WO2022269186A1

WO2022269186A1 - Interface for delivering tactile stimulation

Info

Publication number: WO2022269186A1
Application number: PCT/FR2022/051200
Authority: WO
Inventors: Thomas DAUNIZEAU; Sinan HALIYO; Vincent Hayward
Original assignee: Sorbonne Universite; Centre National De La Recherche Scientifique
Priority date: 2021-06-25
Filing date: 2022-06-21
Publication date: 2022-12-29
Also published as: FR3124617A1

Abstract

The present invention relates to an interface (1) for delivering tactile stimulation, comprising a first face (3), intended to be explored by touch, and called the tactile face, and a second face (4) provided with at least one actuator (5), said at least one actuator (5) being configured to be excited so as to generate and transmit acoustic waves to the tactile face, the interface (1) being characterized in that the second face (4) comprises at least one zone (7) for confining acoustic waves generated by said at least one actuator (5), said at least one confining zone (7) being delineated at least partially by acoustic mirrors (6) formed from an acoustic metamaterial configured to reflect acoustic waves of frequencies comprised in a predetermined interval, called the band gap, said band gap including the carrier frequency of the acoustic waves generated by said at least one actuator (5).

Description

TOUCH STIMULATION INTERFACE

[0001]! The present invention relates to a tactile stimulation interface. The invention makes it possible in particular to spatially locate tactile stimuli.

[0002] A tactile stimulation interface is intended to restore tactile information, such as a texture, a relief, a variable roughness in time and/or space, an illusion of pressing on a flexible material, of pressing a key.

[0003] The tactile exploration of surfaces is omnipresent in daily interactions with new digital and computer technologies, whether it involves sliding a finger on a smartphone or interacting with a touchpad. However, existing devices often lack convincing haptic feedback. Accordingly, a goal of haptic research is to improve user experience by creating tactile stimuli. Among many technological options, the attention of the scientific community has recently focused on ultrasonic lubrication and vibrotactile feedback. The first option exploits transverse ultrasonic waves (from 20 kHz to 200 kHz) as a means of modulating the apparent friction of a smooth surface. The second option uses waves at much lower frequencies (from 0 Hz to 500 Hz) to directly stimulate the mechanoreceptors of the human finger.

[0004] Ultrasonic lubrication, originally used in industrial applications, relies in the haptic domain on transverse ultrasonic waves established in a plate to create an air cushion between the skin and the surface. With this technique, the normal load applied by the fingertip to the surface is shared between the air cushion and the asperities of the stratum corneum of the skin in intimate contact with the surface. The effective contact surface is reduced as well as the friction.

[0005] Since humans are sensitive to changes in friction, virtual haptic features can be generated on a smooth surface. To date, however, ultrasonic lubrication is limited to global interactions, as standing waves must be established across an entire plate. [0006] Since human beings are sensitive to vibrations, virtual haptic characteristics can be generated by directly vibrating a part of the body in the frequency range that can be perceived by the mechanoreceptors (from 0 Hz to 500 Hz). To date, however, vibrotactile feedback is limited in that the vibrations propagate through the medium containing the actuators which prevents precise vibration control and high haptic fidelity.

[0007] Several current solutions allowing haptic localization are based on a software approach, such as for example time reversal and the inverse filter. This requires significant computing power, incompatible with the constraints of real-time servoing of haptic systems.

[0008] State-of-the-art solutions that localize ultrasound in plates have the defect of having very low vibration amplitudes, insufficient to generate a cushion of air that significantly lubricates the contact. [0009] The state-of-the-art solutions that localize the vibrotactile signals greatly depend on the shape of the actuators and the boundary conditions for fixing the device.

The present invention aims to remedy these drawbacks.

[0011] The subject of the invention is a tactile stimulation interface, comprising a first face, intended to be explored by touch, and called the tactile face, and a second face provided with at least one actuator, said at least one actuator being configured to be energized to generate and transmit acoustic waves to the touch face.

In the interface according to the invention, the second face comprises at least one confinement zone for the acoustic waves generated by said at least one actuator, said at least one confinement zone being delimited at least in part by acoustic mirrors made by an acoustic metamaterial configured to reflect acoustic waves of frequencies included in a predetermined interval, called forbidden band. The forbidden band advantageously includes the carrier frequency of the acoustic waves generated by said at least one actuator. carrier frequency is the frequency of a sine wave which is then modulated by a signal which contains the haptic information.

Said at least one actuator can be a piezoelectric actuator or an electromagnetic actuator.

[0015] In general, the metamaterial may comprise periodically arranged resonators.

[0016] The forbidden band of the acoustic metamaterial can be included in a frequency range below 500 Hz.

[0017] In this case, the metamaterial may comprise periodically arranged resonators.

[0018] In this case, the resonators can be tungsten, copper, steel or lead balls, surrounded by silicone.

[0019] The first face and the second face can form a plate.

[0020] The plate can be made of metal, silicon or glass.

[0021] The band gap of the acoustic metamaterial can be within a frequency interval ranging from 20 kHz to 200 kHz.

[0022] The metamaterial can also comprise in this case periodically arranged resonators.

[0023] The resonators can be aluminum cylinders of circular or rectangular section. As a variant, the resonators can be tungsten, copper, steel or lead balls mounted on an aluminum cylinder of circular or rectangular section.

Said at least one acoustic wave confinement zone can be a surface with orthogonal edges or a circular surface.

Other advantages and features of the present invention will result from the description which follows, given by way of non-limiting example and made with reference to the appended figures:

[0026] [Fig. 1] is a top perspective view of a tactile stimulation interface according to the invention, in accordance with a first embodiment, [0027] [Fig. 2] is a perspective view from below of a tactile stimulation interface according to the invention, in accordance with a first embodiment,

[0028] [Fig. 3] is a perspective view from below of a tactile stimulation interface according to the invention, in accordance with a second embodiment,

[0029] [Fig. 4] is a detail view of the tactile stimulation interface in figure 3,

[0030] [Fig. 5] is a first top perspective view of a tactile stimulation interface according to the invention, in accordance with a third embodiment, and

[0031] [Fig. 6] is a second top perspective view of a tactile stimulation interface according to the invention, in accordance with a third embodiment.

[0032] DETAILED DESCRIPTION

In Figures 1 and 2, one can see schematically represented an example of touch interface 1 according to the invention comprising a plate 2 comprising a first face 3 and a second face 4 opposite the first face 3.

The first face 3 is intended to be explored by touch, for example by the fingers of a user. The first face 3 is designated touch surface.

In the example shown, the touch face 3 is flat but the present invention also applies to curved touch surfaces and curved plates. The term "plate" is not limited to a flat element, but to any element offering a great length compared to its thickness and which can be flat at least in part and/or having one or more curvatures.

The tactile face 3 can be intended to be touched by the pulp of a finger 8 or several fingers. It is also conceivable that the tactile surface 3 is capable of applying stimulation to any part of the user's body sensitive to touch.

The second face 4 is provided with one or more actuators 5, so that when the actuator(s) 5 are excited, they transmit vibrations (acoustic waves) to the plate 2. The actuators are for example piezoelectric ceramic actuators, such as PZT (lead titano-zirconate), fixed on the second face 4, for example by gluing. As a variant, the actuators can be made by interdigitated electrodes deposited directly on the second face 4 in the case where the latter is made of a piezoelectric material, such as LiNb03 (lithium niobate). As a variant, the actuators can be electromagnetic and fixed on the second face 4, for example by gluing.

The object of the invention is to spatially locate tactile stimuli. To obtain a localized vibration zone, the interface according to the invention implements acoustic mirrors 6. In mechanical terms, an acoustic mirror is equivalent to an embedded boundary condition. This type of condition is difficult to achieve in practice. For example, a polymeric bond would not be sufficient to prevent the propagation of vibrational energy because of its excessive flexibility.

The invention uses acoustic metamaterials which have the particularity of preventing the propagation of vibrations over a certain frequency range.

These metamaterials then behave like acoustic mirrors, which makes it possible to delimit areas of tactile rendering.

Acoustic metamaterials are artificial structures whose acoustic properties on a macroscopic scale do not exist in nature, these metamaterials have for example a negative refractive index or a negative density. They can be designed to have a forbidden band (band gap in English), that is to say a frequency range in which the acoustic waves do not propagate.

[0042] Thus, acoustic mirrors 6 made of metamaterials are spatially arranged to create acoustic wave confinement zones 7, which are called waveguides. The waveguides 7 can for example be of rectangular shape. The metamaterials are optimized so that the bandgap includes the carrier frequency of the haptic signal. This carrier frequency can be at low frequencies in the vibrotactile domain (frequencies below 500 Hz) or at high frequencies for ultrasonic lubrication (from 20 kHz to 200 kHz). This forbidden band results from the collective action of local resonators 9 which can be periodically arranged to form the metamaterial. Local resonators are elements having a resonant frequency close to the forbidden band. A periodic arrangement of the resonators is however not necessary to guarantee their proper functioning, but this facilitates the modeling and manufacturing stages.

In a variant, the forbidden band can result from destructive interference due to the diffraction of acoustic waves on the periodic structure. The process is analogous to Bragg diffraction taking place in crystals. This variant is nevertheless limited to acoustic waves whose wavelength is close to the periodicity of the structure. Local resonators 9 do not have this limitation and are thus good candidates for creating compact metamaterials, adapted to haptic constraints.

The vibrotactile domain is governed by low frequencies, below 500 Hz, and this requires resonators whose sizes can be large. To reach such low frequency ranges, it is necessary to increase the mass and reduce the stiffness of the resonators. This is done by modifying their geometry and/or their materials. For example, the use of tungsten, of very high density, as mass and silicone, very flexible, as spring makes it possible to center the band gap around 290 Hz with a structure with a periodicity of 15 mm.

In Figure 1, each acoustic mirror 6 comprises three rows of twenty resonators 9. In Figure 2, the acoustic mirrors 6 comprise 2 rows of resonators 9.

Several embodiments can be considered. They correspond to various versions of the invention, varying the shape and material of the local resonators, their dimensions and their periodicity.

In a first embodiment, as illustrated in Figures 1 and 2, the resonators 9 are slender cylinders of circular section. One can for example use aluminum cylinders with a diameter of 3.5 mm and a length of 14.5 mm, the spatial period of the structure being 7 mm. They can also be made of other materials with low damping such as metal, silicon or glass.

In a second embodiment, as illustrated in Figures 3 and 4, the resonators 9 are tungsten balls mounted on aluminum rods. It is for example possible to use tungsten beads with a diameter of 3 mm which are bonded to a structure printed in three dimensions in aluminium, the spatial period of the structure being 4 mm.

The first and the second embodiment implement ultrasonic acoustic waves.

[0051] For ultrasonic waves, a metal, silicon or glass plate can be used.

In a third embodiment, as illustrated in Figures 5 and 6, the resonators are tungsten balls coated with silicone. One can for example use as resonators tungsten balls with a diameter of 7.5 mm coated with silicone with a Shore hardness of 00-30, the spatial period of the structure being 15 mm. As illustrated in FIGS. 5 and 6, the interface comprises sixteen vibrotactile zones 7, which are waveguides of for example square shape, and which are delimited by the acoustic mirrors 6 comprising the tungsten balls encapsulated in a cylinder of silicon. The resonators can be arranged in a matrix of PMMA (polymethyl methacrylate).

The third embodiment implements acoustic waves whose frequency is in the vibrotactile domain (frequencies below 500 Hz). The forbidden band can be centered on a frequency of 290 Hz. The balls can be made of tungsten, copper, steel or lead.

[0054] Some techniques are limited to locating vibrations only at the level of the actuator. The invention does not suffer from this limitation since the entirety of a waveguide can vibrate thanks to a single actuator placed somewhere on the waveguide. Generally speaking, the actuator has a size less than or equal to that of the waveguide.

[0055] Certain devices with localized haptic rendering stimulate the finger at frequencies which are a function of the geometry of the actuators, of the plate and boundary conditions. The operating frequency of the interface according to the invention can be adjusted by modifying the forbidden band, that is to say by changing the resonator.

The spatial resolution of current solutions depends on the dimensions of the actuator. The spatial resolution of the invention depends on the dimensions of the resonator.

The localized tactile rendering areas are separated by several rows of resonators. In practice, a sufficient number of rows are made to create an acoustic mirror with good reflection. The area made up of these rows is a metamaterial that reflects vibrations. Consequently, it does not vibrate and therefore constitutes a dead zone in which no tactile stimulus can be generated. To reduce the size of the dead zones, it is possible to reduce the number of rows. It is thus possible to envisage implementing two or three rows.

The spatial arrangement of the acoustic metamaterial is fixed during its manufacture. The tactile signal sent in the waveguide can nevertheless always be modulated in time.

[0059] The touch interface plate may be flat. You can also use a curved plate without affecting its operation. It is also possible to produce an acoustic metamaterial in a volume with a three-dimensional spatial periodicity.

[0060] Different applications of the tactile stimulation interface according to the invention can be envisaged.

[0061] It is difficult to implement haptic feedback on a large surface, for example on a computer screen or a car door, in particular because of the actuation power required. For some applications, however, it is not necessary for the haptic feedback to take place over the entirety of said surface. Acoustic metamaterials then offer a solution to delimit the vibration zone and thus reduce the power required.

[0062] Ultrasonic lubrication is currently limited to surfaces whose edges are orthogonal. This condition is necessary for the establishment of regular vibration patterns that guarantee homogeneous lubrication. For ergonomic reasons, many common objects have irregular or rounded edges (for example a car dashboard, a computer mouse or a joystick). Acoustic metamaterials can then create a waveguide with orthogonal edges to overcome irregularities and roundings, which would make possible the modulation of friction on common objects on which artificial textures could then be simulated.

[0063] Many everyday applications require tactile exploration with two hands, whether it is the perception of textures or the reading of Braille. However, most existing touch interfaces have identical haptic feedback over their entire surface and are therefore limited to interactions with a single finger. The use of acoustic metamaterials to create tactile stimuli (vibrations, frictions) localized under each finger opens the door to more realistic multipoint interactions.

[0064] Localized ultrasonic lubrication makes it possible to spatially modify the apparent coefficient of friction of a plate. Local friction reduction can be used to selectively set objects in motion. For example, with an inclined ultrasonic plate, an object placed on a lubricated area can be set in motion while the same object on a non-lubricated area will be static. Applications in the field of conveying and sorting are possible.

[0065] Recent game controllers incorporate high-fidelity vibrotactile feedback with the presence of two actuators arranged on either side of the controller. However, the lack of vibration isolation between the left and right parts is a source of crosstalk between the two channels. The integration of an acoustic metamaterial in the center of the controller makes it possible to isolate the two parts, thus improving the fidelity of the haptic feedback.

[0066] With the advent of virtual and augmented realities, numerous haptic jackets have appeared. These consist of a matrix of actuators attached to a flexible medium carried by the user. The propagation of vibrations through this medium harms fidelity by "blurring" the feedback haptic. This adverse effect can be avoided with the use of an acoustic metamaterial to isolate each tactile rendering area.

Claims

[Claim 1] [Tactile stimulation interface (1), comprising a first face (3), intended to be explored by touch, and called the touch face, and a second face (4) provided with at least one actuator (5), said at least one actuator (5) being configured to be excited so as to generate and transmit acoustic waves to the tactile face (3), the interface (1) being characterized in that the second face (4) comprises at at least one confinement zone for the acoustic waves (7) generated by said at least one actuator (5), said at least one confinement zone (7) being delimited at least in part by acoustic mirrors (6) made of an acoustic metamaterial configured to reflect acoustic waves of frequencies included in a predetermined interval, called forbidden band, said forbidden band including the carrier frequency of the acoustic waves generated by said at least one actuator (5).

[Claim 2] Interface (1) according to Claim 1, characterized in that the said at least one actuator (5) is a piezoelectric actuator or an electromagnetic actuator.

[Claim 3] Interface (1) according to Claim 1 or 2, characterized in that the metamaterial comprises resonators (9) arranged periodically.

[Claim 4] Interface (1) according to one of Claims 1 to 3, characterized in that the forbidden band of the acoustic metamaterial is included in a frequency interval lower than 500 Hz.

[Claim 5] Interface (1) according to Claim 3, characterized in that the resonators (9) are balls of tungsten, copper, steel or lead, surrounded by silicone.

[Claim 6] Interface (1) according to one of Claims 1 to 3, characterized in that the first face (3) and the second face (4) form a plate.

[Claim 7] Interface (1) according to Claim 6, characterized in that the plate (2) is made of metal, silicon or glass.

[Claim 8] Interface (1) according to Claim 6 or 7, characterized in that the forbidden band of the acoustic metamaterial is comprised in a frequency interval ranging from 20 kHz to 200 kHz. [Claim 9] Interface (1) according to Claim 3, characterized in that the resonators

(9) are aluminum cylinders of circular or rectangular section.

[Claim 10] Interface (1) according to claim 3, characterized in that the resonators (9) comprise balls of tungsten, copper, steel or lead, mounted on an aluminum cylinder of circular or rectangular section. [Claim 11] Interface (1) according to one of Claims 1 to 10, characterized in that the said at least one acoustic wave confinement zone (7) is a surface with orthogonal edges or a circular surface^ j