Apparatus and method for sensing the degree and touch strength of a human body on a sensor

• US 20030210809A1
• Filed: 05/07/2002
• Published: 11/13/2003
• Est. Priority Date: 05/07/2002
• Status: Active Grant

• Current Assignee: Mcquint, Inc.
• Original Assignee: Mcquint, Inc.
• Inventors: Kim, Wonchan
• Granted Patent: US 7,006,078 B2
• Time in Patent Office: Days
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing

Abstract

An improvement in sensor for detecting contact with a human resistive element is disclosed. This design uses additional components to avoid discharging capacitors through the human resistive element, thereby sparing the user the uncomfortable sensation associated therewith and increasing the power requirements of the device. In addition, designs are utilized which multiple sensing points are multiplexed to achieve greater resolution while with a lower pin count at the signal processing chip.

Claims

1. A sensor for sensing the contact level of a human body comprising:

a first capacitor having one end connected to ground;

a second capacitor connected in series with said first capacitor and defining a node therebetween;

a charging element, for delivering a charge to said first capacitor;

a sensing point connected in series with said second capacitor, said sensing point being capable of defining a resistance when in contact with a human resistive element; and

an output device for detecting when the voltage at said node falls below a pre-defined threshold value as the result of the leakage of said charge from said first capacitor to said second capacitor.

2. The sensor of claim 1 further comprising a signal processing device coupled to said output device.

6. The sensor of claim 1 wherein said sensing point comprises a plurality of sensing points connected in parallel.

7. The sensor of claim 6 wherein any number of said plurality of sensing points may be in contact with a human resistive element at any give time.

3. A sensor for sensing the contact level of a human body comprising:

a first capacitor having one end connected to ground;

a second capacitor connected in series with said first capacitor and defining a node therebetween;

a charging element, for delivering a charge to said first capacitor;

a sensing point connected in series with said second capacitor, said sensing point being capable of defining a resistance when in contact with a human resistive element;

wherein said first and second capacitors, when combined with said resistance of said sensing point form an RC circuit which causes the charge stored on said first capacitor to flow to said second capacitor, causing the voltage at said node to fall; and

an output device for detecting when the voltage at said node falls below a pre-defined threshold value.

4. The sensor of claim 3 further comprising a signal processing device coupled to said output device.

5. The sensor of claim 3 wherein said output device is an inverter.

8. A sensor for sensing the contact level of a human body comprising:

a plurality of sensing devices arranged in parallel, each of said sensing devices having a selection node initially connected to ground;

a capacitor, connected in series with said plurality parallel of sensing devices, defining a node therebetween;

a current source for delivering a charge to said capacitor;

a current sink for draining said current from said capacitor; and

an output device for outputting a signal based on the voltage at said node.

9. The sensor of claim 8 wherein each of said sensing devices comprises:

a draining capacitor connected to said node;

a sensing point in series with said draining capacitor; and

an isolating capacitor in series with said sensing point and connected to said selecting node;

wherein said sensing point defines a resistance to ground when in contact with a human body part.

10. The sensor of claim 9 further comprising a signal processing device coupled to said output device.

11. The sensor of claim 8 wherein said current source is a transistor connected between a voltage source and said node and wherein said current sink is a transistor connect between said node and ground.

12. The sensor of claim 8 wherein said output device is a selected from a group consisting of a comparator and in inverter.

13. The sensor of claim 9 wherein said each of said sensing points in said sensing devices comprise a plurality of sensing points arranged in a parallel relationship.

14. A method for sensing the level of contact between a sensing point and a human body comprising the steps of:

charging a first capacitor;

allowing said charge to leak from said first capacitor to a second capacitor when a sensing point connected to said second capacitor comes in contact with a human body; and

signaling when said voltage across said first capacitor falls below a threshold value.

15. The method of claim 14 further comprising the step of re-charging said first capacitor when the voltage across said first capacitor reaches a pre-defined voltage below said threshold voltage.

16. The method of claim 14 wherein said sensing point connected to said second capacitor comprises a plurality of sensing points connected to said second capacitor and further comprising the step of:

allowing said charge to leak from said first capacitor to said second capacitor when one or more of said plurality of said sensing points comes in contact with a human body.

21. The method of claim 15 wherein said step of applying a selecting voltage comprises applying a selecting voltage to a plurality of sensing devices.

17. A method for sensing the level of contact between a sensing point and a human body comprising the steps of:

providing a first capacitor;

providing a second capacitor connected in series with said first capacitor and defining a node therebetween;

providing a sensing point in series with said second capacitor, said sensing point defining a resistance between ground and said second capacitor when in contact with a human body;

charging said first capacitor until a predetermined voltage at said node is reached;

monitoring the leakage of said charge stored on said first capacitor to said second capacitor via the decrease in voltage at said node; and

signaling when said voltage at said node falls below a pre-defined threshold value.

18. A method for sensing the level of contact between a sensing point and a human body comprising the steps of:

charging a first capacitor connected between ground and a node to a voltage below a threshold voltage;

applying a selecting voltage to one of a plurality of sensing devices, said selecting voltage causing the voltage at said node to rise to a voltage above said threshold voltage;

outputting a signal if said voltage at said node falls below said threshold voltage; and

deselecting said selected sensing device by grounding said selecting node.

19. A method of claim 18 wherein said charging step comprises the steps of:

discharging said first capacitor;

charging said first capacitor such that the voltage at said node rises to a voltage above a threshold voltage

draining said first capacitor such that the voltage at said node falls to a voltage below said threshold voltage.

20. The method of claim 18 further comprising the step of:

allowing current to flow from said first capacitor to said sensing device when said sensing device is in contact with a human body.

22. An improvement to a sensor for sensing human contact comprising a sensing point capable of defining a resistance to ground when in contact with a human resistive element and a first capacitor connected in series with said sensing point, said improvement comprising:

a second capacitor arranged in series between said sensing point and said first capacitor such that, when said sensing point defines a resistance, current is transferred from said first capacitor to said second capacitor instead of through said human resistive element.