Capacitance detecting apparatus including first and second variable capacitors which vary with the distance to an object

• US 7,768,272 B2
• Filed: 09/07/2007
• Issued: 08/03/2010
• Est. Priority Date: 09/08/2006
• Status: Active Grant

• Current Assignee: Aisin Seiki Co., Ltd. (Aisin Corp.)
• Original Assignee: Aisin Seiki Co., Ltd. (Aisin Corp.)
• Inventors: Kato, Manabu, Fujioka, Eiji
• Primary Examiner(s): NATALINI, JEFF WILLIAM
• Application Number:
  US11/851,947
• Publication Number:
  US 20080252303A1
• Time in Patent Office: 1,061 Days
• Field of Search: 324/672, 324/663
• US Class Current: 324/672
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2017/9602 characterised by the type or shape of the sensing electrodes
• CPC Class Codes: H03K 2217/960725 Charge-transfer

Abstract

A capacitance detecting apparatus includes: a first on/off switch; a first reference capacitor; a second on/off switch; a third on/off switch; a first sensor electrode; a fourth on/off switch; a second reference capacitance; a fifth on/off switch; a sixth on/off switch; a second sensor electrode; a comparator; switch controlling means for alternately repeating a second switch operation and a third switch operation following a first switch operation; counting means for counting a number of times for repeating the second switch operation; and judging means for judging changes in capacitances related to the first and second sensor electrodes, based upon the number of times for repeating the second switch operation counted by the counting means before a level of voltage at the first input terminal and a level of voltage at the second input terminal are reversed.

Claims

1. A capacitance detecting apparatus comprising:

a first variable capacitor having a first sensor electrode at one end, the first sensor electrode being adapted to face a measured object and storing an electric charge at an amount corresponding to an electric potential of the first sensor electrode, the first capacitor being configured to output a first capacitance which varies in response to a distance between the first sensor electrode and the measured object;

a second variable capacitor having a second sensor electrode at one end, the second sensor electrode being adapted to face the measured object and storing an electric charge at an amount corresponding to an electric potential of the second sensor electrode, the second capacitor being configured to output a second capacitance which varies in response to a distance between the second sensor electrode and the measured object;

a first reference capacitor configured to be connected to the first variable capacitor; and

a second reference capacitor configured to be connected to the second variable capacitor;

wherein the electric charge stored at the first sensor electrode is discharged and stored at the first reference capacitor, the electric charge stored at the second sensor electrode is discharged and stored at the second reference capacitor, so that the first capacitance of the first variable capacitor and the second capacitance of the second variable capacitor are detected based upon a difference between an electric potential at one end of the first reference capacitor and an electric potential at one end of the second reference capacitor, and

wherein the electric potential of the first sensor electrode and the electric potential of the second sensor electrode change at an identical increment/decrement and in opposite directions.

2. A capacitance detecting apparatus according to claim 1, wherein an area of the first sensor electrode is equal to an area of the second sensor electrode.

3. A capacitance detecting apparatus according to claim 2, wherein the first sensor electrode is structured with an arbitrary quantity of electric conductor, the second sensor electrode is structured with an arbitrary quantity of electric conductor, and the center of mass of the first sensor electrode matches the center of mass of the second sensor electrode.

4. A capacitance detecting apparatus according to claim 3, wherein the first sensor electrode is symmetrical relative to at least two symmetry planes crossing the matched centers of mass, and the second sensor electrode is symmetrical relative to the at least two symmetry planes crossing the matched centers of mass.