Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
1999-06-29
2001-07-10
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S514180, C324S661000
Reexamination Certificate
active
06257061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a capacitive-type apparatus for detecting a physical quantity such as an acceleration, an angular velocity, or a pressure.
2. Description of the Related Art
In a typical capacitive physical-quantity detection apparatus, a movable electrode and a fixed electrode are opposed to each other to form a capacitor, and a physical quantity is detected on the basis of the capacitance of the capacitor.
There are known capacitive physical-quantity detection apparatuses of various types which are designed to implement self diagnoses. In a self-diagnosis mode of operation of such a known apparatus, an electrostatic force is generated between a movable electrode and a fixed electrode to produce a state where a pseudo physical quantity is deemed to be acting on the movable electrode.
Self diagnosis is carried out by inspecting a response of an apparatus sensing portion to the pseudo physical quantity.
Japanese published unexamined patent application 5-322921 corresponding to U.S. Pat. No. 5,506,454 discloses a system for diagnosing characteristics of a capacitive acceleration sensor. In a diagnosis mode of operation of the system, a signal applicator serves as a means for applying a diagnosis signal to a fixed electrode so that a force corresponding to an acceleration is exerted onto a movable electrode. Diagnosis is carried out by inspecting a response of the sensor to the acceleration-corresponding force.
U.S. Pat. No. 5,540,095 discloses an accelerometer including two fixed electrodes opposed to a movable electrode. In a self-test mode of operation of the accelerometer, a carrier voltage level fed to one of the fixed electrodes is made different from a normal value to apply a pseudo physical quantity to the movable electrode. Self test is implemented by inspecting a response of an accelerometer sensing portion to the applied pseudo physical quantity.
U.S. Pat. No. 5,583,290 discloses a micromechanical sensing apparatus including two fixed electrodes opposed to a movable electrode. During a normal mode of operation of the apparatus, carrier signals having different center voltages are applied to the fixed electrodes respectively, and detection is made as to the capacitance of a capacitor formed by the fixed electrodes and the movable electrode. In a self-test mode of operation of the apparatus, a voltage fed to the movable electrode is made different from a normal value to apply a pseudo physical quantity to the movable electrode. Self test is implemented by inspecting a response of an apparatus sensing portion to the applied pseudo physical quantity.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a capacitive physical-quantity detection apparatus which can implement self diagnosis in a new way.
A first aspect of this invention provides a capacitive physical-quantity detection apparatus comprising a movable electrode (
2
d
) which is displaced in response to a physical quantity; a fixed electrode (
3
,
4
) opposed to the movable electrode to form a capacitor in conjunction with the movable electrode; signal applying means (
23
,
24
) for applying a first signal between the movable electrode and the fixed electrode, the first signal being periodic and having at least a first time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis; a C-V conversion circuit (
21
) for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period; a signal processing circuit (
22
) for processing the voltage generated by the C-V conversion circuit into a second signal depending on the physical quantity; and changing means (
23
) for changing the first signal in the second time period between a state for execution of self diagnosis and a state for unexecution of self diagnosis; wherein the first signal in the state for execution of self diagnosis applies a pseudo physical quantity to the movable electrode.
A second aspect of this invention is based on the first aspect thereof, and provides a capacitive physical-quantity detection apparatus wherein a frequency of the first signal is higher than a resonance frequency of the movable electrode in a direction of displacement of the movable electrode.
A third aspect of this invention is based on the first aspect thereof, and provides a capacitive physical-quantity detection apparatus wherein the changing means comprises means for changing a potential at the movable electrode.
A fourth aspect of this invention is based on the first aspect thereof, and provides a capacitive physical-quantity detection apparatus wherein the changing means comprises means for changing a potential at the fixed electrode.
A fifth aspect of this invention is based on the first aspect thereof, and provides a capacitive physical-quantity detection apparatus wherein the C-V conversion circuit comprises an operational amplifier (
21
a
) having first and second input terminals, the first input terminal being connected to the movable electrode, and wherein the changing means comprises means for applying a first predetermined voltage (V/2) to the second input terminal during unexecution of self diagnosis, and means for applying a second predetermined voltage (V1) to the second input terminal during execution of self diagnosis.
A sixth aspect of this invention is based on the first aspect thereof, and provides a capacitive physical-quantity detection apparatus wherein the C-V conversion circuit comprises an operational amplifier (
21
a
), and the changing means comprises means for connecting the movable electrode and an input terminal of the operational amplifier during unexecution of self diagnosis, and means for applying a predetermined voltage (V1) to the movable electrode during execution of self diagnosis.
A seventh aspect of this invention is based on the first aspect thereof, and provides a capacitive physical-quantity detection apparatus wherein the changing means comprises means for applying a periodic signal to the fixed electrode during unexecution of self diagnosis, and means for applying a predetermined voltage (V1) to the fixed electrode during execution of self diagnosis.
An eighth aspect of this invention provides a capacitive physical-quantity detection apparatus comprising a movable electrode (
2
d
) which is displaced in response to a physical quantity; a fixed electrode (
3
,
4
) opposed to the movable electrode to form a capacitor in conjunction with the movable electrode; signal applying means (
24
) for, during execution of self diagnosis, applying a first signal between the movable electrode and the fixed electrode, the first signal being periodic and having at least a first time period for detection of a capacity variation and a second time period for displacement of the movable electrode to implement self diagnosis, and for, during unexecution of self diagnosis, applying a second signal between the movable electrode and the fixed electrode, the second signal being periodic and having at least a third time period for detection of a capacity variation, the second signal being void of a time period for displacement of the movable electrode to implement self diagnosis; a C-V conversion circuit (
21
) for generating a voltage which depends on a variation in a capacitance of the capacitor during the first time period and the third time period; and a signal processing circuit (
22
) for processing the voltage generated by the C-V conversion circuit into a third signal depending on the physical quantity; wherein the signal applying means comprises means (
23
) for generating an electrostatic force between the movable electrode and the fixed electrode in response to the first signal in the second time period, and for applying a pseudo physical quantity to the movable electrode in response to the electrostatic force.
A ninth aspect of this invention is based on the first aspect thereof, and provides a capacitive physical-quantity detection a
Nonoyama Shigeru
Yamauchi Shigenori
Denso Corporation
Kwok Helen
Pillsbury & Winthrop LLP
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