Robust Optical Touch - Screen Systems And Methods Using A Planar Transparent Sheet

• US 20130135259A1
• Filed: 11/27/2012
• Published: 05/30/2013
• Est. Priority Date: 11/28/2011
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: King, Jeffrey Stapleton, Pikula, Dragan, Walker, Richard Clayton
• Granted Patent: US 9,046,961 B2
• Time in Patent Office: Days
• US Class Current: 345/175
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• CPC Class Codes: G06F 2203/04109 FTIR in optical digitiser, i.e. touch detection by frustrating the total internal reflection within an optical waveguide due to changes of optical properties or deformation at the touch location
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen
• CPC Class Codes: G06F 3/0428 by sensing at the edges of the touch surface the interruption of optical paths, e.g. an illumination plane, parallel to the touch surface which may be virtual sensing beam interruptions in a planar beam grid of an optical touch-screen G06F3/0421

Abstract

An optical touch screen that utilizes a planar transparent sheet and that is configured to determine the position of a touch event on the transparent sheet is disclosed. Light-source elements and light-sensing elements are operably disposed at the transparent sheet perimeter. Light is detected over lines-of-sight between the light-source elements and the light-sensing elements. Attenuated lines-of-sight due to a touch event are determined. Polygons are established by overlapping triangles defined by the limiting lines of sight for each light-sensing element. Polygons with attenuations below the attenuation threshold are eliminated. The centers of the remaining polygons are then determined to establish the locations of the touch events. The systems and methods provide robust detection of multiple touch events.

Claims

1. A method of establishing positions of touch events on a transparent sheet having a perimeter, with light-source elements and light-sensing elements operably disposed adjacent the perimeter, comprising:

a) using the light-sensing elements, measuring intensity values of light from the light-source elements, the light traveling internally within the transparent sheet over lines-of-sight between the light-source elements and the light-sensing elements;

b) determining limiting lines-of-sight for each light-sensing element based on the intensity values as compared to an attenuation threshold;

c) overlapping triangles defined by the limiting lines-of-sight for each light-sensing element to establish one or more polygons; and

d) determining centers of the one or more polygons to establish the touch event positions.

2. The method of claim 1, wherein each polygon has an associated attenuation based on the measured intensity values, and further comprising:

eliminating any polygons whose associated attenuation is below the attenuation threshold.

3. The method according to claim 1, further comprising determining the intensity of the touch event based on a comparison of the detector signal strength to a signal threshold.

4. The method according to claim 1, wherein the transparent sheet is substantially transparent to infrared (IR) light, and wherein the light from the light-source elements comprises an IR wavelength.

5. The method according to claim 4, further comprising filtering the IR light with a band-pass filter disposed adjacent the light-sensing elements, the band-pass filter configured to be substantially opaque to visible light and IR light having an IR wavelength different from the IR light emitted by the light-source elements.

6. The method according to claim 1, further comprising:

generating from the light-sensing elements respective detector signals representative of the intensity values as detected by the light-sensing elements; and

processing the detector signals to determine the limiting lines-of-sight.

7. The method according to claim 6, wherein generating the detector signal includes:

making a first photocurrent measurement with one of the light-sensing elements when the light-source elements are turned off;

making a second photocurrent measurement with the same one of the light-sensing elements when the light-source elements are turned on; and

subtracting the first photocurrent from the second photocurrent.

8. The method according to claim 6, wherein generating the detector signal includes processing the detector signal with an electrical circuit having an amplifier, and wherein the method further includes:

making integrated photocurrent measurements for a fixed total time Δ

T;

breaking the fixed total time Δ

T into N intervals to define N sub-measurements that have corresponding time intervals Δ

T/N;

adding together the N sub-measurements to simulate a single integration; and

dynamically choosing N to avoid overloading the amplifier.

9. The method according to claim 1, wherein the perimeter includes a plurality of corners, and including arranging the light-sensing elements one adjacent each of the plurality of corners.

10. The method of claim 1, wherein there are n light-sensing elements, and further comprising:

determining a first set of the triangles for a first one of the light-sensing elements;

determining a second set of the triangles for a second one of the light-sensing elements;

determining a first set of the polygons from the first and second sets of triangles;

determining a third set of the triangles for a third one of the light-sensing elements and establishing intersections of the third set of triangles with the first set of polygons to form a second set of the polygons; and

repeating the previous step up until the n^th light-sensing element to arrive at a final set of polygons used in act d) to establish the touch event positions.

11. The method of claim 1, wherein determining the centers of one or more polygons comprises for each polygon:

determining attenuation values within the polygon; and

calculating a center-of-mass of the polygon based on the attenuation values within the polygon and identifying the center-of-mass as the polygon center.

12. The method of claim 1, wherein determining the centers of one or more polygons comprises for each polygon:

assuming a constant value for the attenuation within the polygon; and

calculating the geometric center of the polygon as the polygon center.

13. The method of claim 1, wherein the measured intensity values are converted to detector signal strengths by the light-sensing elements, and further comprising:

establishing a baseline measurement of light traveling over the lines-of-sight;

defining a threshold detector signal strength based on the baseline measurement; and

comparing the detector signal strengths associated with the attenuated lines-of-sight to the threshold signal strength to determine whether the touch event occurred.

14. The method of claim 13, further comprising:

adjusting the baseline measurement based on changes in the detector signal strength; and

adjusting the threshold signal strength based on the adjusted baseline measurement.

15. A touch-screen system for sensing a location of one or more touch events, comprising:

a transparent sheet having a perimeter and a top surface where the one or more touch events occur;

a plurality of light-source elements that emit light and that are operably disposed adjacent the perimeter to couple the light into the transparent sheet to travel therein via total internal reflection;

a plurality of light-sensing elements operably disposed adjacent the perimeter to detect the light from the light-sensing elements and in response thereto generate detector signals having a signal strength representative of a detected light intensity, wherein the one or more touch events cause attenuation of the light intensity along at least one of the lines-of-sight corresponding to the select light-sensing element; and

a controller operably coupled to the light-source elements and the light-sensing elements and configured to control the emission of the light from the light-source elements and process the detector signals to;

I. compare the detector signal strength in each light-sensing element to an attenuation threshold to establish a one or more triangles as defined by limiting ones of the attenuated lines-of-sight for the given light-sensing element;

II. establish locations of at least one polygon formed by at least one intersection of the one or more triangles; and

III. calculate a center of the at least one polygon to define locations of corresponding one or more touch events.

16. The system according to claim 15, wherein the controller is further configured to determine the intensity of the touch event based on a comparison of the detector signal strength to a signal threshold.

17. The system according to claim 15, wherein the transparent sheet is substantially transparent to infrared (IR) light, wherein the emitted light from the light sources comprises IR light, and wherein the light-sensing elements are configured to detect the IR light.

18. The system according to claim 15, wherein the perimeter includes a plurality of corners, and wherein the light-sensing elements are disposed one adjacent each of the plurality of corners.

19. The system according to claim 15, further comprising a display unit disposed adjacent the bottom surface of the transparent sheet so that a user views the display unit through the transparent sheet.

20. The system according to claim 15, further comprising band-pass filters disposed one adjacent each of the light-sensing elements, the band-pass filters each configured to be substantially opaque to visible light and IR light having an IR wavelength different from the IR light emitted by the light-source elements.

21. The system according to claim 15, further comprising an electrical circuit operably coupled to one of the light-sensing elements, the electrical circuit being configured to provide a compensating current that reduces or eliminates an interfering current that arises due to interfering illumination.

22. The system according to claim 21, wherein the electrical circuit includes a digital-to-analog converter operably connected to a processor that provides a feedback control signal thereto to vary the compensating current.