FR3148306A1 - Control of a haptic feedback interface - Google Patents

Abstract

Control of a haptic feedback interface The present description relates to a haptic feedback device comprising a plate defining a contact surface intended to be touched by an external body and piezoelectric actuators (14) configured to vibrate the plate, the piezoelectric actuators being connected in parallel to a first inductive element (Lp) and to a circuit (2) for applying an alternating voltage via a second series inductive element (Ls). Figure for the abstract: Fig. 3

Description

Control of a haptic feedback interface

This description relates generally to haptic feedback interfaces and, more particularly, to the electronic control of such an interface. This description applies to haptic feedback interfaces equipping, for example, display screens.

A haptic feedback interface is based on the combination of piezoelectric actuators and a surface intended for a user's touch. The actuators can be controlled at an ultrasonic frequency so as to vibrate the surface and provide the user with a sensation of surface texture. One haptic feedback technique, called ultrasonic lubrication, consists of producing a friction modulation effect on the contact surface.

The control or piloting of piezoelectric actuators is a critical aspect of the operation of a haptic feedback interface because this control determines the quality of the haptic feedback provided by the contact surface.

There is a need for improvement in the control processes and systems of haptic feedback interfaces.

One embodiment overcomes all or part of the drawbacks of the control or piloting methods and circuits of haptic feedback interfaces.

One embodiment provides a haptic feedback device comprising a plate defining a contact surface intended to be touched by an external body and piezoelectric actuators configured to vibrate the plate, the piezoelectric actuators being connected in parallel to a first inductive element and to a circuit for applying an alternating voltage via a second series inductive element, wherein:
- the value of the second inductive element is chosen to be at least ten times greater than the ratio between the equivalent electrical resistance of the actuator and plate assembly and the mechanical resonance pulsation of this assembly; and
- the Lp value of the first inductive element is chosen by applying the following formula:
(4) where Ls represents the value of the second inductive element, ω0 the mechanical resonance pulsation, C0 the static capacitance of the piezoelectric actuators and Cm the equivalent capacitance of the actuator and plate assembly.

According to one embodiment, the device comprises a transformer for amplifying said alternating voltage, a primary winding of the transformer being in parallel with the first inductive element, a secondary winding of the transformer being in parallel with all of the piezoelectric actuators.

According to one embodiment, the values of the static capacitance and the equivalent capacitance of the actuator and plate assembly correspond to the values brought back to the primary of the transformer.

According to one embodiment, the device further comprises a circuit for controlling the control frequency of the actuators so that it corresponds to the mechanical resonance frequency of the actuator and plate assembly.

According to one embodiment, the servo circuit uses a phase shift measurement between the voltage at the terminals of the actuator and plate assembly and the voltage supplied by the circuit for applying an alternating voltage or the current flowing in the actuator and plate assembly.

According to one embodiment, the servo circuit comprises at least one piezoelectric sensor configured to measure a voltage, the phase shift between this voltage and the voltage at the terminals of the actuator and plate assembly or the voltage supplied by the circuit for applying an alternating voltage, being used to servo the control frequency.

According to one embodiment, the mechanical resonance frequency is between 20 and 200 kHz, preferably between 60 and 80 kHz.

According to one embodiment, the plate constitutes the plate of a dashboard screen of a motor vehicle.

According to one embodiment, the first inductance (Lp) is between 200 and 400 µH.

According to one embodiment, the second inductance (Ls) is between 5 and 20 µH.

According to one embodiment, the plate is coupled to a multilayer structure.

According to one embodiment, the multilayer structure comprises a touch display screen comprising a system for detecting a contact or a position of a contact point on the screen.

These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in connection with the attached figures, among which:

there represents, in a very schematic manner, a cross-sectional view of an example of an electronic device equipped with a haptic interface;

there is a very schematic and partial bottom view of the device of the ;

there is a very schematic perspective view of the device of Figures 1A and 1B;

there represents an equivalent electrical diagram of a haptic device associated with a passive inductive circuit according to one embodiment;

there represents an equivalent electrical diagram of a haptic device associated with a passive inductive circuit according to another embodiment;

there illustrates the variations in vibration amplitude as a function of frequency for a conventional system and for a system according to the embodiments described;

there , there , there and the illustrate the modification of the frequency response of the system according to the embodiments described, induced by a variation of the mechanical damping; and

there , there , there and the illustrate the modification of the frequency response of the system according to the embodiments described, induced by a variation of the mechanical resonance frequency.

The same elements have been designated by the same references in the different figures. In particular, the structural and/or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been shown and are detailed. In particular, the production of the structural elements of the haptic interface are not shown, the embodiments described being compatible with usual structures.

Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") together, this means that these two elements can be connected or be connected by means of one or more other elements.

In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

Unless otherwise specified, the expressions "approximately", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

There represents, in a very schematic and partial manner, a cross-sectional view of an example of an electronic device 1 equipped with a haptic interface.

There is a very schematic and partial bottom view of device 1 of the .

There is a very schematic perspective view of the device 1 of figures 1A and 1B.

An electronic device 1 equipped with a haptic interface is generally made of a plate 10, for example made of glass, covering for example a display screen 12 (LCD or other), typically a touch screen. The plate can in certain cases be covered in part or completely by a layer such as a decorative film or any other surface treatment, which does not prevent vibration. The plate 10 is equipped, on the rear face and, in the example shown, out of line with the touch screen 12, with piezoelectric actuators 14, for example piezoelectric ceramics. The piezoelectric actuators 14 are generally distributed in two strips located on two opposite sides of the plate 10 and are controlled by an excitation circuit or driver 2. The role of the actuators 14 is to create, in the plate 10, a high-frequency wave (for example from 20 kHz to 200 kHz). The vibrations generated at the plate 10 provide, at its external interface surface with a user (typically a finger D), an effect perceived by the user as a friction reduction effect with the surface. The screen 12 is itself controlled by a circuit or driver 16 ( ) and is, for example for an LCD screen, associated with an illuminator 18 on the rear face.

There are different types and shapes of haptic interface devices 1. All these devices have the following common characteristics:
- a plate 10, a front face of which defines a surface for direct or indirect contact with an external body, for example a touch organ (finger, foot, etc.) of a user, and which constitutes the haptic feedback plate;
- piezoelectric actuators 14 configured to vibrate the plate (10); and
- a circuit 2 for controlling and supplying the piezoelectric actuators.

The actuators 14 are generally powered by periodic alternating voltages. The frequency of the voltages is chosen to be close to the resonance frequency of the electromechanical system, typically around a frequency between 20 kHz and 200 kHz. The amplitude of the control voltages of the actuators 14 is generally of the order of a hundred volts. These are examples and other frequency and amplitude values are possible depending on the application. The actuators may be actuators with amplified deformation (for example thanks to an amplification structure fixed to the plate, such as that described in document FR3091414A). The plate 10 may be coupled to a multilayer structure, integrating or not a screen. For example in the case of an LCD screen, the actuators, amplified or not, are in contact with the plate; in another example, the multilayer structure may comprise an OLED screen, and the actuators, amplified or not, may be in direct or indirect contact with the plate, for example by being placed behind the screen.

The quality of the haptic feedback provided to the user depends on the resonance conditions of the generated ultrasonic waves (in particular their amplitude). However, these waves are sensitive to environmental factors of the device 1 such as, for example, the temperature, the state of the device casing, the contacts of the user's finger, etc. These variations in these environmental factors are likely to modify the mechanical resonance frequency and alter the haptic feedback and the texture effects perceived by the user.

A classic approach to overcome this phenomenon is to control the control signals, whether in frequency or amplitude, from either a dedicated piezoelectric sensor or from measurements of the variation of the actuator supply current or the phase of the AC signal. These closed-loop control systems are effective but have several disadvantages: a latency in the feedback effect, a significant computational load on a microcontroller provided in the device (particularly significant if this latency must be overcome), an increase in implementation costs linked to the addition of the sensor or the appearance of audible noise resulting from the amplification of the measurement noise by the loop. The computational load generally requires having a microcontroller dedicated to the haptic functionality.

According to the embodiments described, it is planned to interpose, between the control circuit 2 and the piezoelectric actuators 14, a passive inductive circuit (shown schematically by a block 3 in ), sized to form a self-adaptive system without servo-control. This inductive circuit is a parallel-series circuit consisting of at least one inductive element in parallel with the actuators, i.e. connecting the terminals of each actuator together, and at least one inductive element in series with the actuators, i.e. intercalated between an output terminal of the control circuit and a terminal of each actuator 14. In practice, in a haptic interface of the type to which the described embodiments apply, the number of actuators 14 fixed to the plate 10 may for example be between 10 and 100.

There represents an equivalent electrical diagram of a haptic device comprising a passive inductive circuit 3 according to one embodiment.

The assembly consisting of the piezoelectric actuators 14 and the plate 10 constitutes an electromechanical system that can be modeled by a branch, called motional, in parallel with a branch, called static. The motional branch models the vibration behavior (mechanical resonance) and comprises, in series, a resistance Rm, a capacitance Cm and an inductance Lm. The static branch models the electromagnetic behavior, linked to the capacitances of the dielectric materials (typically ceramic) between the electrodes of the actuators, and consists of a capacitance C0. In simplified terms, the value of the resistance Rm is linked to the spacing between the two strips of actuators 14 (the length or the width of the plate according to the two opposite sides where the actuators are arranged) and the capacitance C0 represents the equivalent capacitance of the dielectrics of all the actuators 14 in parallel. Still in a simplified way, the capacitance Cm is linked to the elasticity of the plate between the two actuator strips and the inductance Lm is linked to the inertia of the plate between the two actuator strips.

In the example of the , it is assumed that the electrodes 142 and 144 are connected, via the passive inductive circuit 3, to the control circuit 2.

The control circuit, not detailed, provides a control signal between two terminals 22 and 24. This control signal has for example the form of an alternating signal, for example square, at a frequency f, of voltage (U0).

Circuit 3 forms a parallel inductance (inductive element Lp) in parallel with capacitor C0, i.e. whose terminals or ends 32 and 34 are connected, preferably connected, to electrodes 142 and 144, and a series inductance (inductive element Ls) connecting one of the terminals of the parallel inductive element, for example terminal 32 (therefore electrode 142), to one of the output terminals, for example terminal 22, of control circuit 2. The other terminal of parallel inductive element Lp, for example terminal 34 (therefore electrode 144), is connected to the other output terminal, for example terminal 24, of control circuit 2.

The square alternating signal of voltage U0 provided by the circuit 2 is transformed, for example by the filtering effect of the inductive element Ls, into a sinusoidal alternating signal of voltage Up at the terminals 142 and 144 of the piezoelectric actuators 14. The current flowing in the motional branch, or series, of the system consisting of the actuators 14 and the plate 10 is, in the present description, denoted Im. This current Im is proportional to the vibration amplitude under the effect of the control signal and is therefore representative of the vibration behavior of the system.

According to the embodiments described, it is planned to size the inductive elements Lp and Ls according to the characteristics of the electromechanical system so that the current Im (in the motion branch) is, around the mechanical resonance frequency of the system, insensitive to variations in the frequency of the excitation signal and the impedance of the electromechanical system. More precisely, it is planned to size the inductive elements Lp and Ls so that the current Im varies by less than +/- 25% in a range of +/- 1kHz around the resonance frequency for variations of +/- 5% of the resonance frequency and +/- 50% of the impedance.

In practice, this leads to dimensioning the series inductance Ls so that its value is significantly higher (at least ten times higher) than the ratio between the resistance Rm and the mechanical resonance pulsation ω0 of the system (actuators + plate).

According to an embodiment of a method for dimensioning a passive inductive circuit 3, it is planned, after having determined the values of the elements C0, Rm, Cm and Lm of the electromagnetic system, and the frequency f0 or pulsation ω0 of the mechanical resonance, to dimension the elements Lp and Ls by using the following formulas:
[Math 1]
(1) [Math 2]
either (2) [Math 3]
For example and (3)
[Math 4]
(4) The parameters of the electromechanical system can be determined by measurements of the electrical response of the actuators, for example voltage and/or current and/or impedance measurements.

For example, the capacitance C0 is estimated by low-frequency measurements outside the mechanical resonance range(s), and the impedance Zm of the motional branch is estimated at the mechanical resonance frequency of the system. The values Rm, Cm and Lm are for example deduced from a measurement of the impedance Zm using an impedance meter using equations that will be described later. The mechanical resonance frequency f0 depends on the geometry of the plate 10 and the arrangement of the piezoelectric actuators 14. In order to obtain the desired ultrasonic vibration effect, the electromechanical system is geometrically adapted for a mechanical resonance frequency preferably between 20 kHz and 200 kHz, more preferably between 65 and 90 kHz.

There represents an equivalent electrical diagram of a haptic interface associated with a passive inductive circuit 3 according to another embodiment.

According to this embodiment, a transformer is used to amplify, by a factor corresponding to the transformation ratio N, the amplitude of the control signal provided by the circuit 2 to control (drive) the piezoelectric ceramics.

Compared to the method of realization of the , an inductive transformer 4, with a transformation ratio N, is introduced into the control circuit of the piezoelectric actuator 14. In this embodiment, the parallel inductance Lp then corresponds to the primary winding of the transformer. The secondary winding of the transformer is in parallel with all of the actuators, i.e. connected, preferably connected, to terminals 142 and 144.

Relations (1) to (4) mentioned above remain valid provided that the values C0, Rm and Cm appearing in these formulas are considered as being the values brought back to the primary of the transformer, i.e. respectively N ² C0, Rm/N ² and N ² Cm.

In the following description, we take as an example the case of the but everything that is described as well as the formulas transposes to the case of the by applying the values brought back to the primary, the impedance Zm of the motional branch seen from the primary being then divided by N ² .

Whether in the case of the or in that of the , a square alternating signal of voltage U ₀ having, in harmonic mode, a form:
[Math 5]
(5)
leads to a voltage Up at the terminals of the load consisting of the electromagnetic system (piezoelectric actuators + plate) having the absolute value:
[Math 6]
(6)
where Z represents the impedance of the load with imaginary part Im{Z} and real part Re{Z} and can also be written:
[Math 7]
(7)
where Zm represents the impedance of the motional branch and can be written:
[Math 8]
(8)
or even:
[Math 9]
(9)
with :
[Math 10]
(10)

In the presence of transformer 4, relations (6) to (10) remain valid provided that, like the parameters C0, R0 and Cm of the load, the value of the inductance Lm is that brought back to the primary of the transformer, i.e. Lm/N ² .

According to one method of implementing the passive inductive circuit dimensioning method, the parameters C0, Rm, Cm and Lm are first determined. To do this, measurements of the impedance Z of the load are carried out, for example by an impedance meter over a relatively wide frequency band, for example between 10 kHz and 100 kHz, and the parameters C0, Rm, Lm and Cm are extracted by the inverse method on the basis of equations (7) and (8). The mechanical resonance frequency ω0 is then determined from equation (10).

Once these determinations have been made, the series inductance Ls is sized from equation (1) so that at mechanical resonance, the effect of the load on the current Im is negligible and thus obtains a self-adaptive effect.

In order for the electromechanical system to have a vibration response that varies little or is quasi-constant around the mechanical resonance frequency, the inductance Lp is sized so that the frequency representing, for the system, the minimum of the vibration amplitude, corresponds to the mechanical resonance frequency f0. The relationship between this pulsation ωa at the minimum vibration amplitude and the mechanical resonance pulsation ω0 is given by the following equation:
[Math 11]
(11)

When the pulsation ωa at the minimum vibration amplitude and the pulsation ω0 of mechanical resonance are equal, we obtain equation (4).

There illustrates the variation of vibration amplitude as a function of frequency for a conventional system and for a system according to the embodiments described.

We assume the case of a haptic interface whose mechanical resonance frequency is approximately 68 kHz. In a conventional system (without a self-adaptive passive inductive circuit), the vibration amplitude 51 represented here by the ratio Im/ω has a peak at the mechanical resonance f0 and the maximum vibration amplitude is therefore obtained by making the frequency of the control signal coincide with the mechanical resonance frequency f0. On the other hand, this amplitude is very sensitive to frequency variations. With a passive inductive circuit 3 as described, the shape of the vibration amplitude 53 has two peaks corresponding to the electrical resonance frequencies fe of the inductive circuit associated with the capacitance C0 on either side of the mechanical resonance frequency f0, the latter representing a minimum between these two frequencies fe.

By making the frequency of the minimum vibration between the two electrical resonance peaks coincide with the mechanical resonance frequency f0 using the described dimensioning, a minimum amplitude variation around this frequency f0 is obtained. The price to pay is higher consumption. However, the advantage that this represents in terms of stability justifies it. The embodiments described are, however, more particularly suited to systems for which energy consumption is not a critical issue. This is the case, for example, for equipment for motor vehicles such as dashboards.

Figures 6A, 6B, 7A and 7B illustrate the modification of the frequency response of the system according to the embodiments described, induced by a variation of the mechanical damping, for example under the effect of the temperature or of an external mechanical disturbance (such as a finger or any object which would come into contact with the system). This variation is simulated by a variation of the resistance Rm in the electrical model.

Figures 6A and 6B show the voltage Up as a function of frequency for several resistance values Rm. Figures 7A and 7B illustrate the corresponding vibration amplitudes.

Figures 6A and 7A illustrate the case of a usual system. The voltage Up remains constant (speed 61, ) because it only undergoes transformer 4. In terms of vibration amplitude ( ), this is, at the mechanical resonance frequency f0, very sensitive to the variation in resistance and decreases with the increase in resistance Rm. The speeds 70, 71, 72, 73 and 74 correspond to respective resistance values Rm of 40, 80, 120, 160 and 200 ohms.

Figures 6B and 7B illustrate the case of a system equipped with a passive inductive circuit as described. It can then be seen that, for the same voltage value U0, the voltage Up varies to present a minimum at the mechanical resonance frequency f0. This minimum is very sensitive to the value of the resistance Rm. This effect compensates for the loss of vibration amplitude, which becomes almost insensitive to variations in the resistance Rm. Shapes 65, 66, 67, 68 and 69 ( ) correspond to respective resistance values Rm of 40, 80, 120, 160 and 200 ohms. The speeds 75, 76, 77, 78 and 79 ( ) correspond to respective resistance values Rm of 40, 80, 120, 160 and 200 ohms.

Figures 8A, 8B, 9A and 9B illustrate the modification of the frequency response of the system according to the embodiments described, induced by a variation of the mechanical resonance frequency, for example under the effect of temperature or a non-linear variation of the elasticity of the materials constituting the system or the effect of an external mechanical disturbance (such as a finger or any object coming into contact with the system). This variation is simulated by a variation of the capacitance Cm in the electrical model.

Figures 8A and 8B show the shapes of the ratio of the voltage Up to the voltage U0 as a function of the frequency for several values of capacitance Cm. Figures 9A and 9B illustrate the corresponding vibration amplitudes.

Figures 8A and 9A illustrate the case of a usual system. The Up/U0 ratio remains constant (speed 80, ) because the voltage U0 only undergoes the transformer 4. The effect of the variation of the resonance frequency due to the variation of the capacitance Cm is visible on the vibration amplitude ( ) which has a resonance peak shifting towards low frequencies as the capacitance Cm increases. The 91, 92, 93, 94, 95, 96, 97, 98 and 99 ( ) correspond to respective capacitance values Cm of 0.41nF, 0.43nF, 0.44nF, 0.45nF, 0.46nF, 0.47nF, 0.48nF, 0.49nF, and 0.51nF (unit nF for nanofarads).

THE and 9B illustrate the case of a system equipped with a passive inductive circuit as described. It can be seen that the minimum voltage Up shifts towards low frequencies as the capacitance Cm increases, thus compensating for the effect on the vibration amplitude which becomes almost insensitive to a variation in the mechanical resonance frequency. Shapes 81, 82, 83, 84, 85, 86, 87, 88 and 89 ( ) correspond to respective capacitance values Cm of 0.41nF, 0.43nF, 0.44nF, 0.45nF, 0.46nF, 0.47nF, 0.48nF, 0.49nF, and 0.51nF (unit nF for nanofarads). The shapes 101, 102, 103, 104, 105, 106, 107, 108 and 109 ( ) correspond to respective capacitance values Cm of 0.41nF, 0.43nF, 0.44nF, 0.45nF, 0.46nF, 0.47nF, 0.48nF, 0.49nF, and 0.51nF (unit nF for nanofarads).

We can therefore see that with the addition of a passive inductive circuit, series/parallel, the system is made less sensitive to variations in environmental conditions.

The embodiments described are also compatible with the addition of a loop for regulating or controlling the excitation frequency of the system. This makes it possible to optimize the operation of the interface without harming the computing resources. Indeed, thanks to the self-adaptive circuit, the frequency adjustment requirements are reduced and the frequency regulation loop no longer needs to be performed in real time. It is therefore less demanding in computing resources.

As an example, it may be provided that this frequency control circuit comprises one or more piezoelectric sensors, for example placed on one of the piezoelectric actuators and/or on the plate. This or these sensors are configured to measure a voltage, and the phase shift between this voltage, and the voltage Up at the terminals of the actuator and plate assembly or the voltage U0 provided by the circuit for applying an alternating voltage, is used to control the control frequency.

As specific examples of embodiment, a haptic device comprising a plate having a length of between 15 and 40 centimeters and a width of between 10 and 20 centimeters, and two strips of around twenty piezoelectric actuators may have the following parameters:
Capacitance C0: between 10 and 40 nF;
Resistance Rm: between 10 and 70 ohms;
Inductance Lm: between 5 and 20 mH;
Capacitance Cm: between 200 and 600 pF; and
frequency f0: between 60 and 80 kHz.

A passive inductive circuit 3 can then, with a transformer having a transformation ratio of the order of 10, for example present the following values:
series inductance Ls: between 5 and 20 µH, for example of the order of 10 µH; and
parallel inductance Lp: between 200 and 400 µH, for example of the order of 300 µH.

Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, although the embodiments and examples described are more specifically aimed at the field of motor vehicle dashboard displays, they apply more generally to any haptic feedback interface.

Finally, the practical implementation of the embodiments and variants described is within the reach of the person skilled in the art from the functional indications given above. In particular, other modes of characterization of the actuators may be provided, provided that they make it possible to obtain indications on the characteristic parameters C0, Rm, Cm and Lm. Furthermore, although reference has been made to a plate constituting a display screen, the embodiments described are transposed to a plate (10) that is completely or partly transparent to which a screen is attached, or a non-transparent plate without a screen. The plate may or may not be tactile. More generally, the solution described applies to any haptic structure comprising an interface plate, for example and in a non-limiting manner:
- a plate with or without screen;
- a plate against an LCD screen with piezoelectric actuators (amplified or not) placed under the plate;
- a plate against an OLED type screen (multilayer structure), with piezoelectric actuators, amplified or not, placed behind the multilayer structure of the screen therefore without direct contact with the plate;
- a plate against another layer or multilayer structure without a screen; or a plate against another layer or multilayer structure with a screen;
- a plate with piezoelectric actuators, these actuators being able to be fixed on a vibration amplification structure itself fixed to the plate;
- a plate coupled to a multilayer structure, for example, comprising a touch display screen comprising a system for detecting a contact or a position of a contact point on the screen.

Claims (12)

Haptic feedback device comprising a plate (10) defining a contact surface intended to be touched by an external body (D) and piezoelectric actuators (14) configured to vibrate the plate (10), the piezoelectric actuators being connected in parallel to a first inductive element (Lp) and to a circuit (2) for applying an alternating voltage via a second series inductive element (Ls),
in which:
- the value of the second inductive element (Ls) is chosen to be at least ten times greater than the ratio between the equivalent electrical resistance (Rm) of the actuator and plate assembly and the mechanical resonance pulsation (ω0) of this assembly; and
- the Lp value of the first inductive element is chosen by applying the following formula:
(4) where Ls represents the value of the second inductive element, ω0 the mechanical resonance pulsation, C0 the static capacitance of the piezoelectric actuators (14) and Cm the equivalent capacitance of the actuator and plate assembly. Device according to claim 1, comprising a transformer (4) for amplifying said alternating voltage, a primary winding (41) of the transformer being in parallel with the first inductive element (Lp), a secondary winding of the transformer being in parallel with all of the piezoelectric actuators. Device according to claim 2, in which the values of the static capacitance (C0) and of the equivalent capacitance of the actuator and plate assembly (Cm) correspond to the values brought back to the primary of the transformer (4). Device according to any one of claims 1 to 3, further comprising a circuit for controlling the control frequency of the actuators (14) so that it corresponds to the mechanical resonance frequency of the actuator assembly (14) and plate (10). Device according to claim 4, in which the control circuit uses a measurement of phase shift between the voltage (Up) at the terminals of the actuator and plate assembly and the voltage (U0) supplied by the circuit (2) for applying an alternating voltage or the current (Im) flowing in the actuator and plate assembly. Device according to claim 5, in which the control circuit comprises at least one piezoelectric sensor configured to measure a voltage, the phase shift between this voltage, and the voltage (Up) at the terminals of the actuator and plate assembly or the voltage (U0) supplied by the circuit for applying an alternating voltage, being used to control the control frequency. Device according to any one of claims 1 to 6, in which the mechanical resonance frequency is between 20 and 200 kHz, preferably between 60 and 80 kHz. Device according to any one of claims 1 to 7, in which the plate (10) constitutes the plate of a dashboard screen of a motor vehicle. Device according to any one of claims 1 to 8, in which the first inductance (Lp) is between 200 and 400 µH. Device according to any one of claims 1 to 9, in which the second inductance (Ls) is between 5 and 20 µH. Device according to any one of claims 1 to 10, wherein the plate (10) is coupled to a multilayer structure. Device according to claim 11, in which the multilayer structure comprises a touch display screen comprising a system for detecting a contact or a position of a contact point on the screen.