Active fabric with tunable stiffness

Abstract

A device includes a first plurality of first fibers, a second plurality of second fibers, and a third plurality of tiles. The first fibers extend longitudinally. The second fibers extend transversely relative to the first fibers. The third plurality of tiles are coupled to one another by the first fibers and the second fibers to form an array. Each of the tiles is coupled with at least one of the first fibers and at least one of the second fibers. At least one of the tiles is displaceable along at least one of the first fibers and the second fibers to change a configuration of the array between a first state and a second state.

Description

ACTIVE FABRIC WITH TUNABLE STIFFNESSRELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore patent application no. 10202401559Y filed on May 31 , 2024, the contents of which are hereby incorporated by reference in their entirety for all purposes.TECHNICAL FIELD

[0002] The present disclosure relates to robotic devices, and more particularly to shape-variable devices.BACKGROUND

[0003] Robotic devices are industrially useful in a broad range of practical applications. For example, wearable robotic devices have the potential to actively assist humans with physical load-bearing tasks, haptic perception, etc. Conventional wearable robotic devices face several technical challenges. In the case of conventional fluidically-actuated devices, the devices may suffer from large volumetric changes during actuation which can be undesirable in wearable applications where compactness and portability is often required. In the case of devices that operate based on phase-change materials, the response times are relatively long, limiting the use of phase-change materials in applications that may require “real-time” or rapid response.SUMMARY

[0004] In one aspect, a device includes a first plurality of first fibers, a second plurality of second fibers, and a third plurality of tiles. The first fibers extend longitudinally. The second fibers extend transversely relative to the first fibers. The third plurality of tiles are coupled to one another by the first fibers and the second fibers to form an array. Each of the third plurality of tiles is coupled with at least one of the first fibers and at least one of the second fibers. At least one of the third plurality of tilesis displaceable along at least one of the first fibers and the second fibers to change a configuration of the array between a first state and a second state.

[0005] The array includes at least two adjacent ones of the third plurality of tiles being spaced apart from one another if the array is in the first state, and in which the at least two adjacent ones of the third plurality of tiles are in a pressed abutment with one another if the array is in the second state.

[0006] The second state may be characterized by the array forming a tessellation of a predetermined shape from the at least two of the third plurality of tiles being in abutment with one another.

[0007] The first state may be characterized by the array forming a default state, the array in the default state being flexibly deformable.

[0008] In another aspect, the device may further include a ratchet, the first fibers being coupled to and configurable by the ratchet to vary the tension in at least one of the tension in first fibers and the length of the first fibers.

[0009] In yet another aspect, the device may further include a sensor, a motor, and a controller. The controller may be configured to control the motor in response to signals from the sensor. The motor may be coupled to the first fibers to controllably change the configuration of the array between the first state and the second state.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] To aid understanding, various embodiments of the present disclosure will be described with reference to the following figures:

[0011] FIG. 1A to FIG. 1C are schematic diagrams showing bio-inspired structures of the active fabric, according to embodiments of the present disclosure

[0012] FIG. 1 D to FIG. 1 H are schematic diagrams of a method of configuring the active fabric according to embodiments of the present disclosure.

[0013] FIG. 2A and FIG. 2B are schematic diagrams of a tile of the present disclosure.

[0014] FIG. 2C and FIG. 2D are schematic diagrams showing parts of an array of interconnected tiles forming the active fabric.

[0015] FIG. 2E is a schematic diagram of the parts of the array of FIG. 2D showing different relative displacements between pairs of adjacent tiles.

[0016] FIG. 3A to FIG. 3E are images demonstrating the mechanical compliance, flexibility, and high rigidity achievable by the active fabric.

[0017] FIG. 4A shows a comparison between a conventional fabric and the proposed active fabric.

[0018] FIG. 4B is a chart showing a comparison between various conventional fabrics and the active fabric of the present disclosure.

[0019] FIG. 5 is a diagram showing the universality and customizability of the active fabric for use with different target body parts.

[0020] FIG. 6A shows a deformation process of a beam composed of cubic tiles and trapezoidal tiles with varying inclined angles under cantilever-bending tests.

[0021] FIG. 6B is a chart showing a comparison of experimental and FEM results under cantilever-bending loading at given tensile forces in the fibers.

[0022] FIG. 6C shows stiffness tuning under various tensile forces in the fibers.

[0023] FIG. 6D shows the force-displacement curves under bending tests in one experiment, in which the active fabric was represented as a one-dimensional model.

[0024] FIG. 6E shows the tessellation of a 2D plane into architectured tiles with interlocking and non-interlocking configurations, respectively.

[0025] FIG. 6F shows experimental results under three-point bending tests at given confining stresses in the fibers.

[0026] FIG. 6G(i) shows force-time curves recorded under four different confining stresses during high-energy impact.

[0027] FIG. 6G(ii) shows force-time curves recorded under four different confining stresses during low-energy impact.

[0028] FIG. 6H shows the maximum impact force extracted from FIG. 6G(i) and FIG. 6G(ii).

[0029] FIG. 7A is a schematic diagram of a wrist assistive device based on the active fabric useful for tremor suppression.

[0030] FIG. 7B shows rigid and soft states of the assistive device.

[0031] FIG. 70 shows the respective maximum tremor angles in flexion and extension directions under soft and rigid states.

[0032] FIG. 7D shows the respective maximum tremor angles in adduction and abduction directions under soft and rigid states.

[0033] FIG. 7E shows the mean absolute value of EMG signals of tremors along flexion and extension directions.

[0034] FIG. 7F shows the IMU signals of tremors along flexion and extension directions.

[0035] FIG. 7G shows the mean absolute value of EMG signals of tremors in adduction and abduction directions.

[0036] FIG. 7H shows the IMU signals of tremors in adduction and abduction directions.

[0037] FIG. 8A and FIG. 8B are schematic diagrams of an elbow assistive device based on the active fabric useful for muscle fatigue reduction.

[0038] FIG. 8C shows a rigid state and a soft state of the assistive device.

[0039] FIG. 8D(i) shows the mean absolute value of EMG signals of holding a weight of 500 g.

[0040] FIG. 8D(ii) shows the mean absolute value of EMG signals of holding a weight of 2000 g.

[0041] FIG. 8E(i) is a schematic diagram illustrating a drilling protocol to test the device.

[0042] FIG. 8E(ii) shows the mean absolute value of EMG signals during drilling protocol.

[0043] FIG. 8F(i) is a schematic diagram illustrating a fatigue test of statically holding a 2 kg weight with the device in a soft state and in a rigid state.

[0044] FIG. 8F(ii) shows the mean absolute value of EMG signals during the fatigue test.

[0045] FIG. 8G are charts showing: the mean frequency (MNF) of the EMG signals from the fatigue test, and the median frequency (MDF) of the EMG signals from the fatigue test.

[0046] FIG. 9A and FIG. 9B are schematic diagrams showing the device in the form of an actuated elbow exoskeleton based on the active fabric, useful for assisting in lifting heavy loads.

[0047] FIG. 9C shows a control scheme of the device.

[0048] FIG. 9D is a schematic diagram illustrating a weightlifting protocol used in the tests.

[0049] FIG. 9E shows the mean absolute value of EMG signals during the tests.

[0050] FIG. 9F are images showing a process of relaxing.

[0051] FIG. 9G shows the cyclic tests and results with the elevation angle increasing from about 27° to about 44°.

[0052] FIG. 10A is a schematic diagram of the device under impact testing in which the device can be used as part of a protective armor or a protective wearable with controllable impact protection.

[0053] FIG. 10B shows the force-time curves recorded under soft and rigid states during high-energy impact.

[0054] FIG. 10C shows the force-time curves recorded under soft and rigid state during low-energy impact

[0055] FIG. 10D shows the maximum impact force extracted from FIG. 10B and FIG. 10C.

[0056] FIG. 10E shows the device in the form of a helmet in which the active fabric includes electrothermal actuators integrated with the active fabric.

[0057] FIG. 10F illustrates a comparison of a commercial helmet and the helmet of FIG. 10E in a packing process. The right figure demonstrates the height difference of about 6 cm in two cases.

[0058] FIG. 10G(i) are images showing a morphing process of the helmet under the actuation of electrothermal heating.

[0059] FIG. 10G(ii) shows a drop weight impact test setup.

[0060] FIG. 10H are images showing the deformation of the active fabric helmet under various actuating voltages during the impact test. The maximum deformation was about 2.5 cm, about 1 .7 cm, and about 1.3 cm for the three actuating voltages 5 Volts (V), 10 V, and 20 V, respectively.

[0061] FIG. 11A to FIG. 11C are schematic diagrams illustrating multi-stable configurations of device.DETAILED DESCRIPTION

[0062] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0063] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. As used herein, the singular ‘a’ and ‘an’ may be construed as including the plural “one or more” unless apparent from the context to be otherwise. In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0064] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0065] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0066] Terms such as “first” and “second” are used in the description and claims only for the sake of brevity and clarity, and do not necessarily imply a priority or order, unless required by the context.

[0067] Some methods may be described in terms of steps, stages, phases, or the like, merely to aid understanding and / or for convenient reference. The delineation between one step and another step may be merely for convenient reference in thepresent disclosure. It will be understood that in actual implementation there may not be a clear division or transition from one step to another subsequent step. There may be a certain amount of overlap among the steps and / or more than one step may occur or be performed concurrently in time, etc., unless the context dictates otherwise.

[0068] In the present disclosure, the term “segmented architecture” refers to a structure that is made up of a plurality of segments. Examples of a segmented architecture include the protective coverings of some organisms found in nature. For example, the outer armor of an armadillo 100 is formed by bands of dermal bone covered in small scales of keratin. The scales 101 are held together by collagen fibers 102. The armor of the armadillo offers robust protection to the animal and is also capable of flexible morphing, e.g., adapting to the armadillo rolling itself up to form a ball shape (FIG. 1A).

[0069] According to various embodiments of the present disclosure, a proposed active fabric 110 is configured with a segmented architecture. The active fabric 110 includes a plurality of tiles 111 coupled together by fibers 112. The active fabric 110 can be controllably and reversibly switched between at least two states (e.g., a first state 510 and a second state 520) as illustrated in FIG. 1B. For example, the active fabric 110 in the first state may be similar to a compliant and soft flexible sheet of fabric. The same active fabric 110 in the second state may be similar to a conformably rigid article. The active fabric 110 may be configured to be in the first state by default, e.g., the default state or an unactuated state. The active fabric 110 may be configured to be in the second state when actuated, e.g., an actuated state. As illustrated in FIG. 1C, the active fabric may be a wearable article that can concurrently change in shape and stiffness when changing between the first state and the second state.

[0070] FIG. 1 D to FIG. 1 H schematically illustrate a method of configuring an embodiment of the active fabric 110.

[0071] A target surface 120 (FIG. 1D) may serve as a reference for a shape of the active fabric in a second state or a target state. For example, the method may include a step of predetermining the target shape of the active fabric in a targetstate. The target surface 120 may be subject to a step of 3D (three-dimensional) scanning to reconstruct a 3D target surface model 121 (FIG. 1E) or So.

[0072] As illustrated in FIG. 1F, in a step of parameterization, the reconstructed 3D target surface model 121 may be parameterized 122, e.g., by u and v (e.g., So (u, v) = <x (u, v), y (u, v), z (u, v)>, while u and ve [0 l]). This helps to generate a rectangular pattern To. The pattern edges may be augmented with normalized vectors (e.g., nlj, and nl71 17) to construct a tile topology 113 (FIG. 1G) in a step of tessellation.

[0073] The tile topology may be flattened to show a plurality of tessellated tiles 111. Each of the tiles 111 may be 3D printed as a rigid piece. Each tile 111 is formed with a plurality of channels or through holes. Fibers 112 are threaded through respective channels of each tile 111 (FIG. 1 H). The active fabric 110 includes a plurality of rigid tessellated tiles 111 interconnected by flexible fibers 112.

[0074] Morphing the proposed active fabric from 2D (two-dimensional) “flat” shapes to target 3D geometries involves programing the Gaussian curvature of the surface into individual architectured tiles. According to Gauss' Theorema Egregium, the Gaussian curvature (K = k1 k2, where k1 and k2 are the two principal curvatures) cannot be changed without changing the length or the area (isometries). Conventional approaches to achieve morphing focused on programming localized strains or incorporating folds into soft materials to modify the surface metric, transitioning flat surfaces (K = 0) into non-developable surfaces (K 0). However, the restricted achievable geometries and the intrinsic softness limit their practical applications.

[0075] In contrast, according to the present disclosure, an inverse-design method is proposed to tessellate the target surface into architectured tiles, enabling both morphing abilities and mechanical tunability.

[0076] In one example, the following method was used to tessellate the target surfaces into non-interlocking particles (tiles) and build architectured fabrics from the particles (tiles). (1) Thermoplastic sheets were used to create molds mirroring the human body surface via a rubbing technique. After cooling and stiffening, themolds were 3D scanned (CR-Scan 01 , Creality), and the output files were processed to construct models of the target surface. (2) Mapping was employed to tessellate the target surface SO to a rectangular pattern TO. (3) The pattern edges were augmented with normalized vectors to construct the particle (tile) topology. (4) The tessellated particles were flattened on the plane through rigid body movement and rotation. The target surface was tessellated into interlocking particles. In some examples, the tessellated particles or the tiles are each sized and shaped so that adjacent tiles are matingly engageable with one another. In some examples, each one of the tiles is matingly engageable with at least one other of the tiles. After flattening, holes (diameter = 1 mm) were made through the particles along a longitudinal direction and a transverse direction for inserting the actuating ligaments.

[0077] 3D printing was employed to fabricate the tessellated particles (tiles). For some of the prototypes or samples, a commercial FDM 3D printer (Raise3D Pro2, Raise3D Technologies Inc) with PLA filament (3D Aura Pte Ltd) for large scale fabrication were employed. For the samples with smaller sizes, Stereolithography (SLA) 3D Printing (Form3, FormLabs, USA) for rapid fabrication were used.

[0078] Three kinds of fibers (also referred to interchangeably as “actuating fibers” or “actuating ligaments”) were employed in the prototypes. These include steel wires (e.g., available from Zhongyu Company, China) of diameter 0.3 mm for tuning the boundary stress in real-time.

[0079] For the 2D samples (e.g., the plane interlocking / non-interlocking samples and the dome samples), prestressed TPU wires with diameters of 1 .0 mm (Zhongyu Company, China) were used. UV glue was applied to secure the two ends of the TPU wires onto the boundaries of the tiles.

[0080] For some of the samples, shape memory alloy springs e.g., outside diameter of 4 mm and the wire diameter of 0.6 mm were used as electrothermal actuators (available from Baohong Company, China).

[0081] The fibers 112 may be selected according to the application of the device 110 and / or configuration of the tiles 111.

[0082] In the FEM simulations, the fibers were threaded through the holes in the tessellated tiles, which were represented by 3D 8-node linear isoparametric elements with rigid body constraints. In the tests, the front end of the fiber may be tied to the first tile, and the last tile may be fixed to provide a stable base for actuation. Tensile loading may be applied to the end of the fiber, pulling the tiles together into the designed shape.

[0083] FIG. 2A and FIG. 2B present different schematic views of the tile 111 according to embodiments of the present disclosure. The tile 111 is a three- dimensional solid article with a low aspect ratio, e.g., the tile may have relatively larger major surfaces 200 and a relatively thinner edge surface 400. The tile 111 may have a first major surface 210 and a second major surface 220. The first major surface 210 and the second major surface 220 may generally oppose one another.

[0084] One example of the active fabric 110 includes a plurality of tiles 111. Among the plurality of tiles 111 in one piece of the active fabric 110, different ones of the tiles 111 may be similarly or differently configured. For example, the first major surface 210 and the second major surface 220 of one or more of the tiles 111 may be parallel to one another. For example, the first major surface 210 and the second major surface 220 of one or more of the tiles 111 may not be parallel to one another. For example, the first major surface 210 and the second major surface 220 may have similar shapes. For example, the first major surface 210 and the second major surface 220 may have dissimilar shapes. For example, the first major surface 210 and the second major surface 220 may be of similar areas or size. For example, the first major surface 210 and the second major surface 220 may be of dissimilar areas or size. For example, the first major surface 210 and the second major surface 220 may be configured with a similar curvature or with dissimilar curvatures.

[0085] The tile 111 may be coupled with one or more fibers 112. The fibers 112 may be disposed non-parallel to one another. A fiber 112 may be threaded through a hole in the tile 111 from one part of the edge surface 400 to another part of the edge surface 400. In the example illustrated, a first fiber 310 may extend from a first part of the edge surface 410, across the major surfaces, and extend out of the tile 111 at a first opposing part of the edge surface 412. A second fiber 320 may extendfrom a second part of the edge surface 420, across the major surfaces, and extend out of the tile 111 at a second opposing part of the edge surface 422. The fiber 112 may be controllably configured in terms of having more tension applied thereto or having less tension applied thereto. The fiber 112 may be controllably configured in terms of being lengthened or being shortened. The fiber 112 may be controllably configured in terms of being more tensioned or less tensioned and concurrently being lengthened or shortened.

[0086] Any one or more tiles 111 in a piece of the active fabric 110 may have two or more fibers 112 threaded therethrough via the edge surfaces. In some examples, with respect to one tile 111 , the first fiber 310 may be threaded through a first hole431 in the tile and the second fiber 320 may be threaded through a second hole432 in the same tile. The first hole 431 extends through the whole tile length (t1) of the tile and the second hole 432 extends through the whole tile width (t2) of the tile, so that the first fiber 310 and the second fiber 320 may extend out from respective parts of the edge surface 400 of the tile. The tiles may be coupled to the fibers by slidable engagement. In one tile 111 , each of the plurality of fibers 112 may be disposed independently of any other of the plurality of fibers 112. For example, each of the first fiber 310 and the second fiber 320 threaded through the same tile 111 may be operated independently of the other fiber. In the present disclosure, for the sake of brevity, operating a fiber includes changing an amount of tension of the fiber and / or a length of the fiber. Operating the fiber may include enabling the tiles coupled to the fiber to exhibit relative displacement between adjacent tiles. The array or the active fabric may be configured with one or more of the tiles being simultaneously displaceable along the first fiber and the second fiber in response to a change in the tension and / or the length of the fiber.

[0087] FIG. 2C is a schematic side view of a part of the active fabric 110. Opposing edge surfaces 413,414 of immediately adjacent tiles 111 are shown spaced apart from one another. The same first fiber 310 extends through the two tiles 111. If tension is applied to the first fiber 310, or if the length of the fiber is shortened, the opposing edge surfaces 413,414 may be displaced, relative to the first fiber 310, such that the opposing edge surfaces 413,414 are drawn closer to one another. Insome cases, the relative displacement brings the opposing edge surfaces 413,414 into abutment or physical contact with one another, generating an abutment force between these surfaces. In some cases, the immediately adjacent tiles 111 are brought into an abutting engagement with one another when first fiber 310 is tensioned or actuated. The first fiber 310 enabling this change may be referred to as an actuating fiber.

[0088] In a first state, although linked by the first fiber 310, the two tiles 111 have some degree of freedom to move relative to one another. In a second state, an abutting engagement between the two tiles confers a greater overall stiffness to the two tiles 111 , compared to the first state. In some examples, at least two of the tiles undergo a first relative displacement relative to one another; and simultaneously, at least two other tiles undergo a second relative displacement relative to one another. The first relative displacement and the second relative displacement may be different from one another.

[0089] The tile 111 configured with an edge surface 400 is capable of an abutting engagement with a complementary and opposing edge surface of an immediately adjacent tile 111. The tile 111 in this manner distinguishes from scales (e.g., fish scales or reptilian scales, etc.) which provide a flexible total coverage area by having the scales overlap one another to different degrees. Scales are therefore preferably very thin to facilitate overlapping and sliding over one another. In contrast, adjacent tiles 111 of the present embodiment are configured to abut one another at the respective edge surfaces.

[0090] The schematic diagram of FIG. 2C is a simplified illustration that presents a partial “two-dimensional” diagram solely to aid understanding. The active fabric 110 is a three-dimensional article with other tiles 111 distributed along the fiber 321 , and yet other tiles 111 distributed along the fiber 322. In terms of the active fabric (a plurality of tiles 111 interlinked by a plurality of fibers 112), the change that can be effected by varying the tension in the fibers 112 involves a concurrent change in shape and stiffness, with the achievable shape and the achievable stiffness being at least in part predetermined by the configuration of the respective tiles 111.

[0091] As schematically illustrated in FIG. 2D, the active fabric 110 may include tiles 111 of different shapes and sizes at different parts of the active fabric 110. The length of the fiber exposed between immediately adjacent tiles (P) may be controllably varied at different parts of the active fabric 110. FIG. 2E shows the array or active fabric 110 of FIG. 2D after undergoing a change of the configuration in response to a change in at least one of a tension of the first fiber and a length of the first fiber. In this example, at least two of the tiles (e.g., A1 and A2) undergo a first relative displacement relative to one another, and simultaneously, at least two others of the tiles (e.g., A3 and D4) undergo a second relative displacement relative to one another. It can be seen from the illustrations that the first relative displacement and the second relative displacement may be different from one another.

[0092] The tile-and-fiber configuration allows for assembly, separation, rotation, and sliding of the tiles 111 and can provide both strong protection and high mobility (morphing ability). The tiles are architectured, rigid tiles may be inversely configured based on a target body geometry and connected using flexible actuating fibers. The active fabric remains soft, flexible, and conformable to the contours of an external body (e.g., a human body part) in an unactuated state. Applying confining stress through the actuating fibers, the architectured tiles may in response assemble to form the target shape with a high stiffness, simultaneously conforming to the body part and offering robust support or protection to the body part.

[0093] Prototypes of the active fabric 110 were made and tested. Similar to conventional fabrics, the proposed active fabric 110 exhibits a high degree of flexibility. For example, as shown in FIG. 3A, when the active fabric 110 is draped across an elbow, the active fabric 110 is flexible enough to bend along with bending of the elbow.

[0094] The active fabric 110 is compliant or conformable to a substrate. For example, the active fabric 110 could drape conformably and closely over a spherical object (FIG. 3B)

[0095] Advantageously, the active fabric 110 is characterized by easy foldability for compact packing. The active fabric 110 could be folded up into a small flat shape like a folded napkin (FIG. 3C).

[0096] When the active fabric 110 is subjected to confining stresses by actuation of the fibers, the tiles assemble with edges of immediately adjacent tiles in physical abutment with one another. The fibers may be tensioned and / or shortened so that the adjacent tiles are in a pressed abutment with one another, physically contacting one another via the respective edge surfaces. The active fabric 110 can be transitioned into a highly rigid structure (FIG. 3D). As shown, it was experimentally verified that an example of the active fabric 110 was capable of supporting a 3000 g (grams) weight 910, which is equivalent to more than over 50 times its own weight (about 60 g) (FIG. 3E). That is, the active fabric 110 was proven capable of exhibiting a surprisingly high load capacity when tensile stress is applied to the fibers.

[0097] Compared to a conventional fabric 900, the proposed active fabric 110 offers at least two advantages (FIG. 4A). Firstly, the active fabric 110 has an active morphing ability and can achieve rapid reversible, active shape morphing. In contrast, the conventional fabric can only undergo a passive change in shape when it is pushed by a force external of the fabric itself. In the active morphing of the active fabric 110, the active fabric 110 can be controllably re-shaped by itself.

[0098] Secondly, the active fabric 110 has a comparatively higher loading capacity than a conventional fabric 900. The loading capacity of the active fabric 110 (as tested in the prototypes) was high enough to enable the active fabric to serve as part of an exoskeleton or robotic end-effector. To contrast, the conventional fabric 900 is incapable of displacing (e.g., elevating) and supporting an object 902, while the active fabric 110 is capable of displacing (e.g., elevating) and supporting the same object 902.

[0099] FIG. 4B shows that the active fabric combines the softness akin to conventional fabrics with an achievable rigidity comparable to robotic assistive devices, providing mechanical tunability absent in conventional fabrics. Further, the active fabric was found to compare favorably against conventional stiffness-variabledevices (e.g., those including fluid-driven actuators and others including phase changing materials). The comparison was made based on estimated volume change ratios and stiffness variation ratios as key metrics. The proposed active fabric clearly outperformed conventional device. The proposed active fabric was able to change in stiffness more rapidly and achieve a stiffness that is more than 350 times that achievable by the conventional device. The volume after actuation (change in size) was found to be minimal or negligible compared to conventional devices, making the active fabric a significantly more suitable candidate for use in wearable applications.

[0100] Conventional methods to achieve irregular 3D shape morphing often necessitate materials with a large admissible strain range and complex curvature encoding, leading to large volumes after actuation. This can be observed in conventional devices that are inflation-driven. Conventional morphing strategies utilizing programmable localized strain can achieve saddle shapes in some instances, but the conventional device is limited in applications by its intrinsic softness.

[0101] The diagram of FIG. 5 illustrates four target body areas selected to illustrate the customizability and adaptability of the proposed active fabric for a broad range of applications. The four target body areas include: (a) the neck which exemplifies a target shape with negative Gaussian curvatures (ki <0 and k2<0); (b) the wrist which exemplifies another target shape with negative Gaussian curvatures (ki>0 and k2<0); (c) the elbow which exemplifies a target shape with positive Gaussian curvatures (ki>0 and k2>0); and (d) the knee which exemplifies another target shape with positive Gaussian curvatures (ki>0 and k2>0). In the experiments, the method above was carried out for each of the different target shapes, e.g., including steps of: (i) performing a 3D scan of the target body surface; (ii) tessellating the scanned surface into architectured tiles (also referred to as tessellated particles); and (iii) flattening the tessellated particles, and inserting soft ligaments through the flattened tessellated particles.

[0102] FIG. 5 further illustrates the proposed active fabric being disposed on or worn by a human body, confirming that the proposed active fabric can overcome thechallenges of non-developable surfaces with negative Gaussian curvatures (K < 0) on the human body, such as the neck and wrist shapes. For example, the neck shape could be tessellated into 6x8 architectured tiles and the wrist shape into 8x10 architectured tiles. The tiles were assembled with prestressed flexible fibers. After actuation, the active fabric could conform well to the human neck and wrist while providing mechanical support with high rigidity.

[0103] The morphing capabilities of the active fabric was extended to two non- developable surfaces with positive Gaussian curvatures (K > 0), namely, the elbow joint and the knee joint. The target elbow shape and the target knee shape were tessellated into 8x10 and 8x8 architectured tiles, respectively. By actuating the assembled tiles using tensioned fibers, the active fabrics were found to conform well to the target shapes with substantial geometrical alterations while minimizing the device volume after actuation.

[0104] Mechanical Characterization

[0105] The active fabric 110 of the present disclosure can achieve tunable stiffness. The physical contact between immediately adjacent tiles 111 can be controllably manipulated by controlling the tensile stresses within the fibers 112.

[0106] To assess the stiffness and tunability of the active fabric under varying tensile stresses in the fibers, bending tests were conducted experimentally as well as simulated using finite element methods (FEM). For the purpose of the analysis, a simplified configuration of the active fabric in one dimension was used. A beam (e g., FIG. 6A) was subjected to various loads. The beam was composed of nine tiles in the form of nine cubic particles of sides 10 mm (millimeters) confined by steel fibers (diameter of 0.3 mm).

[0107] The bending deformation of a cantilever beam under loadings were measured experimentally and by FEM. The force-displacement curves for all conditions with fiber tensile forces ranging from 10 N to 22 N, were recorded as shown in FIG. 6B. The dashed lines represent the FEM results, the solid lines represent the average experimentally measured values, and the shaded areas denote the standard deviation between three independent tests. The results demonstrate a good agreement between FEM and experimental results,showcasing the elastoplastic behavior of the beam under loading. This behavior can be attributed to the separation and slip between the tiles. Specifically, the deformation process of the beam under cantilever-bending deformation can be divided into two stages: (i) a pre-separation stage or a closely packed state, in which the tiles were tightly confined by the steel fibers, and the segmented beam can be treated as a continuous beam, with the effective elastic modulus dependent on the pre-applied forces in the fibers, and (ii) a separation stage of a loosely linked state, in which the tiles were separate, and the elasticity of the steel fiber dominates the mechanical behavior, representing the plateau region in the curves. Importantly, the force-displacement curves rise significantly with the tensile forces in the fiber increasing from 10 N (Newtons) to 22 N. This may be attributed to the stronger boundary confinement on the samples, resulting in a higher effective elastic modulus in the closely packed state.

[0108] As illustrated in FIG. 6A, to further investigate the influences of the geometries of architectured tiles, e.g., with inclined angles (a), on the mechanical performances, the cubic tiles in the beam were replaced by trapezoidal tiles. To maintain the consistency in tile dimensions, a square medial section with L=10 mm and the same height (h = 10 mm) were maintained in all the samples. The trapezoidal tiles with varying inclined angles (e.g., 60°, 70°, 80°, 90°) were formed into the segmented beams. Cantilever-bending test were conducted experimentally and by FEM. To quantitatively characterize the effects of geometrical parameters of the tiles on the mechanical performances, the slopes of the initial elastic regime (displacement within 0-1 mm) from the force-displacement curve were used as stiffness.

[0109] FIG. 6C presents the stiffness as a function of the applied fiber tensile force in FEM and experimental results. It was observed that as the applied tensile force increases from 10 N to 22 N, stiffness increases from about 0.22 N / mm to about 0.56 N / mm. With the inclined angle decreasing from 90° to 60°, the stiffness increases from about 0.5 N / mm to about 1.0 N / mm. This augmentation in stiffness may be attributed to the tiles with smaller inclined angles requiring larger opening angles under loading, resulting in larger force responses and higher stiffness.

[0110] The stiffness of the beam without any tensile forces in the fiber, i.e., in a soft state, was also characterized. FIG. 6D shows the force-displacement curves under bending tests in one experiment, in which the active fabric was represented as a one-dimensional model composed of nine tiles (cubic particles) linked by a metal fiber. The results point to different mechanical properties of model in a soft state in which the tiles are loosely linked and in a stiff state in which the tiles are closely packed. The results indicate that the stiffness ratio can exceed approximately 350 times between the stiff state and the soft state. While conventional “smart” fabrics (e.g., liquid metals) may be able to achieve stiffness tuning ratios over 1000 times, the present active fabric 110 uniquely offers a practical solution that addresses the traditional issue of a slow response time. The present active fabric 110 advantageously enables real-time rapid tuning of stiffness, making it suitable for various applications that require fast control and feedback, e.g., wearable robotic assistive devices.

[0111] The test sample was expanded from one-dimensional beams to two- dimensional plates. Two configurations were tested. As illustrated in FIG. 6E, one configuration of the active fabric 110 was obtained from tessellating the 2D plane into 5x11 architectured tiles, without interlocking (610) between the tiles. Also illustrated in FIG. 6E is another configuration of the active fabric, obtained from tessellating the 2D plane into 5x11 architectured tiles, with interlocking (620) between the tiles. The tetrahedron interlocking configuration serves to restrict relative movement and increase contact between the immediately adjacent tiles. To provide the boundary confinement, pre-tensioned TPU (thermoplastic polyurethane) wires were employed as the fibers. The pre-strains in the fibers were 57.1% and the corresponding tensile forces were 6.4 N in both. Three-point bending tests were conducted to investigate the mechanical response of the two configurations, with and without topological interlocking (FIG. 6F). It could be clearly observed that the interlocking configuration exhibits a higher force compared to the non-interlocking configuration. This may be attributed to the interlocking topology enhancing contact between both horizontal and vertical edge surface of the tiles, effectively restricting relative movement between adjacent tiles, and increasing theload-bearing capacity. The active fabric 110 is thus shown to be configurable to further enhance its stiffness, e.g., with the incorporation of a topological interlocking of the architectured tiles.

[0112] Besides quasi-static loading, the impact response of the active fabric was also investigated. To quantify the impact protection capability of the active fabric, impact tests at two different levels of impact energies were conducted. In these experiments, the active fabric was configured in a dome shape (e.g., FIG 3D) when subjected to the tests. Pre-tensioned TPU wires were used as the fibers and tensioned to vary the pre-strains (e.g. 20%, 40%, 70%, and 100%, corresponding to 2.7 N, 5.2 N, 8.0 N, and 10.1 N of pre-tension, respectively) and to provide various confining tensions. Two impact energies, about 10 milli Joules (mJ) and about 175 mJ, were used for representing a low energy impact and a high energy impact, respectively. The recorded force responses from the impacts are presented in FIG. 6G(i) and FIG. 6G(ii), respectively. In other words, the force-time curves were recorded under four different confining stresses. The lines represent average values, while shaded areas denote standard deviation between three independent tests. The maximum impact force against the pre-strains under the two impact energy levels was plotted and shown in FIG. 6H based on the maximum impact force values from FIG. 6G(i) and FIG. 6G(ii). It is found that when the impact energy is small (about 10 mJ), the test samples with a smaller pre-tension provide lower impact force responses. Conversely, when the impact energy is large (about 175 mJ), the test samples with a larger pre-tension respond with lower impact forces. This may be attributed to the following reasons. At low impact energy, the test sample with a smaller pre-tension dissipates the same amount of energy while undergoing larger deformations in their yielding regime, resulting in a lower maximum impact force. At high impact energy, the softer test samples may undergo larger deformations, reaching the densification regime where the maximum impact force increases drastically. Under this condition, test samples with higher prestrains appear to perform better. Compared to conventional body armors with fixed properties, the active fabric can offer superior impact protection capabilities by being able to dynamically tune its mechanical properties. This controllability allowsthe active fabric to provide a more optimized or customized response to different impact energies, e.g., becoming stiffer for high impact energies to provide enhanced protection.

[0113] Wrist Assistive Device

[0114] The active fabric 110 of the present disclosure has a wide range of practical applications. In one aspect, embodiments of the present disclosure include a device 700 that includes the active fabric 110.

[0115] Tremors, characterized by involuntary muscle shaking which can significantly impact the ability to perform small daily activities, are unfortunately prevalent among Parkinson's patients. Conventional tremor suppressing devices are often bulky and lack ergonomic compliance, imposing significant discomfort on the wearer.

[0116] FIG. 7A is a schematic diagram illustrating a prototype of a wrist assistive device 701 according to one embodiment of the device 700. Unlike conventional tremor suppressing devices, the wrist assistive device 701 of the present disclosure offers a relatively compact and ergonomic solution with a tunable stiffness. The wrist assistive device 701 may be soft and / or flexible when the patient needs to flex the wrist, and the same wrist assistive device 701 may be stiff enough to provide the necessary support to help suppress tremors and to enable the patient to carry out many small tasks essential to independent living, e.g., hold a spoon or cup without spilling the contents, etc.

[0117] The prototype for the wrist assistive device 701 (FIG. 7A) was about 256 g of which about 80 g was the active fabric 110. It was fairly lightweight and not too heavy to be worn for long periods of time. One example of a suitable tessellation for the active fabric may be similar to that shown in row (b) column (Hi) of the diagram of FIG. 5. For the sake of brevity, a longitudinal direction 181 may be defined by a length of the wrist assistive device and a transverse direction 182 may be defined tangential relative to the longitudinal device. To enable the active fabric 110 to effectively at least partially wrap around the wrist, pre-tensioned TPU wires were used as the fibers 112 in the transverse direction 182 (also referred to as transverse fibers) and steel wires were used as the fibers 112 extending in thelongitudinal direction 181 (also referred to as longitudinal fibers 130 or the first fibers 310).

[0118] The pre-tension in the transverse fibers creates a tendency for the edge surfaces of the tiles to abuttingly mate or matingly engage with one another along a tangential direction and form partial rings of tiles about the wrist. Applying tension in the longitudinal fibers creates a tendency for the partial rings to abuttingly mate or matingly engage and form a broad and rigid support about the wrist.

[0119] The device 700 may include a tensioning device. For example, the wrist assistive device 701 may include a ratchet 131 to control the tension in the fibers 112 along the longitudinal direction 181. The longitudinal fibers 130 may be wound about a winding reel 135 forming a part of the ratchet 131 . By adjusting the tensile stress in the longitudinal fibers 130 using the ratchet 131 , the wrist assistive device 701 can be transformed reversibly between a soft state 710 and a rigid state 720 (FIG. 7B). The switch from the soft state 710 to the rigid state 720, or vice versa, is easy and fast, requiring only a simple turning of the ratchet 131.

[0120] Tests were conducted to verify if the wrist assistive device 701 could indeed offer minimal restriction under free constraints while effectively suppressing tremors during daily tasks. To quantitatively evaluate the performance of the wrist assistive device 701, a wearable surface electromyographic acquisition system (EMG) 132 was disposed on the arm at the Brachioradialis muscle to measure muscle activity and a wearable inertial measurement unit (IMU) 133 was disposed on the back of the hand to record hand accelerations. The IMU 133 and / or the EMG 132 may be configured to communicate wirelessly with a computing device 740 (FIG. 7A and FIG. 7B). For the purposes of testing the prototype, the computing device 740 was configured to acquire IMU signals and EMG signals to measure the performance of the prototype. In actual use, the IMU 133, the EMG 132, and the computing device 740 may be omitted. Alternatively, the IMU 133 and / or the EMG 132 may be optionally integrated with the wrist assistive device 701 and configured for remote health monitoring, etc.

[0121] The suppression performance on the wrist for the flexion and extension motions were tested. Participants were instructed to oscillate their hands along theflexion and extension directions at frequencies of 2 to 5 Hertz (Hz), and the amplitudes are presented in FIG. 7C. As observed, when the wrist assistive device 701 (or the active fabric 110) is in the soft state 710, the wrist can move freely, with an angle between the flexion and extension limits of approximately 95°. This angle decreases to about 33° when the wrist assistive device 701 (or the active fabric 110) becomes stiff.

[0122] The accelerations during the oscillations were further analyzed. To minimize subjective influence, muscle activity was measured using EMG sensors in FIG. 7E. The mean absolute value of the E MG signals of tremors along flexion and extension directions were plotted over time. The measurements show that muscle activities significantly increase when oscillation starts, e.g., time (t) = 5 seconds (s), and that the two muscle activity curves under both the soft state and the stiff state (i.e., the rigid state) share close amplitudes, indicating similar forces used for oscillation.

[0123] The IMU signals of tremors along flexion and extension directions were plotted over time. The hand accelerations decrease significantly under the rigid state compared to the soft state (FIG. 7F).

[0124] The suppression performance on the wrist in adduction and abduction motions were tested. The angle between the pronation and supination limits decreases from about 67° to about 17° when the wrist assistive device 701 (or the active fabric 110) transitioned from a soft state 710 to a rigid state 720 (FIG. 7D). The muscle activity in terms of the mean absolute value of EMG signals of tremors in adduction and abduction directions were measured and shown in FIG. 7G. TheIMU signals of tremors in an adduction direction and an abduction direction were also plotted over time, as shown in FIG. 7H.

[0125] To quantify the tremor suppression effect, a suppression efficiency may be used as shown in equation (1):where i represents the rotation direction, Acc(i, R~) and cc(i,S) denote the tremor acceleration along the t direction under the rigid state ( / ?) and the soft state (5), respectively.

[0126] The suppression efficiency along the flexion and extension directions was found to be approximately 77.92% ± 9.64% with the active fabric of the present disclosure.

[0127] The suppression effect in adduction and abduction directions were also determined. While maintaining consistent muscle activity for oscillation, the suppression efficiency was determined to be approximately 78.56% ± 1 .58%.

[0128] The wrist assistive device 701 of the present disclosure operates on the basis of the proposed active fabric, and demonstrated a relatively high degree of effectiveness in tremor suppression while adding negligible restrictions to the daily movement. The wrist assistive device 701 of the present disclosure compares favorably against conventional tremor suppression devices utilizing active suppression mechanisms. For example, the present wrist assistive device 701 is less than one-tenth the weight of the conventional Wearable Orthosis for Tremor Assessment and Suppression (WOTAS) but has almost two times the suppression efficiency of the conventional WOTAS. For example, the conventional tremor suppression orthosis (TSO) has a comparable suppression efficiency but permits only one degree of freedom and weighs more than 20 times heavier than the present wrist assistive device 701 .

[0129] Elbow Assistive Device

[0130] Work-related Musculoskeletal Disorders (WMSDs) affecting the upper extremities is a significant concern in modern workplaces.

[0131] FIG. 8A illustrates a prototype of an elbow assistive device 702 according to another embodiment of the device 700, which can be used as an upper limb assistive device to mitigate WMSD-related issues. The elbow assistive device 702 may be used for supporting the elbow during extended periods of weight-holding tasks by counteracting the effects of gravity, arm weight, and the load being handled, thereby reducing the risk of WMSDs. Unlike conventional upper limb exoskeletons which are heavy and rigid, the device 700 based on the proposed active fabric 110 is comparatively lightweight and offers large supporting forces while seamlessly conforming to the human body part. The prototype of FIG. 8A was only about 485 g, about 230 g of which was the active fabric 110.

[0132] The tessellation in this example was similar to that illustrated in FIG. 5. Similar to the wrist assistive device, pre-tensioned TPU wires were used as fibers along the transverse directions to form a curved shape for partially wrapping around the elbows. Steel wires serve as actuating fibers along the longitudinal direction, with a ratchet 131 (to wind / unwind a wire reel 135) employed to control the tensile stress in the steel wires. To evaluate the system's effectiveness, EMG sensors 132 were employed to measure Biceps Brachii muscle activities (FIG. 8B). A working scenario was simulated involving the participants wearing the elbow assistive device 702 and holding weights over long periods of time, a typical physical activity of labor workers (FIG. 8C).

[0133] By adjusting tension in the steel wires (longitudinally extending fibers 112), the active fabric 110 could transition between a soft state 710 and a rigid state 720. Comparing muscle activities when participants hold weights under these two states (FIG. 8D(i) and FIG. 8D(ii)), we observe a significant decrease of about 16.8% and about 26.2% in the mean absolute value of the EMG signals corresponding to muscle activity when holding 500 g and 2000 g of weight, respectively.

[0134] Another working scenario involving the participants holding an electric drill during drilling was simulated (FIG. 8E(i)). The process may be divided into three stages: in the first stage (0 s to 5 s), the participant was in a static standing state and the target muscle was in a relaxed state. In a second stage (5 s to 15 s), the participant was holding the drill which weighed about 1.5 kilograms (kg), while the muscle activity increases accordingly. Based on the EMG measurements, using the elbow assistive device 702 of the present disclosure resulted in about 25.2% decrease in the EMG amplitude in this stage.

[0135] In a third stage (15 s to 25 s), the participant started to drill into a wall. Owing to the vibrational forces present during drilling, muscle activity was expected to increase across the board. Based on the EMG measurements, as shown in FIG. 8E(ii), when the device 700 was in a soft state 710, there was a slight increase in muscle activity to hold the drill steady. Surprisingly, when the device 700 was in a rigid state 720, the muscle activity in the third stage remained at almost the samelevel as in the third stage, i.e., about 28.1% lower compared to the same activity with the device 700 in the soft state 710.

[0136] In a third working scenario, participants held weights for an extended period to test the device for muscle fatigue reduction (FIG. 8F(i)). EMG signals (mean absolute values) corresponding to muscle activities were recorded over six minutes. The resulting chart of FIG. 8F(ii) clearly shows that the muscle experienced less fatigue with the device in the rigid state. To characterize the physiological changes occurring in the muscle, the mean frequency (MNF) and the median frequency (MDF) were determined (FIG. 8G). A decrease in these values is indicative of an increase in muscle fatigue.where fmeanis the mean frequency of the EMG signal, fsis the sampling frequency, fmedis the median frequency, and P f) is the power spectrum density of the signal.

[0137] Utilizing Fourier transform to analyze EMG signals, a decrease of 3.87% and 4.69% could be observed in MNF and MDF, respectively, with the device 700 in the soft state. Conversely, with the device 700 in the rigid state, there was only a small decrease of 1.74% and 1.92% in MDF and MNF, respectively, indicating less fatigue. These experiments validate the effectiveness of the elbow assistive device 702 in serving as an exosuit for reducing muscle activity during static work. The muscle reduction function can find many useful applications. For example, in factory working conditions where prolonged static holding tasks are common, the device 700 can be used to reduce muscle fatigue and in turn significantly enhance worker comfort, productivity, and promote a more sustainable and efficient working environment.

[0138] Powered Exoskeleton

[0139] Exoskeletons can be useful for helping a user to lift heavy loads. Unfortunately, conventional exoskeletons themselves can be relatively heavy or bulky owing to the pneumatic actuators or heavy motors required to power the exoskeleton. As such, the user ends up using extra energy just to carry the weight of the conventional exoskeleton.

[0140] In addition to various applications in which the active fabric 110 serves to provide support (such as but not limited to the examples described above), the active fabric 110 of the present disclosure can also be used as in powered devices such as but not limited to actuated exoskeletons (also referred to herein as powered exoskeletons). To demonstrate that the proposed device 700 is not simply useful for supporting static weights, a prototype of an actuated elbow exoskeleton incorporating the proposed active fabric was made and tested in scenarios involving dynamic lifting weights.

[0141] FIG. 9A to FIG. 9C illustrate the prototype of a proposed actuated exoskeleton 703 which only weighed about 820 g, of which about 230 g was the active fabric 110. Similar to the other examples described above, pre-tensioned TPU fibers were used to assemble the tiles in the transverse directions. Along the longitudinal directions, fibers 112 in the form of steel wires were utilized to thread through the tiles. A motor 140 (secured to a backpack or at the back of the user) was employed to actuate the steel wires (e.g., via a winding reel 135) and to assemble the tiles. To transmit the assistive force to the human arm, the end of the device was connected to the shoulder by a thermoplastic plate and fasteners. An I MU 133 was mounted on the back of the hand and configured to record real-time acceleration and to send control signals to the motor 140. When the hand acceleration exceeds the pre-set threshold, a microcontroller (e.g., Raspberry Pi Zero W) would trigger an admittance signal to a velocity controller to activate the motor 140. The control system 145 may be integrated into a control box and securely located on the waist with palm belts.

[0142] As schematically illustrated in FIG. 9D, tests involving the lifting of the arm with the assistance of the exoskeleton 703 were conducted. From the results (FIG.9 E), it is evident that the muscle activity remained consistently low throughout the arm-lifting process with the aid of the exoskeleton.

[0143] Next, tests involving a weight-lifting scenario were performed (FIG. 9D) and EMG sensors were used to measure Biceps Brachii muscle activity (FIG. 9E). The process may be divided into four stages. In the first stage (0 s ~ 5 s), the participant was in a relaxed state without holding weight with low muscle activity. In the second stage (5 s ~15 s), the participant held a weight (1 kg) and muscle activity was observed to increase significantly. The motor was not activated at this stage, and the two curves of the two states almost coincided. In the third stage (15 s ~ 23 s), the participant was instructed to oscillate the hand to send signals for actuating the motor. The motor began running, and the exoskeleton applied assistive forces to the arm while lifting the weight, resulting in a decrease of about 40.9% in muscle activity compared to the non-activated case. In the fourth stage (23 s ~ 30 s), the participant held the weight after lifting, with muscle activity dropping (about 25.2%) compared to the lifting stage.

[0144] Furthermore, unlike passive devices requiring manual control of fiber tension, the actuated exoskeleton 703 can control tension automatically and switch between soft and rigid states easily under motor actuation. This function was further evaluated in terms of the repeatability and durability of the exoskeleton 703 by conducting cyclic tests (FIG. 9F and FIG. 9G). The exoskeleton 703 of the present disclosure completed over 150 cycles (cyclic test on elevation angle increasing from about 27° to about 44°). The tests confirmed the device's excellent reliability and consistent performance throughout repeated use. Compared with conventional exoskeletons with rigid mechanical linkages and joints, the proposed active fabric exoskeleton can assist joints while conforming to human bodies. Moreover, the proposed device minimizes the device volume after actuation. Compared with pneumatic actuation, the proposed device requires a smaller motor actuation, i.e., smaller power consumption by the motor, while producing a superior mechanical response.

[0145] Protective Armor

[0146] Conventional body armors fall into two categories: soft body armor made from flexible fabrics to mitigate low-energy impacts, and rigid body armor reinforced with metal or ceramic to withstand high-energy impacts. The fixed mechanical properties limit their adaptability to varying levels of impact energy.

[0147] In contrast, the tunability of the proposed active fabric 110 can address this limitation. In another aspect, embodiments of the device 700 includes protective armor 704 or protective wearables with tunable stiffness for controllable impact protection.

[0148] To demonstrate this advantage, tests were conducted using an elbow assistive device. For the tests, a medical silicone prosthesis was covered with the elbow assistive device of FIG. 8A to form a part of a protective armor 704. A force sensor was embedded in the soft fillings of the arm to record impact forces (FIG. 10A). Impact mitigation capability was measured under two impact energy levels: about 10 mJ and about 50 mJ, representing low and high energy impacts, respectively. By adjusting the tensile stress in the fibers, the impact force under soft and rigid states for both energy levels were recorded (FIG. 10B and FIG. 10C). Comparing the maximum impact force measured (FIG. 10D), it was evident that the active fabric significantly reduced the maximum impact force. Additionally, the soft fabric state exhibited the lowest maximum impact force under low-energy impacts, while the rigid state showed superior performance under high-energy impacts. This could be because the softer samples could experience larger deformations under high impact energies and entered a densification regime where maximum impact force undergo a substantial increase. This tunability enables the active fabric to adapt effectively to diverse impact energies, providing enhanced protection.[01491 Helmet

[0150] A foldable helmet 705 with impact protection capability was made based on the active fabric. Electrothermal materials in the form of soft fibers 112 were inserted through the tiles 111. The fibers 112 undergo linear contraction when heated, providing the tensile stress to assemble the tiles into the target shape. Upon cooling, the helmet 705 returns to a flat shape under gravity with a low stiffness (FIG. 10E). This smart, active shape morphing ability confers the helmet with a "flat packing"characteristic. Compared to rigid commercial helmets, the helmet 705 of the present disclosure can be compactly packed in a flat state, reducing packing costs while maintaining desired shape and function. Comparison of a commercial helmet and the active fabric helmet during packing process demonstrated a height difference of about 6 cm (FIG. 10F and FIG. 10G(i)). To showcase the impact protection tunability, drop-weight impact tests (mass=100 g, height=40 cm) were conducted under various actuating voltages (5 V, 10 V, and 20 V) (FIG. 10G(ii)). The deformation under impact was recorded (FIG. 10H). The maximum penetration depth decreases with increasing actuating voltage, with the helmet 705 remaining almost undamaged at 20 V actuation, demonstrating its robust impact protection capability.

[0151] Advantages

[0152] According to embodiments of the present disclosure, the device 700 includes an active fabric 110 comprised of rigid architectured tiles 111 interconnected by flexible actuating fibers 112. The active fabric can retain its compliance and flexibility in its initial state (e.g., default state), where no tensile stress is exerted on the fibers. When subjected to tensile stresses by the fibers, the tiles swiftly assemble to assume the target shape, seamlessly conforming to the body's contours in various postures. The amplified contact stresses between tiles induced by the fibers’ tensile forces transform the initially compliant fabrics into rigid structures. This high rigidity provides mechanical support and assistance to the extremities, offering a unique advantage over rigid assistive devices by enabling rapid and seamless transitions between compliant softness and conformable rigidity, rendering the active fabric suitable for comfortable everyday wear.

[0153] By tessellating the target surface into these architectured tiles and controlling their assembly through the tension in fibers, the active fabric can reversibly switch between exhibiting a compliant softness and a conformable rigidity. Compared to other assistive devices, the device of the present disclosure offers several advantages.

[0154] In contrast to conventional assistive devices with rigid linkages and joints, the active fabric can remain compliant to the body in the soft state and candynamically morph to match body contours in the rigid state, ensuring comfortable and effective support.

[0155] The active fabric is highly customizable according to the user’s body areas and can be customized to provide personalized assistance.

[0156] Unlike conventional fluidically-driven fabrics with large volumes after actuation or thermal-driven fabrics with slow responses, the proposed active fabric can achieve stiffness tuning through changing the contact forces between rigid tiles. This enables rapid stiffness transitions while minimizing the device volume after actuation, which is crucial for practical daily use.

[0157] Unlike conventional protective armors, the proposed active fabric can adapt to varying impact energies by tuning its mechanical properties for effective impact mitigation and protection.

[0158] It is further envisioned to incorporate multi-stable configurations to enhance versatility across different postures. For example, one device incorporating two or more differently tessellated active fabrics. For example, as schematically illustrated in FIG. 11A to FIG. 11C, the array or the active fabric 110 may include tiles 111 which can be relatively displaced with respect to one another by changing a tension or a length of at least one of the fibers 112 extending through the tiles 111. FIG. 11A may represent a part of the array in a first state. FIG. 11B may represent the part of the array in a second state. FIG. 11C may represent the part of the array in another second state. In the second state, at least one of the tiles 111 is in a pressed abutment with another of the tiles 111. The overall stiffness of the array in the state shown in FIG. 11 B or FIG. 11C is higher than that of the array in the state shown in FIG. 11 A. The array can be described as having multi-stable configurations.

[0159] It is also further envisioned to include self-locking features at the tile interfaces to achieve a higher mechanical response upon assembly.

[0160] The prototypes were made by manually inserting soft fibers through 3D- printed tiles. It is envisioned to use multi-material 3D printing techniques to streamline the fabrication process, enabling rapid and scalable production.

[0161] As demonstrated with the helmet, various actuation methods may be used, including but not limited to manual operation of a ratchet, motorized control of the fibers, heating / cooling for electrochemical actuation, magnetic actuation, etc.

[0162] The placement and tension of the fibers may be optimized based on criteria such as minimal stress concentration, efficient tile actuation, etc.

[0163] As shown in the case of the actuated elbow assistive device, sensors and feedback mechanisms may be integrated with the active fabric so that the fabric can automatically adjust its stiffness, e.g., in response to environmental changes without manual intervention.

[0164] Both experimental and simulation results show that the proposed active fabric is characterized by both tunable mechanical properties and shape morphing abilities, offering a promising approach for designing robotic assistive devices with optimized comfort and functionality. Furthermore, the active fabric can find a broad range of applications, e.g., from small-scale robotic systems to large-scale deployable structures. For instance, the active fabric can be used to design adaptive shelters that can adjust their shape and stiffness in response to disaster situations where lightweight and portable structures are needed.

[0165] Alternatively described, in one aspect, the present application discloses active fabrics for robotic assistive devices, including: architectured tiles tessellated from the target surfaces and interconnected with flexible actuating fibers, in which the actuating fibers could be steel wires, soft TPU wires and shape memory wires that can provide the confining stresses to assemble the tiles; and in which the mechanical properties could be controlled by tuning the contact between the tiles by manipulating the tensile stresses within the actuating fibers. In another aspect, there is disclosed wrist assistive devices based on the active fabrics, including: active fabrics to adapt to the wrist shape; pre-tensioned TPU wires as fibers along the horizontal (transverse) directions to encase the wrist, and the steel wires along the longitudinal directions tuned by the ratchet. In yet another aspect, there are elbow assistive devices based on the active fabrics, including: active fabrics to adapt to the elbow shape; pre-tensioned TPU wires as fibers along the horizontal(transverse) directions to encase the elbow, and steel wires along the longitudinal directions tuned by the ratchet.

[0166] According to various embodiments of the present disclosure, a device 700 includes a first plurality of first fibers 310, a second plurality of second fibers 320, and a third plurality of tiles 111. The first fibers extend longitudinally 181. The second fibers extend transversely 182 relative to the first fibers. The third plurality of tiles are coupled to one another by the first fibers and the second fibers to form an array or active fabric 110. Each of the third plurality of tiles is coupled with at least one of the first fibers and at least one of the second fibers. At least one of the third plurality of tiles is displaceable along at least one of the first fibers and the second fibers to change a configuration of the array between a first state 510 and a second state 520.

[0167] In some embodiments, the array includes at least two adjacent ones of the third plurality of tiles being spaced apart from one another if the array is in the first state, and in which the at least two adjacent ones of the third plurality of tiles are in a pressed abutment with one another if the array is in the second state.

[0168] In some embodiments, each one of the third plurality of tiles is matingly engageable with at least one other of the third plurality of tiles.

[0169] In some embodiments, the first fiber is threaded through a first hole in each one of the third plurality of tiles, and in which the second fiber is threaded through a second hole in each one of the third plurality of tiles. Relative to any one tile of the third plurality of tiles, the first hole extends throughout a tile length of the tile and the second hole extends throughout a tile width of the tile, the tile length and the tile width being differently oriented linear dimensions of the tile.

[0170] In some embodiments, one or more of the third plurality of tiles is simultaneously displaceable along the first fiber and the second fiber in response to a change in at least one of a tension of first fiber and a length of the first fiber.

[0171] In some embodiments, the array undergoes the change of the configuration in response to a change in at least one of a tension of the first fiber and a length of the first fiber, in which the change of the configuration includes: (i) at least two of the third plurality of tiles undergoing a first relative displacementrelative to one another; and simultaneously, (ii) at least two other of the third plurality of tiles undergoing a second relative displacement relative to one another, in which the first relative displacement and the second relative displacement are different from one another.

[0172] According to various embodiments of the present disclosure, the second state is characterized by the array forming a tessellation of a predetermined shape from the at least two of the third plurality of tiles being in abutment with one another.

[0173] In some embodiments, the first state is characterized by the array forming a default state, the array in the default state being flexibly deformable.

[0174] In some embodiments, the first state is characterized by the array forming a flat shape.

[0175] In some embodiments, the array in the second state is characterized by a higher stiffness than the array in the first state.

[0176] In some embodiments, each of the tiles includes two major surfaces and an edge surface between the two major surfaces.

[0177] In some embodiments, the first fibers and the second fibers extend into / out of the tiles at the respective edge surface.

[0178] In some embodiments, opposing ones of the respective edge surface of adjacent ones of the third plurality of tiles are complementarily shaped to matingly engage one another in the second state.

[0179] In some embodiments, a stiffness of the array is controllably changeable by changing an abutment force between the opposing ones of the respective edge surface of the adjacent ones of the third plurality of tiles in abutment with one another.

[0180] In some embodiments, the respective major surfaces of the adjacent ones of the tiles in abutment with one another form respective continuous surfaces.

[0181] In some embodiments, the configuration of the array is changeable between the first state and the second state by changing at least one of a tension in the first fibers and a length of the first fibers.

[0182] In some embodiments, the first fibers are under a higher tension in the second state than in the first state.

[0183] In some embodiments, the second fibers are under a pretension in the first state.

[0184] In some embodiments, the device further includes a ratchet, the first fibers being coupled to and configurable by the ratchet to vary the tension in at least one of the first fibers and the length of the first fibers.

[0185] In some embodiments, the array in the second state is characterized by a wrist shape.

[0186] In some embodiments, the array in the second state is characterized by an elbow shape.

[0187] In some embodiments, the array in the second state is characterized by a helmet shape.

[0188] According to various embodiments, the device further includes: a sensor, a motor, and a controller. The controller may be configured to control the motor in response to signals from the sensor. The motor is coupled to the first fibers to controllably change the configuration of the array between the first state and the second state.

[0189] According to various embodiments, the device may be configured as any one or more of the following: an assistive device, an exoskeleton, and a protective device.

[0190] All examples described herein, whether of apparatus, methods, materials, or products, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the claimed invention.

Claims

CLAIMS1 . A device comprising: a first plurality of first fibers, the first fibers extending longitudinally; a second plurality of second fibers, the second fibers extending transversely relative to the first fibers; and a third plurality of tiles, the third plurality of tiles being coupled to one another by the first fibers and the second fibers to form an array, each of the third plurality of tiles being coupled with at least one of the first fibers and at least one of the second fibers, wherein at least one of the third plurality of tiles are displaceable along at least one of the first fibers and the second fibers to change a configuration of the array between a first state and a second state.

2. The device as recited in claim 1, wherein the array comprises at least two adjacent ones of the third plurality of tiles being spaced apart from one another if the array is in the first state, and wherein the at least two adjacent ones of the third plurality of tiles are in a pressed abutment with one another if the array is in the second state.

3. The device as recited in claim 2, wherein each one of the third plurality of tiles is matingly engageable with at least one other of the third plurality of tiles.

4. The device as recited in claim 2 or claim 3, wherein the first fiber is threaded through a first hole in each one of the third plurality of tiles, and wherein the second fiber is threaded through a second hole in each one of the third plurality of tiles, and wherein relative to any one tile of the third plurality of tiles, the first hole extends throughout a tile length of the tile and the second hole extends throughout a tile width of the tile, the tile length and the tile width being differently oriented linear dimensions of the tile.

5. The device as recited in claim 4, wherein one or more of the third plurality of tiles is simultaneously displaceable along the first fiber and the second fiber in response to a change in at least one of a tension of first fiber and a length of the first fiber.

6. The device as recited in any one of claims 2 to 4, wherein the array undergoes the change of the configuration in response to a change in at least one of a tension of the first fiber and a length of the first fiber, the change of the configuration comprising: at least two of the third plurality of tiles undergoing a first relative displacement relative to one another; and simultaneously, at least two other of the third plurality of tiles undergoing a second relative displacement relative to one another, wherein the first relative displacement and the second relative displacement are different from one another.

7. The device as recited in claim 2 or claim 3, wherein the second state is characterized by the array forming a tessellation of a predetermined shape from the at least two of the third plurality of tiles being in abutment with one another.

8. The device as recited in claim 2 or claim 3, wherein the first state is characterized by the array forming a default state, the array in the default state being flexibly deformable.

9. The device as recited in claim 8, wherein the first state is characterized by the array forming a flat shape.

10. The device as recited in any one of claims of 7 to 9, wherein the array in the second state is characterized by a higher stiffness than the array in the first state.

11. The device as recited in any one of claims 7 to 10, wherein each of the tiles includes two major surfaces and an edge surface between the two major surfaces.

12. The device as recited in claim 11 , wherein the first fibers and the second fibers extend into / out of the tiles at the respective edge surface.

13. The device as recited in claim 11 or claim 12, wherein opposing ones of the respective edge surface of adjacent ones of the third plurality of tiles are complementarily shaped to matingly engage one another in the second state.

14. The device as recited in claim 13, wherein a stiffness of the array is controllably changeable by changing an abutment force between the opposing ones of the respective edge surface of the adjacent ones of the third plurality of tiles in abutment with one another.

15. The device as recited in any one of claims 11 to 14, wherein the respective major surfaces of the adjacent ones of the tiles in abutment with one another form respective continuous surfaces.

16. The device as recited in any one of claims 11 to 15, wherein the configuration of the array is changeable between the first state and the second state by changing at least one of a tension in the first fibers and a length of the first fibers.

17. The device as recited in any one of claims 11 to 16, wherein the first fibers are under a higher tension in the second state than in the first state.

18. The device as recited in any one of claims 11 to 17, wherein the second fibers are under a pretension in the first state.

19. The device as recited in any one of claims 16 to 18, further comprising a ratchet, the first fibers being coupled to and configurable by the ratchet to vary in at least one of the tension in the first fibers and the length of the first fibers.

20. The device as recited in any one of claims 16 to 19, wherein the array in the second state is characterized by a wrist shape.

21. The device as recited in any one of claims 16 to 19, wherein the array in the second state is characterized by an elbow shape.

22. The device as recited in any one of claims 16 to 19, wherein the array in the second state is characterized by a helmet shape.

23. The device as recited in any one of claims 16 to 19, further comprising : a sensor; a motor; and a controller, the controller being configured to control the motor in response to signals from the sensor, wherein the motor is coupled to the first fibers to controllably change the configuration of the array between the first state and the second state.

24. The device as recited in claim 23, wherein the device is configured as any one or more of the following: an assistive device, an exoskeleton, and a protective device.

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