Touch interface for driving an external member using ultrasonic vibrations

Abstract

The invention relates to a method for controlling an interface comprising a pad, the method comprising a) detecting contact on the pad; b) determining a position of the point of contact on the pad; c) on the basis of the position resulting from b), determining a haptic pattern to be applied to the contact member at the point of contact, wherein the haptic pattern comprises a movement of the pad at the point of contact; d) using a processing unit, calculating a control signal to be applied to each actuator so as to produce the haptic pattern at the point of contact, and wherein each actuator induces a progressive bending wave that propagates along the pad so as to create a vibration of the pad at the point of contact, thereby causing the pad to move at the point of contact; e) repeating steps a) to d).

Description

[0001]Tactile interface enabling the training of an external organ by ultrasonic vibrations Description TECHNICAL FIELD The technical field of the invention relates to tactile interfaces. PRIOR ART Tactile interfaces, such as touch screens, have already been described, enabling information to be intuitively encoded to the user, via a sensation felt at the finger, under the effect of a vibration of the screen. In a first type of application, the screen vibrates at a relatively low vibration frequency, generally a few hundred Hz. The interface is called vibrotactile. The vibrations are directly felt by the finger. Application examples are described in Pantera L et al. “Multitouch vibrotactile feedback on a tactile screen by the inverse filter technique: vibration amplitude and spatial resolution”, IEEE transactions on haptics, Vol.13, No.3, July-Sept. 2020. In a second type of application,the slab vibrates at an ultrasonic frequency: in this frequency range, touch is not, or is only slightly, directly sensitive. However, under the effect of an ultrasonic vibration, an air film is created between the finger and the surface, reducing the friction of the finger on the slab. Thus, when a finger is moving along a slab, the friction of the latter on the slab can be modulated when the slab vibrates at an ultrasonic frequency. By modulating the friction, a sensation of texturing can be perceived, as described in Cai Z "Ultraloop: Active lateral force feedback using resonant traveling waves" or in Garcia "2MoTac: Simulation of button click by superposition of two ultrasonic plate waves". In this publication, ultrasonic vibrations make it possible to feel a button click effect. US20120326999 describes a haptic interface, of the tactile surface type, configured to move an external body,the latter being able to be a finger or a stylus. The invention described below aims to produce a haptic effect aimed at directing the finger of a user, or another external organ (stylus for example), so that the finger slides, along a slab, in a given direction. The objective is for example to guide a finger of a user to reach a target, or follow a predetermined trajectory along the slab. The invention can thus be aimed at visually impaired people, or whose field of observation does not target the slab, for example drivers of a vehicle. DISCLOSURE OF THE INVENTION A first object of the invention is a method for controlling an interface, the interface comprising: - a slab, configured to be touched by a contact member, at a point of contact, the slab extending along a plane perpendicular to a transverse axis, the slab extending, in the plane, along a longitudinal axis; - actuators, arranged against the slab,each actuator being configured to induce an ultrasonic vibration of the slab when it is subjected to a control signal; - a position sensor (15), configured to detect a position of the contact point on the slab; the method comprising: a) detecting a contact on the slab; b) determining a position of the contact point on the slab; c) from the position resulting from b), determining a displacement of the slab at the contact point; d) using a processing unit, calculating a control signal to be applied to each actuator so as to produce the displacement of the slab at the contact point, each actuator inducing a progressive bending wave propagating along the slab, so as to form a vibration of the slab at the contact point, causing the displacement of the slab at the contact point; e) repeating steps a) to d), until a criterion for stopping the iterations is reached,or output of the algorithm. Step c) may comprise a determination of a periodic displacement of the slab, at the point of contact, at the ultrasonic frequency, such that during each period: - the displacement of the slab combines a displacement along the transverse axis and a displacement along the plane of the slab; - the displacement of the slab, in the plane of the slab, progresses according to an orientation angle, relative to the longitudinal axis, when the displacement, along the transverse axis, progresses towards the external member, so as to induce a sliding of the contact member, along the slab, according to said orientation angle. During each period, the displacement of the slab, along the transverse axis, and the displacement of the slab, in the plane of the slab, may be linked by a periodic time function, describing an ellipse. The slab extending along a lateral axis, perpendicular to the longitudinal axis, during each period, the displacement,at the point of contact, in the plane of the slab, may include: - a longitudinal component, along the longitudinal axis, depending on the orientation angle; - a lateral component, along the lateral axis, depending on the orientation angle; - so as to induce sliding of the member, by a combination of the longitudinal component and the lateral component. The longitudinal component may depend on a spatial derivative, along the longitudinal axis, of the displacement along the transverse axis. The lateral component may depend on a spatial derivative, along the lateral axis, of the displacement along the transverse axis. According to one possibility, a ratio between the displacement, along the transverse axis, and the displacement, in the plane of the slab,is greater than 0.3. According to one possibility: - step a) comprises a detection of several contact points spaced from each other; - step b) comprises a determination of the position of each contact point; - step c) comprises a determination of the displacement of the slab at each contact point, each contact point being assigned an orientation angle; - step d) comprises a calculation of the control signal to be applied to each actuator so as to obtain, at each contact point, the displacement determined during step c). Step d) may comprise an inversion of a direct model, the direct model establishing a relationship between a displacement at each contact point and a control signal from each actuator. Step d) may comprise: - di) formation of a response matrix comprising, for each actuator, a displacement of the slab, at each contact point,as a function of the actuator control signal; - dii) determining a pseudo-inverse of the response matrix, so as to define the control signal of each actuator. Sub-step di) may comprise an extraction, from a memory, of unit displacements, each unit displacement corresponding to a displacement, along the transverse axis or in the plane, generated at each contact point, by an actuator controlled by a unit control signal, the unit displacement being defined for each actuator during a calibration. The calibration may comprise a successive command of each actuator, and a measurement of a displacement of the slab, along the transverse axis, at different points of the slab. The calibration may comprise a modeling of a successive command of each actuator, and a modeling of a displacement of the slab, along the transverse axis, or in the plane of the slab,at different points of the slab. A second subject of the invention is an interface comprising: - a slab, configured to be touched by one or more contact members, at one or more contact points, - actuators, arranged against the slab, each actuator being configured to cause a vibration of the slab when it is subjected to a control signal; - a position sensor, configured to detect a position of the contact point; - a processing unit, configured to implement steps a) to d) of a method according to the first subject of the invention;. The interface may be a haptic interface, configured to control a device. The invention will be better understood upon reading the description of the exemplary embodiments presented in the remainder of the description,in connection with the figures listed below. FIGURES Figure 1 shows a diagram of an example of a slab forming a haptic interface according to the invention. Figure 2 shows the main processing steps for controlling the actuators of the slab to generate haptic feedback. Figure 3A shows a position of a point of contact of a finger on a slab. Figure 3B shows displacements of the slab (y-axis – unit µm) as a function of time (x-axis – unit ms) along an X axis, a Y axis and a transverse Z axis, so as to generate a sliding of a finger parallel to the X axis. Figure 3C shows the displacements of the slab along the Z axis (y-axis – unit µm) as a function of displacements of the slab along the X axis (x-axis – unit µm),corresponding to the time displacements shown in Figure 3B. Figure 3D shows the displacements of the slab along the Z axis (ordinate axis - unit µm) as a function of displacements of the slab along the Y axis (abscissa axis - unit µm), corresponding to the time displacements shown in Figure 3B. Figure 3E shows displacements of the slab (ordinate axis - unit µm) as a function of time (abscissa axis - unit ms) along the X axis, the Y axis and the transverse Z axis, so as to generate a sliding of the finger parallel to the Y axis. Figure 3F shows the displacements of the slab along the Z axis (ordinate axis - unit µm) as a function of displacements of the slab along the X axis (abscissa axis - unit µm), corresponding to the time displacements shown in Figure 3E. Figure 3G shows the slab displacements along the Z axis (ordinate axis - unit µm) as a function of the slab displacements along the Y axis (abscissa axis - unit µm),corresponding to the time displacements shown in Figure 3E. Figure 4A shows a position of several contact points of a finger on a slab. Figure 4B shows displacements of the slab (y-axis – unit µm) as a function of time (x-axis – unit ms) along the X axis, the Y axis and the transverse Z axis, so as to generate a sliding of a first finger parallel to the X axis. Figure 4C shows displacements of the slab (y-axis – unit µm) as a function of time (x-axis – unit ms) along the X axis, the Y axis and the transverse Z axis, so as to generate a sliding of a second finger in a direction of 45° relative to the X axis (or the Y axis). Figure 4D shows the displacements of the slab along the Z axis (ordinate axis - unit µm) as a function of displacements along - the Y axis (abscissa axis - unit µm), top curve, - the X axis (abscissa axis - unit µm), middle curve,- as well as the displacement along the Y axis (ordinate axis – unit µm) as a function of the displacement along the X axis (abscissa axis – unit µm), bottom curve. corresponding to the temporal displacements of the first finger shown in Figure 4B. Figure 4E shows the displacements along the Z axis (ordinate axis – unit µm) as a function of displacements along - the Y axis (abscissa axis – unit µm), top curve, - the X axis (abscissa axis – unit µm), middle curve, - as well as the displacement along the Y axis (ordinate axis – unit µm) as a function of the displacement along the X axis (abscissa axis – unit µm), bottom curve. corresponding to the temporal displacements of the first finger shown in Figure 4C. Figure 4F shows slab displacements (y-axis – unit µm) as a function of time (x-axis – unit ms) along the X-axis, the Y-axis and the transverse Z-axis,so as to generate a sliding of a first finger parallel to the Y axis. Figure 4G shows displacements (y-axis – unit µm) as a function of time (x-axis – unit ms) along an X axis, a Y axis and a transverse Z axis, so as to generate a sliding of a second finger parallel to the X axis. Figure 4H shows the displacements of the slab along the Z axis (y-axis – unit µm) as a function of displacements along - the Y axis (x-axis – unit µm), top curve, - the X axis (x-axis – unit µm), bottom curve, corresponding to the temporal displacements of the first finger shown in Figure 4F. Figure 4I shows the displacements of the slab along the Z axis (ordinate axis - unit µm) as a function of displacements along - the Y axis (abscissa axis - unit µm), top curve, - the X axis (abscissa axis - unit µm), bottom curve,corresponding to the temporal displacements of the first finger shown in Figure 4G. DISCLOSURE OF PARTICULAR EMBODIMENTS Figure 1 shows a haptic interface 1, intended to be touched by an external member 3, for example a finger, to control a device 2. The device may be, in a non-limiting manner, a consumer appliance, the dashboard of a vehicle, a device for identifying a person, or a device for assisting a visually impaired or disabled person. In the examples shown in this application, the external member 3 is a finger, which corresponds to most of the applications envisaged. Alternatively, the external member 3 may be a stylus, or any other means for acting on the interface 1. In the present case, the interface is haptic, but it may be a slab, forming an interface configured to control a movement of an object, for example particles, or small objects,millimeter-sized. The object must have sufficient inertia so that the plate can be moved relative to it during vibrations. The haptic interface comprises a slab 10, rigid, transparent or opaque. The slab 10 may for example comprise glass or a metal, or an organic compound, for example plexiglass. The slab 10 is delimited by a contact surface 11, intended to be touched by the external member. The thickness e of the slab 10 is preferably less than 10 mm, or even less than 5 mm. The thickness e is adjusted according to the dimensions of the slab, and the mechanical properties of the material forming the slab (rigidity, solidity). It is for example between 1 and 5 mm for glass or a material such as plexiglass. The slab 10 extends parallel to a longitudinal axis X and a lateral axis Y. The lateral axis and the longitudinal axis define the plane of the slab P, XYThe thickness of the slab is defined along a transverse axis Z, perpendicular to the contact surface 11. The slab 10 is coupled to actuators 12 q , for example piezoelectric actuators, ^^ being an integer designating each actuator, with 1 ≤ ^^ ≤ ^^. ^^ corresponds to the number of actuators. Each actuator is configured to move the slab, by generating a vibration in an ultrasonic frequency range, extending beyond 20 kHz, typically in the spectral band [20 kHz – 100 kHz]. Each actuator 12 q is powered by a control signal ^^ ^ , so as to generate a vibration whose characteristics (amplitude, frequency) are configured to produce a predetermined haptic feedback from the interface. The control signals ^^ ^ are transmitted, via a control circuit 13 to each actuator 12 q . In this example, each piezoelectric actuator 12 qcomprises a piezoelectric material, for example AlN, ZnO or PZT, arranged between two electrodes. Each actuator can be connected to the slab by gluing. According to one variant, the actuators 12 qmay be electromagnetic or electromechanical actuators. The touch surface 11 comprises a position sensor 15, for example of the capacitive type. The position sensor 15 is connected to conductive tracks 14, arranged in a two-dimensional network. The conductive tracks 14 are adjacent to the contact surface 11. The conductive tracks extend parallel to the slab 10, or in the slab 10, below the contact surface 11. When the slab 10 is opaque, the conductive tracks 14 may be made from a standard conductive material, for example a metal. When the slab 10 is transparent, the conductive tracks 14 are preferably made from a transparent conductive material, for example a conductive oxide, a standard material being ITO (Indium Tin Oxide). The conductive tracks 14 preferably extend along rows (parallel to the X axis) and columns (parallel to the Y axis).The conductive tracks can be polarized according to a polarization voltage. The slab 10 comprises an insulating layer extending between the conductive tracks 14 and the contact surface 11, so as to allow detection, by capacitive effect, of a contact with the finger 3 of a user, or any other type of external organ. The position sensor 15 is configured to generate a position signal ^^ comprising the number ^^ and the position ^^^ ൌ ^^^^, ^^^^ of contact points on the contact surface 11. The conductive tracks 14 make it possible to form a mesh on the slab, defining mesh points ^^, each point of the mesh corresponding to a position capable of being detected by the position sensor. The number of positions is determined as a function of the spatial resolution of the position sensor, which depends on the spacing between the conductive tracks 14.It is possible to take into account a number of positions lower than that determined by the spatial resolution of the position sensor. This involves taking into account the support surface of a finger, extending along a diameter of a few mm, for example 5 mm. Thus, the spatial resolution of the position sensor and the conductive tracks makes it possible to define a maximum number of positions ^^. ^^௫ . The haptic interface 1 takes into account a number ^^ of different positions, likely to be occupied by the finger 3 on the contact surface 11, with ^^ ^^^ ^^௫ . The position sensor is not necessarily capacitive. It can be a resistive touch sensor or an infrared optical sensor. The interface 1 comprises a processing unit 20, supplied, at different measurement times, by the position signal ^^ generated by the position sensor 15. The processing unit 20 is intended to address a control signal ^^ ^to the control circuit 13, so that the latter transmits each control signal ^^ ^ respectively to each actuator 12 q . The control circuit comprises, for example, digital-to-analog converters, so as to form an analog control signal for each actuator from digital instructions resulting from the processing unit 20. The processing unit 20 is configured to determine a vibration pattern as a function of the position of each finger 3 contacting the contact surface 11. The haptic pattern tends to induce a sliding of the finger towards a target T on the slab. Thus, at each position (^^^, ^^^) detected, the haptic interface defines a haptic pattern tending to make the finger slide according to an orientation angle ^^ ^The processing unit 20 comprises a microprocessor, connected to a memory 25 in which instructions are stored allowing implementation, by the microprocessor, of certain steps described in connection with FIG. 2. Preferably, the actuators 12 qare distributed under the slab, advantageously forming a regular mesh. Figure 2 illustrates the main steps of an iterative process implemented by the haptic interface 1: 100: at a measurement instant, one or more fingers ^^ touch the slab. ^^ is an integer designating the number of fingers simultaneously touching the slab. The detection of a contact on the slab triggers steps 110 to 140 described later. 110: the position of each finger touching the slab is determined by the position sensor 15. This results in the formation of a position signal ^^ for each point of contact. The position signal has 2 components: ^^^, ^^^ for each point of contact detected. The index ^^ designates each finger in contact with the slab. : determination of a haptic pattern for each point of contact in contact with the slab.This involves determining a haptic pattern which, when felt, causes the finger to slide along the slab along a trajectory making an orientation angle ^ with a reference axis, for example the X axis. The trajectory depends on the position of the finger relative to the target position T, i.e. a position that the finger is desired to reach. Step 120 is implemented by the processing unit, depending on the position of the finger ^^^, ^^^ and the target position T. When several fingers touch the slab, a target position ^^. ^ can be assigned to each finger. During this step, we define a target displacement ^^⃗^ ^^^^, ^^^, ^^^, applied to the slab, at each contact point, so that each finger reaches the target position assigned to it. The displacement of the slab, at the contact point (^^^, ^^^), and at time ^^, can be written in a vector form: The displacement thus includes a longitudinal component ^^ ௫ , along the longitudinal axis X, a lateral component ^^ ௬ along the lateral Y axis and a transverse component ^^ ௭ along the transverse axis Z. Each term of the displacement vector ^^⃗^ ^^^^, ^^^, ^^^ corresponds to a progressive harmonic wave propagating in the plane P XY of the slab. In the frequency domain, the displacement ^^ ^ (w) , at frequency (^^) is written: The maximum amplitude of each displacement is a few µm, for example 1 µm or 2 µm. Step 130: Determination of the control signal ^^ ^ ^^^^ of each actuator 12 q , so as to obtain the target displacement ^^^⃗ ^^^^, ^^^, ^^^ at each contact point ^^^^, ^^^). During this step, the processing unit 20 calculates the control signal ^^ ^^^^^ to be applied to each actuator 12q to obtain each desired displacement ^^^⃗ ^^^^, ^^^, ^^^ at each contact point. The method comprises an extraction of a response matrix of the slab ^^^, determined for the contact point ^^^^, ^^^), from the memory 25, and an inversion of a direct model, so as to estimate each control signal. Sub-: extraction of a response matrix. This involves extracting, from the memory 25, a response matrix ^^ ^ , each term of which is associated with an actuator 12 q , at the point of contact^^^^, ^^^) and to a direction of movement of the slab (X axis, Y axis or Z axis). Each term corresponds to a movement of the slab, according to one of said directions of movement, at the point of contact ^^^^, ^^^), when the actuator is subjected to a predetermined control signal, for example unitary, equal to 1 V. The terms forming the response matrix ^^ ^, are stored in the memory 25, for all or part of the points of the mesh defined by the position sensor. Thus, each term ^^^^௫ , ^^^^௬, ^^^^௭ of the response matrix ^^^ is a displacement of the slab, at the contact point ^^^^, ^^^^ by a unit signal applied to an actuator ^^, along the respective axes X, Y and Z. The response matrix is ​​of dimension ^3, ^^^. Preferably the response matrix ^^ ^ is defined in a frequency form ^^ ^ ^^^^. So, we use different response matrices for different frequency components ^^. The dimension of each matrix ^^ ^ ^^^^ is [3, ^^] If we take into account ^^ fingers touching ^^ distinct contact points, the response matrix becomes: Thus, for N contact points, the dimension of the response matrix is ​​[3^^, ^^] Sub-step 132: inversion of the direct model. From the response matrix ^^ ே^^^^, we can form a direct model, defining a displacement of the slab, in three dimensions, at each point of contact, as a function of the control signal applied to the actuators. For a single point of contact, at the position^^^^w^ ൌ ^^^^^^^^^^^^^ (6) for a single point of contact^^ ^ ^^^^where ^^^(w) is defined in (2), ^^^^^^^ is defined in (4) and ^^^^^^ ൌ ^⋮ ^ (7) ^^ ொ ^^^^ ^^^^^^ is a control vector, comprising a control signal ^^ ^ to be addressed to each actuator 12 q to obtain the desired haptic effect. When there are ^^ contact points ^^^^, ^^^^ … .. , the direct model becomes:^^ே^^^^ ൌ ^^ே^^^^^^^^^^ (8)^^ ^௫ ^^^^ ^^ ே௫ ^^^^ Where ^^ ே ^^^^ is a vector concatenating the displacements of the slab ^ ^^ ^௬ ^^^^ ^ … ^ ^^ ே௬ ^^^^ ^, in ^^ ^௭ ^^^^ ^^ ே௭^^^^ each contact point, along the X, Y and Z axes. Inversion of the direct model (6) gives: Inversion of the direct model (8) gives: Each control signal can be determined by inversion of the direct model (6), (8), by inverse filtering. For example, it is possible to determine a pseudo inverse ^^ ି^ ^ , ^^ே ି^ of the transfer matrix. Using a pseudo inverse of Moore-Penrose is a preferred option, as it allows minimizing the norm of the vector. Step 133: Transition to the time domain In this step, the control vector ^^^^^^ is transitioned into the time domain, from each vector ^^^^^^. Each term of the control vector ^^^^^^ is a time control signal addressed to each actuator: Where ℜ denotes the real part operator. When multiple frequencies are implemented, the signal can be obtained by inverse Fourier transform. More precisely, the transition to the time domain makes it possible to define a time sequence for controlling each actuator 12 q , this sequence extending over a duration ^t between 5 ms and 100 ms. The time sequence corresponds to the control signal ^^ ^ ^ ^^ ^ of each actuator 12 qduring the duration ^t. The duration ^t is preferably between a few ms, for example 3 ms and 5 ms, and a few tens of ms, for example 10 ms or 20 ms. 140: During step 140, each actuator is activated according to the control signal so as to generate an actuation sequence during the duration ^t. We then return to step 100, waiting for a detection of a contact at another position. The iterations continue until a criterion for stopping the iterations is reached. This may be the member reaching the intended target position, or the detection of no contact on the plate or a contact outside an area of ​​the slab in which the finger does not have to be guided. It may also be a usage duration exceeded.A particularity of the invention is that to orient the sliding of the finger, at the point of contact (^^^, ^^^) according to the orientation angle ^^^, the slab is preferably animated, at the point of contact, by an elliptical displacement, according to an ultrasonic frequency, the orientation of which, relative to the plane of the slab, depends on the orientation angle ^^. ^ . By elliptical displacement, we mean a displacement whose successive amplitudes, respectively in the plane P XY of the slab and along the transverse axis Z, are connected by an elliptical function. The ellipse is described at each period of the displacement. Generally speaking, during each period, the displacement, in the plane of the slab P XY , progresses according to the orientation angle ^, when the displacement, according to the transverse axis, progresses towards the external organ. Thus, at the level of the point of contact, we combine a vibration normal to the plane P XYof the slab, that is to say along the transverse axis, to a vibration tangential to this plane. The elliptical displacement results in a modulation of an asymmetric friction force, of non-zero average value, favoring a sliding of the finger along the slab, according to the orientation angle ^^ ^ . Such a friction force is felt in the ultrasonic spectral range. The amplitudes of the respective vibrations along the X and Y axes depend on the orientation angle ^^ ^ The vibration amplitude, along each axis, is higher as the orientation angle, relative to each axis, is small. In this example, the amplitude along the X and Y axes depend respectively on the cosine and sine of the orientation angle ^^ ^ . To produce such a displacement, the components of the movement, in the plane P XYand along the transverse axis Z, are in quadrature, that is to say:^^௫^^^^ ൌ ^^^^௫^^௭^^^^ (12)^^௬^^^^ ൌ ^^^^௬^^௭^^^^ (13)and: -^^௫ ൌ ^^ cos ^^^ (14)- ^^௬ ൌ ^^ sin ^^^ (15) ^^ is an ellipse ratio of the motion. The ellipse ratio of the motion corresponds to the displacement in the plane P XY with respect to the displacement along the transverse axis Z. When ^^^ is oriented along the X axis, ^^௫ ൌ ^^, ^^௬ ൌ 0 and when ^^^ is oriented along the Y axis,^^௫ ൌ 0, ^^௬ ൌ ^^In the case of a slab, of small thickness ^^, undergoing bending, the displacements in the plane of the slab P XY and along the transverse axis Z are connected by: Thus, the displacements along the X and Y axes depend on the spatial derivatives of the displacement along Z, along the respective X and Y axes. The displacement along the transverse Z axis can be expressed as:^^^௭^^^^, ^^^, ^^^ ൌ A cos^െ^^^^^^ cos ^^^ ^ ^^^ sin ^^^^ ^ ^^^^ ^ ^^^ (20)Where ^^ is a wave number and A is the amplitude of the vibration generating the displacement. Given (16) and (17): By setting ^^ ൌ െ^^^^^^ cos ^^^ ^ ^^^ sin ^^^^ ^ ^^^ (23), we obtain^^^௭^^^^ ൌ ^^௭^^^^, ^^^, ^^^ ൌ ^^ cos^^^^^ ^ ^^^^ (24) Expressions (20) and (26) correspond to a propagation of a progressive harmonic wave "out of plane", of amplitude ^^ along the transverse axis Z, propagating along the plane PXY according to the direction vector (cos ^^^, sin ^^^). According to (16) and (17), the spatial derivatives along the axes X and Y of the progressive wave "out of plane" make it possible to obtain the displacement waves in the plane ^^^௫ ^ ^^ ^ et ^^^௬^ ^^ ^ described by (21), (22), (25) and (26), with respective amplitudes^ ^ A ଶ^^ cos ^^^ and Aଶ^^ sin ^^^.^ ^ The terms ଶ^^ cos ^^^ and ଶ^^ sin ^^^ correspond to the ellipse ratio ^^ previously mentioned. In the frequency domain, expressions (24) to (26) become:^^^௭^^^^ ൌ ^^^^ (27)^^^௫^^^^ ൌ ^^A^^ ^ ଶ^^ cos ^^^ (28)^^ ^^^^ ൌ ^^^^ ^ ௬ A^ ଶ^^ sin ^^^ (29)with ^^^ ^ఝ^ ൌ ^^^^ ^ (30).Taking into account (27) to (30), when N = 1 (a single point of contact): (9) becomes: ି^ ^^ ^ ^^^^^^௫ ^^^ … ^^^ொ௫^^^^ ^^A ^ ^ ^ ^ ^ ^ ଶ^^ cos ^^^^ ⋮^ ൌ ^ ^^^^௬^^^^ … ^^^ொ௫^^^^^ ൦ ^^A ^ ^ ^^^ sin ^^^൪ (31) ^^ ^^^^ ^^ ^ ଶ ொ^^௭ ^^^ … ^^^ொ௫^௪^ ^ ^ ^^ When N > 1 (multiple contact points): ^^ ^ ^^^ ^^^^ … ^^ ^^^^ି^ é ^A^ ଶ^^ cos ^^^ù é ^௫ ^ொ௫ ù ê ^ ú ê^^^^௬^^^^ … ^^^ொ௫^^^^ú ^^A ^ ^ ^^ sin ^^^ê ଶ ^ ^^^ ê^^^^௭^^^ … ^^^ொ௫^^^^ú ê ^ ^ ú ^^^^^ ú ^ ⋮ ^ ൌ e ⋮ … ⋮ ú ê ⋮ (32) ொ ê êே^௫ ^ … ^^ேொ௫^^^^ú ê ^^A ^ ^ ú ^^ ^^^^^^ ^^^ ே ^^ cos ^^ேú ^ ^ ^^^^ … ú ଶ êே^௬ ^^ேொ௫^^^^ú ê ^^A ^ ^ ë^^ே^௭^^^^ … ^^ேொ௫^^^^ûê ே ଶ^^ sin ^^ேú ë ^ ^ ^ே û In the implementation of expressions (31) or (32), the terms forming the matrices ^^ ^ ^^^^ or ^^ ே ^^^^ result from a calibration, described later. The orientation angles ^^ ^ depend on the position of the contact point and the position, on the slab, of the target that we want to reach with the finger. It is preferable that the ellipse ratio ^^ is close to 1, so that during each period, the displacement in the plane P XY approximates the displacement along the transverse Z axis. This maximizes the impression of force exerted on the finger. So, preferably, ^^ ^ 0.3 or ^^ ^0.5. Or, ^^ ൌ^ ଶ ^^ (33). The wave number is related to the pulsation ^^ by a dispersion relation: Where ^^ is the surface mass (mass per unit area, -2^ kg.m ), such that ^^^ ൌ ^^ ൈ ^^ (35), ^^ being the density and ^^ the stiffness (unit Nm) with ^^ ൌ ^^^^ଷ / ൫12^1 െ ^^ଶ^൯, ^^ and ^^ being respectively the Young's modulus and the Poisson's ratio of the slab 10. Taking into account (33) and (34): The pulsation ^^ is defined according to the mechanical properties of the slab (Young's modulus, thickness), so as to obtain ^^ ^ 0.3 or ^^ ^ 0.5. This relationship is usually verified in the frequency domain of ultrasound. Calibration The matrices ^^ ^ ^^^^ or ^^ ே^^^^ are established from terms and stored during a calibration phase, corresponding to a step 90. During the calibration, each actuator is supplied with a predetermined signal, for example sinusoidal, and the displacement, in particular along the transverse axis Z, of the slab is measured. Each term of these matrices corresponds to a ratio between the displacement measured on the applied control signal. The displacement is measured after reaching a steady state on the slab, i.e. a few ms after activation of the actuator. The displacement can be measured with a laser vibrometer. In a complementary or alternative way, the calibration can be carried out by simulation. The calibration can be carried out on certain points of the slab, and be interpolated to cover all the mesh points defined by the position sensor.In order to reduce the number of measurements during calibration, we can take advantage of the fact that the displacements along the P plane. XY can be deduced from the displacement along the transverse axis Z, by the relation Thus, each term of a response matrix, relating to a displacement along the X axis or the Y axis, can be deduced from a measurement of a displacement along the transverse Z axis, using (40) or (41). Thus, the calibration phase can be limited to a measurement (or a simulation) of the displacement along the Z axis in response to the sequential actuation of each transducer. Modeling Simulations were carried out taking into account a glass slab, with dimensions 100 x 125 x 2 mm, actuated by 32 piezoelectric actuators distributed under the slab. Each modeled actuator had dimensions 10 x 10 x 0.3 mm. The contact point on the slab was determined randomly. In a first series of simulations, only one contact point was considered. In Figure 3A, the actuators (squares) and the contact point (black dot) are represented.The objective was to obtain a displacement of the finger parallel to the X axis, with a displacement amplitude, along the transverse axis, of 1 µm. The frequency of the control signals was 50 KHz. A control sequence of the actuators was determined, so as to obtain an elliptical displacement, tending to move the finger along the X axis. Figure 3B represents the displacement (y-axis - µm), as a function of time, of the contact point, respectively along the X, Y and Z axes (abscissa axis - ms). After a transient period of 2 ms, a displacement, along the X axis, of amplitude 0.5 µm, and a negligible displacement along the Y axis are observed. The amplitude along the Z axis is of the order of 1 µm. When t > 5 ms, the actuation ceases, which results in a transient regime, until the displacement of the slab along each axis is zero.Figure 3C represents the displacement along the Z axis (ordinate axis - µm) as a function of the displacement along the X axis (abscissa axis - µm). The displacements along the X and Z axes, at successive times of the actuation sequence, describe an ellipse, at a frequency of 50 KHz, or 50,000 revolutions, along the ellipse, per second. In Figure 3C, an arrow F1 indicates the direction in which the displacements follow one another. When the slab approaches the finger (^^. ௭^ 0^, the displacement of the slab tends to push the latter along the X axis, towards the positive direction, according to arrow F2. Figure 3D represents the displacement along the Z axis (ordinate axis - µm) as a function of the displacement along the Y axis (abscissa axis - µm). We note the absence of displacement along the Y axis. We then simulated a sequence of control of the actuators with the objective of sliding the finger along the slab, at an angle ^ of 90°, i.e. parallel to the Y axis. Figure 3E represents the sequences of displacements along the three axes, at the point of contact, as a function of time (abscissa axis - ms) in a manner analogous to Figure 3B. Figure 3F represents the displacement along the Z axis (ordinate axis - µm) as a function of the displacement along the X axis (abscissa axis - µm). We note the absence of movement along the X axis.Figure 3G represents the displacement along the Z axis (ordinate axis - µm) as a function of the displacement along the Y axis (abscissa axis - µm). The amplitudes of the displacements along the Y and Z axes, at successive instants of the actuation sequence, describe an ellipse, at the period of 50 KHz. In Figure 3G, an arrow F1 indicates the direction in which the displacements follow one another. When the slab approaches the finger (^^௭ ^ 0^, the displacement of the slab tends to push the latter along the Y axis, towards the positive direction, according to the arrow F2. During a second series of tests, an implementation of the process was simulated by taking into account two different contact points. These are represented in Figure 4A. The objective was to form haptic patterns allowing a displacement along the X axis (^1 = 0°) at the first contact point, and a displacement at an angle (^2 = 45°) at the second contact point.Figures 4B and 4C respectively show the sequences of displacements obtained for each contact point, along the X, Y and Z axes (ordinate axis - µm) as a function of time (abscissa axis - ms). In Figure 4D, for the first contact point, the displacement along the Z axis (ordinate axis - µm) as a function of the displacement along the Y axis (abscissa axis - µm) (top figure), the displacement along the Z axis as a function of the displacement along the X axis (middle figure), and the displacement along the Y axis as a function of the displacement along the X axis (bottom figure) are shown. In Figure 4E, for the second point of contact, the displacement along the Z axis as a function of the displacement along the Y axis (top figure) and the displacement along the Z axis as a function of the displacement along the X axis (middle figure), and the displacement along the Y axis as a function of the displacement along the X axis (bottom figure) are shown.In Figures 4D and 4E, arrow F1 shows the chronological direction of the evolution of the displacements. Arrow F2 shows the direction of the displacement obtained. In Figure 4D, we observe a displacement along the X axis, in the direction x > 0. In Figure 4E, we observe simultaneous displacements, and of the same value, along the X axis (towards x > 0) and along the Y axis (towards y > 0). This results in a displacement along ^2= 45°. Figures 4F and 4G show respectively the sequences of displacements obtained for each contact point, along the X, Y and Z axes (ordinate axis - µm), as a function of time (abscissa axis - ms). The objective is then to induce a displacement of the first contact point along the Y axis, and of the second contact point along the X axis.In Figure 4H, the displacement along the Z axis is represented as a function of the displacement along the Y axis (top figure) and the displacement along the Z axis as a function of the displacement along the X axis (bottom figure), for the first point of contact. In Figure 4I, the displacement along the Z axis is represented as a function of the displacement along the Y axis (top figure) and the displacement along the Z axis as a function of the displacement along the X axis (bottom figure), for the second point of contact. In Figures 4H and 4I, arrow F1 shows the chronological direction of the evolution of the displacements. Arrow F2 shows the direction of the displacement obtained. In Figure 4H, we observe a displacement along the Y axis, in the direction y > 0. In Figure 4I, we observe simultaneous displacements, and of the same value, along the X axis (towards x > 0).The invention makes it possible to control, by combining progressive flexion waves, a sliding of an external body along a touch screen, in a predetermined direction. The invention can be implemented independently of the dimensions of the screen. Although described in connection with a haptic interface, the invention can be implemented to allow a movement of objects on a screen forming an interface, under the effect of ultrasonic vibrations as previously described.

Claims

CLAIMS 1. Method for controlling an interface, the interface comprising - a slab (10), configured to be touched by a contact member (3), at a contact point, the slab extending along a plane (P XY ) perpendicular to a transverse axis (Z), the slab extending, in the plane, along a longitudinal axis (X); - actuators (12 q ), arranged against the slab, each actuator being configured to induce an ultrasonic vibration of the slab when it is subjected to a control signal (^^ ^); - a position sensor (15), configured to detect a position of the contact point on the slab; the method comprising: a) detecting a contact on the slab; b) determining a position of the contact point on the slab; c) from the position resulting from b), determining a displacement of the slab at the contact point; d) using a processing unit, calculating a control signal to be applied to the actuator so as to obtain the displacement at the contact point, each actuator inducing a progressive bending wave propagating along the slab, so as to form a vibration of the slab at the contact point, causing a displacement of the slab at the contact point; e) repeating steps a) to d), until a criterion for stopping the iterations is reached;the method being such that step c) comprises a determination of a periodic displacement of the slab, at the point of contact, at the ultrasonic frequency, such that during each period: - the displacement of the slab combines a displacement along the transverse axis (Z) and a displacement along the plane of the slab (P; XY ); - the displacement of the slab, in the plane of the slab (P XY ), progresses according to an orientation angle (^), relative to the longitudinal axis, when the displacement, according to the transverse axis, progresses towards the external member, so as to induce a sliding of the contact member, along the slab, according to said orientation angle; the method being characterized in that step d) comprises an inversion of a direct model, the direct model establishing a relationship between a displacement at each point of contact and a control signal of each actuator.

2. Method according to claim 1, in which during each period, the displacement of the slab, along the transverse axis, and the displacement of the slab, in the plane of the slab, are linked by a periodic time function, describing an ellipse.

3. Method according to any one of the preceding claims, in which the slab extending along a lateral axis (Y), perpendicular to the longitudinal axis, during each period, the displacement, at the point of contact, in the plane of the slab, comprises: - a longitudinal component (^^ ^௫ ), along the longitudinal axis, depending on the orientation angle; - a lateral component ^^^ ^௬^, along the lateral axis, depending on the orientation angle; - so as to induce a sliding of the member, by a combination of the longitudinal component and the lateral component.

4. Method according to claim 3, in which the longitudinal component depends on a spatial derivative, along the longitudinal axis, of the displacement along the transverse axis.

5. Method according to any one of claims 3 or 4, in which the lateral component depends on a spatial derivative, along the lateral axis, of the displacement along the transverse axis.

6. Method according to any one of the preceding claims, in which a ratio between the displacement, along the transverse axis, and the displacement, in the plane of the slab, is greater than 0.

3. 7.Method according to any one of the preceding claims, in which - step a) comprises a detection of several contact points spaced from each other; - step b) comprises a determination of the position of each contact point; - step c) comprises a determination of the displacement of the slab at each contact point, each contact point being assigned an orientation angle; - step d) comprises a calculation of the control signal to be applied to each actuator so as to obtain, at each contact point, the displacement determined during step c).

8. Method according to any one of the preceding claims, in which step d) comprises:. - di) forming a response matrix comprising, for each actuator, a displacement of the slab, at each point of contact, as a function of the actuator control signal; - dii) determining a pseudo-inverse of the response matrix, so as to define the control signal of each actuator.

9. Method according to claim 8, in which sub-step di) comprises an extraction, from a memory, of unit displacements, each unit displacement corresponding to a displacement, along the transverse axis or in the plane, generated at each point of contact, by an actuator controlled by a unit control signal, the unit displacement being defined for each actuator during a calibration.

10. Method according to claim 9, in which the calibration comprises a successive control of each actuator, and a measurement of a displacement of the slab, along the transverse axis, at different points of the slab. 11.Method according to claim 10, in which the calibration comprises a modeling of a successive command of each actuator, and a modeling of a displacement of the slab, along the transverse axis, at different points of the slab.

12. Interface comprising: - a slab (10), configured to be touched by one or more contact members (3), at one or more contact points, - actuators (12. q ), arranged against the slab, each actuator being configured to cause a vibration of the slab when it is subjected to a control signal (^^ ^ ); - a position sensor (15), configured to detect a position of the contact point; - a processing unit (20), configured to implement steps a) to d) of a method according to any one of the preceding claims.

13. Interface according to claim 12, wherein the interface is a haptic interface, configured to control a device (2).

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