Optical Touchscreen with Improved Illumination

• US 20090058833A1
• Filed: 08/29/2008
• Published: 03/05/2009
• Est. Priority Date: 08/30/2007
• Status: Active Grant

• Current Assignee: Smart Technologies ULC (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Next Holdings Ltd. (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Newton, John
• Granted Patent: US 8,432,377 B2
• Time in Patent Office: Days
• US Class Current: 345/175
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen

Abstract

In an optical touch display system, light from a primary source can be retroreflected to a detector in the absence of an object in the detection area. When an object is present, its position can be triangulated based on the direction of its shadows at the detectors. Accuracy can be improved with a secondary light source positioned off-axis from the primary light sources so that minimal light from the secondary source is retroreflected to the detectors. Instead, when an object is present, light from the secondary source may be reflected directly from the object. Each detector signal representing light due to the primary light source can be corrected to remove light reflected directly from the object based on identifying and removing a signal component representing light from the secondary light source. In some embodiments, this is facilitated by phasing the primary and secondary light sources.

Claims

1. A touch detection system, comprising:

a light detection system having an optical center;

a retroreflector positioned along at least one edge of a touch surface in a touch area;

a primary illumination system configured to emit light across the touch surface so that at least some of the light from the primary illumination system is retroreflected to the light detection system in the absence of an object in the touch area; and

a secondary illumination system configured to emit light across the touch surface so that, in the absence of an object in the touch area, less light from the secondary illumination system is retroreflected to the detection system than from the primary illumination system;

wherein the light detection system is configured to detect a pattern of light received by the light detection system from the touch area.

2. The touch detection system set forth in claim 1, wherein:

the primary illumination system is positioned remote from the retroreflector and emits light in a fan-shaped pattern having an apex, the apex of the fan from the primary illumination system aligned with the optical center of the detection system; and

the secondary illumination system is positioned remote from the retroreflector and configured to emit light across the touch surface in a fan-shaped pattern having an apex, the apex of the fan from the secondary illumination system not aligned with the optical center of the detection system.

3. The touch detection system set forth in claim 1, wherein the light detection system and primary illumination system are incorporated into a single optical unit and the system comprises two of the optical units, each optical unit positioned remote from the retroreflector and each other.

4. The touch detection system set forth in claim 3, further comprising at least one computing device interfaced with the optical units and secondary illumination system, the at least one computing device configured to determine a position at which an object has interfered with light traveling across the touch surface based on evaluating patterns of detected light.

5. The touch detection system set forth in claim 3, wherein, for each optical unit, the at least one computing device is configured to:

identify a detected pattern representing light that ultimately originated from a primary illumination system; and

identify a detected pattern representing light that ultimately originated from the secondary illumination system.

6. The touch detection system set forth in claim 5, wherein the at least one computing device is configured to identify a patterns of light based on the time the pattern was detected relative to the time at which the primary and secondary illumination systems were emitting light.

7. The touch detection system set forth in claim 4, wherein, the at least one computing device is configured to determine the position at which an object has interfered with light traveling across the touch surface by subtracting the detected pattern representing light that ultimately originated from the secondary illumination system from the detected pattern representing light that ultimately originated from the primary illumination system.

8. The touch detection system set forth in claim 1, wherein the primary illumination system comprises a plurality of light sources configured to mimic the light emission of a point source.

9. A method of detecting the position of an object in a touch area, the method comprising:

emitting light in a primary pattern towards one or more edges defining a touch area of a touch surface, the primary pattern emitted so that, in the absence of an object in the touch area, at least some of the light will be retroreflected to a detection system;

emitting light in a secondary pattern across the touch surface, the secondary pattern emitted so that, in the absence of an object in the touch area, at least some of the light from the secondary pattern will not be retroreflected to the detection system;

detecting light received by the detection system and generating a detected light signal;

adjusting the detected light signal to yield a corrected light signal based on the intensity of detected light that ultimately originated from the secondary pattern; and

determining, from the corrected light signal, if an object is interfering with the transmission of light in the touch area and a location of the object relative to the touch area.

10. The method set forth in claim 9, wherein adjusting the detected light signal comprises subtracting a detected light signal representing light ultimately originating in the secondary pattern from a detected light signal representing light ultimately originating in the primary pattern.

11. The method set forth in claim 9, wherein, for at least part of a time a primary pattern is emitted, a secondary pattern is not emitted.

12. The method set forth in claim 9, wherein determining the location of the object relative to the touch area comprises:

identifying the direction of a shadow cast by the object at first and second detector locations; and

triangulating the location of the object based on the direction of the shadow relative to each detector and the spatial arrangement of the first and second detector locations.

13. The method set forth in claim 9, wherein the step of emitting light in a primary pattern comprises emitting light in a primary pattern from a plurality of primary sources, each source associated with a respective detection system so that, in the absence of an object in the touch area, at least some of the light from each source will be retroreflected its associated detection system.

14. A computer system configured to be interfaced with a touch detection system, the computer system comprising at least one computing device configured to:

direct a primary illumination source and a secondary illumination source to emit light across a touch surface having a touch area;

receive, from each of at least two detectors, data representing a pattern of light received from the touch area by each detector;

perform a correction operation on the data representing each pattern of received light; and

based on the data resulting from the correction operation, determine a location of an object relative to the touch area.

15. The computer system set forth in claim 14, wherein the correction operation comprises removing a component of light representative of light directly reflected from an object in the touch area.

16. The computer system set forth in claim 14, wherein the at least one computing device is configured to direct the primary illumination source and secondary illumination source to emit light in a phased manner.

17. The computer system set forth in claim 16, wherein the at least one computing device is configured to:

separate (a) a pattern of light returned from the touch area while the primary illumination source is emitting light, and (b) a pattern of light returned from the touch area while the secondary illumination source is emitting light; and

in performing a correction operation, subtract pattern (b) from pattern (a).