Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2001-09-26
2004-11-30
Williams, Hezron (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514290, C073S514340
Reexamination Certificate
active
06823735
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an acceleration sensor for detecting an acceleration, and more particularly to an acceleration sensor for detecting an acceleration, based on a sliding vibration produced by application of acceleration.
An acceleration sensor is installed in equipment, and monitors an abnormal condition of the equipment by detecting an acceleration and vibration of the equipment. For example, the acceleration sensor is used to prevent errors in reading and writing data that result from vibration and shock in a hard disk drive, to prevent hand shaking in a video camera, to actuate an air bag in a vehicle, etc.
With a reduction in size and an improvement of the performance of equipment in which an acceleration sensor is to be installed, there has been a demand for the development of a small-sized, high-performance acceleration sensor capable of being mounted on a surface of the equipment. As such a small-sized acceleration sensor, an acceleration sensor using a piezoelectric element has been conventionally put into practice. Disclosed examples of such an acceleration sensor include an acceleration sensor that detects an acceleration by using a deflection of a piezoelectric single crystal (Japanese Patent Application Laid-Open No. 11-211748/1999, etc.), and an acceleration sensor that detects an acceleration by using a deflection of piezoelectric ceramic (Japanese Patent Application Laid-Open No.6-273439/1994, etc.). Moreover, a packaging method that enables compact housing of an acceleration sensor has been proposed (Japanese Patent Application Laid-Open No. 9-318650/1997, etc.).
According to the acceleration sensors using a deflection of a piezoelectric single crystal or a deflection of piezoelectric ceramic as mentioned above, by increasing the deflection to increase the stress, the detection sensitivity can be improved. Therefore, in order to improve the detection sensitivity for high performance, the mass needs to be increased to produce a larger deflection, resulting in a problem that the acceleration sensor becomes heavier and larger in size. On the other hand, when the piezoelectric element is made thicker, it does not easily deflect and causes a problem of a lowering of the detection sensitivity. Then, for an improvement of the detection sensitivity, there have been proposals to make the piezoelectric element thinner, to stick two pieces of extremely thin piezoelectric elements together, etc, but such proposals are associated with problems that the fabrication process is complicated and the cost is increased.
Therefore, the applicant of the present invention proposed acceleration sensors capable of detecting an acceleration with good sensitivity by a small-sized structure (Japanese Patent Application Laid-Open No. 2000-97707 and Japanese Application No.12-131714/2000). Such an acceleration sensor comprises a vibrator and a weight section which is connected to the vibrator and supported at a position different from the position of the center of gravity of an assembly of the vibrator and weight section, and finds the magnitude of an applied acceleration by detecting the amount of characteristic (sliding vibration) of the vibrator corresponding to an angular moment produced at the weight section by application of acceleration.
FIG. 1
is an explanatory view illustrating the detection principle of this acceleration sensor. The acceleration sensor includes a vibrator
100
, a weight section
200
and detection section
300
respectively connected to the vibrator
100
. The weight section
200
is supported at a support point S, and the position of this support point S is different from the position of the center of gravity G of the vibrator
100
and weight section
200
. When an acceleration in one direction (the direction of a void arrow in
FIG. 1
) is applied to such an acceleration sensor, an angular moment (arrow A in
FIG. 1
, size MLa (where M: the mass of the weight section
200
, L: the length from the support point S to the center of gravity of the weight section
200
, a: the applied acceleration)) about the support point S is produced. This angular moment causes a sliding vibration of the vibrator
100
(arrow B in FIG.
1
). The detection section
300
detects a signal resulting from the sliding vibration corresponding to such an angular moment. Since the size of the angular moment is proportional to the magnitude of acceleration to be detected, the acceleration can be detected by detecting this signal.
Besides,
FIG. 2
is a perspective view showing one example of the structure of such an acceleration sensor. An acceleration sensor
50
comprises a rectangular parallelepiped vibrator
51
formed of a single crystal piezoelectric body, a long rectangular parallelepiped weight section
52
and a flat rectangular parallelepiped substrate
53
. Here, although the vibrator
51
is formed of a single crystal piezoelectric body, needless to say, there is no problem even if the vibrator
51
is made of other piezoelectric body such as piezoelectric ceramics. Others are the same as below. The vibrator
51
is bonded to one end portion of the weight section
52
through an adhesive layer
54
. An end portion of the vibrator
51
, which faces the substrate
53
, is substantially divided into two regions in its longitudinal direction, and electrodes
55
are formed on the respective front surfaces. Moreover, a pattern of electrodes
56
is formed on the front surface of the substrate
53
(a face facing the vibrator
51
), and the electrodes
55
and
56
are bonded together through an adhesive layer
57
.
In the case where the acceleration sensor
50
having such a structure is bonded to a specimen, when an acceleration (the void arrow direction in
FIG. 2
) in one direction (the width direction) is applied, an angular moment about the support point is produced at the weight section
52
by the positional difference between the center of gravity of the weight section
52
and the support point, and sliding vibrations of different orientations in the width direction are produced in both of the divided regions of the vibrator
51
. Then, by drawing a voltage resulting from these sliding vibrations from the electrodes
55
via the electrodes
56
of the substrate
53
and by amplifying and detecting the voltage signal, the acceleration is detected.
Besides, the applicant of the present invention has also proposed an acceleration sensor constructed by dividing a face of the vibrator
51
on the weight section
52
side instead of a face on the substrate
53
side as described above.
The present inventor et al. are pursuing the development and improvement of such an acceleration sensor that has a small-sized structure and a high detection sensitivity without increasing the size of the vibrator itself to achieve high performance because it detects sliding vibration instead of deflective vibration.
In such an acceleration sensor, when the formation pattern of the electrodes
56
on the substrate
53
shown in the structure of
FIG. 2
is asymmetrical or when the respective electrodes
56
have different thickness, the vibrator
51
inclines and causes a problem that the detection sensitivity varies.
Further, even when a resonance frequency of the vibrator
51
itself is set out of an operating frequency band of the acceleration sensor
50
, if a resonance frequency of the substrate
53
is included within the operating frequency band, a signal of the resonance frequency of the substrate
53
is received, which causes a problem that flat detection sensitivity characteristics can not be obtained within the operating frequency band.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide an acceleration sensor capable of reducing variation in the detection sensitivity and progressing the flatness of the detection sensitivity within an operating frequency band by improving a previously proposed acceleration sensor.
An acceleration sensor according to the first aspect of the present invention is an acceleration sens
Ishikawa Hiroshi
Machida Atsushi
Armstrong Kratz Quintos Hanson & Brooks, LLP
Fujitsu Limited
Saint-Surin Jacques
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