Force sensing semiconductive touchpad

• US 5,943,044 A
• Filed: 05/15/1997
• Issued: 08/24/1999
• Est. Priority Date: 08/05/1996
• Status: Expired due to Term

• Current Assignee: Interlink Electronics Incorporated
• Original Assignee: Interlink Electronics Incorporated
• Inventors: Martinelli, Robert M., Martinelli, John K., Ritchey, Wendell W., Pickett, Mark C., Yaniger, Stuart J.
• Primary Examiner(s): Shankar, Vijay
• Application Number:
  US08/857,134
• Time in Patent Office: 831 Days
• Field of Search: 345/173, 345/174, 345/175, 345/178, 345/179, 178/18.01, 178/18.03, 178/18.06, 178/18.07, 178/19.03, 178/19.04
• US Class Current: 345/174
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/038 Control and interface arrangements therefor, e.g. drivers or device-embedded control circuitry
• CPC Class Codes: G06F 3/041 Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: G06F 3/0488 using a touch-screen or digitiser, e.g. input of commands through traced gestures

Abstract

A touchpad assembly and method for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad assembly is provided. The touchpad assembly includes X and Y position and pressure sensitive semiconductor resistance sensor layers. The X and Y sensors have a pair of spaced apart X and Y conductive traces running across opposite ends such that a resistance RX connects the pair of X traces and a resistance RY connects the pair of Y traces. The X and Y sensors come into contact at a contact point when an object asserts a pressure on the touchpad. The contact point is connected to each trace by a variable pressure resistance RZ associated with the X and Y sensors and variable position resistances of the X and Y resistances. First and second pair of timing capacitors are connected to respective ones of the pairs of X and Y traces. A microprocessor controls and monitors charging time of the capacitors to determine the position and asserted pressure of the object touching the touchpad.

Claims

1. A touchpad for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad, the touchpad comprising:

a pad having a touch surface and a bottom surface;

a first sensor layer disposed adjacent the bottom surface of the pad;

a first pair of spaced apart conductive traces running across opposite ends of the first sensor layer in a first direction such that a first resistance between the opposite ends of the first sensor layer connects the first pair of conductive traces;

a second sensor layer; and

a second pair of spaced apart conductive traces running across opposite ends of the second sensor layer in a second direction generally perpendicular to the first direction such that a second resistance between the opposite ends of the second sensor layer connects the second pair of conductive traces;

the second sensor layer being disposed beneath the first sensor layer such that the first and second sensor layers come into contact at a contact point when an object asserts a pressure on the touch surface of the pad, wherein the contact point is connected to each conductive trace by a variable pressure resistance associated with the first and second sensor layers and variable position resistances of the first and second resistances, wherein the variable pressure resistance varies inversely as a function of the pressure asserted and the variable position resistances vary proportionally as a function of the distance of the contact point from the conductive traces.

2. The touchpad of claim 1 further comprising:

a first pair of timing capacitors each connected to a respective one of the first pair of conductive traces; and

a second pair of timing capacitors each connected to a respective one of the second pair of conductive traces.

3. The touchpad of claim 2 further comprising:

a microprocessor operative with the timing capacitors, wherein the microprocessor controls and monitors charging time of the timing capacitors to determine the position and asserted pressure of the object on the touch surface of the pad.

4. The touchpad of claim 3 wherein:

the charging time of a timing capacitor is a function of the variable pressure resistance and the variable position resistance connecting the contact point to the one of the conductive traces that the timing capacitor is connected.

5. The touchpad of claim 3 wherein:

the microprocessor drives the first pair of conductive traces to a given voltage so that current flows from the contact point through the variable pressure resistance, the variable position resistances, and the second pair of conductive traces to the second pair of timing capacitors, wherein the microprocessor monitors the charging time for the current to charge the second pair of timing capacitors to determine the position of the object along the first direction.

6. The touchpad of claim 5 wherein:

current flows from the contact point through the variable pressure resistance, a variable position resistance connecting the contact point and one of the second pair of conductive traces, the one of the second pair of conductive traces, and then to one of the second pair of timing capacitors, wherein the microprocessor monitors the charging time for the current to charge the one of the second pair of timing capacitors to determine the distance of the object from the one of the second pair of conductive traces along the first direction.

7. The touchpad of claim 6 wherein:

current flows from the contact point through the variable pressure resistance, a variable position resistance connecting the contact point and the other one of the second pair of conductive traces, the other one of the second pair of conductive traces, and then to the other one of the second pair of timing capacitors, wherein the microprocessor monitors the charging time for the current to charge the other one of the second pair of timing capacitors to determine the distance of the object from the other one of the second pair of conductive traces along the first direction.

8. The touchpad of claim 3 wherein:

the microprocessor drives the second pair of conductive traces to a given voltage so that current flows from the contact point through the variable pressure resistance, the variable position resistances, and the first pair of conductive traces to the first pair of timing capacitors, wherein the microprocessor monitors the charging time for the current to charge the first pair of timing capacitors to determine the position of the object along the second direction.

9. The touchpad of claim 8 wherein:

current flows from the contact point through the variable pressure resistance, a variable position resistance connecting the contact point and one of the first pair of conductive traces, the one of the first pair of conductive traces, and then to one of the first pair of timing capacitors, wherein the microprocessor monitors the charging time for the current to charge the one of first pair of timing capacitors to determine the distance of the object from the one of the first pair of conductive traces along the second direction.

10. The touchpad of claim 9 wherein:

current flows from the contact point through the variable pressure resistance, a variable position resistance connecting the contact point and the other one of the first pair of conductive traces, the other one of the first pair of conductive traces, and then to the other one of the first pair of timing capacitors, wherein the microprocessor monitors the charging time for the current to charge the other one of the first pair of timing capacitors to determine the distance of the object from the other one of the first pair of conductive traces along the second direction.

11. The touchpad of claim 1 wherein:

the variable pressure resistance falls within a range having the same order of magnitude of the first and second resistances of the first and second sensor when the asserted pressure is between 15 to 100 grams.

12. The touchpad of claim 1 wherein:

the variable pressure resistance enables conduction of current when the asserted pressure is around 10 grams.

13. The touchpad of claim 1 wherein:

each of the sensor layers comprise carbon, resin, filler, and solvent, wherein each of the sensor layers have a 1;

5 ratio of the filler to a blend of the carbon, the resin, and the solvent.

14. The touchpad of claim 13 wherein:

the filler is stannous oxide.

15. A touchpad assembly for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad assembly, the touchpad assembly comprising:

a pad having a touch surface and a bottom surface;

a first sensor layer disposed adjacent the bottom surface of the pad;

a first pair of spaced apart conductive traces running across opposite ends of the first sensor layer in a first direction such that a first resistance between the opposite ends of the first sensor layer connects the first pair of conductive traces;

a second sensor layer;

a second pair of spaced apart conductive traces running across opposite ends of the second sensor layer in a second direction generally perpendicular to the first direction such that a second resistance between the opposite ends of the second sensor layer connects the second pair of conductive traces;

the second sensor layer being disposed beneath the first sensor layer such that the first and second sensor layers come into contact at a contact point when an object asserts a pressure on the touch surface of the pad, wherein the contact point is connected to each conductive trace by a variable pressure resistance associated with the first and second sensor layers and variable position resistances of the first and second resistances, wherein the variable pressure resistance varies inversely as a function of the pressure asserted and the variable position resistances vary proportionally as a function of the distance of the contact point from the conductive traces;

a first pair of timing capacitors each connected to a respective one of the first pair of conductive traces;

a second pair of timing capacitors each connected to a respective one of the second pair of conductive traces; and

a microprocessor operative with the timing capacitors, wherein the microprocessor controls and monitors charging time of the timing capacitors to determine the position and asserted pressure of the object on the touch surface of the pad.

16. The touchpad of claim 15 wherein:

the charging time of a timing capacitor is a function of the variable pressure resistance and the variable position resistance connecting the contact point to the one of the conductive traces that the timing capacitor is connected.

17. A touchpad assembly for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad assembly, the touchpad assembly comprising:

a pad having a touch surface and a bottom surface;

an X position sensor layer disposed adjacent the bottom surface of the pad, the X position sensor layer having a pair of spaced apart X conductive traces running across opposite ends of the X sensor layer along a Y direction such that a resistance RX between the opposite ends of the X sensor layer connects the pair of X conductive traces;

a Y position sensor layer having a pair of spaced apart Y conductive traces running across opposite ends of the Y sensor layer along an X direction generally perpendicular to the Y direction such that a resistance RY between the opposite ends of the Y sensor layer connects the pair of Y conductive traces, wherein the Y sensor layer is disposed beneath the X sensor layer such that the X and Y sensor layers come into contact at a contact point when an object asserts a pressure on the touch surface of the pad, wherein the contact point is connected to each conductive trace by a variable pressure resistance RZ associated with the X and Y sensor layers and variable position resistances of the X and Y resistances, wherein the variable pressure resistance RZ varies inversely as a function of the pressure asserted and the variable position resistances vary proportionally as a function of the distance of the contact point from the conductive traces;

a first pair of timing capacitors each connected to a respective one of the pair of X conductive traces;

a second pair of timing capacitors each connected to a respective one of the pair of Y conductive traces; and

a microprocessor operative with the timing capacitors, wherein the microprocessor controls and monitors charging time of the timing capacitors to determine the position and asserted pressure of the object on the touch surface of the pad.

18. A method for providing a signal to a computer representative of a position and asserted pressure of an object touching a touchpad having X and Y position and Z pressure sensitive sensor layers, wherein the X and Y sensor layers come into contact at a contact point when the object touches the touchpad, the method comprising:

providing a pair of spaced apart X conductive traces running across opposite ends of the X sensor layer along a Y direction such that a resistance RX between the opposite ends of the X sensor layer connects the pair of X conductive traces;

providing a pair of spaced apart Y conductive traces running across opposite ends of the Y sensor layer along an X direction generally perpendicular to the Y direction such that a resistance RY between the opposite ends of the Y sensor layer connects the pair of Y conductive traces;

driving the X conductive traces to a given voltage so that current flows from the contact point through a variable pressure resistance RZ across variable position resistances to the pair of Y conductive traces;

determining the position of the object along a Y direction on the Y sensor layer as a function of the current flowing from the contact point to the pair of Y conductive traces, wherein the current varies as a function of the variable pressure resistance RZ and the variable position resistances connecting the pair of Y conductive traces to the contact point;

driving the Y conductive traces to a given voltage so that current flows from the contact point through a variable pressure resistance RZ across variable position resistances to the pair of X conductive traces;

determining the position of the object along an X direction on the X sensor layer as a function of the current flowing from the contact point to the pair of X conductive traces, wherein the current varies as a function of the variable pressure resistance RZ and the variable position resistances connecting the pair of X conductive traces to the contact point; and

determining the Z pressure of the object touching the touchpad from the currents flowing from the contact point to the pairs of X and Y conductive traces.

19. The method of claim 18 wherein:

determining the position of the object along a Y direction on the Y sensor layer as a function of the current flowing from the contact point to the pair of Y conductive traces comprises determining the time required for the current to charge a pair of timing capacitors connected to respective ones of the pair of Y conductive traces.

20. The method of claim 18 wherein:

determining the position of the object along an X direction on the X sensor layer as a function of the current flowing from the contact point to the pair of X conductive traces comprises determining the time required for the current to charge a pair of timing capacitors connected to respective ones of the pair of X conductive traces.