Patent Description:
Touch screen panels having force-sensing capabilities can enhance user experience through three-dimensional multi-touch interaction.

In a touch panel, drive and sensing electrodes are used for projective capacitive touch detection. To add force-detection capabilities, a piezoelectric layer, an electrode (which may be the drive or sensing electrode) and a counter electrode, which is held at a fixed voltage or ground, are employed. Additional dielectric layers such as PET thin film, adhesives and a protective cover may be included to integrate the layers and provide mechanical protection of electrode structures. Together, the configuration of the layers in the sensor stack defines a sensor architecture.

Examples of touch sensors combining capacitive sensing with piezoelectric based force-detection are described in <CIT>. This document also describes examples of embedded touch panels (in which electrodes are interspersed with display elements such as polarisers etc), in which a patterned electrode is positioned between a user input surface and the drive and sensing electrodes. Further examples of touch sensors combining capacitive sensing with piezoelectric based force-detection capabilities are described in <CIT>.

Recently, there has been interest in producing displays which are flexible, see for example <CIT> (A1) and <CIT> (A1). Sufficient flexibility may permit such displays to be folded-up or rolled-up for storage. The attraction of such flexible displays is to provide a larger display area without having to increase the overall size of a device including the flexible display. Such flexible displays may receive input from flexible touch panels laminated to, or integrated with the flexible display panel. <CIT> describes a display device including a flexible substrate having a display region including a plurality of pixels, each of the plurality of pixels having a pair of electrodes and a display element therebetween; a first electrode layer provided on the plurality of pixels; a second electrode layer provided on the first electrode layer; a third electrode layer provided on the second electrode layer; a piezoelectric material layer provided between the first electrode layer and the second electrode layer; and a flexible material layer provided between the second electrode layer and the third electrode layer.

<CIT> describes a sensing device for measuring flexural deformations of a surface. Such a sensing device may be used as a user interface in portable electronic devices. The sensing device comprises at least one cell. The cell comprises a first electrode, a central electrode, a second electrode, a first piezoelectric sensing layer placed between the first electrode and the central electrode, a second piezoelectric sensing layer placed between the central electrode and the second electrode, and a circuit connected to the first, second and the central electrodes. The circuit is configured to measure a first electrical signal between the first electrode and the central electrode, and a second electrical signal between the second electrode and the central electrode. At least one of the first electrical signal and the second electrical signal is responsive to an external stress applied on the sensing device.

<CIT> describes a touch type input terminal capable of carrying out various operation inputs. A touch type input terminal includes a base substrate, a piezoelectric sensor and an electrostatic sensor which are flat membrane-shaped, respectively. The electrostatic sensor includes a plurality of segment electrodes on a first main surface of a base film and a plurality of common electrodes on a second main surface. The piezoelectric sensor includes a piezoelectric film formed of PLLA drawn uniaxially. Displacement detecting electrodes are formed on a third main surface to be one of main surfaces of the piezoelectric film so as to divide the third main surface into four portions. Displacement detecting electrodes are formed on a fourth main surface to be the other main surface of the piezoelectric film so as to be opposed to the displacement detecting electrodes on the third main surface.

<CIT> describes an electronic apparatus with a main body, a stress sensor, and a detection unit. The main body has flexibility. The stress sensor has a piezoelectric film that deforms due to stress that is generated when the main body is bent. The stress sensor detects stress generated at an end portion and a center portion of the main body. The stress sensor is configured such that, in the cases where the end portion and the center portion are bent at a same curvature, a first output value outputted on the basis of the stress generated at the end portion is different from a second output value outputted on the basis of the stress generated at the center potion. The detection unit detects that the first output value and/or the second output value exceeded a predetermined threshold value.

<CIT> describes an electronic device that includes a flexible body, a stress sensor, and a detector. The stress sensor has a piezoelectric film that is deformed by a stress resulting from bending of the body. The stress sensor detects stresses that develop respectively at an end part and a central part of the body. When the end part and the central part are bent at the same radius of curvature, the stress sensor outputs output values such that a first output value based on a stress having developed at the end part is different from a second output value based on a stress having developed at the central part. Moreover, the detector detects at least one of the first output value and the second output value having exceeded a given threshold.

According to a first aspect of the invention there is provided an apparatus including a flexible touch panel. The flexible touch panel includes a layer of piezoelectric material arranged between a number of first electrodes and at least one second electrode. The apparatus also includes a device connected to the first electrodes and configured to receive piezoelectric signals from the first electrodes. The device is also configured to determine whether the received piezoelectric signals are indicative of a change in a bending state corresponding to one or more radii of curvature of the flexible touch panel. The device is also configured, in response to the received piezoelectric signals are indicative of a change in the bending state, to determine a change in the one or more radii of curvature based on tracking a total duration and/or a total charge associated with the bending state, and to output the change in the one or more radii of curvature. The device is also configured, in response to the received piezoelectric signals are not indicative of a change in the bending state and the flexible touch panel apparatus is in an awake mode, to determine, locations corresponding to one or more user interactions based on the received piezoelectric signals and/or capacitance measurements of the first electrodes, and to output the locations corresponding to one or more user interactions.

A bending state may corresponding to a radius of curvature of less than or equal to a largest dimension of the flexible touch panel. A bending state does not correspond to a user interaction such as a tap, swipe, press and so forth. The device may be a touch controller. The device may include one or more digital electronic processors and memory. The flexible touch panel may be supported on, or within, a frame which includes one or more hinges, the frame and the flexible touch panel being foldable about each hinge.

The frame may extend around the perimeter of the flexible touch panel. The frame may include one or more support panels. Each support panel may retain a portion of the flexible touch panel in contact with that support panel. Each support panel may be bonded to a contacting portion of the flexible touch panel across some or all of the area of the support panel. The support panel or support panels may leave a gap around each hinge. The frame may permit the flexible touch panel to curve in a region around each hinge.

The device may also be configured to determine a bending state comprising an angle of each hinge.

The device may also be configured to, for each hinge, determine a bending state comprising a closed status in response to the frame and the flexible touch panel being folded about that hinge, and determine a bending state comprising an opened status in response to the frame and the flexible touch panel being unfolded about that hinge.

The frame and the flexible touch panel may be folded about a hinge if that hinge makes an angle of less than a folded (or closed) angle. The folded angle may be less than or equal to <NUM> degrees, less than or equal to <NUM> degrees, less than or equal to <NUM> degrees, or less than or equal to <NUM> degrees. The frame and the flexible touch panel may be unfolded about a hinge if that hinge makes an angle of more than an unfolded (or opened) angle. The unfolded angle may be greater than or equal to <NUM> degrees, greater than or equal to <NUM> degrees, greater than or equal to <NUM> degrees, or greater than or equal to <NUM> degrees.

The device may be configured to determine a bending state of the flexible touch panel based on a duration for which signals received from one or more first electrodes corresponding to a hinge are saturated.

The device may be configured to determine a bending state of the flexible touch panel based on a total charge and/or a rate of charge generated on one or more first electrodes corresponding to a hinge.

A given first electrode may correspond to a given hinge if the given first electrode lies within a predetermined distance of the hinge, or spans across the hinge.

The flexible touch panel may be configured to enable the apparatus to be rolled-up into a substantially cylindrical configuration. The flexible touch panel and the apparatus may be capable of being rolled up into a scroll-like configuration. The substantially cylindrical configuration may correspond to a predetermined radius of curvature.

The apparatus may also include a roller about which the flexible touch panel is configured to be wrapped. The flexible touch panel may be connected to the roller along all or part of one edge of the flexible touch panel.

The device may be configured to determine a bending state comprising a fraction of the flexible touch panel which is rolled up in the substantially cylindrical configuration and/or a fraction of the flexible touch panel which is unrolled.

The flexible touch panel may include first electrodes oriented substantially parallel to an axial direction of the substantially cylindrical configuration. The flexible touch panel may include first electrodes oriented at an angle of less than <NUM> degrees, less than <NUM> degrees, less than <NUM> degrees or less than <NUM> degrees to the axial direction of the substantially cylindrical configuration. The device may be configured to determine when a region of the flexible touch panel corresponding to a particular first electrode transitions between the substantially cylindrical configuration and an unrolled state based on signals received from that first electrode.

The frame may include one or more displays. A display included in the frame may be rigid or flexible. A display may be a liquid crystal display. A display may be a plasma display. A display may be an organic light emitting diode display. A display may be an electronic ink display. A display may be an electrophoretic display.

The flexible touch panel may be laminated to a flexible display. The flexible touch panel may be integrally formed with a flexible display. A flexible display may be an organic light emitting diode display. A flexible display may be an electronic ink display. A flexible display may be an electrophoretic display.

The electronic device may be configured to switch between two or more operating modes in dependence upon the determined bending state of the flexible touch panel.

The electronic device may be configured to enter a low power mode in response to determining a bending state corresponding to one or more radii of curvature of the flexible touch panel is less than a first predetermined threshold. The electronic device may be configured to enter a full power mode in response to determining a bending state corresponding to one or more radii of curvature of the flexible touch panel is greater than a second predetermined threshold.

The second predetermined threshold may be equal to the first predetermined threshold. The second predetermined threshold may be greater than the first predetermined threshold. The low power mode may include switching off the display.

The low power mode may include using a secondary display to display notifications. A secondary display may be smaller than a main display. A secondary display may be of a different type to a main display. For example, a main display may be an organic light emitting diode display and a secondary display may be an electronic ink display or a black and white liquid crystal display. A secondary display may have a lower resolution than a main display.

The frame may include one hinge, and the electronic device may be configured to operate in a tablet mode in response to determining that the angle of the hinge is more than an unfolded angle, and to operate in a laptop mode in response to determining that the angle of the hinge is between the unfolded angle and a folded angle.

The folded angle may be less than the unfolded angle. The folded angle may be less than or equal to <NUM> degrees, less than or equal to <NUM> degrees, less than or equal to <NUM> degrees, or less than or equal to <NUM> degrees. The unfolded angle may be greater than or equal to <NUM> degrees, greater than or equal to <NUM> degrees, greater than or equal to <NUM> degrees, or greater than or equal to <NUM> degrees. In the tablet mode, a first region of the flexible touch panel on one side of the hinge and a second region of the flexible touch panel on the other side of the hinge may both function to provide touchscreen input to the display. In the laptop mode, a first display region laminated to or integrated with the first region of the flexible touch panel may display output and the first region of the flexible touch panel may be used to provide touchscreen input. In the laptop mode, a second display region laminated to or integrated with the second region of the flexible touch panel may display a keyboard, a track-pad, a slider and/or other input controls, and the second region of the flexible touch panel may be used to provide keyboard, track-pad, slider and/or other input respectively.

The electronic device may be configured to only receive touchscreen input from a fraction of the flexible touch panel which is unrolled. The electronic device may be configured to only display output using a region of the flexible display corresponding to the fraction of the flexible touch panel which is unrolled. The device may be further configured to scale output from an application and/or operating system executed by one or more processors of the electronic device to fit on the fraction of the flexible display corresponding to the fraction of the flexible touch panel which is unrolled.

According to a second aspect of the invention, there is provided a method including receiving piezoelectric signals from one or more first electrodes of a flexible touch panel. The flexible touch panel includes a layer of piezoelectric material arranged between a plurality of first electrodes and at least one second electrode. The method also includes determining whether the received piezoelectric signals are indicative of a change in a bending state corresponding to one or more radii of curvature of the flexible touch panel. The method also includes, in response to the received piezoelectric signals are indicative of a change in the bending state, determining a change in the one or more radii of curvature based on tracking a total duration and/or a total charge associated with the bending state, and outputting the change in the one or more radii of curvature. The method also includes, in response to the received piezoelectric signals are not indicative of a change in the bending state and the flexible touch panel apparatus is in an awake mode, determining locations corresponding to one or more user interactions based on the received piezoelectric signals and/or capacitance measurements of the first electrodes, and outputting the locations corresponding to one or more user interactions.

The flexible touch panel may be supported within a frame which comprises one or more hinges, the frame and the flexible touch panel being foldable about each hinge.

The method may also include, for each hinge, determining a bending state comprising a closed status in response to the frame and the flexible touch panel being folded about that hinge, and determining a bending state comprising an opened status in response to the frame and the flexible touch panel being unfolded about that hinge.

The flexible touch panel may be configured to enable the flexible touch panel to be rolled-up into a substantially cylindrical configuration.

The method may also include determining a fraction of the flexible touch panel which is rolled up in the substantially cylindrical configuration and/or a fraction of the flexible touch panel which is unrolled.

The flexible touch panel may be associated with a display.

The flexible touch panel and the display may be included in an electronic device. The method may also include causing the electronic device to switch between two or more operating modes in dependence upon the bending state of the flexible touch panel.

The method may also include causing the electronic device to enter a low power mode in response to determining a bending state corresponding to one or more radii of curvature of the flexible touch panel is less than a first predetermined threshold. The method may also include causing the electronic device to enter a full power mode in response to determining a bending state corresponding to one or more radii of curvature of the flexible touch panel is greater than a second predetermined threshold.

The method, the flexible touch panel, the flexible display and/or the electronic device may include features corresponding to any features of the first aspect.

According to a third aspect of the invention, there is provided a non-transitory computer readable medium storing a computer program configured such that, when the computer program is executed by a data processing apparatus, the data processing apparatus is caused to carry out the method according to the second aspect.

Touchscreen panels including a layer of piezoelectric material for force sensing have been described which have been bonded to, or integrated within, rigid displays. A rigid display is a conventional feature of a smart-phone, tablet computer, laptop computer, and so forth.

The present specification is based, at least in part, on the inventors realisation that integrating a layer of piezoelectric material into a flexible touchscreen panel may enable additional functionality in addition to, or instead of, detecting the force applied by a user interaction. In particular, a layer of piezoelectric material within a flexible touch panel may enable simple, integrated detection of events including, but not limited to folding, unfolding, rolling and/or un-rolling of the flexible touch panel. A layer of piezoelectric material may also be used to monitor an angle between two flat portions of a flexible touch panel.

In addition to flexible touchscreens, the methods and apparatuses of the present specification are also applicable to a touch panel which is not bonded to, or integrated with, a display, and which is instead used as an input peripheral to another device.

Referring to <FIG> and <FIG>, an example of a force-sensing touch panel system <NUM> (also referred to as touch panel system <NUM>) is shown.

The touch panel system <NUM> includes a first flexible force-sensing touch panel <NUM> (also referred to as first flexible touch panel <NUM>) and a force-sensing touch-controller <NUM> (also referred to as touch-controller <NUM>).

The first flexible touch panel <NUM> includes a layer structure <NUM> having a first face <NUM> and a second, opposite, face <NUM>, a number of first electrodes <NUM> and a number of second electrodes <NUM>.

The layer structure <NUM> includes one or more layers, including at least a layer of piezoelectric material <NUM>. Each layer included in the layer structure <NUM> is generally planar and extends in first x and second y directions which are perpendicular to a thickness direction z. The one or more layers of the layer structure <NUM> are arranged between the first and second faces <NUM>, <NUM> such that the thickness direction z of each layer of the layer structure <NUM> is perpendicular to the first and second faces <NUM>, <NUM>. The first electrodes <NUM> are disposed on the first face <NUM> of the layer structure <NUM>, and the second electrodes <NUM> are disposed on the second face <NUM> of the layer structure <NUM>.

In this way, when an applied force causes the touch panel <NUM> to deform, a resulting piezoelectric polarisation generated in the layer of piezoelectric material <NUM> will induce potential differences between the first and second electrodes <NUM>, <NUM>. Charges will flow to/from the first and second electrodes <NUM>, <NUM> to cancel out the polarisation electric field, and the touch controller <NUM> measures charge values corresponding to each first and second electrode <NUM>, <NUM>, for example using one or more charge amplifiers. Based on the measured induced charges, the touch controller <NUM> may estimate the locations corresponding to one or more user interactions, as well as the corresponding applied forces.

Optionally, the touch controller <NUM> may use the first and second electrodes <NUM>, <NUM> as transmitting and/or receiving electrodes for conventional mutual capacitance measurements. When the touch controller <NUM> performs capacitance measurements, these may be alternated with piezoelectric force measurements, or may be simultaneous (concurrent) with piezoelectric force measurements. For example, for concurrent force and capacitance measurements, the touch controller <NUM> may be configured as described in <CIT>, or as described in <CIT>, and the entire contents of both documents are hereby incorporated by reference. In particular, suitable combined force and capacitance touch panel systems are shown in, and described with reference to, Figures <NUM> to <NUM> of <CIT>. Furthermore, suitable combined force and capacitance touch panel systems are shown in, and described with reference to, Figures <NUM> to <NUM> of <CIT>.

In other examples, the touch controller <NUM> may determine the positions of one or more user interactions entirely using conventional capacitance measurements conducted using the first and second electrodes <NUM>, <NUM>. In such examples, the touch controller <NUM> may use piezoelectric signals from the first and second electrodes <NUM>, <NUM> solely to determine a bending state of the first flexible touch panel <NUM>.

The first touch panel <NUM> is flexible, in the sense that the first flexible touch panel <NUM> may be bent to a radius of curvature of <NUM>, or less without experiencing significant plastic deformation or other damage during <NUM>,<NUM> or more cycles of bending and unbending. In some examples, "flexible" may correspond to the ability to reversibly deform to a radius of curvature of between <NUM> to <NUM>. In other examples, "flexible" may correspond to the ability to reversibly deform to a radius of curvature of between <NUM> to <NUM>.

The first electrodes <NUM> each extend in the first direction x and the first electrodes <NUM> are disposed in an array evenly spaced in the second direction y with a pitch dy. The second electrodes <NUM> each extend in the second direction y and the second electrodes <NUM> are disposed in an array evenly spaced in the first direction x with a pitch dx. In this example, the pitches dx and dy are equal, although in other examples electrode pitches dx and dy need not be equal. The first and second electrodes <NUM>, <NUM> take the form of diamond-patterned electrodes known from mutual-capacitance based touchscreens. Each first electrode <NUM> is electrically coupled to the touch controller <NUM> via respective traces <NUM>, and each second electrode <NUM> is coupled to the touch controller <NUM> via respective traces <NUM>. In this way, the first and second electrodes <NUM>, <NUM> define a Cartesian coordinate system, which may be employed for sensing a location of a force applied to the touch panel <NUM>. The location is an x, y coordinate, i.e. the coordinate system defined by the first and second electrodes <NUM>, <NUM> lies in an x-y plane, perpendicular to the thickness direction z. As mentioned hereinbefore, location of one or more user interactions may be based on piezoelectric force measurements and/or capacitance measurements.

Preferably, the piezoelectric material <NUM> is a piezoelectric polymer such as polyvinylidene fluoride (PVDF). However, the piezoelectric material <NUM> may alternatively be provided by any piezoelectric material which may be made sufficiently flexible. In practice, this corresponds to a suitable piezoelectric material being capable of being made thin enough to bend without cracking, whilst still providing a detectable signal from the electrodes <NUM>, <NUM>. The first and second electrodes <NUM>, <NUM> may be indium tin oxide (ITO) or indium zinc oxide (IZO). However, the first and second electrodes <NUM>, <NUM> may be metal films such as aluminium, copper, silver or other metals suitable for deposition and patterning as a thin film. The first and second electrodes <NUM>, <NUM> may be conductive polymers such as polyaniline, polythiphene, polypyrrole or poly(<NUM>,<NUM>-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS). For flexibility, the first and second electrodes <NUM>, <NUM> may preferably be formed from a metal mesh; nanowires, optionally silver nanowires; graphene; and/or carbon nanotubes.

If the piezoelectric material <NUM> is manufactured by a monoaxial stretching method, then it may have a higher piezoelectric coefficient in parallel to the machined direction.

When using such materials, it may be beneficial to align the machined direction having a higher piezoelectric coefficient to be perpendicular to a bending/folding axis, in order to increase a piezoelectric signal generated in response to bending/folding about the bending/folding axis.

The conductive traces <NUM>, <NUM> may be made of the same materials as the first and second electrodes <NUM>, <NUM>. Alternatively, the conductive traces <NUM>, <NUM> may be made of a material having a higher conductivity than the material used for the first and second electrodes <NUM>, <NUM>. The conductive traces <NUM>, <NUM> are generally much thinner in the plane defined by the first and second directions x, y than the corresponding first and/or second electrodes <NUM>, <NUM>.

The layer structure <NUM> may include only the layer of piezoelectric material <NUM>, such that the first and second opposite faces <NUM>, <NUM> are faces of the layer of piezoelectric material <NUM>. This structure is preferred for a flexible touch panel <NUM>, because each additional layer increases thickness of the first flexible touch panel <NUM>, which is detrimental to flexibility.

Alternatively, the layer structure <NUM> may include one or more dielectric layers <NUM> (<FIG>) which are stacked between the layer of piezoelectric material <NUM> and the first face <NUM> of the layer structure <NUM>. The layer structure <NUM> may include one or more dielectric layers <NUM> (<FIG>) stacked between the second face <NUM> of the layer structure <NUM> and the layer of piezoelectric material <NUM>. Preferably, one or more dielectric layer(s) <NUM> (<FIG>) include layers of a polymer dielectric material such as polyethylene terephthalate (PET), or layers of pressure sensitive adhesive (PSA) material. However, one or more dielectric layer(s) (<FIG>) may include layers of a ceramic insulating material such as aluminium oxide, if these may be produced with sufficient flexibility.

When the first touch panel <NUM> is intended to overlie a display, all of the components of the first touch panel <NUM> overlying said display should preferably be formed of transparent materials, or have dimensions thin enough to avoid obscuring the display, or be aligned with gaps between pixels of the display.

Although in practice, the first and second electrodes <NUM>, <NUM> are typically formed into an orthogonal Cartesian grid, this is not essential. The first and second electrodes <NUM>, <NUM> may meet at any angle and still provide a coordinate system. In general, the first and second electrodes <NUM>, <NUM> may be shaped to define any coordinate system suitable for locating user interactions with the first flexible touch panel <NUM>.

First and second electrodes <NUM>, <NUM> forming a diamond-pattern are not required, and other shapes may be used, including simple rectangular electrodes <NUM>, <NUM>.

Referring also to <FIG>, a second flexible force-sensing touch panel <NUM> (also referred to as the second flexible touch panel <NUM>) is shown.

The second touch panel <NUM> includes the layer structure <NUM>, the first electrodes <NUM> and the second electrodes <NUM>, and additionally includes a counter electrode <NUM> (sometimes also referred to as a "common electrode") and a second layer structure <NUM> having third and fourth opposite faces <NUM>, <NUM>. The layout of the first and second electrodes <NUM>, <NUM> in plan view is the same as for the first flexible touch panel <NUM>.

In contrast to the first flexible touch panel <NUM>, the first and second electrodes <NUM>, <NUM> are spaced apart by the second layer structure in the second flexible touch panel <NUM>. In the second flexible touch panel <NUM>, the first and second electrodes <NUM>, <NUM> are both on the same side of the layer of piezoelectric material <NUM>. In this way, when an applied force causes the touch panel <NUM> to deform, resulting piezoelectric polarisation generated in the layer of piezoelectric material <NUM> will induce potential differences between the counter electrode <NUM> and the first electrodes <NUM>, and between the counter electrode <NUM> and the second electrodes <NUM>. The counter electrode <NUM> may be patterned or unpatterned, and takes the form of a single conductive region in either case. The counter electrode <NUM> is substantially co-extensive with the coordinate system defined by the first and second electrodes <NUM>, <NUM>.

The counter electrode <NUM> is made of indium tin oxide (ITO) or indium zinc oxide (IZO). Alternatively, the counter electrode <NUM> may be a metal mesh film such as aluminium, copper, silver or other metals suitable for deposition and patterning as a thin film. The counter electrode <NUM> may be made of a conductive polymer such as polyaniline, polythiphene, polypyrrole or poly(<NUM>,<NUM>-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS).

The second layer structure <NUM> includes one or more dielectric layers <NUM>. Preferably, the number of dielectric layers <NUM> is minimised to maintain flexibility of the second flexible touch panel <NUM>. Each dielectric layer <NUM> is generally planar and extends in first x and second y directions perpendicular to the thickness direction z. The one or more dielectric layers <NUM> of the second layer structure <NUM> are arranged between the third and fourth faces <NUM>, <NUM> such that the thickness direction z of each dielectric layer <NUM> of the second layer structure <NUM> is perpendicular to the third and fourth faces <NUM>, <NUM>. The second electrodes <NUM> are disposed on the fourth face <NUM> of the second layer structure <NUM>. The first electrodes <NUM> may be supported on the second face <NUM> of the first layer structure <NUM> or on the first face <NUM> of the second layer structure <NUM>.

Preferably, the dielectric layer(s) <NUM> include layers of a polymer dielectric material such as PET or layers of PSA materials. However, the dielectric layer(s) <NUM> may include layers of a ceramic insulating material such as aluminium oxide, if these may be produced with sufficient flexibility.

Referring also to <FIG>, a flexible force-sensing touchscreen <NUM> (also referred to as the flexible touchscreen <NUM>) is shown.

The flexible touchscreen <NUM> includes a flexible touch panel <NUM> stacked between a flexible display <NUM> and a flexible protective cover <NUM>. In the example shown in <FIG>, the flexible touch panel <NUM> is the second flexible touch panel <NUM>. Although the example shown in <FIG> includes the second flexible touch panel <NUM> with the counter electrode <NUM> closer to the display <NUM>, in other examples, the orientation of the second flexible touch panel <NUM> may be reversed in the thickness direction z. When a counter electrode <NUM> is closest to the cover <NUM>, the counter electrode <NUM> may be patterned to prevent electrostatic screening of the first and second electrodes <NUM>, <NUM>.

In other examples, the flexible touch panel <NUM> may be the first flexible touch panel <NUM>, or any other suitable flexible touch panel which includes a layer of piezoelectric material <NUM>. In general, the flexible touch panel <NUM> may be reversible in the thickness direction z.

The flexible display <NUM> may be any type of flexible display such as, for example, an organic light-emitting diode (OLED) display, a liquid crystal display (LCD), a plasma display, an electrophoretic display, and so forth. The cover <NUM> is typically formed from a flexible polymer. Preferably, the cover <NUM> is flexible, whilst also being resistant to scratching, for example polycarbonate.

Although shown in <FIG> as being laminated to the flexible display <NUM>, in other examples of a flexible touchscreen <NUM> the flexible touch panel <NUM> may be integrally formed with the flexible display <NUM>.

In some examples, the flexible display <NUM> may emit light from both sides.

Referring also <FIG>, a third flexible force-sensing touch panel <NUM> (also referred to as the third flexible touch panel <NUM>) is shown.

The third flexible touch panel <NUM> is the same as the second flexible touch panel <NUM>, except that the second layer structure <NUM> is omitted, and the first and second electrodes <NUM>, <NUM> are disposed in a co-planer configuration on the second face <NUM> of the first layer structure <NUM>. Each first electrode <NUM> is a continuous conductive region extending in the first direction x, including several diamond segments <NUM> evenly spaced in the first direction x and connected to one another in the first direction x by relatively narrower bridging segments <NUM>. Each second electrode <NUM> includes several diamond-shaped pad segments <NUM> evenly spaced in the second direction y in the similar way to the first electrodes <NUM>. However, unlike the first electrodes <NUM>, the diamond-shaped pad segments <NUM> of the second electrodes <NUM> are interspersed with, and separated by, the first electrodes <NUM>. The diamond-shaped pad segments <NUM> corresponding to each second electrode <NUM> are connected together by conductive jumpers <NUM>. The jumpers <NUM> each span a part of a first electrode <NUM> and the jumpers <NUM> are insulated from the first electrodes <NUM> by a thin layer of dielectric material (not shown) which may be localised to the area around the intersection of the jumper <NUM> and the first electrode <NUM>.

Alternatively, a thin (<<NUM>) dielectric layer (not shown) may overlie the second face <NUM> of the first layer structure <NUM> and the first and second electrodes <NUM>, <NUM>. Conductive traces (not shown) extending in the second direction y may be disposed over the dielectric layer (not shown), each conductive trace (not shown) overlying the diamond-shaped pad segments <NUM> making up one second electrode <NUM>. The overlying conductive traces (not shown) may connect the diamond-shaped pad segments <NUM> making up each second electrode <NUM> using vias (not shown) formed through the thin (<<NUM>) dielectric layer (not shown).

The third flexible touch panel <NUM> may provide the flexible touch panel <NUM> of the flexible touchscreen <NUM>.

Referring also to <FIG>, bending of a flexible touch panel <NUM>, or a flexible touchscreen <NUM> including a flexible touch panel <NUM> is shown.

A first bend <NUM> has a radius of curvature R<NUM>, measured with respect to a neutral axis <NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM>. A second bend <NUM> has a radius of curvature R<NUM> measured with respect to a neutral axis <NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM>.

For clarity of illustration, the neutral axis <NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM> is only explicitly shown in a central, un-deformed region of the flexible touchscreen <NUM> or flexible touch panel <NUM>. Although drawn at the central thickness of the flexible touchscreen <NUM> or flexible touch panel <NUM>, in practice the neutral axis <NUM> does not need to run through the central thickness of flexible touchscreen <NUM> or flexible touch panel <NUM>. For example, the neutral axis <NUM> will not be central unless the layers forming the flexible touchscreen <NUM> or flexible touch panel <NUM> have mirror symmetry about a central plane.

In addition to determining locations of user interactions and/or applied forces, the touch controller <NUM> may also use the piezoelectric signals generated in the first and second electrodes <NUM>, <NUM> to estimate one of more radii of curvature R<NUM>, R<NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM>, or changes in the radii of curvature R<NUM>, R<NUM>. As the flexible touchscreen <NUM> or flexible touch panel <NUM> is deformed, piezoelectric signals will be generated provided that the piezoelectric layer <NUM> is displaced from the neutral axis <NUM>. The strains resulting from bending of the flexible touchscreen <NUM> or flexible touch panel <NUM> will be substantially larger than the strains resulting from a normal user interaction with the flexible touchscreen <NUM> or flexible touch panel <NUM>. This difference in the typical amplitude of piezoelectric signals for user interactions and for bending may be used by the touch controller <NUM> to differentiate and track bending of the flexible touchscreen <NUM> or flexible touch panel <NUM>. Additionally, because of the spatial resolution available using the first and second electrodes <NUM>, <NUM> it may be possible to track multiple bends <NUM>, <NUM> in a flexible touch panel. Moreover, the spatial pattern of bending the flexible touchscreen <NUM> or flexible touch panel <NUM> to a radius R<NUM>, R<NUM> about an implied origin may be further differentiated from conventional user interactions such as taps, swipes and so forth by the different spatial patterns of which electrodes <NUM>, <NUM> generate piezoelectric signals.

For example, a conventional tap will generate piezoelectric signals from a cluster of first and second electrodes <NUM>, <NUM> near to the tapped location. By contrast, deforming the flexible touchscreen <NUM> or flexible touch panel <NUM> into the bending state shown in <FIG> will excite piezoelectric signals in all of the first electrodes <NUM>, as all of the first electrodes <NUM> run perpendicular to the first and second bends <NUM>, <NUM>. At the same time, two clusters of second electrodes <NUM> proximate to the first and second bends <NUM>, <NUM> respectively will provide piezoelectric signals to the touch controller <NUM>.

In dependence on one or more radii of curvature which the touch controller <NUM> measures for the flexible touchscreen <NUM> or flexible touch panel <NUM>, an electronic device <NUM> (<FIG>) incorporating the flexible touchscreen <NUM> or flexible touch panel <NUM> may switch between two or more operating modes. For example, the electronic device <NUM> may switch to an idle or sleep mode when folded up, then wake-up to full functionality when unfolded to an open configuration.

In general terms, determining a radius of curvature of a flexible touch panel <NUM> based on signals received from one or more of the electrodes <NUM>, <NUM> should be understood to encompass determining any bending state of the flexible touch panel <NUM> or a flexible touchscreen <NUM> incorporating the flexible touch panel <NUM>. Bending states may include, but are not limited to, a folded, unfolded, partially unfolded, rolled, unrolled or partially unrolled state of the flexible touchscreen <NUM> or flexible touch panel <NUM>. A bending state may also include an angle between two portions of the flexible touchscreen <NUM> or flexible touch panel <NUM>. Any determined bending state is physically linked to a radius of curvature or a range thereof, such that determining that a flexible touchscreen <NUM> or flexible touch panel <NUM> is rolled up is equivalent to determining that a radius of curvature of the flexible touchscreen <NUM> or flexible touch panel <NUM> is within a certain range. However, a numerical estimate of a corresponding radius of curvature may or may not be generated during the process of determining a bending state.

Referring also to <FIG>, a first electronic device <NUM> is shown in an open, unfolded or flat configuration.

Referring also to <FIG>, a cross-section of the first electronic device <NUM> is shown along the line labelled A-A' in <FIG>.

Referring also to <FIG>, a cross-section of the first electronic device <NUM> is shown along the line labelled B-B' in <FIG>.

In the first electronic device <NUM>, the flexible touchscreen <NUM> or flexible touch panel <NUM> is supported by (or within) a frame <NUM> which includes a hinge <NUM>. The hinge <NUM> enables the frame <NUM> and the supported flexible touchscreen <NUM> or flexible touch panel <NUM> to be folded about a hinge axis <NUM>. The frame <NUM> is provided in first and second portions 31A, 31B, which are joined at the hinge <NUM>. The hinge <NUM> may take the form of several physical hinges spaced apart from one another, but for the purposes of explanation all physical hinges along a single hinge axis <NUM> shall be referred to as a single hinge <NUM>.

The frame <NUM> may extend around the perimeter of the flexible touchscreen <NUM> or flexible touch panel <NUM>. In some examples, the frame <NUM> may include one or more support panels <NUM>. The flexible touchscreen <NUM> or flexible touch panel <NUM> may be retained in contact with the support panels <NUM>, for example by physical constraints which permit sliding (<FIG>) or by bonding (or otherwise securing) the support panels <NUM> to the flexible touchscreen <NUM> or flexible touch panel <NUM> (<FIG>). In any event, the support panels <NUM> should leave space about the hinge axis <NUM> to avoid an excessively small bending radius R<NUM>, R<NUM> for the flexible touchscreen <NUM> or flexible touch panel <NUM>. In some examples, support panels <NUM> may be integrally formed as extensions of the frame portions 31A, 31B.

By designing the electronic device <NUM> to have first or second electrodes <NUM>, <NUM> in parallel with the hinge axis <NUM>, maximum signal will be generated on the first or second electrodes <NUM>, <NUM> corresponding in position to the hinge <NUM> about which the folding and unfolding happens. Therefore, reading the signal from a single first or second electrode <NUM>, <NUM> positioned corresponding to the hinge <NUM> will have the least gain requirements for the touch controller <NUM>. Due to the relatively large amount of charge generated from a first or second electrode <NUM>, <NUM> positioned corresponding to the hinge <NUM>, it may be beneficial for low power applications if the touch controller <NUM> monitors such electrodes, for example, if the bending signal about the hinge is used to wake an electronic device from a low-power idle or sleep mode.

However, monitoring first or second electrodes <NUM>, <NUM> which span across the hinge <NUM> may be beneficial for noise reduction, as the same signal should be seen on all of the first or second electrodes <NUM>, <NUM> which span across the hinge <NUM>. The additional signal-to-noise of such a configuration may be useful if the amount of charge is being tracked, for example, in order to estimate a folding angle θ about the hinge <NUM>. In the open, unfolded or flat configuration, the angle is θ = <NUM>°.

In some examples, the frame <NUM> may support (or contain) a flexible touchscreen <NUM> which includes a flexible touch panel <NUM> laminated to, or integrally formed with, a flexible display <NUM>. In other examples, the frame <NUM> may support a flexible touch panel <NUM> and the frame <NUM> and/or support panels <NUM> may include (or take the form of), one of more rigid or flexible displays. A display included in the frame <NUM> or a support panel <NUM> may be a liquid crystal display, a plasma display, an organic light emitting diode display, an electronic ink display, an electrophoretic display, and so forth.

Although a single hinge <NUM> is shown in <FIG>, <FIG>, in other examples two or more hinges <NUM> may be included in the frame <NUM>. The touch controller <NUM> may track the angle θ of each hinge separately.

When the frame <NUM> folds about the hinge(s) <NUM> by an angle θ, there are several alternatives for how the flexible touchscreen <NUM> or flexible touch panel <NUM> may adopt a corresponding configuration. These options depend on the mechanical constraints applied to the flexible touchscreen <NUM> or flexible touch panel <NUM> by the frame <NUM> and/or the support panels <NUM>.

Referring also to <FIG>, cross sections of a first configuration 30A are shown respectively for the lines A-A' and B-B' in <FIG>.

In the first configuration 30A, the flexible touchscreen <NUM> or flexible touch panel <NUM> is securely attached (for example bonded or glued) to the first frame portion 31A (and optionally a corresponding first support panel 34A), whilst being able to slide relative to the second frame portion 31B (and optionally a corresponding second support panel 34B).

For example, referring again to <FIG>, in the flat configuration an edge of the flexible touchscreen <NUM> or flexible touch panel <NUM> may be a distance dflat in the first direction x from the edge of the second frame portion 31B. Referring in particular to <FIG>, as the electronic device in the first configuration 30A is bent about the hinge <NUM>, the distance between the edges of the flexible touchscreen <NUM> or flexible touch panel <NUM> and the edge of the second frame portion 31B may be decreased to a distance dθ < dflat as the flexible touchscreen <NUM> or flexible touch panel <NUM> slides with respect to the second frame portion 31B (and optionally the second support panel 34B).

One option for retaining the flexible touchscreen <NUM> or flexible touch panel <NUM> in contact with the second frame portion 31B is to include a retaining lip <NUM> at the edges of the second frame portion 31B, to form a channel <NUM> which receives the edges of the flexible touchscreen <NUM> or flexible touch panel <NUM>. A spring (not shown) may be positioned in the channel <NUM> in order to maintain a biasing force on the edge of the flexible touchscreen <NUM> or flexible touch panel <NUM>.

An advantage of the first configuration 30A is that a radius of curvature of the flexible touchscreen <NUM> or flexible touch panel <NUM> about the hinge <NUM> and hinge axis <NUM> may be maximised for a particular angle θ. Whilst this reduces the maximum piezoelectric signal generated from bending, the reduced strain may help to extend the lifetime of the flexible touchscreen <NUM> or flexible touch panel <NUM>.

Referring also to <FIG>, cross sections of a second configuration 30B are shown respectively for the lines A-A' and B-B' in <FIG>.

In the second configuration 30B, the flexible touchscreen <NUM> or flexible touch panel <NUM> is securely attached to the first frame portion 31A and a first supporting panel 34A. The flexible touchscreen <NUM> or flexible touch panel <NUM> are also securely attached to the second frame portion 31B and a second supporting panel 34B. The first supporting panel 34A extends partway from a distal end of the first frame portion 31A towards the hinge <NUM>, and the second supporting panel 34B extends partway from a distal end of the second frame portion 31B towards the hinge <NUM>. The support panels 34A, 34B leave a gap about the hinge <NUM> to permit bending of the flexible touchscreen <NUM> or flexible touch panel <NUM>. The support panels 34A, 34B may be extensions of the respective frame portions 31A, 31B.

As the device in the second configuration 30B is folded about the hinge <NUM>, the flexible touchscreen <NUM> or flexible touch panel <NUM> cannot slide, and instead buckles inwards towards the hinge <NUM> at first bend points <NUM>, before bending in the same sense as the hinge <NUM> about a second, re-curved bend point <NUM>. The frame portions 31A, 31B and/or the supporting panels 34A, 34B may be shaped to ensure that upon bending the flexible touchscreen <NUM> or flexible touch panel <NUM> buckles inwards towards the hinge <NUM>, instead of outwards away from the hinge <NUM>. Additionally or alternatively, the flexible touchscreen <NUM> or flexible touch panel <NUM> may be pre-stressed when it is bonded to the frame portions 31A, 31B, to ensure that buckling occurs in a desired direction.

Compared to the first configuration 30A, the second configuration 30B may be associated with a smaller radius of curvature R<NUM>, R<NUM> for a given angle θ, at least for angles closer to a flat configuration with θ = <NUM>. As the frame portions 31A, 31B fold back on themselves, the difference between the first and second configurations 30A, 30B may become less significant.

The methods of the present specification are not limited to the first and second configurations 30A, 30B. The methods of the present specification are considered to be applicable to any configuration of a frame <NUM> supporting a flexible touchscreen <NUM> or flexible touch panel <NUM> to enable bending about one of more hinges <NUM>.

Referring also to <FIG>, a folded or closed configuration <NUM> of the first electronic device <NUM> is shown.

The folded or closed configuration <NUM> corresponds to the hinge <NUM> being moved to an angle θ which is less than a threshold closed angle θclose, for example the threshold closed angle θclose may be substantially equal to zero so that the first electronic device <NUM> is folded back on itself as shown in <FIG>.

In practice, the threshold closed angle θclose may be larger than zero, for example, the threshold closed angle θclose may be less than or equal to <NUM> degrees, less than or equal to <NUM> degrees, less than or equal to <NUM> degrees, or less than or equal to <NUM> degrees.

Referring also to <FIG>, an unfolded, open or flat configuration <NUM> of the first electronic device <NUM> is shown.

The unfolded, open or flat configuration <NUM> corresponds to the hinge <NUM> being moved to an angle θ which is more than a threshold open angle θopen, for example the threshold open angle θopen may be substantially equal to <NUM>° (π) so that the first electronic device <NUM> is opened out flat as shown in <FIG>.

In practice, the threshold open angle θopen may be less than <NUM>° (π), for example the threshold open angle θopen may be greater than or equal to <NUM> degrees, greater than or equal to <NUM> degrees, greater than or equal to <NUM> degrees, or greater than or equal to <NUM> degrees.

Referring also to <FIG>, an intermediate configuration <NUM> of the first electronic device <NUM> is shown.

The intermediate configuration <NUM> corresponds to the hinge <NUM> being moved to an angle θ which is between the threshold closed angle θclose and the threshold open angle θopen, i.e. θclose < θ < θopen.

In some examples, the touch controller <NUM> may simply be configured to detect folding of the first electronic device <NUM> into the folded configuration <NUM> and unfolding of the first electronic device <NUM> into the unfolded configuration <NUM>. However, in other examples, the touch controller <NUM> may alternatively track an estimated radius of curvature R<NUM>, R<NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM>, for example by tracking a total charge on one or more first and/or second electrodes <NUM>, <NUM>. The estimated radii of curvature R<NUM>, R<NUM> may be mapped to corresponding angles θ based on calibration experiments moving the flexible touchscreen <NUM> or flexible touch panel <NUM> from a known configuration <NUM>, <NUM> to an intermediate configuration <NUM> of known angle θ. Subsequently, the electronic device <NUM> may use the estimated angle θ to control an operating mode of the electronic device <NUM>.

In other examples, the touch controller <NUM> may track an estimated radius of curvature R<NUM>, R<NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM> based on a duration for which an output of one or more charge amplifiers connected to respective first or second electrodes <NUM>, <NUM> have become saturated.

In some examples, explicit determination of the radii of curvature R<NUM>, R<NUM> may be omitted, and the piezoelectric signals mapped directly to corresponding angles θ. In other examples, explicit determination of the radii of curvature R<NUM>, R<NUM> and the corresponding angles θ may be omitted, and the piezoelectric signals mapped directly to corresponding operating modes of the first electronic device <NUM>.

The touch controller <NUM> may control an operating mode of the first electronic device <NUM> in a variety of ways, based on an imposed radius of curvature of the flexible touchscreen <NUM> or flexible touch panel <NUM> and the corresponding angle θ, as detected using the piezoelectric material layer <NUM> and electrodes <NUM>, <NUM>.

For example, the touch controller <NUM> may determine whether the electronic device <NUM> is in the closed configuration <NUM>, or whether the electronic device is in an opened configuration. An opened configuration may correspond to the flat or unfolded configuration <NUM>, or an opened configuration may correspond to anything other than the closed configuration <NUM>, i.e. either one of the flat or unfolded configuration <NUM> or the intermediate configuration <NUM>.

The first electronic device <NUM> may be configured to enter a low power mode, or sleep mode, in response to determining that the electronic device <NUM> is in a closed configuration <NUM>. For example, in a low power mode, the display <NUM> may be deactivated and the touch controller <NUM> may power down a capacitive touch sensing mode carried out using the first and second electrodes <NUM>, <NUM>.

In some examples, the first electronic device <NUM> may include a secondary display (not shown) which is mounted on, or integrated into, a surface of the frame <NUM> or a support panel <NUM> opposite to the flexible touchscreen <NUM> or flexible touch panel <NUM>. In this way, the secondary display (not shown) remains visible when the first electronic device <NUM> is in the folded or closed configuration <NUM>. In the low power mode, the secondary display (not shown) may be used to display notifications, for example, to inform a user that a message or e-mail has been received. Typically, a secondary display (not shown) will be smaller than a main display such as flexible display <NUM>, and the secondary display (not shown) may be of a different type and/or a lower resolution than a main display. For example, a main display may be an organic light emitting diode display and a secondary display (not shown) may be an electronic ink display or a black and white liquid crystal display.

The first electronic device <NUM> may be configured to operate in more than two modes in dependence on the radius of curvature of the flexible touchscreen <NUM> or flexible touch panel <NUM> and the corresponding angle θ.

For example, in addition to being configured to enter a low power mode, or sleep mode, in response to determining that the electronic device <NUM> is in a closed configuration <NUM>, the first electronic device <NUM> may be configured to operate in a tablet mode in response to determining the flat, unfolded or open configuration <NUM> and to operate in a laptop mode in response to determining the intermediate configuration <NUM>.

In the tablet mode, a first region of the flexible touchscreen <NUM> or flexible touch panel <NUM> on one side of the hinge, for example overlying the first frame portion 31A, functions to provide touchscreen input. Similarly, a second region of the flexible touch panel on the other side of the hinge, for example overlying the second frame portion 31B, also provides touchscreen input.

In the laptop mode, a first display region laminated to or integrated with the first region of the flexible touch panel displays output and the first region of the flexible touch panel is used to provide touchscreen input, whereas a second display region laminated to or integrated with the second region of the flexible touch panel displays a keyboard, a track-pad, a slider and/or other input controls, and the second region of the flexible touch panel is used to provide keyboard, track-pad, slider and/or other input respectively.

The control of an electronic device <NUM> based on a radius of curvature of the flexible touchscreen <NUM> or flexible touch panel <NUM> and the corresponding angle θ about a hinge <NUM> is not limited to the hereinbefore described examples, and more and/or different operating modes of the first electronic device <NUM> may be implemented based on the estimated radius of curvature of the flexible touchscreen <NUM> or flexible touch panel <NUM> obtained using piezoelectric signals.

The functionality of controlling an electronic device <NUM> based on a radius of curvature of the flexible touchscreen <NUM> or flexible touch panel <NUM> and the corresponding angle θ about a hinge <NUM> may also be integrated with detecting the forces and/or locations applied by one or more user interactions.

Referring also to <FIG>, a process flow diagram of a control method is shown.

Piezoelectric signals are received from the first and/or second electrodes <NUM>, <NUM> by the touch controller <NUM> (step S1).

The touch controller <NUM> determines whether the received piezoelectric signals are indicative of a folding/unfolding event (step S2). For example, a folding/unfolding event may correspond to saturation of amplifier outputs corresponding to one or more first or second electrodes <NUM>, <NUM> (<FIG>). Alternatively, a folding/unfolding event may correspond to one or more piezoelectric signals exceeding a threshold pre-calibrated to distinguish between user interactions and a folding/unfolding event.

If no folding/unfolding event is detected (step S2|No), and the electronic device <NUM> is in an active, awake or full power mode (step S3|Yes), the touch controller <NUM> detects any active user interactions using piezoelectric signals and/or capacitance measurements (step S4), and then outputs the user interaction locations (step S5). In some examples, the touch controller <NUM> will also output an estimated force corresponding to each user interaction. Whilst the electronic device <NUM> remains active (step S5|Yes), further piezoelectric signals are obtained (step S1).

If no folding/unfolding event is detected (step S2|No), and the electronic device <NUM> is in a low power or sleep mode (step S3|No), then detection of user interactions is skipped and the electronic device <NUM> continues to monitor the piezoelectric signals (step S5|Yes, step S1).

If a folding/unfolding event is detected (step S2|Yes), then the touch controller <NUM> starts tracking a total duration and/or total charge associated with the folding/unfolding event (step S7).

Further piezoelectric signals are obtained (step S8), and the touch controller <NUM> determines whether the folding/unfolding event is still occurring (step S9). The determination may be made as described hereinbefore (at step S2). Alternatively, the conditions for determining the end of a folding/unfolding event (step S9|No) may be different to the conditions for determining the start of a folding/unfolding event (step S2lYes). For example, a threshold signal level for the end of a folding/unfolding event (step S9|No) may be set lower than a threshold signal level for the start of a folding/unfolding event (step S2|Yes).

If the folding/unfolding event is still in progress (step S9|Yes), then the touch controller <NUM> continues tracking a total duration and/or total charge associated with the folding/unfolding event (step S7), and further piezoelectric signals are obtained (step S8).

Once the folding/unfolding event has finished (step S9|No), the touch controller <NUM> determines, based on the total duration and/or total charge which were recorded, an estimated change Δθ in the angle θ (step S10). The change Δθ in the angle θ and/or the new angle θ are output (step S11).

Based on the output change Δθ in the angle θ and/or the new angle θ, the first electronic device <NUM> may switch operating modes (step S12). For example, the electronic device <NUM> may switch from an active mode to a low power, idle or sleep mode, or the electronic device <NUM> may switch from tablet mode to a laptop mode.

Referring also to <FIG>, a schematic example is shown for a case that a folding/unfolding event causes a charge amplifier connected to a first or second electrode <NUM>, <NUM> to become saturated.

<FIG> plots a schematic example of a piezoelectric signal <NUM> against time. During a first, unfolding period <NUM>, the piezoelectric signal <NUM> saturates (to a positive rail voltage +Vs) with a polarity indicating an unfolding. The touch controller <NUM> detects the unfolding, and once this process is completed, initiates a second period <NUM> corresponding to detecting user interactions <NUM>. After the first, unfolding period <NUM> has finished, the touch controller <NUM> may need to re-calibrate parameters used for piezoelectric force and/or capacitance detection, for example the touch controller <NUM> may need to re-calibrate DC-offsets.

During a third, folding period <NUM>, the piezoelectric signal <NUM> becomes saturated (to a negative rail voltage -Vs) with the opposite polarity to the unfolding period <NUM>. The touch controller <NUM> detects the folding, and once this process is completed, initiates a fourth period <NUM> corresponding to a low power, idle or sleep mode.

In the example of <FIG>, the touch controller <NUM> may determine or estimate a change in the radius of curvature R<NUM>, R<NUM> about the hinge <NUM>, corresponding to a change Δθ in the angle θ, based on the total duration of the first or third periods <NUM>, <NUM>. Based on typical pre-calibrated opening and/or closing rates of a human user, the touch controller <NUM> may estimate the difference between, for example, completely or partially folding the first electronic device <NUM>. In some examples, explicit calculation of estimate a change in the radius of curvature R<NUM>, R<NUM>, the change Δθ and/or the angle θ may be omitted and the parameters of the piezoelectric signal <NUM> may be directly correlated to an unfolding or folding event.

Referring also to <FIG>, a second schematic example is shown for the case that a folding/unfolding event causes a charge amplifier connected to a first or second electrode <NUM>, <NUM> to become saturated.

<FIG> plots a schematic example of a piezoelectric signal <NUM> against time. During a fifth, folding period <NUM>, the piezoelectric signal <NUM> becomes saturated with a polarity indicating folding of the first electronic device <NUM>, causing the touch controller <NUM> to initiate a sixth period <NUM> of a low power idle or sleep mode.

During a seventh, unfolding period <NUM>, the piezoelectric signal <NUM> becomes saturated with a polarity indicating unfolding of the first electronic device <NUM>. However, the duration of the seventh period <NUM> is relatively shorter than the fifth period <NUM>, indicating that the first electronic device <NUM> have been only partially unfolded to the intermediate configuration <NUM>. After detecting a partial unfolding based on the duration of the seventh, unfolding period <NUM>, the touch controller may activate an appropriate input mode, and during an eighth, active period <NUM> the touch controller may detect user interactions based on piezoelectric signals <NUM> and/or capacitance measurements.

In some examples, explicit calculation of estimate a change in the radius of curvature R<NUM>, R<NUM>, the change Δθ and/or the angle θ may be omitted and the parameters of the piezoelectric signal <NUM> may be directly correlated to a complete or partial folding or unfolding event.

Saturation of an amplifier may occur in a touch controller <NUM> for a piezoelectric force sensing touch panel because the amplifier requires sufficient gain to detect the relatively weak signals resulting from a user interaction. The relatively much larger strains associated with large-scale bending or folding of a flexible touchscreen <NUM> or flexible touch panel <NUM> may cause an amplifier calibrated for detecting user interactions to saturate. Although changes in the radius of curvature R<NUM>, R<NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM> may be tracked using the duration of saturation, the result of the saturation is that information about the bending is lost.

Estimates may be improved by analysing the rising and falling edges of a saturated folding/unfolding event, in order to estimate a rate at which a hinge <NUM> has been actuated. Using the rising and falling edges to estimate initial and final velocities of the movement may be useful to refine estimates of the change in radius of curvature R<NUM>, R<NUM> and the associated angle θ of the hinge <NUM>. However, improved estimates may also be obtained by changing the gain of amplifiers reading out piezoelectric signals from at least some of the first and/or second electrodes <NUM>, <NUM> to avoid saturation of folding/unfolding signals.

Referring also to <FIG>, a schematic example is shown for a case that a folding/unfolding event does not cause a charge amplifier connected to a first or second electrode <NUM>, <NUM> to become saturated.

<FIG> plots a schematic example of a piezoelectric signal <NUM> against time. During a ninth, unfolding period <NUM>, the piezoelectric signal <NUM> exhibits a broad and relatively high peak in the signal <NUM>, which exceeds a pre-calibrated threshold Vthresh with a polarity indicating an unfolding action. The threshold Vthresh may be pre-calibrated using data from regular user interactions, and may be set so as to exclude regular user interactions such as taps, swipes and so forth. In effect, the threshold Vthresh should be set high enough that only a relatively extreme strain such as resulting from large-scale bending of the flexible touchscreen <NUM> or flexible touch panel <NUM> will exceed the threshold Vthresh. The touchscreen controller <NUM> may maintain a buffer of previous signal <NUM> values, so that when the threshold Vthresh is exceeded, the rising edge may be traced back and the total charges associated with the unfolding (or folding) event may be numerically integrated. By comparing the total charge recorded against calibration data obtained for known changes in the radius of curvature R<NUM>, R<NUM> and the corresponding angle θ, the touch controller <NUM> may identify that the first electronic device <NUM> has been opened and activated a tenth, active period <NUM>, during which user interactions <NUM> may be detected using piezoelectric signals <NUM> and/or capacitance measurements.

During an eleventh, folding period <NUM>, a peak having a polarity indicating a folding event exceeds the negative of the threshold -Vthresh, triggering the touch controller <NUM> to again track the total charge recorded. The touch controller <NUM> determines that the first electronic device <NUM> has been closed to the folded configuration, and triggers a twelfth period <NUM> in a low power idle or sleep mode.

During a third, folding period <NUM>, the piezoelectric signal <NUM> becomes saturated with the opposite polarity to the unfolding period <NUM>. The touch controller <NUM> detects the folding, and once this process is completed, initiates a fourth period <NUM> corresponding to a low power idle or sleep mode.

In some examples, explicit calculation of estimate a change in the radius of curvature R<NUM>, R<NUM>, the change Δθ and/or the angle θ may be omitted and the total charge recorded for a peak exceeding the threshold Vthresh may be directly correlated to a corresponding angle and/or operating mode of the first electronic device <NUM>.

Estimates of the change in the changes in the radius of curvature R<NUM>, R<NUM> and the corresponding angle θ may be further refined by taking into account the slopes of rising and falling edges of folding/unfolding peaks. For example, if a decay rate of a signal on a charge amplifier output is measured during a calibration step, then the decay rate may be adjusted for based on the gradient of the piezoelectric signal <NUM>, in order to obtain a more accurate estimate of the total charge recorded.

Although more accurate for detecting folding and unfolding events, decreasing the gain of a charge amplifier will also reduce the amplitude of signals corresponding to user interactions. Another issue is that the quantisation error of an analog-to-digital convertor (ADC) set to capture the signals from folding and unfolding events may have insufficient resolution to capture user interactions accurately. There are several approaches to mitigate such problems. For example, each amplifier output, or at least some amplifier outputs, may be connected to a pair of ADCs in which one is set to a relatively narrow voltage range to capture user interactions whilst the other is set to a relatively wide voltage range to capture folding/unfolding events. This would only need to be done for first or second electrodes <NUM>, <NUM> proximate to the hinge <NUM>, or for one or two electrode <NUM>, <NUM> which span the hinge <NUM>, minimising any added complexity.

Additionally or alternatively, amplifiers connected to first or second electrodes <NUM>, <NUM> proximate to, or one or two spanning the hinge <NUM>, may be read using more precise ADCs then the other electrodes <NUM>, <NUM>. For example, amplifier outputs corresponding to most of the electrodes <NUM>, <NUM> may be read using <NUM>-bit ADCs, and an amplifier output corresponding to an electrode <NUM>, <NUM> running along the hinge <NUM> may be read using a <NUM>- or <NUM>-bit ADC. For a given bandwidth, more precise ADCs are usually more expensive, however, the impact is mitigated by the fact that high precision to catch user interactions and folding/unfolding events on the same channel is not required for every electrode <NUM>, <NUM>.

Referring also to <FIG>, experimentally measured piezoelectric signals <NUM> are shown.

The data shown in <FIG> were obtained using an electrode <NUM>, <NUM> arranged on top of and parallel to a hinge <NUM>. For these data, negative polarity indicates a folding event <NUM> and positive polarity indicates an unfolding event <NUM>. Based on the total durations of folding events <NUM> and unfolding events <NUM>, it was possible to switch the display of an example of the first electronic device <NUM> of the first configuration 30A on and off by respectively unfolding and folding the first electronic device <NUM>.

The magnitude of piezoelectric signals <NUM>, <NUM> generated by electrodes <NUM>, <NUM> of a flexible touchscreen <NUM> or flexible touch panel <NUM> in response to large-scale bending such as folding or unfolding may be utilised for waking up an electronic device such as the first electronic device <NUM> from a very low power idle or sleep mode.

In particular, the piezoelectric signals <NUM>, <NUM> generated by electrodes <NUM>, <NUM> of a flexible touchscreen <NUM> or flexible touch panel <NUM> are generated by the applied strain, and do not require any driving signal from the touch controller <NUM>.

Referring also to <FIG>, a low power excitation detection circuit <NUM> is shown.

The circuit shown in <FIG> may be connected to an electrode <NUM>, <NUM> which is proximate to, or spans, a hinge <NUM> of the first electronic device <NUM>. The circuit <NUM> utilises micropower signal conditioning electronics to produce a 5V digital output signal <NUM> when excited by a piezoelectric signal <NUM>, <NUM> generated by an electrode <NUM>, <NUM>. The output signal <NUM> may be used to wake-up other components of the electronic device <NUM> such as, for example, the touchscreen controller <NUM>, the display such as flexible display <NUM>, wireless communications, and so forth.

The circuit <NUM> uses a LTC1541 integrated circuit to provide sensor gain and conversion to digital-compatible output using very low power. The front-end filter is needed to eliminate spurious signals caused by pick-up. The quiescent current draw of the circuit <NUM> was measures as <NUM>µA.

Referring also to <FIG>, a second electronic device <NUM> is shown.

The second electronic device <NUM> includes a flexible touchscreen <NUM> or flexible touch panel <NUM> which may be rolled-up into a substantially cylindrical configuration, for example a scroll-like configuration <NUM> having an inner end <NUM> rolled up inside the scroll <NUM> and an outer end <NUM> at the outside of the scroll <NUM>. The flexible touchscreen <NUM> or flexible touch panel <NUM> may be integrated with a flexible battery (not shown) and/or flexible electronics (not shown) providing the touch controller <NUM> and optionally data processing capabilities, so that the scroll <NUM> may function as an independent device. Alternatively, the scroll <NUM> may be configured for wired or wireless coupling to an external device which may provide the touch controller <NUM>, a display driver (not shown), power and/or data processing capabilities. In some examples the second electronic device <NUM> may be a roll-up keyboard and/or touch enabled display.

The second electronic device <NUM> includes electrodes <NUM> running parallel to an axis about which the scroll <NUM> is rolled-up. The electrodes <NUM> may be first or second electrodes <NUM>, <NUM>, and the other electrodes <NUM>, <NUM> may be substantially perpendicular to the axis about which the scroll <NUM> is rolled-up. Electrodes <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM> are shown in sequence from the outer end <NUM> of the flexible touchscreen <NUM> or flexible touch panel <NUM>. Further electrodes <NUM>n for n > <NUM> are not shown for clarity of the figure, but the second electronic device <NUM> may include any number N of electrodes <NUM><NUM>,.

The substantially cylindrical configuration of the scroll corresponds to a predetermined radius of curvature Rscroll and the touch controller <NUM> may be pre-calibrated to determine when one or more of the electrodes <NUM>n transitions to, or from, the substantially cylindrical scroll-like configuration <NUM> by comparing estimated changes in the radius of curvature Rn around an nth electrode <NUM>n to the predetermined radius of curvature Rscroll. In the same way as for the first electronic device <NUM>, the second electronic device <NUM> tracks changes in the radius of curvature Rn around an nth electrode <NUM>n based on monitoring a duration for which a corresponding amplifier statures, or based on monitoring a total charge associated with a peak of a piezoelectric signal <NUM> which exceeds a threshold Vthresh (see <FIG>).

In some examples explicit estimation of the radius of curvature Rn around an nth electrode <NUM>n may be omitted, and transitions to, or from, the substantially cylindrical scroll-like configuration <NUM> may be determined based directly on the piezoelectric signals <NUM>n from the nth electrode <NUM>n (and optionally adjacent electrodes <NUM>n-<NUM>, <NUM>n+<NUM> and so forth).

Referring also to <FIG>, a third electronic device <NUM> is shown.

The third electronic device <NUM> is the same as the second electronic device <NUM>, except that it includes a roller <NUM> about which the flexible touchscreen <NUM> or flexible touch panel <NUM> may be wrapped. The roller <NUM> may help to ensure a consistent change in the local radius of curvature Rn around an nth electrode <NUM>n as it is rolled into or out of the substantially cylindrical scroll-like configuration <NUM>.

The flexible touchscreen <NUM> or flexible touch panel is preferably connected to the roller <NUM> along the inner end <NUM>. The roller <NUM> may include the touch controller <NUM>, a display driver (not shown), a power supply (not shown), one or more processors (not shown), memory (not shown), a wireless communications module (not shown) and so forth. In other words, the roller <NUM> may house the components necessary for the third electronic device <NUM> to function as a smart phone, a tablet computer, and similar devices.

Referring also to <FIG>, as the second or third electronic device <NUM>, <NUM> is rolled-up or unrolled, the electrodes <NUM>n will display corresponding piezoelectric signals <NUM>n indicative of changing between a flat configuration and the predetermined radius of curvature Rscroll in sequence.

For example, if the second or third electronic device <NUM>, <NUM> was to be unrolled starting from the configuration illustrated in <FIG>, the first electrode <NUM>n to experience an unrolling event would be the fifth electrode <NUM><NUM>, and a piezoelectric signal <NUM><NUM> output from a corresponding charge amplifier may become saturated (to a positive or negative supply rail, depending on the polarisation of the layer of piezoelectric material <NUM>).

If the second or third electronic device <NUM>, <NUM> continues to be unrolled, a saturated piezoelectric signal <NUM><NUM> will then be observed for the sixth electrode <NUM><NUM>, and so forth.

In this way, the touch controller <NUM> may track the rolling and unrolling of the second or third electronic device <NUM>, <NUM> between a flat configuration and the substantially cylindrical scroll-like configuration <NUM>.

In other examples, rolling and unrolling may be detected by piezoelectric signals <NUM>n exceeding a threshold Vthresh, instead of saturating.

The second or third electronic device <NUM>, <NUM> may be configured to enter a low power idle or sleep mode in response to any part of the flexible touchscreen <NUM> or flexible touch panel <NUM> having a radius of curvature Rn with a pre-calibrated range of the predetermined radius Rscroll. The second or third electronic device <NUM>, <NUM> may then wake-up to a full power mode when the flexible touchscreen <NUM> or flexible touch panel <NUM> is fully unrolled.

In other examples, the touch controller <NUM> of the second or third electronic device <NUM>, <NUM> may determine and track the fraction f of the flexible touchscreen <NUM> or flexible touch panel <NUM> which is rolled up in the substantially cylindrical scroll-like configuration <NUM> and the fraction <NUM>-f of the flexible touchscreen <NUM> or flexible touch panel <NUM> which is unrolled and flat. Based on the fractions f, <NUM>-f, the touch controller <NUM> may only measure user interactions from the fraction <NUM>-f of the flexible touchscreen <NUM> or flexible touch panel <NUM> which is unrolled and flat. Furthermore, when the second or third electronic device <NUM>, <NUM> includes a flexible display <NUM> laminated to, or integrated with, the flexible touch panel <NUM>, a display driver (not shown) of the second or third electronic device <NUM>, <NUM> may be configured to only display output on the unrolled fraction <NUM>-f. The second or third electronic device <NUM>, <NUM> may be configured to re-scale display output provided from an application and/or operating system executed by one or more processors (not shown) of the second or third electronic device <NUM>, <NUM>, so that the display output fits on the unrolled fraction <NUM>-f.

Although the second and third electronic devices <NUM>, <NUM> have been described as having electrodes <NUM>n oriented parallel to an axis about which the devices <NUM>, <NUM> are rolled-up, the orientation need not be precise. For example, the electrodes <NUM> (which may be first or second electrodes <NUM>, <NUM>) may be oriented at an angle of less than <NUM> degrees, less than <NUM> degrees, less than <NUM> degrees or less than <NUM> degrees to the axial direction about which the second or third electronic devices <NUM>, <NUM> are rolled-up.

Claim 1:
Apparatus comprising:
a flexible touch panel (<NUM>) comprising a layer of piezoelectric material (<NUM>) arranged between a plurality of first electrodes (<NUM>, <NUM>) and at least one second electrode (<NUM>, <NUM>);
a device (<NUM>) connected to the first electrodes and configured:
to receive piezoelectric signals from the first electrodes (S1);
to determine whether the received piezoelectric signals are indicative of a change in a bending state corresponding to one or more radii of curvature (R<NUM>, R<NUM>) of the flexible touch panel (S2);
in response to the received piezoelectric signals are indicative of a change in the bending state:
to determine a change in the one or more radii of curvature based on tracking a total duration and/or a total charge associated with the bending state (S7, ..., S10); and
to output the change in the one or more radii of curvature (S11);
in response to the received piezoelectric signals are not indicative of a change in the bending state and the flexible touch panel apparatus is in an awake mode (S3):
to determine locations corresponding to one or more user interactions based on the received piezoelectric signals and/or capacitance measurements of the first electrodes (S4); and
to output the locations corresponding to one or more user interactions (S5).