EP4097571A1

EP4097571A1 - Method for the tactile stimulation of a finger sliding over a touch surface, and haptic interface implementing this method

Info

Publication number: EP4097571A1
Application number: EP21700789.7A
Authority: EP
Inventors: Vincent Hayward; Damien FAUX; Enrique RISQUEZ; Rafal PIJEWSKI
Original assignee: Actronika SAS
Current assignee: Actronika SAS
Priority date: 2020-01-31
Filing date: 2021-01-22
Publication date: 2022-12-07
Also published as: WO2021151784A1; FR3106911B1; FR3106911A1

Abstract

One aspect of the invention relates to a method for the tactile stimulation of a finger sliding over a touch surface (20) of a haptic interface (10), comprising, when a finger is detected in contact with the touch surface (110), an operation (120-140) of determining a direction of sliding of the finger over the touch surface and an operation (160) of generating movements of the touch surface (20), in the plane of said surface, in a direction orthogonal to the direction of sliding of the finger, the operation of determining the direction of sliding comprising the following steps: - measuring (120) the Cartesian coordinates (x, y) of a point of contact of the finger on the touch surface, - determining (130) the direction of the speed of sliding (u) of the point of contact on the touch surface, and - determining (140), in the plane (P) of the touch surface, a direction (v) orthogonal to the direction of the speed of sliding. Another aspect of the invention relates to a haptic interface (10) implementing this method.

Description

DESCRIPTION

TITLE: Method of tactile stimulation of a sliding finger on a tactile surface and haptic interface implementing this method

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for generating tactile stimuli intended to be felt by the user of a haptic interface. The invention also relates to a haptic interface implementing this method.

The invention finds applications in the fields of haptics to provide tactile sensations to users of haptic interfaces and, in particular, when the user is in sliding contact with the tactile surface of the haptic interface.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

It is known, in the field of haptics, to seek to artificially reproduce, on a smooth surface, the tactile sensations felt by a person when he touches certain materials or textures, or when he uses certain objects presenting internal mobility, such as hairy textiles, switch buttons, serrated wheels, etc.

[0004] It is known, in particular, to provide tactile sensations to the user of a haptic interface - also called a screen with tactile feedback - to simulate, for example, the pressing of a key or the feeling of a texture when the user is in physical contact with the haptic interface, in particular when he places his finger on the tactile surface of the haptic interface. There are devices designed to provide such sensations. These devices generally include a hardware arrangement capable of moving the contact surface, or tactile surface, under the effect of a control signal generated in response to the detection of a point of contact between the user's finger and said finger. tactile surface.

These devices are intended for static contact of the finger (or other part of the user's body) with the contact surface, that is to say the support of a finger at a location on the surface of contact. However, many uses of haptic interfaces require sliding contact of the fingers on the contact surface, for example, to zoom in on a display area, to reach with the finger a targeted location on the contact surface, or to reproduce a texture field presented in a region of the contact surface, or to simulate tilting a slide switch reproduced by the interface. It has been noticed that the devices offering small oscillatory displacements of the contact surface to stimulate the finger are hardly suitable for sliding contacts because the effect of small oscillatory displacements is considerably attenuated, the sliding contact being less suitable for transmitting mechanical signals. vibration than static contact. In addition, mechanical signals are often masked by the friction noise generated by the sliding of the finger on the contact surface.

[0006] Several reproduction techniques, on a generally smooth tactile surface, tactile sensations corresponding to textured surfaces have been disclosed which all aim to respond to this problem of sliding contact. One of these techniques proposes to force the contact surface to vibrate at an ultrasonic frequency (that is to say a frequency greater than 20 KHz). This technique has been described in the article by T. Watanabe and S. Fukui, entitled “A method for controlling tactile sensation of surface roughness using ultrasonic vibration”, IEEE International Conference on Robotics and Automation, 1995, pp. 1134-1139]. Improvements have also been described, notably in the publication by M. Wiertlewski, RF Friesen & JE Colgate, entitled "Partial squeeze film levitation modulâtes fingertip friction", Proceedings of the National Academy of Sciences, 2016, 113 (33): 9210- 9215. In this technique, the contact surface is generally a thin plate of metal, glass or ceramic, on which piezoelectric transducers are attached. The excitation frequency is chosen to correspond to a natural frequency of the thin plate so as to establish a bending standing wave in the solid domain of this plate. The thin plate is designed so that bending standing waves take place at sufficiently high frequencies and wavelengths are sufficiently short compared to the size of a finger. Thus, when the amplitude of the vibration exceeds a few micrometers, the coefficient of friction between the finger and the thin plate decreases sharply. The methods for tactile reproduction of textures are generally based on a principle of detecting the position of the sliding contact of a moving finger in a two-dimensional field and of modulating the coefficient of friction by modulating the amplitude of the ultrasonic vibration. . These methods generally implement an algorithm for calculating the scalar value of a function T of the position (x, y) of the finger which represents a texture in the domain D. The amplitude A is then as follows: A = T (x, y), V (x, y) GD

Another technique provides a haptic interface in which the contact surface is a rigid thin plate made of a dielectric material comprising an electrode on the rear face of said plate. When a strong oscillating electric potential difference is established between the finger and the electrode, electric charges migrate into the finger and the Coulomb force attracts the finger towards the plate, which has the effect of increasing the coefficient of friction. . Such a technique has been described in the publications "Perception by the skin of electrically induced vibrations", by Mallinckrodt, E., Hughes, A. and Sleator, W. Jr, 1953, Science 118: 277-278 and "Contact mechanics between the human finger and a touchscreen under electroadhesion ”, de Ayyildiz, M., Scaraggi, M., Sirin, O., Basdogan, C., & Persson, BN, 2018, Proceedings of the National Academy of Sciences, 115 (50) , 12668-12673. The implementation of the method for tactile reproduction of textures is similar to that described previously for the first technique with the difference that, in this technique, the excitation signal increases the coefficient of friction instead of decreasing it, as in the previous one. technical.

[0008] Yet another technique proposes to cause vibrations in a rigid surface in contact with a sliding finger. The vibrations can be carried out in the direction normal to the contact surface, as described in the article “Toward quality texture display: vibrotactile stimuli to modify material roughness sensations”, by Asano, S., Okamoto, S., Matsuura, Y ., and Yamada, Y., 2014, Advanced Robotics, 28 (16), 1079-1089. The vibrations can also be effected in the direction tangential to the contact surface, as described in the publication "Perceptual constancy in the reproduction of Virtual tactile textures with surface displays", de Bochereau, S., Sinclair, S., & Hayward, V., 2018, ACM Transactions on Applied Perception (TAP), 15 (2), 10 or the publication "The spatial spectrum of tangential skin displacement can encode tactual texture", by Wiertlewski, M., Lozada, J., and Hayward , V., 2011, IEEE Transactions on Robotics, 27 (3), 461-472. Variants have also been proposed in which the vibrations are carried out in arbitrary directions as a function of the relative amplitude of the normal and tangential components, as described in the patent application US 2018/0267612 A1. However, in many applications, it is undesirable to vibrate the contact surface according to a component normal to said surface because the haptic interfaces comprising such a contact surface then emit sound waves, which are all the more intense as the frequencies used are high and the dimensions of the surface large, which is detrimental to the quality of the man-machine interface.

[0009] These different techniques for reproducing tactile sensations have a common drawback, namely the high intrinsic sensitivity to the conditions of sliding of the finger on the contact surface. The term “sliding conditions” is understood to mean the sliding speed, the normal force, that is to say the force of the pressure on the contact surface, the duration of the contact, the state of hygrometry of the finger. , the humidity of the ambient conditions and the presence of liquid or solid lubricants on the contact surface or on the finger. In fact, all of these conditions tend to greatly modify the amplitude of the frictional force due to the sliding of the finger and, consequently, limit the ability of the methods to modulate the sliding force to reproduce textures or isolated tactile signals during the process. sliding. This problem is particularly critical and is the subject of research to design techniques for regulating the frictional force in closed loops to make it independent of sliding conditions. The article “Overcoming the variability of fingertip friction with surface-haptic force-feedback”, by Huloux, N., Monnoyer, J., Boyron, M., & Wiertlewski, M., 2018, International Conférence on Human Haptic Sensing and Touch Enabled Computer Applications (pp. 326-337), Springer, reviews some of these regulatory techniques. The article "Closed loop application of electroadhesion for increased precision in texture rendering", by Grigorii, R. V., & Colgate, J. E., 2020, arXiv preprint: 2001 .01868 describes a similar technique to compensate for unwanted variations in the coefficient of friction. However, these different regulation techniques all have the drawback of considerably increasing the complexity of the methods and haptic interfaces intended to reproduce tactile sensations.

[0010] There is therefore a real need for a method making it possible to reproduce, on a smooth surface, texture sensations when a user's finger is in sliding contact with said surface.

SUMMARY OF THE INVENTION

To respond to the problems mentioned above of intrinsic sensitivity to the conditions of sliding of the finger on the contact surface, the applicant proposes a method of tactile stimulation of a finger sliding on a tactile surface in which the movements of the tactile surface are effected in the plane of said surface, in a direction orthogonal to the direction of sliding of the finger.

According to a first aspect, the invention relates to a method of tactile stimulation of a finger sliding on a tactile surface of a haptic interface, comprising, when a finger is detected in contact with the tactile surface, an operation of determining a direction of sliding of the finger on the touch surface and an operation of generating displacements of the touch surface, in the plane of said surface, in a direction orthogonal to the direction of sliding of the finger.

This stimulation method makes it possible to generate movements of the touch surface, which can artificially reproduce, on the smooth surface of the touch surface, the tactile sensations felt by a person when they touch certain materials or textures.

Advantageously, the operation of determining the sliding direction comprises the following steps: measuring the Cartesian coordinates (x, y) of a point of contact of the finger on the touch surface, determining the direction of the displacement velocity of the point of contact on the tactile surface, and determining, in the plane of the tactile surface, a direction orthogonal to the direction of the velocity of movement.

[0015] The point of contact is the location of the user's finger on the touch surface. Of course, the user can be in direct contact with the haptic interface 10, by means of a part of his body and in particular of a finger, or in indirect contact, by means of suitable equipment. such as a stylus or a touchscreen glove. The remainder of the description will be given for the example of a user's finger, it being understood that it may be another part of the user's body or suitable equipment.

In addition to the characteristics which have just been mentioned in the previous paragraph, the tactile stimulation method according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or in any technically possible combination: the operation of generating movement of the touch surface consists in activating at least one actuator adapted to generate a displacement of the touch surface in its own plane. it comprises, after the operation of determining the direction of sliding of the finger, an operation of determining an amplitude of the tactile stimulation. the movement of the touch-sensitive surface is controlled in direction and in amplitude it comprises a step of processing signals for measuring the coordinates of the point of contact in order to limit noises generating measurement uncertainty. the direction of the velocity of movement is determined by differentiating, over time, the coordinates of the point of contact of the finger on the touch surface. the direction of the displacement velocity is determined by detecting the force applied by the finger on the touch surface in a plane tangent to said touch surface, this force being aligned with the displacement velocity the direction of the displacement velocity is determined by optical or acoustic detection of the trajectory of the finger on the touch surface.

Another aspect of the invention relates to a haptic interface implementing the above method and comprising: a touch surface, an actuation system on which the touch surface is mounted, adapted to generate a displacement of said surface , a device for detecting and locating at least one point of contact between the finger and the touch surface, and a processing unit suitable for at least determining the direction of sliding of the finger on the touch surface and for controlling the actuator .

This haptic interface can have one or more additional characteristics among the following, considered individually or in any technically possible combination: the touch surface is suspended from a fixed frame by elastic suspensions. elastic suspensions are thin sections of elastomer. the actuation system comprises at least two actuators arranged orthogonally with respect to one another, under the touch surface.

BRIEF DESCRIPTION OF THE FIGURES

[0019] Other advantages and characteristics of the invention will become apparent on reading the following description, illustrated by the figures in which:

[0020] Figure 1 shows a schematic top view of the touch surface of a haptic interface according to the invention;

[0021] Figure 2 shows, in the form of a functional diagram, an example of steps of the tactile stimulation method according to the invention;

[0022] Figure 3 shows a schematic top view of a haptic interface according to one embodiment of the invention;

[0023] Figure 4 shows a schematic top view of a haptic interface according to another embodiment of the invention, and

[0024] Figure 5 shows a schematic perspective view of an example of an actuator and touch surface of the haptic interface of Figure 4.

DETAILED DESCRIPTION

An exemplary embodiment of a method of tactile stimulation of a finger on a tactile surface, when the user's finger is in sliding contact with said surface, is described in detail below, with reference to the drawings annexed. This example illustrates the characteristics and advantages of the invention. It is however recalled that the invention is not limited to this example.

In the figures, identical elements are identified by identical references. For reasons of legibility of the figures, the size scales between elements represented are not respected.

Figure 1 shows, in a schematic top view, a touch surface 20, for example the surface of a mobile phone touch screen, with a sliding contact 12, represented by its trajectory L. This sliding contact 12, like all sliding contacts on a tactile surface, extends in a reference plane P (x, y) where x and y are unit vectors and the two main directions of the plane P of the tactile surface 20, or contact surface. The sliding contact 12 comprises a zone 14, with a centroid C, corresponding to the zone of contact of the finger with the touch surface 20. The sliding contact 12 extends along a path L, specific to each sliding contact, in the reference (x, y). In other words, the path L corresponds to the path traveled by the centroid C of the contact zone 14 in the frame (x, y), the zone 14 being represented in FIG. 1 at any instant t of this path.

The centroid C being mobile and its position being measured in the global frame of reference (x, y), a local frame of reference (u, v) can be defined. If the sliding speed g is: where s is the curvilinear abscissa, then the sliding velocity vector - also called sliding velocity - tangent to the trajectory L of the contact zone 14 is w = gu, where u is the unit vector indicating the direction of the velocity slip defined

A vector v = kxu can then be defined, orthogonal to the trajectory L and in the direction of which the sliding velocity g is zero if k is a vector normal to the touch surface 20. The vector v thus defines the orthogonal direction to the direction u of the slip velocity.

The tactile stimulation method according to the invention proposes to generate movements of the tactile surface 20, in the plane P, in a direction orthogonal to the sliding trajectory L of the finger. It proposes in particular to determine the direction u of the finger sliding velocity and the direction v orthogonal to the direction u in order to define the direction of displacement of the movements of the touch surface 20. The trajectory can be a trajectory chosen by the user and which, therefore, is not known in advance by the interface. On the contrary, the trajectory can be known in advance, for example when the interface indicates a path to follow or when the touch surface is long and narrow. Whatever the trajectory (known in advance or not), the method according to the invention consists of moving the touch surface in a direction orthogonal to this trajectory. When the trajectory is not known in advance, the method determines the trajectory from the Cartesian coordinates of the point of contact. When the trajectory is known in advance, the method determines this trajectory from data previously stored in the interface.

An example of the various operations and steps of the method are shown in a functional diagram in Figure 2. In this example of the FIG. 2, the tactile stimulation method 100 comprises a first operation 110 which consists in detecting the presence of a finger in contact with the tactile surface 20. This detection of a finger in contact with the tactile surface can be carried out by means of various techniques commonly used in touch devices such as touch screens of smartphones, distribution kiosks, cash registers or other computer devices. The most common techniques use capacitive methods. Other methods can of course be used.

When the presence of a finger on the touch surface is detected, that is to say when a point of contact is detected (test 110), the method comprises, in step 120, the determination of the position of the contact zone 14 by measuring the Cartesian coordinates x and y of the point of contact in the coordinate system (x, y) of the tactile surface 20.

[0033] The method then comprises, in step 130, the estimation of the direction u of the sliding velocity, more or less precisely. Indeed, even an approximate determination is sufficient for the implementation of the method of the invention. Several methods, more or less easy to implement and providing more or less precise results, can be used to determine the direction u of the velocity of sliding of the finger on the touch surface. One method is based on the calculation of the position increment of the contact point. This method consists in detecting the position of the contact zone 14 of the finger in order to deduce therefrom the direction of sliding by differentiation over time. It will be clear to those skilled in the art that this method gives imprecise results when the sliding speed is low and the resolution of the detection of the position of the contact point is low. There are, however, algorithmic ways to make the estimation reliable even in the presence of measurement uncertainties. An example of such an algorithm is described, for example in the article entitled "A New computational model of friction applied to haptic rendering" by Hayward, V. and Armstrong, B. published in Experimental Robotics VI, Peter Corke and James Trevelyan (Eds), Lecture Notes in Control and Information Sciences, Vol. 250, Springer-Verlag, 2000, pp. 403-412.

[0034] Improvements can also be envisaged in order to limit the noise generating measurement uncertainty. For example, the uncertainty due to differentiating a noisy signal can be reduced by processing the signal. The processing can be, for example, smoothing or any other form of filtering, such as filtering of Kalman. The uncertainty of the measurements can also be improved by using asymptotic observers and state reconstructors without differentiation.

Another method of determining the direction of the finger sliding velocity is based on measuring the tangential force applied to the touch surface by the finger. This method consists of detecting the force applied to the tactile surface in the plane tangent to said surface and deducing therefrom the direction of sliding, since this force is always aligned with the sliding velocity. This method has the advantage of providing a reliable sliding direction value even when the speed is low, or even zero.

The measurement of the force applied to the touch surface can be carried out, for example, by means of strain gauges or optical micro-displacement sensors. It can also be carried out by measurements linked to the properties of the area of contact of the finger with the tactile surface, such as, for example, the estimation of the area of contact of the finger with the surface or the measurement of the surface density of the actual contact. finger with the surface.

[0037] Other methods, for example extrinsic to the touchscreen interface, can be used to estimate the direction of the finger slide velocity. These methods can, for example, implement optical, acoustic or magnetic means to detect or infer the trajectory of the finger in contact with the tactile surface.

Once the direction of the finger sliding velocity has been estimated, the method 100 proposes to determine, in step 140, the direction v orthogonal to the trajectory of the finger on the touch surface. This orthogonal direction v can be determined by calculation from the direction u, as explained previously in connection with FIG. 1. The vector v is easily calculated by taking the cross product of the vector u by a vector k, a unit vector orthogonal to the tactile surface, according to the formula v = k x u.

The method 100 can then include a step 150 consisting in determining the amplitude of the stimulation of the finger. The amplitude α of the stimulation can be determined using known methods. It can, for example, be determined by calculating the scalar value of a function T of the position (x, y) of the finger which represents a texture in a domain D. The amplitude a is then as follows: a = r (x, y), V (x, y) ED

For example if you want to create a periodic roughness effect when the finger slides in the direction of in the rectangular domain

D = {x, y} such that x G [—c, c], y G [- d, d], then where a ₀ represents the amplitude of the displacements of the tactile surface in the direction v and where l represents the spatial frequency of the periodic texture. If, in another example, we want to create a silky texture effect, then we can choose a function T (x, y) such that its value is a realization of a random process which follows a normal law in x and in y , ie white noise.

The method 100 finally comprises a step 160 of generating the movements of the touch surface. These movements are intended to be performed in the own plane P of the touch surface 20, that is to say the plane of the largest x and y dimensions of the touch surface. In other words, the displacements are carried out according to the direction x, the direction y or any intermediate direction in the reference mark (x, y). The direction of the displacements, or movements, of the tactile surface is in the direction v, orthogonal to the trajectory L of the sliding contact, determined in step 140. These displacements or movements are implemented with a stimulation amplitude, for example. the amplitude a determined in step 150 of the method of FIG. 2. Thus, the actuation of the tactile surface is controlled taking into account the amplitude and the direction of the stimulation.

Thus, the method 100 has the effect of causing a tactile stimulation of the finger, independent of the sliding movements of this finger on the tactile surface, also independent of the noises of friction of the finger on said surface. These stimuli can, for example, recreate the effect of a texture and simulate a texture on the touch surface.

As shown in Figure 2, the various steps of the method 100 are performed in a loop, at a predefined rate, as long as the stimulation is desired, which is controlled by step 170. Preferably, the loop is repeated. at a high rate so that the user can feel the stimulation in real time. The method according to the invention, and in particular the method according to the example of Figure 2, can be implemented in a haptic interface such as that shown in Figures 3 and 4. According to this example, the interface haptic 10 comprises: a touch-sensitive surface 20 via which the user can interact with said haptic interface, a detection and localization device ensuring the detection of finger contact on the touch-sensitive surface, an actuation system 30, under the touch-sensitive surface 20, ensuring a movement of said touch-sensitive surface 20, and a processing unit 40 ensuring the implementation of the method of the invention and the control of the actuators 30.

The tactile surface 20, also called the contact surface, is the face of the haptic interface 10 through which the user comes into contact with said interface. The tactile surface 20 can be a rigid plate, for example made of a transparent material, of rectangular shape, as shown in FIGS. 3 and 4. Those skilled in the art will understand that the tactile surface can take other shapes than rectangular, for example circular, triangular or trapezoidal. It can also take other forms than a plaque. It can be, for example, semi-spherical with a domed face. It can also be a part of arbitrary shape, having left surfaces or ruled surfaces. In these more general cases, the calculations described below can easily be extended by considering the plane P to be the plane tangent to the left surface or adjusted to the point of contact, as is well known to those skilled in the art familiar with the geometry of the surfaces.

The detection and location device, not shown in the figures, detects the contact of the user's finger and determines the Cartesian coordinates x and y of the point of contact in the reference (x, y) of the touch surface 20. Such a detection and location device is well known in the field of tactile surfaces and will therefore not be described in more detail.

The actuation system 30 of the haptic interface generates the movements in two main directions of the touch surface 20 which, when combined, generates movements in any desired direction. Indeed, the actuation system is configured to apply small movements to the touch surface. 20, in the plane of said tactile surface, that is to say the plane tangent to the contact of the finger with the surface. The actuation system 30 may include low mechanical impedance actuators designed to produce a force which causes displacement by overcoming the inertial, viscous and elastic forces which oppose displacement or high mechanical impedance actuators forcing displacement. Actuators can be driven by electrodynamic motors, variable reluctance motors, or piezoelectric motors. Whether they are high or low impedance, the actuators are mounted so as to be integral with the touch surface 20 and distributed under the whole of said surface. In the example of Figure 3, the actuation system comprises two actuators (shown in dotted lines in Figure 3), arranged so as to produce orthogonal forces along the bisecting lines 35 and 36 of the touch surface 20 to cause arbitrary displacements in the plane of said tactile surface. In the example of FIG. 4, the actuator system 30 comprises four actuators 31, 32, 33, 34 (shown in dotted lines in FIG. 4) positioned orthogonally two by two, each actuator being positioned at the periphery of the touch surface , under said tactile surface 20. The actuators are positioned symmetrically, two by two, with respect to the bisectors of the tactile surface, so as to cause arbitrary movements in the plane of the tactile surface.

The actuation system 30 also includes elastic suspensions 22 which can take many forms. The elastic suspensions 22 can, for example, be suspensions made using thin sections, adhesive elastomers, or deformable supports. In the example of FIG. 5, the touch surface 20 is suspended from a fixed frame 21 by the thin sections 22 allowing small movements of the touch surface in the plane P. The thin sections 22 are intended to introduce connections elastic between rigid elements of a structure represented here by the tactile surface 20 and the fixed frame 21.

The processing unit 40, an example of which is shown schematically in Figures 3 and 4, processes the data received from the detection and location device and controls the actuation system 30. The processing unit 40 implements an algorithm designed to calculate the small displacements of the tactile surface 20 on which the stimulated finger slides. This algorithm implements the steps of the method of the invention, and in particular the steps of FIG. 2. The processing unit 40 is associated with an input-output system making it possible to acquire the data of the detection and localization device and to produce commands intended to activate the actuation system 30. The actuation system drives the touch surface 20 in small displacements carried out in the plane P of the tactile surface and orthogonal to the direction of sliding of the finger on said surface.

Although described through a number of examples, variants and embodiments, the method of tactile stimulation of a finger sliding on a tactile surface according to the invention comprises various variants, modifications and improvements which will appear in such a way. obvious to those skilled in the art, it being understood that these variants, modifications and improvements form part of the scope of the invention.

Claims

[Claim 1] A method of tactile stimulation of a finger sliding on a tactile surface (20) of a haptic interface (10), comprising, when a finger is detected in contact with the tactile surface (110), an operation ( 120-140) for determining a direction of sliding of the finger on the touch-sensitive surface and an operation (160) for generating displacements of the touch-sensitive surface (20), in the plane of said surface, in a direction orthogonal to the direction sliding the finger the operation of determining the sliding direction comprising the following steps:

- measure (120) the Cartesian coordinates (x, y) of a point of contact of the finger on the touch surface,

- determine (130) the direction of the sliding speed (u) of the point of contact on the touch surface, and

- determining (140), in the plane (P) of the tactile surface, a direction (v) orthogonal to the direction of the sliding speed.

[Claim 2] A method according to claim 1, characterized in that the operation (160) of generating movements of the touch-sensitive surface (20) consists in activating at least one actuator (31, 32, 33, 34) adapted to generate a displacement of the tactile surface in its own plane (P).

[Claim 3] A method according to any one of claims 1 to 2, characterized in that it comprises, after the operation (130) of determining the direction of the sliding speed of the finger, an operation (150) of determination of an amplitude of the tactile stimulation.

[Claim 4] A method according to claims 2 and 3, characterized in that the movement of the touch surface is controlled in direction and in amplitude.

[Claim 5] A method according to any one of claims 1 to 4, characterized in that it comprises a step of processing the measurement signals of the coordinates of the point of contact to limit noise generating measurement uncertainty.

[Claim 6] A method according to any one of claims 1 to 5, characterized in that the direction of the sliding speed (u) is determined by differentiation, over time, of the coordinates of the point of contact of the finger on the tactile surface.

[Claim 7] A method according to any one of claims 1 to 5, characterized in that the direction of the sliding speed (u) is determined by detecting the force applied by the finger on the touch surface in a tangent plane. to said tactile surface, this force being aligned with the displacement velocity.

[Claim 8] A method according to any one of claims 1 to 5, characterized in that the direction of the sliding speed (u) is determined by optical, acoustic or magnetic detection of the trajectory of the finger on the touch surface.

[Claim 9] A haptic interface (10) implementing the method according to any one of claims 1 to 8, comprising:

- a tactile surface (20),

- an actuation system (30) on which the touch-sensitive surface is mounted, adapted to generate a displacement of said surface,

- a device for detecting and locating at least one point of contact between the finger and the touch surface, and

- a processing unit (40) suitable for at least determining the direction of the sliding speed of the finger on the touch surface and for controlling the actuator.

[Claim 10] Interface according to claim 9, characterized in that the tactile surface (20) is suspended from a fixed frame (21) by elastic suspensions (22).

[Claim 11] An interface according to claim 10, characterized in that the resilient suspensions are thin sections (22) or made of elastomeric materials.

[Claim 12] Interface according to any one of claims 9 to 11, characterized in that the actuation system (30) comprises at least two actuators (31, 32) arranged orthogonally with respect to one another, under the touchpad (20).