Method for generating haptic effects by focused ultrasound waves

Abstract

The invention relates to a method for generating a haptic effect at a target point (R) of a solid by means of at least two piezoelectric actuators (Si) capable of emitting waves at a given instant t under the action of a control signal, said control signal having an ultrasonic frequency and being capable of generating vibrations on the surface of the solid, thereby generating an ultrasonic lubrication effect ("squeeze film" effect) at the target point (R), characterized in that the respective control signal of each actuator (Si) is calculated as a function of the distance (di) between this actuator and the target point (R) to be actuated, so that the surface deformations obtained at the considered target point are superimposed to generate there a haptic effect greater than that obtained by means of a single actuator.

Description

Technical Field

[0001] The present invention relates to the field of surfaces capable of generating a tactile feedback effect, in particular surfaces that generate a tactile feedback effect by ultrasonic lubrication when a user's finger touches these surfaces. Background Art

[0002] It is known that ultrasonic lubrication of a surface can be used to produce a tactile effect in the form of a texture perception under the user's finger by changing the coefficient of friction of the surface, also known as the "squeeze film effect". As is already known from document WO2008116980 A1, this effect is obtained by vibrating the surface by applying an ultrasonic standing wave.

[0003] This effect requires large ultrasonic displacements of the surface, which are now achieved by exploiting the overall resonance of the surface (elastic thin plate). When the surface is elastic in nature and absorbs little energy from the ultrasonic vibrations applied to it (such as a glass surface, for example), this resonance acts as a passive amplifier and gives good results.

[0004] Conversely, achieving high-quality tactile feedback—i.e., large surface displacement amplitudes that are well perceived by the user and acceptable energy efficiency—is difficult when the medium used to provide tactile feedback is too large or strongly dissipates surface elastic waves in the ultrasonic frequency domain, or when the point on the surface to be actuated is far from the actuator. Furthermore, in dissipative media, the piezoelectric actuator generating ultrasonic vibrations must be positioned close to the point on the surface where the effect is to occur, which precludes application to transparent surfaces unless a transparent piezoelectric actuator is available. Summary of the Invention

[0005] Objectives of the invention

[0006] The general goal of the present invention is to extend the field of application of tactile feedback by ultrasonic lubrication to a wider variety of carriers, such as relatively dissipative carriers, such as wood or plastic materials, or more generally so-called viscoelastic media, or media that are elastic but thicker than media for which the ultrasonic lubrication effect has been used.

[0007] The invention also aims to enable well-perceivable haptic feedback to be obtained at points of the surface remote from where the actuator is located, as this may be useful for example with glass surfaces in the construction industry.

[0008] The invention also aims to enable multi-point haptic feedback, ie differentiated but simultaneous haptic feedback at different points of an entity.

[0009] Principle of the Invention

[0010] The present invention describes a method of achieving this localized ultrasonic lubrication phenomenon under the user's finger by means of focused ultrasound.

[0011] The present invention utilizes the principle of wave focusing, specifically surface elastic waves in the ultrasonic frequency range, to achieve large displacement amplitudes at a focal point in media that are either too dissipative or too far from the actuator to actuate. This is achieved by optimizing actuator control to produce a texture sensation beneath the user's finger by varying the coefficient of friction near the focal point.

[0012] Subject matter of the invention

[0013] The subject of the present invention is therefore to provide a piezoelectric actuator (S i ) A method for generating a tactile effect at a target point (R) of an entity, wherein the at least two piezoelectric actuators (S i ) is capable of emitting a wave at a given moment t under the action of a control signal, wherein the control signal has an ultrasonic frequency and is capable of generating vibrations on the surface of the solid, thereby generating an effect called "ultrasonic lubrication" (or in English, a "squeeze-film" effect) at a target point (R), characterized in that each actuator (S i ) is based on the distance (d) between the actuator and the target point (R) to be actuated. i ) is calculated such that the surface deformations obtained at the considered target point superimpose to generate a haptic effect there that is greater than that obtained by means of a single actuator.

[0014] According to one embodiment, the piezoelectric actuator (S i ) The vibrations generated on the surface of a solid correspond to bending waves.

[0015] The subject of the invention is also a device for producing a haptic effect at a target point (R) of an entity, characterized in that it comprises: at least two actuators (S1, S2) capable of emitting a surface wave at a given moment (t1, t2) under the action of a control signal for controlling each actuator; and control means configured so that the respective control signal emitted to each actuator is calculated as a function of the distance between this actuator and the target point (R) to be actuated, so that the surface deformations obtained at the target point considered are superimposed to produce there a haptic effect greater than that obtained with the aid of a single actuator.

[0016] According to one embodiment, the solid body is a viscoelastic solid, such as wood or a plastic material.

[0017] Preferably, the entity exhibits isotropic wave propagation in order to simplify the calculation of the delay times between control signals in order to obtain a good focus at the intended target point.

[0018] According to one embodiment, the entity is a surface transparent to light and the plurality of actuators are located at the edge of said surface.

[0019] According to another embodiment, the entity is a surface that is opaque to light, and the plurality of actuators are located at various points on the surface, eg in areas where the actuators are not visible.

[0020] According to an advantageous embodiment, the actuator is a piezoelectric actuator. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention will be described in more detail with the aid of the accompanying drawings, in which:

[0022] - Figure 1 The principle of focusing elastic surface waves from two actuators on a solid is shown;

[0023] - Figure 2 is a schematic diagram of a group of ultrasonic actuators arranged in a straight line and driven to generate elastic surface waves focused on a point on a solid body;

[0024] - Figure 3 A possible use of points for actuating a transparent surface according to the method of the invention is shown. DETAILED DESCRIPTION

[0025] Figure 1 The figure illustrates the principle of the summation of elastic waves O1 and O2 emitted by two point sources S1 and S2, respectively, spaced at distances d1 and d2 from each other, at the point to be actuated. Sources S1 and S2 each emit a wave, such as an ultrasonic wave generated by a piezoelectric actuator (not shown). In the case of flexural surface waves (in the specific case of thin plates, the wave type is Lamb A0), the wavefronts F1 and F2 of waves O1 and O2 intersect at point R, causing a deformation there that is perpendicular to the plane of the surface containing sources S1 and S2 and, in general, produces an ultrasonic displacement, denoted by w.

[0026] By the point (where i=1, 2) at the two sources at point The out-of-plane displacement w obtained at is expressed by the following relationship:

[0027]

[0028] in, Indicates that at point s i At the initial time t i The source function emitted at , and The source and focus The Green's function between them. Time t = t0 corresponds to the wave from two sources S1 and S2 at point The time of constructive addition. Emission time t i It is defined based on the known velocity of bending waves in the medium through the following relationship:

[0029] t i = t0 - d i / c(ω) (2).

[0030] Therefore, Equation 1 expresses the relationship between the two sources and the The sum of the convolutions between the receiving points at .

[0031] In the case where the signal to be generated consists of a single frequency (in other words, a single-frequency signal), equation (1) holds true and the time delay t of equation (2) i corresponds to a phase shift. In fact, for a single-frequency signal, the vibration can be written in the Fourier domain in the form of a complex number, the absolute value of which corresponds to the amplitude of the oscillation, and the independent variable reflects the spatiotemporal distribution of the vibration. Moreover, when a single-frequency signal is emitted from several sources, it is important that the independent variables of these different contributions take the same value at the target point (R) (the case of in-phase vibration). Moreover, let For the source point S i The independent variable of the vibration perceived at the target point (R) after the launch, under the conditions of plane wave approximation and omitting the terms related to time oscillation, is:

[0032]

[0033] in:

[0034] - The target point (R) and the source point S i The distance between

[0035] - k is the wave number.

[0036] To obtain signals from each source that are in phase at the destination (R), it is best to add a phase shift to the additional source, which is expressed as:

[0037] k Δ d

[0038] Among them, Δ dis the distance difference between a source point taken as an (arbitrary) reference and (one or more) additional source points. As an example, in the specific case of two source points S1 and S2 and taking point S1 as the reference, the vibration perceived at the target point (R) consists of the sum of the contributions of S1 and S2:

[0039] .

[0040] This focusing principle can be applied to focus surface ultrasound waves from a large number of sources.

[0041] In fact, when the sum of the two waves generated by the two actuators alone produces an out-of-plane displacement obtained at a point on the plane, or when the point to be actuated is too far from the actuators and the propagation medium is viscoelastic, this displacement may not be sufficient to be felt by the finger. In these cases, it is useful to use a larger number of actuators, which are arranged out of the way of the surface to be actuated, but then it is necessary to drive the ultrasonic vibrations so that the tactile feedback can be generated in a coherent manner at the targeted point.

[0042] Figure 2 An embodiment using multiple sources is shown in FIG. In this figure, a region C1 of relatively small size is shown, which is an isotropic entity that should be actuated by multiple actuators, in particular 11 piezoelectric actuators, referenced S1 to S2. 11 .like Figure 2 As schematically shown in the enlarged view at the bottom, each actuator S i Actuated by a control signal, the vibration wave 10 is transmitted. According to the present invention, the wave train is shifted in time so that it constructively sums at the target point C1. For example, the control signal applied to actuator S6 closest to the target area C1 is delayed relative to the control signal of the adjacent actuator. This delay is calculated to maximize the displacement resulting from the summation of the waves from all actuators at the target point C1.

[0043] Of course, if several target points are to be targeted, it is only necessary to recalculate the delay time of the control signal of each actuator so as to maximize the focusing of the ultrasonic wave at the considered points.

[0044] This approach makes it possible to envision many new applications for producing well-perceivable haptic effects.

[0045] Figure 3An example application, by no means limiting, is schematically illustrated in FIG. A set of actuators (not shown) are arranged in a row in an area 30 at the edge of a building's door or window glass. A haptic effect, achieved through ultrasonic lubrication, is desired at a point 31 of the door or window glass, distant from area 30. Given the distance between the edge of the door or window glass and the target point 31, prior art techniques cannot produce a haptic effect perceptible at the target point 31 unless a large, visible actuator is positioned directly near the target point. In contrast, the present invention enables the relocation of a series of actuators to a more distant area, where they are not obstructive in the visual plane, while still achieving actuation that is readily perceptible at the target point 31. Furthermore, several target points can be targeted, requiring only the calculation of the control signal delay pattern to maximize the displacement of the glass surface at any targeted point.

[0046] Invention Advantages

[0047] The present invention makes it possible to achieve the stated objectives. In particular, the method according to the present invention makes it possible to generate an ultrasonic lubrication-type haptic effect at points on a surface that are remote from the location of the piezoelectric actuator, or at points on a surface whose material is viscoelastic. The present invention thus makes it possible to significantly expand the scope of application of haptic feedback technology using the ultrasonic lubrication effect, such as in the fields of smart building glazing or automotive glazing, as well as other application areas, such as furniture made of materials such as wood or plastic.

Claims

1. With the help of at least two piezoelectric actuators (S i ) a method for generating an ultrasonic lubrication tactile effect at a target point (R) on a surface of a solid, wherein the at least two piezoelectric actuators (S i ) is capable of generating vibration at a target point (R) in an ultrasonic domain under the action of a control signal to produce an effect called ultrasonic lubrication at the target point (R), characterized in that, Each actuator (S i ) is based on the propagation speed of the control signal emitted by the actuator in the entity and the distance (d i ), the delay law of the control signal is determined so that the delay law of the control signal from all piezoelectric actuators (S i ) at the target point (R) is maximized for generating an ultrasonic lubrication tactile effect at the target point (R) that is greater than that obtained by means of a single actuator, wherein a phase shift is added to the piezoelectric actuators (Si) such that signals from the respective piezoelectric actuators (Si) are obtained that are in phase at the target point (R), In which, with the help of the delay law of the control signal, the wavefronts of the ultrasonic waves from all piezoelectric actuators (Si) intersect at the target point (R) and produce a deformation there, which is perpendicular to the plane of the surface containing the piezoelectric actuator (Si) and produces a constructive ultrasonic displacement at the target point (R).

2. The method according to claim 1, characterized in that By piezoelectric actuator (S i )The vibrations generated on the surface of a solid correspond to Lamb waves.

3. A device for generating an ultrasonic lubrication tactile effect at a target point (R) of a body according to a method according to any one of claims 1 to 2, characterized in that It includes: At least two actuators (S1, S2), said at least two actuators (S1, S2) being capable of operating in a manner suitable for controlling each actuator (S i ) at a given moment t under the action of a control signal of the actuator; and a control component of the actuator, which is configured so that the corresponding control signal emitted to each actuator is based on the propagation speed of the control signal in the entity and the distance (d) between the actuator and the target point (R) to be actuated. i ) is calculated based on the delay law, so that the delay from all piezoelectric actuators (S i ) is maximally displaced at the target point (R) for generating an ultrasonic lubrication tactile effect at the target point (R) that is greater than that obtained by means of a single actuator.

4. The device according to claim 3, characterized in that This entity is a viscoelastic entity.

5. The device according to claim 3 or claim 4, characterized in that The entity exhibits isotropic wave propagation.

6. The device according to claim 5, characterized in that The entity is a surface transparent to light, and in that a plurality of actuators are located at the edge of said surface.

7. The device according to claim 5, characterized in that The solid body is a surface that is opaque to light and in that a plurality of actuators are located at various points on the surface.

8. The device according to claim 5, characterized in that The actuator is a piezoelectric actuator.

9. The device according to claim 5, characterized in that The actuator is an amplified actuator.

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