TOUCH SENSING APPARATUS AND METHOD OF OPERATING THE SAME

• US 20110227874A1
• Filed: 12/02/2009
• Published: 09/22/2011
• Est. Priority Date: 12/05/2008
• Status: Active Grant

• Current Assignee: FlatFrog Laboratories AB
• Original Assignee: FlatFrog Laboratories AB
• Inventors: Wall, Henrik, Fåhraeus, Christer, Wassvik, Ola, Christiansson, Tomas
• Granted Patent: US 8,581,884 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 3/0325 using a plurality of light emitters or reflectors or a plurality of detectors forming a reference frame from which to derive the orientation of the object, e.g. by triangulation or on the basis of reference deformation in the picked up image
• 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

A touch sensing apparatus is controlled to determine the position of one or more objects (7) that interact with a touch surface (1). The apparatus includes a group of emitters (2) arranged to emit light to illuminate at least part of the touch surface (1), a light detector (4) arranged to receive light from the group of emitters (2), and a processing element (7). Each emitter (2) is controlled to transmit a code by way of the emitted light such that the code identifies the respective emitter (2). The codes may at least partly be transmitted concurrently. The codes may be selected such that a value of an autocorrelation of each code is significantly higher than a value of a cross-correlation between any two codes of different emitters (2). The processing element processes an output signal from the light detector (4) to separate the light received from the individual emitters (2) based on the transmitted codes, and to determine the position of the object/objects (7) based on the light received from the individual emitters (2), e.g. using triangulation or image reconstruction such as an algorithm for transmission tomography.

Claims

1-26. -26. (canceled)

27. A touch sensing apparatus, comprising:

a light transmissive element that defines a touch surface;

a set of emitters arranged around the periphery of the touch surface to emit beams of light into the light transmissive element, wherein the beams of light propagate inside the light transmissive element while illuminating the touch surface such that an object touching the touch surface causes an attenuation of the propagating light, wherein each beam of light diverges in the plane of the touch surface as the beam propagates through the light transmissive element;

a set of light detectors arranged around the periphery of the touch surface to receive light from the set of emitters on a plurality of light paths, wherein each light detector is arranged to receive light from more than one emitter; and

a processing element configured to determine, based on output signals of the light detectors, a light energy value for each light path;

to generate a transmission value for each light path based on the light energy value; and

to operate an image reconstruction algorithm on at least part of the thus-generated transmission values so as to determine the position of the object on the touch surface.

28. The apparatus of claim 27, wherein the image reconstruction algorithm is an algorithm for transmission tomography with a fan beam geometry.

29. The apparatus of claim 27, wherein the processing element is configured to generate the transmission values by dividing the light energy value by a background value.

30. The apparatus of claim 29, wherein the background value represents an energy value for the light path without the object touching the touch surface.

31. The apparatus of claim 30, wherein the background value is pre-set, derived during a separate calibration step, or derived from one or more preceding output signals.

32. The apparatus of claim 29, wherein the processing element is configured to generate the transmission value as a logarithm of the quotient between the light energy value and the background value.

33. The apparatus of claim 27, wherein the processing element is configured to interpolate one of the light energy values and the transmission values of the incoming light paths to each detector, such that all incoming light paths to the detector have the same mutual angle.

34. The apparatus of claim 27, wherein each emitter is controlled to transmit a code by way of the emitted light such that the code identifies the respective emitter, and wherein the processing element is configured to separate, based on the output signals of the light detectors, the light received from individual emitters based on the transmitted codes.

35. The apparatus of claim 27, wherein the image reconstruction algorithm generates a two-dimensional distribution of transmission or attenuation values within the touch surface.

36. A method in a touch sensing apparatus, said touch sensing apparatus comprising a light transmissive element that defines a touch surface, a set of emitters arranged around the periphery of the touch surface to emit beams of light into the light transmissive element, wherein the beams of light propagate inside the light transmissive element while illuminating the touch surface such that an object touching the touch surface causes an attenuation of the propagating light, and wherein each beam of light diverges in the plane of the touch surface as the beam propagates through the light transmissive element, said apparatus further comprising a set of light detectors arranged around the periphery of the touch surface to receive light from the set of emitters on a plurality of light paths and generate a set of output signals that represents the light energy received by each detector, wherein each light detector is arranged to receive light from more than one emitter, said method comprising:

determining, based on the set of output signals, a light energy value for each light path;

generating a transmission value for each light path by dividing the light energy value by a background value; and

operating an image reconstruction algorithm on at least part of the thus-generated transmission values so as to determine the position of the object on the touch surface.

37. A computer-readable medium storing processing instructions that, when executed by a processor, performs the method according to claim 36.

38. The method of claim 36, wherein the image reconstruction algorithm is an algorithm for transmission tomography with a fan beam geometry.

39. The method of claim 36, wherein said generating comprises:

dividing the light energy value by a background value.

40. The method of claim 39, wherein the background value represents an energy value for the light path without the object touching the touch surface.

41. The method of claim 40, wherein the background value is pre-set, derived during a separate calibration step, or derived from one or more preceding output signals.

42. The method of claim 39, wherein said generating comprises:

calculating a logarithm of the quotient between the light energy value and the background value.

43. The method of claim 36, further comprising:

interpolating one of the light energy values and the transmission values of the incoming light paths to each detector, such that all incoming light paths to the detector have the same mutual angle.

44. The method of claim 36, further comprising:

controlling each emitter to transmit a code by way of the emitted light such that the code identifies the respective emitter, and said determining comprises;

separating, based on the output signals of the light detectors, the light received from individual emitters based on the transmitted codes.

45. The method of claim 36, wherein the image reconstruction algorithm generates a two-dimensional distribution of transmission or attenuation values within the touch surface.