Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-02-02
2001-03-13
Kwok, Helen C. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514360
Reexamination Certificate
active
06199430
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an acceleration sensor, for example, which is built in a gas or other flow meter so as to shut off a valve of a gas pipe or in a stove so as to extinguish flame when detecting earthquake vibrations and the like, or which detects accelerations in many directions on a two-dimensional plane at approximately the same sensitivity.
2. Related Arts
JP-A-6-123631 and JP-A-6-123632 disclose a semiconductor acceleration sensor capable of being used for the above field. The semiconductor acceleration sensor has an anchor part supported by four beams such that it can move in X, Y directions and a movable electrode which moves together with the anchor part. This sensor detects accelerations in the X, Y directions based on a change in capacity between the movable electrode and a fixed electrode provided on a substrate side, so that it detects acceleration in every direction on an X-Y plane.
However, to obtain the magnitude of acceleration in a diagonal direction on the X-Y plane based on the detected accelerations in the X, Y directions, it is necessary that the acceleration sensor has an arithmetic circuit for synthesizing the detected accelerations in the X, Y directions to process as a signal.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problem. An object of the present invention is to provide an acceleration sensor capable of directly detecting acceleration in every direction approximately parallel to a surface of a substrate with high detecting accuracy.
According to the present invention, an acceleration sensor has an anchor part disposed on a substrate, a movable electrode having a cylindrical movable electrode side face, a beam connecting the anchor part and the movable electrode, and a fixed electrode having a cylindrical fixed electrode side face that makes a specific interval with the movable electrode side face when no acceleration is applied to the movable electrode. The beam is elastically deformed to displace the movable electrode in a direction approximately parallel to the surface of the substrate by acceleration. The acceleration is detected based on a change in interval between the movable electrode side face and the fixed electrode side face.
Accordingly, because the movable electrode and the fixed electrode have the cylindrical movable electrode and fixed electrode side faces, the acceleration sensor can detect acceleration applied to the movable electrode in every direction approximately parallel to the surface of the substrate.
Preferably, the fixed electrode includes a detecting fixed electrode for detecting the acceleration and a sensitivity controlling fixed electrode for controlling sensitivity of the acceleration, which are electrically insulated from one another, and first and second potential differences between the movable electrode and the detecting fixed electrode and between the movable electrode and the sensitivity controlling fixed electrode are independently controlled. As a result, the sensitivity of the acceleration can be readily controlled, resulting in high detecting accuracy.
The fixed electrode electrode may include a plurality of detecting fixed electrodes and a plurality of sensitivity controlling fixed electrodes surrounding the movable electrode. In this case, when the second potential difference is applied between the movable electrode and all of the plurality of sensitivity controlling fixed electrodes, a detecting operation of the acceleration sensor can be checked by applying a third potential difference, which is different from the second potential difference, between at least one of the plurality of sensitivity controlling fixed electrodes and the movable electrode. Accordingly, the operation check including sensitivity adjustment of the acceleration sensor can be easily performed even after the manufacturer of the sensor is finished.
The acceleration sensor may have a lower electrode disposed on the substrate to face the movable electrode with an interval and having an electrical potential the same as that of the movable electrode. In this case, no electrostatic attracting force is produced between the movable electrode and the substrate, so that the movable electrode can move in parallel to the surface of the substrate, resulting in high detecting accuracy of the acceleration.
The acceleration sensor may have a current preventing member between the substrate and a movable part composed of the movable electrode and the beam, for preventing a current from flowing between the substrate and the movable part. Accordingly, erroneous detection can be prevented. The current preventing member may be composed of an insulation film disposed on at least one of surfaces of the substrate and the movable part facing one another.
The acceleration sensor may have contacting state keeping means for keeping the movable electrode in contact with the fixed electrode after the acceleration, which causes the contact, disappears. Accordingly, the acceleration sensor can memorize the state where the acceleration is applied thereto.
The sensitivity controlling fixed electrode can serve as the contacting state keeping means by producing an electrostatic attracting force with the movable electrode therebetween to keep the contacting state.
The detecting fixed electrode can have a protrusion for contacting the movable electrode and for preventing the movable electrode from attaching the sensitivity controlling fixed electrode. Further, by controlling the size of the protrusions, the interval between the detecting fixed electrode and the movable electrode is changed to control the detecting state of the acceleration sensor.
Preferably, the acceleration sensor has a deformation preventing film disposed on the beam on an opposite side of the substrate to apply a force to the beam in a direction opposite to a gravitational direction. As a result, the beam is prevented from deforming in the gravitational direction, so that the beam can keep the movable electrode parallel to the substrate. The movable electrode is prevented from hanging down toward the substrate by its self-weight, resulting in high detecting accuracy.
Preferably, a thickness of the movable electrode is thinner than that of the anchor part, and surfaces of the anchor part, the movable electrode, and the beam on an opposite side of the substrate are on a plane in a state where no gravitational force is applied to the movable electrode and the beam. In this case, even if the movable electrode hangs down by its self-weight, the movable electrode contacts the fixed electrode to detect acceleration with high accuracy.
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Hattori Koji
Ishio Seiichiro
Kano Kazuhiko
Murata Minoru
Ohtsuka Yoshinori
Denso Corporation
Kwok Helen C.
Pillsbury & Winthrop LLP
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