Capacitance change detection device

• US 20050218913A1
• Filed: 03/24/2005
• Published: 10/06/2005
• Est. Priority Date: 03/30/2004
• Status: Active Grant

• Current Assignee: Aisin Seiki Co., Ltd. (Aisin Corp.)
• Original Assignee: Aisin Seiki Co., Ltd. (Aisin Corp.)
• Inventors: Hatano, Rikuo, Inaba, Hisashi, Kurachi, Kohei
• Granted Patent: US 7,098,675 B2
• Time in Patent Office: Days
• US Class Current: 324/678
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/94031 Calibration involving digital processing

Abstract

A capacitance change detection device includes a sensor electrode, and an electrode capacitance measurement device for measuring capacitance of the sensor electrode on the basis of a correlation value based on a reference capacitance at every first predetermined time. A detection signal is generated when a current measurement value of capacitance is changed by equal to or greater predetermined threshold value than a measurement value obtained a second predetermined time before the current measurement value is measured. The capacitance change detection device further includes a sensitivity compensation capacitance for generating capacitance variations equivalent to specific variations of capacitance of the sensor electrode, and being switched between a connected state and a disconnected state. The threshold value is determined as a difference between measurement values of capacitance of the sensor electrode measured at the connected state and at the disconnected state. The threshold value is renewed at every third predetermined time.

Claims

1. A capacitance change detection device comprising:

a sensor electrode at which capacitance varies;

an electrode capacitance measurement means for measuring capacitance of the sensor electrode on the basis of a correlation value based on a predetermined reference capacitance at every first predetermined time;

wherein

a detection signal is generated when a current measurement value of capacitance of the sensor electrode measured by the electrode capacitance measurement means is changed by equal to or greater predetermined threshold value than a measurement value obtained a second predetermined time before a timing that the current measurement value is measured;

a predetermined sensitivity compensation capacitance for generating capacitance variations equivalent to a specific variations of capacitance of the sensor electrode generated by existence of a specific object at capacitance of the sensor electrode;

wherein

the sensitivity compensation capacitance is configured to be switched between a connected state at which the sensitivity compensation capacitance is connected to the sensor electrode and a disconnected state at which the sensitivity compensation capacitance is disconnected from the sensor electrode; and

the threshold value is determined as a difference between a measurement value of capacitance of the sensor electrode measured by the electrode capacitance measurement means at the connected state and a measurement value of capacitance of the sensor electrode measured by the electrode capacitance measurement means at the disconnected state; and

the threshold value is configured to be renewed at every third predetermined time.

3. The capacitance change detection device according to claim 1, further comprising:

a first opening and closing switch provided between first and second ends of the reference capacitance;

a first electric potential source connected to the first end of the reference capacitance;

a second opening and closing switch configured to connect the second end of the reference capacitance and a first end of the sensor electrode;

a third opening and closing switch provided between the first and second ends of the sensor electrode, the second end of the sensor electrode being connected to a second electric potential or free air;

an electric potential measurement means for measuring electric potential at the second end of the reference capacitance;

a switch control means for carrying out a switch control for repeating a second switch operation at which the second opening and closing switch being turned to be a closed state and returned to an open state and a third switch operation at which the third opening and closing switch being turned to be a closed state and returned to an open state alternately after performing a first switch operation at which the first opening and closing switch being turned to be a closed state and returned to an open state;

a count means for counting the number of a repeat of the second switch operation;

the electrode capacitance measurement means including the electric potential measurement means, the switch control means, and the count means;

wherein

the electrode measurement means measures the number of the repeat of the second switch operation, as the correlation value, counted by the count means until an electric potential at the second end of the reference capacitance measured by the electric potential measurement means is varied by a predetermined potential from an initial potential after the first switch operation; and

a reference capacitance change means for changing the reference capacitance.

2. A capacitance change detection device comprising:

a sensor electrode at which capacitance is varied;

an electrode capacitance measurement means for measuring capacitance of the sensor electrode on the basis of a correlation value based on a predetermined reference capacitance at every first predetermined time;

wherein

a detection signal is generated when a current measurement value of capacitance of the sensor electrode measured by the electrode capacitance measurement means is changed by equal to or greater predetermined threshold value than a measurement value obtained a second predetermined time before a timing that the current measurement value is measured;

and wherein

the threshold value is determined as a value which is determined on the basis of the measurement value measured the second predetermined time before the time of the measurement.

4. The capacitance change detection device according to claim 2, further comprising:

a first opening and closing switch provided between first and second ends of the reference capacitance;

a first electric potential source connected to the first end of the reference capacitance;

a second opening and closing switch configured to connect the second end of the reference capacitance and a first end of the sensor electrode;

a third opening and closing switch provided between the first and second ends of the sensor electrode, the second end of the sensor electrode being connected to a second electric potential or free air;

an electric potential measurement means for measuring electric potential at the second end of the reference capacitance;

a switch control means for carrying out a switch control for repeating a second switch operation at which the second opening and closing switch being turned to be a closed state and returned to an open state and a third switch operation at which the third opening and closing switch being turned to be a closed state and returned to an open state alternately after performing a first switch operation at which the first opening and closing switch being turned to be a closed state and returned to an open state;

a count means for counting the number of a repeat of the second switch operation;

the electrode capacitance measurement means including the electric potential measurement means, the switch control means, and the count means;

wherein

the electrode measurement means measures the number of the repeat of the second switch operation, as the correlation value, counted by the count means until an electric potential at the second end of the reference capacitance measured by the electric potential measurement means is varied by a predetermined potential from an initial potential after the first switch operation; and

a reference capacitance change means for changing the reference capacitance.