WO2020236064A1

WO2020236064A1 - Touch-sensing apparatus with two frame elements

Info

Publication number: WO2020236064A1
Application number: PCT/SE2020/050482
Authority: WO
Inventors: Håkan Bergström; Tomas Svensson; Thomas Craven-Bartle
Original assignee: Flatfrog Laboratories Ab
Priority date: 2019-05-17
Filing date: 2020-05-11
Publication date: 2020-11-26

Abstract

A touch sensing apparatus is disclosed, comprising a panel that defines a touch surface extending in a plane having a normal axis, a plurality of emitters 5 and detectors arranged along a perimeter of the panel, wherein the plurality of emitters and detectors are fixed to a first frame element extending along the perimeter, a second frame element mounted to the first frame element and extending along said perimeter, wherein the second frame element comprises first and second light directing surfaces, wherein the emitters are arranged to 0 emit light and the first and second light directing surfaces are arranged to receive the light and direct the light across the touch surface substantially parallel to the touch surface.

Description

TOUCH-SENSING APPARATUS WITH TWO FRAME ELEMENTS

Technical Field

The present invention pertains to touch-sensing apparatus that operate by propagating light above a panel. More specifically, it pertains to optical and mechanical solutions for controlling and tailoring the light paths above the panel via fully or partially randomized refraction, reflection or scattering.

Background Art

In one category of touch-sensitive panels known as‘above surface optical touch systems’, a set of optical emitters are arranged around the periphery of a touch surface to emit light that is reflected to travel and propagate above the touch surface. A set of light detectors are also arranged around the periphery of the touch surface to receive light from the set of emitters from above the touch surface. I.e. a grid of intersecting light paths are created above the touch surface, also referred to as scanlines. An object that touches the touch surface will attenuate the light on one or more scanlines of the light and cause a change in the light received by one or more of the detectors. The location (coordinates), shape or area of the object may be determined by analyzing the received light at the detectors. Optical and mechanical characteristics of the touch-sensitive apparatus affects the scattering of the light between the emitters/detectors and the touch surface, and the accordingly the detected touch signals. For example, variations in the alignment of the opto-mechanical components affects the detection process which may lead to a sub-optimal touch detection

performance. Factors such as signal-to-noise ratio, detection accuracy, resolution, the presence of artefacts etc, in the touch detection process may be affected. While prior art systems aim to improve upon these factors, e.g. the detection accuracy, there is often an associated compromise in terms of having to incorporate more complex and expensive opto-mechanical modifications to the touch system. This typically results in a less compact touch system, and a more complicated manufacturing process, being more expensive. To reduce system cost, it may be desirable to minimize the number of electro-optical components. Some prior art systems rely on precise alignment of the various components of the touch sensing apparatus such as the light emitters- and detectors for improved control of the performance. Such systems may however be cumbersome to reliably implement due to the small tolerances with respect to the alignment of the components. Such precise alignment may be difficult to achieve in mass production.

Summary

An objective is to at least partly overcome one or more of the above identified limitations of the prior art.

One objective is to provide a touch-sensitive apparatus which provides for minimizing the effect of misaligned opto-mechanical components thereof, to improve the accuracy and resolution of the touch detection, while providing for a touch sensing apparatus which is robust and easy to assemble.

One or more of these objectives, and other objectives that may appear from the description below, are at least partly achieved by means of touch- sensitive apparatuses according to the independent claims, embodiments thereof being defined by the dependent claims.

According to a first aspect, a touch sensing apparatus is provided, comprising a panel that defines a touch surface extending in a plane having a normal axis, a plurality of emitters and detectors arranged along a perimeter of the panel, wherein the plurality of emitters and detectors are fixed to a first frame element extending along the perimeter, a second frame element mounted to the first frame element and extending along said perimeter, wherein the second frame element comprises first and second light directing surfaces, wherein the emitters are arranged to emit light and the first and second light directing surfaces are arranged to receive the light and direct the light across the touch surface substantially parallel to the touch surface.

Some examples of the disclosure provide for a touch sensing apparatus that has a better signal-to-noise ratio of the detected light.

Some examples of the disclosure provide for a touch-sensing apparatus with improved resolution and detection accuracy of small objects. Some examples of the disclosure provide for a touch-sensing apparatus with a more uniform coverage of scanlines across the touch surface.

Some examples of the disclosure provide for a touch-sensing apparatus with less detection artifacts.

Some examples of the disclosure provide for a more compact touch sensing apparatus.

Some examples of the disclosure provide for a touch sensing apparatus that is less costly to manufacture.

Some examples of the disclosure provide for a touch sensing apparatus that is more reliable to use.

Some examples of the disclosure provide for a more robust touch sensing apparatus.

Some examples of the disclosure provide for a touch sensing apparatus which can accommodate larger variations in the alignment of the opto mechanical components thereof while maintaining high touch detection accuracy and resolution.

Still other objectives, features, aspects and advantages of the present disclosure will appear from the following detailed description, from the attached claims as well as from the drawings.

It should be emphasized that the term“comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Brief Description of Drawings

These and other aspects, features and advantages of which examples of the invention are capable of will be apparent and elucidated from the following description of examples of the present invention, reference being made to the accompanying drawings, in which;

Fig. 1a is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure;

Fig. 1 b is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure;

Fig. 1c is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure;

Fig. 1d is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure;

Fig. 2a is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure;

Fig. 2b is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure;

Fig. 3a is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure;

Fig. 3b is a schematic illustration, in a cross-sectional side view, of a touch-sensing apparatus, according to one example of the disclosure; and

Figs. 4a-b are schematic illustrations of light paths reflected by a frame element having first and second light directing surfaces where the angle of the frame element is varied.

Detailed Description of Example Embodiments

In the following, embodiments of the present invention will be presented for a specific example of a touch-sensitive apparatus. Throughout the description, the same reference numerals are used to identify corresponding elements.

Fig. 1a is a schematic illustration of a touch-sensing apparatus 100 comprising a panel 101 that defines a touch surface 102 extending in a plane 103 having a normal axis 104. The panel 101 is a light transmissive panel in one example. The touch-sensing apparatus 100 comprises a plurality of emitters 105 and detectors 106 arranged along a perimeter 107 of the panel 101. Fig. 1a shows only an emitter 105 for clarity of presentation, while Fig. 1d illustrates how light is transmitted from an emitter 105 to a detector 106 across the touch surface 102. The plurality of emitters 105 and detectors 106 are fixed to a first frame element 108 extending along the perimeter 107. The emitters 105 and detectors 106 thus have a substantially fixed position relative the first frame element 108. The emitters 105 and detectors 106 may be mounted to a PCT or substrate 117 which is fixed to the first frame element 108. The substrate 117 may be fixed to the first frame element 108 by screws, pins, clasps, clips, clamps, adhesives, or any other fixation element. The substrate 117 may be arranged in a groove 118 of the first frame element 108, which may provide for a facilitated assembly and an interlocking effect of the substrate 117 into the first frame element 108. Fig. 1a shows a spacing between the substrate 117 and the groove 118 for a facilitated distinguishing of the different

component, and it should be understood that substrate 117 may fit tightly into the groove 118. Additional fixation elements, such as exemplified above, may additionally be arranged to fix the position of the substrate 117 and the emitters 105/detectors 106 mounted thereon relative the first frame element 108. The substrate 117 may be mounted with an angle relative the panel 101 as exemplified in Figs. 1a-b. The substrate 117 may also be mounted essentially in parallel with the plane 103 in which the panel 101 extends, as shown in the example of Fig. 1c. Arranging the substrate 117 essentially in parallel with the panel 101 provides for minimizing the width of the touch sensing apparatus 100 in a direction perpendicular to the plane 103, i.e. along the normal axis 104. A more compact touch sensing apparatus 100 may thus be provided. It should be understood however that the substrate 117 may be arranged with varying angles relative the panel 101 for also maximizing the amount of light 112 reflected towards the touch surface 102.

The touch sensing apparatus 100 comprises a second frame element 109. The second frame element 109 is mounted to the first frame element 108, e.g. by screws (as exemplified in Fig. 1a), pins, clasps, clips, clamps, or any other fixation element, during assembly of the touch sensing apparatus 100. The second frame element 109 extends along the perimeter 107 of the panel 101. The second frame element 109 comprises first and second light directing surfaces 110, 111. The emitters 105 are arranged to emit light 112. The first and second light directing surfaces 110, 111 , are arranged to receive the light 112 and direct the light across the touch surface 102 substantially parallel to the touch surface 102. Fig. 1a shows an example of a path of such light 112, as it is reflected by the first and second light directing surfaces 110, 111 , to be directed in parallel with the touch surface 102. Attenuation of the light 112 e.g. by an object touching the touch surface 102 provides for the detection of the touch position as described above. Having the emitter 105 fixed to a first frame element 108 and two light reflecting surfaces, i.e. the aforementioned first and second light directing surfaces 110, 111 , arranged at the second frame element 109 to direct the light to the touch surface 102 provides for accommodating a relative displacement or movement between the first and second frame elements 108, 109, while maintaining the reflected light parallel with the touch surface 102. A displacement or misalignment between the first and second frame elements 108, 109, caused e.g. during manufacturing when the first and second frame elements 108, 109, are mounted together, may thus be effectively mitigated. Figs. 4a-b show a schematic representation of an emitter 105 mounted to a first frame element 108, and first and second light directing surfaces 110, 111 , of a second frame element 109. Fig. 4b shows a

displacement of the second frame element 109 relative the first frame element 108 with an angle (v) from the default vertical position in Fig. 4a. The direction of the light 112 being reflected from the second light directing surface 111 is unaffected by the angling of second frame element 109 relative the first frame element 108, when comparing Figs. 4a-b. I.e. the horizontal reflection of the light 112 from the second light directing surface 111 is sustained. The change in direction of the light reflected by the first light directing surface 110, when tilted an angle (v), is thus effectively cancelled out by the corresponding tilt of the second light directing surface 111 with the angle (v). I.e. the increase in the incident angle of the light 112 on the first light directing surface 110, relative its normal (N), produces a corresponding decrease of the incident angle on the second light directing surface 111 , relative its normal (N’). The schematic illustration in Figs. 4a-b shows an exaugurated angle (v), but it should be understood that the illustrated principle applies to the touch sensing apparatus 100, thus allowing for compensating any off-set in the default positioning of the first frame element 108 relative the second frame element 109. Figs. 2a-b and 3a-b illustrate further examples where the second frame element 109 has been off-set with an angle (v) relative the first frame element 108, as will be described further below. In each case, the light 112 is reflected parallel with the touch surface 102, as the reflection at the two light directing surfaces 110, 111 , of the second frame element 109 cancels out the shift in the direction of light reflection at the displacement angle (v) as explained above. Manufacturing may thus be facilitated, as tolerances may be more readily complied with. Alignment issues between the first and second frame elements 108, 109, can be minimized and compensated. Mass production of the touch sensitive apparatus may thus be facilitated and less costly.

The first and second light directing surfaces 110, 111 , may be arranged at opposite sides of the panel 101 , as shown in the example of Fig. 1a. This provides for compact touch sensing apparatus 100. The first light directing surface 110 may be arranged below the panel 101 and the second light directing surface 111 may be arranged above the panel 101 , at the touch surface 102.

A normal (N) of the first light directing surface 110 may be perpendicular to a normal (N’) of the second light directing surface 111 , as schematically illustrated in Figs. 4a-b. This provides for an effective cancellation of any misalignment (v) between the first and second frame elements 108, 109, of the touch sensing apparatus 100.

The light 112 may be reflected between the first and second light directing surfaces 110, 111 , and a third light reflecting surface 113 on the first frame element 108, as illustrated in Figs. 1a-b, 2a, 3a. This may provide for a compact touch sensing apparatus 100 as the maximum dimension in a direction 104’ perpendicular to the normal 104, along the periphery 107, may be reduced when the path of the light 112 is folded by an additional reflection at the third light reflecting surface 113. I.e. the emitters 105 and/or detectors 106 may be placed closer to the panel sides 120, and with a minimal interference with further display elements 122 arranged under the panel 101. It is conceivable however that in some applications the emitter 105 and/or detectors 106 are arranged to emit/receive light directly to/from the first light reflective surface 110, as exemplified in Figs. 2b, 3b.

The third light directing surface 113 may comprises a diffusive light scattering element 113. The diffusive light scattering element 113 effectively acts as a light source for diffusively emitted light. This provides for increasing the width of the scanlines across the touch surface 102 and improved detection of small objects. The distance between the diffusive light scattering element 113 and the light directing surfaces 110, 111 , may be maximized so that diffusively scattered light may spread over a wider angle and thereby increasing the width of the scanlines further. This provides for improved detection of small objects, particularly at the touch surface 102 closer to the edges 120 of the panel 101. Figs. 1 b-c show examples where the separation between the diffusive light scattering element 113 and the first light directing surface 110 has been increased, compared to the example in Fig. 1a. Different examples of diffusively scattering elements 113 are described further below.

The emitters 105 may thus be arranged to emit the light 112 onto the third light reflecting surface 113. It is conceivable that further light reflective surfaces may be arranged in the light path between the emitters 105/detectors 106 and the touch surface 102. Any plurality of diffusively reflective surfaces 113 may be arranged along such light path to optimize the scanline width and the minimize light loss. The first light directing surface 110 and/or the second light directing surface 111 may comprise specularly reflective surfaces. Having a diffusive light scattering element 113 arranged in the path of the light 112 provides for an optimized coverage of light in the plane 103 of the touch surface 102. The position and characteristics of the diffusive light scattering element 113 in relation to the emitters 105, detectors 106, and the panel 101 may be varied for optimization of the performance of the touch-sensing apparatus 100 to various applications. Further variations are conceivable within the scope of the present disclosure while providing for the advantageous benefits as generally described herein. The described examples refer primarily to aforementioned elements in relation to the emitters 105, to make the presentation clear, although it should be understood that the corresponding arrangements may also apply to the detectors 106. Different variations of the diffusive light scattering element 108 have been described further below.

The emitters may emit light along an optical axis 114 forming an acute angle (a) with the normal axis 104 of the panel 101 , as schematically illustrated in Fig. 2a. This allows for a compact arrangement of the emitters 105 along the perimeter 107 while providing for emitting light onto the third light directing element 113 of the first frame element 108 and subsequent reflection on first and second light directing elements 110, 111 , on the second frame element 109.

A section 115 of the second frame element 109 extending between the first and second light directing surfaces 110, 111 , may be rigid so that a displacement angle (v) of the first light directing surface 110 relative the normal axis 104 produces a corresponding displacement angle (v) of the second light directing surface 111 relative the normal axis 104. This provides for an effective compensation for any displacement angle (v) between the first and second frame elements 108, 109. The light 112 may thus be accurately reflected in parallel with the touch surface 102 despite misalignment as explained above.

The aforementioned section 115, extending between the first and second light directing surfaces 110, 111 , may be separated from the first frame element 108 with a gap 116, as exemplified in Figs. 1 b-c, so that the first and second light directing surfaces 110, 111 , are movable relative the first frame element

108 with said displacement angle (v). Hence, having a gap 116 separating the first and second frame elements 108, 109, may provide for minimizing any transfer of force to the first frame element 108 from the second frame element 109, in case the latter would be exposed to a force. The second frame element

109 may thus be deflected with the displacement angle (v) with a minimized influence on the first frame element 108.

The first light directing surface 110 may accordingly be arranged to receive the emitted light 112 from the emitter 105 and direct said light 112 to the second light directing surface 111. The second light directing surface 111 reflects the light in parallel with the touch surface 102 while the first and second light directing surfaces 110, 111 , may be displaced with the displacement angle (v) relative the normal axis 104.

The panel 101 comprises a rear surface 119, opposite the touch surface 102, and panel sides 120 extending between the touch surface 102 and the rear surface 119. The first and second light directing surfaces 110, 111 , may be arranged within the panel sides 120, along a direction 104’ perpendicular to the normal axis 104, to receive light from the emitters 105, or to direct light to the detectors 106, through the panel 101. Figs. 1a-c and 2a-b show examples where the first and second light directing surfaces 110, 111 , are arranged to direct the light 112 through the panel 101. This provides for further reducing the dimensions of the touch sensing apparatus 100 in a direction 104’ perpendicular to the normal axis 104, which may be desirable in some applications where the amount of space in this direction restricted.

The first and second light directing surfaces 110, 111 , may be arranged outside the panel sides 120, along a direction 104’ perpendicular to the normal axis 104, to receive light from the emitters 105, or to direct light to the detectors 106, around the panel sides 120, as schematically illustrated in Figs. 3a-b.

Directing the light 112 around the panel 101 provides for minimizing reflection losses and maximizing the amount of light available for the touch detection process.

As shown in the examples of Figs. 1a-c, 2a-b, 3a-b, the emitters 105, and detectors 106, are arranged opposite the rear surface 119 of the panel 101 for a compact optical arrangement. It is conceivable however that in some examples the emitters 105 and/or the detectors 106 are arranged at least outside or at least partly outside the panel sides 120, in a direction 104’ perpendicular to the normal axis 104.

A support element 121 may be arranged between the panel sides 120 and the second frame element 109, as exemplified in Fig. 1a, to provide for a stabilizing function between the second frame element 109 and panel 101.

A width (wi) of the of the first light directing surface 110 may be wider than a width (W2) of the of the second light directing surface 111 , as schematically illustrated in Figs. 1 b-c. This provides for an improved compensation for any misalignment between the first and second frame elements 108, 109.

A width (W3) of the of the third light directing surface 113 may be wider than a width (wi ) of the of the first light directing surface 110, as schematically illustrated in Figs. 1 b-c. This provides for a further improved compensation for any misalignment between the first and second frame elements 108, 109.

The wavelength of the light 112 may be preferably above 850 nm, such as 940 nm for increasing the reflection. The amount of light available for the touch detection may thus be increased.

The second light directing surface 111 above the touch surface 102 has a normal axis. In one example it is desirable to minimize the angle between the normal axis of the second light directing surface 111 and the light received from the first light directing surface 110. This provides for increasing the intensity of the light reflected to the touch surface 102. In one example it is desirable to minimize the angle between the normal axis of the second light directing surface 111 and the light reflected to the touch surface 102 (the horizontal direction of the light above the touch surface 102 in e.g. Fig. 1a). This provides for further increasing the intensity of the light reflected to the touch surface 102.

The first and second frame elements 108, 109, may be manufactured with the same tool so that manufacturing errors may also be compensated with the first and second light directing surfaces 110, 111. The first and second light directing surfaces 110, 111 , may be formed by milling of mirrored surfaces with such tool. A diamond milling tool may be used, such as a 45 degree diamond fly cutting tool.

The second light directing surface 111 may comprise a diffusive light scattering element.

As mentioned, the third light directing element 113 may comprise a diffusive light scattering element 113. Further examples of diffusive light scattering elements 113 will now be described.

The diffusive light scattering element 113 may be formed from a grooved surface, wherein the grooves generally run vertically or be substantially randomized. The groove density is preferably greater than 10 per mm in a horizontal plane. Optionally, the groove depth is up to 10 microns. Preferably, the average groove width is less than 2 microns. The grooves forming the diffusive light scattering element 113 can be formed by scratching or brushing of the surface. The diffusive light scattering element 113 may be formed from a surface of the first frame element 108 directly. Frame element 108 may be an extruded profile component or, alternatively, frame element 108 is made from brushed sheet metal. Preferably, frame element 108 is formed from anodized metal, such as anodized aluminum. The same may apply to the second frame element 109. Grooves for diffusively reflecting the light may be formed from scratching or brushing the anodized layer of the aluminum. In one embodiment, the anodization is a reflective type. In one example, the anodized metal, e.g. anodized aluminium, is cosmetically black in the visible spectral range, but diffusively light scattering in the near infrared range, e.g. wavelengths above 800 nm. It may be particularly advantageous to use wavelengths above 940 nm where many anodized materials start to reflect significantly (e.g. around 50%). A diffusive light scattering element 113 may be arranged at, or in, the surface receiving the emitted light 112 from the emitters 105. It can also be

implemented by distributing scattering particles (e.g. T1O2) in the bulk of at least part of the frame element 108.

The diffusive light scattering element 113 may be configured as an essentially ideal diffuse reflector, also known as a Lambertian or near- Lambertian diffuser, which generates equal luminance in all directions in a hemisphere surrounding the diffusive light scattering element. Many inherently diffusing materials form a near-Lambertian diffuser. In an alternative, the diffusive light scattering element 108 may be a so-called engineered diffuser with well-defined light scattering properties. This provides for a controlled light management and tailoring of the light scattering abilities. A film with groove-like or other undulating structures may be dimensioned to optimize light scattering at particular angles. The diffusive light scattering element 113 may comprise a holographic diffuser. In a variant, the engineered diffuser is tailored to promote diffuse reflection into certain directions in the surrounding hemisphere, in particular to angles that provides for the desired propagation of light above and across the touch surface 102.

The diffusive light scattering element may be configured to exhibit at least 50% diffuse reflection, and preferably at least 90% diffuse reflection.

The diffusive light scattering element 113 may be implemented as a coating, layer or film applied by e.g. by anodization, painting, spraying, lamination, gluing, etc. In one example, the scattering element 1 13 is implemented as matte white paint or ink. In order to achieve a high diffuse reflectivity, it may be preferable for the paint/ink to contain pigments with high refractive index. One such pigment is T1O2, which has a refractive index n=2.8. The diffusive light scattering element 1 13 may comprise a material of varying refractive index. It may also be desirable, e.g. to reduce Fresnel losses, for the refractive index of the paint filler and/or the paint vehicle to match the refractive index of the material on which surface it is applied. The properties of the paint may be further improved by use of EVOQUE™ Pre-Composite Polymer Technology provided by the Dow Chemical Company. There are many other coating materials for use as a diffuser that are commercially available, e.g. the fluoropolymer Spectralon, polyurethane enamel, barium-sulphate-based paints or solutions, granular PTFE, microporous polyester, GORE® Diffuse Reflector Product, Makrofol® polycarbonate films provided by the company Bayer AG, etc.

Alternatively, the diffusive light scattering element 1 13 may be

implemented as a flat or sheet-like device, e.g. the above-mentioned

engineered diffuser, diffuser film, or white paper which is attached by e.g. an adhesive. According to other alternatives, the diffusive light scattering element 1 13 may be implemented as a semi-randomized (non-periodic) micro-structure on an external surface possibly in combination with an overlying coating of reflective material.

A micro-structure may be provided on such external surface and/or an internal surface by etching, embossing, molding, abrasive blasting, scratching, brushing etc. The diffusive light scattering element 113 may comprise pockets of air along such internal surface that may be formed during a molding procedure. In another alternative, the diffusive light scattering element 1 13 may be light transmissive (e.g. a light transmissive diffusing material or a light transmissive engineered diffuser) and covered with a coating of reflective material at an exterior surface. Another example of a diffusive light scattering element 113 is a reflective coating provided on a rough surface.

The diffusive light scattering element 113 may comprise lenticular lenses or diffraction grating structures. Lenticular lens structures may be incorporated into a film. The diffusive light scattering element 113 may comprise various periodical structures, such as sinusoidal corrugations provided onto internal surfaces and/or external surfaces. The period length may be in the range of between 0.1mm-1 mm. The periodical structure can be aligned to achieve scattering in the desired direction.

Hence, as described, the diffusive light scattering element 113 may comprise; white- or colored paint, white- or colored paper, Spectralon, a light transmissive diffusing material covered by a reflective material, diffusive polymer or metal, an engineered diffuser, a reflective semi-random micro structure, in-molded air pockets or film of diffusive material, different engineered films including e.g. lenticular lenses, or other micro lens structures or grating structures. The diffusive light scattering element 113 preferably has low NIR absorption.

In a variation of any of the above embodiments wherein the diffusive light scattering element provides a reflector surface, the diffusive light scattering element may be provided with no or insignificant specular component. This may be achieved by using either a matte diffuser film in air, an internal reflective bulk diffusor or a bulk transmissive diffusor. This allows effective scanline

broadening by avoiding the narrow, super-imposed specular scanline usually resulting from a diffusor interface having a specular component, and providing only a broad, diffused scanline profile. By removing the super-imposed specular scanline from the touch signal, the system can more easily use the broad, diffused scanline profile. Preferably, the diffusive light scattering element has a specular component of less than 1 %, and even more preferably, less than 0.1 %. Alternatively, where the specular component is greater than 0.1%, the diffusive light scattering element is preferably configured with surface

roughness to reduce glossiness. E.g. micro structured.

The touch sensing apparatus may further comprise a shielding layer (not shown). The shielding layer may define an opaque frame around the perimeter of the panel 101. The shielding layer may increase the efficiency in providing the diffusively reflected light in the desired direction, e.g. by recycling the portion of the light that is diffusively reflected by the diffusive light scattering element 113 in a direction away from the panel 101.

The panel 101 may be made of glass, poly(methyl methacrylate) (PMMA) or polycarbonates (PC). The panel 101 may be designed to be overlaid on or integrated into a display device or monitor (not shown). It is conceivable that the panel 101 does not need to be light transmissive, i.e. in case the output of the touch does not need to be presented through panel 101 , via the mentioned display device, but instead displayed on another external display or

communicated to any other device, processor, memory etc.

As used herein, the emitters 105 may be any type of device capable of emitting radiation in a desired wavelength range, for example a diode laser, a VCSEL (vertical-cavity surface-emitting laser), an LED (light-emitting diode), an incandescent lamp, a halogen lamp, etc. The emitter 105 may also be formed by the end of an optical fiber. The emitters 105 may generate light in any wavelength range. The following examples presume that the light is generated in the infrared (IR), i.e. at wavelengths above about 750 nm. Analogously, the detectors 106 may be any device capable of converting light (in the same wavelength range) into an electrical signal, such as a photo-detector, a CCD device, a CMOS device, etc.

With respect to the discussion above, "diffuse reflection" refers to reflection of light from a surface such that an incident ray is reflected at many angles rather than at just one angle as in "specular reflection". Thus, a diffusively reflecting element will, when illuminated, emit light by reflection over a large solid angle at each location on the element. The diffuse reflection is also known as "scattering". The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope and spirit of the invention, which is defined and limited only by the appended patent claims.

For example, the specific arrangement of emitters and detectors as illustrated and discussed in the foregoing is merely given as an example. The inventive coupling structure is useful in any touch-sensing system that operates by transmitting light, generated by a number of emitters, across a panel and detecting, at a number of detectors, a change in the received light caused by an interaction with the transmitted light at the point of touch.

Claims

1. A touch sensing apparatus (100) comprising

a panel (101 ) that defines a touch surface (102) extending in a plane (103) having a normal axis (104),

a plurality of emitters (105) and detectors (106) arranged along a perimeter (107) of the panel, wherein the plurality of emitters and detectors are fixed to a first frame element (108) extending along the perimeter,

a second frame element (109) mounted to the first frame element and extending along said perimeter, wherein the second frame element comprises first and second light directing surfaces (110, 111),

wherein the emitters are arranged to emit light (112) and the first and second light directing surfaces are arranged to receive the light and direct the light across the touch surface substantially parallel to the touch surface.

2. A touch sensing apparatus according to claim 1 , wherein the first and second light directing surfaces are arranged at opposite sides of the panel.

3. A touch sensing apparatus according to claim 1 or 2, wherein a normal (N) of the first light directing surface (110) is perpendicular to a normal (N’) of the second light directing surface (111 ).

4. A touch sensing apparatus according to any of claims 1 - 3, wherein said light is reflected between the first and second light directing surfaces and a third light reflecting surface (113) on the first frame element.

5. A touch sensing apparatus according to claim 4, wherein the third light directing surface (113) comprises a diffusive light scattering element.

6. A touch sensing apparatus according to claim 4 or 5, wherein the emitters are arranged to emit said light onto the third light reflecting surface.

7. A touch sensing apparatus according to any of claims 4 - 6, wherein the emitters emit light along an optical axis (114) forming an acute angle (a) with the normal axis (104) of the panel.

8. A touch sensing apparatus according to any of claims 1 - 7, wherein a section (115) of the second frame element (109) extending between the first and second light directing surfaces is rigid so that a displacement angle (v) of the first light directing surface relative the normal axis (104) produces a corresponding displacement angle (v) of the second light directing surface relative the normal axis (104).

9. A touch sensing apparatus according to claim 8, wherein said section, extending between the first and second light directing surfaces, is separated from the first frame element (108) with a gap (116) so that the first and second light directing surfaces are movable relative the first frame element with said displacement angle (v).

10. A touch sensing apparatus according to claim 8 or 9, wherein the first light directing surface (110) is arranged to receive the emitted light from the emitter and direct said light to the second light directing surface (111 ), wherein the second light directing surface reflects the light in parallel with the touch surface while the first and second light directing surfaces are displaced with said displacement angle (v) relative the normal axis (104).

11. A touch sensing apparatus according to any of claims 1 - 10, wherein the emitters and detectors are mounted on a substrate (117) being arranged in a groove (118) of the first frame element (108).

12. A touch sensing apparatus according to any of claims 1 - 11 , wherein the panel comprises a rear surface (119), opposite the touch surface, and panel sides (120) extending between the touch surface and the rear surface, wherein the first and second light directing surfaces are arranged within the panel sides, along a direction (104’) perpendicular to the normal axis (104), to receive light from the emitters, or to direct light to the detectors, through the panel.

13. A touch sensing apparatus according to any of claims 1 - 11 , wherein the panel comprises a rear surface (119), opposite the touch surface, and panel sides (120) extending between the touch surface and the rear surface,

wherein the first and second light directing surfaces are arranged outside the panel sides, along a direction (104’) perpendicular to the normal axis (104), to receive light from the emitters, or to direct light to the detectors, around the panel sides.

14. A touch sensing apparatus according to any of claims 1 - 13, wherein the panel comprises a rear surface (119), opposite the touch surface, and panel sides (120) extending between the touch surface and the rear surface,

wherein the emitters and/or the detectors are arranged at least partly opposite the rear surface and within the panel sides, in a direction (104’) perpendicular to the normal axis (104).

15. A touch sensing apparatus according to any of claims 1 - 14, wherein the panel comprises a rear surface (119), opposite the touch surface, and panel sides (120) extending between the touch surface and the rear surface,

wherein a support element (121 ) is arranged between the panel sides and the second frame element (109).

16. A touch sensing apparatus according to any of claims 1 - 15, wherein a width (wi ) of the of the first light directing surface (110) is wider than a width (W2) of the of the second light directing surface (111 ).

17. A touch sensing apparatus according to claim 4, wherein a width (W₃) of the of the third light directing surface (113) is wider than a width (wi) of the of the first light directing surface (110).

18. A touch sensing apparatus according to any of claims 1 - 17, wherein the first light directing surface (110) and/or second light directing surface (111 ) comprises a specularly reflective surface.

19. A touch sensing apparatus according to any of claims 1 - 17, wherein the second light directing surface (111 ) comprises a diffusive light scattering element.