Adhesive for haptic device

Abstract

The present invention relates to an adhesive (30) for a haptic device (1), the adhesive (30) being transparent, having a glass transition temperature of less than –50°C and having, for a frequency of greater than or equal to 40 kHz, preferably of between 60 and 120 kHz, a damping factor of less than 0.4 and preferably less than 0.1. The invention also relates to a haptic device (1) configured to produce haptic feedback by means of friction modulation, comprising a plate (10) which is intended to be touched by a user, and in particular by the finger (D) of a user, to which plate a stack (20) is attached by means of an adhesive (30) of this kind, the plate being provided with at least one haptic actuator (14) capable of vibrating the plate.

Description

DESCRIPTION TITLE: Adhesive for haptic device The present application is based on, and claims the priorities of, European patent application number EP 23307085.3 filed on November 29, 2023 entitled “Vibration absorbing adhesive for haptic device” and French patent application number FR 24 / 01842 filed on February 26, 2024 entitled “Adhesive for haptic device”, which are considered to be an integral part of this description within the limits provided by law. Technical field

[0001] This description generally relates to devices having an ultrasonic haptic feedback interface. This description applies, for example, to display screens. It also relates to the glues / adhesives used in this type of device. Prior art

[0002] An ultrasonic haptic feedback interface is based on the combination of piezoelectric actuators and a surface intended for a user's touch. The actuators can be controlled at an ultrasonic frequency so as to vibrate the surface and cause an acoustic levitation effect on the pad of a user's finger, which results in the modulation of the coefficient of friction between the finger and the contact surface. This effect is known as "ultrasonic lubrication." It creates a textured sensation on the contact surface.

[0003] The various adhesives used in such devices play an important role in the transmission of vibrations necessary for the implementation of ultrasonic lubrication.

[0004] Furthermore, it is sometimes necessary, in such devices, that this vibration is not transmitted from one element to another, for example to avoid attenuation phenomena, or to contain the vibration in a specifically delimited interaction zone. Summary of the invention

[0005] There is a need to provide an adhesive for a haptic device which, on the one hand, does not prevent the propagation of vibrations in the contact surface, to which it is attached, and on the other hand, when two elements are glued to each other by means of this adhesive, limits the transmission of vibrations from one element to the other (typically from the contact surface to the upper layer of a touch display, in particular in the frequency range 40-400 kHz and preferably 60-120kHz.

[0006] This aim is achieved by an adhesive for a haptic device, the adhesive being transparent, having a glass transition temperature of less than -50°C and having, for a frequency greater than or equal to 40kHz, preferably between 40 and 400 kHz, even more preferably between 60 and 120 kHz, a damping factor of less than 0.4 and, preferably, less than 0.1.

[0007] According to a particular embodiment, the adhesive has a refractive index of between 1.4 and 1.54.

[0008] According to a particular embodiment, the adhesive has a peel strength greater than 5 N / 20 mm.

[0009] According to a particular embodiment, the adhesive has a Haze factor of less than 2.

[0010] According to a particular embodiment, the adhesive is a polysiloxane.

[0011] According to a particular embodiment, the adhesive has a thickness of between 20 μm and 500 μm, preferably between 175 and 300 μm.

[0012] The invention also relates to a haptic device configured to produce haptic feedback by friction modulation, in particular friction modulation using a bending wave, a shear wave or a compression-expansion wave at an ultrasonic frequency, the device comprising a plate, preferably made of glass or plastic, intended to be touched by a user, and in particular by the finger of a user, on which a stack is fixed by means of an adhesive, as defined previously, said plate being provided with at least one haptic actuator capable of setting it into vibration.

[0013] According to a particular embodiment, the stack comprises an upper layer, made of plastic or glass, on which the adhesive is fixed.

[0014] According to a particular embodiment, the upper layer is a layer for detecting contact of a user, in particular a finger of a user, with the plate or a layer for detecting the position of contact of a user, in particular a finger of a user, with the plate.

[0015] According to a particular embodiment, the upper layer is a polarizer.

[0016] According to a particular embodiment, the stack comprises a liquid crystal display screen, preferably arranged between two polarizers, one of the polarizers forming the upper layer.

[0017] According to a particular embodiment, the stack comprises an OLED screen.

[0018] The invention also relates to an automobile dashboard comprising a haptic device as described previously. Brief description of the drawings

[0019] These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which:

[0020] Figure 1A represents, in a very schematic and partial manner, a sectional view of an electronic device equipped with a haptic interface, according to a particular embodiment;

[0021] Figure 1B represents, in a very schematic and partial manner, a sectional view of an electronic device equipped with a haptic interface, presenting a stack according to a particular embodiment;

[0022] Figure 2A represents, in a very schematic and partial manner, a sectional view of an electronic device equipped with a haptic interface, according to a particular embodiment;

[0023] Figure 2B represents, in a very schematic and partial manner, a bottom view of an electronic device equipped with a haptic interface, according to a particular embodiment;

[0024] Figure 3 represents, in a very schematic and partial manner, a perspective view of an electronic device equipped with a haptic interface, according to a particular embodiment;

[0025] Figure 4 is a graph representing curves of evolution of the damping factor as a function of the Young's modulus of an OCA adhesive, according to a particular embodiment.

[0026] In the various figures, the different elements and components are not necessarily represented at the same scale relative to each other. Description of the embodiments

[0027] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments and examples may have the same references and may have identical structural, dimensional and material properties.

[0028] For the sake of clarity, only the steps and elements useful for understanding the methods and examples of embodiment described have been represented and are detailed.

[0029] Unless otherwise specified, when two elements are connected together, this means directly connected without intermediate elements other than conductors, and when two elements are connected (in English "coupled") together, this means that these two elements can be connected or be connected by means of one or more other elements.

[0030] In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or orientation qualifiers, such as the terms "horizontal", "vertical", etc., unless otherwise specified, reference is made to the orientation of the figures.

[0031] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0032] There are different types and shapes of haptic interface devices.

[0033] All devices equipped with a haptic interface have at least the following common characteristics (figures 1A, 1B, 2A, 2B and 3): - a plate 10, a front face of which defines a surface for direct or indirect contact with an external body, for example a touch organ (finger D, foot, etc.) of a user, and which constitutes the haptic feedback plate; - one or more piezoelectric actuators 14, fixed to the plate 10, and configured to set the plate 10 into vibration, - a circuit 2 for controlling and supplying the piezoelectric actuators 14.

[0034] For a better understanding of the figures, the circuit 2 for controlling and supplying the piezoelectric actuators 14 is not shown in all the figures.

[0035] The plate 10 is a contact surface intended to be touched directly by the user (for example, with a fingertip D), or a stylus.

[0036] The contact surface may be part of a telephone ('smartphone'), a tablet, an automobile dashboard, and in particular an automobile control panel, a machine control panel, an element used in home automation such as a dimmer switch (air conditioning, light) or other user interfaces. The contact surface may be a window, including a cover or protective window placed over a screen, or an automobile windshield.

[0037] The plate 10 is preferably transparent. The plate 10 is made of a rigid material that can be subjected to vibrations and / or transmit vibrations. The plate 10 is capable of being vibrated, in particular upon contact with the finger D of a user. The plate is capable of producing an ultrasonic lubrication effect, for example, when it is brought into contact with a finger D. The plate 10 may be made of glass ('cover glass') or plastic, for example polycarbonate or PMMA.

[0038] A contact or contact position sensing layer may be positioned in the plate 10, or alternatively above and / or below.

[0039] The plate 10 has a first face (upper face) and a second face (lower face).

[0040] The plate 10, and in particular the upper face, may in certain cases be covered in part or in full by a layer such as a decorative film or any other surface treatment, which does not prevent vibration.

[0041] At least one actuator 14 is fixed on the second face of the plate 10. Several haptic actuators can be arranged on the second face. The actuators are arranged out of line with the stack 20. Alternatively at least one actuator can be fixed on the top of the plate, that is to say on its upper face, or on the edge of the plate.

[0042] The piezoelectric actuators 14 are generally distributed in two strips located on two opposite sides of the plate 10 or on a single strip located on one side only.

[0043] The actuators 14 are controlled by an excitation circuit 2 ('driver'). The role of the actuators 14 is to create, in the plate 10, a high-frequency wave. The vibrations generated at the level of the plate 10 provide, at its external interface surface with a user (typically a finger D), an effect perceived by the user as an effect of reducing friction with the surface.

[0044] High frequency is typically understood to mean a frequency greater than or equal to 40kHz. The frequency is preferably between 40 and 400 kHz. A frequency range between 60 and 120 kHz is particularly well suited to bending waves (i.e. out-of-plane waves). For longitudinal waves known as "compression-expansion waves" (i.e. in-plane waves), frequencies around 150kHz are particularly suitable.

[0045] The actuators 14 are generally powered by periodic alternating voltages. The frequency of the voltages is chosen to be close to the resonance frequency of the electromechanical system, typically around a frequency between 20 kHz and 200 kHz. The amplitude of the control voltages of the actuators 14 is typically between about ten and about a hundred volts, for example 20 V for small screens and around 150 V for large screens. These are examples and other frequency and amplitude values ​​are possible depending on the application. The actuators may be amplified deformation actuators, as described, for example, in application WO 2020 / 141264 A1.

[0046] The piezoelectric actuators 14 are, for example, piezoelectric ceramics or piezoelectric thin layers or thick films.

[0047] The device 1 may further comprise one or more of the following elements (represented or not in the figures): a circuit 16 ('driver') for controlling the screen, a strain gauge, a force or pressure detector, for example an infrared detector or a mechanical detector.

[0048] In addition to the previously mentioned elements, the haptic device comprises a stack 20. The plate 10 is coupled to the stack 20 by means of an adhesive 30.

[0049] The stack 20 is a multi-layer structure comprising several layers. It may comprise, for example, three layers 21, 22, 23. The upper layer 21 of the stack 20 may be fixed to the underlying layer 22 by means of an adhesive, for example identical to that between the plate 10 and the upper layer 21.

[0050] The stack 20, and more particularly, the upper layer 21 of the stack 20 (in other words the layer on which the adhesive 30 is fixed), is fixed on the second face of the plate 10. The upper layer 21 of the stack is in contact with the adhesive 30.

[0051] The upper layer 21 of the stack 20 may be a polarizer 18 or a contact or position detection layer, for example for detecting the position or contact of a finger D of a user. The polarizer 18 is, for example, made of a polymer material, in particular polysiloxane ('silicone') or polyethylene (PE). The detection layer may be made of glass or polymer.

[0052] The stack 20 may comprise one or more layers for detecting the position of a finger D and / or contact of a finger D on the external surface of the device. The detection layers may be of the capacitive or resistive type.

[0053] The stack 20 may or may not incorporate a display screen, typically a touch screen.

[0054] As shown in Figures 2A and 3, the stack 20 preferably comprises a display, for example a liquid crystal display (LCD) comprising a liquid crystal display module 12 (LCM). The LCM module 12 is preferably disposed between two polarizers 18.

[0055] For example, in the case where the stack includes an LCD screen, the actuators 14, amplified or not, are in contact with the plate 10.

[0056] Alternatively, stack 20 includes an OLED display.

[0057] We will now describe in more detail the adhesive 30 for haptic device 1.

[0058] It can be an OCA (optically clear adhesive) or an OCR (optically clear resin) resin.

[0059] The adhesive 30 is preferably laminated onto the elements to be joined. The surfaces of the two elements may be made of the same material or different materials.

[0060] The adhesive 30 makes it possible to limit the dissipation of waves, for example bending, compression or shear, between the plate 10 and the multilayer stack 20. The adhesive 30, by its elasticity and its specific properties, aims to allow a mechanical decoupling effect of the stack 20 and the plate 10 where the haptic feedback is generated. In this way, an attenuation of the waves within the plate 10. The adhesive 30 is suitable for devices implementing flexural waves, but it is particularly effective for longitudinal waves known as “compression-expansion”.

[0061] Adhesive 30 must meet several criteria in order to be used in a haptic device.

[0062] For automotive applications, the temperature range is typically between -40°C and 85°C. The frequencies used are high frequencies (ultrasonic frequencies), typically above 40 kHz. For example, they can be between 60 and 120 kHz for bending waves or around 150 kHz for longitudinal waves.

[0063] The properties specified below are advantageously met for the temperature range and / or for the frequency range mentioned above. The OCA / OCR is stable in these working ranges.

[0064] We will choose an adhesive 30 meeting several, or even all, of the following parameters:

[0065] - have a glass transition temperature Tg lower than -50°C;

[0066] - in the temperature range between 20 and 60 °C, at high frequency (for example 40kHz), and for tan <5 of approximately 0.2 the Young's modulus E is between 4xl0 7 Pa and 2xl0 8 No ;

[0067] - the adhesive material is a polysiloxane (also called silicone), for example polydimethylsiloxane (PDMS);

[0068] - the refractive index ('refraction index') is between 1.4 and 1.54;

[0069] - peel strength is greater than 5 N / 20mm;

[0070] - the Haze factor is less than 2 (advantageously, the Haze factor remains less than 2, even after 500h at 105°C);

[0071] - for frequencies greater than or equal to 40 kHz, and preferably for frequencies between 60 and 120 kHz, the damping factor is less than or equal to 0.4, preferably less than or equal to 0.2 and even more preferably less than or equal to 0.1;

[0072] - the thickness of the adhesive is between 20 pm and 500 pm, preferably between 175 and 300 pm;

[0073] - the adhesive material is transparent (i.e. the transmittance of light radiation (typically for wavelengths between 300 and 850 nm) through the adhesive is greater than 70%, preferably greater than 80% and even more preferably greater than 90%);

[0074] - Poisson's ratio v is between approximately 0.40 and 0.50.

[0075] Such an adhesive is advantageously used in a haptic device.

[0076] Such an adhesive is particularly interesting in industrial fields such as automobiles, digital devices, etc.

[0077] A haptic device comprising such an adhesive makes it possible to produce and maintain haptic feedback by modulating the coefficient of friction on the surface of the plate in contact with the user. This haptic feedback technique is also called "ultrasonic lubrication". In particular, such a device is configured to produce haptic feedback by friction modulation, implementing a flexion wave or a compression-expansion wave at an ultrasonic frequency.

[0078] By way of illustration and not limitation, the plate 10 and the adhesive 30 of the device 1 may have the characteristics listed in the following table:

[0079] The values ​​given in the table above are approximate values ​​which are to be understood to be within 10%, preferably within 5%.

[0080] Figure 4 shows the loss (or damping) factor as a function of the Young's modulus of an OCA EQCA adhesive expressed in Pascal. Plate 10 is a glass plate, 1.3 mm thick. Each curve gives the evolution of the tand-EocA couple at isovalue of the attenuation coefficient of the bending waves propagating along plate 10 (indicated by a number associated with the curve). The material properties will be chosen so as to be able to position themselves under the attenuation curve 2.0, and even more preferably under the curve 1.0. A damping factor value lower than 0.1 will be preferred, which will allow an acceptable attenuation level to be respected over a wider range of material elasticity.

[0081] To characterize the mechanical properties of these materials, a commonly used technique is analysis dynamic mechanical (DMA). However, this type of test is limited to standard frequencies (up to 100 Hz).

[0082] The material properties of the OCA / OCR can be obtained by acoustic characterization at the working frequency (notably above 40 kHz, and in particular at frequencies between 60-120 kHz for fields such as the automotive field) or estimated from a master curve (result of a DMA test).

[0083] The construction of these master curves allows, from the values ​​obtained at low frequency and translation factors a T and b T , to estimate the values ​​of Young's modulus E and the damping factor tan 5 at high frequency. Different temperatures can be used for the construction of the curves.

[0084] It is thus possible to obtain the storage modulus (real part of Young's modulus) and the loss factor (damping) as a function of frequency at higher frequencies than those tested by DMA.

[0085] The construction of master curves is, for example, described in the article by Rouleau et al. (“Characterization and modeling of the viscoelastic behavior of a self-adhesive rubber using dynamic mechanical analysis tests”, J. Aerosp. Technol. Manag. 7 (2) (2015)).

[0086] In the description, the following acronyms, symbols, Greek letters may correspond to:

[0087] - OCR: “optical clear resin” in English;

[0088] - OCA: “optical clear adhesive” in English;

[0089] - Tg: glass transition temperature;

[0090] - LCD: liquid crystal display;

[0091] - OLED: organic light-emitting diode or "organic light-emitting diode" in English;

[0092] - DMA: dynamic mechanical analysis or “Dynamic mechanical analysis” in English;

[0093] - LCM: Liquid Crystal Display Module or "Liquid Crystal Module" or "LCD Module" in English;

[0094] - E: Young's modulus;

[0095] - G*: the complex Coulomb modulus,

[0096] - tan 5: the damping factor also called loss factor,

[0097] - v: Poisson's ratio,

[0098] - PDMS: polydimethylsiloxane,

[0099] - PMMA: poly (methyl methacrylate) or in English “poly (methyl methacrylate)”.

[0100] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0101] Finally, the practical implementation of the embodiments and variants described is within the reach of the person skilled in the art from the functional indications given above.

Claims

CLAIMS 1. Adhesive (30) for a haptic device, the adhesive (30) being transparent, having a glass transition temperature of less than - 50°C, and having, for a frequency greater than or equal to 40kHz, preferably between 60 and 120 kHz, a damping factor of less than 0.4 and, preferably, less than 0.

1.

2. Adhesive (30) according to claim 1, having a refractive index between 1.4 and 1.

54.

3. Adhesive (30) according to one of the preceding claims, having a peel strength greater than 5 N / 20 mm.

4. Adhesive (30) according to any one of the preceding claims, having a Haze factor of less than 2.

5. Adhesive (30) according to any one of the preceding claims, the adhesive being a polysiloxane.

6. Adhesive (30) according to any one of the preceding claims, having a thickness of between 20 pm and 500 pm, preferably between 175 and 300 pm.

7. Haptic device (1) configured to produce haptic feedback by ultrasonic lubrication, in particular a modulation of the coefficient of friction using a bending wave, a shear wave or a compression-expansion wave at an ultrasonic frequency, the device comprising a plate (10), preferably made of glass or plastic, intended to be touched by a user, and in particular by the finger (D) of a user, on which is fixed a stack (20) by means of an adhesive (30), as defined in any one of the claims previous, said plate being provided with at least one haptic actuator (14) capable of setting it into vibration.

8. Device according to claim 7, in which the stack (20) comprises an upper layer (21), made of plastic or glass, on which the adhesive (30) is fixed.

9. Device (1) according to claim 8, wherein the upper layer (21) is a layer for detecting a contact of a user with the plate (10) or a layer for detecting the position of a contact of a user with the plate (10).

10. Device (1) according to claim 8, wherein the upper layer (21) is a polarizer.

11. Device (1) according to claim 10, wherein the stack (20) comprises a liquid crystal display screen (12), preferably arranged between two polarizers (18), one of the polarizers forming the upper layer (21).

12. Device (1) according to one of claims 7 to 10, in which the stack (20) comprises an OLED screen.

13. Automotive dashboard comprising a haptic device (1) according to one of claims 7 to 12.

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