
of the base vibration body 22 is grounded. Therefore, the sides of
the second and third piezoelectric elements 23b and 23c that are in
contact with the common electrode 4 (second side) are grounded. The
output of the oscillator 27a is input to the drive electrode 65a
provided on the first side of the first piezoelectric element 23a.
The resistors 25a and 25b are resistors for applying a bias voltage
0 (V) to the signals.
[0076] The base vibration body 22 is caused of the bending
vibration in the direction perpendicular to the first side surface
22a and the second side surface 22b of the base vibration body 22
by the alternating voltage signal Vd output from the oscillator 27a
being input to the first side and the second side of the first
piezoelectric element 23a. The vibration is transferred to the
second and third piezoelectric elements 23b and 23c to be converted
into electric signals for output. At this time, an impedance Zsb1
of the second piezoelectric element 23b and an impedance Zsc1 of
the third piezoelectric element 23c become minimum, and the
alternating voltage signal Va1 across both ends of the resistor 25a
and the alternating voltage signal Vb1 across both ends of the
resistor 25b become maximum. In other words, the magnitude of the
bending vibration of the base vibration body 22 is proportional to
the magnitude of the alternating voltage signals Va1 and Vb1.
[0077] When the angular velocity .omega.o with the longitudinal
axis as the center is not imparted to the vibration element 21, the
impedance Zsb1 and the impedance Zsc1 become the same level Zs1,
and the alternating voltage signals Va1 and Vb1 also become the
same signal. Thus, the output of the differential amplifier 29a
becomes 0. The amplitude of the alternating voltage signal across
both ends of the resistors 25a and 25b at this time is represented
by Av1.
[0078] When the angular velocity .omega.o with the longitudinal
axis as the center is imparted to the vibration element 21, the
base vibration body 22 bends and vibrates in a direction different
from that up to that point, and the impedance Zsb1 and the
impedance Zsc1 are changed in level. As a result, a difference is
caused between the alternating voltage signals Va1 and Vb1, and a
detection signal corresponding to the Coriolis force appears in the
output of the differential amplifier 29a. Assuming that the mass of
the vibration element 21 is represented by m, the magnitude Vs1 of
the detection signal can be expressed by Expression (3).
Vs1.varies.m*Av1*.omega.o (3)
[0079] Because the second and third piezoelectric elements 23b and
23c are used only as the detection piece, the resistance Rb of the
resistors 25a and 25b is larger the better in view of detection
efficiency.
[0080] Here, the inventors of the present invention have made a
circuit of the vibration gyro sensor shown in FIG. 12 and conducted
a measurement on the detection signal from the detection electrodes
65b and 65c (see FIG. 7B). The circuit shown in FIG. 12 is
different from that shown in FIG. 11 in that the electrode 65a of
the first piezoelectric element 23a in FIG. 10 is grounded and the
oscillator 28a is connected to the common electrode 4 on the second
side surface 22b of the base vibration body 22. The alternating
voltage signal -Vd input by the oscillator 28a is a signal same in
magnitude as the alternating voltage signal Vd input by the
oscillator 27a of FIG. 11 but with an inverse phase.
[0081] By the alternating voltage signal -Vd output by the
oscillator 28a being input to both sides of the first piezoelectric
element 23a, being input between the second piezoelectric element
23b and the resistor 25a connected in series, and being further
input between the third piezoelectric element 23c and the resistor
25b connected in series, the base vibration body 22 is caused of
the bending vibration in the direction perpendicular to the first
side surface 22a and the second side surface 22b thereof. At this
time, the impedance Zsb2 of the second piezoelectric element 23b
and the impedance Zsc2 of the third piezoelectric element 23c
become minimum. In addition, the alternating voltage signal Va2
across both ends of the resistor 25a and the alternating voltage
signal Vb2 across both ends of the resistor 25b become maximum.
[0082] When the angular velocity .omega.o with the longitudinal
axis as the center is not imparted to the vibration element 21, the
impedance Zsb2 and the impedance Zsc2 become the same level Zs2,
and the alternating voltage signals Va2 and Vb2 also become the
same signal. Therefore, the output of the differential amplifier
29a becomes 0. The amplitude of the alternating voltage signals of
the resistors 25a and 25b at this time is represented by Av2.
Results of the actual measurement of the alternating voltage
signals Va2 and Vb2 when the resistance Rb of the resistors 25a and
25b is set as the following Expression (4) are as expressed by
Expressions (5) to (7). As compared with the alternating voltage
signals Va1 and Vb1 in the circuit shown in FIG. 10, the
alternating voltage signals Va2 and Vb2 are larger in amplitude and
have the same phase.
RbZs2 (4)
Va2=1.8*Va1 (5)
Vb2=1.8*Vb1 (6)
Va2=Vb2 (7)
[0083] In addition, the amplitude Av2 of the alternating voltage
signal across both ends of the resistors 25a and 25b can be
expressed by Expression (8).
Av2=1.8*Av1 (8)
[0084] As described above, as compared with the alternating voltage
signals Va1 and Vb1 of the circuit shown in FIG. 10, the reason why
the alternating voltage signals Va2 and Vb2 are increased as much
as 1.8 times is that not only the first piezoelectric element 23a
but also the second and third piezoelectric elements 23b and 23c
function as the drive piece. In other words, the second and third
piezoelectric elements 23b and 23c each function as both the drive
piece and the detection piece.
[0085] On the other hand, when the angular velocity .omega.o with
the longitudinal axis as the center is imparted to the vibration
element 21, the base vibration body 22 bends and vibrates in a
direction different from that up to that point due to the
generation of the Coriolis force, and the level of the impedance
Zsb2 and impedance Zsc2 changes. As a result, a difference is
caused between the alternating voltage signals Va2 and Vb2, and a
detection signal corresponding to the Coriolis force appears in the
output of the differential amplifier 29a. Assuming that the mass of
the vibration element 21 is represented by m, the magnitude Vs2 of
the detection signal can be expressed by Expression (9).
Vs2.varies.m*Av2*o=1.8*m*Av1*.omega.o (9)
[0086] Here, returning to the description on the vibration gyro
sensor 100 according to the embodiment shown in FIGS. 8 and 9, the
circuit of the vibration gyro sensor 100 is structured like a
circuit having the circuit shown in FIG. 11 and that shown in FIG.
12 integrated. Specifically, the alternating voltage signal Va of
the resistor 25a and the alternating voltage signal Vb of the
resistor 25b are obtained by respectively synthesizing the signals
Va1 and Vb1 shown in FIG. 11 and the signals Va2 and Vb2 shown in
FIG. 12.
[0087] When the angular velocity .omega.o with the longitudinal
axis as the center is imparted to the vibration element 21, a
detection signal corresponding to the Coriolis force appears in the
output of the differential amplifier 29a. Assuming that the mass of
the vibration element 21 is represented by m, the magnitude Vs of
the detection signal can be expressed by Expression (10).
Vs=Vs1+Vs2=2.8*m*Av1*.omega.o (10)
[0088] Specifically, Vs is 2.8 times as large as Av1, whereby the
detection sensitivity can be further improved than the circuit
merely provided with the phase inversion circuit.
[0089] FIG. 13 is a diagram showing a time chart of voltage
waveforms of the detection electrodes in the circuits shown in
FIGS. 9, 11, and 12. Specifically, the diagram shows the
alternating voltage signal Vd input by the oscillator 27a, the
alternating voltage signal -Vd input by the oscillator 28a, and the
alternating voltage signals Va1, Vb1, Va2, Vb2, Va, and Vb of the
resistors 25a and 25b at a time when the angular velocity .omega.o
with the longitudinal axis as the center is not imparted to the
vibration element 21.
[0090] As described above, according to the vibration gyro sensor
100 according to the embodiment shown in FIGS. 8 and 9, a drive
signal can be input between the drive electrode 65a provided on the
first side of the first piezoelectric element 23a and the common
electrode 4 provided on the second side thereof in a state where a
bias voltage is applied to the detection electrodes 65b and 65c.
Accordingly, the vibration element 21 operates so that the drive
signal corresponding to the bias voltage is input between the
common electrode 4 and the detection electrodes 65b and 65c in the
second and third piezoelectric elements 23b and 23c. In other
words, the second and third piezoelectric elements 23b and 23c as
the detection piece also function as the drive piece. As a result,
detection sensitivity of the detection electrodes 65b and 65c can
be further improved without an increase in power supply voltage,
and a high S/N can therefore be realized.
[0091] FIG. 14A is a perspective view of a vibration element
according to another embodiment of the present invention. A
vibration element 31 includes a base body 130 and a vibration arm
132 provided so as to extend from the base body 130. FIG. 14B is a
sectional view of the vibration arm 132 showing a surface
perpendicular to the longitudinal axis (Z-axis) thereof. In the
description hereinbelow, descriptions on members, functions, and
the like similar to those of the vibration element 21 and the
vibration gyro sensor 100 according to the embodiment shown in
FIGS. 8, 9, and the like will be simplified or omitted, and
descriptions will be mainly given on differences.
[0092] Typically, the vibration element 31 can be produced by MEMS.
As shown in FIG. 14B, for example, a conductive film 34d to be the
common electrode is formed on a silicon substrate 133, and a
piezoelectric film 33 is formed on the conductive film 34d. Then, a
drive electrode 34a, a first detection electrode 34b, and a second
detection electrode 34c having a predetermined long and thin shape
are formed on the piezoelectric film 33 by a photolithography
technique. The piezoelectric film 33, the drive electrode 34a, the
first detection electrode 34b, and the second detection electrode
34c constitute a piezoelectric element. Specifically, the drive
electrode 34a, the first detection electrode 34b, and the second
detection electrode 34c are provided on the first side of the
piezoelectric element and the common electrode 34d is provided on
the second side opposed to the first side.
[0093] Lead electrodes including lead wires 136, electrode pads
138, and bumps 134a to 134d are formed on the base body 130. It is
only necessary that the lead electrodes also be formed by the
photolithography technique. The bump 134a is connected to the drive
electrode 34a and the bumps 134b and 134c are connected to the
first and second detection electrodes 34b and 34c, respectively. In
addition, the bump 134d is connected to the common electrode 34d.
The electrodes are externally connected to a control circuit such
as an IC (control circuit including the circuit constituted by the
blocks shown in FIG. 15) via those bumps 134a to 134d. The bumps
134a to 134d are formed of, for example, gold, copper, or aluminum,
but are not limited thereto.
[0094] Upon formation of the drive electrode 34a, the first and
second detection electrodes 34b and 34c, the lead wires 136, and
the like as described above, a vibration element as shown in FIG.
14A is cut out from the silicon wafer.
[0095] FIG. 15 is a block diagram showing a structure of the
vibration gyro sensor including the vibration element 31 shown in
FIGS. 14A and 14B. The structure and operation of the vibration
gyro sensor 200 are the same as those of the vibration gyro sensor
100 shown in FIG. 8.
[0096] The vibration gyro sensor 200 includes an addition circuit
36, an oscillation circuit 37, a phase inversion circuit 38, a
differential amplifier circuit 39, and resistors 35a and 35b. An
output of the phase inversion circuit 38 is input to the common
electrode 34d and an output of the oscillation circuit 37 is input
to the drive electrode 34a. Also in the vibration gyro sensor 200,
the first and second detection electrodes 34b and 34c not only
function as the detection piece but also as the drive piece. Thus,
detection sensitivity can be further improved as compared with the
circuit merely provided with the phase inversion circuit, without
an increase in power supply voltage, and a high S/N can therefore
be realized.
[0097] FIG. 16A is a schematic diagram showing a vibration element
according to yet another embodiment of the present invention. FIG.
16B is a sectional diagram taken along the line A-A of FIG.
16A.
[0098] A vibration element 41 includes a base body 140 and three
vibration arms 141 to 143 provided so as to extend from the base
body 140. The vibration element 41 can also be produced by MEMS,
for example. As shown in FIG. 16B, the three vibration arms 141 to
143 respectively include base arms 147a to 147c made of
silicon.
[0099] A piezoelectric film 148a is formed on the base arm 147a of
the vibration arm 141 in the middle, and a first drive electrode
145a and first and second detection electrodes 146a and 146b are
provided on a first side of the piezoelectric film 148a. In
addition, a common electrode 144a is provided on a second side of
the piezoelectric film 148a opposed to the first side.
[0100] A piezoelectric film 148b is formed on the base arm 147b of
the vibration arm 142, and a common electrode 144b is provided on
the first side of the piezoelectric film 148b. In addition, a
second drive electrode 145b is provided on the second side of the
piezoelectric film 148b. Similarly, a piezoelectric film 148c is
formed on the base arm 147c of the vibration arm 143, and a common
electrode 144c is provided on the first side of the piezoelectric
film 148c. Further, a third drive electrode 145c is provided on the
second side of the piezoelectric film 148c.
[0101] As in the embodiment shown in FIG. 14, the base body 140 is
provided with lead electrodes (not shown).
[0102] FIG. 17 is a block diagram showing a structure of a
vibration gyro sensor including the vibration element 41 shown in
FIGS. 16A and 16B. An output of an oscillation circuit 47 is input
to the first, second, and third drive electrodes 145a, 145b, and
145c. An output of a phase inversion circuit 48 is input to the
common electrodes 144a, 144b, and 144c. The first and second
detection electrodes 146a and 146b are connected with resistors 45a
and 45b, respectively, for applying a bias voltage Vref (common
potential) to the output signals.
[0103] The vibration gyro sensor 300 structured as described above
is driven so that the vibration arms 142 and 143 on both sides
vibrate at the same phase and with the same amplitude and the
vibration arm 141 in the middle vibrates at an inverse phase and
with twice the amplitude as the vibration arms 142 and 143 on both
sides. Focusing on the vibration arm 141 in the middle, because the
vibration arm 141 has a structure similar to that in the
embodiments shown in FIGS. 8 and 14, detection sensitivity of the
first and second detection electrodes 146a and 146b can be improved
without an increase in power supply voltage, and a high S/N can
therefore be realized.
[0104] Note that the second and third drive electrodes 145b and
145c do not always have to be input with a drive signal. In this
case, the vibration arms 142 and 143 on both sides vibrate by a
rebound caused by the vibration of the vibration arm 141 in the
middle.
[0105] FIG. 18 is a schematic perspective view of a digital camera
as an example of an electronic apparatus mounted with the vibration
gyro sensor 100, 200, or 300. FIG. 19 is a block diagram showing a
structure of the digital camera.
[0106] A digital camera 260 has a main body 261 to which the
vibration gyro sensor 100 (200, 300) is mounted. The main body 261
is a frame or a casing made of, for example, metal or resin. The
vibration gyro sensor 100 (200, 300) is packaged in a size of a
several mm square. For detecting an angular velocity around at
least to two axes, a single vibration gyro sensor 100 (200, 300) is
mounted with at least two vibration elements 21 (31, 41) (see FIGS.
8, 14, and 17).
[0107] As shown in FIG. 19, the digital camera 260 includes the
vibration gyro sensor 100 (200,300), a control section 510, an
optical system 520 equipped with a lens and the like, a CCD 530,
and a shake correction mechanism 540 for executing shake correction
with respect to the optical system 520.
[0108] Coriolis force of the two axes is detected by the vibration
gyro sensor 100 (200, 300). The control section 510 uses the shake
correction mechanism 540 to perform the shake correction in the
optical system 520 based on the detected Coriolis force.
[0109] The embodiments of the present invention are not limited to
those described above, and various other embodiments may also be
employed.
[0110] The shape, size, material, and the like of the substrate,
wire, and arm parts that constitute the vibration elements 21, 31,
and 41 can appropriately be changed.
[0111] The electronic apparatus mounted with the vibration gyro
sensor 100 (200, 300) according to the embodiments of the present
invention is not limited to the digital camera. Examples of the
electronic apparatus include a laptop computer, PDA (Personal
Digital Assistance), electronic dictionary, audio/visual device,
projector, cellular phone, game instrument, car navigation device,
robot device, and other electrical appliances.
* * * * *