Input device based on frustrated total internal reflection

• US 20040252091A1
• Filed: 06/14/2003
• Published: 12/16/2004
• Est. Priority Date: 06/14/2003
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Ma, Hongshen, Paradiso, Joseph A.
• Granted Patent: US 7,432,893 B2
• Time in Patent Office: Days
• US Class Current: 345/87
• 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

Abstract

A touch panel in which two or more light sensors emit light into a transparent panel at an angle to sustain transmission through the panel by total internal reflection. The transmitted light is detected at an array of light detection positions around the periphery of the panel opposite to each light source. When an object contact the surface of the panel, light transmitted along the pathway from a given source past the contact point to one of the detection points is attenuated by the frustrated total internal reflection (FTIR) effect. Each contact causes two or more intersecting light beams having known end points to be attenuated, enabling a connected processor to determine the position and size of the contact area.

Claims

1. Apparatus for detecting the location of an object comprising, in combination,

a transparent panel defining two opposing surfaces and having an index of refraction greater than air,

a light detector optically coupled to said panel for detecting light transmitted within said transparent panel at a plurality of spaced apart detection points on one of said surfaces,

a first light source optically coupled to said panel for transmitting light into said panel at an angle so that light from a first position propagates by internal reflection within said panel to a first set of said spaced apart detection points,

a second light source optically coupled to said panel for transmitting light into said panel at an angle so that light from a second position propagates by internal reflection within said panel to a second set of said spaced apart detection points, and

a data processor connected to said light detector for processing signals indicating changes in the light intensity at individual ones of said first and second sets of detection points to produce an output indication which specifies one or more locations on said surfaces where the presence of an adjacent object has caused a change in the internal reflection characteristics of said panel.

2. Apparatus for detecting the location of an object as set forth in claim 1 wherein said adjacent object is in physical contact with said panel at said one or more locations on said surfaces.

3. Apparatus for detecting the location of an object as set forth in claim 1 wherein both said first light source and said second light source are diode lasers.

4. Apparatus for detecting the location of an object as set forth in claim 1 wherein light from said first light source and from said second light source are both coupled to said panel by a prism having a light receiving surface and a light transmitting surface in contact with said panel.

5. Apparatus for detecting the location of an object as set forth in claim 1 wherein said light detector comprises a plurality of semiconductor light sensors each of which is optically coupled to said panel at one of said spaced apart detection points.

6. Apparatus for detecting the location of an object as set forth in claim 1 wherein said illumination source includes means for modulating the light from said first light source and from second light source with an identifying characteristic indicative of the source from which it is emitted, and wherein said light detector includes means responsive to the modulation of the received light at each of said detection points for determining the source from which said received light was emitted.

7. Apparatus for detecting the location of an object as set forth in claim 6 wherein said identifying characteristic is the timing of said modulation.

8. Apparatus for detecting the location of an object as set forth in claim 7 wherein said first light source and said second light source are turned on and off at different times and wherein said light detector determines the source from which light is received at one of said detection points by the time when said light is received.

9. Apparatus for detecting the location of an object as set forth in claim 1 wherein said plurality of spaced-apart detection points are positioned around the periphery of said panel.

10. Apparatus for detecting the location of an object as set forth in claim 1 wherein optical sensors are positioned at each of said detection points.

11. Apparatus for detecting the location of an object as set forth in claim 10 wherein said optical sensors are connected in a ring configuration to supply data identifying each of said detectors and changes in the light intensity at said detection points.

12. Apparatus for detecting the location of an object as set forth in claim 1 wherein said transparent panel is positioned to overlay a display screen which displays computer generated content which is produced in part in response to said output indication form said data processor.

13. Apparatus for detecting the location of an object as set forth in claim 1 wherein said first light source and said second light source are light emitting diodes.

14. Apparatus for detecting the location of an object as set forth in claim 1 wherein said transparent panel is a store window.

15. A touch sensitive device for determining the relative location of a point of contact between an object and a surface comprising, in combination,

a transparent panel defining said surface,

two or more light sources for emit light into said transparent panel at an angle to sustain transmission through said panel by total internal reflection,

sensing means for determining the intensity of light received at each of an array of light detection positions around the periphery of said panel, and

means coupled to said sensing mean for identifying the attenuation of light transmitted along each one of plural intersecting light pathways, each of said pathways extending from an identified one of said light sources past said point of contact to an identified one of said light detection positions,

processing means for processing data identifying said plural intersecting pathways for determining the location of said point of contact.

16. A touch sensitive device for determining the relative location of a point of contact between an object and a surface as set forth in claim 15 wherein each given one of said light sources emits light that is modulated to identify said given source.

17. A touch sensitive device for determining the relative location of a point of contact between an object and a surface as set forth in claim 15 wherein said transparent panel is substantially rectangular and wherein said light detection positions are located along the periphery of said panel opposite to said light sources.

18. A touch sensitive device for determining the relative location of a point of contact between an object and a surface as set forth in claim 15 wherein said light sources are diode lasers.

19. A touch sensitive device for determining the relative location of a point of contact between an object and a surface as set forth in claim 15 wherein said light sources are light emitting diodes.

20. A touch sensitive device for determining the relative location of a point of contact between an object and a surface as set forth in claim 15 wherein said light sources are turned on and off at different times and wherein said light detector determines the source from which light is received at one of said detection points by the time when said light is received.