Interface for tactile stimulation using time reversal and for providing enhanced sensations

Description

TECHNICAL FIELD AND STATE OF THE PRIOR ART

[0001] The present invention relates to a time-reversal tactile stimulation interface providing enhanced sensations and to a method of controlling such an interface.

[0002] A tactile stimulation interface is intended to restore tactile information, such as a texture, a relief, a roughness varying in time and / or space, an illusion of pressing a flexible material, of pressing a key.

[0003] Such interfaces are used, for example, in the field of human-machine interfaces. They can also be used in the fields of optics, acoustics, chemistry, and automated manufacturing...

[0004] Some interfaces use an array of actuators, such as piezoelectric or electrostatic, arranged beneath the surface in areas where the fingers are intended to come into contact. When one of the actuators is activated, the entire surface vibrates, and the user, touching the surface with multiple fingers, feels the same stimulation on all fingers.

[0005] WO 2013 / 182611 A1 describes a time-reversal tactile stimulation interface, allowing the display of tactile stimuli of variable shapes and dimensions.

[0006] US 2012 / 0326999 A1 describes a touch interface device that includes a touch-sensitive surface configured to contact an object, first and second actuation assemblies operatively coupled to the touch-sensitive surface, and a controller operatively coupled to the first and second actuation assemblies. The controller operates the first and second actuation assemblies such that the touch-sensitive surface has variable contact with the object to apply a force to the object on the touch-sensitive surface.

[0007] US 2011 / 0199342 A1 describes an apparatus and method for providing non-contact raised, indented, or textured sensations to an object remote from a display device using ultrasonic waves. Methods involving raised, indented, or textured sensations on an object proximate to or in contact with a display device using airborne ultrasound or ultrasonic waves are also described.

[0008] There are tactile interfaces using the time-reversal process, for example described in the paper C. Hudin, J. Lozada, and V. Hayward, "Localized Tactile Feedback on a Transparent Surface through Time-Reversal Wave Focusing," IEEE Transactions on Haptics, vol. 8, no. 2, pp. 188-198, Apr. 2015 .The interface comprises a glass plate and actuators arranged in contact with and on the periphery of the glass plate. The piezoelectric actuators propagate acoustic waves in the glass plate. The implementation of a time reversal method has the advantage of allowing a vibration to be generated in a localized manner on the surface of the plate and allows the different fingers to be stimulated separately; this tactile feedback is also called "multitouch localized tactile feedback".

[0009] This paper proposes to repeat the time-reversal focusing process to form a train of surface displacement pulses to provide intensified stimulation.

[0010] We seek to further enrich the sensations felt by the user. STATEMENT OF THE INVENTION

[0011] It is therefore an aim of the present invention to offer a tactile stimulation interface making it possible to generate different stimulations in different places on the interface and offering enriched sensations.

[0012] The aim stated above is achieved by a tactile stimulation interface according to claim 1 and by a method for controlling a tactile stimulation interface according to claim 9. This document also describes a tactile stimulation interface implementing a time reversal method, said interface comprising a surface intended to be explored tactilely by a user and at least one actuator intended to apply a force to the surface, means for controlling said actuator, said control means determining the force by the time reversal method. The control means send control signals to said actuator so that, to generate the same stimulation, the at least one actuator generates pulses by focusing acoustic waves at a point whose location on the surface varies over time.The different locations of the impulses are located in the area covered, for example, by the fingertip in contact with the surface.

[0013] In other words, the control means control the actuator so as to modulate at least spatially the location of the focal point to generate the same haptic pattern, thereby rendering a wide range of tactile sensations.

[0014] Indeed, the inventors found that the perceived dimension of the focal point by the user was of the order of 1 mm to 2 mm, smaller than the actual size of the focusing task which is of the order of 5 mm. They then determined that by moving the focal point over time to generate the same stimulation, the spatial dimension perceived by the user was greater, which made it possible to offer richer vibrotactile feedback than by repeated focusing at the same point on the surface. The stimulation is for example clicks of variable shapes and perceived amplitudes, a certain stiffness to reproduce the pressing of a button, a texture...

[0015] This spatial modulation of the focal point is made possible by the good spatial resolution of the time reversal process.

[0016] For example, the displacement of the pulse point takes place under the contact area, for example under the pad of the finger exploring the surface. For example, the distance between two focal points is between 100µm and 1mm.

[0017] By performing a rapid point movement, an object larger than the size of a point can be simulated

[0018] Preferably, a learning step makes it possible to establish a database of the impulse responses returned at a certain number of points on the surface, for example distributed in the form of a grid, and the impulse responses between the points of the database are determined by spatial interpolation.

[0019] Very advantageously, the focusing can be repeated over time and modulated in time and / or amplitude.

[0020] Furthermore, the effort applied for example by the finger(s) and / or their position can be taken into account to spatially and advantageously temporally modulate the focus.

[0021] The surface is for example supported by a glass plate

[0022] Preferably, the actuators, for example piezoelectric, are in contact with the outer edge of the glass plate. The surface can then be transparent and can be that of a touch screen.

[0023] The present invention then relates to a tactile stimulation interface comprising a surface intended to be explored tactilely by at least one organ of a user, at least one actuator intended to apply a force to said surface, and means for controlling said at least one actuator, said control means being intended to send to the actuator signals corresponding to the forces to be applied to said surface as a function of the tactile stimulation to be generated on the surface, said forces being determined by a time reversal method. The control means are such that, for at least one given tactile pattern, said at least one actuator is controlled so that it generates in at least one area of ​​said surface, pulses by focusing at least one acoustic wave at a point whose location on the surface varies over time, so as to tactilely stimulate said organ according to the given tactile pattern.

[0024] Advantageously, the control means are capable of controlling said at least one actuator so that it generates pulses in several distinct zones by focusing acoustic waves at a point whose location on the surface varies over time, so as to tactilely stimulate several organs according to given tactile patterns.

[0025] The tactile stimulation interface may advantageously comprise means for detecting the presence of said at least one organ intended to be tactilely stimulated, the detection means being for example of the capacitive type, and / or means for detecting the contact force between the at least one organ intended to be tactilely stimulated and the surface.

[0026] The tactile stimulation interface can include several actuators.

[0027] In an exemplary embodiment, the surface is carried by a plate, the actuator(s) being located in contact with the plate at at least one edge thereof. Advantageously, the plate is transparent.

[0028] The present invention also relates to a method for controlling a tactile stimulation interface according to the invention, so as to tactilely stimulate at least one organ according to a given tactile pattern in at least a first area of ​​the surface, comprising a spatial modulation of at least one focal point of at least one acoustic wave generated by said at least one actuator.

[0029] The process may include the steps: a) determining a returned impulse response for a first point of said area, b) convolving said returned impulse response to said given tactile pattern, c) generating a signal based on the result of said convolution and sending said signal to said at least one actuator and generating pulses to said first point, d) repeating steps a), b) and c) for n other points of said area, n being an integer greater than or equal to 1, at least one point of the n points being distinct from the first point.

[0030] Steps a), b), c) and d) can be carried out simultaneously for the first zone and for a second zone distinct from the first zone, and during step c) the signal sent to said actuator is the sum of the signal generated for the first zone and the signal generated for the second zone.

[0031] Advantageously, the force exerted by the organ on the surface is measured and is taken into account in the generation of the signal.

[0032] According to a characteristic of the invention, the pattern may have a variable amplitude and / or a variable pulse generation frequency.

[0033] In an exemplary embodiment, during step a), the returned impulse response is chosen from a database.

[0034] In another exemplary embodiment, during step a), the returned impulse response is determined by interpolation between at least two returned impulse responses chosen from a database.

[0035] Advantageously, the presence of the organ intended to be tactilely stimulated is detected prior to step a). BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be better understood on the basis of the following description and the attached drawings in which: there Figure 1A is a top view of an exemplary embodiment of a tactile stimulation interface, the Figure 1B is a sectional view of the Figure 1A according to the AA plan, the Figure 1C is a detail view of the Figure 1B at the level of an actuator, the figure 2 is a schematic representation of the successive focal points that can be excited by a touch interface according to the invention, the Figures 3A to 3F are schematic representations of examples of temporal modulation of the displacement amplitude in µm at the focal point as a function of time in ms at different frequencies, the figure 4 is a schematic representation of an example of a method for controlling a tactile stimulation interface according to the invention, the Figure 5is a schematic representation of an example of spatial modulation of the focal point, the figure 6 is a schematic representation of another example of spatial modulation of the focal point, the figure 7 is a schematic representation of another example of spatial modulation of the focal point. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0037] In the present application, it is considered, for the sake of simplicity, that the touch surface is intended to be touched by the pad of a finger D or several fingers. But the surface of the interface according to the invention is capable of applying stimulation to any part of the user's body sensitive to the sense of touch.

[0038] Furthermore, in the present application, the term “tactile pattern” or “tactile feedback” means a set of movements generated in a stimulation zone of the surface of the interface resulting from the activation of the actuators, felt by the part(s) of the body in contact with the surface, in order to reproduce a sensation such as a button being pressed, a texture, a click, etc.

[0039] The term "focus point" refers to the point where the acoustic waves are focused and which is the site of a large amplitude displacement of the surface, and the term "stimulation zone" refers to the area where the tactile pattern is to be generated by successively generating several focus points to reproduce the same haptic pattern.

[0040] On the Figures 1A to 1C , we can see a first example of the embodiment of a touch interface according to the invention.

[0041] The tactile interface I1 comprises a frame 2, an element 3 provided with a surface 4 held on the frame 2, and on which for example one or more fingers can come into contact, and actuators 6 fixed on the element 3 and capable of applying a mechanical stress to the surface 4, the stress being oriented transversely relative to the surface. The suspended part of the surface 4 forms a surface intended to be explored tactilely.

[0042] Element 3 is, in the example shown, in the form of a plate.

[0043] The frame forms a rigid support for the plate 3. Advantageously, a damping material 9 is interposed between the plate 3 and the frame. Advantageously, the damping material 9 is an adhesive foam, which in addition to attenuating vibrations in the plate 3, holds the plate 3 on the frame.

[0044] The actuators 6 are fixed, for example by gluing on the face 11 of the plate 3 opposite the surface 4. In the example shown, the actuators are mounted along the edges of the plate. In another example, the actuators could be arranged at any point of the element 3. In addition, the actuators could be on the touch surface 4.

[0045] Surface 4 is intended to be the seat of bending waves or transverse waves generated by the constraints applied by the actuators. According to the invention, the bending waves are focused so as to produce tactile stimulation at the focal point.

[0046] The element 3 carrying the surface 4 is for example a rigid substrate, transparent or not. The substrate can be flat or curved. The substrate can comprise one or more materials. In addition, it can have a thickness of between 0.1 mm and 5 mm.

[0047] For example, the element 3 carrying the surface 4 is for example a transparent plate made of glass, polycarbonate, PMMA, or a non-transparent plate made of metal, ceramic, plastic or other.

[0048] The implementation of a transparent substrate makes it possible, for example, to adapt the interface to a screen, for example to a touchscreen tablet screen.

[0049] In the example shown, the actuators are piezoelectric actuators. They comprise a piezoelectric material and two electrodes on either side of the piezoelectric material allowing a potential difference to be applied to it. Applying a potential difference across the terminals of the piezoelectric actuator produces tangential forces on the surface of the plate. This force curves the surface of the plate. This results in a displacement in the direction perpendicular to the plane of the surface.

[0050] Alternatively, the actuators can be electromagnetic. In this case, a force perpendicular to the plane of the surface is produced by the action of an electromagnetic field on a magnet. The magnet or coil is secured to the surface.

[0051] In the example shown, the interface comprises thirty-two actuators, however this number is not limiting. For example, one can provide 1, 10 or several dozen actuators, for example 40, distributed on the support along the edges of the plate.

[0052] The interface also includes a control unit UC intended to generate signals to the actuators so that they apply forces to the surface, so as to generate bending waves at a given focal point.

[0053] The forces applied by the actuators 6 on the surface 4 are calculated by a time reversal process, which allows the actuators to generate constructively interfering waves at one or more given points on the surface and at a desired time. The user feels, not the waves propagating in the plate but the impulse produced at the point(s) and at the desired time due to the constructive interference. The gain of the actuators is adjusted so that the amplitude everywhere else, outside the focal point, is such that the vibration is not perceived. The contrast, which designates the ratio of the amplitude at the focal point to the mean square amplitude at any other point, is therefore a critical quantity that must be maximized to produce a clearly perceived stimulation at the focal point without creating a stimulus at another point.In the example shown, the contrast for a single focus is C=43 and the amplitude at the focus point reaches a=14 µm.

[0054] The adhesive foam, present in the example, serves on the one hand to hold the plate on its support and on the other hand to attenuate its vibrations. This attenuation makes it possible to reduce the attenuation constant τ and thus reduce the focusing repetition period T r without altering the repeated focusing contrast Ĉ , according to the expression given below. This attenuation can also be adjusted by an appropriate choice of material for the plate or by adding a film to its surface.

[0055] Advantageously, sensors detecting the presence of the user's fingers on the interface can also be implemented, which makes it possible to generate tactile stimulation only in the areas currently being explored by the fingers. The power consumption of the interface can then be reduced, which is particularly interesting in the case of tactile stimulation interfaces applied to portable devices. These may be, for example, optical or capacitive sensors.

[0056] Finger position detection is achieved, for example, by capacitive means, with the plate bearing the surface forming one of the plates of a variable-capacitance capacitor and the fingertip forming the other plate. Furthermore, it is possible to track the movement of the fingers.

[0057] A device capable of measuring the value of the interaction force exerted locally or on the entire interface can also be added, in order to link the impulses produced by focusing to the forces exerted by the finger(s) in contact with the plate.

[0058] We will briefly describe the principle of time reversal focusing.

[0059] The principle of time reversal of waves is based on the invariance of the equation of wave propagation by time reversal and on the principle of reciprocity.

[0060] Either h ( xa |x q, there is | yq ,t) the out-of-plane displacement of the surface recorded over time t at a point with coordinates ( xa, there is ) after a pulse signal has been emitted by an actuator in ( xq ,yq ) . We call h ( xa | xq , there is | yq ,t) the impulse response between the pointsa and q.

[0061] Considering that the response of the plate and actuator system is linear, if the actuator located at q no longer emits a pulse but a signal sq ( t ) , the displacement at the point a is then given by: u ( xa,y a,t ) = h ( xa | xq, there is | yq ,t ) ⊗ sq ( t ) with ⊗ the convolution operator.

[0062] Thus, if the actuator located at q emits, no longer an impulse but the impulse response returned temporally from time T to the initial time t = 0, or s q t = h x a x q y a y q , T − t avec 0 < t < T , the displacement produced at any point b will be: u x b y b t = h x b x q y b y q , t ⊗ s q t = h x b x q y b y q , t ⊗ h x a x q y a y q , T − t = ∫ 0 t h x b x q y b y q , t − ξ h x a x q y a y q , T − ξ dξ

[0063] The displacement is thus the result of the integral of the product of two functions which are a priori not correlated, the result of which is therefore of zero mean. At any point b and any instant t, we have a displacement of zero mean which constitutes a background vibration present over the entire plate. On the other hand, at instant t = T corresponding to the end of the emission phase by the actuator, we obtain at the point a a move: u x a y a T = ∫ 0 T h x a x q y a y q , T − ξ d <mprescripts / > <none / > 2 ξ

[0064] This time we integrate a strictly positive quantity. The result is a non-zero displacement of large amplitude. This displacement is obtained only at the point a and right now T, hence the focusing of waves in space and time.

[0065] In the case where Q actuators are used, their contributions add up to give: u x y t = ∑ q = 1 Q u q x y t

[0066] Contrast is defined as the ratio between the displacement at the focal point at time T and the standard deviation of this displacement at any point b. It is obtained by the relation: C = BT c Qτ 1 − e − 2 T / τ Q + 1 τ 1 − e − 2 T τ + T c

[0067] With Q the number of actuators, T the duration of the reversal window, τ the vibration attenuation time constant in the plate and T c the characteristic time of the plate or modal density of the plate in seconds, or natural mode per Hz and B = f max - f min the bandwidth, in hertz, of the signals emitted by the actuators.

[0068] Since the focus is repeated over time with a period T r , the contrast is affected according to the relationship: C ^ = C 1 − e − 2 T r / τ

[0069] To preserve contrast, successive focusings are repeated with a period T r ≥ τ.

[0070] The average frequency of the signals defines the maximum resolution achievable by the relation: R s = D ρ s 4 8 2 πf m

[0071] With R s spatial resolution, or width at half maximum of the focal point, f m = f max + f min 2 the average frequency of the emitted signals, D the bending rigidity and ρ s the mass per unit area of ​​the plate. The impulse responses h(t) can be obtained either experimentally by actually recording the impulse responses, or by simulation, or analytically when the geometry remains simple.

[0072] A database of impulse responses returned at different points on the surface is then created; this database is used to generate the signals sent to the actuators. This may be at all points on the surface or according to a very tight mesh, in order to provide high resolution in the stimulation. Alternatively and in a particularly advantageous manner, a database of impulse responses is created at a given number of points on the surface, for example distributed in the form of a grid or a contour of the surface, and the impulse responses between the points of the grid are determined, for example by interpolation, which thus makes it possible to determine an impulse response at any point on the surface, and to reduce the time taken to create the database and its size.Interpolation can be done using different methods, for example Fourier interpolation, the Compressed Sensing method, fundamental solution methods, or a method based on a variational form of the propagation equation.

[0073] The duration of the surface movements is variable, for example in the order of 10 ms to 100 ms, depending on the pattern to be reproduced and the desired contrast, and the efforts can be repeated at the desired frequency and amplitude. The contrast and amplitude obtained at the focal point depend on the dimension of the interface, the vibration damping and the number of actuators. The number of actuators can be chosen according to the interface.

[0074] According to the invention, for the same tactile pattern, also referred to as a "stimulation event", it is planned to spatially modulate the focal point, i.e. to move the focal point in the stimulation zone. In the prior art, to obtain a haptic pattern, the actuator(s) are controlled to cause a displacement of the surface at a single point on the surface, this displacement being able to be repeated over time. According to the invention, the displacement of the surface takes place successively at different points on the surface located in the stimulation zone in contact with the fingertip. For example, on the figure 2 , we can see a finger on a surface and in transparency the different locations of the focal point PF i , the index i corresponding to the order of occurrence of the displacement of the location during the stimulation event.

[0075] For example, the fingertip is in contact with the surface having an area of ​​1 cm 2< , this area corresponding to the stimulation area, and the focal point is moved successively in the stimulation area of ​​1 cm 2< . For example, the distance between the two successive locations of the focal point is of the order of 0.1 mm to 1 mm. The inventors determined that the size of each focal point actually felt by the user was between 0.1 mm and 2 mm, which is significantly smaller than the size of the focal spot which is the area set in motion by the focusing of the constructive waves. This is for example confirmed by the document G. Von Bekesy, "Similarities between hearing and skin sensations," Psychological review, vol. 66, no. 1, pp. 1-22, Jan. 1959 which shows a spatially extended but short-term displacement is perceived as punctate.Thus, by moving the point where the waves are focused, the stimulated area of ​​the fingertip is larger than that of a single fixed focal point, which improves sensation and allows for the generation of complex patterns and therefore enriches communication. Moving the focal point has the effect of exciting more mechanoreceptors and producing a more intense stimulus.

[0076] The relative arrangement of the focal points can be variable. For example, this arrangement can correspond to a circle, a spiral, a triangle, a square, a hexagon, a straight or curved line, etc. It should be noted that, according to the invention, the user does not distinguish this shape, but it is chosen to make the stimulation richer.

[0077] This modulation of the location of the focal point makes it possible to significantly enrich the range of tactile sensations felt by the user.

[0078] On the figure 4 , we can see a schematic representation of the method of generating signals to actuators of a touch interface according to the invention.

[0079] In the example shown, the control unit simultaneously generates stimulation zones a and b for two fingers D1 and D2.

[0080] It is desired to generate a first tactile pattern in zone a and a second tactile pattern in zone b. According to the invention, for at least one pattern, several focal points are associated in each stimulation zone. It will be understood that the interface may comprise patterns comprising several focal points.

[0081] Each zone has a generation map Pa, Pb of the focal points. For zone a, the focal points are designated PFai, and for zone b, the focal points are designated PFbi, i designating the generation order of the point. For zone a, the focal points will be distributed on a straight line and for zone b, the focal points will be distributed on a spiral. Any other distribution is possible. As explained above, the user is not able to feel the type of distribution of the points, he only feels a tactile stimulation.

[0082] In an exemplary embodiment, the distribution of the focal points may vary in the same area over time.

[0083] The location of each focus point is determined by its coordinates in the (x, y) frame designated (xai, yai) and (xbi, ybi).

[0084] Each pattern is defined by an amplitude of surface displacement at each focus point and by a frequency of repetition of the focus points, the frequency and amplitude being able to be constant or variable.

[0085] In the example shown, the pattern in area a is defined by the function Ua(xai, yai, t) and the pattern in area b is defined by the function Ub(xbi, ybi, t).

[0086] In the example shown in the figure 4 , the pattern in area a has a constant frequency amplitude variation and the pattern in area b has a constant frequency amplitude variation.

[0087] It will be understood that the patterns can be of any type and for example have a variable amplitude at variable frequency. In addition, the characteristics of the pattern can be modified depending on other parameters such as the force exerted by the finger on the surface as will be described below.

[0088] In a first step, the contact of the finger(s) with the surface can be detected, so as to only generate stimulation in the presence of fingers.

[0089] In a next step, the signal to be sent to each actuator is determined.

[0090] For zone a and pattern Ua, we want to excite point PFa1 first.

[0091] First, the returned impulse response database BD is searched for the returned impulse response at point Pfa1. Either the response exists because it has been determined previously, or it is determined by spatial interpolation as explained above (step 100). This response is designated hq(xai, yai, Tt).

[0092] Each impulse response is then convolved to the temporal pattern Ua (step 102).

[0093] The same steps are performed for area b at point PFb1 (steps 104 and 106), the returned impulse response is convolved to the pattern Ub.

[0094] A signal corresponding to the sum of the signals calculated for each point (step 108) is sent to an actuator. In the case where there are several actuators in the surface, this set of operations is carried out simultaneously for each actuator of the surface. Each actuator emits its own impulse response, depending in particular on its position in the surface and the type of actuator.

[0095] Very advantageously, a signal amplification step 110 takes place.

[0096] The above steps are repeated for all focus points PFa2 to PFan and PFb2 to PFbn.

[0097] In the example shown, the generation frequencies of the focus points PFai and PFbi vary over time and are different from each other.

[0098] Each zone a and b then comprises a cloud of focusing points, the focusing points being excited successively.

[0099] The excitation time of each focus point may vary from one focus point to another.

[0100] On Figure 5, we can see an example of spatial and temporal modulation of the focus point along the X axis. We can see the successive location of the focus points PFai for example. In this example, the focus points reappear periodically at the same locations. In addition, the Ua pattern is shown, which has a constant amplitude and a constant frequency of generation of the focus points.

[0101] On the figure 6 , we can see another example of spatial and temporal modulation of the focal point along the X axis.

[0102] In this example, we consider three sliding focal points a1, a2, a3, which move over time. The displacement of each point over time is linear and only one of the points is activated. The focus at point a1 alternates with that at points a2 and a3. The amplitudes are the same at points a1, a2, a3. The patterns for each point are designated Ua1, Ua2, Ua3. The perceived amplitude is maximum.

[0103] As a result, the points cross area a.

[0104] In the examples of the Figures 5 and 6 , the focus points are arranged in a line, but they could be arranged in a two-dimensional pattern, for example in a circle.

[0105] On the figure 7 , the focus points are generated on a line with an evolving amplitude. The focus points could be arranged in a two-dimensional pattern, for example on a circle.

[0106] On the Figures 3A to 3F , we can see different examples of temporal modulation of the amplitude Amp of displacement in µm at the focal point as a function of time t in ms. For the modulations of the Figures 3A, 3C, and 3F , the frequency is for example 200 Hz and for the modulations of the Figures 3B, 3D and 3F , the frequency is for example 500 Hz.

[0107] On the Figure 3A and 3B , temporal modulations are repetitions of the displacement at the same amplitude and constant frequency, which corresponds to an aggressive pattern. Among all the displacements PF i , at least two occur in different locations.

[0108] On the Figure 3C and 3D , the temporal modulations are repetitions of the displacement at increasing, then decreasing amplitude and at constant frequency, which corresponds to a progressive pattern. Among all the displacements PF i , at least two take place at different locations.

[0109] On the Figures 3E and 3F, temporal modulations are repetitions of the displacement at decreasing amplitude and the same frequency, which corresponds to an aggressive pattern at the beginning, which gradually softens. Among all PFi displacements, at least two occur in different locations.

[0110] It will be understood that for each stimulation event, focusing takes place at least in two different focusing points. It can therefore be considered that, for a stimulation event, 10 focusing points are excited but only two are in different locations.

[0111] Also very advantageously, it is possible to modulate the characteristics of the movement as a function of the value of the force applied by the user's finger and the position of the finger (step 112). For example, if a focus is produced each time the exerted force crosses a threshold, the illusion of pressing on a surface having a certain stiffness is produced. It is this method which allows the restitution of a sensation of stiffness. A high pressing force makes it possible to focus on a larger surface.

[0112] The interface advantageously includes means for determining the force applied by the user to the surface. For example, a force sensor integrated into the plate support can be used, which makes it possible to measure the total force applied to the surface. For a measurement of the force exerted locally, a matrix of piezoresistive sensors, for example, could be used.

[0113] Advantageously, the interface may also include one or more sensors. For example, this may be a temperature sensor for the environment in which the interface is located. Indeed, the temperature can modify the propagation speed of the waves in the surface. This temperature information can therefore be used to correct the signals sent to the actuators to take into account this change in propagation speed.

[0114] The invention can also be used, very advantageously, to guide the movements of the user. For example, a decrease in the discretized focusing amplitude on a line makes it possible to guide a finger towards this direction. A low amplitude gives the impression of facilitating a movement of the finger towards the direction with decreasing amplitude, which encourages the user to move his or her finger in this direction.

Claims

1. Tactile stimulation interface including a surface (4) intended to be explored tactilely by at least one of a user's organs, at least one actuator (6) intended to apply a force on said surface (4), and means for controlling said at least one actuator, said control means being intended to send the actuator (6) signals corresponding to the forces to be applied to said surface according to the tactile stimulation to be generated on the surface, said forces being determined by means of a time reversal method, the tactile stimulation interface being characterised in that, for at least one tactile stimulation in a given stimulation zone (a, b) of the surface, said stimulation zone being in contact with the user's organ according to a given tactile pattern, the control means are configured to control said at least one actuator (4) such that it generates in said at least one given stimulation zone (a, b) of the surface in contact with the user's organ, pulses by focusing at least one acoustic wave at a point, the location of which on the surface in said given stimulation zone varies over time, so as to stimulate said organ tactilely according to the given tactile pattern.

2. Tactile stimulation interface according to claim 1, wherein the given stimulation zone corresponds to a surface area substantially equal to that of the user's organ.

3. Tactile stimulation interface according to claim 1 or 2, wherein the control means are configured to control said at least one actuator such that it generates in several different given stimulation zones pulses by focusing acoustic waves at a point of each given stimulation zone, the location of which on the surface varies in a given stimulation zone over time, so as to stimulate several organs tactilely according to given tactile patterns.

4. Tactile stimulation interface according to claim 1, 2 or 3, including means for detecting the presence of said at least one organ intended to be stimulated tactilely, the detection means being for example of capacitive type.

5. Tactile stimulation interface according to one of claims 1 to 4, including means for detecting the contact force between the at least one organ intended to be stimulated tactilely and the surface.

6. Tactile stimulation interface according to one of claims 1 to 5, including several actuators (6).

7. Tactile stimulation interface according to one of claims 1 to 6, wherein the surface is borne by a plate, the actuator (s) (6) being located in contact with the plate at the level of at least one edge thereof.

8. Tactile stimulation interface according to claim 7, wherein the plate is transparent.

9. Method for controlling a tactile stimulation interface according to one of claims 1 to 8, so as to stimulate at least one organ tactilely according to a given tactile pattern in at least a first given stimulation zone of the surface, including a spatial modulation of at least one focusing point of at least one acoustic wave generated by said at least one actuator.

10. Method for controlling a tactile stimulation interface according to claim 9, so as to stimulate at least one organ tactilely according to a given tactile pattern in at least a first given stimulation zone of the surface, including the steps of: a) determining a reversed impulse response for a first point of said given stimulation zone, b) convolving said reversed impulse response to said given tactile pattern, c) generating a signal based on the result of said convolution and sending said signal to said at least one actuator and generating pulses at said first point, d) repeating steps a), b) and c) for n other points of said given stimulation zone, n being an integer greater than or equal to 1, at least one point of the n points being different from the first point.

11. Control method according to claim 10, wherein steps a), b), c) and d) are carried out simultaneously for the first given stimulation zone and for a second given stimulation zone different from the first given stimulation zone, and during step c), the signal sent to said actuator and the sum of the signal generated for the first given stimulation zone and the signal generated for the second given stimulation zone.

12. Control method according to one of claims 9 to 11, wherein the force exerted by the organ on the surface is measured and is taken into account in the generation of the signal.

13. Control method according to one of claims 9 to 12, wherein the pattern has a variable amplitude and / or a variable pulse generation frequency.

14. Control method according to one of claims 9 to 13, wherein, during step a), the reversed impulse response is selected in a database.

15. Control method according to one of claims 9 to 14, wherein, during step a), the reversed impulse response is determined by interpolation between at least reversed impulse responses selected in a database.