Vibrotactile interface with haptic feedback dependent on pressure force

Abstract

A method for controlling a haptic interface, the haptic interface comprising a slab (10), configured to be touched by one or more contact elements (3), at one or more contact points; actuators (12p), arranged against the slab, each actuator being configured to induce a vibration of the slab when subjected to a control signal (); detectors (14i), coupled to the slab, each detector being configured to produce a detection signal () dependent on the intensity of a force exerted on the slab, at each contact point; the method comprising estimating the intensity of the force exerted by each contact element at each contact point and generating haptic feedback dependent on each intensity. Figure 3A.

Description

Title of the invention: Vibrotactile interface with haptic feedback dependent on the force applied technical field

[0001] The technical field of the invention relates to vibrotactile type touch interfaces EARLIER ART

[0002] Vibrotactile interfaces are vibrating interfaces that allow a user to perceive tactile sensations simply by applying a finger to the interface. A vibration on a rigid interface can intuitively encode information to the user through a sensation felt at the fingertip. This is particularly important when visual information is absent or degraded. This is the case, for example, with tactile interfaces designed for visually impaired users, or tactile interfaces located outside the user's field of vision, such as a driver of a vehicle. A vibrotactile interface makes it possible to transmit precise spatial and temporal information.

[0003] A vibrotactile interface exploits the sensitivity of skin mechanoreceptors to vibratory stimuli, which produce a deformation of the skin. Mechanoreceptors are generally sensitive to vibrations at frequencies typically between 10 Hz and 1 kHz, with high sensitivity observed between 200 Hz and 300 Hz. The amplitude of the vibration is also an important parameter, as the minimum amplitude to trigger tactile stimulation depends on the vibration frequency. It is considered that the lower the frequency, the higher the amplitude must be for the vibration to be perceived. The amplitude can, for example, be a few milliseconds or a few tens of milliseconds. Another important parameter, conditioning the tactile stimulation, is the shape of the vibration wave, as well as its duration, which can range from 0.1 s to a few seconds.The delay between two consecutive vibrations can also affect the stimulation perceived by the user.

[0004] Thus, touch interfaces make it possible to provide haptic feedback through vibratory patterns triggered by the touch interface being touched by a finger. The vibratory patterns are predetermined so that the resulting tactile sensations are easily detectable. These sensations can, for example, mimic sensations induced by mechanical devices, such as a cursor, scroll wheel, or button. Developments have also led to the creation of "tactons," contraction of the Anglo-Saxon terms "tactile" and "icons", which are localized and structured sensory information.

[0005] Certain touch interfaces allow for the measurement of the pressure force exerted by a finger. Such interfaces have been described, for example, in documents US5241308 or US55210813, where the position and pressure force of a finger are estimated by capacitive effect. Document US201000053116 describes a touchscreen combining capacitive detection of a finger's position with specific force sensors, so as to discriminate between intentional finger contact, exerted with a certain force, and accidental contact.

[0006] The inventor has designed a more advanced touch interface, allowing the simultaneous measurement of a force exerted by several fingers, and allowing haptic feedback to be controlled according to the force exerted. Description of the invention

[0007] A first object of the invention is a method for controlling a haptic interface, the haptic interface comprising: - a slab, configured to be touched by one or more contact elements, at one or more points of contact, - actuators, arranged against the slab, each actuator being configured to induce a vibration of the slab when it is subjected to a control signal; - detectors, coupled to the slab, each detector being configured to produce a detection signal depending on the intensity of a force exerted on the slab, at each point of contact;

[0008] the process comprising: a. determination of a position of each point of contact on the slab, at a measurement instant; b. from the detection signal generated by different detectors, at the time of measurement; estimation of a force exerted on the slab, at each point of contact; c. from the position of each contact point and the force exerted at each contact point, definition of a haptic feedback of the slab, the haptic feedback including a target displacement assigned to each contact point of the slab; d. from the haptic feedback of the slab, defined in c), determination of a control signal to be applied to the actuators, so as to obtain the target displacements assigned to each point of contact; e. addressing a control signal to each actuator, according to each control signal determined during step d); f. reiteration of steps a) to e) by incrementing the measurement time, steps a) to e) being reiterated until a stopping criterion for the iterations is reached;

[0009] steps a) to f) being implemented by a processing unit connected to a memory, the memory comprising response functions of an assembly formed by the slab, each actuator and each detector.

[0010] According to one possibility, step b) involves an inversion of a direct detection model, the direct detection model determining, for each detector, a detection signal as a function of a force exerted at each point of the slab. The direct detection model may take into account the control signal addressed to each actuator.

[0011] Step b) may include: - bi) extraction, from memory, of a detection matrix, each term of which corresponds to a detection signal generated, in a detector, by a unit support exerted in a position on the slab, the unit support being a predetermined support force, the detection matrix being stored in memory; - bii) formation of a detection vector, comprising the detection signal resulting from the detectors; - biii) from the detection matrix and the detection vector, estimation of a force vector, each term of which corresponds to an estimate of the force exerted at each point of contact.

[0012] Step b) may include taking into account a time delay applied to the detection matrix.

[0013] According to one possibility, the detection matrix is ​​stored in memory, in the frequency domain, in different frequency bands.

[0014] According to one possibility: - substep bi) involves an extraction, from memory, of a charge transfer matrix, each term of which corresponds to a charge generated, in a detector, by a unit voltage applied to an actuator, the unit voltage being predetermined. - substep bii) involves the formation of a control vector, comprising the actuation signal of each actuator from a previous iteration; - substep biii) includes an estimation of the force vector from the load transfer matrix and the control vector.

[0015] Step c) may involve an inversion of a direct control model, the direct control model determining, for each actuator, the control signal as a function of each target displacement. The direct control model may take into account the force exerted on the plate at each point of contact.

[0016] According to one possibility, step c) comprises: - ci) extraction, from memory, of a displacement matrix, each term of which corresponds to a displacement of the slab induced, at a point, by a unit voltage applied to an actuator, the unit voltage being a predetermined voltage, the displacement matrix being stored in memory; - cii) formation of a displacement vector, including the target displacements; - ciii) from the displacement matrix and the displacement vector, estimation of a control vector, each term of which corresponds to a control signal to be applied to each actuator.

[0017] Step c) may include taking into account a time delay applied to the displacement matrix.

[0018] The displacement matrix can be stored in memory, in the frequency domain, in different frequency bands;

[0019] According to one possibility - substep ci) involves an extraction, from memory, of a charge transfer matrix, each term of which corresponds to a charge generated, in a detector, by a voltage applied to an actuation transducer; - substep cii) involves the formation of a force vector, comprising the force estimated at each point of contact during step b); - substep ciii) includes an estimation of the control vector from the load transfer matrix and the force vector.

[0020] Following step e) of an iteration and step b) of a subsequent iteration, the method may include an estimation of an impedance of the contact member.

[0021] A second object of the invention is a haptic interface comprising: - a slab, configured to be touched by one or more contact elements, at one or more points of contact, - actuators, arranged against the slab, each actuator being configured to cause a vibration of the slab when it is subjected to a control signal; - detectors, coupled to the slab, each detector being configured to produce a detection signal depending on the intensity of a force exerted on the slab, at each point of contact; - a processing unit, configured to implement steps a) to f) of a process according to the first object of the invention.

[0022] The invention will be better understood upon reading the description of the exemplary embodiments presented later in this description, in connection with the figures listed below. FIGURES

[0023] Fig. 1 shows a general view of a haptic interface enabling an implementation of the invention.

[0024] Fig. 2A shows a configuration of a haptic interface, in which each actuator and each detector forms the same piezoelectric transducer.

[0025] Fig. 2B shows another configuration of a haptic interface, in which each actuator and each detector forms the same piezoelectric transducer.

[0026] Fig. 2C shows a configuration of a haptic interface, in which the actuators and detectors are piezoelectric transducers different from each other and are two by two concentric.

[0027] Fig. 2D shows another configuration of a haptic interface, in which the actuators and detectors are piezoelectric transducers different from each other.

[0028] Fig. 2E shows a configuration of a piezoelectric transducer, which can function as an actuator or as a detector.

[0029] Fig. 2F shows another configuration of a piezoelectric transducer, which can function as an actuator and as a detector.

[0030] Fig. 3A schematically illustrates the main components of an example of a haptic interface according to the invention.

[0031] Fig. 3B represents the main steps implemented by the haptic interface described in relation to Fig. 3A.

[0032] Figure 3C is a detail of a force estimation step, described in the [Fig.3B]

[0033] Fig. 3D is a detail of a step in determining a control signal, described in Fig. 3B.

[0034] Fig. 4A illustrates an extraction of a reduced detection matrix, by extracting certain columns of a tensor stored in a memory, in the frequency domain.

[0035] Fig. 4B illustrates an extraction of a displacement matrix, by extracting certain lines of a tensor stored in memory, in the frequency domain.

[0036] Figure 4C illustrates the extraction of a reduced displacement transfer matrix by extracting certain columns from a tensor stored in memory. Description of specific implementation methods

[0037] Fig. 1 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, without limitation, a consumer appliance, the dashboard of a vehicle, a person identification device, or a device to assist a visually impaired or disabled person.

[0038] In the examples shown in this application, the external part 3 is a finger, which corresponds to most of the envisaged applications. Alternatively, the external part 3 could be a stylus, or any other means of acting on the interface 1.

[0039] The haptic interface comprises a rigid, transparent or opaque slab 10. The slab 10 may, for example, be made of glass, metal, or an organic compound, such as plexiglass. The slab 10 is delimited by a contact surface 11, intended to be touched by an external organ, in particular a finger. 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, strength). For example, it is between 1 and 5 mm for glass or a material such as plexiglass.

[0040] The slab can form a touch screen, by including light sources, for example of the OLED (organic light-emitting diode) type.

[0041] The slab 10 is coupled to actuators 12p, for example piezoelectric actuators, where p is an integer designating each actuator. Each actuator is configured to move the slab, generating a vibration of variable amplitude and frequency, preferably within a frequency range of 10 Hz to 1 kHz, preferably including a frequency band between 200 Hz and 300 Hz, which is a frequency band at which tactile sensation is particularly felt. Each actuator 12p is powered by a control signal Vp, so as to generate a vibration whose characteristics (amplitude, frequency) are configured to produce haptic feedback from the interface. The control signals Vp are transmitted, via a control circuit 13, to each actuator 12p.

[0042] In this example, each piezoelectric actuator 12p comprises a piezoelectric material, for example AIN, ZnO, or PZT, arranged between two electrodes. Each actuator can be bonded to the slab. According to one embodiment, the actuators 12p can be electromagnetic, electromechanical, or piezoresistive.

[0043] The slab 10 is coupled to detectors 14, for example piezoelectric transducers, i being an integer denoting each detector. Each detector 14 is configured to generate a detection signal Q as a function of the intensity of the pressure force exerted by the finger. The detection signal Q is collected by a circuit detection 15. The detection signal Q. is formed by charges induced by the pressure of the finger on the detector 14;. Each detector 14; can be made of a piezoelectric material as described in connection with the actuators 12p.

[0044] The touch surface 11 includes a position sensor 17, for example, of the capacitive type. The position sensor 17 is connected to conductive tracks 16, arranged in a two-dimensional lattice. The conductive tracks 16 are adjacent to the contact surface 11. The conductive tracks extend parallel to the panel 10, or within the panel 10, below the contact surface 11. When the panel 10 is opaque, the conductive tracks 16 may be made of a common conductive material, for example, a metal. When the panel 10 is transparent, the conductive tracks 16 are preferably made of a transparent conductive material, for example, a conductive oxide, a common material being ITO (Indium Tin Oxide). The conductive tracks 16 extend, for example, in rows and columns. The conductive tracks can be biased according to a bias voltage.The interface includes an insulating layer extending between the conductive tracks 16 and the contact surface 11, enabling capacitive detection of contact with a user's finger 3, or any other type of external device. The position sensor 16 is configured to generate a position signal Sm containing the number and position of contact points on the sensing surface 11. The conductive tracks 16 form a mesh on the slab, defining N mesh points, each point of the mesh corresponding to a position that can be detected by the position sensor. The number N of positions is determined according to the spatial resolution of the position sensor. It is possible to consider a number of positions less than that determined by the spatial resolution of the position sensor.This involves taking into account the contact surface of a finger, extending over a diameter of a few mm, for example 5 mm. Thus, the spatial resolution of the position sensor and the conductive tracks allows for the definition of a maximum number of positions Nmax. The haptic interface takes into account a number N of different positions that can be occupied by the finger on the contact surface 11, with N < Nmax.

[0045] The device includes a processing unit 20, supplied, at different measurement times, by the detection signals Q. generated by the detection circuit 15 and by the position signal Sm generated by the position sensor 17. The processing unit 20 is intended to address a control signal Vp to the control circuit 13, so that the latter transmits each control signal Vp respectively to each actuator 12p.

[0046] The processing unit 20 is configured to determine a haptic pattern based on the position of each finger 3 contacting the contact surface 11, but also based on the pressure force exerted by each finger 3. The processing unit 20 includes a microprocessor, connected to a memory 25 in which instructions are stored allowing the microprocessor to implement certain steps described in connection with [Fig.3A].

[0047] Preferably, the actuators and detectors are distributed under the slab, advantageously forming a regular grid. The actuators and detectors can be arranged in different configurations, shown schematically in Figures 2A to 2D. These figures represent a top view of the actuators and detectors, with the slab shown in transparency.

[0048] Figure 2A shows a configuration in which each transducer acts as both an actuator and a detector. Each upper electrode is connected, via a resistor R, to the output of a voltage amplifier A. The resistor R and the voltage amplifier form part of the actuation circuit and the measurement circuit. When a voltage Vp, forming the control signal, is applied across the terminals of the amplifier A, a voltage is established between the upper and lower electrodes, inducing a vibration of the actuator. Applying a pressure force to the upper electrode compresses the transducer, generating a detection signal by integrating a charge Q resulting from the compression. However, in such a configuration, the charge Q resulting from the compression may be small compared to the electrical charge generated by the biasing of the amplifier by the control signal Vp.

[0049] A first alternative, shown in [Fig. 2B], consists of using a switch C, the switching of which allows the upper electrode to be connected either to the previously described voltage amplifier, in which case the transducer functions as an actuator, or to a charge amplifier A', to form the detection signal. The switch provides a physical separation between the control signal and the detection signal.

[0050] Figures 2C to 2D show alternatives in which the actuators 12p are separated from the detectors 14. Figure 2C shows a configuration comprising pairs formed by an actuator 12p and a detector 14 arranged concentrically. The upper electrode of the actuator is annular and extends over a larger area than the upper electrode of the detector, the latter being disc-shaped. A voltage amplifier A is provided to allow the upper electrode of the actuator to be excited by the control signal Vp. A charge amplifier A' allows a detection signal to be formed from charges formed at the upper electrode of the detector.

[0051] In [Fig.2D], a configuration comprising actuators 12; separated from detectors 14p is shown.

[0052] Figures 2E and 2F show possible transducer configurations. Figure 2E shows a transducer comprising a piezoelectric PZT material, on either side of which extend two electrodes El and E0. Electrode E0 extends between plate 10 and the PZT material. Electrode E0 can be connected to ground while a potential is measured or applied to electrode EL. Alternatively, electrode E0 and electrodes El can be connected to two opposite potentials.

[0053] In [Fig. 2E], two electrodes El and E2, electrically isolated from each other, are positioned opposite electrode E0. Electrode El is annular, and electrode E2 is located at the center of electrode El. One electrode, for example El, can be used to apply a potential to the PZT, while electrode E2 allows for measurement. This corresponds to the configuration shown in [Fig. 2C].

[0054] Regardless of the embodiment, it is preferable that the upper electrode of an actuator 12p extend over a larger area than that of a detector 14. The diameter of the upper electrode of the actuator 12p can be on the order of 10 mm to 30 mm, so as to allow sufficient deformation of the slab to be felt by the finger. Since the production of electrical charges by compression is easier to measure, the upper electrode of the detectors can be smaller, for example, a diameter on the order of or less than 5 to 10 mm.

[0055] Preferably, the actuators 12p extend, between the upper and lower electrodes, with a thickness of between 100 µm and 500 µm. The detectors 14; are thicker, for example, greater than 500 µm or greater than 1 mm, so as to limit their intrinsic capacitance.

[0056] The actuation circuit 13 and the detection circuit 15 are connected to the processing unit 20, the latter being configured to generate control signals, addressed to the actuation circuit 13, so that the actuators produce vibrations forming a haptic pattern providing predetermined haptic feedback. Each haptic pattern depends on the position of the contact on the contact surface and the force exerted on the latter.

[0057] The invention takes advantage of an independent measurement of the pressure exerted at the level of each finger contacting the slab 10, and of a possibility of modulating the vibration pattern so that the haptic feedback depends on the pressure exerted.

[0058] Figure 3A schematically illustrates the main components of the haptic interface. The slab 10 includes: - P actuators 12p, P being an integer greater than or equal to 2, controlled by the control circuit 13, the latter transmitting a signal to each actuator according to a control signal Vp addressed by the processing unit 20; - the detectors 14;, connected to the detection circuit 15, the latter producing a detection signal i dependent on a support force Fm exerted by each finger applied against the slab. - the conductive tracks 16, connected to the position sensor 17, the latter producing a position signal Sm dependent on the position of each contactm on the slab.

[0059] The processing unit 20 is connected to the detection circuit 15 and the position sensor 17, from which it receives the detection signal Q and the position signal Sm, respectively. The processing unit 20 comprises three processing blocks: - a processing block 21 allows estimating a force Fm applied at each contact point m from the position signal Sm and each detection signal Q, possibly taking into account a control signal Vp, - a haptic block 22, configured to define a target displacement {j} at the level of each finger contacting the tile 10. The haptic block includes a haptic memory, in which vibration patterns are stored for different configurations of each finger touching the tile. Each configuration is defined according to parameters such as: number of fingers in contact with the tile, position of each finger contacting the tile, and intensity of the pressure force exerted by each of the fingers contacting the tile. - a control block 23, configured to generate a control signal Vp addressed to the control circuit 13 of the actuators 12p, so as to obtain, at each finger contacting the tile 10, a displacement Um providing the haptic feedback defined by the haptic block 22. The displacement Uin of the tile, at each point of contact, must be as close as possible to the target displacement Ù. The control signal Vp is established from the target displacements Üm defined by the haptic block 22, possibly taking into account the force exerted by each finger contacting the tile.

[0060] Each block can be implemented by one or more microprocessors. Each block can be composed of functions programmed in a computer environment spécifique, par exemple Matlab ou Python. Le bloc de traitement 21 et le bloc commande 23 peuvent mettre en œuvre un filtrage inverse, comme décrit par la suite.

[0061] Figure 3B illustrates the main steps of an iterative process implemented by the haptic interface 1:

[0062] Step 100: at a measurement instant, one or more fingers m touch the slab. M is an integer denoting the number of fingers simultaneously touching the plate.

[0063] Etape 110 : la position de chaque doigt touchant la dalle est déterminée par le capteur de position 17. Il en résulte une formation d'un signal de position Sm pour chaque position.

[0064] Step 120: The pressure exerted by each finger is converted into a detection signal Q by the detectors 14. The detection signal corresponds, for example, to a quantity of charges generated by each detector.

[0065] Step 130: This step is implemented by the processing block 21 of the processing unit 20. It involves estimating a support force p exerted at the time of measurement by each fingerm. This step is described in more detail later, in relation to [Fig. 3C].

[0066] Step 140: This step is implemented by the haptic block 22 of the processing unit 20. It involves determining a target displacement [Jm] for each finger, so as to form a haptic feedback from the interface and provide sensory information to the user which depends on the number of fingers, their positions on the slab and the pressure force they exert.

[0067] Step 150: This step is implemented by the control block 23 of the processing unit 20. It involves defining a control signal Vp for each actuator 12p, so as to obtain the displacement Um of the slab in each finger, as close as possible to the target displacement l / m. This step is described in more detail later, in relation to [Fig. 3D].

[0068] Step 160: Activation of each actuator 12p according to the control signals defined in step 150, to produce haptic feedback resulting from the movement of the plate at each contact point. The haptic feedback can be combined with other types of stimulation, for example, the emission of an audible or visual signal. When the plate forms a touchscreen, the image displayed on the screen can vary according to the haptic feedback.

[0069] Following step 160, steps 100 to 160 are repeated, with the measurement time being incremented.

[0070] Steps 130, 140 and 150 are performed by the processing unit 20, preferably in the time domain. They assume consideration of functions of response from the slab, some of them being stored in memory 25 in the frequency domain.

[0071] A first frequency response function is a detection matrix Hc, where each term n) corresponds to a complex detection signal generated, in a detector 14, by a unit harmonic support exerted at a position n on the slab. The unit harmonic support, of unit amplitude, is a support force exerted at a predetermined frequency and of predetermined intensity, for example, 1 N. The detection matrix Hc is stored in the memory 25 of the processing unit 20. The detection matrix Hc has one dimension, where I corresponds to the number of detectors and N corresponds to the number of positions considered. All or part of the detection matrix He, and more particularly its inverse Hc', is used in step 130; Hc' denotes the inverse or a pseudo-inverse, for example, a Moore-Penrose pseudo-inverse.

[0072] A second frequency response function is a displacement matrix Ha, each term of which corresponds to a displacement of the slab induced, at a point, by a unit voltage applied to an actuator 12p. The unit voltage is a predetermined voltage, for example IV. The displacement matrix Ha has one dimension (V,P), where P corresponds to the number of actuators and N corresponds to the number of positions considered. The displacement matrix Ha is stored in memory 25 of the processing unit 20. All or part of the displacement matrix Ha, and more particularly its inverse Ha, is used in step 150. When the displacement matrix Ha is not invertible, Ha denotes a pseudo-inverse, for example, a Moore-Penrose pseudo-inverse.

[0073] A third, optional response function is a charge transfer matrix G, each term of which (pp. / ) corresponds to a charge generated in a detector 14 by a unit voltage applied to an actuator 12p. The charge transfer matrix is ​​stored in a memory 25 of the processing unit 20. The charge transfer matrix G has one dimension (PJ). The charge transfer matrix G is stored in the memory 25 of the processing unit 20. The charge transfer matrix G can be used in step 130.

[0074] A fourth, optional response function is a displacement transfer matrix Æ, where each term ^(n, ti) corresponds to a displacement induced, at a position n of the slab 10, by a unit force exerted at a contact point located at another position. The displacement transfer matrix is ​​stored in memory 25 of the processing unit 20. The displacement transfer matrix K has one dimension (^,^). The displacement transfer matrix K is stored in memory 25 of processing unit 20. All or part of the displacement transfer matrix can be used in step 150.

[0075] In this example, the matrices Ha, Hc described above are stored in memory 25 in frequency form for W frequency bands w. The matrices F and G are stored in memory 25 in time form.

[0076] The operation of the haptic interface 1 is governed by expressions, describing relationships between the displacements generated at the level of each finger in contact with the slab, the force exerted on the fingers, as well as the measured detection signals and the control signals addressed to the actuators.

[0077] The displacement of the slab Un at a point n is such that:

[0078] u = ZLjhVp + .KnmFm (1) n JF finished m

[0079] where: - Hanp is a term in the displacement matrix Ha addressing the point on the slab of rank n and the actuator of rank - Vp is the control signal addressed to actuator 12p. - ^nm is a term in the matrix F addressing the point of the slab of rank n and the finger in contact with the slab of rank m.

[0080] Fm corresponds to the force applied by the finger at position m on the slab.

[0081] Expressed in matrix form, (1) becomes:

[0082] U = HaV+KF(2)

[0083] V is a control vector, each term of which corresponds to the control signal Vp addressed to each actuator 12p. V is of dimension (P, 1).

[0084] The detection signal Q, detected by a detector 14, is such that: 100851 - Gip is a term in matrix G addressing actuator 12p and detector 14i* - ^cin is a term in the detection matrix Hc addressing detector 14; and each point of the mesh of rank n.

[0086] Expressed in matrix form, (3) becomes

[0087] Q = GV + HCF(4.)

[0088] Expressions (1) to (4) define a direct model, translating the effect, on the slab, of constraints exerted on the latter, the constraints being able to include both an electrical constraint (the control signals V addressed to each actuator), and a mechanical one (the force F exerted on the slab by each finger in contact).

[0089] The matrices Hc, K, and G determine the slab responses, both the mechanical response, in this case a displacement of the slab at different points, and the electrical response, in this case the detection signal of each detector. Equations (1) and (2) correspond to a direct control model, as it allows the determination of the slab displacement in response to a control signal. Equations (3) and (4) correspond to a direct detection model, as it describes the detection of loads under the effect of a force exerted on the slab.

[0090] The direct models defined in relation to expression (1) to (4) use matrices Ha, Hc, K defined for the mesh points corresponding to each detected contact point. Knowing the position of the contact points, the matrices Ha, K are formed from tensors K, defined for each mesh point and stored in memory 25.

[0091] Memory 25 stores the set of tensors K for each point of the mesh. During steps 130 and 150, terms of these tensors corresponding to each position m detected by the position sensor 17 can be extracted from memory 25. The extractions from the tensors K are described by the continued, in connection with figures 4A to 4C.

[0092] Figure 3C describes the sub-steps of step 130. During step 130, the direct detection model is reversed, so as to estimate the force F exerted by each finger in contact with the slab, the number M of which and the position on the slab is provided by the position sensor 17. F is a vector, of dimension (Af, 1) of which each term Pm is an estimate of the force Fm applied by the finger at position m.

[0093] The inversion of the direct detection model can be established by determining g1. To this end, in a substep 131, columns of the tensor Hc corresponding to each position m contacted by a finger are extracted from memory 25. Figure 4A represents such an extraction. In the example shown in Figure 4A, the tensor Hc has dimensions (Z, N, W). From the tensor Hc, W detection matrices Hc of dimensions (Z, M) are extracted, each column of which is associated with a position m detected by the position sensor 17. In other words, in each frequency band, a detection matrix Hc is used, formed from the column or columns whose index n corresponds to a detected position m.

[0094] In a substep 132, a pseudo-inverse of each matrix Hc is calculated in each frequency band w.

[0095] In step 133, the term delay is applied, which, in the frequency domain, represents a time delay between the application of the force and its measurement. T corresponds to a time delay on the order of a few milliseconds. Working in the frequency domain facilitates the formalization of the time delay r.

[0096] During a substep 134, a charge vector Q of dimension (1,1) is formed, each term of which is the detection signal Q of a detector 14;.

[0097] In a substep 135, the mechanical effect of the control signal V applied to the actuators on the slab is taken into account. During the first iteration, an initial control signal resulting from an initialization is considered. The initial control signal can, for example, be predetermined or zero in all frequency bands. In subsequent iterations, the control signal V resulting from the previous iteration is taken into account. Substep 135 is optional. Preferably, it is not implemented during the first iteration.

[0098] During a substep 136, the matrix G is taken into account.

[0099] During a substep step 137, the direct control model is reversed. One possibility is that the inversion of the direct control model is performed by estimating the inverse of the Hc matrix resulting from step 134, for example, a pseudo-inverse as previously described. Equation (5) is one way to invert the direct control model, according to a first approach.

[0100] F = ej^Hc\Q-GV) (5)

[0101] According to one embodiment, a simplified direct control model is implemented, neglecting the influence of the actuators on each detection signal. The simplified electrical model is thus:

[0102] Q = HCF(6)

[0103] and its inversion is:

[0104] F = e^ <! *He] Q (7)Onestime que l’expression (5) est préférable, car moins entachée error.

[0105] With respect to the actual force exerted at each point, forming a vector F, F = e^^F- In other words, the estimation error is a time error

[0106] Implementing expression (7) leads to a larger error, because:

[0107] F^e^H^ÇQ+GV) (8)

[0108] The matrix product GV corresponds to an estimation error of F.

[0109] Each exerted force can be expressed in the time domain by an inverse Fourier transform, for example an inverse fast Fourier transform (IFFT),

[0110] f = IFFT(F)(9)

[0111] The transition to the time domain is optional. It corresponds to substep 138.

[0112] Figure 3D describes the substeps of step 150. During step 150, the forward detection model is inverted so as to estimate the control signal Vp to be addressed to each actuator to obtain the target displacement {J determined by the haptic block 22.

[0113] The inversion of the direct detection model can be established by determining Ha. To this end, in a substep 151, rows of the tensor Ha corresponding to each position m contacted by a finger are extracted from memory 25. Figure 4B represents such an extraction. In the example shown in Figure 4B, the tensor Ha of dimension (N, P, W) defined for different spectral bands w is represented. From the tensor Ha, matrices Ha of dimensions {M, P} are extracted, each row of which is associated with a position m detected by the position sensor 17. In other words, in each frequency band, a matrix Ha is used, formed from the row or rows whose index n corresponds to a detected position m.

[0114] In a substep 152, a pseudo-inverse H^ of each matrix Ha is calculated in each frequency band

[0115] In step 153, the delay term e~jürr is applied, representing, in the frequency domain, a time delay between the generation of the control signal and the formation of vibrations on the slab. The delay ' is as defined in step 133.

[0116] During a substep 154, a target displacement vector U, of dimension (1), is formed, each term of which corresponds to a target displacement to be applied at position m.

[0117] During a substep 155, the electrical effect on the slab of the force applied at each contact position is taken into account, in the form of the force vector F defined in step 137. Substep 156 is optional.

[0118] In a step 156, the terms corresponding to each position m are extracted from the tensor K, as illustrated in Figure 4C. This allows the formation of a matrix K,

[0119] During a substep 157, the direct control model is inverted. According to one possibility, the inversion of the direct control model is performed using the inverse of the Ha matrix, for example a pseudo-inverse as previously described. Equation (10) is one way of inverting the direct control model, according to a first approach.

[0120] v = Ù-KF)^ (10)

[0121] According to one embodiment, a simplified direct control model is implemented, neglecting the influence of the actuators on each detection signal. The simplified electrical model is thus:

[0122] U = HaV(ll)

[0123] and its inversion is:

[0124] ^^><^(12)

[0125] Expression (10) is considered preferable, as it is less tainted by error. Compared to the determined target displacement, the actual displacement exerted is U — In other words, the estimation error is a simple delay.

[0126] Implementing expression (12) leads to a larger error, because

[0127] U = e^^V + KF (13). KF corresponds to an error term.

[0128] The signals are finally expressed in the time domain by an inverse Fourier transform, for example an inverse fast Fourier transform (IFFT).

[0129] v = IFFT(V) (14)

[0130] The transition into the time domain corresponds to substep 138. This allows control signals to be addressed to each actuator, defined in the time domain.

[0131] The invention can be applied to identity control applications. As soon as at least one finger is detected on the contact surface, the vibrating pattern (or haptic pattern) emits vibrations of certain amplitudes. The force exerted by the finger, in response to this vibration, can be considered as a mechanical impedance, which depends on the finger. The invention allows for the simultaneous estimation of the mechanical impedance on several fingers. Such control can also allow for discrimination between a finger and another object contacting the interface.

Claims

1. Demands Method for controlling a haptic interface, the haptic interface comprising - a slab (10), configured to be touched by one or more contact elements (3), at one or more points of contact, - actuators (12p), arranged against the slab, each actuator being configured to induce a vibration of the slab when it is subjected to a control signal (Vp); - detectors (14;), coupled to the slab, each detector being configured to produce a detection signal (Q.) depending on the intensity of a force exerted on the slab, at each point of contact; the process comprising: a. determination of a position of each point of contact on the slab, at a measurement instant; b. from the detection signal generated by different detectors, at the time of measurement; estimation of a force (Fm, F) exerted on the slab, at each point of contact; c. from the position of each contact point and the force (Ffn) exerted at each contact point, definition of a haptic feedback of the slab, the haptic feedback including a target displacement Ü) assigned to each contact point of the slab; d. from the haptic feedback of the slab, defined in c), determination of a control signal (Vp, V) to be applied to the actuators, so as to obtain the target displacements assigned to each point of contact; e. addressing a control signal to each actuator, according to each control signal determined during step d); f. reiteration of steps a) to e) by incrementing the measurement time, steps a) to e) being reiterated until a stopping criterion for the iterations is reached; steps a) to f) being implemented by a processing unit (20) connected to a memory (25), the memory comprising response functions of an assembly formed by the slab, each actuator and each detector; the process being characterized in that step c) comprises an inversion of a direct control model, the direct control model determining, for each actuator, the control signal (Vp) as a function of each target displacement.

2. A method according to claim 1, wherein step b) comprises an inversion of a direct detection model, the direct detection model determining, for each detector, a detection signal (Q., Q) as a function of a force exerted at each point of the slab.

3. Method according to claim 2, wherein the direct detection model takes into account the control signal addressed to each actuator.

4. A method according to any one of claims 2 or 3, wherein step b) comprises: - bi) extraction, from memory (25), of a detection matrix (fie), each term of which corresponds to a detection signal generated, in a detector, by a unit support exerted at a position on the slab, the unit support being a predetermined support force, the detection matrix being stored in memory, the detection matrix forming the direct detection model; - bii) formation of a detection vector (O), comprising the detection signal resulting from the detectors; - biii) from the detection matrix and the detection vector, estimation of a force vector (F), each term of which corresponds to an estimate of the force exerted at each point of contact.

5. A method according to claim 4, wherein step b) includes taking into account a time delay applied to the detection matrix.

6. Method according to claim 5, wherein the detection matrix is ​​stored, in memory, in the frequency domain, in different frequency bands.

7. A method according to any one of claims 4 to 6, wherein: - substep bi) comprises an extraction, from memory, of a charge transfer matrix (G), each term of which corresponds to a charge generated, in a detector, by a unit voltage applied to an actuator, the unit voltage being predetermined; - substep bii) comprises the formation of a control vector (V), comprising the actuation signal of each actuator (12p) from a previous iteration; - substep biii) comprises an estimation of the force vector from the charge transfer matrix and the control vector.

8. A method according to any one of the preceding claims, wherein the direct control model takes into account the force exerted on the plate at each point of contact.

9. A method according to any one of the preceding claims, wherein step c) comprises: - ci) extracting from memory a displacement matrix (Hay) in which each term corresponds to a displacement of the slab induced, at a point, by a unit voltage applied to an actuator, the unit voltage being a predetermined voltage, the displacement matrix being stored in memory, the displacement matrix forming the direct control model; - cii) forming a displacement vector (£7), comprising the target displacements; - ciii) from the displacement matrix and the displacement vector, estimating a control vector (V), in which each term corresponds to a control signal (Vp) to be applied to each actuator.

10. A method according to claim 9, wherein step c) includes taking into account a time delay applied to the displacement matrix.

11. A method according to any one of claims 9 or 10, wherein - the displacement matrix is ​​stored in memory, in the frequency domain, in different frequency bands.

12. A method according to any one of claims 9 to 11, wherein: - substep c1) includes an extraction, from memory, of a charge transfer matrix, each term of which corresponds to a charge generated, in a detector, by a voltage applied to an actuation transducer; - substep c2) includes a formation of a force vector, comprising the force estimated at each point of contact during step b); - substep c3) includes an estimation of the control vector from the charge transfer matrix and the force vector.

13. A method according to any one of the preceding claims comprising, following step e) of an iteration and step b) of a subsequent iteration, an estimation of a mechanical impedance of the contact member from an estimation of the force exerted by the finger in response to a vibration of the contact surface.

14. Haptic interface comprising: - a slab (10), configured to be touched by one or more contact members (3), at one or more points of contact, - actuators (12p), arranged against the slab, each actuator being configured to cause a vibration of the slab when it is subjected to a control signal (^); - detectors (140), coupled to the slab, each detector being configured to produce a detection signal (ô;) depending on the intensity of a force exerted on the slab, at each point of contact; - a processing unit (20), configured to implement steps a) to f) of a method according to any one of the preceding claims.

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