Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2000-12-05
2004-11-02
Williams, Hezron (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504110, C073S504120
Reexamination Certificate
active
06810737
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resonant element used as an angular velocity sensor, acceleration sensor, filter, or the like, and to a vibration adjustment method therefor.
2. Description of the Problems Leading to the Present Invention
FIG. 9A
is a perspective view showing a previous resonant element invented by the inventor of the present invention.
FIG. 9B
is a sectional view taken along the line I—I in FIG.
9
A.
The resonant element shown in
FIGS. 9A and 9B
is a resonant element
1
which is a microelement produced utilizing a conventional silicon micromachining technique and the like. The resonant element
1
is produced by forming a nitride film
3
on a silicon fixed substrate
2
, then forming a polysilicon film
4
thereover, and forming these films
3
and
4
into a predetermined set pattern by dry etching or the like.
As shown in
FIGS. 9A and 9B
, above the top surface
2
a
, which is a plane in the X-Y plane direction of the fixed substrate
2
, a vibrator
5
is disposed in a state isolated from the fixed substrate
2
. The vibrator
5
functions as a planar vibrating body
6
. The vibrator
5
is supported via support beams
7
so as to be vibratable in the X-direction. One end side of each of the support beams
7
is fixed to the fixed substrate
2
via a fixing portion
8
.
On the right and left sides (as viewed in
FIG. 9A
) of the vibrator
5
, movable-side comb electrodes
10
(
10
a
and
10
b
) are each formed outwardly in the X-direction, and fixed-side comb electrodes
11
(
11
a
and
11
b
) are each disposed inwardly in the X-direction at positions opposed to the movable-side comb electrodes
10
and interdigitated therewith in a spaced relationship. The movable-side electrodes
10
and the fixed-side comb electrodes
11
are each connected to outside electrode pads (not shown) via conductive patterns (not shown), and thereby form exciting means
12
.
For example, when AC voltages which are different in phase from each other by 180°, are applied to the fixed-side comb electrodes
11
a
and
11
b
while maintaining the movable-side comb electrodes
10
a
and
10
b
at a predetermined constant voltage (0 volt for example), electrostatic forces in directions opposite to each other occur between the movable-side comb electrodes
10
a
and the fixed-side comb electrodes
11
a
, and between these movable-side comb electrodes
10
b
and the fixed-side comb electrodes
11
b
, and by these electrostatic forces, the vibrator
5
is caused to be subjected to an excitation vibration in the X-direction.
In the resonant element
1
with the above-described features, when the resonant element
1
is rotated around the Y-axis while being caused to be subjected to an excitation vibration in the X-direction, as described above, a Coriolis force occurs in the Z-direction orthogonal to the X-Y plane direction. This Coriolis force is applied to the vibrator
5
(planar vibrating body
6
), and the vibrator
5
vibrates in the direction of the Coriolis force. By measuring the electric signal corresponding to the magnitude of the vibration amplitude of the vibrator
5
due to the Coriolis force occurring at this time, for example, the magnitude of a rotational angular velocity can be detected.
In the case where the resonant element
1
is used as an angular velocity sensor, there is provided a detecting portion for measuring the electric signal corresponding to the magnitude of vibration amplitude of the vibrator
5
due to a Coriolis force.
When the resonant element
1
is produced, the resonance frequency of the vibrator
5
(planar vibrating body
6
) in the direction of a Coriolis force (Z-direction) is previously set at the design stage to the resonance frequency in the X-direction, and the shape, dimensions, weight, etc. of the vibrator
5
are designed and implemented so that the resonance frequency is obtained. In many cases, however, the shape, dimensions, weight, etc. of the vibrator
5
are not implemented as designed because of the machining accuracy of the silicon micromachining technique. Accordingly, deviation of the resonance frequency of the vibrator
5
from the designed frequency often occurs. If the vibration of the vibrator
5
is in a resonant state, the amplitude thereof is greatly amplified by virtue of the Q (quality factor) value related to the structure, but if the frequency deviates, a problem arises in that the amplitude is not amplified nearly as much, resulting in the sensitivity of the resonant element being significantly reduced. It is therefore necessary to adjust the resonance frequency of the vibrator
5
to the set frequency in design by performing trimming with respect to the vibrator
5
and/or the support beams
7
by, for example, a complicated machining process.
The resonant element
1
is, however, a minute element, therefore, it is practically impossible, because of the accuracy of conventional mechanical trimming techniques, to perform trimming of the minute planar vibrating body
6
and/or the support beams
7
so as to have the desired dimensions, shape, and weight, etc. It has, therefore, been difficult to adjust the resonance frequency of the planar vibrating body
6
to a set value.
In the resonant element
1
, therefore, a conductive layer
15
for providing an electrostatic attractive force
14
is provided on the fixed substrate
2
at the position opposed to the vibrator
5
with an interval interposed in the Z-direction, as illustrated in
FIGS. 9A and 9B
.
As shown in
FIG. 9A
, the conductive layer
15
is connected to a conductive pad
17
via a conductive pattern
16
. By controlling the voltage to be applied to the conductive layer
15
via the conductive pattern
16
and conductive pad
17
, the resonance frequency of the vibrator
5
is adjustable to a set value.
Once a DC voltage is applied to the conductive layer
15
, an electrostatic attractive force acts on the vibrator
5
, and this acts on the vibrator
5
as an electrostatic spring. Specifically, when the vibrator
5
vibrates in a direction such that the vibrator
5
approaches the fixed substrate
2
, the electrostatic attractive force acts in the direction such that the amplitude is increased, so that the application of the DC voltage to the conductive layer
15
has an effect of generating a force in the direction opposite to the direction of the force of a mechanical spring. This results in a reduction in the resonance frequency of the vibrator
5
in the Z-direction. Since this reduced amount of the resonance frequency varies in accordance with the magnitude of the electrostatic attractive force
14
applied, a fine-adjustment of the resonance frequency of the vibrator
5
from the natural frequency thereof to the lower frequency side can be performed by adjusting the magnitude of the DC voltage applied to the conductive layer
15
.
Utilizing this effect, by designing the natural resonance frequency of the vibrator
5
in the Z-direction to be slightly higher than the most sensitive resonance frequency (the frequency equal to the resonance frequency in the X-direction), in other words, by designing the resonance frequency of the vibrator
5
in the Z-direction to be higher than the resonance frequency thereof in the excitation vibrational direction by the exciting means
12
, the vibrator
5
can be resonated at a predetermined resonance frequency by adjusting the magnitude of the DC voltage applied to the conductive layer
15
.
However, although the adjustment of the resonance frequency for the vibrator
5
has been performed by providing the conductive layer
15
, in some cases, characteristics such as S/N (signal-to-noise) ratio have deteriorated due to an increase in the noise of the resonant element
1
.
Investigation by the present inventor into the reason for the deterioration of the characteristics, has found that the deterioration of characteristics is attributable to the vibrating conditions of the vibrator
5
.
FIGS. 8A and 8B
each show vibrating states of the vibrator
5
Keating & Bennett LLP
Murata Manfacturing Co., Ltd.
Saint-Surin Jacques M.
Williams Hezron
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