WO2025226151A1

WO2025226151A1 - Functional haptic device

Info

Publication number: WO2025226151A1
Application number: PCT/NL2025/050191
Authority: WO
Inventors: Tom BRUINING; Samuël Alexander Ming WEIMA; Thierry Kilian SLOT; Danqing Liu; Dirk Jan Broer
Original assignee: Eindhoven Technical University
Current assignee: Eindhoven Technical University
Priority date: 2024-04-25
Filing date: 2025-04-24
Publication date: 2025-10-30
Anticipated expiration: 2026-10-25
Also published as: NL2037539B1

Abstract

The present invention relates to a functional haptic device comprising a haptic coating. The present invention also relates to a method for manufacturing the haptic coating wherein the haptic coating is manufactured on basis of a shape memory liquid crystal network. Furthermore, the present invention relates to a haptic image display comprising such a functional haptic device.

Description

Title: Functional haptic device

Description:

Haptic technology, also known as kinaesthetic communication or 3D touch, refers to any technology that can create an experience of touch by applying forces, vibrations, or motions to the user. These technologies can be used to create virtual objects in a computer simulation, to control virtual objects, and to enhance remote control of machines and devices. Haptic devices may incorporate tactile sensors that measure forces exerted by the user on the interface. Simple haptic devices are common in the form of game controllers, joysticks, and steering wheels.

US 2013/0154984 relates to a haptic system comprising a panel-type display device, an information selection haptic panel which is set on a top surface of said panel-type display device, a shape memory alloy which contracts upon electrification and heating to make said information selection haptic panel move, and an insulating heat conductor which disperses heat which was generated by said shape memory alloy.

In an article written by Astam Mert O. et al, "Active Surfaces Formed in Liquid Crystal Polymer Networks", Applied Materials & Interfaces, vol. 14, no. 20, 10 February 2022 (2022-02-10), pages 22697-22705 discloses the use of liquid crystal networks as stimuli-responsive materials for soft actuators and sensors. Liquid crystal networks (LCNs) are commonly synthesized by photopolymerizing reactive mesogens, i.e. monoacrylate and diacrylate reactive mesogens. Mixtures of reactive mesogens are often formulated to control monomer properties, for instance, nematic phase transition temperature, allowing for room temperature processing. In the monomeric state, prior to the polymerization of the network, various molecular configurations can be established by methods developed in the liquid crystal display industry. Upon decreasing the order of the established molecular alignment, the polymer network contracts along the general molecular orientation axis (director) and expands in the perpendicular direction. Thereby, actuation can be achieved using an external stimulus, such as temperature, electric field, or light.

US 2020/115483 discloses a method of synthesizing a shape-programmable liquid crystal elastomer, the method comprising filling an alignment cell with liquid crystal monomers, wherein the liquid crystal monomers align to a surface of the alignment cell; and polymerizing the liquid crystal monomers with a dithiol chain transfer agent, wherein the alignment cell is configured to impose a director orientation on a portion of the shape-programmable liquid crystal elastomer, wherein the liquid crystal monomers are mesogenic diacrylates.

US 2016/313607 discloses a method of making a shape-programmable liquid crystal elastomer comprising preparing an alignment cell having a surface programmed with a plurality of domains, filling a cavity of the alignment cell with a monomer solution, monomers of the monomer solution configured to align to the surface of the alignment cell, polymerizing aligned monomers of the monomer solution by Michael Addition, and cross-linking the polymers to form a cross-linked liquid crystal elastomer, wherein cross-linking traps monomer alignment into a plurality of voxels, each voxel of the plurality having a director orientation.

US 2021/149489 discloses a touchpad apparatus comprising a bottom layer comprising processing circuitry, a tactile pixel layer disposed on top of the bottom layer, the tactile pixel layer comprising a plurality of tactile pixels, wherein the processing circuitry is configured to control operation of the plurality of tactile pixels through application of one or more stimuli to each tactile pixel and each tactile pixel is independently operable, and a surface layer disposed on top of the tactile pixel layer, the surface layer comprising a deformable material. Each tactile pixel comprises a top plate comprising a plurality of vertices; and a support strut coupled to each vertex of the plurality of vertices, each support strut comprising a liquid crystal elastomer (LCE) hinge disposed between a first rigid portion and a second rigid portion.

US 2017/068318 discloses an electronic device, comprising a housing, a flexible display mounted in the housing, and a tactile output device having electrodes to which signals are applied to deform a portion of the flexible display, wherein the electrodes form electromagnets and wherein the tactile output device includes ferromagnetic material that receives magnetic fields from the electromagnets. The ferromagnetic material comprises a ferrofluid and the tactile output device comprises electroactive polymer that is deformed upon application of electric fields from the electrodes.

CN116453399 discloses an electroactive polymer driven braille display device comprising display units arranged in an array, wherein the display units comprise a negative electrode plate, a positive electrode plate and an electroactive polymer, wherein a closed space is provided between the negative electrode plate and the positive electrode plate. The negative electrode plate is provided with a braille dot circular hole that is connected to the closed space which is filled with the electroactive polymer, wherein the upper and lower ends of the electroactive polymer are respectively attached to the negative electrode plate and the positive electrode plate.

US 2010/0302199 relates to a user interface device, comprising a plurality of sensors; a processor; an interface circuit connected to the sensors and arranged to provide electrical signals from each of the sensors to the processor; and a user- touchable portion comprising a movable ferromagnetic material positioned relative to the plurality of sensors such that movement of the ferromagnetic material by a user causes a change in the electrical signals from at least one of the sensors, wherein the processor is arranged to analyze the electrical signals from each of the sensors and determine the location of the movement on the user-touchable portion.

An object of the present invention is to develop programmable and locally deformable surfaces capable of large deformations in microscale.

Another object of the present invention is to apply haptic technology at a smaller scale, making the technology suitable for devices that value compactness and lightness.

Another object of the present invention is to integrate haptic surfaces into devices thereby creating differences that can be sensed by touch

The present invention thus relates to a functional haptic device, comprising:

A circuit board provided with a plurality of individual elements;

A haptic coating; wherein electrical information is applied to the circuit board to activate one or more individual elements for deforming corresponding portions of the haptic coating. The present inventors thus found a device that includes a haptic coating of which its surface can be switched between a flat state and a state with protrusions by a change in temperature.

In an example the haptic coating is directly applied on the circuit board.

In an example a glue layer is positioned between the circuit board and the haptic coating.

In an example the plurality of individual elements of the circuit board are organized in a matrix of columns and rows driven by an array of transistors.

In an example the transistors controlling the matrix of columns and rows are controlled by a positive or negative potential.

In an example the elements in which both the positive and negative transistors are activated provide a local electrical signal that is used for deforming corresponding portions of the haptic coating.

In an example the step of providing a local electrical signal is controlled by switching the voltage on and off in a controlled manner.

In an example the local electrical signal results into electrically-induced heating within the haptic coating thereby changing the haptic state of the haptic coating.

In an example the temperature of the electrically-induced heating is sufficient to lower the order parameter of the haptic coating, especially wherein the temperature of the heating is above the isotropic temperature of the haptic coating. In an example the material does not actually go fully isotropic.

In an example the haptic state of the haptic coating below the isotropic temperature of the haptic coating is identified as a first state and the haptic state of the haptic coating above the isotropic temperature of the haptic coating is identified as a second state.

In an example the first state is a dented state, and the second state is a flat state.

In an example the first state is a flat state, and the second state is a state with protrusions.

In an example the haptic coating is manufactured according to a method for manufacturing a shape memory liquid crystal network, comprising the following: preparing a mixture of reactive components; applying the mixture on a substrate; crosslinking the reactive components of the mixture thereby forming a layer consisting of a loosely crosslinked network onto the substrate; pressing the surface of the layer of the substrate in a desired shape thereby forming a local alignment within the molecules of the pressed area; polymerizing the molecules of the pressed area for arresting the prior formed local alignments thereby obtaining the substrate provided with the haptic coating.

In an example the substrate provided with the haptic coating is provided with a flexible bilayer.

In an example the substrate is a flexible or rigid substrate, such as glass or plastic.

In an example the shape memory liquid crystal network is obtained in two stages, wherein in a first stage a loosely crosslinked network is obtained by reaction between a liquid crystalline diacrylate and a dithiol in the presence of tri- or four functional thiol, and wherein in a second stage a deformation is established in the network that causes orientation of the obtained liquid crystal chains that are fixed by a photo crosslinking reaction.

In an example the shape memory liquid crystal network is obtained in two stages, wherein in a first stage a loosely crosslinked network is obtained by reaction between a liquid crystalline diacrylate and an amine, and wherein in a second stage a deformation is established in the network that causes orientation of the obtained liquid crystal chains that are fixed by a photo crosslinking reaction.

In an example the loosely crosslinked network is obtained via a photo crosslinking reaction in the presence of a photoinitiator, or a via thermal crosslinking reaction in the presence of a thermal free-radical initiator.

The present invention relates to a haptic image display comprising such a functional haptic device. An example of such a haptic image display is a braille display.

The haptic device according to the present invention can change its surface texture to provide haptic feedback to a user. The technology can also be used to make a refreshable braille display.

Besides haptics in general, the present invention can be used in applications for visually impaired people, too. Examples are braille and tactile displays. Current braille is usually static, and braille books are expensive and hard to come by. This can be overcome to an extent by audiobooks, but audio descriptions of pictures or graphs are limited. Making the contours of an image or graph tangible makes it much easier to understand. With the present invention, a braille or tactile display can be created that is more simple, low profile and easier to integrate into other technologies. The present invention can be incorporated into smartphones, the interiors of cars or on gaming controllers.

The present invention can be made into a transparent system so that it can even be applied over the top of screens on various smart devices, e.g. phones, tablets, or smart watches, wherein the surface of the screen can then locally be changed to provide tangible buttons or different surface textures. This means that the surface of a tablet can switch between a smooth surface for use with fingers and a paper like surface to provide a better writing or drawing experience with a stylus. The present invention can also be fully flexible when flexible electronics are used. This allows for applications on flexible displays, folding smartphones, or flexible wearables.

To synthesize the liquid crystal elastomer material, a two step crosslinking reaction is used. For this reaction, the reaction mixture contains a reactive liquid crystal diacrylate monomer, a chain extender dithiol and a crosslinker tetrafunctional thiol which reacts together via a catalysed addition reaction. The molecular ratios are chosen such that after this oligomerization reaction the end groups of the oligomer chains are thiols. This creates a flat, lightly crosslinked film. In the next step the film is pressed with a stamp to introduce surface reliefs and it is photo crosslinked in this state. For this second reaction the reaction mixture contains a di-vinyl chain extender and a tetrafunctional vinyl crosslinker which react under UV light with the oligomer to form a more densely crosslinked, but still flexible, network. This reaction is initiated by a photoinitiator but can also be carried out thermally in the presence of a thermal free- radical initiator. After completion of this reaction stable state one is formed after which the mould can be removed. The surface of this second mould determines the topography of the surface that is stable at room temperature. The film can now reversibly switch between state one (dented) and by heating above the isotropic temperature of the polymer film to the flat state two. By cooling, the sample switches back to the dented state. In an example a flexible bilayer is then added to the first layer to introduce the capability of making protrusions or bumps. When the bottom layer switches from a dented to a flat state, the bilayer is pushed from a flat state into a corrugated state. The transition between flat and corrugated can be experienced by touch.

The accompanying drawings, which are included to provide a further understanding of the disclosed subject matter, are incorporated in, and constitute a part of this specification. The drawings also illustrate embodiments of the disclosed subject matter and together with the detailed description serve to explain the principles of embodiments of the disclosed subject matter. No attempt is made to show structural details in more detail than may be necessary for a fundamental understanding of the disclosed subject matter and various ways in which it may be practiced.

Figure 1 shows an overview of reagents for preparing a shape memory liquid crystal network.

Figure 2 shows a method for manufacturing a surface that switches between flat in a non-activated state to corrugated in an activated state.

Figures 3 i-v show the local actuation ability when activating heating elements in different configurations.

Figure 4 shows the height of a single protrusion over time when heating and cooling over six cycles using a demonstrator device.

Example 1 : preparing a mixture of reactive components

The reagents mentioned in the examples have been shown in Figure 1.

Chemical component 4-(6-(acryloyloxy)hexyloxy)phenyl-4-(6- (acryloyloxy)hexyloxy)benzoate (Reagent# 1) was used in the reaction mixture in a quantity of 61.5 wt.%. Chemical component 3,6-dioxa-1 ,8-octanedithiol (chain extender, Reagent# 2) was used in the reaction mixture in a quantity of 16.3 wt.%. Chemical component polyfunctional thiol pentaerythritol tetrakis(3- mercaptopropionate) (Reagent# 3) was used in the reaction mixture in a quantity of 13.4 wt.%. This polyfunctional thiol is used to slightly crosslink the oligomer formed in a first reaction step. Chemical component being a reactive difunctional vinyl ether, namely triethylene glycol divinyl ether (Reagent# 4) was used in the reaction mixture in a quantity of 4.0 wt.%. Chemical component being a polyfunctional vinyl crosslinker, i.e. glyoxal bis(diallyl acetal) (Reagent# 5) was used in the reaction mixture in a quantity of 0.3 wt.%. Together with the reactive difunctional vinyl ether it reacts under UV light at the second reaction step to set the final surface topography. As inhibitor 2,6-di-tertbutyl-4-methylphenol (Reagent# 6) was used in a quantity of 0.6 wt.%. As the photoinitiator for the second reaction Irgacure 184 (Ciba Specialty Chemicals, Reagent# 7) was added in a quantity of 1 .9 wt.%. After the formation of a liquid crystal elastomer layer, a flexible bilayer is added. This bilayer consists of 89 wt.% tripropylene glycol diacrylate. The aforementioned chain extender for making the layer more flexible was used in a quantity of 9 wt.%. Irgacure 184 was used as photoinitiator in a quantity of 2 wt.%.

Example 2: Fabricating a surface that switches between flat in a non-activated state to dented in an activated state.

A glass substrate is covered with an initial reaction mixture consisting of Reagents# 1 to 7 as mentioned above. This is allowed to react until full conversion of the acrylate groups is reached thereby obtaining a flat, loosely crosslinked layer.

According to Figure 2 a substrate 1 is covered with the initial reaction mixture consisting of Reagents# 1 to 7 as shown in Figure 1. This is allowed to react until full conversion of the acrylate groups is reached thereby leaving a flat, loosely crosslinked layer. Next a structured mould 3 is pressed on the loosely crosslinked coating by weight until the coating deforms to adopt these surface reliefs. In this stage the completion of the reaction takes place by polymerization of the vinyl and thiol end groups as shown in Figure 1 , reagents with reference numbers 2 to 5, initiated by UV light actuating Reagent# 7, see Figure 1 . Then mould 3 is removed to provide a dented coating 5 which is the final active layer. This layer is then covered with a bilayer mixture consisting of reactants# 2,7 and 8. Such bilayer mixture is then cured using UV light to give a flat layer 6 that fills the dents of layer 5 below. By raising the temperature to Ti the coating surface deforms thereby giving coating 7 and reshaping bilayer 6 to the final surface 8. By cooling to temperature T2, the coating deforms back to its initial state 5 and 6, respectively. Typically, temperature T1 is the same or close to the nematic to isotropic transition of the liquid crystal network. In of case of the reagents given in Figure 1 that temperature is around 40°C. Temperature T2 is room temperature or close to that.

Example 3: Construction of a functional haptic device

The tactile coating as obtained in Example 2 was integrated in a demonstrator device to convert electrical information into tactile information. For this application, a Braille-row was chosen. The Braille row has six characters, where each character consists of six individual elements. The haptic coating is controlled by a voltage, which switches the coating between the flat and protruded states.

To drive the individual elements, a circuit was developed that addresses the individual regions of the haptic coating. The starting point for a functional demonstrator is to use electrically-induced heating. Here, electricity is locally converted into heat within the coating, which changes the haptic state of the coating. The regions are actuated by switching the voltage on and off in a controlled manner. The amount of actuation is controlled by pulse-width modulation of the control signal. This way, the amount of power delivered to the individual regions can be controlled and adjusted for different coating materials.

The individual elements are organized in a matrix (rows and columns) which are driven by an array of transistors. A small microcontroller unit controls the signals for the driving module. The transistors controlling the rows control the power influx, whereas the columns control the negative potential. This way, only the elements that have both transistors (plus and minus) activated are heating (and thus actuating).

The coating is directly bonded to a printed circuit board. In another example a glue layer is first applied onto the printed circuit board and the coating is applied bonded on the glue layer. Printed circuit boards are strong and durable and have the advantage that the electronics can be integrated on one of the sides of the boards using surface-mount technology. Printed circuit boards are coated with Mylar (polyethylene terephthalate) to which the present haptic coating can be adhered by a thin layer of glue.

The device was programmed using the commonly available Arduino platform. The demonstrator device can run a demo program by itself with the push of a button. The device can also be controlled via USB to display multiple braille characters on demand and function as a real-time braille display.

This demonstrator will not only demonstrate the functionality of the haptic coating, but it will mark the start of an area where it is possible to integrate haptic information flow in all kinds of commercial products.

Example 4: Construction of a functional haptic device

In another example, the tactile coating as obtained in Example 2 was integrated in a demonstrator device with a three by three grid of resistive heating elements. The material was placed on the device with a layer of thermal paste acting as an adhesive and heat conductor to quickly dissipate unwanted temperature. The tactile coating was placed on the device so that each heating element aligned with the programmed spots in the material that form protrusions when heated. To demonstrate the local actuation ability, the heating elements were activated in different configurations and the material response was measured using interferometry. Figure 3 i shows the material when none of the elements are heated, whereas Figure 3 ii shows the material when all nine heating elements are activated, resulting in a corrugated surface with nine bumps. When a single heating element is activated, a single bump protrudes from the surface as depicted in Figures 3 iii and iv, without effect to the neighbouring material. Finally, when a row of 3 heating elements is heated, a row of 3 bumps protrudes from the surface.

The speed of actuation in this demonstration setup was measured using a profilometer. Figure 4 depicts the height of a single protrusion over time when heating and cooling over six cycles using the demonstrator device. When heating, a sharp increase in height is observed, reaching a 138 pm bump height within 9.5 seconds. When removing the heating stimulus, the material returns to its flat room temperature state within 5 seconds.

Claims

1. A functional haptic device, comprising:

A circuit board provided with a plurality of individual elements;

A haptic coating; wherein electrical information is applied to the circuit board to activate one or more individual elements for deforming corresponding portions of the haptic coating.

2. A functional haptic device according to claim 1 , wherein the haptic coating is directly applied on the circuit board.

3. A functional haptic device according to claim 1 , wherein a glue layer is positioned between the circuit board and the haptic coating.

4. A functional haptic device according to any one or more of claims 1-3, wherein the plurality of individual elements of the circuit board are organized in a matrix of columns and rows driven by an array of transistors.

5. A functional haptic device according to claim 4, wherein the transistors controlling the matrix of columns and rows are controlled by a positive or negative potential.

6. A functional haptic device according to any one of claims 4-5, wherein for elements in which both the positive and negative transistors are activated provide a local electrical signal that is used for deforming corresponding portions of the haptic coating.

7. A functional haptic device according to claim 6, wherein the step of providing a local electrical signal is controlled by switching the voltage on and off in a controlled manner.

8. A functional haptic device according to any one of the preceding claims, wherein the local electrical signal results into electrically-induced heating within the haptic coating thereby changing the haptic state of the haptic coating.

9. A functional haptic device according to claim 8, wherein the temperature of the electrically-induced heating is sufficient to lower the order parameter of the haptic coating, especially wherein the temperature of the heating is above the isotropic temperature of the haptic coating.

10. A functional haptic device according to claim 9, wherein the haptic state of the haptic coating below the isotropic temperature of the haptic coating is identified as a first state and the haptic state of the haptic coating above the isotropic temperature of the haptic coating is identified as a second state.

11. A functional haptic device according to claim 10, wherein the first state is a dented state, and the second state is a flat state.

12. A functional haptic device according to claim 10, wherein the first state is a flat state, and the second state is a state with protrusions.

13. A functional haptic device according to any one of the preceding claims, wherein the haptic coating is manufactured according to a method for manufacturing a shape memory liquid crystal network, comprising the following: preparing a mixture of reactive components; applying the mixture on a substrate; crosslinking the reactive components of the mixture thereby forming a layer consisting of a loosely crosslinked network onto the substrate; pressing the surface of the layer of the substrate in a desired shape thereby forming a local alignment within the molecules of the pressed area; polymerizing the molecules of the pressed area for arresting the prior formed local alignments thereby obtaining the substrate provided with the haptic coating.

14. A functional haptic device according to claim 13, wherein the substrate provided with the haptic coating is provided with a flexible bilayer.

15. A functional haptic device according to any one of claims 13-14, wherein the substrate is a flexible or rigid substrate, such as glass or plastic.

16. A functional haptic device according to any one of claims 13-15, wherein the shape memory liquid crystal network is obtained in two stages, wherein in a first stage a loosely crosslinked network is obtained by reaction between a liquid crystalline diacrylate and a dithiol in the presence of tri- or four functional thiol, and wherein in a second stage a deformation is established in the network that causes orientation of the obtained liquid crystal chains that are fixed by a photo crosslinking reaction.

17. A functional haptic device according to any one of claims 13-15, wherein the shape memory liquid crystal network is obtained in two stages, wherein in a first stage a loosely crosslinked network is obtained by reaction between a liquid crystalline diacrylate and an amine, and wherein in a second stage a deformation is established in the network that causes orientation of the obtained liquid crystal chains that are fixed by a photo crosslinking reaction.

18. A functional haptic device according to any one of claims 16-17, wherein the loosely crosslinked network is obtained via a photo crosslinking reaction in the presence of a photoinitiator, or a via thermal crosslinking reaction in the presence of a thermal free-radical initiator.

19. A haptic image display comprising a functional haptic device according to any one of the preceding claims.

20. A haptic image display according to claim 19, wherein the image display is a braille display.