U.S. patent application number 09/778737 was filed with the patent office on 2001-08-23 for angular velocity sensor capable of preventing unnecessary oscillation.
Invention is credited to Isogai, Toshiki, Iwaki, Takao, Kano, Kazuhiko.
Application Number | 20010015101 09/778737 |
Document ID | / |
Family ID | 26585949 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015101 |
Kind Code |
A1 |
Iwaki, Takao ; et
al. |
August 23, 2001 |
Angular velocity sensor capable of preventing unnecessary
oscillation
Abstract
An angular velocity sensor has a weight portion that can be
drive-oscillated in a driving direction and be oscillated in a
detecting direction when an angular velocity is applied, and
unnecessary oscillation suppressing electrodes that can generate an
electrostatic force to be applied to the weight portion in the
detecting direction. The electrostatic force prevents the weight
portion from being drive-oscillated in a direction other than the
driving direction. As a result, unnecessary oscillation of the
weight portion can be prevented even when the angular velocity
sensor has a processing error.
Inventors: |
Iwaki, Takao; (Chiryu-city,
JP) ; Kano, Kazuhiko; (Toyoake-city, JP) ;
Isogai, Toshiki; (Nagoya-city, JP) |
Correspondence
Address: |
LAW OFFICE OF DAVID G POSZ
2000 L STREET, N.W.
SUITE 200
WASHINGTON
DC
20036
US
|
Family ID: |
26585949 |
Appl. No.: |
09/778737 |
Filed: |
February 8, 2001 |
Current U.S.
Class: |
73/504.02 ;
73/514.18 |
Current CPC
Class: |
G01C 19/5719
20130101 |
Class at
Publication: |
73/504.02 ;
73/514.18 |
International
Class: |
G01P 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2000 |
JP |
2000-46793 |
Oct 26, 2000 |
JP |
2000-327504 |
Claims
What is claimed is:
1. An angular velocity sensor comprising: a basal portion; a weight
portion connected to the basal portion; a beam portion connecting
the weight portion to the basal portion and supporting the weight
portion to allow the weight portion to be drive-oscillated in a
first direction, and to be oscillated in a second direction when an
angular velocity is applied around an angular velocity axis in a
state where the weight portion is drive-oscillated, the angular
velocity axis being perpendicular to the first direction and the
second direction; and unnecessary oscillation suppressing means for
applying an external force to the weight portion in the second
direction to prevent the weight portion from being drive-oscillated
in a direction other than the first direction.
2. The angular velocity sensor of claim 1, wherein the weight
portion includes a plurality of weight portions which are
displaceable independently of each other.
3. The angular velocity sensor of claim 1, wherein the weight
portion includes first and second weight portions connected to each
other by a connection beam.
4. The angular velocity sensor of claim 1, wherein the weight
portion includes first and second weight portions that are
drive-oscillated in anti-phase to each other.
5. The angular velocity sensor of claim 1, wherein the unnecessary
oscillation suppression means generates an electrostatic force as
the external force to be applied to the weight portion.
6. The angular velocity sensor of claim 5, wherein the unnecessary
oscillation suppression means has basal portion side comb-teeth
electrodes protruding from the basal portion, and weight portion
side comb-teeth electrodes protruding from the weight portion to be
engaged with the basal portion side comb-teeth electrodes, and
generates an electrostatic force between the basal portion side
comb-teeth electrodes and the weight portion side comb-teeth
electrodes.
7. The angular velocity sensor of claim 6, wherein one of the
weight portion side comb-teeth electrodes is positioned to be
closer to either one of two basal side comb-teeth electrodes
adjacent thereto rather than a center of a gap between the two
basal side comb-teeth electrodes.
8. The angular velocity sensor of claim 1, wherein the unnecessary
oscillation suppressing means is composed of a piezoelectric
element that is formed on the beam portion for applying the
external force to the weight portion by utilizing a strain produced
in the piezoelectric element.
9. The angular velocity sensor of claim 1, wherein the unnecessary
oscillation suppressing means is composed of a member that
generates a Lorentz's force as the external force applied to the
weight portion.
10. The angular velocity sensor of claim 9, wherein: the member is
composed of a wiring member formed on the weight portion via the
beam portion, and one of a permanent magnet and an electromagnet
externally provided; and a current flowing in the wiring member is
made to interact with the one of the permanent magnet and the
electromagnet to generate the Lorentz's force.
11. The angular velocity sensor of claim 1, further comprising a
driving member for drive-oscillating the weight portion by an
electrostatic force generated between the weight portion and the
basal portion.
12. The angular velocity sensor of claim 17 further comprising a
monitoring member for monitoring a physical quantity of driving
oscillation of the weight portion.
13. The angular velocity sensor of claim 12, wherein a driving
amplitude of the driving oscillation of the weight portion is
controlled to be constant by a negative feedback using a result
obtained by the monitoring member.
14. The angular velocity sensor of claim 1, wherein: the weight
portion has a first weight portion, and a second weight portion
that is connected to the first weight portion via a driving beam
and connected to the basal portion via a detecting beam; the first
weight portion is drive-oscillated in the first direction; both the
first weight portion and the second weight portion are oscillated
by the detecting beam in the second direction when the angular
velocity is applied around the angular velocity axis in the state
where the first weight portion is drive-oscillated; and the angular
velocity is detected based on oscillation of the second weight
portion in the second direction.
15. The angular velocity sensor of claim 1, wherein: the weight
portion has a first weight portion that is connected to the basal
portion via a driving beam, and a second weight portion that is
connected to the first weight portion via a detecting beam; the
first weight portion and the second weight portion are
drive-oscillated in the first direction; the second weight portion
is oscillated in the second direction by the detecting beam when
the angular velocity is applied around the angular velocity axis in
the state where the first weight portion and the second weight
portion are drive-oscillated; and the angular velocity is detected
based on oscillation of the second weight portion in the second
direction.
16. An angular velocity sensor for detecting an angular velocity
applied around an angular velocity axis, comprising: a basal
portion; a weight portion connected to the basal portion to be
drive-oscillated in a first direction to perform driving
oscillation, and to be oscillated in a second direction to perform
detecting oscillation to detect the angular velocity when the
angular velocity is applied to the weight portion performing the
driving oscillation, the first direction and the second direction
being perpendicular to the angular velocity axis; and an
unnecessary oscillation suppressing member integrally provided with
the weight portion to generate an external force that is applied to
the weight portion in the second direction to prevent the weight
portion from being drive-oscillated in the second direction when no
angular velocity is applied.
17. The angular velocity sensor of claim 16, wherein: the
unnecessary oscillation suppressing member includes a weight
portion side electrode integrated with the weight portion, and a
basal portion side electrode integrated with the basal portion and
facing the weight portion side electrode; and the weight portion
side electrode and the basal portion side electrode generate an
electrostatic force as the external force by a voltage applied
therebetween.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
Japanese Patent Applications No. 2000-46793 filed on Feb. 18, 2000,
and No. 2000-327504 filed on Oct. 26, 2000, the contents of which
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an angular velocity sensor
having a weight portion connected to a basal portion via a beam
portion so as to detect angular velocity based on the oscillation
of the weight portion. The sensor is applicable to an angular
velocity sensor unit such as a vehicular control system, a
vehicular turn-over detecting system, a navigation system and a
blur preventing system of optical devices which need to sense
angular velocity.
[0004] 2. Description of the Related Art
[0005] Oscillation type angular velocity sensors formed by
processing a semiconductor substrate (SOI substrate and the like)
by using micro-machining technology for the purpose of
miniaturization and cost reduction have been reported lately. For
instance, Japanese Patent Application Laid-open Nos. Hei. 9-119942,
Hei. 6-123632, Hei. 8-220125, Hei. 11-248733 and other have
proposed such angular velocity sensors.
[0006] These angular velocity sensors have a weight portion
(oscillator) that is excited and oscillated in a first direction
(driving direction, x-axis direction). When the weight portion is
turned about an angular velocity axis (z-axis), Corioli's force is
generated at the weight portion in a second direction (detecting
direction, y-axis direction) that crosses at right angles with the
first direction. This Corioli's force is transmitted to a detecting
element having movable and stationary electrodes by a beam portion,
i.e., by an oscillation spring. In the detecting element, a
capacity between the movable electrode and the stationary electrode
changes due to the displacement of the movable electrode, thus
detecting an output value of the angular velocity.
[0007] When it is supposed that the sensor could be fabricated
conforming to its design without any processing error in the beam
structure composing the angular velocity sensor, the sensor will
operate accurately as described above. However, when the beam
portion as the oscillation spring, the driving electrode and others
have processing errors (e.g., the thickness of the beam portion is
erroneous), the oscillation may leak in the y-axis direction, i.e.,
in the detecting direction, for instance even if the weight portion
should be oscillated only in the x-axis direction during the
driving oscillation thereof. In such a case, the capacity of the
detecting portion changes even if the angular velocity is zero,
causing an error in the output value of the angular velocity.
[0008] Accordingly, it has been required to process the prior art
sensors as accurately as possible in order to prevent the leak of
driving oscillation of the weight portion in the detecting
direction (hereinafter referred to as unnecessary oscillation) and
the processing precision has determined the performance of the
sensor. However, the processing error is inevitable in the angular
velocity sensor that is formed by processing the semiconductor
substrate, and there is a limit in the reduction of the unnecessary
oscillation.
SUMMARY OF THE INVENTION
[0009] The present invention has been made in view of the above
problems. An object of the present invention is, in an oscillation
type angular velocity sensor having a weight portion, to reduce an
error in output value of angular velocity by eliminating leak
(unnecessary oscillation) of oscillation of the weight portion in a
detecting direction caused by a processing error.
[0010] According to the present invention, briefly, an angular
velocity sensor has a weight portion that can be drive-oscillated
in a first direction, and can be oscillated in a second direction
when an angular velocity is applied around an angular velocity
axis, vertical to the first and second directions, in state where
the weight portion is drive-oscillated. The angular velocity sensor
further has unnecessary oscillation suppressing means for applying
an external force to the weight portion in the second direction to
prevent the weight portion from being drive-oscillated in a
direction other than the first direction.
[0011] Thus, in the angular velocity sensor of the invention, the
unnecessary oscillation suppressing means applies the external
force to the weigh portion in the second direction, and cancels an
oscillation component in the second direction that causes
unnecessary oscillation in the driving oscillation. As a result,
the weight portion can be drive-oscillated only in the first
direction even when a beam portion has a processing error. No leak
of oscillation of the weight portion occurs in the second
(detecting) direction, and an error in output value of the sensor
can be lowered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Other objects and features of the present invention will
become more readily apparent from a better understanding of the
preferred embodiments described below with reference to the
following drawings, in which;
[0013] FIG. 1 is a plan view showing an angular velocity sensor in
a first embodiment of the invention;
[0014] FIG. 2 is a cross-sectional view taken along line II-II in
FIG. 1;
[0015] FIGS. 3A and 3B are explanatory views showing a state where
unnecessary oscillation occurs and a state where the unnecessary
oscillation is suppressed;
[0016] FIGS. 4A and 4B are graphs for explaining a case where AC
voltage is applied to unnecessary oscillation suppressing
electrodes in the first embodiment;
[0017] FIGS. 5A to 5D are graphs for explaining effects of
unnecessary oscillation suppression with respect to an angular
velocity output in the first embodiment;
[0018] FIG. 6 is a plan view showing an angular velocity sensor as
another example of the first embodiment;
[0019] FIG. 7 is a plan view showing an angular velocity sensor in
a second embodiment of the invention;
[0020] FIG. 8 is a plan view showing an angular velocity sensor as
another example of the second embodiment;
[0021] FIG. 9 is a plan view showing an angular velocity sensor in
a third embodiment of the invention;
[0022] FIG. 10 is a plan view showing an angular velocity sensor in
a fourth embodiment of the invention;
[0023] FIG. 11 is a plan view showing an angular velocity sensor as
another example of the fourth embodiment;
[0024] FIG. 12 is a plan view showing an angular velocity sensor in
a fifth embodiment of the invention;
[0025] FIG. 13 is a plan view showing an angular velocity sensor in
a sixth preferred embodiment of the invention;
[0026] FIG. 14 is a plan view showing an angular velocity sensor in
a seventh preferred embodiment of the invention;
[0027] FIG. 15 is a plan view showing an angular velocity sensor in
an eighth preferred embodiment of the invention; and
[0028] FIG. 16 is a plan view showing an angular velocity sensor in
a ninth preferred embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] (First Embodiment)
[0030] An angular velocity sensor 100 of a first embodiment will be
explained below with reference to FIGS. 1 and 2. It is noted that
the same or corresponding parts in each embodiment described below
will be denoted by the same reference numerals throughout the
following drawings. The angular velocity sensor 100 is a chip
manufactured by micro-machine processing using the known
semiconductor manufacturing technology.
[0031] The angular velocity sensor 100 is composed of a substrate
(SOI substrate or the like) in which a first semiconductor
substrate (silicon substrate or the like) 101 and a second
semiconductor substrate (silicon substrate or the like) 102 are
bonded via an insulating film layer (silicon oxide film or the
like) 103. An opening 104 and a pedestal portion 105 are formed by
removing the second semiconductor substrate 102 and the insulating
film layer 103 by means of anisotropic etching or the like and the
first semiconductor substrate 101 is formed in a diaphragm shape in
correspondence to the opening 104.
[0032] Trenches 1 are formed in the first semiconductor substrate
101 and defines a movable portion, a stationary portion and
respective electrodes thereof which are electrically isolated from
each other. The angular velocity sensor 100 has a rectangular
weight portion 3 being the movable portion parted by the trenches 1
within a basal portion 2 being the stationary portion. The weight
portion 3 is connected to the basal portion 2 through four beam
portions 4 provided respectively at the four corners thereof.
[0033] Each of the beam portions 4 is formed into a letter "L" such
that it bends at right angles and has a degree of freedom both in
the driving direction x (x-axis direction, first direction) and in
the detecting direction y (y-axis direction, second direction).
Accordingly, the beam portions 4 support the weight portion 3 so
that the weight portion 3 can be displaced in the driving direction
x and in the detecting direction y which cross at right angles from
each other within a horizontal plane vertical to the angular
velocity axis z. The weight portion 3 can oscillate in both the
directions x, y.
[0034] Comb-teeth electrodes 5, 6, 7, 8, 7a, 8a, 9, 10, 9a and 10a
which protrude like a comb from each side are formed at the right
and left sides of the weight portion 3 and the respective sides of
the basal portion 2 facing them via the trenches 1. Driving
electrodes (means for drive-oscillating the weight portion 3) 5, 6
for drive-oscillating (driving to oscillate) the weight portion 3
in the driving direction x are formed at the center of the weight
portion 3.
[0035] In the driving electrodes 5, 6, the driving movable
electrode 5 at the side of the weight portion 3 and the driving
stationary electrode 6 at the side of the basal portion 2 are
disposed so that their respective comb teeth are arranged at equal
intervals from each other. When a predetermined AC voltage is
applied to both the driving electrodes 5, 6 to generate
electrostatic force, the weight portion 3 can be drive-oscillated
(driven to be oscillated) in the driving direction x by the
elasticity of the beam portions 4.
[0036] Unnecessary oscillation suppressing electrodes 7, 8, 7a and
8a, which function not only as unnecessary oscillation suppressing
means but also as electrostatic force generating means for
generating electrostatic force as external force that is to be
applied to the weight portion 3, are formed on both the sides of
the driving electrodes 5, 6 (on both the upper and lower sides in
FIG. 1) at the right and left sides of the weight portion 3.
[0037] The unnecessary oscillation suppressing electrodes includes
unnecessary oscillation suppressing movable electrodes (weight
portion side comb-teeth electrodes) 7, 7a provided at the side of
the weight portion 3 and unnecessary oscillation suppressing
stationary electrodes (basal portion side comb-teeth electrodes) 8,
8a provided at the side of the basal portion 2. The unnecessary
oscillation suppressing movable electrodes 7, 7a, and the
unnecessary oscillation suppressing stationary electrodes 8, 8a
attract (approach) each other due to electrostatic force that is
generated by a predetermined DC or AC voltage applied across the
movable electrodes 7, 7a, and the stationary electrodes 8, 8a.
[0038] Accordingly, the unnecessary oscillation (displacement) in
the detecting direction (y-axis direction) of the weight portion 3
can be suppressed in the driving oscillation thereof. Here, the
unnecessary oscillation suppressing movable electrodes 7, 7a are
positioned eccentrically so that they are closer to either one of
the neighboring unnecessary oscillation suppressing stationary
electrodes 8, 8a rather than the center of the gap of the
unnecessary oscillation suppressing stationary electrodes 8, 8a
neighboring at both the sides of them.
[0039] When a first pair of the unnecessary oscillation suppressing
electrodes 7, 8 and a second pair of unnecessary oscillation
suppressing electrodes 7a, 8a located on the left side of the
weight portion 3 in FIG. 1 are compared, the deviating directions
of the movable electrodes 7, 7a at the center of the gap of the
stationary electrodes 8, 8a adjacent thereto are opposite to each
other in the first pair of the unnecessary oscillation suppressing
electrodes 7, 8 and in the second pair of the unnecessary
oscillation suppressing electrodes 7a, 8a. This is the same at the
right side of the weight portion 3. Thus, the displacement
suppressing directions, with respect to the weight portion 3, in
the first pair of the unnecessary oscillation suppressing
electrodes 7, 8 and in the second pair of the unnecessary
oscillation suppressing electrodes 7a, 8aare opposite to each other
in the detecting direction y.
[0040] For instance, in case of the first pair of the unnecessary
oscillation suppressing electrodes 7, 8 and the second pair of the
unnecessary oscillation suppressing electrodes 7a, 8alocated on the
left side of the weight portion 3, the movable electrode 7 is
attracted downward along the detecting direction y in the first
pair of the unnecessary oscillation suppressing electrodes 7, 8
when the electrostatic force is generated. On the other hand, the
movable electrode 7a is attracted upward along the detecting
direction y in the second pair of the unnecessary oscillation
suppressing electrodes 7a, 8a. Therefore, the first pair of the
unnecessary oscillation suppressing electrodes 7, 8 and the second
pair of the unnecessary oscillation suppressing electrodes 7a, 8a
can be properly (selectively) used corresponding to the orientation
in the detecting direction y of the unnecessary oscillation of the
weight portion 3.
[0041] Angular velocity detecting electrodes (angular velocity
detecting means) 9, 10, 9a and 10a are formed on both the sides
(both up and down sides in FIG. 1) of the driving electrodes 5, 6
and the unnecessary oscillation suppressing electrodes 7, 8, 7a,
and 8a, and on the left and right sides of the weight portion 3.
The angular velocity detecting electrode can detect angular
velocity by a change of electrostatic capacity caused by
displacement (displacement of the weight portion 3 in the detecting
direction y) of the opposed gap between the angular velocity
detecting movable electrodes 9, 9a on side of the weight portion 3
and the angular velocity detecting stationary electrodes 10, 10a on
the side of the basal portion 2.
[0042] The respective driving, unnecessary oscillation suppressing
and angular velocity detecting comb-teeth electrodes described
above are electrically independent of one another and are
respectively connected to electrode pads 11 formed on the basal
portion 2 by, for instance, evaporating aluminum. Each pad 11 is
electrically connected to an external circuit not shown by wire
bonding or the like and is capable of independently controlling the
potential of each comb-teeth electrode.
[0043] Next, the operation of the present embodiment will be
explained based on the structure of the angular velocity sensor 100
described above. Basically, the angular velocity sensor 100 detects
angular velocity based on the oscillation of the weight portion 3
in the detecting direction y which occurs when the angular velocity
is applied around the angular velocity axis z while
drive-oscillating the weight portion 3 in the driving direction
x.
[0044] A rectangular wave or sine wave voltage signal (driving
signal) is applied to the driving movable electrode 5 by the
above-mentioned external circuit not shown. Then, the weight
portion 3 performs driving oscillation along the driving direction
x that is allowed by the degree of freedom of the beam portions 4
in the driving direction x. Because the sensitivity of the angular
velocity sensor is almost proportional to the amplitude of the
driving oscillation, resonance drive (driving method in which
frequency of driving voltage is made to coincide with intrinsic
oscillation of an oscillation system), which may enlarge the
driving amplitude, is often used.
[0045] When the resonance drive is performed, the amplitude is
proportional to a value Q of the driving oscillation. The value Q
in gas is determined mainly by a coefficient of viscosity of the
gas, and the greater the coefficient of viscosity is, the smaller
the value Q becomes in general. Further, the smaller the pressure
of the gas is, the smaller the coefficient of viscosity becomes in
the gas. Therefore, the smaller the pressure of the gas is, the
better the sensitivity of the angular velocity sensor becomes in
case of the resonance drive. Accordingly, the sensitivity of the
angular velocity sensor can be enhanced by devising a vacuum
package or the like.
[0046] However, non-resonance oscillation is used intentionally in
the air in the present embodiment by taking preference of reducing
the production cost over the enhancement of the sensor sensitivity.
It is needless to say that the present embodiment is effective for
the resonance drive. Here, because the driving amplitude has a
temperature dependency (mainly due to the temperature dependency of
the coefficient of viscosity of gas), a control called Auto Gain
Control (AGC) is often used. Here, the AGC will be explained
briefly.
[0047] For instance, in case of the angular velocity sensor 100
described above, the driving electrodes 5, 6 on the right side,
among the driving electrodes 5, 6 provided on the right and left
sides of the weight portion 3, are used as oscillation monitoring
electrodes for monitoring the physical quantities (driving
amplitude, driving speed and others) of the driving oscillation in
the weight portion 3. In this case, the driving movable electrode 5
on the side of the weight portion 3 functions as an oscillation
monitoring movable electrode and the driving stationary electrode 6
on the side of the basal portion 2 function as an oscillation
monitoring stationary electrode. Accordingly, only the driving
electrodes 5, 6 on the left side generate the driving force when
the driving signal is applied.
[0048] When the weight portion 3 is displaced in the driving
direction x by the driving oscillation thereof, an overlap length
of the oscillation monitoring electrodes 5, 6 is changed.
Accordingly, the electrostatic capacity between the oscillation
monitoring electrodes 5, 6 is changed. The above-described external
circuit converts the change in electrostatic capacity into a change
in voltage to monitor the physical quantities (driving amplitude,
driving speed and others) of the driving oscillation.
[0049] For instance, the control of fixing the driving amplitude by
applying feedback (by conducting negative feedback) to the driving
voltage based on the amplitude (driving amplitude) of the driving
oscillation obtained as a result of the above-mentioned monitoring
is the AGC. The use of the AGC is advantageous because it can
remove the temperature dependency of the driving amplitude and can
suppress the temperature drift of the sensitivity. It is not
necessary to use the AGC all the time when it is not required so
much to suppress the temperature drift of the sensitivity.
[0050] It is noted that a strain gage and an electromagnetic
detection for detecting a change in magnetic flux penetrating a
wiring member may be used in addition to the oscillation monitoring
electrodes 5, 6, i.e., the comb-teeth electrodes, as means for
monitoring the oscillation. In case of using the strain gauge, for
instance, a piezoelectric element is provided on the beam portion 4
and monitors the driving oscillation by the degree of distortion of
the beam portion 4. In case of using the electromagnetic detection,
for instance, a wiring member is formed on the weight portion 3 via
the beam portion 4, and a magnet provided above the wiring member
monitors the change in magnetic flux penetrating the wiring
member.
[0051] Then, when angular velocity around the angular velocity axis
z vertical to the substrate plane (substrate plane of the first
semiconductor substrate 101) is added to the weight portion 3 which
is drive-oscillated linearly along the driving direction x,
Corioli's force Fc=2 mv.OMEGA. (m: mass of the weight portion 3, v:
velocity of driving oscillation, .OMEGA.: angular velocity) acts in
the detecting direction y. When the Corioli's force Fc acts on the
weight portion 3, the weight portion 3 oscillates in the detecting
direction y due to the degree of freedom of the beam portions 4 in
the detecting direction y.
[0052] The sensitivity of the angular velocity sensor may be
enhanced significantly by making the intrinsic oscillation
frequency in the detecting direction y coincide with the intrinsic
oscillation frequency in the driving direction x and by resonantly
driving it (di-resonance). The sensitivity of the angular velocity
sensor may be also enhanced significantly by making the frequency
of the driving voltage coincide with the intrinsic oscillation
frequency in the detecting direction y without resonantly driving
it. It is not necessary to always devise as described above.
[0053] If the electrostatic capacity of the detecting electrodes 9,
10 becomes C0+.DELTA.C, the electrostatic capacity of the detecting
electrodes 9a, 10a becomes C0-.DELTA.C (C0: initial capacity,
.DELTA.C: change in capacity by the Corioli's force). Here, because
.DELTA.C.varies.Fc.varies..OMEGA., and .DELTA.C is proportional to
the angular velocity .OMEGA., it is possible to detect the angular
velocity .OMEGA. by differentially detecting the capacities of the
detecting electrode 9, 10 and the detecting electrodes 9a, 10a.
[0054] FIGS. 3 and 4 are explanatory graphs showing the operation
of the suppression of unnecessary oscillation using the unnecessary
oscillation suppressing electrodes 7, 8, 7a and 8a which are
unnecessary oscillation suppressing means of the present
embodiment. When there is a processing error (processing error of
the beam portion 4 in particular) in the angular velocity sensor
100, as shown in FIG. 3A, the direction of driving oscillation is
not parallel with the driving direction x and deviates obliquely by
an angle .theta. from the driving direction x with an oscillation
component in the detecting direction y. Because the oblique
oscillation causes noise, it is desirable to cancel that and to set
as shown in FIG. 3B.
[0055] In order to cancel the oblique oscillation, the following
method is taken in the present embodiment. It is supposed that the
driving oscillation is oblique as shown in FIG. 3A (this is called
as unnecessary oscillation). The angle of deviation .theta. of the
unnecessary oscillation from the driving direction x (x-axis
direction) is measured in advance by experiments or the like before
shipping the sensor. Then, DC voltage V is applied across the
second pair of the unnecessary oscillation suppressing electrodes
7a, 8a.
[0056] As shown in FIG. 3B, then, the weight portion 3 receives
electrostatic force F in the detecting direction y (y-axis
direction) (that is, in the direction in which the direction of the
driving oscillation is corrected), and the direction of the driving
oscillation can be corrected by setting an appropriate value to the
value of the DC voltage V described above.
[0057] It is also possible to apply not the DC voltage described
above but AC voltage having the same frequency with the driving
frequency as shown in FIG. 4, as a method for correcting the
driving oscillation direction. When the unnecessary oscillation
occurs as shown in FIG. 3A, the weight portion 3 (driving movable
electrode 5) is displaced periodically in the detecting direction y
(y-axis direction) as shown in FIG. 4A. The AC voltage is applied
across the second pair of the unnecessary oscillation suppressing
electrodes 7a, 8a in accordance to the period of the displacement.
This method is advantageous because the electrostatic force is
maximized at the maximum displacement of unnecessary
oscillation.
[0058] As a result, as shown in FIG. 4B, the unnecessary
oscillation is eliminated. When the direction of the unnecessary
oscillation (oblique oscillation) leaks in the opposite direction
from that of FIG. 3A (for instance, when the angle of deviation is
-.theta. in FIG. 3A), the DC or AC voltage may be applied across
the first pair of unnecessary oscillation suppressing electrodes 7,
8 this time in the same manner as described above. The potential of
the unnecessary oscillation suppressing stationary electrode 8 or
8a not used in the first and second pairs of the unnecessary
oscillation suppressing electrodes is equalized with that of the
unnecessary oscillation suppressing movable electrodes 7, 7a.
[0059] According to the present embodiment, the first pair of the
unnecessary oscillation suppressing electrodes 7, 8 and the second
pair of the unnecessary oscillation suppressing electrodes 7a, 8a
are provided by four each. Although they are one set by four and it
is most simple and advantageous to control them in the same way,
they may be controlled separately. Further, although the
unnecessary oscillation suppressing electrodes are provided at both
the sides of the driving electrodes sandwiched therebetween, they
may be provided only at one side. However, it is preferable to
dispose as shown in the figure from the aspect of symmetry.
Although FIG. 4A shows the sine wave, the wave may be a rectangular
wave.
[0060] It is required to finish these adjustments related to the
suppression of unnecessary oscillation before the sensor is shipped
off. That is, the external circuit not shown should be adjusted
before the shipping so that the DC or AC voltage for suppressing
the unnecessary oscillation is applied to the first pair of the
unnecessary oscillation suppressing electrodes 7, 8 or to the
second pair of the unnecessary oscillation suppressing electrodes
7a, 8a during the usage of the sensor.
[0061] The effect of the unnecessary oscillation suppressing
electrodes 7, 8, 7a and 8a to the angular velocity output value
will be explained with reference to FIGS. 5A to 5D. FIG. SA shows
the displacement of the weight portion 3 (driving movable electrode
5) in the detecting direction y (y-axis direction) when unnecessary
oscillation exists, the unnecessary oscillation suppressing
electrodes 7, 8, 7a and 8a are not used, and angular velocity is
zero. The displacement in the detecting direction y causes changes
in capacity of the detecting electrodes 9, 10, 9a, and 10a and
interferes the detection as noise.
[0062] In fact, when the unnecessary oscillation exists and the
unnecessary oscillation suppressing electrodes 7, 8, 7a and 8a are
not used, as shown in FIG. 5B, an angular velocity signal S1 caused
by the angular velocity and a signal S2 caused by the unnecessary
oscillation appear mixedly (even though their phases deviate from
each other by about 90 degrees) when the angular velocity is
applied.
[0063] FIGS. 5C and 5D show the cases when the unnecessary
oscillation suppressing electrodes 7, 8, 7a and 8a are used in
contrary. When there is no angular velocity (see FIG. 5C), no
displacement occurs in the detecting direction y, and there is no
output. However, when the angular velocity is applied (see FIG.
5D), it is possible to detect only the angular velocity signal S1,
thereby realizing ideal detection of the angular velocity.
[0064] As described above, according to the present embodiment, the
unnecessary oscillation suppressing means 7, 8, 7a and 8a can
cancel the oscillation component of the weight portion 3 in the
detecting direction y, which is the unnecessary oscillation
component in the driving oscillation in the driving direction x, by
applying the external force to the weight portion 3 in the
detecting direction y. As a result, it is possible to suppress the
unnecessary oscillation of the weight portion 3 in the direction
other than the driving direction x and to drive and oscillate the
weight portion 3 favorably only in the driving direction x.
[0065] It is also possible to reduce the error of the angular
velocity output value by eliminating the leak of the driving
oscillation of the weight portion 3 in the detecting direction y
caused by the processing error of the beam portions 4 and others.
The reduction of the error of the angular velocity output value is
connected to the reduction of the temperature change at the zero
point of the angular velocity output value.
[0066] The present embodiment is also characterized in that one
that generates the electrostatic force as the external force to be
applied to the weight portion 3 is used as the unnecessary
oscillation suppressing means. The present embodiment is provided
with the unnecessary oscillation suppressing stationary electrodes
(basal portion side comb-teeth electrodes) 8, 8a protruding
comb-likely from the basal portion 2 and the unnecessary
oscillation suppressing movable electrodes (weight portion side
comb-teeth electrodes) 7, 7a protruding comb-likely from the weight
portion 3 so as to bite in the gaps of the stationary electrodes 8,
8a, and the electrostatic force is produced between these
electrodes.
[0067] The unnecessary oscillation suppressing electrodes 7 and
others in the present embodiment can be fabricated readily by using
the micro-machining technology for manufacturing the angular
velocity sensor 100, which simplifies the manufacturing process,
requires less number of parts and enables the miniaturization. The
comb structure such as the unnecessary oscillation suppressing
electrodes in the present embodiment is advantageous in that it
allows a very large electrostatic force to be generated per unit
area of the chip composing the sensor and it requires less voltage
accordingly.
[0068] Further, on both sides of the respective unnecessary
oscillation suppressing electrodes 7, 7a, the basal portion side
comb-teeth electrodes 8, 8a are disposed to define a gap
therebetween, and the respective comb-teeth electrodes 7, 7a are
positioned so that they come closer to either one of the adjacent
basal portion side comb-teeth electrodes 8, 8a rather than the
center of the gap. Therefore, each of the basal portion side
comb-teeth electrodes 7, 7a which are the movable electrode is
attracted to the closer one of the basal portion side comb-teeth
electrodes 8, 8a which are the stationary electrodes by the
electrostatic force. As a result, it is possible to change the
oscillation direction of the weight portion 3 readily to the normal
state.
[0069] Also, in the present embodiment, the driving electrodes 5,
6, which are the comb-teeth electrodes, are used as means (driving
means) for drive-oscillating the weight portion 3, and generate an
electrostatic force between the weight portion 3 and the basal
portion 2. The weight portion 3 is driven so as to oscillate by the
electrostatic force. Therefore, as compared to electromagnetic
driving and piezoelectric driving, the electrostatic driving using
the electrostatic force simplifies the process, requires less
number of parts and enables the miniaturization.
[0070] FIG. 6 shows another example of the angular velocity sensor
of the present embodiment. Although an angular velocity sensor 150
shown in FIG. 6 has basically the same structure as that of the
angular velocity sensor 100 shown in FIG. 1, it is different in
that oscillation monitoring electrodes 12, 13 for monitoring a
physical quantity of driving oscillation are formed
additionally.
[0071] In the angular velocity sensor 100 shown in FIG. 1, no
oscillation monitoring electrode is provided specifically and
either ones of the driving electrodes 5, 6 provided at the right
and left sides of the weight portion 3 (e.g., the right side
driving electrodes 5, 6) are used as the oscillation monitoring
electrodes. Therefore, the driving force is applied to the weight
portion 3 only at the left side in the angular velocity sensor 100
shown in FIG. 1.
[0072] On the other hand, in the angular velocity sensor 150 shown
in FIG. 6, the weight portion 3 is driven from both the right and
left sides. This is considered to be advantageous in the aspects of
the symmetry and of the magnitude of the driving amplitude. For
instance, when the driving voltage is equal, the driving amplitude
obtained in the sensor 150 shown in FIG. 6 should be able to about
twice as compared to that shown in FIG. 1. The other effects of the
angular velocity sensor 150 are the same as those described
above.
[0073] (Second Embodiment)
[0074] Next, a second embodiment will be explained by aiming mainly
at the differences from the first embodiment. FIG. 7 shows an
angular velocity sensor 200 of the present embodiment and FIG. 8
shows an angular velocity sensor 250 as another example of the
present embodiment. Although there is one weight portion 3 in the
first embodiment described above, the present embodiment is
different from the first embodiment mainly in that a plurality of
weight portions 3, each of which is almost the same, are formed
(two in this embodiment).
[0075] The angular velocity sensor 200 in FIG. 7 includes two parts
B, each of which corresponds to the angular velocity sensor 100
shown in FIG. 1, and which are provided in parallel in the y-axis
direction. The angular velocity sensor 250 in FIG. 8 includes two
parts C, each of which corresponds to the angular velocity sensor
150 shown in FIG. 6, and which are provided in parallel in the
x-axis direction. Here, a part of the reference numerals are
omitted in FIGS. 7 and 8. The electrode pads 11 are disposed at the
outer peripheral part in the angular velocity sensor 250 in FIG. 8,
so that the shape of the trenches 1 is changed more or less from
that shown in FIG. 6.
[0076] Next, the operations of the sensors 200 and 250 of the
present embodiment will be explained by aiming mainly at the
differences from that of the first embodiment. The operation of
each weight portion 3 is substantially the same as that of the
first embodiment. However, the merit of the present embodiment will
be exhibited specifically when the weight portions 3 are
drive-oscillated so that the phases of the driving oscillations are
opposite to each other in the relationship of the respective weight
portions 3. This is because the disturbance acceleration can be
canceled by reversing the phases of the driving oscillations. This
point will be explained in detail below.
[0077] First, both the weight portions 3 are drive-oscillated along
the driving direction x in the phases opposite to each other. In
case of the sensor having one weight portion 3, because the
intervals of the detecting electrodes 9, 10, 9a, and 10a change
when acceleration (disturbance acceleration) is added from the
outside in the same direction as the Corioli's force, the
acceleration may cause noise. That is, even if angular velocity is
zero, it seems as if the angular velocity is generated.
[0078] However, in the present embodiment, the angular velocity
signals from the two weight portions 3, which are drive-oscillated
in the phases opposite to each other, are in anti-phase each other,
while the signals caused by the disturbance acceleration are in
in-phase each other. Therefore, the influence of the disturbance
acceleration can be removed by subtraction (taking the difference)
of the outputs of the two weight portions 3. The present embodiment
also has a merit that the sensitivity is doubled as compared to the
first embodiment. It is also possible to measure the acceleration
by addition (taking the sum) of the outputs of the two weight
portions 3. Thus, it is possible to realize a sensor that can
measure both the acceleration and angular velocity by processing
the signals.
[0079] The several weight portions 3 may be disposed independently
of one another without being connected. Accordingly, the
arrangement of the weight portions 3 becomes free and the sensor
may be miniaturized as a whole. It simply lowers the cost and
improves the yield. Although the two weight portions 3 are formed
on the same chip in the example shown in the figure, it is also
possible to dispose each of the weight portions 3 on separate
chips, respectively. It also contributes to the improvement of the
yield.
[0080] When the several weight portions 3 are not connected to each
other, it is not necessary to provide a beam for connecting the
weight portions 3. Therefore, several driving electrodes 5, 6 can
be attached easily around the individual weight portion 3 as the
driving means. In the example shown in the figure, two sets of the
comb-like driving electrodes 5, 6 are formed at both the upper and
lower sides of the individual weight portion 3 to enlarge the
driving force. For instance, when the two weight portions 3 are
connected to each other by a beam 20 as in a third embodiment
described next, the driving electrodes 5, 6 are provided only at
one side of the weight portion 3 because the beam becomes an
obstacle.
[0081] (Third Embodiment)
[0082] Next, the third embodiment will be explained by aiming
mainly at the differences from the first embodiment. The present
embodiment is modified from the second embodiment and is
characterized in that at least two weight portions are connected by
at least one connection beam.
[0083] FIG. 9 shows an angular velocity sensor 300 of the present
embodiment having two weight portions 3 similarly to the angular
velocity sensor 250 shown in FIG. 8. However, unlike the angular
velocity sensor 250, there is no inner side driving electrodes 5, 6
(the right side of the left weight portion 3 and the left side of
the right weight portion 3), and the two weight portions 3 are
connected by the connection beam (coupled beam) 20 that is capable
of displacing the two weight portions 3 in both the driving
direction x and the detecting direction y. The sensor 300 has a
shape in which two parts D having the same shape are arranged on
the right and left sides.
[0084] Next, the operation of the present embodiment will be
explained mainly focusing on the differences from the second
embodiment. The operation of oscillating the weight portions 3
in-phase or in anti-phase is the same as the second embodiment. The
following points are also the same as the second embodiment.
[0085] That is, the influence of the acceleration can be removed by
taking the difference of the output signals of the two weight
portions 3, the sensitivity is almost doubled as compared to the
first embodiment, and the acceleration can be measured by taking
the sum of the outputs from the two weight portions 3. Accordingly,
the sensor capable of measuring the angular velocity and
acceleration at the same time can be realized.
[0086] By the way, the present embodiment has the following merits
because the connection beam 20 connects the two weight portions 3.
The two weight portions 3 form a coupled oscillation system by
connecting them by the connection beam 20. Accordingly, even if the
right and left sides weight portions 3 and the beam portions 4 and
others connected thereto could not be structured symmetrically due
to the processing errors or the like, the frequency characteristics
of the amplitudes of both the weight portions 3 have peaks (maximum
values) at the same frequency (intrinsic frequency).
[0087] Therefore, the amplitudes of both the weight portions 3 have
closer values to each other when resonance is utilized. By the way,
when the connection beam 2 is not provided and there arises a
processing error, it is very difficult to bring the amplitudes of
the right and left sides weight portions 3 in coincidence with each
other because the intrinsic frequencies of both the weight portions
3 do not coincide. Even if the amplitudes can be made to coincide,
the amplitude is small because the frequencies deviate from the
resonant point. In consequence, the sensitivity is low, which is
disadvantageous.
[0088] (Fourth Embodiment)
[0089] Next, a fourth embodiment will be explained. The present
embodiment is modified from the first embodiment and the
differences from the first embodiment will be explained with
reference to FIGS. 10 and 11. FIG. 10 shows an angular velocity
sensor 400 of the present embodiment and FIG. 11 shows an angular
velocity sensor 450 as another example of the present
embodiment.
[0090] First, the angular velocity sensor 400 shown in FIG. 10 will
be explained. The present embodiment is different from the first
embodiment in that the weight portion 3 comprises a first weight
portion (driving weight portion) 3a capable of drive-oscillating in
the driving direction x, and two second weight portions (detecting
weight portion) 3b connected to the first weight portion 3a by
driving beams 4a and connected to the basal portion 2 by detecting
beams 4b.
[0091] That is, the first weight portion 3a is connected to the
basal portion 2 via the second weight portions 3b by the driving
beams 4a. The beam portion of the present invention is composed of
the driving beams 4a and the detecting beams 4b in the present
embodiment.
[0092] It is advantageous to design the four driving beams 4a,
connected to the second weight portions 3b, have the degree of
freedom only in the driving direction x and the present embodiment
is constructed as described above. However, it is not always
necessary to construct as such as long as the first weight portion
3a displaces mainly in the driving direction x.
[0093] The four unnecessary oscillation suppressing electrodes 7,
8, 7a and 8a and two detecting electrodes 9, 10, 9a and 10a are
provided at each of the second weight portions 3b and the basal
portion 2 facing thereto. While the second weight portion 3b is
connected and fixed to the basal portion 2 by the two detecting
beams 4b, these detecting beams 4b are designed so as to have the
degree of freedom mainly in the detecting direction y.
[0094] Accordingly, the first weight portion 3a can be
drive-oscillated in the driving direction x by the voltage applied
across the driving movable electrode 5 formed on the first weight
portion 3a and the driving stationary electrode 6 formed on the
basal portion 2 facing thereto. Then, when angular velocity is
applied around the angular velocity axis z during this driving
oscillation, both the weight portions 3b are oscillated in the
detecting direction y by the detecting beams 4b.
[0095] The driving electrodes 5, 6 on one side of the first weight
portion 3a may be used as the oscillation monitoring electrodes
also in this angular velocity sensor 400. Here, oscillation
monitoring electrodes 12, 13 for monitoring the physical quantity
of the driving oscillation of the first weight portion 3a may be
formed additionally like the angular velocity sensor 450 shown in
FIG. 11 which is another example of the present embodiment.
[0096] Briefly, the difference between FIGS. 10 and 11 is the same
as the difference between FIGS. 1 and 6 in the first embodiment.
That is, when the AGC is used, the first weight portion 3a is
driven from either one side of the left and right sides in the
angular velocity sensor 400 shown in FIG. 10. On the other hand,
the first weight portion 3a is driven from both the sides in the
angular velocity sensor 450 shown in FIG. 11 and it is considered
to be advantageous in the aspects of the symmetry and the magnitude
of the driving amplitude.
[0097] Next, the operation of the sensor of the present embodiment
will be explained. When periodic voltage is applied to the external
circuit not shown, the first weight portion 3a is drive-oscillated
along the driving direction x due to the degree of freedom of the
driving beams 4a in the driving direction x. At this time, because
the second weight portions 3b are not drive-oscillated (displaced),
the capacities between the detecting electrodes 9, 10, 9a and 10a
barely change by the simple driving oscillation. This is one
characteristic point of the present embodiment and accordingly, the
sensors 400 and 450 of the present embodiment can be attained with
less noise and good resolution as compared to the first
embodiment.
[0098] The resonant driving or non-resonant driving described above
may be adopted also in the present embodiment. It is also
advantageous to adopt the ACG control because it allows the
temperature dependency of the driving amplitude to be removed and
the temperature drift of the sensitivity to be suppressed.
[0099] When angular velocity is applied around the angular velocity
axis z when the first weight portion 3a is drive-oscillated, both
the weight portions 3a and 3b oscillate in the detecting direction
y due to the degree of freedom of the detecting beams 4b in the
detecting direction y. At this time, the angular velocity .OMEGA.
can be detected by detecting differentially the capacity of the
detecting electrodes 9, 10 and the capacity of the detecting
electrodes 9a, 10a substantially in the same manner as the first
embodiment.
[0100] The method for suppressing the unnecessary oscillation
caused by the processing error (processing error of the driving
beams 4a in particular) in the angular velocity sensors 400 and 450
can be executed by using the unnecessary oscillation suppressing
electrodes 7, 8, 7a and 8a similarly to the first embodiment.
Accordingly, as explained referring to FIGS. 5A to 5D, no output is
outputted when angular velocity is zero and only an angular
velocity signal is detected when the angular velocity is applied in
the same manner with what described in the first embodiment. Thus,
ideal detection of the angular velocity can be performed.
[0101] (Fifth Embodiment)
[0102] Next, a fifth embodiment will be explained. The present
embodiment is modified and provided by combining the fourth
embodiment with the second embodiment and the difference from the
fourth embodiment will be mainly explained below. FIG. 12 shows an
angular velocity sensor 500 of the present embodiment. While the
first weight portion 3a and the second weight portions 3b
constitute one weight portion 3 in the fourth embodiment, the
present embodiment is different from the fourth embodiment mainly
in that several (two in this example) weight portions 3, each of
which is almost the same, are provided.
[0103] The angular velocity sensor 500 shown in FIG. 12 has two
parts E, each of which corresponds to the angular velocity sensor
450 shown in FIG. 11, are provided in parallel in the x-axis
direction. In FIG. 12, a part of the reference numerals are
omitted. The shapes of the trenches 1 are changed more or less from
those shown in FIG. 11 so that the electrode pads 11 are disposed
at the outer peripheral part in the angular velocity sensor
500.
[0104] Next, the operation of the sensor 500 of the present
embodiment will be explained by aiming mainly at the differences
from those of the fourth embodiment. The operation of the first
weight portion 3a and the second weight portions 3b in each of the
weight portions 3 is the same as that of the fourth embodiment. The
merit of the present embodiment will be exhibited specifically when
the weight portions 3 are drive-oscillated so that the respective
first weight portions 3a are oscillated in anti-phase because the
disturbance acceleration can be canceled by the same reasons as
described in the second embodiment.
[0105] That is, when both the first weight portions 3a are
drive-oscillated along the driving direction x in anti-phase to
each other and angular velocity is applied around the angular
velocity axis z, the weight portions 3a, 3b oscillate in the
detecting direction y in anti-phase to each other in the respective
weight portions 3 due to the degree of freedom of the detecting
beams 4b in the detecting direction y. At this time, the influence
of the disturbance acceleration can be removed by taking the
difference of the outputs from the two second weight portions 3b.
Further, the sensitivity is doubled as compared to the fourth
embodiment.
[0106] It is also possible to measure the acceleration by taking
the sum of the outputs from the two second weight portions 3b in
contrary. Accordingly, a sensor capable of measuring the
acceleration and angular velocity in the same time can be realized.
The present embodiment can also exhibit the effects obtained by
keeping the several weight portions 3 independent of each other
without connecting them. That is, the sensor can be miniaturized as
a whole, the cost is lowered, the yield is improved, and the
several driving electrodes can be disposed easily, similarly to the
second embodiment.
[0107] (Sixth Embodiment)
[0108] Next, a sixth embodiment will be explained. The present
embodiment is modified from the fifth embodiment, i.e., is a
combination of the third embodiment and the fourth embodiment. The
differences from the fifth embodiment will be mainly explained with
reference to FIG. 13 showing an angular velocity sensor 600 of the
present embodiment.
[0109] The angular velocity sensor 600 has two weight portions 3
each composed of the first weight portion 3a and the second weight
portions 3b similarly to the angular velocity sensor 500 shown in
FIG. 12. However, it is different in the following points.
Specifically, there is no inner side driving electrodes 5, 6 (the
right side of the left first weight portion 3a and the left side of
the right side first weight portion 3a). The two first weight
portions 3a are connected by the connection beam (coupled beam) 20
that is capable of displacing the two weight portions 3 in both the
driving direction x and detecting direction y. It should be noted
that the sensor 600 has two parts F that have the same shape and
are arranged on the right and left sides.
[0110] Next, the operation of the present embodiment will be
explained mainly focusing on the differences from the fifth
embodiment. The operation of oscillating the first weight portions
3a in-phase or in anti-phase is the same as the fifth embodiment.
The following points are also the same as the fifth embodiment.
[0111] Specifically, the influence of the acceleration can be
removed by taking the difference of the output signals of the two
second weight portions 3b. The sensitivity is almost doubled as
compared to the fourth embodiment. Further, the acceleration can be
measured by taking the sum of the outputs from the two second
weight portions 3b. Thus, the sensor capable of measuring the
angular velocity and acceleration at the same time can be realized
depending on a signal processing method.
[0112] Further, because the two first weight portions 3a are
connected by the connection beam 20 in the present embodiment, the
effect obtained by a coupled oscillation system composed of the two
weight portion 3 can be exhibited similarly to the third
embodiment.
[0113] (Seventh Embodiment)
[0114] Next, a seventh embodiment will be explained. The present
embodiment is modified from the first embodiment, and the
differences from the sensor 100 in the first embodiment will be
explained with reference to FIG. 14. FIG. 14 shows an angular
velocity sensor 700 of the present embodiment.
[0115] The present embodiment is different from the first
embodiment in that the weight portion 3 is composed of first weight
portions (driving weight portions) 3c, which are connected with the
basal portion 2 by the driving beams 4a and are capable of being
drive-oscillated in the driving direction x (first direction), and
a second weight portion (detecting weight portion) 3d that is
connected to the first weight portions 3c by the detecting beams
4b. The second weight portion 3d can be displaced not only in the
driving direction x but also in the detecting direction y (second
direction) accordingly.
[0116] That is, the second weight portion 3d is connected to the
first weight portions 3c by the detecting beams 4b and the first
weight portions 3c are connected to the basal portion 2 via the
driving beams 4a. The beam portion of the present invention is
composed of the driving beams 4a and the detecting beams 4b in the
present embodiment. The four unnecessary oscillation suppressing
electrodes 7, 8, 7a and 8a and two detecting electrodes 9, 10, 9a
and 10a are provided at the second weight portion 3d and the basal
portions 2 facing thereto, respectively.
[0117] Similarly to the fourth embodiment, the four driving beams
4a connected to the first weight portions 3c are designed so as to
have the degree of freedom mainly in the driving direction x and
the two detecting beams 4b connected to the second weight portion
3d are designed so as to have the degree of freedom mainly in the
detecting direction y. That is, because the second weight portion
3d is connected to the first weight portions 3c, the second weight
portion 3d has the degree of freedom not only in the driving
direction x similarly to the first weight portion 3c but also in
the detecting direction y relatively with respect to the first
weight portions 3c.
[0118] Then, the first weight portions 3c can be drive-oscillated
in the driving direction x together with the second weight portion
3d by the effect of the driving beams 4a when voltage is applied
between the driving movable electrode 5 formed on the respective
first weight portions 3c and the driving stationary electrode 6
formed on the basal portion 2 facing thereto. Then, when angular
velocity is applied around the angular velocity axis z during this
driving oscillation, the second weight portion 3d oscillates in the
detecting direction y by the detecting beams 4b.
[0119] The oscillation monitoring electrodes 12, 13 are also formed
on the first weight portions 3c and the basal portion 2 facing
thereto also in the angular velocity sensor 700. The oscillation
monitoring electrodes 12, 13 are used to monitor the physical
quantity of the driving oscillation similarly to the first
embodiment.
[0120] Next, the operation of the sensor of the present embodiment
will be explained more specifically. When periodic voltage is
applied to the external circuit not shown, the first weight
portions 3c are drive-oscillated along the driving direction x
together with the second weight portion 3d due to the degree of
freedom of the driving beams 4a in the driving direction x. Here,
the first weight portion 3c is not drive-oscillated (displaced),
the capacity between the detecting electrodes 9, 10, 9a and 10a
changes due to the simple driving oscillation (pure oscillation in
the driving direction).
[0121] Although it seems a demerit of the present embodiment
differing from the fourth embodiment, it actually poses almost no
problem because the influence of the driving oscillation may be
canceled by taking the sum of the outputs of the adjacent two
detecting electrodes.
[0122] The resonant driving or non-resonant driving described above
may be adopted also in the present embodiment. It is also
advantageous to adopt the ACG because it can remove the temperature
dependency of the driving amplitude and can suppress the
temperature drift of the sensitivity.
[0123] When angular velocity is applied around the angular velocity
axis z in state where the first weight portions 3c and the second
weight portion 3d are drive-oscillated, the second weight portion
3d oscillates in the detecting direction y due to the degree of
freedom of the detecting beams 4b by the Corioli's force applied to
the second weight portion 3d. At this time, the angular velocity
.OMEGA. can be detected by detecting differentially the capacity of
the detecting electrodes 9, 10 and the capacity of the detecting
electrodes 9a, 10a in the same manner as in the first
embodiment.
[0124] Here, the first weight portions 3c, the driving electrodes
5, 6 and the oscillation monitoring electrodes 12, 13 are not
displaced in the detecting direction by the detecting oscillation.
It means that the detecting oscillation is not influenced by the
electrostatic forces of the driving electrodes 5, 6 and the
oscillation monitoring electrodes 12, 13, resulting in accurate
detection of the angular velocity.
[0125] Further, although the spring constant of the detecting beams
4b is often reduced as compared to that of the driving beams 4a to
increase the sensitivity in general, the detecting beams are
positioned inside of the driving beams connected to the basal
portion in the present embodiment. Therefore, the resonant
frequency in the direction of the angular velocity axis z can be
readily increased. It is very advantageous to realize the sensor
having less noise because it is possible to readily avoid the
unnecessary oscillation by which the weight portion resonates in
direction of the angular velocity axis z.
[0126] The method for suppressing the unnecessary oscillation
caused by the processing error (processing error of the driving
beams 4a in particular) in the angular velocity sensor 700 can be
executed by using the unnecessary oscillation suppressing
electrodes 7, 8, 7a and 8a similarly to the first embodiment.
Accordingly, as described in the first embodiment referring to
FIGS. 5A to 5D, no output is outputted at all when angular velocity
is zero and only an angular velocity signal is detected when the
angular velocity is applied.
[0127] (Eighth Embodiment)
[0128] Next, an eighth embodiment will be explained. The present
embodiment is a modification provided by combining the seventh
embodiment with the second embodiment, and the differences from the
seventh embodiment will be mainly explained. FIG. 15 shows an
angular velocity sensor 800 of the present embodiment. Although the
seventh embodiment has one weight portion 3 composed of the two
first weight portions 3c and the second weight portion 3d, the
present embodiment is different from the seventh embodiment in that
several (two in this example) weight portions 3, each of which is
almost the same, are provided.
[0129] Specifically, the angular velocity sensor 800 shown in FIG.
15 has two parts G, each of which corresponds to the angular
velocity sensor 700 shown in FIG. 14 and which are provided in
parallel in the x-axis direction. A part of the reference numerals
are omitted in FIG. 15.
[0130] Next, the operation of the sensor 800 of the present
embodiment will be explained by aiming mainly at the differences
from the seventh embodiment. The operation of the first weight
portion 3c and the second weight portion 3d in each of the weight
portions 3 is substantially the same as that of the seventh
embodiment. However, the merit of the present embodiment will be
exhibited specifically when the two weight portions 3 are
drive-oscillated in anti-phase to each other because the
disturbance acceleration can be canceled due to the same reason as
that of the second embodiment.
[0131] That is, when both the weight portions 3 are
drive-oscillated along the driving direction x in anti-phase to
each other and angular velocity is applied around the angular
velocity axis z, the weight portions 3c in the respective weight
portions 3 oscillate in the detecting direction y in anti-phase to
each other due to the degree of freedom of the detecting beams 4b
in the detecting direction y. At this time, the influence of the
disturbance acceleration can be removed by taking the difference of
the outputs from the two second weight portions 3d. The present
embodiment also has a merit that the sensitivity is doubled as
compared to the seventh embodiment.
[0132] It is also possible to measure the acceleration by taking
the sum of the outputs from the two second weight portions 3d in
contrary. Accordingly, a sensor capable of measuring the
acceleration and angular velocity at the same time can be realized
by processing the signals. The present embodiment can also exhibit
the effects obtained by keeping the plurality of weight portions 3
independent from each other without connecting them. That is, the
sensor can be miniaturized as a whole, the cost is reduced, the
yield is improved, and the several driving electrodes can be
positioned readily, similarly to the second embodiment.
[0133] (Ninth Embodiment)
[0134] Next, a ninth embodiment will be explained. The present
embodiment is modified from the eighth embodiment, and is a
combination of the seventh embodiment and the third embodiment. The
differences from the eighth embodiment will be mainly explained
with reference to FIG. 16 showing an angular velocity sensor 900 of
the present embodiment.
[0135] Although the angular velocity sensor 900 has two weight
portions 3 composed of the first weight portion 3c and the second
weight portions 3d similarly to the angular velocity sensor 800
shown in FIG. 15, it is different in that there is no inner side
driving electrodes 5, 6 (the right side of the left first weight
portion 3c and the left side of the right side first weight portion
3c) and no oscillation monitoring electrodes 12, 13. It is further
different in that two first weight portions 3c of the two weight
portions 3 are connected by the connection beam (coupled beam) 20
that is capable of displacing the two first weight portions 3c in
both the driving direction x and detecting direction y. The sensor
900 has two parts H having the same shape and arranged on the right
and left sides.
[0136] Next, the operation of the present embodiment will be
explained mainly focusing on the differences from the eighth
embodiment. The operation of oscillating the respective weight
portions 3 (the first weight portion 3c and the second weight
portion 3d) in-phase or in anti-phase is the same as that in the
eighth embodiment. The following points are also the same as those
in the eighth embodiment.
[0137] Specifically, the influence of the acceleration can be
removed by taking the difference of the output signals of the two
second weight portions 3d, the sensitivity is almost doubled as
compared to the seventh embodiment, and the acceleration can be
measured by taking the sum of the outputs from the two second
weight portions 3d. Accordingly, the sensor capable of measuring
the angular velocity and acceleration in the same time can be
realized depending on a signal processing method.
[0138] Further, because the two first weight portions 3c are
connected by the connection beam 20 in the present embodiment, the
effect obtained by the coupled oscillation system formed by the two
weight portions 3 can be exhibited similarly to the third
embodiment.
[0139] (Other Embodiments)
[0140] While the respective embodiments have been described above,
the following points may be cited as items common to all of the
embodiments. At first, the method by means of the electrostatic
force has been mainly described as the method for suppressing the
unnecessary oscillation in the respective embodiments. This is
because the method using the electrostatic force can simplify the
manufacturing process, requires less number of parts, and allows
the miniaturization.
[0141] However, it is also possible to use a piezoelectric element
as unnecessary oscillation suppressing means. In this case, for
instance, a piezoelectric thin film (piezoelectric element, not
shown) such as PZT is formed on the beam portion 4 or the driving
beam 4a, and external force is applied to the weight portion 3 in
the detecting direction y by utilizing strain produced when an
electrical signal is applied to the piezoelectric thin film.
Accordingly, the unnecessary oscillation can be suppressed. Because
the piezoelectric element can produce, by the applied voltage,
large strain for suppressing the unnecessary oscillation of the
weight portion, the required voltage is small.
[0142] A member that generates Lorentz's force as the external
force to be applied to the weight portion 3 may be adopted as the
unnecessary oscillation suppressing means. Specifically, for
instance, a wiring member not shown may be formed on the weight
portion 3 or the second weight portion 3b via the beam portion 4 or
the detecting beam 4b so that current flowing in this wiring member
interacts with a permanent magnet or an electromagnet (not shown)
provided at the outside, as means for generating the Lorentz's
force. Then, the Lorentz's force can be controlled by regulating
the current flowing through the wiring member or by controlling the
current flowing through the electromagnet. In this control method,
the leakage of the voltage to the detection side used for the
unnecessary oscillation suppressing means becomes less liable to
affect the detection of the angular velocity by flowing DC current
in the wiring member on the weight portion. When the permanent
magnet is used, power consumption can be decreased.
[0143] The unnecessary oscillation suppressing means using the
Lorentz's force has a merit that the voltage applied to the wiring
member or the electromagnet is less liable to cause noise by
leakage thereof to the angular velocity detecting side, and the
value is small even if it leaks. It also can generate the Lorentz's
force through simple processes by providing the wiring member on
the weight portion via the beam portion.
[0144] There may be three or more weight portions 3 in the second,
third, fifth and sixth embodiments described above. In the third
and sixth embodiments, at least two of the several weight portions
3 should be connected by the connection beam 20. The two weight
portions 3 may be connected by several (more than one) connection
beams 20.
[0145] Further, the electrostatic driving or electrostatic
detection using the comb-teeth electrodes have been exemplified as
the driving means for drive-oscillating the weight portion 3 and
the angular velocity detecting means in the respective angular
velocity sensors described above. However, the present invention is
not limited to that. The present invention is applicable regardless
of the driving method and the detecting method. For instance, the
present invention can exhibit the similar effects also in the
angular velocity sensor adopting the driving or detection method
using electromagnetic force or a piezoelectric element and a strain
gage.
[0146] While the present invention has been shown and described
with reference to the foregoing preferred embodiments, it will be
apparent to those skilled in the art that changes in form and
detail may be made therein without departing from the scope of the
invention as defined in the appended claims.
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