Touch interface enabling training of an external organ by ultrasonic vibrations

Abstract

Method for controlling an interface, comprising a slab, the method comprising detecting a contact on the slab; determining a position of the contact point on the slab; from the position resulting from b), determining a haptic pattern to be applied to the contact member, at the contact point, the haptic pattern comprising a displacement of the slab at the contact point; using a processing unit, calculating a control signal to be applied to each actuator so as to produce the haptic pattern 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; repeating steps a) to d).

Description

Title of the invention: Touch interface enabling training of an external organ by ultrasonic vibrations Technical field

[0001] The technical field of the invention concerns touch interfaces. PREVIOUS ART

[0002] Touch interfaces, such as touch screens, have already been described, making it possible to intuitively encode information for the user, via a sensation felt at the finger level, under the effect of a vibration of the screen.

[0003] In a first type of application, the slab 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. Examples of application are described in Hudin C 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.

[0004] 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.

[0005] 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.

[0006] The invention described below aims to produce a haptic effect aimed at directing a user's finger, 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 user's finger to reach a target, or follow a predetermined trajectory along the slab. The invention can thus be aimed at visually impaired people, or people whose field of observation does not target the slab, for example drivers of a vehicle. Statement of the invention

[0007] 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 contact point, 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;

[0008] the method comprising: a. detection of contact on the slab; b. determination of a position of the contact point on the slab; c. from the position resulting from b), determination of a displacement of the slab 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 displacement of the slab at the point of contact, each actuator inducing a progressive bending wave propagating along the slab, so as to form a vibration of the slab at the point of contact, causing the displacement of the slab at the point of contact; e. repetition of steps a) to d), until a criterion for stopping the iterations is reached, or the algorithm exits.

[0009] Step c) may include 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 movement of the slab, in the plane of the slab, progresses according to an orientation angle, relative to the longitudinal axis, when the movement, 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.

[0010] During each period, the displacement of the slab, along the transverse axis, and the displacement of the slab, in the plane of the slab, can be linked by a periodic time function, describing an ellipse.

[0011] 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 comprise: - 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 a sliding of the organ, by a combination of the longitudinal component and the lateral component.

[0012] The longitudinal component may depend on a spatial derivative, along the longitudinal axis, of the displacement along the transverse axis.

[0013] The lateral component may depend on a spatial derivative, along the lateral axis, of the displacement along the transverse axis.

[0014] 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.

[0015] According to one possibility: - step a) includes detection of several contact points spaced apart from each other; - step b) includes a determination of the position of each contact point; - step c) includes a determination of the displacement of the slab at each point of contact, each point of contact being assigned an orientation angle; - step d) includes 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).

[0016] 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.

[0017] Step d) may comprise: - di) formation of 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) determination of a pseudo-inverse of the response matrix, so as to define the control signal of each actuator.

[0018] 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.

[0019] A second object 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

[0020] The interface may be a haptic interface, configured to control a device.

[0021] The invention will be better understood upon reading the description of the exemplary embodiments presented in the remainder of the description, in conjunction with the figures listed below. FIGURES

[0022] [Fig.l] shows a diagram of an example of a slab forming a haptic interface according to the invention.

[0023] [Fig.2] shows the main processing steps for controlling the actuators of the panel to generate haptic feedback.

[0024] [Fig.3A] shows a position of a contact point of a finger on a slab.

[0025] [Fig.3B] shows displacements of the slab (y-axis - unit pm) in function of time (abscissa 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.

[0026] [Fig.3C] shows the displacements of the slab along the Z axis (ordinate axis - unit pm) as a function of slab displacements along the X axis (abscissa axis - unit pm), corresponding to the time displacements represented in [Fig.3B].

[0027] [Fig.3D] shows the displacements of the slab along the Z axis (ordinate axis - unit pm) as a function of slab displacements along the Y axis (abscissa axis - unit pm), corresponding to the time displacements represented in [Fig.3B].

[0028] [Fig.3E] shows displacements of the slab (ordinate axis - unit pm) 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.

[0029] [Fig.3F] shows the displacements of the slab along the Z axis (ordinate axis - unit pm) as a function of displacements of the slab along the X axis (abscissa axis - unit pm), corresponding to the time displacements represented in [Fig.3E].

[0030] [Fig.3G] shows the displacements of the slab along the Z axis (ordinate axis - unit pm) as a function of displacements of the slab along the Y axis (abscissa axis - unit pm), corresponding to the time displacements represented in [Fig.3E].

[0031] [Fig.4A] shows a position of several contact points of a finger on a slab.

[0032] [Fig.4B] shows displacements of the slab (ordinate axis - unit pm) 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 a first finger parallel to the X axis.

[0033] [Fig.4C] shows displacements of the slab (ordinate axis - unit pm) 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 a second finger along a direction of 45° relative to the X axis (or the Y axis).

[0034] [Fig.4D] shows the displacements of the slab along the Z axis (ordinate axis - unit pm) as a function of displacements along - the Y axis (abscissa axis - unit pm), top curve, - the X axis (abscissa axis - unit pm), middle curve, - as well as the displacement along the Y axis (ordinate axis - unit pm) as a function of the displacement along the X axis (abscissa axis - unit pm), bottom curve.

[0035] corresponding to the temporal displacements of the first finger represented in [Fig.4B],

[0036] [Fig.4E] shows the displacements along the Z axis (ordinate axis - unit pm) as a function of displacements along - the Y axis (abscissa axis - unit pm), top curve, - the X axis (abscissa axis - unit pm), middle curve, - as well as the displacement along the Y axis (ordinate axis - unit pm) as a function of the displacement along the X axis (abscissa axis - unit pm), bottom curve.

[0037] corresponding to the temporal displacements of the first finger represented in [Fig.4C].

[0038] [Fig.4F] shows displacements of the slab (ordinate axis - unit pm) 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 a first finger parallel to the Y axis.

[0039] [Fig.4G] shows displacements (ordinate axis - unit pm) as a function of time (abscissa 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.

[0040] [Fig.4H] ​​shows the displacements of the slab along the Z axis (ordinate axis - unit pm) as a function of displacements along - the Y axis (abscissa axis - unit pm), top curve, - the X axis (abscissa axis - unit pm), bottom curve,

[0041] corresponding to the temporal displacements of the first finger represented in [Fig.4F].

[0042] [Fig.41] shows the displacements of the slab along the Z axis (ordinate axis - unit pm) as a function of displacements along - the Y axis (abscissa axis - unit pm), top curve, - the X axis (abscissa axis - unit pm), bottom curve,

[0043] corresponding to the temporal displacements of the first finger represented in [Fig.4G], PRESENTATION OF PARTICULAR EMBODIMENTS

[0044] [Fig.l] represents a haptic interface 1, intended to be touched by an external organ 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.

[0045] 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 making it possible to act on the interface 1.

[0046] 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, of millimetric size. The object must have sufficient inertia so that the plate can be moved relative to the latter during vibrations.

[0047] 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.

[0048] 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 PXY. The thickness of the slab is defined along a transverse axis Z, perpendicular to the contact surface IL.

[0049] The slab 10 is coupled to actuators 12q, for example piezoelectric actuators, ? being an integer designating each actuator, with 1 < # < Q. Q 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].

[0050] Each actuator 12q is powered by a control signal Sq, so as to generate a vibration whose characteristics (amplitude, frequency) are configured to produce a predetermined haptic feedback from the interface. The control signals Sq are transmitted, via a control circuit 13 to each actuator 12q.

[0051] In this example, each piezoelectric actuator 12q comprises a piezoelectric material, for example AIN, ZnO or PZT, arranged between two electrodes. Each actuator can be connected to the slab by gluing. According to a variant, the actuators 12q can be electromagnetic or electromechanical actuators.

[0052] 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 can 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 in rows (parallel to the X axis) and columns (parallel to the Y axis). The conductive tracks can be biased according to a bias 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 contact with the finger 3 of a user, or any other type of external organ.

[0053] The position sensor 15 is configured to generate a position signal P comprising the number n and the position p _ \ of contact points on the surface r n — y n I contact 11. The conductive tracks 14 make it possible to form a mesh on the slab, defining mesh points M, each point of the mesh corresponding to a position capable of being detected by the position sensor. The number of positions is determined according to the spatial resolution of the position sensor, which depends of 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 Mmax. The haptic interface 1 takes into account a number M of different positions, likely to be occupied by the finger 3 on the contact surface 11, with M < Mtnax.

[0054] The position sensor is not necessarily capacitive. It can be a resistive touch sensor or an infrared optical sensor.

[0055] The interface 1 comprises a processing unit 20, supplied, at different measurement times, by the position signal P generated by the position sensor 15. The processing unit 20 is intended to address a control signal Sq to the control circuit 13, so that the latter transmits each control signal Sq respectively to each actuator 12q. The control circuit comprises, for example, digital-analog converters, so as to form an analog control signal for each actuator from digital instructions resulting from the processing unit 20.

[0056] 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 (xn^ y„) detected, the haptic interface defines a haptic pattern tending to make the finger slide according to an orientation angle θn.

[0057] 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].

[0058] Preferably, the actuators 12q are distributed under the slab, advantageously forming a regular mesh.

[0059] [Fig.2] illustrates the main steps of an iterative process implemented by the haptic interface 1:

[0060] Step 100: at a measurement time, one or more fingers m touch the slab. M 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 below.

[0061] Step 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 P for each point of contact.

[0062] The position signal has 2 components: xn> yn for each contact point detected. The index n designates each finger in contact with the slab.

[0063] Step 120: 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 0 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 xn> yn and the target position T. When several fingers touch the slab, a target position Tn can be assigned to each finger.

[0064] During this step, a target displacement u(x„, yn,t) is defined, applied to the slab, at each contact point, so that each finger reaches the target position assigned to it.

[0065] The displacement of the slab, at the point of contact y^, and at the instant can be written in vector form:

[0067] The displacement thus comprises a longitudinal component along the longitudinal axis X, a lateral component along the lateral axis Y and a transverse component uz along the transverse axis Z. Each term of the displacement vector u(Xn, yn,t) corresponds to a progressive harmonic wave propagating in the plane PXY of the slab.

[0068] In the frequency domain, the displacement Un(w), at frequency (^) is written: 'UnxM' (2).

[0069] The maximum amplitude of each displacement is a few pm, for example 1 pm or 2 pm.

[0070] Step 1 3 0: determination of the control signal of each actuator 12q, so as to obtain the target displacement u(x^ yn, t) at each contact point , y )•

[0071] During this step, the processing unit 20 calculates the control signal to be applied to each actuator 12q to obtain each desired movement. u(xn, y , at each contact point. The method comprises an extraction of a response matrix of the slab H,h determined for the contact point (yv X since memory 25, and an inversion of a direct model, so as to estimate each control signal.

[0072] Sub-step 131: extraction of a response matrix. This involves extracting, from the memory 25, a response matrix Hn, each term of which is associated with an actuator 12q, with the contact point (A y ) and with a direction of movement of the slab (axis X, if 'n Y axis or Z axis). Each term corresponds to a displacement of the slab, according to one of the said directions of displacement, at the point of contact (xv), when the actuator is subjected to a predetermined control signal, for example unitary, equal to 1 V. The terms forming the response matrix Hlh are stored in the memory 25, for all or part of the mesh points defined by the position sensor.

[0073] Thus, each term HnqX, Hnqy, H„qz of the response matrix Hn is a displacement of the slab, at the point of contact by a unit signal applied to an actuator ¢, along the respective axes X, Y and Z. The response matrix is ​​of dimension (3. g).

[0074] * TJ ^n\x H nQx (3) H = liii H„,y ... HnQx H„k ... H»Qx,

[0075] Preferably, the response matrix Hn is defined in a frequency form. Thus, different response matrices are used for different components frequency s w.

[0076] • HnQx () = Hn\y(w). • nQx (W.) (4), ^nlz(w) .. HnQx(w).

[0077] The dimension of each matrix Hn(w) cst [3, ô]

[0078] If we take into account X fingers touching N distinct contact points, the matrix of response becomes:

[0079] 'Hnx ... Hlôx1(5) Huy ... HÏQx ••• = .......................... w XBHO) Ot Ci) < tej te: te: S fe: % te; $te:

[0080] Thus, for N contact points, the dimension of the response matrix is ​​[3Ar, Q]

[0081] Sub-step 132: inversion of the direct model.

[0082]

[0083]

[0084]

[0085] From the response matrix we can form a direct model, defining a displacement of the slab, in three dimensions, at each point of contact, depending on the control signal applied to the actuators. For a single point of contact, in the position Un(v^ - H^w)S(w) (6) for a single point of contact where U„(w) is defined in (2), Hn(w) is defined in (4) and / \ S w 1 =

[0086] is a control vector, comprising a control signal Sq to be addressed to each 12q actuator to achieve the desired haptic effect.

[0087] When there are N contact points / \ / \ , the direct model becomes: y, .. y J vrv zV JN!

[0088] [7^) =

[0089] Where is a vector concatenating the displacements of the slab , at each point of contact, along the X, Y and Z axes.

[0090]

[0091] Inversion of the direct model (6) gives:

[0092]

[0093] Inversion of the direct model (8) gives: -1 (10) * • ' ^lQx{w} U ' $l(w) ' AM HNiy(w) . . . Hnq.^w) HNqx(w) ünzM

[0094] Each control signal can be determined by inversion of the direct model (6), (8), by inverse filtering. It is for example possible to determine a pseudo inverse Hn \ Hnx of the transfer matrix. Using a pseudo inverse of Moore-Penrose is a preferred option, as it allows minimizing the norm of the vector.

[0095] Step 133: transition to the time domain

[0096] During this step, the control vector s(t) is passed into the time domain, from each vector S(h>). Each term of the control vector S(t) is a time control signal addressed to each actuator: [OO97] (H)

[0098] Where p denotes the real part operator.

[0099] When multiple frequencies are implemented, the signal sq( t ) can be obtained by inverse Fourier transform.

[0100] More precisely, the transition to the time domain makes it possible to define a time sequence for controlling each actuator 12q, this sequence extending over a duration At of between 5 ms and 100 ms. The time sequence corresponds to the control signal Sq^t) of each actuator 12q during the duration At. The duration At 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.

[0101] Step 140: During step 140, each actuator is activated according to the control signal, so as to generate an actuation sequence during the duration At.

[0102] 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 time exceeded.

[0103] A particularity of the invention is that to orient the sliding of the finger, at the point of contact lx«' yn) according to the orientation angle 6n, 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 6n. By elliptical displacement, we mean a displacement whose successive amplitudes, respectively in the plane PXY of the slab and along the transverse axis Z, are linked by a function in the form of an ellipse. The ellipse is described at each period of the displacement.

[0104] Generally speaking, during each period, the displacement, in the plane of the PXY slab, progresses according to the orientation angle 0, when the displacement, according to the transverse axis, progresses towards the external organ.

[0105] Thus, at the point of contact, a vibration normal to the PXY plane of the slab, i.e. along the transverse axis, is combined with a vibration tangential to this plane. The elliptical displacement results in a modulation of a friction force

[0106]

[0107]

[0108]

[0109]

[0110] [YES]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122] asymmetric, with a non-zero average value, favoring a sliding of the finger along the slab, according to the orientation angle dn. Such a friction force is felt in the ultrasonic spectral domain. The amplitudes of the respective vibrations along the X and Y axes depend on the orientation angle 0n. 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 6n. To produce such a displacement, the components of the movement, in the PXY plane and along the transverse Z axis, are in quadrature, that is to say: = jaxUz(w) (12) ^M = jayUz(w) And : ax = acos0n (14) - av = asin0„ (15) “ is an ellipse ratio of the motion. The ellipse ratio of the motion corresponds to the displacement in the PXY plane relative to the displacement along the transverse Z axis. When is oriented along the X axis, ax = a, ay = 0 and when 8n is oriented along the Y axis, = 0, ay = a In the case of a slab of small thickness e, undergoing bending, the displacements in the plane of the slab PXY and along the transverse axis Z are linked by: ux(xn, yn, yn, t) (16) Uy(xn, yn, t) = 5^7 (xw yn, t) (17) 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 axis Z can be expressed as: unz (x„, yn, t) = A cos (- k (X„cos0„ + ) + oY+0) (20) Where £ is a wave number and A is the amplitude of the vibration causing the displacement. Considering (16) and (17): Unx (yn, t) = Af fccos^ sin (- k (x^cos^ + jHsin0tt) + œt + ¢) (21) Uny (xn yn, t) = Af Asin^ sin (- k (x„cosé)„ + j^sin^) + œt + 0) (22) By setting ¢ - -kÇ xnCOS0n + jnsin0H) + (pn (23), we obtain

[0123] unz{t) =uz(xn,y^t)=A cos( œt + tpn) (24)

[0124] unx(t) -Ux^y^t) = A^kcosOn sïn(œt + ipn) (25)

[0125] ujj) = Uy(xtJ> yn,t)= Ajksin6n sin( early + (p^ (26)-

[0126] Expressions (20) and (26) correspond to a propagation of an “out-of-plane” progressive harmonic wave, of amplitude A along the transverse axis Z, propagating along the plane PXY along the direction vector (COS0„, sin0H). According to (16) and (17), the spatial derivatives along the X and Y axes of the “out-of-plane” progressive wave make it possible to obtain the displacement waves in the plane UnxÇt) and Uny(t) described by (21), (22), (25) and (26), of respective amplitudes Af kcosO„ and Af Æsin<9„-

[0127] The terms jkcos6n and 7&sin0B correspond to the ellipse ratio a previously mentioned.

[0128] In the frequency domain, expressions (24) to (26) become:

[0129]

[0130]

[0131]

[0132] One^^~Year^ a) = jÀn%kœs0n (28) Uny( (O ) = jÀn^ksïn3„ (29) with An - Ae^ (30).

[0133] Considering (27) to (30), when N = 1 (a single point of contact): (9) becomes:

[0134] Hn^w) ... H„Qx(w) H 1üy iw) ... H nQx {w) jk^kw^ ' ' • ^nQx{w) '

[0135]

[0136] When N > 1 (multiple contact points):

[0137] In the implementation of expressions (31) or (32), the terms forming the matrices or H y(w) result from a calibration, described later. The orientation angles 3n depend on the position of the contact point and the position, on the slab, of the target that one wishes to reach with the finger.

[0138] It is preferable that ellipse ratio a is close to 1, so that during each period, the displacement in the PXY plane approaches the displacement along the transverse Z axis. This maximizes the impression of force exerted on the finger. Thus, preferably, ">0.3 or ">0.5.

[0139] Now, a = jk (33).

[0140] The wave number is linked to the pulsation w by a dispersion relation:

[0141] n^~ (34). " = VVd

[0142] Where Ps is the surface mass (mass per unit area, kg.m2), such that ps — pxe (35), P being the density

[0143] and D the rigidity (unit Nm) with D = Ye3 / ( 12( 1 - v2) ), Y and v being respectively the Young's modulus and the Poisson's ratio of the slab 10.

[0144] Considering (33) and (34):

[0145] ,A\i / 4 F”(35)

[0146] The pulsation w is defined as a function of the mechanical properties of the slab (Young's modulus, thickness), so as to obtain a >0.3 or "> 0.5. This relationship is usually verified in the frequency domain of ultrasound. Calibration

[0147] The matrices Hn(w) or Hy(w) 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.

[0148] Complementarily or alternatively, the calibration can be carried out by simulation.

[0149] Calibration can be performed on certain points of the slab, and be interpolated to cover all the mesh points defined by the position sensor.

[0150] In order to reduce the number of measurements during calibration, one can take advantage of the fact that the displacements along the PXY plane can be deduced from the displacement along the transverse axis Z, by the relation

[0151] „ zx (40) and „ (41). iinqx(.M)-2 dx ' œ 1 tlnqy(œ) — 2 (W)

[0152] 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. Modelings

[0153] 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.

[0154] In a first series of simulations, only one contact point was considered. In [Fig.3A], the actuators (squares) and the contact point (black dot) are shown. 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 pm. The frequency of the control signals was 50 KHz.

[0155] A control sequence of the actuators was determined, so as to obtain an elliptical displacement, tending to move the finger along the X axis. [Fig.3B] represents the displacement (ordinate axis - pm), 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 is observed, along the X axis, of amplitude 0.5 pm, and a negligible displacement along the Y axis. The amplitude along the Z axis is of the order of 1 pm. When t > 5 ms, the actuation ceases, which results in a transient regime, until the displacement of the slab along each axis is zero.

[0156] Figure 3C represents the displacement along the Z axis (ordinate axis - pm) as a function of the displacement along the X axis (abscissa axis - pm). The displacements along the X and Z axes, at successive times of the actuation sequence, describe an ellipse, at the frequency of 50 KHz, or 50,000 revolutions, along the ellipse, per second. In Figure 3C, an arrow Fi indicates the direction in which the displacements follow one another. When the slab approaches the finger (H > o). the displacement of the slab tends to push the latter along the X axis, towards the positive direction, according to the arrow F2.

[0157] [Fig.3D] represents the displacement along the Z axis (ordinate axis - pm) as a function of the displacement along the Y axis (abscissa axis - pm). We note the absence of displacement along the Y axis.

[0158] We then simulated a sequence of control of the actuators with the objective of sliding the finger along the slab, at an angle 0 of 90°, i.e. parallel to the Y axis. Figure 3E represents the sequences of movements along the three axes, at the point of contact, as a function of time (abscissa axis - ms) in a manner analogous to the Figure 3B. Figure 3F represents the displacement along the Z axis (y-axis - pm) as a function of the displacement along the X axis (abscissa axis - pm). We note the absence of displacement along the X axis. Figure 3G represents the displacement along the Z axis (y-axis - pm) as a function of the displacement along the Y axis (abscissa axis - pm). 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 Fi indicates the direction in which the displacements follow one another. When the slab approaches the finger (u7 > q), the displacement of the slab tends to push the latter along the Y axis, towards the positive direction, according to the arrow F2.

[0159] During a second series of tests, an implementation of the method was simulated by taking into account two different contact points. These are shown in [Fig.4A]. The objective was to form haptic patterns allowing movement along the X axis (0i = 0°) at the first contact point, and movement at an angle (02 = 45°) at the second contact point.

[0160] Figures 4B and 4C respectively show the sequences of displacements obtained for each contact point, along the X, Y and Z axes (ordinate axis -pm) as a function of time (abscissa axis -ms).

[0161] In [Fig.4D], for the first point of contact, the displacement along the Z axis (ordinate axis - pm) is shown as a function of the displacement along the Y axis (abscissa axis - pm) (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). In [Fig.4E], for the second point of contact, the displacement along the Z axis is shown 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). In Figures 4D and 4E, the arrow F1 shows the chronological direction of the evolution of the displacements. The arrow F2 shows the direction of the displacement obtained. In [Fig.4D], we observe a displacement along the X axis, in the direction x > 0. In [Fig.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 02 = 45°.

[0162] Figures 4F and 4G respectively show the sequences of movements obtained for each contact point, along the X, Y and Z axes (ordinate axis - pm), as a function of time (abscissa axis - ms). The objective is then to induce a movement of the first contact point along the Y axis, and of the second contact point along the X axis.

[0163] In [Fig.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 [Fig.41], 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 41, the arrow F1 shows the chronological direction of the evolution of the displacements. The arrow F2 shows the direction of the displacement obtained. In [Fig.4H], a displacement along the Y axis is observed, in the direction y > 0. In [Fig.41], simultaneous displacements, and of the same value, are observed, along the X axis (towards x > 0).

[0164] The invention makes it possible to control, by combining progressive bending 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.

[0165] Although described in connection with a haptic interface, the invention can be implemented to allow movement of objects on a slab forming an interface, under the effect of ultrasonic vibrations as previously described.

Claims

1. Claims Method of 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 (PXy) perpendicular to a transverse axis (Z), the slab extending, in the plane, along a longitudinal axis (X); - actuators (12q), arranged against the slab, each actuator being configured to induce an ultrasonic vibration of the slab when it is subjected to a control signal (¾); - a position sensor (15), configured to detect a position of the contact point on the slab; the process comprising: a. detection of contact on the slab; b. determination of a position of the contact point on the slab; c. from the position resulting from b), determination of a displacement of the slab at the point of contact; d. using a processing unit, calculating a control signal to be applied to the actuator so as to obtain the displacement at the point of contact, each actuator inducing a progressive bending wave propagating along the slab, so as to form a vibration of the slab at the point of contact, causing a displacement of the slab at the point of contact; e. repeating steps a) to d), until a criterion for stopping the iterations is reached; the method being characterized in 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 (PXY);

2.

3.

4.

5.

6.

7. - the displacement of the slab, in the plane of the slab (PXY ), progresses according to an orientation angle (0), 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. 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. 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 along the longitudinal axis, depending on the orientation angle; - a lateral component / V along the lateral axis, dependent \uny) of the orientation angle; - so as to induce a sliding of the organ, by a combination of the longitudinal component and the lateral component. 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. 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. 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. A method according to any preceding claim, wherein - step a) includes detection of several contact points spaced apart from each other; - step b) includes determining the position of each contact point; - step c) includes a determination of the displacement of the slab at each point of contact, each point of contact being assigned an orientation angle; - step d) includes a calculation of the control signal to be applied to each actuator so as to obtain, at each point of contact, the displacement determined during step c).

8. A method according to any preceding claim, wherein step d) comprises an inversion of a direct model, the direct model establishing a relationship between a displacement at each contact point and a control signal of each actuator.

9. Method according to claim 8, in which step d) comprises: - di) formation of a response matrix comprising, for each actuator, a displacement of the slab, at each point of contact, as a function of the control signal of the actuator; - dii) determination of a pseudo-inverse of the response matrix, so as to define the control signal of each actuator.

10. Method according to claim 9, 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.

11. Method according to claim 10, 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.

12. 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.

13. Interface comprising: - a slab (10), configured to be touched by one or more contact members (3), at one or more contact points, - actuators (12q), arranged against the slab, each actuator being configured to cause a vibration of the slab when it is subjected to a control signal (¾); - 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.

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

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