Patent Description:
In one category of touch-sensitive apparatuses a set of optical emitters are arranged around the perimeter of a touch surface of a panel to emit light that is reflected to propagate across the touch surface. A set of light detectors are also arranged around the perimeter of the touch surface to receive light from the set of emitters from the touch surface. a grid of intersecting light paths are created across 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 coordinates, shape or area of the object may be determined by analysing the received light at the detectors. In one category of touch-sensitive apparatuses the light is reflected to propagate above the touch surface, i.e. the intersecting light paths extend across the panel above the touch surface. In some applications it is desirable to utilize the pressure of the interaction object, such as a stylus, against the touch surface for controlling the touch interaction. Such control may be desirable both in terms of varying the display of the touch operations on the screen, such as writing or drawing with different shapes of brushes or patterns, and for controlling different operations of a particular touch application. Previous techniques for such touch control typically rely on complex input devices, such as styluses, having various integrated sensors. This increases the complexity and limits the user's choices input devices. This may hinder the development towards highly customizable and intuitive touch systems.

<CIT> discloses a device that includes an electronic display formed with a stackup of layers and an array of optical sensing elements embedded on at least one layer of the stackup or on a chassis of the electronic display and a circuit connected to the optical sensing elements. The circuit is configured to relate output from the optical sensing elements to pressure applied on the electronic display.

<CIT> discloses an optical-touch calibration method and an optical-touch panel are disclosed herein. The optical-touch calibration method is suitable for the optical-touch panel including a projective light source and a line optical sensor.

<CIT> discloses a coordinate detecting apparatus including a light emitting element that is provided in a peripheral portion surrounding a surface of a display and emits a light in a direction parallel to the surface of the display; a light receiving element that is provided in the peripheral portion surrounding the surface of the display and receives the light emitted from the light emitting element.

<CIT> discloses a pressure sensing-based touch panel and display device. The touch panel comprises a touch screen, infrared light emitters arranged below the touch screen and an infrared light receiver. The touch screen is deformed and bent by pressing, infrared light emitted by any infrared light emitter, after being reflected by the touch screen, is received by a corresponding infrared light receiver, and an included angle theta is formed between the infrared light emitted towards the touch screen by the infrared light emitter and a perpendicular line perpendicular to the touch screen.

<CIT> discloses a a pressure induction-based optical realization device.

<CIT> discloses a light-based touch sensitive device, including a housing, a surface encased in the housing, a layer of elastic material above the surface, a plurality of light pulse emitters mounted in the housing, that transmit light pulses through the layer, a plurality of light pulse receivers mounted in the housing, that receive the light pulses transmitted through the layer, and a calculating unit, mounted in the housing and connected to the receivers, that determines a location of a pointer that touches the layer and creates an impression in the layer, based on outputs of the receivers.

<CIT> discloses an optical touch-sensitive device that is able to determine the locations of multiple simultaneous touch events. The optical touch-sensitive device includes multiple emitters and detectors. Each emitter produces optical beams which are received by the detectors. Touch events disturb the optical beams. Touch event templates are used to determine the actual touch events based on which optical beams have been disturbed.

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-sensing apparatus which provides for facilitated user interaction and control of touch response, while keeping the cost of the touch interaction system at a minimum.

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-sensing apparatuses according to the independent claims, embodiments thereof being defined by the dependent claims.

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.

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;.

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> are schematic illustrations, in cross-sectional side-views, of a touch sensing apparatus <NUM> and a panel <NUM> thereof having different positions with respect to a normal <NUM> of a touch surface <NUM> of the panel <NUM>, whereas <FIG> shows a top-down view of a touch sensing apparatus <NUM>. The touch sensing apparatus <NUM> thus comprises a panel <NUM> that defines a touch surface <NUM>. The panel <NUM> may be designed to be overlaid on or integrated into a display device or monitor (not shown). The panel <NUM> may be made of any solid material (or combination of materials) such as glass, poly(methyl methacrylate) (PMMA) and polycarbonates (PC).

The panel <NUM> has a perimeter <NUM>. The touch sensing apparatus <NUM> comprises a plurality of emitters <NUM> arranged along the perimeter <NUM>, as schematically shown in <FIG>. The emitters <NUM> are arranged to emit light <NUM> across the panel <NUM>. The touch sensing apparatus <NUM> further comprises a plurality of detectors <NUM> arranged along the perimeter <NUM>. In use, as the emitters <NUM> emit light <NUM>, the detectors <NUM> are arranged to receive at least part of the emitted light as detection light <NUM>'. The schematic side view in <FIG> shows the emitted light <NUM> being reflected against the touch surface <NUM> as the panel <NUM> has a first shape or position with respect to a normal <NUM> of the touch surface <NUM>. Detectors <NUM> receive at least part of the reflected light, referred to as detection light <NUM>'. <FIG> shows a touch interaction object or touch object <NUM> applying a pressure onto the touch surface <NUM>. The touch object <NUM> may be a user's hand, a stylus or other object the user utilizes to interact with the touch sensing apparatus <NUM>. The pressure applied by the touch object <NUM> deflects the panel <NUM> along the normal <NUM> of the touch surface <NUM>. The amount of deflection of the panel <NUM> is exaggerated in the illustration of <FIG> for a clearer presentation.

The touch sensing apparatus <NUM> is configured to determine, as the touch object <NUM> deflects the panel <NUM> along the normal <NUM> of the touch surface <NUM>, a difference in the received detection light <NUM>' between deflection of the panel <NUM> from a first position (p<NUM>) to a second position (p<NUM>) along the normal <NUM>. The deflection of the panel <NUM> along the normal <NUM> will have effect on the number of reflection paths for the emitted light <NUM> towards the detectors <NUM>. Thus, the amount of received detection light <NUM>' at the detectors <NUM> will be affected by the deflection, i.e. the curvature of the panel <NUM> relative the normal <NUM>. For example, the deflection of the panel <NUM> from the essentially flat shape in <FIG> to the curved shape as schematically illustrated in <FIG>, as the touch object <NUM> applies a force and pressure on the panel <NUM>, increases the number of reflection paths on the touch surface <NUM> towards the detectors <NUM>. The amount of received detection light <NUM>' at the detectors <NUM> increases as a result. Likewise, the amount of detection light <NUM>' decreases as the number of reflection paths of the light is reduced, i.e. when the curvature of the panel <NUM> is reduced, such as moving from the curved shape (<FIG>) to a less curved, or essentially flat shape (<FIG>), relative the normal <NUM>. Thus, the touch sensing apparatus <NUM> is configured to determine the difference in the received detection light <NUM>' as the panel <NUM> moves between positions (p<NUM>) and (p<NUM>), e.g. as shown in <FIG>. As illustrated in <FIG> the light <NUM>, <NUM>', propagates above the touch surface <NUM>, i.e. the intersecting light paths extend across the panel <NUM> above the touch surface <NUM>. The variation in the position and number of reflections on the touch surface <NUM>, as the panel <NUM> moves, as described above, is thus be utilized for detecting differences in the received detection light <NUM>'. Utilizing the reflections paths on the touch surface <NUM>, as opposed to reflection of light inside the panel <NUM>, provides in examples for a more robust and reliable detection of different pressures on the panel <NUM>, as described further below. A more reliable and facilitated detection is provided as complex considerations of how panel deflection would affect light propagation inside the panel <NUM> may be dispensed with. Instead, utilizing the reflections paths on the touch surface <NUM> provides for a direct link between the variation in detection light <NUM>' and the changes in curvature of the touch surface <NUM>, as the panel <NUM> is deflected by applying different pressures. The emitters <NUM> are thus be arranged to emit light <NUM> above the touch surface <NUM>, and the amount of deflection of the panel <NUM> determines an amount and/or direction of reflection of the light <NUM> on the touch surface <NUM>. A difference in the received detection light <NUM>' can thus be detected as the deflection varies. the deflection of the panel <NUM> determines the difference in the received detection light <NUM>'. <FIG> show another example of the panel <NUM> being deflected along the direction of the normal <NUM> as a touch object <NUM> applies a pressure on the panel <NUM>. <FIG> show an example similar to the example discussed above in relation to <FIG>, i.e. the panel <NUM> is deflected between a first position p<NUM> (<FIG>) where the touch object <NUM> does not apply a pressure, and a second position p<NUM> (<FIG>). The amount of deflection or relative distance between the first and second positions p<NUM>, p<NUM>, is indicated as Δd<NUM> in this example.

<FIG> show an example where the pressure applied by the touch object <NUM> onto touch surface <NUM> and panel <NUM> increases from a first pressure value (<FIG>) to a second pressure value (<FIG>) being higher than the first pressure value. The first position p<NUM> indicated in <FIG> corresponds to the second position p<NUM> in <FIG>, and the second position p<NUM> in <FIG> corresponds to the additional deflection of the panel <NUM> along the normal <NUM> as the pressure is increased further. The amount of deflection or relative distance between the first and second positions p<NUM>, p<NUM>, is indicated as Δd<NUM> in this example. As described above, the touch sensing apparatus <NUM> is configured to determine the difference in the received detection light <NUM>' as the panel <NUM> moves between positions (p<NUM>) and (p<NUM>), e.g. as shown in <FIG>, and/or as shown in <FIG> where the pressure on the panel <NUM> and the associated variation in the amount of deflection of the panel <NUM> varies, e.g., as a user applies more or less pressure on the touch surface <NUM> while maintaining contact with the touch surface <NUM>.

The touch sensing apparatus <NUM> is configured to determine a pressure of the touch object <NUM> against the touch surface <NUM> based on the determined difference in received detection light <NUM>'. Thus, based on the increase or decrease in the amount of received detection light <NUM>', the touch sensing apparatus <NUM> determines the pressure applied onto the panel <NUM> and the touch surface <NUM> thereof. For example, as discussed above, detecting an increase in the amount of received detection light <NUM>' at the detectors <NUM> can be associated with an increased amount of deflection of the panel <NUM> along the normal direction <NUM>, e.g. an increase in Δd<NUM> or Δd<NUM>, and an increase in the amount of pressure applied by the touch object <NUM> on the panel <NUM>. Likewise, detecting a decrease in the amount of received detection light <NUM>' at the detectors <NUM> can be associated with a decreased amount of deflection of the panel <NUM> and a decrease in the amount of pressure applied by the touch object <NUM> on the panel <NUM>. The touch sensing apparatus <NUM> may thus be configured to control the touch interaction based on the determined variation in pressure. The user may accordingly use any touch object <NUM> for touch interaction since the pressure onto the touch surface <NUM> is determined based on the deflection of the panel <NUM>, independently of the type of touch object <NUM>. The user may thus use passive touch objects <NUM>, such as the user's hand, or any passive stylus or brush, without the need of pressure sensors in the touch object <NUM> itself. This provides for a more intuitive touch interaction and a greater freedom for the user to use individual styluses or brushes.

An example is illustrated in <FIG>, showing diagrams of a varying force being applied onto the touch surface <NUM> by a touch object (<FIG>), and pressure values determined from the resulting deflection of the panel <NUM> (<FIG>). The force applied by the touch object onto the touch surface <NUM> is measured by a force sensor connected to the touch object. The applied force progressively increases over a time period before being removed from the touch surface <NUM>, as shown in the diagram of <FIG>. Pressure values are continuously determined based on detected differences in the received detection light <NUM>' upon deflection of the panel <NUM> by the applied force, as shown in the diagram of <FIG>. The pressure values have been normalized and scaled to the corresponding minimum and maximum force values from the force sensor on the touch object. The calculated pressure or force values follows the force measured by the force sensor closely over time, both in terms of absolute values and the derivative, i.e. the responsiveness over time to the variations of the applied force. An accurate and responsive detection of pressure on the touch surface <NUM> is provided.

Detecting the pressure as described above provides for a less complex touch sensing apparatus <NUM>. In addition to the mentioned benefits of utilizing passive touch objects <NUM>, there is further no need to implement pressure sensors along the panel <NUM> itself. Determining the pressure based on the detected difference in the received detection light <NUM>' thus provides for a robust and facilitated control of touch input based on touch pressure while allowing for a less complex and costly touch sensing apparatus <NUM>. A facilitated control and modelling of the touch response is also provided due to the improved pressure detection, e.g. when modelling the influence of the amount of pressure applied when writing or drawing on the touch surface, such as modelling the dynamics and visual touch response of a brush when the pressure on the brush is varied. The touch sensing apparatus <NUM> may allow producing a display of a virtual brush with a more accurate brush-like shape in such example.

The touch sensing apparatus <NUM> may accordingly be configured to output a control signal to display a visual output depending on the pressure, such as a shape of a brush which dynamically varies in size, shape and/or direction depending on the amount of pressure applied. The graphical rendering of strokes from a brush or pen may thus be modified depending on the pressure value. Thickness, opacity or other graphical aspect can be modified. Alternatively, or in addition, the touch sensing apparatus <NUM> may be configured to control the touch sensing apparatus <NUM> based on the pressure. A user may for example use a "knocking gesture", as a short highpressure interaction gesture, which is distinguished from a softer touch on the touch surface <NUM> to input a control command. Such gesture can be assigned to functions in the application such as moving elements in and out of the background, (un)pinning or (un)locking elements that was knocked on, trigger a "force" that will move graphical elements towards or away from the knock position, trigging a global effect such as "new document", "close document" or other global command. It is conceivable that various other sequences of pressure values can be assigned a special meaning in different touch applications, such as double-clicking by two rapid increases in pressure allows trigging an event without lifting the pen from the surface.

The touch sensing apparatus <NUM> may be configured to determine the pressure continuously based on detected differences in the received detection light <NUM>' upon deflection of the panel <NUM>. For example, as illustrated in <FIG>, and in <FIG>, the variation in the received detection light <NUM>' may be continuously determined as a user applies a varying pressure onto the touch surface <NUM>, causing the panel <NUM> to deflect between varying positions along the normal <NUM>. A continuously increase or decrease in the pressure may thus be determined based on the increasing or decreasing amount of received detection light <NUM>'. This provides for an enhanced touch input interaction with the touch sensing apparatus <NUM>.

The touch sensing apparatus <NUM> may be configured to determine the pressure based on a difference between received detection light <NUM>' upon deflection of the panel <NUM> and a reference background signal of detection light <NUM>'. For example, the reference background signal can be determined when the panel <NUM> has the position shown in <FIG> or <FIG>, when the touch object <NUM> does not apply a pressure onto the panel <NUM>. As mentioned above in relation to e.g. <FIG>, it is also conceivable that the variation or difference in the detection light <NUM>' is determined for any change in the position of the panel <NUM> along the normal <NUM>, i.e. for any deflection of the panel <NUM> as the user interacts with the touch surface <NUM>, to determine an associated variation in the pressure. The touch interaction may then be controlled based on the pressure variation as elucidated above.

The pressure may be determined as being proportional to the aforementioned difference in the detection light <NUM>' being received at the detectors <NUM>. the pressure may be determined as increasing as the distance Δd<NUM> or Δd<NUM> in the example of <FIG> increases. Vice versa, a decrease in Δd<NUM> or Δd<NUM> may be determined as an associated decrease in the pressure, since the curvature of the panel <NUM> and the number of reflection paths of the light towards the detectors <NUM> decreases. This provides for a less complex, yet effective and robust estimate of the pressure on the panel <NUM>.

For a given difference in the received detection light <NUM>' between a first emitter and a first detector, the pressure may be determined as inversely proportional to a length (Δed) between the first emitter and the first detector. For example, turning to <FIG>, the length between the emitter denoted with reference numeral <NUM> and the detector denoted with reference numeral <NUM> may be regarded as the aforementioned length Δed. In one example, a difference (v) is detected in the received detection light <NUM>' at detector <NUM>. Considering different lengths (Δed) between the current emitter and detector <NUM>, <NUM>, for a given thickness of the panel <NUM> along normal <NUM>, it may be determined that for shorter lengths (Δed) the panel <NUM> deflects less, compared to longer lengths (Δed) for the same pressure. as the length Δed increases the deflection (Δd<NUM> or Δd<NUM>) will increase, given a certain pressure at a location (x,y) on the touch surface <NUM>. Thus, for detected difference (v), the associated pressure (P) may be determined as inversely proportional to the length (Δed), i.e. P ∝ <NUM>/Δed. as Δed increases less pressure is required to deflect the panel <NUM> a certain distance (Δd<NUM> or Δd<NUM>). Vice versa, for shorter lengths Δed, a greater pressure is needed to deflect the panel <NUM> a corresponding distance (Δd<NUM> or Δd<NUM>). This provides for a robust and effective method to take into account the varying lengths between the different light paths between the emitters and detectors <NUM>, <NUM>, for determining the pressure. The light paths, or scan lines, may be represented by a signal matrix, with the signal levels of the light from each emitter to each detector. A pressure may thus effectively be determined for each signal level or light path. Accordingly, the pressure may be determined as inversely proportional to each of the associated lengths (Δed) between the emitters and detector pairs in the signal matrix. The estimated pressure may be determined as a mean value of such individual pressure values.

For a given difference in the received detection light <NUM>', between a first emitter <NUM> and a first detector <NUM>, the pressure (P) may be determined as inversely proportional to the length Δl between a position (x,y) of the touch object <NUM> on the touch surface <NUM> and the first emitter <NUM>, or the first detector <NUM>, i.e. P ∝ <NUM>/Δl. For example, if a pressure is applied close to the perimeter <NUM>, i.e. close to the emitter <NUM> or detector <NUM> (thus for a short length Δl), the deflection of the panel <NUM> is less compared to a case where the same pressure would be applied close to the center of the panel <NUM>, i.e. with an increase in the length Δl. Thus, for detected difference (v), the associated pressure may be determined as inversely proportional to the length (Δl). as Δl increases less pressure is required to deflect the panel <NUM> a certain distance (Δd<NUM> or Δd<NUM>). Vice versa, for shorter lengths Δl, a greater pressure is needed to deflect the panel <NUM> a corresponding distance (Δd<NUM> or Δd<NUM>). The pressure may be determined as inversely proportional to each of the associated lengths (Δl) between the emitters and detector pairs in the signal matrix.

The pressure may be determined as proportional to the aforementioned difference (v) divided by Δed*Δl; P(k) = v / (Δed*Δl), where k is the number of scanlines. An estimated pressure may be determined as a mean value of the individual pressure values P(k) of the scanlines.

The length Δl may be chosen as the minimum of; the distance between the position (x,y) of the touch object <NUM> on the touch surface <NUM> and the first emitter <NUM>, and the distance between said position (x,y) and the first detector <NUM>.

The touch sensing apparatus <NUM> may be configured to define a region of interest <NUM> around a position (x,y) of the touch object <NUM> on the touch surface <NUM>. The region of interest <NUM> may be a defined area around a currently determined coordinate (x,y) where the touch object <NUM> contacts the touch surface <NUM>. The coordinate (x,y) is determined based on the attenuation of the light as the touch object touches the touch surface <NUM>, as described in the introductory part of the present disclosure. The touch sensing apparatus <NUM> may be configured to determine the aforementioned difference (v) for light passing through the region of interest <NUM>, between respective pairs of emitters <NUM> and detectors <NUM>. the difference (v) in the received detection light <NUM>' at the detectors <NUM>, as the touch object <NUM> applies a pressure on the panel <NUM>, is determined for scanlines passing through the region of interest <NUM>. The touch sensing apparatus <NUM> may be configured to determine an averaged pressure based on the determined differences (v) for the pairs of emitters and detectors associated with the scanlines passing through the region of interest <NUM>. This provides for a more effective determination of the pressure, as it is not necessary to determine the difference (v) for the entire signal matrix. The amount of deflection of the panel <NUM> along the normal <NUM> can be regarded as being largest around the touch coordinate (x,y) where the pressure is applied.

The touch sensing apparatus <NUM> may be configured to determine a first estimate of a pressure at a touch position (x,y) on the touch surface <NUM>. The touch sensing apparatus <NUM> may be configured to calculate a detection light signal difference (v') based on the first estimate of the pressure. The touch sensing apparatus <NUM> may be configured to solve the pressure by iteratively minimizing a differential between a measured value of the difference (v) in the received detection light <NUM>' and the calculated detection light signal difference (v'). a detection light signal difference (v') is calculated for different candidate pressure values until |v-v'| is minimized and the best candidate for the pressure is obtained. The pressure may be iteratively determined at a plurality of positions (x<NUM>. yn) on the touch surface <NUM>, e.g. when a plurality of pressure points is applied on the touch surface <NUM> by a user's hand or other touch objects <NUM>. The plurality of touch positions (x<NUM>. yn) may be determined by the light attenuation as described in the introductory part of the present disclosure. Thus, the associated pressure (p<NUM>. pn) at the plurality of touch positions (x<NUM>. yn) may be determined iteratively as described above. This determination may be done for each scanline in the signal matrix or for a subset of the scanlines in the region of interest <NUM>. The starting guess for (p<NUM>. Pn) may be based on the last calculated pressure for the respective positions in a previous frame, for contact points that was present in such previous frame. For new pressure point interactions, a typical pressure value is assigned as starting guess. It should be noted that although reference is made to determining a pressure throughout the disclosure, it should be understood that this is analogous to determining a force, in which case a conversion factor is applied to convert between pressure and force values.

The touch sensing apparatus <NUM> may be configured to determine a deflection of the panel <NUM> along the normal <NUM> resulting from the first estimate of the pressure at the touch position (x,y). The touch sensing apparatus <NUM> may be configured to calculate the detection light signal difference (v') resulting from such deflection. The deflection resulting from the different candidates of pressure values may be determined by analytical expressions, for given geometries of the panel <NUM>, and/or by FEM-based numerical methods, and/or by empirically by applying known forces to a particular configuration of the touch sensing apparatus <NUM> and panel <NUM> and storing the parameters of the resulting model. The corresponding deflection resulting from the pressure estimates may thus be determined, as well as the associated detection light signal difference (v') resulting from corresponding shapes of the panel <NUM> for these deflection values. The influence of the deflection and shape of the panel <NUM> on the number of reflection paths of the light <NUM>, <NUM>', towards the detectors <NUM> and resulting detection light signal difference (v') may be determined by different models, analogous to the above discussion, e.g. by analytical, numerical and/or empirical models. Once the detection light signal difference (v') is calculated, the pressure may be iteratively determined by minimizing |v-v'| as described above.

The touch sensing apparatus <NUM> may be configured to determine the detection light signal difference (v') based on a plurality of reference detection light signal differences resulting from a respective plurality of reference pressures on the touch surface <NUM>. The reference detection light signal differences may be determined empirically. The best candidates of the associated reference pressures may thus be identified, which minimizes |v-v'|, to obtain the best estimate of the pressure. It is also conceivable that a plurality of reference detection light signal differences and a plurality of reference pressures are utilized in look-up tables to directly identify the best estimate of the pressure based on the currently measured signal difference (v). In one example, the closest comparing look-up tables may be interpolated to obtain the best estimate of the pressure.

The touch sensing apparatus <NUM> may be configured to determine an amount of deflection of the panel <NUM> along the normal direction <NUM> based on the pressure. As mentioned above, the deflection may be determined by analytical, numerical and/or empirical models. The amount of deflection and current shape of the panel <NUM> may be utilized for optimizing the touch detection, e.g. to improve accuracy and/or resolution of the touch detection, and/or to provide characteristics and diagnostics data of the touch sensing apparatus <NUM>, such as the panel <NUM> and related components for attaching the panel <NUM> to frame elements of the touch sensing apparatus <NUM>.

The touch sensing apparatus <NUM> may be configured to determine a vibration amplitude and/or a vibration frequency of the panel <NUM> based on a determined variation of the pressure over time. the deflection of the panel <NUM> may be a result of mechanical vibrations of the panel <NUM>, which may in turn originate from other components of the touch sensing apparatus <NUM>, and/or from motions in the environment surrounding the touch sensing apparatus <NUM>. The vibration characteristics may be utilized for optimizing the touch detection, e.g. to improve accuracy and/or resolution of the touch detection, and/or to provide characteristics and diagnostics data of the touch sensing apparatus <NUM>. In another example, the panel <NUM> may be assumed to vibrate with a particular default frequency, such as <NUM>. If there has not been an interaction on the touch surface <NUM> recently, the source of the vibration can be assumed to originate from the environment around the touch sensing apparatus <NUM>. Such vibration sources can be the on/off state of machinery nearby, a person walking (low amplitude) or jumping (higher amplitude). The vibration events detected in this way may be detected as "gesture", such as a "jump gesture". For example, in a touch application such as a game application, such "jump gesture" may trigger an in-game event. In another example, vibrations in a stand on which the touch sensing apparatus <NUM> may be mounted may result in a slower vibration, e.g. in the <NUM>-<NUM> range. For variable height stands, the frequency of the slower stand oscillations can be used to estimate the current height of the stand.

<FIG> shows a flowchart of a method <NUM> for detecting touch pressure in a touch sensing apparatus <NUM>. The touch sensing apparatus <NUM> comprises a panel <NUM> that defines a touch surface <NUM>. The panel <NUM> has a perimeter <NUM>. The method <NUM> comprises emitting <NUM> light <NUM> across the panel <NUM> with a plurality of emitters <NUM> arranged along the perimeter <NUM>. The method <NUM> comprises receiving <NUM> at least part of said light as detection light <NUM>' with a plurality of detectors <NUM> arranged along the perimeter <NUM>. The method <NUM> comprises determining <NUM>, as a touch object <NUM> deflects the panel <NUM> along a normal <NUM> of the touch surface <NUM>, a difference in the received detection light <NUM>' between deflection of the panel <NUM> from a first position (p<NUM>) to a second position (p<NUM>) along the normal <NUM>. The method <NUM> comprises determining <NUM> a pressure of the touch object <NUM> against the touch surface <NUM> based on said difference. The method <NUM> provides for the advantageous benefits as described for the touch sensing apparatus <NUM> in relation to <FIG> above. The method <NUM> provides for facilitated user interaction and control of touch response in the touch sensing apparatus <NUM>, while keeping the cost of the touch interaction system at a minimum.

A computer program product is provided comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method <NUM> as described above in relation to <FIG>.

Claim 1:
A touch sensing apparatus (<NUM>) for detecting touch pressure, comprising
a panel (<NUM>) that defines a touch surface (<NUM>), the panel having a perimeter (<NUM>),
a plurality of emitters (<NUM>) arranged along the perimeter, wherein the emitters emit light (<NUM>) across the panel,
a plurality of detectors (<NUM>) arranged along the perimeter, whereby the detectors are arranged to receive at least part of said light as detection light (<NUM>') to determine a position (x,y) of a touch object (<NUM>) touching the touch surface based on the attenuation of the light emitted across the panel by the touch object, wherein the touch sensing apparatus is configured to
determine a difference in the received detection light between deflection of the panel from a first position (p<NUM>) to a second position (p<NUM>) along a normal (<NUM>) of the touch surface when the touch object (<NUM>) applies a pressure on the touch surface to deflect the panel and change the curvature of the panel relative the normal,
wherein the light emitted by the emitters is reflected against the touch surface as the panel has the first position and the second position, and
determine the pressure of the touch object against the touch surface based on said difference.