WO2022269171A1

WO2022269171A1 - Tactile stimulation interface with resonant actuators

Info

Publication number: WO2022269171A1
Application number: PCT/FR2022/051167
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: 2022-06-16
Publication date: 2022-12-29
Also published as: FR3125144B1; CA3220056A1; FR3125144A1

Abstract

The present invention relates to a tactile stimulation interface (10), comprising a tactile face and a second face (8) equipped with at least one actuator (1a, 1b, 1c, 1d), the interface (10) being characterized in that the second face (8) comprises at least one acoustic wave confinement area (11), the confinement area (11) being defined by at least one acoustic mirror (9) made of an acoustic metamaterial configured to reflect acoustic waves of frequencies within a predetermined interval, called the band gap, the interface (10) furthermore being characterized in that each acoustic mirror (9) and each actuator (1a, 1b, 1c, 1d) comprises a system configured to generate and transmit acoustic waves to the tactile face (7) and to prevent the propagation of acoustic waves of frequencies within the band gap.

Description

TACTILE STIMULATION INTERFACE WITH ACTUATORS

RESONANTS

[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. Most of these haptic devices stimulate the sense of touch through vibrations. The problem is that it is very difficult to prevent these vibrations from spreading throughout the device and therefore making tactile information “blurry” for the user. To create high-fidelity haptic feedback, especially on body areas with high acuity (the hand for example), it is then necessary to be able to localize tactile stimuli. This is a major goal of haptic research.

[0004] Solutions exist for locating haptic signals, but they have many drawbacks. For example, some depend greatly on the shape of the actuators and the boundary conditions for fixing the device. Others are based on a software approach, such as time reversal and inverse filter. This requires significant computing power, incompatible with the constraints of real-time servoing of haptic systems.

One could consider using acoustic metamaterials from a periodic distribution of local resonators which behave like acoustic mirrors, the latter being spatially arranged to create waveguides. However, this solution has the disadvantage of the presence of zones dead between the waveguides. This results in a reduction in the density of acoustic signals that can be monitored. These passive structures are moreover obtained by discontinuities in matter or geometry. It is therefore impossible to spatially reconfigure them once they are made. The waveguides are thus immutable, which greatly limits their use.

The present invention aims to remedy these drawbacks.

[0007] 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 at least one acoustic mirror produced by 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.

[0009] The carrier frequency is the frequency of a sine wave which is then modulated by a signal which contains the haptic information.

[0010] The interface is further characterized in that said at least one acoustic mirror and said at least one actuator each comprise a system configured to, in a first configuration, generate and transmit acoustic waves to the touch face and to, in a second configuration, preventing the propagation of acoustic waves of frequencies included in the forbidden band.

Said at least one actuator and said at least one acoustic mirror may comprise a resonant actuator. The resonance of the resonant actuator can take place in a translational or rotational movement. In particular, the resonant actuator can oscillate in a translational or rotational movement.

[0012] Each resonant actuator may comprise a mass, a spring, a magnet and a coil.

[0013] The resonant actuator can be configured to generate and transmit acoustic waves to the tactile face when a current passes through the coil and the resonant actuator can be configured to prevent the propagation of acoustic waves of frequencies included in a band prohibited when no current flows through the coil.

[0014] The forbidden band of the acoustic metamaterial can be included in a frequency range below 500 Hz.

[0015] The first face and the second face can belong to a support, such as a plate. The support can be made of any rigid material (metal, glass, plastic, composites). It can also be made of a functional plate such as a capacitive screen which can advantageously measure the spatial position of one or more fingers in contact.

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 following description, given by way of non-limiting example and made with reference to the appended figures:

[0018] [Fig. 1] is a sectional view of a resonant linear actuator used in a tactile stimulation interface according to the invention,

[0019] [Fig. 2] is a perspective view of a tactile stimulation interface according to the invention, and

[0020] [Fig. 3] is a perspective view of the tactile stimulation interface of Figure 2 when implemented by a user.

[0021] DETAILED DESCRIPTION

[0022] A tactile stimulation interface according to the invention implements an active metamaterial, therefore the unitary element is an electromagnetic actuator resonant 1 (figure 1). This resonant actuator is composed of at least a mass 2, a spring 3, a magnet 4, and a coil 5, assembled to perform a translational or rotational movement. These components give it two electronically switchable states, including an "actuator" state when a current is imposed in the coil, and a "resonator" state if the coil is open circuit. In the “resonator” mode and, for a given range of frequencies qualified as forbidden band (band gap in English), the acoustic waves cannot propagate.

Thanks to its design, the actuation frequency of an element 1 in the "actuator" state is intrinsically identical to the resonance frequency of an element in the "resonator" state. This feature allows the elements 1 in the "resonator" state to be de facto acoustic mirrors optimized to reflect the vibrations produced by the elements 1 in the "actuator" state. It is the switching between these two states that reconfigures the acoustic mirrors and thus updates the acoustic wave confinement zones, called waveguides, depending on the use. The modular nature of this new metamaterial opens the door to many applications. This is particularly the case for the haptic domain where the creation of localized vibrotactile stimuli, in other words tactile pixels called "taxels", is a major challenge.

The invention has two main objectives. The first is to remove the dead zones between the waveguides and the second is to spatially reconfigure the latter. For this, the general idea is to build a metamaterial via a unitary element 1 that can be switched between the “actuator” and “resonator” states.

In Figures 2 and 3, there can be seen schematically represented an example of touch interface 10 according to the invention comprising a support 6, such as a plate, comprising a first face 7 and a second face 8 opposite the first side 7.

The first face 7 is intended to be explored by touch, for example by the fingers of a user. The first face 7 is designated touch surface.

In the example shown, the touch face 7 is flat, as well as the support 6, but the present invention also applies to curved touch surfaces. and curved supports. The support can be 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 touch face 7 can be intended to be touched by the pulp of a finger or several fingers 12a, 12b. It is also possible to envisage that the tactile surface 7 is able to apply stimulation to any part of the user's body sensitive to touch.

The second face 8 is provided with one or more linear resonant actuators 1a, 1b, 1c, 1d arranged in FIGS. 2 and 3 on a line in order to form a one-dimensional acoustic metamaterial. It is also possible to envisage arranging the linear resonant actuators 1a, 1b, 1c, 1d on a two-dimensional surface. The unitary element of the touch interface 10 is thus a resonant electromagnetic actuator following a translation movement. This type of actuator is frequently called Linear Resonant Actuator (LRA) in English and is commonly implemented in smartphones. Its resonant frequency is typically between 100 and 300Hz, 170Hz in the case described, which makes it an ideal candidate for haptic applications with vibrotactile feedback. Its small dimensions (10mm x 10mm x 4mm) are ideal for creating a metamaterial with a dense network. Preliminary experiments have demonstrated the ability of a group of several elements in the "resonator" state to block the propagation of acoustic waves generated by an element in the "actuator" state.

Thus, if for example the linear resonant actuator 1a is in the “actuator” state, it transmits vibrations (acoustic waves) of frequency 170 Hz to the plate 6. If the linear resonant actuators 1b, 1c and 1d are in the “resonator” state, their forbidden band is centered on the frequency of 170 Hz and they form an acoustic mirror 9 which reflects the acoustic waves. Thus, the finger 12a of the user located to the left of the interface 10 perceives vibrations, while the finger 12b of the user located to the right of the interface 10 will not perceive any vibrations.

In a second example, if the linear resonant actuator 1a emits vibrations at a frequency outside the forbidden band, for example 270 Hz, then the linear resonant actuators 1b, 1c and 1d no longer form an acoustic mirror and the vibrations emitted by the linear resonant actuator 1a will propagate to the left finger 12a, but also to the right finger 12b of the user. The object of the invention is to spatially locate haptic stimuli.

To obtain a localized vibration zone, the interface according to the invention implements an acoustic mirror 9. 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 metamaterials which have the particularity of preventing the propagation of vibrations over a certain frequency range. The 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 band gap, i.e. a frequency range in which the acoustic waves do not propagate.

Thus, the acoustic mirror 9 consisting of metamaterials is spatially arranged to create an acoustic wave confinement zone 11, which is called a waveguide. The waveguide 11 can for example be of rectangular shape. In Figure 3, the waveguide 11 is the area of the plate 6 located between the actuator 1a in "actuator" mode and the left finger 12a. The metamaterials are in this case automatically optimized so that the forbidden band includes the carrier frequency of the haptic signal. This carrier frequency can be at low frequencies in the vibrotactile domain (frequencies below 500 Hz).

[0036] The support 6 of the touch interface can be flat. You can also use a curved support without affecting its operation. he is also possible to realize an acoustic metamaterial in a volume with a three-dimensional spatial periodicity.

[0037] Most acoustic metamaterials consist of few components. Sometimes in one piece, they are nevertheless most often obtained by combining two materials with radically different properties (Young's modulus and density) (silicone and tungsten for example). In any case, they require few assembly operations which facilitates their manufacture. The new metamaterial proposed here is active thanks to the addition of a coil and a magnet. The integration of these new components can prove to be long and costly, all the more so as the matrix formed from the unitary elements is large. This difficulty can be overcome by using resonant actuators that already exist on the market. This is particularly the case of linear resonant actuators (Linear Resonant Actuators in English) which are commonly implemented in smartphones to provide haptic feedback. Their mass production allows a reduction of the cost and the number of necessary assembly operations.

[0038] For certain applications, it is necessary to have a compact metamaterial. This is all the more critical when the stimulation frequency is low because the dimensions of the resonator then increase inexorably (reduction in stiffness and increase in oscillating mass). A first track is the use of linear resonant actuators which have been developed to be as compact as possible given their use in smartphones.

Another problem also linked to the large number of actuators is energy consumption. This can be critical in portable applications. One solution is to increase the quality factor of the resonator within the unitary element. Thus, less electrical energy is required for the same vibration amplitude.

To make large vibrating zones, several adjacent individual elements must be in the "actuator" state.

[0041] Different applications of the tactile stimulation interface according to the invention can be envisaged. [0042] Some laptop computers have a very elongated touchpad, acting as a touch bar. However, these are devoid of haptic feedback. Resonant linear actuators can be attached under this type of touch bar to generate and localize vibrotactile stimuli. The advantage of this solution is its compactness as well as the absence of constraints on the boundary conditions created by the fixing of the touch bar.

[0043] 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.

[0044] 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. Using resonant linear actuators to form reconfigurable acoustic metamaterial allows for localized tactile feedback. One of the advantages of this solution is the absence of a dead zone, which allows a high density of tactile pixels called “taxels”. This is crucial for touch tablets and smartphones whose surface for interaction with the user is small and whose tactile exploration is carried out by the hands which are endowed with great tactile acuity. Using acoustic metamaterials to create localized tactile stimuli under each finger opens the door to more realistic multi-point interactions.

[0045] 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. Since most of these controllers already use linear resonant actuators to generate haptic feedback, this acoustic metamaterial can simply be achieved by adding additional linear resonant actuators.

[0046] With the advent of virtual and augmented realities, many haptic jackets have appeared. These consist of a matrix of actuators attached to a flexible medium worn by the user. The propagation of vibrations through this medium harms fidelity by "blurring" the haptic feedback. This detrimental effect can be avoided with the use of an acoustic metamaterial to isolate each tactile rendering area. The use of linear resonant actuators to produce this acoustic metamaterial makes it possible to have a low-frequency band gap, centered between 100 Hz and 300 Hz, while minimizing mass and bulk. These constraints are indeed critical for wearable haptic devices such as jackets.

Claims

[Claim 1] [Tactile stimulation interface (10), comprising a first face (7), intended to be explored by touch, and called the touch face, and a second face (8) provided with at least one actuator (1 a, 1b, 1c, 1d), said at least one actuator (1a, 1b, 1c, 1d) being configured to be excited so as to generate and transmit acoustic waves to the tactile face (7), the interface (10) being characterized in that the second face (8) comprises at least one confinement zone for the acoustic waves (11) generated by the said at least one actuator (1a, 1b, 1c, 1d), the said at least a confinement zone (11) being delimited at least in part by at least one acoustic mirror (9) produced by an acoustic metamaterial configured to reflect the 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 ( 1a, 1b, 1c, 1d), the interface (10) being further characterized in that said at least one acoustic mirror (9) and said at least one actuator (1a, 1b, 1c,

1d) each comprise a system configured to, in a first configuration, generate and transmit acoustic waves to the touch face (7) and to, in a second configuration, prevent the propagation of acoustic waves of frequencies included in the forbidden band.

[Claim 2] Interface (10) according to claim 1, characterized in that said at least one actuator (1 a, 1 b, 1 c, 1 d) and said at least one acoustic mirror (9) comprise a resonant actuator.

[Claim 3] Interface (10) according to claim 2, characterized in that the resonant actuator oscillates in a movement of translation or rotation. [Claim 4] Interface (10) according to claim 2 or 3, characterized in that each resonant actuator comprises a mass (2), a spring (3), a magnet

(4) and a coil (5).

[Claim 5] Interface (10) according to claim 4, characterized in that the resonant actuator is configured to generate and transmit acoustic waves to the tactile face when a current passes through the coil and in that the resonant actuator is configured to prevent the propagation of acoustic waves of frequencies within a bandgap when no current passes through the coil. [Claim 6] Interface (10) according to one of Claims 1 to 5, characterized in that the forbidden band of the acoustic metamaterial is included in a frequency interval lower than 500 Hz. [Claim 7] Interface (10) according to one of claims 1 to 6, characterized in that said at least one acoustic wave confinement zone (11) is a rectangular surface with orthogonal edges or a circular surface.! I