Metamaterials based on curved surface origami, methods of manufacturing the same, haptic modules based on curved surface origami, and methods for generating active mechanical haptics

Abstract

Provided are a curved surface origami based metamaterial, a method of manufacturing the same, a curved surface origami based haptic module, and a method of generating active mechanical haptics. The curved surface origami based metamaterial includes a panel having a single curved surface crease extending along a longitudinal direction thereof, the single curved surface crease dividing the panel into two faces at opposite sides thereof. The panel is configured to be folded along the single curved surface crease so as to form a folding angle between the two faces. The folding angle is configured to be adjustable so as to achieve a variable stiffness covering a positive stiffness to a negative stiffness when loaded in a vertical direction of the folded panel.

Description

TECHNICAL FIELD

[0001] The present invention relates to a curved origami based metamaterial, a method of manufacturing the same, a curved origami based haptic module, and a method for generating active mechanical haptics. BACKGROUND

[0002] The emerging meta-universe driven by virtual reality (VR) and augmented reality (AR) technologies is transforming the current digital media of third-person perspective into a future immersive platform that vividly presents the physical environment perceived by the first-person perspective. This is achieved by building virtual environments with real sensory perceptions, including but not limited to vision, hearing, and touch. In this new paradigm of how humans interact with future media, VR / AR technologies are ready to penetrate into a range of industry fields (e.g., entertainment, communication, education, human-computer interaction, remote operation, clinical treatment, and rehabilitation), while enhancing our VR / AR, haptic experiences with advanced software (i.e., communication technologies, various applications, and social networks) and hardware (i.e., VR / AR and haptic devices). Although the latest VR / AR devices provide stereoscopic visual and auditory sensory perceptions, they cannot deliver specific sensory dimensions (i.e., haptics) in the mechanical domain. Substantial progress has been made to make the virtual world touchable by bringing passive haptic experiences to users; however, most of them produce simple, hand-centric motion constraints or vibrations (vibrotactile). This is in sharp contrast to the physical environment that humans perceive via active touch with hands, feet, or other body parts to feel the hardness, softness, and even the breaking instant of a fragile object.

[0003] Active mechanical haptics, which encompass positive stiffness (feeling hardness and softness) and negative stiffness (feeling breaking and dropping instant), are considered to be the core and part of the first sensory perception of humans in daily interactions with the physical environment for exploring / processing information and creating ontological metaphors. Currently, these perceptions are missing in body-centric immersive environments. There have been studies showing that real and active mechanical haptics can simultaneously induce physiological and psychological responses, which are difficult to trigger with visual and auditory stimuli alone. In fact, haptics is fundamentally different from our visual and auditory perceptions, which are passive because we humans receive information as a third person. On the other hand, haptics is primarily active because interactions initiated by actively touching / grasping objects generate a sense of psychological ownership, thereby generating personal and interpersonal concepts. The combination of visual, auditory, and active touch sensory perceptions in AR / VR haptic experiences offers exciting potential for expanding the realism of virtual worlds.

[0004] The present disclosure is provided to solve the above-mentioned deficiencies in the background art. SUMMARY

[0005] Therefore, there is a need for a curved origami based metamaterial, a method of manufacturing the same, a curved origami based haptic module, and a method for generating active mechanical haptics, enabling users to actively generate and perceive mechanical haptics with controllable stiffness, ranging from hard to soft and from positive to negative.

[0006] The present disclosure provides a curved origami based metamaterial, a method of manufacturing the same, a curved origami based haptic module, and a method for generating active mechanical haptics, introducing mechanisms, materials, design principles, system integration, and corresponding sensory perceptions of artificially initiated, body-centric, scalable, and wirelessly controlled haptic devices uniquely realized by curved origami modules, enabling users to actively generate and perceive mechanical haptics with controllable stiffness, ranging from hard to soft and from positive to negative. These active haptic mechanical devices aim to generate artificially triggered mechanical sensory perceptions. These devices are expected to enhance VR / AR experiences beyond visual and auditory perceptions, while providing a range of diversified and immersive experiences.

[0007] In a first aspect of the present disclosure, a curved origami based metamaterial includes panels each having a single curved crease extending along a longitudinal direction thereof, the single curved crease dividing the panel into two faces at opposite sides thereof. The panel is configured to be folded along the single curved crease so as to form a folding angle between the two faces. The folding angle is configured to be adjustable so as to achieve a variable stiffness covering a positive stiffness to a negative stiffness when loaded in a vertical direction of the folded panel.

[0008] In a second aspect of the present disclosure, a method of manufacturing a curved origami based metamaterial includes providing a substrate; cutting panel patterns on the substrate so as to obtain panels each having a single curved crease extending along a longitudinal direction thereof, the single curved crease dividing the panel into two faces at opposite sides thereof. The method further includes folding each panel along the single curved crease so as to form a folding angle between the two faces. The method further includes coupling a connecting member to each panel, the folding angle between the two faces being adjustable by driving the connecting member so as to achieve a variable stiffness covering a positive stiffness to a negative stiffness when loaded in a vertical direction of the folded panel.

[0009] In a third aspect of the disclosure, a method of generating active mechanical haptics includes providing the curved faceted metamaterial of the first aspect of the disclosure. The method further includes presenting, by the at least one processor, a virtual object in a virtual reality / augmented reality (VR / AR) scene to a user. The method further includes enabling the user to load strain in a vertical direction of the folded panel and translating the loaded strain into an interactive operation of the user with the virtual object in the VR / AR scene. The method further includes determining, by the at least one processor, a stiffness-related property of the virtual object under the interactive operation of the user. The method further includes adjusting, by the at least one processor, the fold angle in accordance with the determined stiffness-related property of the virtual object under the interactive operation of the user to achieve a stiffness spanning from positive stiffness to negative stiffness corresponding to the determined stiffness-related property.

[0010] In a fourth aspect of the disclosure, a curved faceted haptics module includes at least one curved faceted metamaterial of the first aspect of the disclosure. The curved faceted haptics module further includes at least one connecting member, wherein each panel is coupled to the at least one connecting member, the connecting member being configured to be driven by a driving system to adjust the fold angle between the two faces of the corresponding panel to achieve a variable stiffness spanning from positive stiffness to negative stiffness when loaded in a vertical direction of the corresponding folded panel.

[0011] Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0012] In the drawings, which are not necessarily drawn to scale, like numerals describe similar components throughout the several views. Like numerals having later leading digits embody different examples of like components. The drawings typically show, in example and not limitation, various embodiments of the disclosure and are used for description with the specification and claims. These embodiments are illustrative and are not intended to be exhaustive or exclusive.

[0013] Figures la-lb A 2D pattern and a 3D configuration of a curved faceted metamaterial according to embodiments of the disclosure are shown, respectively.

[0014] Figure 2a A configuration of a variant Miura origami with straight creases and rigid panels for theoretical modeling of curved faceted metamaterials according to embodiments of the disclosure is shown.

[0015] Figure 2b A force-displacement relationship of one curved faceted metamaterial and one variant Miura origami according to embodiments of the disclosure is shown.

[0016] Figures 3a-3cThe working principle of stiffness manipulation of metamaterials based on curved origami according to embodiments of the present disclosure is illustrated.

[0017] Figure 4a The force-displacement relationship of a metamaterial based on curved origami according to an embodiment of the present disclosure is shown at different adjustment angles.

[0018] Figure 4b The falling accelerations for different adjustable angular static loads in the negative stiffness domain are shown according to embodiments of the present disclosure.

[0019] Figure 5a The normalized force / displacement relationship resulting from the creases, panel, and overall effect according to embodiments of this disclosure is shown.

[0020] Figures 5b-5g The normalized force / displacement relationship of the curved origami module according to embodiments of the present disclosure is shown respectively.

[0021] Figure 6a A phase diagram of the normalized secant stiffness as a function of the crease angle and the adjustment angle according to an embodiment of the present disclosure is shown.

[0022] Figure 6b A cyclic compression test of a curved origami module according to an embodiment of the present disclosure is shown.

[0023] Figure 7 and Figures 8a-b The process of manufacturing a metamaterial based on curved origami according to an embodiment of the present disclosure is shown.

[0024] Figure 9 The process of generating active mechanical tactile sensation according to an embodiment of the present disclosure is illustrated.

[0025] Figures 10a-e The closed-loop tactile sensation of metamaterials based on curved origami, generated according to embodiments of the present disclosure, is illustrated.

[0026] Figures 11a-b The construction and working principle of the tactile in-hand device according to embodiments of the present disclosure are shown respectively.

[0027] Figures 12a-b The structure and working principle of a body-centered, lower limb-triggered pedaling device according to embodiments of the present disclosure are shown respectively. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the disclosure.

[0029] The terms "first", "second", and similar terms used herein do not denote any order, quantity, or importance, but are used to distinguish different constituent elements. "Include" or "comprise" and other similar terms mean that the elements listed after the term encompass the elements listed before the term, but do not exclude other elements.

[0030] Furthermore, although example embodiments are described herein, the scope of the disclosure includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., scenarios where the various embodiments intersect), adaptations, and / or alterations based on the disclosure. The elements of the claims are to be construed in the broadest reasonable manner, and not limited to the examples described herein or by the specification or drawings attached hereto, which are to be regarded as non-exclusive. Accordingly, the specification and examples should be regarded as illustrative rather than restrictive. Thus, it should be understood that the specification and examples are to be construed in the broadest form possible, and that the true scope and spirit of the disclosure are to be indicated by the following claims and their full range of equivalents.

[0031] Construction

[0032] Figure la and Figure lb respectively show a 2D pattern and a 3D configuration of a curved origami-based metamaterial according to an embodiment of the disclosure. As shown in Figure la and Figure lb The curved origami-based metamaterial comprises a panel having a single curved crease extending along its longitudinal direction, which divides the panel into two faces at its two opposite sides. The panel is configured to be folded along the single curved crease to form a folding angle β (see Figure lb ) between the two faces, where the folding angle is configured to be adjustable to achieve a variable stiffness covering from positive stiffness to negative stiffness when loaded in the vertical direction of the folded panel.

[0033] In a preferred embodiment, the single curved crease is configured by a circular-arc shaped cut slot at its portion, as shown in Figure la More preferably, the single curved crease is configured by two end extensions, a middle extension, and two circular-arc shaped cut slots, each of which connects its adjacent end extension and middle extension.

[0034] As shown in Figure la each of the circular-arc shaped cut slots comprises a cut line, where α is the included angle between the normal at the midpoint of the curved crease and the tangent at the end of the curved crease, representing the normalized curvature of the crease; β is the included angle between the two curved panels (i.e. the folding angle), representing the folding of the plastic origami. By simply introducing a circular-arc shaped cut line characterized by an angle α, which is related to the radius p of the circle as where a x b is the geometry of the rectangular panel, the 2D panel is folded along the curved creases to form the curved origami. As shown in Figure lb The folding angle β between the two faces is determined by the plasticity imposed by the folding process, the larger the bending deformation of the curved panel, the smaller β, and the smaller the bending deformation, the larger β.

[0035] As mentioned above, for the sake of illustration, Figure la and Figure lb A rectangular 2D panel is employed in the above. However, the shape of the panel is not limited to this, other shapes such as circular, square or elliptical can also be employed. However, in any of the above shapes, the bending angle (angle a) between the normal at the curved crease midpoint and the tangent at the curved crease end is fixed. In the specific example shown in Figure la The angle a between the horizontal edge and the tangent at the curved crease end is fixed.

[0036] Curved origami belongs to the deformable origami class, and therefore has infinite degrees of freedom. Instead of using the finite element method to obtain the spatial distribution of stress and strain when deformed, an analytical analysis is employed in geometry and mechanics, bridging the curved origami (deformable origami) with the Figure 2a The variant Miura origami (rigid origami) shown in is employed to analyze the mechanical properties of the curved origami in detail. Figure 2a The construction of the variant Miura origami with straight creases and rigid panels for theoretical modeling of the curved origami is shown, where the angle γ is related to the plastic folding angle β, i.e. γ(β), and then the model is employed to predict the stiffness of the curved origami and guide the design selection. The solid line represents the mountain crease, and the dashed line represents the valley crease. After a vertical load is applied at the top of the origami, the curved origami will exhibit different force-displacement relationships according to the competition between bending deformation (providing positive stiffness) and folding deformation along the curved creases (providing negative stiffness). Figure 2b The force-displacement relationships of one curved origami and one variant Miura origami (defined as a = 80° and a / b = 1.25) at different folding angles β (i.e. initial states) 60°, 90° and 120° are shown, where the horizontal axis represents the compressed vertical displacement due to the application of a vertical load at the top of the origami, and the vertical axis represents the normalized force generated by the folded panel accordingly.

[0037] In a preferred embodiment, the folded panel is configured to exhibit both positive and negative stiffness when the folding angle β is within a first range of angles, and to exhibit only positive stiffness when the folding angle β is within a second range of angles, wherein the first range of angles is greater than the second range of angles, while being greater than the threshold angle. For example, from Figure 2b It can be seen that the folded panel exhibits both positive and negative stiffness when the folding angle β is 90° or 120°, and exhibits only positive stiffness when the folding angle β is 60°.

[0038] Further, in this embodiment, if the folding angle β is within the first range of angles, the folded panel is configured to exhibit negative stiffness when the compression vertical displacement is greater than a first displacement threshold, and to exhibit positive stiffness when the compression vertical displacement is less than the first displacement threshold. For example, when the folding angle β is 120°, the normalized force increases with displacement (positive stiffness) and then decreases (negative stiffness).

[0039] Thus, for a given curved origami (i.e. given angle β), the stiffness can be easily adjusted by changing the folding angle β using a curved origami based metamaterial, for example, by using a connection member driving method as shown in FIG. 6, wherein the connection member is configured to include, for example, a cable connecting two faces. Specifically, Figures 3a-3c An initial state of a curved origami based metamaterial with integrated cable and fixed edges is shown, wherein a first hole is cut on one of the two faces and a second hole is cut on the other of the two faces for the cable to pass through the two holes in sequence, for example, a knot of the cable is restrained by the first hole, thereby performing a pulling operation to decrease the folding angle or a releasing operation to increase the folding angle. Figure 3a A change in the folding angle β by a pulling operation using a cable is shown. Figure 3b A bending and origami folding of the panels combined together defines its stiffness when actively pressing the curved origami in the vertical direction is shown. Figure 3c

[0040] Figure 4a A curved origami based metamaterial (wherein a = 80°, β = 120° and a / b = 1.25) is shown to exhibit stiffness across positive and negative ranges at different cable pulling angles Δβ = 0°, 35° and 60° using a cable pulling method as shown in FIG. 6. This establishes the effectiveness of using the cable driving method to adjust the curved origami stiffness in real time. As for the haptic perception, different positive stiffness values reflect the hardness level, while the negative stiffness mimics the feeling of crushing an object or falling. Thus, the acceleration becomes an important indicator to characterize this feature during the process of actively pressing the curved origami with negative stiffness with a constant force. For Figures 3a-3c The acceleration of the static load (i.e. constant force) can be as high as 0.6G (1G for free fall) for the same curved origami in FIG. 6 at β = 120° and Δβ = 0°, 35° and 40°, as shown in FIG. 7. Figure 4a Figure 4b

[0041] In addition to the folding angle β as described above, the stiffness variation of the folded panel can also be a function of the panel material, the panel geometry, the arrangement of the cut grooves, and the bending angle a between the normal at the midpoint of the curved crease and the tangent at the end of the curved crease.

[0042] For example,​​​Figure 5a The figure illustrates the normalized force / displacement relationship generated by the creases, panels, and overall effect. As shown, the creases and panels provide negative and positive stiffness, respectively. Clearly, by appropriately configuring the creases and panels, the mechanical response of curved origami can be designed as needed. Figures 5b-d The normalized force / displacement relationship of curved origami modules with different initial folding angles β is shown in the figure, where the angles α = 50°, 60°, and 70°. Figures 5e-g The figures illustrate the normalized force / displacement relationships of curved origami modules with a fixed initial folding angle β = 120° and different controllable angles Δβ, where angles α = 50°, 60°, and 70°.

[0043] To guide the design of curved origami to achieve a more pronounced mechanical feel, Figure 6a A phase diagram is provided showing the normalized secant stiffness as a function of the crease angle α (30° < α < 85°) and the adjustment angle Δβ, where the initial fold angle β = 120° is specified, representing the actual angle when the cable is pulled, ranging from 0° to 120°. To utilize the most significant stiffness perception, only the maximum negative stiffness is selected when the origami has both positive and negative stiffness ranges. When it has only a positive stiffness range, the maximum positive stiffness is used. From a practical perspective, angle α is a predetermined parameter because it defines the origami pattern. Therefore, this phase diagram provides a design (via angle α) and operational guidelines (via adjustment angle Δβ) for achieving a perceived stiffness using origami. For example, to obtain both positive and negative stiffness, the bending angle α between the tangent at the end of the curved crease and the normal at the midpoint of the curved crease is set between 55° and 85°, and the fold angle β is adjusted between 30° and 130°.

[0044] Similar to the elastic deformation during cable pulling, the deformation when repeatedly pressed on the top of a curved origami surface is also elastic. Figure 6b In each cycle, negative stiffness and positive stiffness can be clearly seen.

[0045] Manufacturing method

[0046] Reference Figure 7 and Figures 8a-b The following describes a method for manufacturing metamaterials based on curved origami according to embodiments of the present invention. In manufacturing the curved origami-based metamaterials, curved origami patterns are created using 2D processing and manual folding. Figure 7 In the manufacturing method 100, the steps include the following steps.

[0047] In step S110, the method includes providing a substrate.

[0048] A variety of materials can be used to make the curved origami pattern. Preferably, the substrate of the panel is made of plastic, metal or alloy. Here, the handheld device (described later) uses a PET (polyethylene terephthalate) film (as an example of plastic) with a thickness of 0.2 mm, and the treading device (described later) uses a 65Mn spring steel plate (as an example of alloy) with a thickness of 0.15 mm.

[0049] At step S120, the method comprises cutting the pattern of the panel on the substrate to obtain the panel, each panel having a single curved crease extending along a longitudinal direction, the crease dividing the panel into two faces at its two opposite sides.

[0050] As shown in FIG. 1, the pattern of the panel includes edges, circular-arc-shaped cutting grooves, and holes of the panel. The contours and creases of the curved origami made of the PET film are made using a Silhouette Cameo 3 cutter (Silhouette America Inc.), and the contours and creases made of the spring steel are made by an industrial engraver. Figure 8a

[0051] At step S130, the method comprises folding each panel along the single curved crease to form a folding angle between the two faces.

[0052] The initial manual folding forms a 3D configuration of the curved origami from a 2D sheet and determines an initial folding angle.

[0053] At step S140, the method comprises coupling a connecting member to each panel, and by driving the connecting member, the folding angle between the two faces can be adjusted to achieve a variable stiffness covering positive stiffness to negative stiffness when loaded in the vertical direction of the folded panel.

[0054] In order to be able to actively control the folding angle in real time, the stiffness adjustment is achieved, as shown in FIG. 2, each panel further has a first hole and a second hole located on both sides of the cutting groove, and the connecting member can be coupled to each panel in the following way. First, a cable can be used as the connecting member, and the cable is sequentially threaded through the first hole and the second hole of each panel, so that both sides of the cable extend out of the corresponding face. Then, one side of the cable (the side opposite to the second hole from the first hole) can be knotted, so that the other side of the cable can be driven while being prevented from passing through the first hole and the second hole. Figure 8a

[0055] ​​In particular, a cable (connection member) is inserted through two holes (i.e. a first hole and a second hole) on the panels of the curved origami, with a knot on one side behind the panel. It is noted that the knot of the cable has a size larger than that of the first hole, so as to be able to maintain against the first hole without passing through the first hole when the other side of the cable is driven to reduce the folding angle. In this way, by pulling and releasing the inserted cable, the movement of the moving panel can be controlled to form an adjustable folding angle with respect to the fixed panel.

[0056] In a preferred embodiment, as shown in FIG. 1, before cutting the panel pattern, a sensor layer for sensing the loaded strain and changing its electrical properties is deposited on the substrate on the origami structure by an easy-to-replicate coating method. Specifically, depositing the sensor layer on the substrate includes coating a suspension including a sensor layer material onto the substrate, and drying in a vacuum oven at 120°C for 6 hours. In a preferred embodiment, the sensor layer can employ various materials, such as silver nanowires (AgNW, XFNano Inc.), graphene, etc. Figure 8b

[0057] Application

[0058] In an embodiment of the present disclosure, a curved origami-based haptic module is provided as an application of curved origami-based metamaterials. The curved origami-based haptic module includes at least one curved origami-based metamaterial and at least one connection member as described above, in which each panel is coupled to at least one connection member configured to be driven by a driving system to adjust the folding angle between two faces of the corresponding panel, thereby realizing variable stiffness covering positive stiffness to negative stiffness when loaded in the vertical direction of the corresponding folded panel.

[0059] Further, in order to establish a two-way interface between the physical world and the virtual world, a closed-loop haptics is constructed using the curved origami-based haptic module, with the curved origami-based metamaterial coated with AgNWs as a medium. Regarding Figure 9 , a method of generating active mechanical haptics is described. As shown in Figure 9 , the generation method 200 includes the following steps.

[0060] In step S210, a curved origami-based metamaterial according to any embodiment of the present disclosure is provided.

[0061] In particular, this step can be performed as follows: the bending angle between the tangent at the end of the curved crease and the normal at the midpoint of the curved crease is pre-set in the range of 55° to 85°, within which the folded panel can exhibit positive stiffness and negative stiffness.

[0062] ​At step S220, the virtual object is presented to the user in a virtual reality / augmented reality (VR / AR) scene by at least one processor.

[0063] At step S230, the user is enabled to exert a strain in a vertical direction of the folded panel, and the exerted strain is translated into an interactive operation of the user with the virtual object in the VR / AR scene.

[0064] Specifically, this step can be performed by means of: disposing a pressing member on top of the plurality of curved paper-based metamaterials to cause the curved paper-based metamaterials to displace in the vertical direction when the user performs a pressing operation and / or a releasing operation on the pressing member; and the stiffness corresponding to the determined stiffness-related characteristic is enabled to be perceived by the user via the pressing member.

[0065] At step S240, the stiffness-related characteristic of the virtual object under the interactive operation of the user is determined by at least one processor.

[0066] At step S250, the folding angle is adjusted according to the determined stiffness-related characteristic of the virtual object under the interactive operation of the user by at least one processor, so as to realize the stiffness covering positive stiffness to negative stiffness corresponding to the determined stiffness-related characteristic.

[0067] Specifically, if the determined stiffness-related characteristic is hard or soft, the folding angle is adjusted to make the folded panel present positive stiffness; if the determined stiffness-related characteristic is broken or dropped, the folding angle is adjusted at an angle greater than that when the folded panel presents positive stiffness, so as to make the folded panel present negative stiffness.

[0068] Further, the method 200 can further include depositing a sensor layer on each panel, so that the pressing operation and / or the releasing operation of the user on the pressing member is sensed as a resistance change by the sensor layer; and the resistance change is converted into a voltage change. Then, the VR / AR processor can perform the following processing: obtaining the voltage change, determining the corresponding interactive operation of the user with the virtual object in the VR / AR scene according to the voltage change, and presenting the corresponding interactive operation of the user with the virtual object in the VR / AR scene.

[0069] In an embodiment of the present application, the corresponding interactive operation of the user with the virtual object includes breaking, crushing, or dropping from the virtual object.

[0070] Figures 10a-e The closed-loop haptics generated based on the curved paper-based metamaterials according to embodiments of the present disclosure are respectively shown in FIGS. 1-3, wherein, Figure 10a FIG. 4 shows a schematic diagram of the curved paper-based metamaterial coated with AgNWs as an interface between a physical environment and a virtual environment, Figure 10bFig. illustrates the system integration and circuit diagram of the haptic device constructed with curved origami, Figure 10c Fig. illustrates the resistance of the coated AgNW sensing layer under cyclic compression at different folding angles of the curved origami (a = 80° and b = 120°), Figure 10d Fig. illustrates the deformation response of the virtual object triggered by the actual deformation of the curved origami module under active cyclic compression, demonstrating the highly synchronized deformation between the physical environment connected by the curved origami and the virtual environment, Figure 10e Fig. illustrates the power consumption of the actuation system in the haptic process.

[0071] By combining the haptic perception generated by the active pressing of the curved origami-based metamaterial with the synchronous visual information from the traditional VR device, a highly immersive, touchable closed-loop virtual world can be constructed, as shown in Figure 10a Here, through the touch or pressing action initiated by the user through the haptic device, the user can actively and physically feel what she / he sees in the VR, where the curved origami-based metamaterial is the key stiffness adjustment component. The virtual scene (e.g., city landscape, ice surface, grassland, see Figure 10a ) serves as the input of the haptic device (e.g., the mat and ball in Figure 10a ). Based on this input, the folding angle b is adjusted by the integrated motor by Db to simulate the expected stiffness response of the content seen by the user in the VR device. Therefore, the user can feel the mechanical stiffness of the object seen in the VR device in real time through active hand gripping or body-centered foot-stepping actions. On the other hand, the active interaction (e.g., pressing) of the user with the curved origami-based metamaterial is recorded as a resistance change, which is achieved by silver nanowires (AgNW) deposited on the origami panel as a sensing layer. These changes are then converted into voltage changes Figure 10b ) using the on-board microcontroller. The voltage changes on the haptic device are wirelessly communicated with the virtual environment engine (e.g., Unity) in the PC, and then wirelessly transmitted into the VR device to provide the necessary changes in real time, such as breaking the ice surface when the user triggers the negative stiffness. Of course, if the determined stiffness-related characteristics of the virtual object under the user's interactive operation will cause changes to the virtual object or its environment, the virtual environment engine can present the corresponding changed VR / AR scene to the user.

[0072] Figure 10cFig. illustrates the relative resistance change (AR / R0) of the sensing layer when periodic and active pressing is performed on the curved origami (nominal strain of 30% with varying height) at different folding angles (β = 120°, Δβ = 0°, 30°, 60°, and 90°). Two features are observed here: first, the resistance change has a high repeatability during the periodic pressing and releasing process; second, the influence of the folding angle Δβ is negligible, which is very important for using a general algorithm (i.e., Δβ-independent algorithm) to change the virtual environment. Therefore, in active human interaction, the virtual environment changes according to the deformation measured by the resistance change. Figure 10d It is shown that the device has very stable virtual-real synchronization via its wireless transmission system. Note that the integrated motor-driven cable is only activated when the folding angle of the curved origami needs to be changed according to the virtual scene. Then, it provides various stiffness perceptions for the user without further complex control algorithms or additional actuation. Therefore, only when the stiffness is adjusted, a power dissipation of about 150 mW is generated Figure 10e , forming an energy-efficient system for artificially triggered active haptics.

[0073] As a specific example of curved origami-based haptics, a handheld haptic device and a body-centered stepping device will be described below.

[0074] The handheld haptic device of the similar object provides artificially triggered active mechanical haptics, whose stiffness perception covers both positive and negative ranges. The device consists of four main subsystems Figure 11a ): 1) five buttons, constructed with curved origami-based metamaterials, which generate virtual-physical environment feedback when actively pressed by the user; 2) an actuation system that adjusts the stiffness of the curved origami-based metamaterials by transmitting motor rotation to cable pulling / release actions; 3) an electronic control component, i.e., a microcontroller, for feedback loops (i.e., stiffness adjustment, actuation, sensing) and wireless transmission; and 4) a support shell for accommodating the buttons according to finger positions, electronic devices, and ergonomic considerations to achieve human gripping actions. The curved origami module connects the virtual environment with the actual perception, providing various stiffness perceptions synchronously based on what is seen, and guiding the user's changes in the virtual environment (not limited to shape) based on their active input by pressing the buttons, achieving the feeling of "what you see is what you feel" Figure 11b .

[0075] On the other hand, a body-centered, lower-limb-triggered stepping device is developed, which integrates a larger-scale curved origami-based metamaterial to support full-body movements and provide corresponding stiffness perceptions, further expanding immersive active mechanical haptics beyond hand-centered experiences. The stepping device consists of four main subsystems Figure 12a) : 1) a mobile haptic platform for tread interaction; 2) a curved origami tessellation for user weight support and feedback generation upon active tread; 3) a base platform for positioning the origami tessellation and supporting the overall structure; 4) an actuation system that adjusts the stiffness of the curved origami by transmitting motor rotation through cables to the origami folds. The two-stage transmission of a parallel worm gear and multi-joint cable enables simultaneous adjustment of the curved origami tessellation stiffness and generation of a variety of closed-loop haptic perceptions. This device enables "immersion as treaded" ( Figure 12b ).

[0076] The active mechanical haptics based on curved origami metamaterials presented herein create a human-centered active haptic experience with high-fidelity stiffness perception in the range from positive to negative, using a sophisticated curved origami as a mediator between virtual and physical environments. This mechanism shifts from existing machine-triggered passive haptics to a more human-triggered interface for interacting with the physical universe. In addition, the newly introduced negative stiffness, in combination with various positive stiffnesses, can significantly enrich the immersive experience of users in virtual worlds by reproducing the moment of crushing an object or a heartbeat upon a stumble, as well as touching and pressing objects of different hardness. The working principle and characteristics, combined with the system integration strategy, make the system easy to replicate. Two demonstration devices (i.e., a handheld device and a tread device) quantitatively verify that users can experience high-fidelity first-person sensory, physiological, and psychological experiences in the constructed highly immersive virtual environment, further affirming the potential for widespread use of the devices.

[0077] The above description is intended to be illustrative and not restrictive. For example, the above examples (or one or more solutions thereof) can be used in combination with each other. For example, other embodiments can be used by one of ordinary skill in the art upon reading the above description. In addition, in the above specific embodiments, various features can be combined together to simplify the disclosure. This should not be interpreted as an intent that features not required to be protected in the disclosure are essential to any claim. On the contrary, the subject matter of the disclosure can be less than the full range of features of a particular disclosed embodiment. Therefore, the following claims are incorporated herein as examples or embodiments in the specific embodiments, each claim alone as a separate embodiment, and it should be considered that these embodiments can be combined with each other in various combinations or arrangements. The scope of the disclosure should be determined with reference to the full scope of the appended claims and the equivalents thereof given to these claims.

[0078] The above-described embodiments are merely exemplary embodiments of the present disclosure and are not intended to limit the present disclosure. The scope of protection of the present application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements to the present application within the spirit and scope of the present disclosure, and such modifications or equivalent replacements should also be considered to fall within the scope of protection of the present application.

Claims

1. A metamaterial based on curved faceted paper, characterized in that, Comprising: a panel having a single curved crease extending along a longitudinal direction thereof, the single curved crease dividing the panel into two faces at opposite sides thereof; the panel being configured to be folded along the single curved crease so as to form a folding angle between the two faces; wherein the folding angle is configured to be adjustable so as to achieve a variable stiffness covering a positive stiffness to a negative stiffness when loaded in a vertical direction of the folded panel.

2. The curved paper-based metamaterial of claim 1, wherein, the single curved crease is configured by a circular-arc shaped cut slot at a portion thereof.

3. The curved faceted paper-based metamaterial of claim 2, wherein, the single curved crease is configured by two end extensions, a middle extension, and two circular-arc shaped cut slots, each of the circular-arc shaped cut slots connecting its adjacent end extension and middle extension.

4. The curved surface origami-based metamaterial of claim 3, wherein, the cut slot comprises a cut line.

5. The curved faceted paper-based metamaterial of claim 1, wherein, a bending angle between a normal at a midpoint of the curved crease and a tangent at an end of the curved crease is fixed.

6. The curved surface origami-based metamaterial of claim 1, wherein, the folded panel is configured to exhibit a positive stiffness and a negative stiffness when the folding angle is within a first angle range, and only a positive stiffness when the folding angle is within a second angle range, wherein the first angle range is greater than the second angle range while being greater than an angle threshold.

7. The curved faceted paper-based metamaterial of claim 6, wherein, if the folding angle is within the first angle range, the folded panel is configured to exhibit a negative stiffness when a compression vertical displacement is greater than a first displacement threshold, and a positive stiffness when the compression vertical displacement is less than the first displacement threshold.

8. The curved surface origami-based metamaterial of claim 6, wherein, the stiffness of the folded panel varies according to a material of the panel, a geometry of the panel, a folding angle, and a bending angle between a normal at a midpoint of the curved crease and a tangent at an end of the curved crease.

9. The curved faceted paper-based metamaterial of claim 2, wherein, the stiffness of the folded panel varies according to a material of the panel, a geometry of the panel, an arrangement of the cut slot, a folding angle, and a bending angle between a normal at a midpoint of the curved crease and a tangent at an end of the curved crease.

10. The curved surface origami-based metamaterial of claim 1, wherein, the bending angle between the tangent at the end of the curved crease and the normal at the midpoint of the curved crease is set within a range of 55° to 85°, and the folding angle is adjusted between 30° to 130°.

11. The curved faceted paper-based metamaterial of claim 1, wherein, the panel is made of plastic, metal, or alloy.

12. The curved paper-based metamaterial of claim 11, wherein, the panel is made of a substrate of plastic, metal, or alloy, on which a sensor layer for sensing a strain of a load and changing an electrical property thereof is deposited.

13. The curved faceted paper-based metamaterial of claim 11, wherein, a first hole is cut on one of the two faces, and a second hole is cut on the other of the two faces, for a connecting member to sequentially pass through the two holes so as to perform a pulling operation for reducing the folding angle or a releasing operation for increasing the folding angle.

14. The curved paper-based metamaterial of claim 13, wherein, a size of at least one of the first hole and the second hole is designed to prevent a knot of the connecting member from passing through.

15. The curved faceted paper-based metamaterial of claim 13, wherein, the connecting member comprises a cable.

16. A method of fabricating a metamaterial based on curved origami, characterized by, Comprising: providing a substrate; cutting a panel pattern on the substrate so as to obtain panels, each panel having a single curved crease extending along a longitudinal direction thereof, the single curved crease dividing the panel into two faces at opposite sides thereof; folding each panel along the single curved crease so as to form a folding angle between the two faces; A connecting member is coupled to each panel, and the folding angle between the two panels is adjusted by driving the connecting member, thereby achieving variable stiffness covering positive stiffness to negative stiffness when loaded in the vertical direction of the folded panel.

17. The method of claim 16, wherein, The single curved crease is configured by a circular-arc-shaped cut slot at a portion thereof.

18. The method of claim 17, wherein, Each panel further has a first hole and a second hole located on both sides of the cut slot; The connecting member is coupled to each panel, further comprising: A cable as the connecting member is sequentially threaded through the first hole and the second hole of each panel, with both sides of the cable extending out of the corresponding panel; One side of the cable is knotted on the side of the first hole opposite to the second hole, so that the other side of the cable can be driven.

19. The method of claim 18, wherein, The size of the knot head of the cable is larger than the size of the first hole, so that when the other side of the cable is driven to reduce the folding angle, it can be maintained against the first hole without passing through the first hole.

20. The method of claim 16, wherein, Further comprising: Before cutting the panel pattern, a sensor layer for sensing the load strain and changing its electrical properties is deposited on the substrate.

21. The method of claim 20, wherein, Depositing the sensor layer on the substrate further comprises: coating a suspension including the material of the sensor layer onto the substrate and drying.

22. The method of claim 18, wherein, The panel pattern includes edges, the circular-arc-shaped cut slot, and the holes of the panel.

23. The method of claim 17, wherein, For each panel, two circular-arc-shaped cut slots are cut, so that there is an intermediate extension between the two cut slots, and each cut slot has an adjacent end extension.

24. The method of claim 17, wherein, The panel is cut into an initial rectangular shape with a horizontal bottom edge, and the circular-arc-shaped cut slot is cut with a normal at the midpoint parallel to the horizontal bottom edge, and the bending angle between the tangent at the end of the cut slot or curved crease and the horizontal bottom edge is set in the range of 55° to 85°.

25. The method of claim 16, wherein, The substrate is made of plastic, metal, or alloy.

26. A method of producing active mechanical haptics, characterized by The method comprises: Providing a curved paper-based metamaterial according to claim 1; Presenting a virtual object in a virtual reality / augmented reality scene to a user by at least one processor; Enabling the user to load strain in the vertical direction of the folded panel, and converting the loaded strain into the user's interactive operation with the virtual object in the virtual reality / augmented reality scene; Determining, by at least one processor, the stiffness-related characteristics of the virtual object under the user's interactive operation; Adjusting, by the at least one processor, the folding angle according to the determined stiffness-related characteristics of the virtual object under the user's interactive operation, thereby achieving a stiffness covering positive stiffness to negative stiffness corresponding to the determined stiffness-related characteristics.

27. The method of claim 26, wherein, Adjusting the folding angle according to the determined stiffness-related characteristics of the virtual object, further comprising: If the determined stiffness-related characteristics are hard or soft, adjusting the folding angle to make the folded panel exhibit positive stiffness; If the determined stiffness-related characteristics are broken or dropped, adjusting the folding angle at an angle greater than when the stiffness is positive, so that the folded panel exhibits negative stiffness.

28. The method of claim 26, wherein, Further comprising: If the determined stiffness-related property of the virtual object under the user's interaction operation is to cause a change in the virtual object or its environment, presenting, by the at least one processor, a changed virtual reality / augmented reality scene to the user corresponding to the change.

29. The method of claim 27, wherein, Enabling the user to load strain in the vertical direction of the folded panel further comprises: providing a pressing member on top of the plurality of the curved-folded-paper-based metamaterials, such that upon a pressing operation and / or a releasing operation of the pressing member by the user, the curved-folded-paper-based metamaterials are displaced in the vertical direction accordingly; and the achieved stiffness corresponding to the determined stiffness-related property is perceivable by the user via the pressing member.

30. The method of claim 29, wherein, Further comprising: depositing a sensor layer on each panel, such that the pressing operation and / or the releasing operation of the pressing member by the user is sensed as a resistance change by the sensor layer; converting the resistance change into a voltage change; performing, by a virtual reality / augmented reality processor, the following processing: obtaining the voltage change, determining a corresponding interaction operation of the user with the virtual object in a virtual reality / augmented reality scene from the voltage change, and presenting the corresponding interaction operation of the user with the virtual object in the virtual reality / augmented reality scene.

31. The method of claim 30, wherein, The corresponding interaction operation of the user with the virtual object comprises breaking, crushing, or falling off from the virtual object.

32. The method of claim 26, wherein, Providing a curved-folded-paper-based metamaterial further comprises pre-setting a bending angle between a tangent at an end of a curved fold and a normal at a midpoint of the curved fold in a range of 55° to 85°, within which range a folded panel is capable of exhibiting positive stiffness and negative stiffness.

33. A curved surface origami based haptic module characterized by, Comprising: at least one curved-folded-paper-based metamaterial according to any one of claims 1-15, at least one connecting member, wherein each panel is coupled to at least one connecting member, the connecting member being configured to be driven by a driving system to adjust a folding angle between two faces of the corresponding panel, thereby achieving a variable stiffness encompassing positive stiffness to negative stiffness when loaded in the vertical direction of the corresponding folded panel.

34. The curved paper-based tactile module of claim 33, wherein, For each curved-folded-paper-based metamaterial, a first hole is cut on one face and a second hole is cut on the other face; the connecting member comprises a cable configured to be sequentially threaded through the first hole and the second hole, thereby being pulled by the driving system to decrease the folding angle or being released by the driving system to increase the folding angle.

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