Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2001-07-20
2003-10-07
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C310S331000
Reexamination Certificate
active
06629462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to detecting angular acceleration (rotational acceleration) and translational acceleration resulting from shock to an electronic device.
2. Description of Related Art
Miniaturization of electronic components has helped drive the rapid adoption and distribution of notebook computers and other types of portable electronics. This has also increased demand for small, surface-mountable, high performance acceleration (shock) detectors in order to assure and improve the reliability of these electronic devices. This is because physical shocks to a high density magnetic storage device while writing to the storage medium can, for example, cause the position of the write head to shift. This can result in data write errors and corruption or even damage to the head. It is therefore necessary and desirable to detect shock to the magnetic storage device and either interrupt the write operation or move the head to a safe position.
As the recording density of magnetic storage devices has increased, the track width on the disk surface has narrowed. This makes it even easier for the position of the head to shift (for the track to shift) at the slightest vibration. Another problem is that, in addition to impact and vibration from external sources acting on the magnetic storage device, small vibrations from the spinning of motors inside the magnetic storage device can also cause the magnetic head to skip tracks.
Vibrations acting on the magnetic storage device include both translational vibration and rotational vibration. For control purposes, it is therefore necessary to distinguish translational acceleration from angular acceleration (referred to below as rotational acceleration), and a sensor capable of detecting translational acceleration and rotational acceleration is needed. Translational acceleration can be detected using a single prior art acceleration sensor. Rotational acceleration can be detected with the greatest sensitivity using two or more acceleration sensors placed as far from each other and from the axis of rotation as possible. If two acceleration sensors are placed equidistantly from and on opposite sides of the rotational axis, the output signals from the acceleration sensors will be opposite sign but the same magnitude when rotational acceleration occurs. This will, however, only be true when the center of rotation is centered between the two acceleration sensors. Furthermore, when two acceleration sensors having the same practical characteristics are located on the same side of relative to the axis of rotation, translational acceleration will be the same at each acceleration sensor and the output signals from the acceleration sensors in response to translational acceleration will have the same magnitude. On the other hand, when rotational acceleration occurs, the output signals from the two acceleration sensors will differ in magnitude because the distance from the axis of rotation to each acceleration sensor differs. Rotational acceleration can therefore be detected by obtaining the difference between the two output signals.
A piezoelectric element, which produces a voltage as a result of deformation of a piezoelectric body in response to strain, can also be used as an acceleration sensor as described in Japanese Patent Laid-open Publication (kokai) No. 10-96742. One piezoelectric element used for an acceleration sensor is flat with a flat cantilevered portion. Strain deformation from acceleration is picked up as vibration of the cantilever portion of the piezoelectric body, thus producing a charge that can be detected to detect acceleration.
The problem is that when the acceleration sensor consists of plural piezoelectric elements, differences occur in the characteristics of the individual piezoelectric elements.
Furthermore, when the acceleration sensor has two piezoelectric elements disposed at separate positions, the sensitivity of the piezoelectric elements may be affected by where the elements are positioned. For example, temperature differences resulting from the position of the elements can offset the sensitivity of each piezoelectric element. In this case differences in the output signals from each piezoelectric element can cause rotational acceleration to be mistakenly detected when translational acceleration occurred, and rotational acceleration cannot be accurately recognized.
Yet further, reducing the distance between piezoelectric elements by housing two piezoelectric elements in the confined space inside a single package also reduces the detection signal difference. As a result, rotational acceleration cannot be detected with high sensitivity.
SUMMARY OF THE INVENTION
With consideration for the problems described above, it is therefore an object of the present invention to provide an acceleration sensor that can be disposed inside a limited space and can detect rotational acceleration with high sensitivity.
To achieve this object, an acceleration sensor according to the present invention has first piezoelectric element having electrodes for outputting a charge produced by strain deformation and second piezoelectric element having electrodes for outputting a charge produced by strain deformation. The first piezoelectric element has at least one piezoelectric body and a support block supporting the piezoelectric body. The second piezoelectric element has at least one piezoelectric body and a support block supporting the piezoelectric body. The electrodes are provided on opposite surfaces of the piezoelectric element, and one surface of the first piezoelectric element and one surface of the second piezoelectric element are effectively parallel to each other.
One surface of the first piezoelectric element and one surface of the second piezoelectric element are substantially parallel to each other so that the vibrating surfaces of the piezoelectric elements are parallel and each piezoelectric element will thus vibrate in the same direction in response to acceleration in a single direction. Yet further preferably, one surface of the first piezoelectric element and one surface of the second piezoelectric element are in the same plane. The piezoelectric elements normally vibrate perpendicular to the cantilever surface, and the surfaces of the cantilever portions of the piezoelectric elements are therefore preferably parallel to each other.
Yet further preferably, the cantilever portion and support block portion of the piezoelectric body in each piezoelectric element are a continuous monolithic portion, but the support block portion can be separate from the cantilever portion.
This configuration makes it possible to dispose first and second piezoelectric elements for detecting acceleration in the same direction in a confined space, and detect rotational acceleration with high sensitivity due to the distance between the support blocks supporting the piezoelectric body of the piezoelectric elements. Rotational acceleration can also be detected without being affected by environmental factors due to the installation.
Further preferably, the first and second piezoelectric elements are cantilevered, having a cantilever portion including a main piezoelectric body surface and a support block portion for supporting the piezoelectric body. The first and second piezoelectric elements are aligned with the longitudinal axes of the cantilever portion with the support block portions disposed to the outside mutually distant in opposite directions along the longitudinal axis, a free end portion of the cantilever of the first piezoelectric element and a free end portion of the cantilever of the second piezoelectric element are pointing to each other. Each free end portion of cantilever is located in mutual proximity to the inside, and the ends of the cantilever portions are substantially mutually parallel.
Yet further preferably, the first piezoelectric element includes one piezoelectric body and the second piezoelectric element includes one piezoelectric body. The direction of polarization of the piez
Koike Takafumi
Otsuchi Tetsuro
Taniguchi Fumihiko
Kwok Helen
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Acceleration sensor, an acceleration detection apparatus,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Acceleration sensor, an acceleration detection apparatus,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Acceleration sensor, an acceleration detection apparatus,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3171570