Determining the location of one or more objects on a touch surface

1. A method in a touch-sensing apparatus, said apparatus comprising a light transmissive panel that defines a touch surface and an opposite surface, a light source arrangement for providing sheets of light inside the panel, wherein each sheet comprises light that propagates by internal reflection between the touch surface and the opposite surface-from one or more incoupling points to a set of outcoupling points, said apparatus further comprising a light sensor arrangement for generating one or more output signals that represent light reaching the outcoupling points, wherein the touch-sensing apparatus is configured such that an object touching the touch surface locally attenuates at least two sheets of light, said method comprising:

identifying, in said output signal(s), a set of signal profiles originating from said object,

determining at least part of an attenuated light path across the panel based on each signal profile, and

identifying the position of the object on the touch surface based on the thus-determined attenuated light paths,

wherein said determining comprises applying a width function which is representative of a dependence of signal profile width on distance to the incoupling point due to light scattering caused by a diffusing structure of at least one of the touch surface and the opposite surface,

wherein at least one of the sheets is generated in the form of a diverging beam originating at the one or more incoupling points, and

wherein said determining includes, for each signal profile associated with said at least one sheet generated in the form of a diverging beam,

identifying outcoupling points corresponding to limits of the signal profile,

reconstructing limiting rays of the attenuated light path by geometrically retracing the thus-identified outcoupling points to a respective incoupling point, and

modifying the distance between the limiting rays by applying said width function, thereby determining the attenuated light path.

2. The method of claim 1 , wherein the width function represents the factual width of the object given the detected signal profile, as a function of distance to the incoupling point.

3. The method of claim 1 , wherein at least one of the sheets is generated by sweeping an essentially collimated beam across a set of incoupling points.

4. The method of claim 1 , wherein said determining further comprises, for each signal profile:

reconstructing a center ray of the attenuated light path by geometrically retracing a center point of the signal profile to one of said incoupling points,

determining a signal width of the signal profile, and

determining an object width at one or more candidate positions along the center ray by applying said width function, thereby determining part of said attenuated light path.

5. The method of claim 4 , wherein said one or more candidate positions are determined by triangulation using a set of center rays that are reconstructed from said set of signal profiles.

6. A method in a touch-sensing apparatus, said apparatus comprising a light transmissive panel that defines a touch surface and an opposite surface, a light source arrangement for providing sheets of light inside the panel, wherein each sheet comprises light that propagates by internal reflection between the touch surface and the opposite surface-from one or more incoupling points to a set of outcoupling points, said apparatus further comprising a light sensor arrangement for generating one or more output signals that represent light reaching the outcoupling points, wherein the touch-sensing apparatus is configured such that an object touching the touch surface locally attenuates at least two sheets of light, said method comprising:

identifying, in said output signal(s), a set of signal profiles originating from said object,

determining at least part of an attenuated light path across the panel based on each signal profile,

generating a set of candidate positions based on the attenuated light paths, and

identifying the position of the object on the touch surface based on the generated set of candidate positions,

wherein said determining comprises applying a width function which is representative of a dependence of signal profile width on distance to the incoupling point due to light scattering caused by at least one of the touch surface and the opposite surface, and

wherein said identifying the positions includes,

calculating a shape measure and/or an area measure for at least one candidate position based on the thus-determined attenuated light paths, and

validating said at least one candidate position based on the shape measure and/or area measure.

7. The method of claim 6 , wherein at least one of the sheets is generated in the form of a diverging beam originating at the one or more incoupling points.

8. A tangible computer readable medium comprising data processing system executable instructions which, when executed on a data-processing system, causes the data-processing system to carry out the method of claim 6 .

9. The method of claim 6 , wherein the width function represents the factual width of the object given the detected signal profile, as a function of distance to the incoupling point.

10. The method of claim 6 , wherein at least one of the sheets is generated by sweeping an essentially collimated beam across a set of incoupling points.

11. A device for determining a position of an object on a touch surface included in a touch-sensing apparatus, said touch-sensing apparatus comprising a light transmissive panel that defines the touch surface and an opposite surface, a light source arrangement for providing sheets of light inside the panel, wherein each sheet comprises light that propagates by internal reflection between the touch surface and the opposite surface from one or more incoupling points to a set of outcoupling points, a light sensor arrangement for generating one or more output signals that represent light reaching the outcoupling points, wherein the touch-sensing apparatus is configured such that an object touching the touch surface locally attenuates at least two sheets of light, said device comprising:

an element for identifying, in said output signal(s), a set of signal profiles originating from the object,

an element for determining at least part of an attenuated light path across the panel based on each signal profile, and

an element for identifying the position of the object on the touch surface based on the thus-determined attenuated light paths,

wherein said element for determining is configured to apply a width function which is representative of a dependence of signal profile width on distance to the incoupling point due to light scattering caused by a diffusing structure of at least one of the touch surface and the opposite surface,

wherein at least one of the sheets is generated in the form of a diverging beam originating at the one or more incoupling points, and

wherein said element for determining is configured to, for each signal profile associated with said at least one sheet generated in the form of a diverging beam,

identify outcoupling points corresponding to limits of the signal profile,

reconstruct limiting rays of the attenuated light path by geometrically retracing the thus-identified outcoupling points to a respective incoupling point, and

modify the distance between the limiting rays by applying said width function, thereby determining the attenuated light path.

12. A touch-sensing apparatus, comprising:

a device for determining a position according to claim 11 .

13. The device of claim 11 , wherein the width function represents the factual width of the object given the detected signal profile, as a function of distance to the incoupling point.

14. The device of claim 11 , wherein at least one of the sheets is generated by sweeping an essentially collimated beam across a set of incoupling points.

15. The device of claim 11 , wherein said element for determining is configured to, for each signal profile:

reconstruct a center ray of the attenuated light path by geometrically retracing a center point of the signal profile to one of said incoupling points,

determine a signal width of the signal profile, and

determine an object width at one or more candidate positions along the center ray by applying said width function, thereby determining part of said attenuated light path.

16. The device of claim 15 , further comprising an element for determining said one or more candidate positions by triangulation using a set of center rays that are reconstructed from said set of signal profiles.

17. A device for determining a position of an object on a touch surface included in a touch-sensing apparatus, said touch-sensing apparatus comprising a light transmissive panel that defines the touch surface and an opposite surface, a light source arrangement for providing sheets of light inside the panel, wherein each sheet comprises light that propagates by internal reflection between the touch surface and the opposite surface from one or more incoupling points to a set of outcoupling points, a light sensor arrangement for generating one or more output signals that represent light reaching the outcoupling points, wherein the touch-sensing apparatus is configured such that an object touching the touch surface locally attenuates at least two sheets of light, said device comprising:

an element for identifying, in said output signal(s), a set of signal profiles originating from the object,

an element for determining at least part of an attenuated light path across the panel based on each signal profile,

an element for generating a set of candidate positions based on the attenuated light paths across the panel, and

an element for identifying the position of the object on the touch surface based on the generated set of candidate positions,

wherein said element for determining is configured to apply a width function which is representative of a dependence of signal profile width on distance to the incoupling point due to light scattering caused by at least one of the touch surface and the opposite surface, and

wherein said element for identifying the positions is configured to,

calculate a shape measure and/or an area measure for at least one candidate position based on the thus-determined attenuated light paths, and

validate said at least one candidate position based on the shape measure and/or area measure.

18. The device of claim 17 , wherein at least one of the sheets is generated in the form of a diverging beam originating at the one or more incoupling points.

19. The device of claim 17 , wherein the width function represents the factual width of the object given the detected signal profile, as a function of distance to the incoupling point.

20. The device of claim 17 , wherein at least one of the sheets is generated by sweeping an essentially collimated beam across a set of incoupling points.