Optical touchscreen with improved illumination

• US 8,432,377 B2
• Filed: 08/29/2008
• Issued: 04/30/2013
• 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
• Primary Examiner(s): Pervan, Michael
• Application Number:
  US12/201,463
• Publication Number:
  US 20090058833A1
• Time in Patent Office: 1,705 Days
• Field of Search: 175/18.01, 175/18.03, 175/18.09, 345/173, 345/175
• 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 and configured to detect patterns of light received from a touch area;

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

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

a secondary illumination system configured to emit light across the touch surface so that, in the presence of the object in the touch area at least some of the light ultimately originating from the secondary illumination system is reflected by the object to the light detection system; and

at least one computing device interfaced with the light detection system and configured to determine a position at which the object present in the touch area has interfered with light traveling across the touch surface by;

generating an error signal based on a secondary detected pattern of the light ultimately originating from the secondary illumination system, wherein the error signal is indicative of the object being sufficiently close to the light detection system to cause a variance in a primary detected pattern of the light ultimately originating from the primary illumination system, and

subtracting the intensity of the error signal from the intensity of the primary detected pattern.

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 a first apex, the first apex aligned with the optical center of the light 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 a second apex, the second apex not aligned with the optical center of the light detection system.

3. The touch detection system set forth in claim 1, wherein the light detection system and the primary illumination system are incorporated into a single optical unit and the touch detection system comprises at least 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, wherein, for each optical unit, the at least one computing device is configured to:

identify the primary detected pattern; and

identify the secondary detected pattern.

5. The touch detection system set forth in claim 4, wherein the at least one computing device is configured to identify a light pattern as being either the primary detected pattern or the secondary detected pattern based on the time the light pattern was detected relative to the time at which the primary and secondary illumination systems were emitting light.

6. 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.

7. The touch detection system set forth in claim 1, wherein the primary illumination system and the secondary illumination system are phased such that, for at least part of the time that the secondary illumination system is emitting light, the primary illumination system is not emitting light.

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

emitting light in a primary pattern towards one or more edges defining the touch area of a touch surface, the primary pattern emitted so that, in the absence of the 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 presence of the object in the touch area, at least some of the light from the secondary pattern will be reflected 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 by;

generating an error signal based on a secondary light signal representing light ultimately originating from the secondary pattern, wherein the error signal is indicative of the object being sufficiently close to the light detection system to cause a variance in a primary light signal representing light ultimately originating from the primary pattern, and

subtracting the error signal from the primary light signal; and

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

9. The method set forth in claim 8, wherein, for at least part of a time the secondary pattern is emitted, the primary pattern is not emitted.

10. The method set forth in claim 8, 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.

11. The method set forth in claim 8, wherein emitting light in the 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 the object in the touch area, at least some of the light from each source will be retroreflected to its associated detection system.

12. The method set forth in claim 8, wherein subtracting the error signal from the primary light signal comprises subtracting a secondary pixel value corresponding to the secondary pattern from a primary pixel value corresponding to the primary pattern.

13. The method set forth in claim 8, wherein subtracting the error signal from the primary light signal comprises subtracting a secondary intensity signal corresponding to the secondary pattern from a primary intensity signal corresponding to the primary pattern.

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, wherein the correction operation comprises;

generating an error signal based on a component of light representative of light directly reflected from an object in the touch area, wherein the error signal is indicative of the object being sufficiently close to the light detection system to cause a variance in the pattern of light received from the touch area, and

subtracting the intensity of the error signal from the intensity of a signal representing the pattern of light received from the touch area; and

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

15. 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.

16. The computer system set forth in claim 15, wherein the at least one computing device is configured to:

separate a first pattern of light returned from the touch area while the primary illumination source is emitting light and a second pattern of light returned from the touch area while the secondary illumination source is emitting light; and

in performing a correction operation, subtract the second pattern from the first pattern.

17. The computer system set forth in claim 16, wherein the at least one computing device is configured to, in separating the first pattern and the second pattern, correlate the first pattern to an interval during which the primary illumination source is emitting light and correlate the second pattern to an interval during which the secondary illumination source is emitting light.