Projected capacitive touch detection with touch force detection using self-capacitance and mutual capacitance detection

• US 9,904,417 B2
• Filed: 04/16/2014
• Issued: 02/27/2018
• Est. Priority Date: 04/16/2014
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Hanauer, Jerry, Curtis, Keith E.
• Primary Examiner(s): Lubit, Ryan A
• Application Number:
  US14/254,407
• Publication Number:
  US 20150301642A1
• Time in Patent Office: 1,413 Days
• Field of Search: None
• CPC Class Codes: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position
• CPC Class Codes: G06F 2203/04106 Multi-sensing digitiser, i.e. digitiser using at least two different sensing technologies simultaneously or alternatively, e.g. for detecting pen and finger, for saving power or for improving position detection
• CPC Class Codes: G06F 2203/04111 Cross over in capacitive digitiser, i.e. details of structures for connecting electrodes of the sensing pattern where the connections cross each other, e.g. bridge structures comprising an insulating layer, or vias through substrate
• CPC Class Codes: G06F 3/04142 the force sensing means being located peripherally, e.g. disposed at the corners or at the side of a touch sensing plate
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A force sensing touch sensor comprises a substrate having a plurality of conductive electrode rows and a plurality of conductive electrode columns substantially perpendicular to and over the plurality of conductive electrode rows on a surface of the substrate, and a force sensor at each corner of the substrate. When a touch is applied to the surface of the touch sensor, the capacitance value will change of a capacitor formed by an intersection of an electrode row and column proximate to the location of the touch to the surface of the touch sensor. These force sensors detect total and proportional force on the touch sensor substrate. This force information is then combined with the touch location(s) previously determined, and the individual touch force(s) can then be interpolated with sufficient resolution for three dimensional (3D) gesturing applications.

Claims

1. An apparatus for determining a location of a touch thereto and a force thereof on a touch sensing surface, comprising:

a first plurality of electrodes arranged in a parallel orientation having a first axis, wherein each of the first plurality of electrodes comprises a self capacitance;

a second plurality of electrodes arranged in a parallel orientation having a second axis perpendicular to the first axis, the first plurality of electrodes are located over the second plurality of electrodes and form a plurality of nodes comprising overlapping intersections of the first and second plurality of electrodes, wherein each of the plurality of nodes comprises a mutual capacitance;

a substrate having the first and second plurality of electrodes disposed thereon, wherein the substrate has a plurality of corners;

a plurality of pressure sensors arranged below the substrate and at each corner of the substrate, wherein each pressure sensor receives pressure caused by a touch from a bottom surface of the substrate;

whereby each of the plurality of pressure sensors measures a portion of a force applied to the substrate during a touch thereto, and

a processing system configured to calculate force point (CFP) and a geometric center of mass (CM) from the pressure values measured by the plurality of pressure sensors, wherein the processing device is further configured to determine a vertical movement of the touches when the CFP matches the CM and to determine a rotational movement when the CFP does not match the CM, and to generate gesture commands corresponding to the vertical movement or the rotational movement with regard to a displayed object that corresponds to the touches.

2. The apparatus according to claim 1, wherein the substrate is light transmissive and the first and second plurality of electrodes comprise Indium Tin Oxide (ITO).

3. The apparatus according to claim 1, wherein the substrate is light transmissive and the first and second plurality of electrodes comprise Antimony Tin Oxide (ATO).

4. The apparatus according to claim 1, wherein the substrate comprises four corners.

5. The apparatus according to claim 1, wherein the processing system comprises a microcontroller comprising a digital processor and memory.

6. The apparatus according to claim 5, wherein the microcontroller further comprises a capacitive touch analog front end.

7. The apparatus according to claim 6, wherein the microcontroller further comprises an analog-to-digital converter (ADC) controller.

8. A method for determining a location of a touch thereto and a force thereof on a touch sensing surface, said method comprising the steps of:

providing a first plurality of electrodes arranged in a parallel orientation having a first axis, wherein each of the first plurality of electrodes comprises a self capacitance;

providing a second plurality of electrodes arranged in a parallel orientation having a second axis perpendicular to the first axis, the first plurality of electrodes are located over the second plurality of electrodes and form a plurality of nodes comprising overlapping intersections of the first and second plurality of electrodes, wherein each of the plurality of nodes comprises a mutual capacitance;

providing a substrate having the first and second plurality of electrodes disposed thereon, wherein the substrate has a plurality of corners;

providing a plurality of pressure sensors arranged below the substrate and at each corner of the substrate, wherein each pressure sensor receives pressure caused by a touch from a bottom surface of the substrate;

scanning the first plurality of electrodes for determining values of the self capacitances thereof;

comparing the values of the scanned self capacitances to determine which one of the first plurality of electrodes has the largest value of self capacitance;

scanning the nodes of the one of the first plurality of electrodes having the largest value of self capacitance for determining values of the mutual capacitances of the respective plurality of nodes;

comparing the values of the scanned mutual capacitances of the respective plurality of nodes on the first electrode having the largest value of self capacitance, wherein the node having the largest value of mutual capacitance is a location of a touch on the touch sensing surface; and

determining a force of the touch on the touch sensing surface from pressure values measured by the plurality of pressure sensors by determining a calculated force point (CFP) and a geometric center of mass (CM) from the pressure values, wherein when the CFP matches the CM a vertical movement of the touches is determined and wherein when the CFP does not match the CM a rotational movement of the touches is determined, and wherein gesture commands corresponding to the vertical movement or the rotational movement are performed with regard to a displayed object that corresponds to the touches.

9. The method as recited in claim 8, wherein the self and mutual capacitance values are measured with an analog front end and an analog-to-digital converter (ADC).

10. The method as recited in claim 9, wherein the self and mutual capacitance values are stored in a memory of a digital device.

11. The method as recited in claim 10, wherein a digital processor in the digital device uses the stored self and mutual capacitance values in determining the touch location of the touch and the force applied by the touch to the touch sensing surface at the touch location.

12. The method as recited in claim 8, wherein the step of determining a force of the touch on the touch sensing surface comprises the step of determining a calculated force point (CFP) by adding together the pressure values measured by the plurality of pressure sensors.

13. A method for determining locations of a plurality of touches thereto and a combined force thereof on a touch sensing surface, said method comprising the steps of:

providing a first plurality of electrodes arranged in a parallel orientation having a first axis, wherein each of the first plurality of electrodes comprises a self capacitance;

providing a second plurality of electrodes arranged in a parallel orientation having a second axis perpendicular to the first axis, the first plurality of electrodes are located over the second plurality of electrodes and form a plurality of nodes comprising overlapping intersections of the first and second plurality of electrodes, wherein each of the plurality of nodes comprises a mutual capacitance;

providing a substrate having the first and second plurality of electrodes disposed thereon, wherein the substrate has a plurality of corners;

providing only four pressure sensors arranged below the first and second plurality of electrodes under the substrate and one of the four pressure sensors at each corner of the substrate, wherein each pressure sensor receives pressure caused by a touch from a bottom surface of the substrate;

scanning the first plurality of electrodes for determining values of the self capacitances thereof;

comparing the values of the scanned self capacitances to determine which ones of the first plurality of electrodes have the largest values of self capacitance;

scanning the nodes of the ones of the first plurality of electrodes having the largest values of self capacitance for determining values of the mutual capacitances of the respective plurality of nodes;

comparing the values of the scanned mutual capacitances of the respective plurality of nodes on the first electrodes having the largest values of self capacitance, wherein the nodes having the largest values of mutual capacitance are locations of touches on the touch sensing surface; and

determining from pressure values measured by the plurality of pressure sensors;

a calculated force point (CFP); and

a geometric center of mass (CM);

comparing the calculated force point with the center of mass to determine an action to be performed, wherein when the CFP matches the CM a vertical movement of the touches is determined and wherein when the CFP does not match the CM a rotational movement of the touches is determined, and wherein gesture commands corresponding to the vertical movement or the rotational movement are performed with regard to a displayed object that corresponds to the touches.

14. The method as recited in claim 13, wherein the self and mutual capacitance values are measured with an analog front end and an analog-to-digital converter (ADC).

15. The method as recited in claim 14, wherein the self and mutual capacitance values are stored in a memory of a digital device.

16. The method as recited in claim 15, wherein a digital processor in the digital device uses the stored self and mutual capacitance values in determining the touch locations of the touches and the respective forces applied by the touches to the touch sensing surface at the touch locations.

17. The method as recited in claim 13, comprising the steps of:

determining the calculated force point (CFP) by adding together the pressure values measured by the plurality of pressure sensors; and

determining the center of mass (CM) by using the touch locations and the pressure values measured by the plurality of pressure sensors.

18. The method as recited in claim 17, further comprising the steps of:

determining an X-offset, XR, of the CFP with respect to the geometric CM; and

determining a Y-offset, YR, of the CFP with respect to the geometric CM.

19. The method as recited in claim 18, wherein the step of determining the X offset, XR, comprises the step of solving XR=(((F1+F3)*(−

W/2))+((F2+F4)*(W/2))/FR, wherein W is a width of a face of the touch sensing surface, and XR is an X offset from the CM to the CFP.

20. The method as recited in claim 18, wherein the step of determining the Y offset, YR, comprises the step of solving YR=(((F1+F2)*(−

H/2))+((F3+F4)*(H/2))/FR, wherein H is a height of a face of the touch sensing surface, and YR is a Y offset from the CM to the CFP.

21. A system for determining locations of touches thereto and a combined force thereof on a touch sensing surface, said system comprising:

a first plurality of electrodes arranged in a parallel orientation having a first axis, wherein each of the first plurality of electrodes comprises a self capacitance;

a second plurality of electrodes arranged in a parallel orientation having a second axis perpendicular to the first axis, the first plurality of electrodes are located over the second plurality of electrodes and form a plurality of nodes comprising overlapping intersections of the first and second plurality of electrodes, wherein each of the plurality of nodes comprises a mutual capacitance;

a substrate having the first and second plurality of electrodes disposed thereon, wherein the substrate has a plurality of corners;

four pressure sensors arranged below the first and second plurality of electrodes and under the substrate, wherein one of the four pressure sensors is arranged at each corner of the substrate, wherein each pressure sensor receives pressure caused by a touch from a bottom surface of the substrate;

a digital processor and memory, wherein digital outputs of the digital processor are coupled to the first and second plurality of electrodes;

an analog front end coupled to the first and second plurality of electrodes and the plurality of pressure sensors;

an analog-to-digital converter (ADC) having at least one digital output coupled to the digital processor;

wherein the analog front end, ADC, and processor are configured;

to measure values of the self capacitances for each of the first plurality of electrodes,

to store the values of the measured self capacitances in the memory;

to measure values of the mutual capacitances of the nodes of at least one of the first electrodes having at least one of the largest values of self capacitance,

to store the values of the measured mutual capacitances in the memory;

to measure and store values of pressures by the plurality of pressure sensors in the memory;

to use the stored self and mutual capacitance values for determining locations of the touches, and

to calculate a force point (CFP) and a center of mass (CM) on the touch sensing surface from the pressure values measured by the plurality of pressure sensors and to compare the calculated force point and the geometric center of mass to determine an action to be performed, wherein when the CFP matches the CM a vertical movement of the touches is determined and wherein when the CFP does not match the CM a rotational movement of the touches is determined, and wherein gesture commands corresponding to the vertical movement or the rotational movement are performed with regard to a displayed object that corresponds to the touches.

22. The system as recited in claim 21, wherein the digital processor, memory, analog front end and ADC are provided by a digital device.

23. The system as recited in claim 21, wherein the digital processor, memory, analog front end and ADC are provided by at least one digital device.

24. The system as recited in claim 22, wherein the digital device comprises a microcontroller.

25. The system as recited in claim 22, wherein the digital device is selected from the group consisting of a microprocessor, a digital signal processor, an application specific integrated circuit (ASIC) and a programmable logic array (PLA).

26. The system as recited in claim 21, wherein the substrate is light transmissive and the first and second plurality of electrodes comprise Indium Tin Oxide (ITO).

27. The system as recited in claim 21, wherein the substrate is light transmissive and the first and second plurality of electrodes comprise Antimony Tin Oxide (ATO).

28. The system according to claim 21, wherein the substrate comprises four corners.