Capacitive sensor systems and methods with increased resolution and automatic calibration

• US 6,940,291 B1
• Filed: 07/22/2003
• Issued: 09/06/2005
• Est. Priority Date: 01/02/2001
• Status: Active Grant

• Current Assignee: iRobot Corporation
• Original Assignee: iRobot Corporation
• Inventors: Ozick, Daniel N.
• Primary Examiner(s): Deb, Anjan
• Assistant Examiner(s): He, Amy
• Application Number:
  US10/624,449
• Time in Patent Office: 777 Days
• Field of Search: 324/658, 324/663, 324/678, 324/686, 324/76.66, 738/623.37, 345/163, 345/173
• US Class Current: 324/658
• CPC Class Codes: G01D 18/006 Intermittent recalibration
• CPC Class Codes: G01D 18/008 with calibration coefficients stored in memory
• CPC Class Codes: G01D 5/2405 by varying dielectric
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/94026 Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input

Abstract

Methods and systems for capacitive proximity and contact sensing employ one or more simple sensors (which may be a conductive fiber or pattern of conductive ink) in communication with a microcontroller. Digital signal processing executed by the microcontroller enables resolution enhancement, automatic and continuous calibration, noise reduction, pattern recognition and the configuration of virtual sensors capable of detecting how an object incorporating the sensors is being manipulated.

Claims

1. A capacitive sensing system comprising:

a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/output (I/O) pin capable of functioning in both an INPUT mode and an OUTPUT mode;

a conductive sense element in electrical communication with the I/O pin, and

a resistance element in electrical communication with the conductive sense element to form an electrical pathway from the conductive sense element to an electrical discharge point;

wherein the microcontroller is further operable to;

at a first time, charge the sense element by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

at a second time, cease placing the selected voltage on the I/O pin;

thereafter, act the I/O pint to the INPUT mode, which causes the conductive sense element to discharge through the resistance element, and measure voltage at the I/O pin, the voltage at the I/O pin being representative of voltage at the sense element; and

measure a parametric value required for voltage at the conductive sense element to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by at least the conductive sense element and a first object that may be in contact or proximity with the conductive sense element whereby the parametric value is representative of contact or proximity between the sense element and the first object and further wherein;

the microcontroller is operable to perform digital signal processing on signals derived from the conductive sense element;

the signal processing includes pattern recognition wherein the microcontroller is operative to implement one or more of a plurality of software applications to perform digital signal processing on signals derived from the conductive sense element to detect one or more selected patterns of contact or proximity between the first object and the conductive sense element; and

the signal processing comprises the synthesis of at least one virtual sensor capable of detecting one or more of the selected patterns of contact or proximity between the first object and the conductive sense element.

3. The system of claim 1 or 2 adapted for embedding in a second object.

4. The system of claim 3 wherein the second object is a toy.

2. A capacitive sensing system comprising:

a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/output (I/O) pin capable of functioning in both an INPUT mode and an OUTPUT mode;

a conductive sense element in electrical communication with the I/O pin, and

a resistance element in electrical communication with the conductive sense element to form an electrical pathway from the conductive sense element to an electrical discharge point;

wherein the microcontroller is further operable to;

at a first time, charge the sense element by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

at a second time, cease placing the selected voltage on the I/O pin;

thereafter, set the I/O pint to the INPUT mode, which causes the conductive sense element to discharge through the resistance element, and measure voltage at the I/O pin, the voltage at the I/O pin being representative of voltage at the sense element; and

measure a parametric value required for voltage at the conductive sense element to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by at least the conductive sense element and a first object that may be in contact or proximity with the conductive sense element, whereby the parametric value is representative of contact or proximity between the sense element and the first object and further wherein;

the microcontroller is operable to perform digital signal processing on signals derived from the conductive sense element;

the signal processing includes pattern recognition wherein the microcontroller is operative to implement one or more of a plurality of software applications to perform digital signal processing on signals derived from the conductive sense element to detect one or more selected patterns of contact or proximity between the first object and the conductive sense element; and

the signal processing comprises the synthesis of multiple virtual sensors from the conductive sense element, each virtual sensor being capable of detecting one of the selected patterns of contact or proximity between the first object and the conductive sense element.

5. A capacitive sensing system comprising:

a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/output (I/O) pin capable of functioning in both an INPUT mode and an OUTPUT mode;

a conductive sense element in electrical communication with the I/O pin, and

a resistance element in electrical communication with the conductive sense element to form an electrical pathway from the conductive sense element to an electrical discharge point;

wherein the microcontroller is further operable to;

at a first time, charge the sense element by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

at a second time, cease placing the selected voltage on the I/O pin;

thereafter, set the I/O pin to the INPUT mode, which causes the conductive sense element to discharge through the resistance element, and measure voltage at the I/O pin, the voltage at the I/O pin being representative of voltage at the sense element; and

measure a parametric value required for voltage at the conductive, sense element to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by at least the conductive sense element and a first object that may be in contact or proximity with the conductive sense element, whereby the parametric value is representative of contact or proximity between the sense element and the first object and further wherein;

the microcontroller is operable to perform digital signal processing on signals derived from the conductive sense element;

the signal processing includes resolution enhancement by taking multiple timing-based measurements of the parametric value, using different, selected timing offsets and then averaging across the multiple timing-based measurements; and

the resolution enhancement further comprises running a timing loop iteratively with different, selected timing delays, and then deriving an average value from the multiple timing-based measurements thereby obtained.

6. A method of capacitive sensing the method comprising:

providing a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/output (I/O) pin capable of functioning in both an INPUT and OUTPUT mode;

providing a conductive sense element in electrical communication with the I/O pin, and

providing a resistance element in electrical communication with the conductive sense element to form an electrical pathway from the conductive sense element to an electrical discharge point;

and configuring the microcontroller to;

at a first time, charge the sense element by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

at a second time, cease placing the selected voltage on the port;

thereafter, set the I/O pin the INPUT mode, which causes the conductive sense element to discharge through the resistance element, and measure voltage at the I/O pin the voltage at the port being representative of voltage at the sense element;

measure a parametric value required voltage at the conductive sense element to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by at least the conductive sense element and a first object that may be in contact or proximity with the conductive sense element, whereby the parametric value is representative of contact or proximity between the sense element and the fist object; and

perform digital signal processing on signals derived from the conductive sense element;

wherein the signal processing includes pattern recognition wherein the microcontroller is operative to implement one or more of a plurality of software applications to perform digital signal processing on signals derived from the conductive sense element to detect one or more selected patterns of contact or proximity between the first object and the conductive sense element; and

the signal processing further comprises synthesizing at least one virtual sensor capable of detecting one or more of the selected patterns of contact or proximity between the first object and the conductive sense element.

8. The method of claim 6 or 7 adapted for embedding in a second object.

9. The method of claim 8 wherein the second object is a toy.

7. A method of capacitive sensing, the method comprising:

providing a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/output (I/O) pin capable of functioning in both an INPUT and OUTPUT mode;

providing a conductive sense element in electrical communication with the I/O pin, and

providing a resistance element in electrical communication with the conductive sense element to form an electrical pathway from the conductive sense element to an electrical discharge point;

and configuring the microcontroller to;

at a first time, charge the sense element by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

at a second time, cease placing the selected voltage on the port;

thereafter, set the I/O pin to the INPUT mode, which causes the conductive so, element to discharge though the resistance element, and measure voltage at the I/O pin, the voltage at the port being representative of voltage at the sense element;

measure a parametric value required for voltage at the conductive sense element to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by at least the conductive sense element and a first object that may be in contact or proximity with the conductive sense element, whereby the parametric value is representative of contact or proximity between the sense element and the first object; and

perform digital signal processing on signals derived from the conductive sense element;

wherein the signal processing includes pattern recognition wherein the microcontroller is operative to implement one or more of a plurality of software applications to perform digital signal processing on signals derived from the conductive sense element to detect one or more selected patterns of contact or proximity between the first object and the conductive sense element; and

the signal processing further comprises synthesizing multiple virtual sensors from the conductive sense element, each virtual sensor being capable of detecting one of the selected patterns of contact or proximity between the first object and the conductive sense element.

10. A method of capacitive sensing, the method comprising:

providing a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/out (I/O) pin capable of functioning in both an INPUT and OUTPUT mode;

providing a conductive sense element in electrical communication with the I/O pin, and

providing a resistance element in electrical communication with the conductive sense element to form an electrical pathway from the conductive sense element to an electrical discharge point;

and configuring the microcontroller to;

at a first time, charge the sense element by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

at a second time, cease placing the selected voltage on the port;

thereafter, set the I/O pin to the INPUT mode, which causes the conductive sense element to discharge through the resistance element, and measure voltage at the I/O pin, the voltage at the port being representative of voltage at the sense element;

measure a parametric value required for voltage at the conductive sense element to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by at least the conductive sense element and a first object that may be in contact or proximity with the conductive sense element, whereby the parametric value is representative of contact or proximity between the sense element and the first object; and

perform digital signal processing on signals derived from the conductive sense element;

wherein the signal processing includes resolution enhancement, the resolution enhancement comprising taking multiple timing-based measurements of the parametric value, using different selected timing offsets, and then averaging across the multiple timing-based measurements; and

the resolution enhancement further comprising running a timing loop iteratively with different, selected timing delays; and

then deriving an average value from the multiple timing-based measurements thereby obtained.

11. A non-contact object identification system, comprising:

a microcontroller, operable to receive electrical power from an electrical power source, and having at least one digital logic input/output (I/O) pin capable of functioning in both an INPUT mode and an OUTPUT mode;

at least two conductive sense elements in electrical communication with the I/O pin, the at least two conductive sense elements forming a binary-coded identification pattern and

a resistance element in electrical communication with each conductive sense element to form an electrical pathway from each conductive sense element to an electrical discharge point;

wherein the microcontroller is further operable to;

at a first time, charge the conductive sense elements by causing a selected voltage to be placed on the I/O pin by setting the I/O pin to the OUTPUT mode in the high state;

at a second time, cease placing the selected voltage on the I/O pin;

thereafter, set the I/O pin to the INPUT mode, which causes the conductive sense elements to discharge though the associated resistance element, and measure voltage at the I/O pin, the voltage at the I/O pin being representative of voltage at the conductive sense elements; and

measure a parametric value required for voltage at the conductive sense elements to decline to a value below a threshold value, the parametric value being representative of an effective capacitance formed by the conductive sense elements and an object in proximity with the conductive sense elements, whereby the parametric value is representative of proximity between the conductive sense elements and such object;

wherein;

when an object having a corresponding binary-coded identification pattern is aligned with the binary-coded identification pattern formed by the conductive sense elements, the alignment is detected by the conductive sense elements and the microcontroller signals identification of the binary-coded object.