Patent Application
20240392478
Biological organisms are able to adjust their anatomical structures, stiffness, and behaviors to accommodate a variety of tasks and environmental demands (Shah D et al., Advanced Materials. 2021 May, 33 (19): 2002882). Octopus tentacles, for example, can access nearly infinite trajectories, yet also form joint-like structures to adapt articulated limb control strategies for precise point-to-point movements (Sumbre G et al., Nature. 2005 February;433 (7026): 595-6; Sumbre G et al., Current Biology. 2006 Apr. 18;16 (8): 767-72). Caterpillars undulate and engage in inchworm gaits but can rapidly curl into a wheel form and propel themselves away from predators (Brackenbury J, Nature. 1997 December;390 (6659): 453; Brackenbury J, Journal of insect physiology. 1999 Jun. 1;45 (6): 525-33). Rapid reconfiguration capabilities make a body versatile; they are a hallmark of biological systems that thrive in the natural, unstructured world. Yet these capabilities have long eluded conventional robots, which are limited by rigid structures and discrete joints.
To extend reconfiguration capabilities to artificial systems, researchers have leveraged continuously deformable materials to create soft robot bodies and actuators. Commonly, multiple actuators are patterned into a soft robot body, and a subset of those actuators is activated to achieve a desired body configuration (Tadokoro S et al., Twelfth IEEE International Conference on Micro Electro Mechanical Systems (Cat. No. 99CH36291) 1999 Jan. 21 (pp. 37-42); Hawkes E et al., Proceedings of the National Academy of Sciences. 2010 Jul. 13;107 (28): 12441-5; Nguyen CT et al., Sensors and Actuators A: Physical. 2017 Nov. 1; 267:505-16; Zhou J et al., IEEE Robotics and Automation Letters. 2018 Jun. 28;3 (4): 3379-86; Shah DS et al., IEEE Robotics and Automation Letters. 2019 Feb. 27;4 (2): 2204-11). For example, several works have presented 3-degree-of-freedom (DOF) actuator modules containing three pneumatic actuators evenly spaced in a cylindrical configuration (Suzumori K et al., IEEE Control systems magazine. 1992 February; 12 (1): 21-7; Shih B et al., 2017 IEEE/RSJ international conference on intelligent robots and systems (IROS) 2017 Sep. 24 (pp. 494-501); Robertson MA et al., Science Robotics. 2017 Aug. 30;2 (9); Martinez RV et al., Advanced materials. 2013 Jan. 11;25 (2): 205-12; Xie R et al., 2018 IEEE International Conference on Robotics and Biomimetics (ROBIO) 2018 Dec. 12 (pp. 618-623)). These pneumatic multi-actuator systems are capable of bending in various directions, yet multiple chambers take up significant radial space and make miniaturizing such systems difficult for applications like minimally invasive surgery, where a smaller outer diameter is desired (Elsayed Y et al., Soft Robotics. 2014 Dec. 1;1 (4): 255-62; Runciman M et al., Soft robotics. 2019 Aug. 1;6 (4): 423-43).
As an alternative to multi-chamber actuators, a single volumetrically expanding soft body can achieve controlled and complex motion when coupled with thin strain-limiting components (like woven meshes or fibers) that bias deformation in a programmed way (Galloway KC et al., 2013 16th International Conference on Advanced Robotics (ICAR) 2013 Nov. 25 (pp. 1-6); Sun Y et al., 2013 IEEE/RSJ International Conference on Intelligent Robots and Systems 2013 Nov. 3 (pp. 4446-4453); Deimel R et al., The International Journal of Robotics Research. 2016 January;35 (1-3): 161-85; Connolly F et al., Proceedings of the National Academy of Sciences. 2017 Jan. 3;114 (1): 51-6). Several recent studies have attempted to create inflatable soft actuators with re-programmable strain-limiting layers, thereby enabling a single actuator to attain multiple trajectories by controlling material properties at the actuator surface. One approach employed reconfigurable tensile strain-limiting adhesive patches that can be manually repositioned over the soft body to direct inflation (Kim SY et al., Nature communications. 2019 Aug. 1;10 (1): 1-8). Other approaches relied on thermally-responsive materials, such as low-melting point-alloy (LMPA) particulate composites (Buckner TL et al., Advanced Functional Materials. 2019 December;29 (50): 1903368; Tonazzini A et al., Advanced Materials. 2016 December;28 (46): 10142-8) and shape memory polymer (SMP) (Firouzeh A et al., 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) 2015 Sep. 28 (pp. 1117-1124); Santoso J et al., Smart Materials and Structures. 2019 Feb. 1;28 (3): 035012) that change stiffness upon heating, to influence the trajectory of pneumatic actuators. Although thermally activated variable-stiffness mechanisms are disposed to large modulus changes and require no human intervention, they often suffer from long response times (Wang L et al., Materials Today. 2018 Jun. 1;21 (5): 563-76). Furthermore, when in the rigid, bulk state (Rich S et al., Advanced Materials Technologies. 2017 December;2 (12): 1700179; McEvoy MA et al., Journal of Composite Materials. 2015 June;49 (15): 1799-808), materials like LMPA and SMP compromise the deformation ability of soft systems because they have coupled tensile and bending stiffnesses. Electrostatic clutches can also modulate tensile stiffness (Diller S et al., 2016 IEEE International Conference on Robotics and Automation (ICRA) 2016 May 16 (pp. 682-689); Hinchet R et al., Advanced Materials Technologies. 2020 April;5 (4): 1900895). However, these clutches require high voltages (>300V) to operate, posing risks for human-orientated applications, and the non-stretchable, two-dimensional components of the clutches limit their free bending in three-dimensions.
A growing body of work seeks to utilize jamming, the sudden change of modulus due to interactions of many constituent parts within a system, to achieve rapid stiffness change in soft robots (Steltz E et al., Electroactive Polymer Actuators and Devices (EAPAD) 2010 Apr. 9 (Vol. 7642, p. 764225) Manti M et al., IEEE Robotics & Automation Magazine. 2016 Sep. 13;23 (3): 93-106; Fitzgerald SG et al., Actuators 2020 December (Vol. 9, No. 4, p. 104); Aktaş B et al., 2020 3rd IEEE International Conference on Soft Robotics (RoboSoft) 2020 May 15 (pp. 879-884)). Existing jamming technologies predominately trigger interactions between subcomponents by applying a vacuum to a sealed domain of material, inducing a compressive force that drives the material together. There are three established classes of jamming-granular jamming, layer jamming, and fiber jamming. Each class is associated with a different dimensionality and tunes stiffness along particular axes (
A recent variant of layer jamming technology, which is also referred to as “stretchable layer jamming,” allows the tuning of tensile stiffness (Choi I et al., IEEE Robotics and Automation Letters. 2017 Oct. 11;3 (1): 450-7; Choi WH et al., IEEE Robotics and Automation Letters. 2019 Apr. 1;4 (3): 2539-46; Shah DS et al., Advanced Functional Materials. 2021 January;31 (1): 2006915). In this technology, individual layers are not connected to all sides of the device, enabling the layers to slide past each other when pulled. Stretchable layer jamming could potentially be applied to modulate moderate tensile strains (<40%), but at the cost of drastically increased bending stiffness (see
Thus, there is a need in the art for improved jamming-based strain-limiting technologies capable of controlling tensile stiffness while retaining low bending stiffness in any direction. The present invention meets this need.
The present invention relates in part to a tensile jamming fiber, comprising: a length extending between a first end and a second end; at least a first and a second segmented elastic fibril, each extending between the first end and the second end and each comprising alternating segments of an elastic material and an inextensible material; and an elastic membrane enclosing the first and second segmented elastic fibrils in an interior space and forming an airtight and watertight housing; wherein the first and second segmented elastic fibrils are fused to the elastic membrane at the first end and the second end, and wherein segments of inextensible material in the first segmented elastic fibril partially overlap segments of inextensible material in the second segmented elastic fibril.
In one embodiment, the interior space of the elastic membrane is configured to support a vacuum. In one embodiment, the elastic membrane comprises one or more ports fluidly connected to the interior space.
In one embodiment, the fiber comprises an unjammed state wherein the interior space of the elastic membrane comprises a positive pressure. In one embodiment, the fiber comprises a jammed state wherein the interior space of the elastic membrane comprises a negative pressure, such that each of the segmented elastic fibrils are compressed together by the elastic membrane.
In one embodiment, the fiber in the unjammed state comprises an elasticity configured to permit stretching the length of the fiber by 200% or more. In one embodiment, the fiber in the jammed state comprises an elasticity configured to permit little to no stretching of the length of the fiber. In one embodiment, the fiber in the unjammed state comprises a first tensile stiffness that is lesser than a second tensile stiffness of the fiber in the jammed state. In one embodiment, the second tensile stiffness is about 20× greater or more than the first tensile stiffness. In one embodiment, the fiber in the unjammed state comprises a first bending stiffness that is substantially the same as a second bending stiffness of the fiber in the jammed state. In one embodiment, the fiber is configured to switch between the unjammed state and the jammed state within a tenth of a second.
In one embodiment, the elastic material and the elastic membrane each comprise a material selected from the group consisting of: silicone rubber, neoprene rubber, nitrile rubber, and latex rubber. In one embodiment, the inextensible material comprises a material selected from the group consisting of: polyester, nylon, acrylic, cotton, and carbon fiber. In one embodiment, each segmented elastic fibril comprises a percentage of inextensible material relative to elastic material, in terms of cross-sections and geometry, that is between about 60% and about 80%.
The present invention relates in part to a linear actuator device comprising a flexible cylindrical body and one or more fibers of the present invention attached thereto.
The present invention relates in part to a planar actuator device comprising a flexible planar body and one or more fibers of the present invention attached thereto.
The present invention relates in part to a method of fabricating a tensile jamming fiber, comprising the steps of: embedding lengths of an inextensible material in parallel in a first sheet of a first elastic material; cutting the first sheet of the first elastic material into rectangular sections such that the embedded lengths of inextensible material in each rectangular section is cut to a desired segment length; arranging the rectangular sections into at least two adjacent rows, wherein each row comprises regularly spaced rectangular sections having embedded segment lengths of inextensible material in alignment, and adjacent rows are offset from each other such that rectangular sections of a first row at least partially overlap rectangular sections of a second row; coating the arranged rectangular sections in a second elastic material to form a second sheet; cutting the second sheet into fibers, wherein each fiber comprises a single row of regularly spaced embedded segment lengths of inextensible material in alignment; bundling at least two fibers in an elastic membrane, wherein the single row of regularly spaced embedded segment lengths of inextensible material in each fiber is offset from each other; and sealing the elastic membrane with the at least two fibers at their respective opposing ends to form an airtight and watertight interior space in the elastic membrane.
In one embodiment, each rectangular section is cut to a uniform size. In one embodiment, the first elastic material, second elastic material, and elastic membrane each comprise a material selected from the group consisting of: silicone rubber, neoprene rubber, nitrile rubber, and latex rubber. In one embodiment, the inextensible material comprises a material selected from the group consisting of: polyester, nylon, acrylic, cotton, and carbon fiber.
The present invention relates in part to a wearable clothing item comprising a fabric material configured to cover at least a portion of a subject's body; a plurality of tensile jamming fibers as described above; a pressure source fluidly connected to the plurality of tensile jamming fibers; and a power source electrically connected to the pressure source.
In one embodiment the fabric material covers at least one joint of the subject's body. In one embodiment the fabric material forms a glove configured to fit on the subject's hand. In one embodiment, the wearable clothing item further comprises a computing device comprising at least one processor, wherein the computing device is communicatively connected to the pressure source and is configured to control the jamming and unjamming of each tensile jamming fiber. In one embodiment the computing device is communicatively connected to a virtual reality or augmented reality device.
The following detailed description of exemplary embodiments of the invention will be better understood when read in conjunction with the appended drawings. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings.
The present invention relates to fiber jamming systems capable of tuning tensile stiffness of soft systems within seconds without the use of high voltage or temperature changes. The systems employ segmented fibrils of interspersed segments of stretchable and non-stretchable materials. Applying a vacuum to the fibrils in an enclosed volume elicits a large interfacial shear resistance to tensile displacement. In the absence of a vacuum, the fibrils are free to stretch and bend in any direction.
It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements typically found in the art. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.
Unless defined elsewhere, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, exemplary methods and materials are described.
As used herein, each of the following terms has the meaning associated with it in this section.
The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
“About” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of +20%, +10%, +5%, +1%, and +0.1% from the specified value, as such variations are appropriate.
The terms “proximal,” “distal,” “anterior,” “posterior,” “medial,” “lateral,” “superior,” and “inferior” are defined by their standard usage indicating a directional term of reference. For example, “proximal” refers to an upper location from a point of reference, while “distal” refers to a lower location from a point of reference. In another example, “anterior” refers to the front of a body or structure, while “posterior” refers to the rear of a body or structure. In another example, “medial” refers to the direction towards the midline of a body or structure, and “lateral” refers to the direction away from the midline of a body or structure. In some examples, “lateral” or “laterally” may refer to any sideways direction. In another example, “superior” refers to the top of a body or structure, while “inferior” refers to the bottom of a body or structure. It should be understood, however, that the directional term of reference may be interpreted within the context of a specific body or structure, such that a directional term referring to a location in the context of the reference body or structure may remain consistent as the orientation of the body or structure changes.
Throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, 6, and any whole and partial increments there between. This applies regardless of the breadth of the range.
The present invention relates to tensile jamming fibers as well as devices making use thereof. The tensile jamming fibers are configured to switch between jammed and unjammed states within a fraction of a second. Tensile jamming fibers in an unjammed state comprise a low tensile stiffness and a low bending stiffness. Tensile jamming fibers can be switched to a jammed state upon application of a vacuum or negative pressure and comprise a high tensile stiffness while maintaining a low bending stiffness.
Referring now to
Each segmented elastic fibril 106 is fused to membrane 108 at first end 102 and second end 104 while lengths of each segmented elastic fibril 106 between first end 102 and second 104 remain separate from membrane 104 and adjacent segmented elastic fibrils 106 by spacing 110. It should be appreciated that spacing 110 is depicted merely to illustrate the separation between adjacent segmented elastic fibrils 106 and membrane 104. In some embodiments, a measurable spacing 110 is not necessary so long as the lengths of each segmented elastic fibril 106 between first end 102 and second 104 are able to move freely relative to adjacent segmented elastic fibrils 106 and membrane 108. Tensile jamming fibers 100 and elastic fibrils 106 therein may have any desired length. Elastic fibrils 106 may have any cross-sectional shape, including round, oval, square, rectangular, triangular, and the like. Likewise, each tensile jamming fiber 100 may have any cross-sectional shape, including round, oval, square, rectangular, triangular, and the like.
Each segmented elastic fibril 102 comprises alternating segments of an elastic material 112 and an inextensible material 114, such that segments of inextensible material 114 in a segmented elastic fibril 106 partially overlap segments of inextensible material 114 in at least one adjacent segmented elastic fibril 106. The regions of overlap between inextensible materials 114 are referred to hereinafter as interface regions 116. Overlapping of adjacent inextensible materials in interface regions 116 may be at least 1% of the total length of one or both elastic fibrils 106 forming the interface region 116. In other embodiments, the interface region 116 may be at least 2%, 3%, 4%, 5%, 10%, 15%, 20%, 30%, 40%, 50% or 60% of the total length of one or both elastic fibrils 106 forming the interface region 116. In some embodiments, the ratio of inextensible material 114 to extensible material 112 in any given elastic fibril 106 may be greater than 50%, greater than 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75% or greater than or equal to 80%. In other embodiments, the ratio of inextensible material 114 to extensible material 112 in any given elastic fibril 106 is between 60-80%. Contemplated elastic materials 112 include but are not limited to silicone rubber, neoprene rubber, nitrile rubber, latex rubber, and the like. In some embodiments, membrane 108 is constructed from a similar elastic material. In some embodiments, membrane 108 is constructed from the same material as elastic material 112. Contemplated inextensible materials 114 include but are not limited to polyester, nylon, acrylic, cotton, carbon fiber, and the like. In some embodiments, inextensible material 114 is constructed from an elastic material having a higher tensile stiffness than elastic material 112. In some embodiments, segments of inextensible material 114 are embedded in a length of elastic material 112 to form a segmented elastic fibril 102. In some embodiments, a segmented elastic fibril 102 is formed from alternating segments of elastic material 112 and inextensible material 114 that are fused end to end. In some embodiments, a segmented elastic fibril 102 is formed from interwoven strands or fibers of elastic material 112 and inextensible material 114. In various embodiments, inextensible material 114 can be provided in the form of threads, strands, fibers, strips, cords, and the like.
Tensile jamming fiber 100 is depicted in
In the jammed state, tensile jamming fiber 100 comprises a high tensile stiffness while substantially maintaining a low bending stiffness, wherein the interior space of membrane 108 comprises a negative pressure such that membrane 108 compresses each segmented elastic fibril 106 against each other. In particular, interface regions 116 between overlapping segments of inextensible materials 114 generate a high shear force that resists tensile loads. In some embodiments, tensile jamming fiber 100 shortens in length in the jammed state. A jammed tensile jamming fiber 100 is highly inelastic and is configured to increase tensile stiffness to 20× of its unjammed tensile stiffness or greater. In some embodiments, a jammed tensile jamming fiber 100 is configured to increase bending stiffness to about 2× of its unjammed bending stiffness.
Each segmented elastic fibril 102 can be characterized by a loading fraction or a loading factor, wherein the loading fraction or factor is a percentage of a segmented elastic fibril 102 that comprises segments of inextensible material 114. Accordingly, a segmented elastic fibril 102 comprising a higher loading fraction or factor, and thereby a higher percentage of segments of inextensible material 114 and interface regions 116 of longer lengths, may have a higher tensile stiffness in an unjammed state and a higher tensile stiffness in a jammed state in comparison to a segmented elastic fibril 102 comprising a lower loading fraction or factor, and thereby a lower percentage of segments of inextensible material 114 and interface regions 116 of fewer lengths. In some embodiments, contemplated loading fractions or factors can be between about 5% and 95%, or about 50% and 90%, or about 70%.
Tensile jamming fiber 100 is configured to alternate between unjammed and jammed states by altering pressure within the interior space of membrane 108. As described above, fluid pumps connected to the one or more ports of membrane 108 enable rapid pressure changes to switch a tensile jamming fiber 100 between unjammed and jammed states within a fraction of a second, or at least within a tenth of a second. It should be understood that the manner in which a tensile jamming fiber 100 is switched between unjammed and jammed states may depend upon external environmental factors. For example, in environments where external pressure is low (e.g., shallow liquid depths, atmospheric pressure, and the like), tensile jamming fiber 100 may be in an unjammed state at rest and may be switched to a jammed state through the application of a negative pressure by fluid pumps connected to the one or more ports of membrane 108 and switched back to an unjammed state by releasing the negative pressure. In another example, in environments where external pressure is very high (e.g., deep ocean depths), tensile jamming fiber 100 may be in a jammed state at rest and may be switched to an unjammed state through the application of a positive pressure by fluid pumps connected to the one or more ports of membrane 108 and switched back to a jammed state by releasing the positive pressure.
In various embodiments, tensile jamming fiber 100 is configured to be switched between unjammed and jammed states under any tensile load. For example, an unjammed tensile jamming fiber 100 can comprise a first length at 0% strain and a second length at 100% strain or near 100% strain. Tensile jamming fiber 100 can be stretched to any length between the first length and the second length with a tensile load and can be jammed while under the tensile load to substantially fix the instant length of tensile jamming fiber 100.
In various embodiments, tensile jamming fiber 100 is configured to be switched to an intermediate state between unjammed and jammed states. For example, an unjammed tensile jamming fiber 100 having a zero or positive pressure within interior space of membrane 108 can comprise a minimum tensile stiffness and a jammed tensile jamming fiber 100 having a total or near total vacuum within interior space of membrane 108 can comprise a maximum tensile stiffness. In some embodiments, a negative pressure in interior space of membrane 108 is selected to tune a tensile stiffness of tensile jamming fiber 100 between the minimum tensile stiffness and the maximum tensile stiffness. In some embodiments, a negative pressure in interior space of membrane 108 is modulated over a period of time to vary a tensile stiffness of tensile jamming fiber 100.
In some embodiments, tensile jamming fibers 100 may include a system for controlling positive and negative pressures, or the inflow and outflow of air or other gas, into a plurality of tensile jamming fibers. For example, in certain embodiments the system may include a multiplexed arrangement of conduits in fluid communication with each tensile jamming fiber, and further may include one or more valves within the flow path to and from each tensile jamming fiber. Additionally, the system may include computing hardware and software programming/logic to control the output of each pressure source and/or the opening and closing of each valve in the system. In this manner, a plurality of tensile jamming fibers can be selectively jammed and unjammed in any combination with one or more pressure sources (e.g. vacuum pump). Accordingly, the system may include any sort of power source (battery or plug-in), microcontroller, microprocessor, computing device, or the like that is communicatively connected (wired or wirelessly) to each valves and each vacuum pump or other pressure source.
Tensile jamming fibers 100 are configured to be scalable to different sizes, both in diameter and length, and are configured to be adaptable to a variety of applications. For example, in some embodiments, tensile jamming fibers 100 may be attached to a harness or mechanical suit and function as artificial muscles, such that jammed tensile jamming fibers 100 may hold a position or hold a weight over prolonged periods of time without requiring input from a wearer or operator.
In some embodiments, tensile jamming fibers 100 may be attached to an actuator, such as in soft robotics. Referring now to
Tensile jamming fibers 100 may overlay, be integrated into, or otherwise layered with any sort of rigid, flexible and/or expandable or retractable surface or material. For example, such surfaces or materials may include but are not limited to natural or synthetic textiles, metal, glass, plastic, wood, composite materials, solid materials, or the like. In certain embodiments, tensile jamming fibers may be applied to fabrics and wearable as clothing, such as gloves, sleeves, shirts, pants, suits, socks, hats, elastic bands or the like. Microplexing conduit systems, one or more pressure sources (e.g. micropumps), power sources, microprocessors, controllers, computing equipment and any processing software or logic may additionally be integrated into the surfaces or materials, including wearable fabrics, as needed. Tensile jamming fibers may also be used as connectors between surfaces or objects. For example, the tensile jamming fibers may function as an extensible cord between two objects, where the distance between the two connected objects is shorter when the fibers are jammed, and larger when the fibers are unjammed. Likewise, in a jammed state, the fibers can be more highly resistive to forces pulling two connected objects away from each other, as opposed to an unjammed state.
As contemplated herein, the tensile jamming fibers and systems of the present invention may be used in various different applications without limitation. For example, tensile jamming fibers may be used in conjunction with virtual or augmented reality platforms. In such embodiments, a computing device incorporated into the wearable item may be communicatively connected to a separate virtual reality or augmented reality device and programming, such that the virtual reality or augmented reality device can instruct the computing device of the wearable item to initiate the jamming and unjamming of selected tensile jamming fibers in the fabric. In certain embodiments, the fibers may be incorporated into wearable fabrics and other items to provide resistance in human joints, and/or to provide haptic forces, sensations or feedback while a person or subject is wearing the gear. In some embodiments, the controlled pattern of jamming and unjamming fibers may create force feedback in users joints via changing stiffness of a garment, or whatever piece of equipment the tensile fibers are integrated with. In other embodiments, the tensile jamming fibers may be integrated into gloves to generate kinaesthetic communication or simulated three-dimensional touch sensations via the pattern of jamming and unjamming fibers within the glove. In other embodiments, the present invention may also be incorporated into medical devices, such as inclusion into steering mechanisms for catheters, probes and other insertion instruments for minimally invasive procedures. For example, having one tensile jamming fibers around the circumference or perimeter of the distal end of a catheter, cannula or guide wire may allow precise angulation in any desired direction by pulling a portion of the distal end via fiber jamming. In still other embodiments, the present invention may be incorporated into the end effector of a robotic arm, wherein the various movements of the end effector are generated by a pattern of jamming and unjamming one or more tensile jamming fibers.
In some embodiments, a wearable clothing item comprises a fabric material configured to cover at least a portion of a subject's body, a plurality of tensile jamming fibers as described herein, a pressure source fluidly connected to the plurality of tensile jamming fibers, and a power source electrically connected to the pressure source. In one embodiment the fabric material covers at least one joint of the subject's body. In one embodiment the fabric material forms a glove configured to fit on the subject's hand. In one embodiment, the wearable clothing item further comprises a computing device comprising at least one processor, wherein the computing device is communicatively connected to the pressure source and is configured to control the jamming and unjamming of each tensile jamming fiber. In one embodiment the computing device is communicatively connected to a virtual reality or augmented reality device.
The present invention relates in part to methods of fabricating tensile jamming fibers. As described elsewhere herein, tensile jamming fibers comprise two or more segmented elastic fibrils encased in an airtight and watertight membrane, wherein the two or more segmented elastic fibrils comprise alternating elastic and inelastic segments arranged such that inelastic segments of adjacent segmented elastic fibrils at least partially overlap.
Referring now to
It should be appreciated that methods of fabricating tensile jamming fibers are not limited to the method steps described above. For example, coating steps may also be accomplished through casting, molding, stamping, and the like. In various embodiments, further postprocessing steps are contemplated, including but not limited to trimming excess material, adding ports to the elastic membrane, attaching the tensile jamming fibers to an actuator, and the like.
The invention is now described with reference to the following Examples. These Examples are provided for the purpose of illustration only and the invention should in no way be construed as being limited to these Examples, but rather should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.
Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the present invention and practice the claimed methods. The following working examples therefore, specifically point out the preferred embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure.
The following study describes “tensile jamming fibers,” a system that rapidly modulates its tensile stiffness while maintaining low bending stiffness in all directions. Tensile jamming fibers are the first technology to occupy the desired range in
After affixing these jamming fibers to the surface of a single-chamber inflatable actuator, the local tensile stiffness is tuned to rapidly and predictably change its trajectory (
The materials and methods are now described.
Each segmented elastic fibril (SEF) had segments of polyester thread embedded discontinuously in a thin silicone substrate (EcoFlex 50, Smooth-On). Several SEFs were stacked and glued together on both ends with a silicone-based adhesive (Sil-Poxy, Smooth-On). A small amount of cornstarch was applied to the surfaces of SEFs to prevent adhesion of silicone. The bundle of SEFs was put inside a silicone membrane and sealed with Sil-Poxy. The detailed manufacturing process is depicted in
Quasi-static tensile testing of jamming fibers was done using an Instron 3345 material tester. For pull-to-failure and non-dynamic tensile tests, extension was applied at 20 mm/min. For three-point bending, compression was applied at 1 mm/min. For cyclic testing, extension was applied at 60 mm/min. Additional details and results regarding characterization are presented in the Supporting Information.
The omnidirectional actuators were made by first creating a silicone (EcoFlex 50, Smooth-On) membrane with embedded parallel polyester threads, and then wrapping the membrane into a cylinder, as described in previous work (Kim SY et al., Nature communications. 2019 Aug. 1;10 (1): 1-8). Jamming fibers were attached on the outside of this cylinder, at even spacing (every) 120°. A modular connection, made out of acrylic and Luer-lock connectors (51525K123 and 51525K213, McMaster-Carr), was added to each end of the cylindrical actuator using Silpoxy. For the gripper demonstration, three modules were attached to an acrylic plate, in a circular pattern (radius of 300 mm), at equal spacing) (120°. The continuum arm was manufactured by attaching two omnidirectional actuators in series and mounting the free end of one of them to a base plate. The shape-shifting membrane was fabricated by casting silicone (EcoFlex30, Smooth-On) in an acrylic mold (
The results are now described.
The technology underpinning tensile jamming fibers is the segmented elastic fibrils (SEFs). Two SEF architectures are developed, each consisting of different interspersed segments of polyester and silicone, labeled as “type A” and “type B” in
Tension tests were conducted on SEFs with varying polyester length percentages (γ) to understand how γ influences stiffness and maximum elongation before failure (
The tensile force (F) required to stretch a tensile jamming fiber to a prescribed displacement (δ) was found to be able to be tuned, and thereby the fiber's tensile stiffness (k=F/δ) by varying the magnitude of vacuum (ΔP) (
Other design parameters contribute to a tensile jamming fiber's effectiveness. A relationship was derived between k and design parameters including γ, vacuum pressure, and number of SEFs (N). The analytical model considers the interfacial shear stiffness (kshear) between SEFs as the primary contribution to the overall tensile stiffness (see
where a is the effective contact ratio (a fitting parameter to account for imperfect contact), G is the shear modulus of silicone (G=E/(2(1+v)), where E is Young's modulus and v is the Poisson ratio), A is the area of contact, and t is the thickness of the silicone under shear on one fibril. t is a function of the applied pressure, since pressure will squeeze and flatten the silicone in the linear elastic regime according to t (ΔP)=t0 (1−(ΔP)/E), where to is the initial thickness of the silicone interface. Since the shear interfaces are parallel, the total stiffness of the jamming fiber is the sum of kshear from all interfaces (SM: Eqs. 13-17).
In the model, SEF slippage that captures the non-linearity of the force-displacement response was also considered. Slip happens when the shear force in the interface exceeds the maximum static friction that can be sustained by the silicone interface between polyester threads in adjacent fibrils. After slip, some interfacial stress is relieved (SM: Eqs. 18 and 19).
With only three fitting parameters (effective contact ratio (a), shear area ratio (e), and coefficient of friction (u)), the model is able to predict the jamming behavior reasonably well. The model predicts that jamming fiber stiffness will increase with increasing γ, N, and ΔP. This prediction is consistent with uni-axial quasi-static tension tests conducted on jamming fibers while varying the same parameters (
Having quantified the influence of critical design variables on a jamming fiber's tensile stiffness, the reliability of the fiber jamming mechanism was evaluated in two ways. First, to assess how well the jammed fibers could induce the same actuator trajectory multiple times, a fiber was kept jammed and subjected to 1,000 cyclic tensile loads. After 1,000 cycles, the fiber retained over 70% of its original tensile force (dropping from 5.1 N to 3.6 N) (
To quantify the time scale of stiffness change in a jamming fiber, jamming was initiated partway through a tensile test while monitoring the mechanical response (see
To achieve multiple trajectories using a single actuator, three jamming fibers were integrated around the circumference of a modular, vertically-extending pneumatic chamber. By applying vacuum to subsets of the jamming fibers, the actuator could bend along various trajectories (
Analytical and finite-element (FE) models were used to predict the deformation trajectories of the single actuator outfitted with jamming fibers (
The angular deviation of the actuator's swept path was calculated from the intended path, which was to divide the hemisphere into twelve equal parts (
Jamming fiber-enabled modular variable-trajectory actuators can be combined to create agile, reconfigurable soft robots. The resulting systems have myriad deformation modes, enabled by the versatility and modularity of individual variable-trajectory actuators. To demonstrate potential applications for this principle, a multi-modal gripper and a multi-trajectory continuum arm were created (
To make a multi-modal gripper, three actuators (each equipped with three jamming fibers) were mounted in parallel to an acrylic base-plate (
In addition to the parallel configuration embodied by the gripper, two actuators were joined in series to create a continuum manipulator with seven controllable degrees of freedom (six fibers and one contiguous inflating core) (
The ability to adapt shape to environmental and developmental triggers is a core function of living beings, and a grand challenge for artificial machines (Shah D et al., Advanced Materials. 2021 May;33 (19): 2002882). Many studies, both those in simulation (Kriegman S et al., arXiv preprint arXiv: 1905.09264. 2019 May 22) and hardware (Shah DS et al., IEEE Robotics and Automation Letters. 2019 Feb. 27;4 (2): 2204-11; Ishida M et al., IEEE Robotics and Automation Letters. 2019 Jul. 25;4 (4): 4163-9; Shah DS et al., Nature Machine Intelligence. 2021 January;3 (1): 51-9; Lee DY et al., Soft robotics. 2017 Jun. 1;4 (2): 163-80; Lin HT et al., Bioinspiration & biomimetics. 2011 Apr. 26;6 (2): 026007; Liu K et al., Science Robotics. 2021 Apr. 7;6 (53)), attest to the benefits shape change confers on robots under changing task demands. Soft robots, in particular, hold promise as the next generation of shape-changing robots due to their capability to undergo large deformations. Inspired by botany (unfolding of flowers (Reyssat E et al., Journal of the Royal Society Interface. 2009 Oct. 6;6 (39): 951-7) and natural curling of seed pods (Armon S et al., Science. 2011 Sep. 23;333 (6050): 1726-30)), researchers have programmed thin, planar sheets to morph into complex surfaces through in-plane growth and out-of-plane buckling (van Rees WM et al., Proceedings of the National Academy of Sciences. 2017 Oct. 31;114 (44): 11597-602). Such an arrangement enables local control of the shape tensor, thereby giving rise to a rich diversity of shapes.
Current artificial shape-changing sheets-those made from composite hydrogels (Gladman AS et al., Nature materials. 2016 April; 15 (4): 413-8) or elastomers (Boley JW et al., Proceedings of the National Academy of Sciences. 2019 Oct. 15;116 (42): 20856-62), for example—often have only one programmed shape and a slow response time. Recent work on liquid crystal elastomer composite shape-morphing surfaces increased the number of possible deformations with a single system, but still required minutes to switch between shapes (Liu K et al., Science Robotics. 2021 Apr. 7;6 (53)). Fast shape-changing systems can be achieved by applying jamming fibers to planar inflatable geometries. The capability of the fibers to tune tensile stiffness on a higher magnitude than bending stiffness allows for effective redistribution of the elastic energy on the thin sheet between stretching and bending, thus effectively altering the resulting shape within seconds. Here, this concept was demonstrated by applying jamming fibers in a grid-like arrangement on each side of a planar pneumatic bladder (
The top and bottom faces of the bladder are connected by silicone pillars, preventing expansion through the thickness and creating a membrane that expands in-plane orthotropically (see
The qualitative deformation behavior of the bladder outfitted in jamming fibers is described well by FEA, while analytical methods reasonably predict deformation of the mid-plane. The local control of shape furnished by the jamming fibers is expected to propel the field of shape-morphing structures to the next level. As a demonstration of concept, a large-scale membrane with patterned jamming fibers was simulated and found to be able to morph to distinct and complex topologies contingent on the subsets of locally jammed fibers (
Pull-to failure tensile tests were conducted (20 mm/min using an Instron 3345 fitted with a 50 N load cell) on individual segmented elasticity fibrils (SEFs) to shed light on the behavior of jamming fibers containing that type of SEF. Six types of SEF, containing differing volume fractions of polyester), were studied: 0%, 60% type A, 60% type B, 70% type A, 70% type B, and 100%. Note that 0% and 100% were selected as control specimens-0% is pure elastomer; 100% is pure polyester thread. A force versus displacement plot of the tests (
Average elongation at failure was calculated from the force-displacement curves (
With an understanding of the mechanics of a single SEF, the fundamental unit that composes jamming fibers, next tested were the fibers themselves. To explore the design space for jamming fibers, unidirectional tensile tests were conducted on combinations of fiber parameters. In particular, three vacuum pressures (−10 kPa, −20 kPa, and −40 kPa), four different numbers of SEFs (N=4, 6, 8, 10), and two ratios of polyester (60% and 70%) were chosen-yielding a representative, though not comprehensive, range of designs. Each fiber used in the tensile tests was 120 mm long.
A set of tensile tests entailed a pull to 12 mm-what was deemed normal operational range for the jamming fibers. 10% strain represents a factor of safety from performance degradation. The test was stopped at 10% strain because it was empirically determined that after 20% strain, the performance of a fiber was markedly degraded. The mean jammed stiffness of each combination is reported in
In addition,
Pull-to-failure tests were performed on several specimens of the selected type (70% N8) to study the maximum elongation and force of the type of fiber at different pressures (
To evaluate the selected jamming fiber's behavior over a number of uses, two cyclic tensile tests were carried out at 60 mm/min displacement rates. Each cyclic test had max extension of 8 mm. In the first test, a fiber was jammed and subjected to 1000 cycles (
In the second cyclic test, three fibers were intermittently unjammed and jammed for 100 cycles and the change in force at each iteration was tracked (
Additionally, tension tests were performed at 20 mm/min to quantify the effect of suddenly transitioning from a jammed state to an unjammed state, and vice-versa. The tests sought to replicate a robotic application where changes to actuator trajectory occur mid-inflation. Three trials on different specimens, corresponding to different jammed pressures, were conducted (
From these jamming transition tests, it was observed that the extent of pre-strain does not significantly influence the resultant force experienced by the fiber. In fact, there is less than 5% difference in maximum force sustained by any of the pressure cases between a and b. However, pre-strain does make the silicone material stiffer due to non-linearity of the elastomeric material and explains the slightly higher final force in the case with pre-strain (
Lastly, 3-point bending tests were conducted on tensile jamming fibers to assess the change in bending modulus between the jammed and unjammed states. Three specimens were tested in both jammed and unjammed states, and at 0 and 90-degree rotations, recording force and displacement (Instron 3345 fitted with a 10 N load cell). The supports on the two ends are separated by 4 cm. Displacement was applied in a quasi-static regime at 40 mm/min. Each specimen was subjected to −80 kPa when jammed. A linear fit of the force displacement curves indicates that bending stiffness (slope of a fitted line) increases by approximately 2-fold when jammed compared to unjammed (
To understand the relationship between key design parameters and the jammed stiffness of the fibers, a minimal mechanical model was constructed. The purpose of the model is twofold. First, it is not tractable to manufacture tensile jamming fiber specimens to test all possible combinations of parameters in the design space, so an analytical model helps depict the general trend of stiffness change when different parameters are tuned. Second, the model can be used to estimate a suitable range of stiffnesses for a jamming fiber to accomplish a set of tasks, effectively providing a lightweight design tool.
Before the derivation, some preliminaries are stated. The individual segmented elastic fibril (SEF) is referred to simply as “fibril” for the rest of this section. The model only considers two fibrils and their shared interface for simplicity of analysis, but at the end of this section, it is proposed how the model could be generalized to include more fibrils. It is assumed that tensile forces are all in-line, due to the fact that the length of the fibril is much greater than its width or height. Polyester and silicone are the two materials in the fibril. Since the Young's modulus of polyester is much larger than that of silicone, it is further assumed for polyester to be inextensible.
In the unjammed state, it is assumed there is no contact between fibrils. Since polyester is treated as inextensible, the jamming fiber's stiffness in the tensile direction is a function of only the stiffness of silicone segments in each fibril (ks) as well as in the surrounding membrane (km). In the jammed state, the fibrils are compressed together by uniform external pressure (ΔP). Thin interfaces form between overlaps of polyester-polyester, polyester-silicone, and polyester-membrane segments; shearing of these interfaces, when pulled, contributes additional stiffness terms (kpp, kps, and kpm, respectively). See the schematic in
These various stiffness terms are defined using material properties and dimensions of fibrils. The tensile stiffness of a single fibril (ks) is modeled as linear:
where E is the Young's modulus of silicone, L is the total length of the fibril, Ac is the cross-section area of that fibril (Ac=d2, assuming square shaped cross-section), and γ is the loading factor (length percentage of the fibril that is polyester). The tensile stiffness of a membrane (km) is likewise modeled as linear:
where Am is the cross-sectional area of the silicone membrane.
The shear interfaces are modeled as Bingham plastics—a nonlinear spring that is linear with displacement until reaching a maximum constant force. The nonlinear behavior arises due to slip, which will be discussed later. Before slip, the slope of the linear region of these springs is simply the shear stiffness of the thin silicone interfaces: kpp, kps and kpm.
The pre-slip shear stiffness of the polyester-polyester interface reads as:
where a is the effective contact ratio (a fitting parameter to account for imperfect contact), G is the shear modulus of silicone
where v is the Poisson ratio), App is the area of shear between polyester and polyester (App=Lppd), and t is the thickness of the silicone under shear on one fibril. This thickness is a function of the applied pressure, since pressure will squeeze and flatten the silicone. Thickness is also represented with a linear elastic model:
where to is the initial thickness of the silicone interface. The shear stiffness of the polyester-silicone interface can be written as:
where Aps is the area between polyester and silicone spring (Aps=Lpsd), t is the same as in Eq. 6, and e is a parameter to account for the fact that not all the area between polyester and the silicone spring is under shear (e≤1). Lastly, the shear stiffness of the polyester-membrane interface is defined as:
where Apm is the area of shear between polyester and silicone membrane (Apm=Lpmd).
Collections of fibrils within the jamming fiber were modeled as springs in parallel, together with the external membrane. For the system of fibrils in the unjammed state, the only stiffness contributions are ks and km. Thus, the unjammed stiffness of the system is:
where N is the number of fibrils in the fiber. Note that neither the membrane dimensions nor its material composition are varied in the present study, so km is a constant.
In the jammed state, stiffness arising from all the interfaces as well as from the silicone spring and membrane are considered (see
This long expression can be simplified based on the observation that kpm and kpp are much larger quantities than ks and kps (for example, for one sample, ks=2:28 and kps=115:26, while kpp and kpm are over 1000.) By eliminating terms with ks and kps from Eq. 10:
To generalize to jamming fibers with N>2, it is observed that, under single stacking, each additional fibril increases the total number of polyester-polyester interfaces by one. Since these interfaces are in parallel, the kpp term can simply be multiplied by the number of interfaces, z=N−1.
The expression can further be simplified by observing that kpm and kpp are approximately equal, as they are both shear stiffnesses of thin silicone: kpm≈kpp≈Kshear. Eq. 12 thus simplifies to:
Plugging in some numbers for n and p into the expression above elucidates a general trend:
Namely, the model predicts higher stiffness with increased number of fibrils, which the experiments confirmed.
So far, stiffness of the jammed fiber has been considered before slip. Slip happens when the shear force in the interface exceeds the maximum static friction that can be sustained by the silicone interface between polyester threads in adjacent fibrils. The maximum force is defined as:
where u is the coefficient of static friction. After slip, the kpp term vanishes in Eq. 10. The stiffness reduces to:
In
The root-mean-square deviation of the model prediction from the experimental results in
Overall, the presented minimal analytical model predicts a larger stiffness for higher number of fibrils, higher pressure, as well as a higher polyester content (higher tensile stiffness for fibrils), which were also observed in the experimental results (
Here, the equilibrium center line ∈
3 is attained by cylindrical thin-walled inflating elastomeric actuators radially outfitted in jamming fibers. Selected are a number of segments i=1 . . . n, an input pressure P for each segment, the number of SEFs on each segment j=1 . . . q, radial locations of jammed fibers for each segment θij, and initial undeformed geometry (i.e. radius, R, wall thickness, T, length L).
Consider radially-constrained cylindrical pneumatic actuators outfitted in jamming fibers along their length such that input pressure P elicits only longitudinal stretch M, curvature K, if applicable, and negligible radial stretch 22. It is assumed that k appears only in the kinematics, and therefore not as a coupled energetic contribution with stretching. The actuators have small thickness relative to their radii (i.e., R>10T).
To predict the deformation of an inflating actuator, a hyper elastic constitutive model is first derived mapping P to A. For the inflating actuator, B=FFT is the left Cauchy-Green deformation tensor and F is the deformation gradient. Assuming the elastomeric material which
it is made from is incompressible gives
The N-term strain energy density of a deformed elastomer is:
Here, μp and αp are fitting constants. Evoking the assumption of incompressibility:
The Cauchy stress tensor may be found from W by the following:
where p is an undetermined hydrostatic pressure to be found using the boundary conditions, and δij is the Kronecker delta. Pure homogeneous deformation is considered to be associated with uniaxial tension which makes F diagonal. Thus, the expression for Cauchy stress simplifies to:
By substituting W into the expression above:
For uniaxial tension, σ2 and σ3=0, so:
From the boundary conditions given above, the unknown hydrostatic pressure can be solved as:
Finally, plugging p to the expression for σ1 gives:
Modeling the cylinder as a thin-walled pressure vessel, by Laplace's law:
Note, the capital variables R; T specify the undeformed configuration, while r; t denote the deformed configuration of the actuator. Yet r=R due to the radially constraining fibers. Since volume is conserved in the incompressible material,
Plugging in Eq. 26 to Eq. 25 and re-arranging gives:
Inflating in a quasi-static regime, Eq. 27 was able to be fit for N=2 to experimental data of P versus λ1 via a least-squares method in MATLAB. The adjusted R2 value for the fit was 0.984. The two-term Ogden model parameters are tabulated as follows: α1=1.915; α2=3.019; μ=3.842; μ 2=−0.3533.Utilizing Eq. 27, a given input P may be mapped to λι. Assuming that jamming fibers, when jammed, are completely inextensible, induced bending of the actuator is assumed to be of a constant K. θij of the jamming fibers determines d1, the direction of curvature, of the ith segment. Three distinct cases are considered for the direction of curvature based on empirical observations: 1) If only one fiber is jammed, curvature is assumed to occur circumferentially aligned with the jammed fiber; 2) if multiple but not all fibers are jammed, curvature is assumed to occur as the geometric midpoint about the circumference of the actuator between jammed fibers (for example, if there are jamming fibers on segment 1 at two locations θ1.1=π/2 and θ1.2=π, bending occurs at the angle @1=3π/4); 3) if jammed fibers are directly opposite one another or all fibers are jammed, then no extension will occur. To find the value of κ, λ1 is used, by projecting onto the plane of curvature and evoking the relation:
To account for n cylindrical segments placed in series to form continuum manipulators, the P to λ1 relationship is applied to each individually. Relative positions of segments are accounted for via homogeneous transformation matrices. Construction of possible D for arbitrary design parameters is thus achieved. Quantitatively, the analytical model tended to under-predict the extent of deformation in actual systems, suggesting that it is a conservative estimate of the actuator's capabilities. However, it captures deformations within a reasonable margin of error (
The minimal analytical model allows for simple prediction of how changing the relative radii of the actuator to jamming fiber would influence deformation. By Eq. 27, for a fixed input pressure, decreasing R will consequently decrease o. The decrease in o will correspond to a decrease in axial stretch (2) given by a nonlinear relationship defined by the two-term Ogden hyper elastic model. The decrease in A correspondingly reduces the curvature defined in Eq. 29. In
Here, possible shapes that can be elicited by inflating a planar, membrane-like surface with jamming fibers on either side are considered. An approximate model of the system gives insight into the rapid, localized shape change that can be demonstrated. The membrane is approximated as a bilayer system with each layer having equal thickness. Findings from non-Euclidian plates are leveraged, as well as incompatible elasticity theory (Efrati E et al., Physical Review E. 2009 Jul. 10;80 (1): 016602; Efrati E et al., Journal of the Mechanics and Physics of Solids. 2009 Apr. 1;57 (4): 762-75), the 3D problem is treated in a dimensionally-reduced fashion. Namely, the membrane is modeled as a 2D mid-plane surface. In differential geometry, 2D surfaces may be fully characterized by two tensors: a metric tensor, (the first fundamental form) a, which contains all information about lateral distances between points, and a curvature tensor, b, (the second fundamental form) which contains information about the local curvatures (Struik DJ. Lectures on classical differential geometry. Courier Corporation; 1961). An elastic sheet is characterized by two additional tensors: a natural metric a, and the natural curvature b. These tensors represent the lateral distances and curvatures that would make the sheet locally stress-free (Klein Y et al., Science. 2007 Feb. 23;315 (5815): 1116-20).
The constrained membrane system, when inflated, is hypothesized to deform so as to minimize the sum of its elastic bending and stretching energies. The total elastic energy of an incompatible non-Euclidean plate is given by (Klein Y et al., Science. 2007 Feb. 23;315 (5815): 1116-20):
Here, v is the Poisson ratio (assumed at 0.5), and h is the thickness of the bilayer system. The first addend of the energy term corresponds to stretching energy and the second to bending energy. Expressions for the natural metric and curvature tensors read as:
Here, Δ0,i and k0.i are mid-plane stretch and curvature of a fictional 1D bilayer beam cut from the 2D bilayer surface in principal direction i. A 1D beam cut from the surface can satisfy the deformation behaviors of individual layers of the bilayer when adhered together, while the 2D system cannot, since it is incompatible. Mid-plane stretch and curvature of the fictional beam can be computed analytically as (Timoshenko S, Analysis of bi-metal thermostats. Josa. 1925 Sep. 1;11 (3): 233-55):
where λtb is the stretch of the top layer relative to the bottom layer in a given principal direction, n is the ratio of moduli of top to bottom layer, and m is the ratio of thickness of top to bottom layer. In this case, m and n=1 since the layers are made of the same material and have the same thicknesses.
The exact orientation of the jamming fibers on either side of the membrane surface will govern the way it deforms when inflated, and result in different equilibrium surfaces. It is assumed that any fibers placed on the membrane act as a homogeneous composite and that the strain gradient across the surface is zero. Three distinct cases of fiber orientation are considered: 1) One side with 90°+0° and the other with 0° or 90° will elicit a cylindrical shape; 2) One side with 90°+0° and the other unconstrained (isotropic growth) will elicit a hemispherical cap shape at lower stretch; 3) Sides with orthogonal activated jamming fibers will exhibit a saddle-like shape.
For case 1, bending is only along one axis, resulting in zero Gaussian curvature. Natural tensors a and b will have only one non-zero diagonal entry each. The problem is thus reduced further to a one-dimensional case in the principal direction of interest, analogous to the classical bimetallic thermostat of Timoshenko (Timoshenko S, Analysis of bi-metal thermostats. Josa. 1925 Sep. 1;11 (3): 233-55). Due to reduction to a 1D beam, relations Eq. 31 and Eq. 32 may be used to compute the resulting midsurface shape.
Cases 2 and 3 are a bit more complicated, since both stretching and bending energy terms compete to inform the equilibrium shape. For case 2, following the example presented in work by Pezzulla et al. (Soft matter. 2016;12 (19): 4435-42), the total energy can be minimized, consisting of the sum of stretching and bending energies given by Eq. 29. Note that before the bifurcation regime exhibited by spherical caps wherein bending becomes energetically favorable over stretching, the natural metric does not diverge much from the metric (Pezzulla M et al., Soft matter. 2016;12 (19): 4435-42). Thus it can be assumed that a=d. Natural tensor b will have two equal non-zero diagonal entries. Generic entries of the second fundamental form read as:
and note that M=0; L=N due to the emergence of symmetric, hemispherical cap. Minimization of the energy in Eq. 29 with respect to L gives analytic relation that can be solved for a single value of L as a function of the non-dimensionalized natural curvature k0:
where the hats indicate non-dimensionalization of the term by 1/h and γ is a dimensionless, shape-dependent parameter (Pezzulla M et al., Soft matter. 2016;12 (19): 4435-42).
Case 3 is tackled by similar energetic arguments as case 2. Natural tensors a and b will have only two non-zero diagonal entries of equal magnitudes, while the natural curvature tensor has entries with opposite-signed values. Fundamental forms of an energetically equivalent monolayer for case 3 are presented eloquently as (van Rees WM et al., Proceedings of the National Academy of Sciences. 2017 Oct. 31; 114 (44): 11597-602):
here, λ is the midplane stretch of the bilayer system.
Using the first and second fundamental forms, the principal curvatures of a surface can be found by solving (Struik DJ. Lectures on classical differential geometry. Courier Corporation; 1961):
The Gaussian curvature and mean curvature are then, respectively:
Since homogeneous fiber distribution is assumed in a given principal direction, local buckling of material between each fiber and thereby much of the topographical nuance of the physical systems are not captured. Furthermore, this simplified model does not account for variations in in-plane strain across the surface. Despite the mechanical simplifications, qualitatively, predictions from this minimal model of jamming-fiber clad membrane midplanes matches the corresponding experiments (
To validate the experiments with a higher degree of fidelity than analytical methods, finite element analysis (FEA) simulations were performed in a commercial software package (ABAQUS). Nonlinear quasi-static analyses considering gravity were performed.
The cylindrical actuators of
Nonlinear quasi-static analysis was performed in ABAQUS/Explicit to simulate the shape deformation of the circular membrane of
The ability to actively tune stiffness is critical to devising next-generation robots that replicate the control and fluidity of biological organisms' motions and shape changes. In lieu of traditional approaches that rely on strain-limiters with immutable material properties, the present study introduces controllable tensile strain-limiters. Jamming fibers combine the desirable features from many different existing stiffness modulation techniques, such as state-of-the-art jamming and thermally activated variable stiffness materials. Jamming fibers exhibit dramatic tensile stiffness changes, rapid response times, minimal contribution to system bulk properties or weight, and highly isolated material changes. They stand in contrast to thermal stiffness-changing systems, where heat diffusion leads to undesired local interference, and stretchable layer jamming, where bending stiffness and tensile stiffness are coupled. At atmospheric pressure, the jamming fibers stretch with low tensile stiffness, having little influence on the trajectory of an actuator. When vacuum is applied, the jamming fibers' tensile stiffness increases by over 20× in less than a tenth of a second, imposing strong directional bias while retaining flexibility in bending.
Tensile jamming technology demonstrates far-reaching potential in soft robotics, enabling great improvements to the workspaces of single-chamber, volumetrically expanding soft actuators, without adding large volume or inducing high bending stiffness. With rapid response and an ability to influence actuator dynamics mid-inflation, such multi-modal actuators are more responsive in applications compared to thermally-activated strain-limiting components and safer for human-oriented applications than high voltage-activated clutches. This improvement in control of trajectories without undesired increases in volume is especially relevant for applications where the cross-sectional area of the actuator needs to be minimized, such as in endoscopic minimally invasive surgery. The radially-constrained single-chamber actuator, with small-footprint 1D elements (tensile jamming fibers), can potentially be made more slender than current multi-chamber actuators (Elsayed Y et al., Soft Robotics. 2014 Dec. 1;1 (4): 255-62; Runciman M et al., Soft robotics. 2019 Aug. 1;6 (4): 423-43) and avoid the large radial expansion needed for multi-chamber actuators to achieve bending.
In the surface (2-dimensional) cases, varying tensile stiffness (coupled with underlying inflation) allows control of Gaussian curvature. The result is the first demonstration of active transition between three types of Gaussian curvatures-on the order of seconds-within the same system. The ability of the tensile jamming fibers to increase tensile stiffness while maintaining a low bending stiffness enables a redistribution between bending energy and stretching energy for the thin surface, which facilitates dramatic shape change. Theoretically, with sufficient number of jamming fibers, an inflating 2D sheet can grow into any target surface (van Rees WM et al., Proceedings of the National Academy of Sciences. 2017 Oct. 31;114 (44): 11597-602), and then change between such shapes. This demonstration paves the way for next-generation shapeshifting robots with ability to adapt to environmental demands and adopt shapes for dynamic camouflage.
Beyond the robotics space, jamming fibers are a useful technology in exosuit-assisted rehabilitation, where selective mobility is tantamount to patient recovery. Additional possible use cases include on-demand sizing for smart garments, and other applications where predictable, rapid, and localized tensile stiffness changes are desired.
In some aspects of the present invention, software executing the instructions provided herein may be stored on a non-transitory computer-readable medium, wherein the software performs some or all of the steps of the present invention when executed on a processor.
Aspects of the invention relate to algorithms executed in computer software. Though certain embodiments may be described as written in particular programming languages, or executed on particular operating systems or computing platforms, it is understood that the system and method of the present invention is not limited to any particular computing language, platform, or combination thereof. Software executing the algorithms described herein may be written in any programming language known in the art, compiled or interpreted, including but not limited to C, C++, C#, Objective-C, Java, JavaScript, MATLAB, Python, PHP, Perl, Ruby, or Visual Basic. It is further understood that elements of the present invention may be executed on any acceptable computing platform, including but not limited to a server, a cloud instance, a workstation, a thin client, a mobile device, an embedded microcontroller, a television, or any other suitable computing device known in the art.
Parts of this invention are described as software running on a computing device. Though software described herein may be disclosed as operating on one particular computing device (e.g. a dedicated server or a workstation), it is understood in the art that software is intrinsically portable and that most software running on a dedicated server may also be run, for the purposes of the present invention, on any of a wide range of devices including desktop or mobile devices, laptops, tablets, smartphones, watches, wearable electronics or other wireless digital/cellular phones, televisions, cloud instances, embedded microcontrollers, thin client devices, or any other suitable computing device known in the art.
Similarly, parts of this invention are described as communicating over a variety of wireless or wired computer networks. For the purposes of this invention, the words “network”, “networked”, and “networking” are understood to encompass wired Ethernet, fiber optic connections, wireless connections including any of the various 802.11 standards, cellular WAN infrastructures such as 3G, 4G/LTE, or 5G networks, Bluetooth®, Bluetooth® Low Energy (BLE) or Zigbee® communication links, or any other method by which one electronic device is capable of communicating with another. In some embodiments, elements of the networked portion of the invention may be implemented over a Virtual Private Network (VPN).
Generally, program modules include routines, programs, components, data structures, and other types of structures that perform particular tasks or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the invention may be practiced with other computer system configurations, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, minicomputers, mainframe computers, and the like. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote memory storage devices.
The storage device 2220 is connected to the CPU 2250 through a storage controller (not shown) connected to the bus 2235. The storage device 2220 and its associated computer-readable media, provide non-volatile storage for the computer 2200. Although the description of computer-readable media contained herein refers to a storage device, such as a hard disk or CD-ROM drive, it should be appreciated by those skilled in the art that computer-readable media can be any available media that can be accessed by the computer 2200.
By way of example, and not to be limiting, computer-readable media may comprise computer storage media. Computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, DVD, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computer.
According to various embodiments of the invention, the computer 2200 may operate in a networked environment using logical connections to remote computers through a network 2240, such as TCP/IP network such as the Internet or an intranet. The computer 2200 may connect to the network 2240 through a network interface unit 2245 connected to the bus 2235. It should be appreciated that the network interface unit 2245 may also be utilized to connect to other types of networks and remote computer systems.
The computer 2200 may also include an input/output controller 2255 for receiving and processing input from a number of input/output devices 2260, including a keyboard, a mouse, a touchscreen, a camera, a microphone, a controller, a joystick, or other type of input device. Similarly, the input/output controller 2255 may provide output to a display screen, a printer, a speaker, or other type of output device. The computer 2200 can connect to the input/output device 2260 via a wired connection including, but not limited to, fiber optic, ethernet, or copper wire or wireless means including, but not limited to, Bluetooth, Near-Field Communication (NFC), infrared, or other suitable wired or wireless connections.
As mentioned briefly above, a number of program modules and data files may be stored in the storage device 2220 and RAM 2210 of the computer 2200, including an operating system 2225 suitable for controlling the operation of a networked computer. The storage device 2220 and RAM 2210 may also store one or more applications/programs 2230. In particular, the storage device 2220 and RAM 2210 may store an application/program 2230 for providing a variety of functionalities to a user. For instance, the application/program 2230 may comprise many types of programs such as a word processing application, a spreadsheet application, a desktop publishing application, a database application, a gaming application, internet browsing application, electronic mail application, messaging application, and the like. According to an embodiment of the present invention, the application/program 2230 comprises a multiple functionality software application for providing word processing functionality, slide presentation functionality, spreadsheet functionality, database functionality and the like.
The computer 2200 in some embodiments can include a variety of sensors 2265 for monitoring the environment surrounding and the environment internal to the computer 2200. These sensors 2265 can include a Global Positioning System (GPS) sensor, a photosensitive sensor, a gyroscope, a magnetometer, thermometer, a proximity sensor, an accelerometer, a microphone, biometric sensor, barometer, humidity sensor, radiation sensor, or any other suitable sensor.
The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by others skilled in the art without departing from the true spirit and scope of the invention.
This application claims priority to U.S. provisional application No. 63/250,402 filed on Sep. 30, 2021, incorporated herein by reference in its entirety.
This invention was made with government support under Grant Nos. 1830870 and 1333468 awarded by the National Science Foundation. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2022/077370 | 9/30/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63250402 | Sep 2021 | US |
