Abstract:
Reconfigurable, expandable-collapsible structures based upon negative Poisson&#39;s ratio (NPR) auxetic unit cells achieve rapidly deployable apparatus, devices and systems. A plurality of joint bodies, each joint body having a plurality of connection features, are coupled to interconnecting link members with opposing ends, each end including connection features that engage with the connection features of the joint bodies. The link members pivot about different axes relative to the joint bodies, thereby forming an expandable and collapsible structure having a height and a width. The link members form an array of geometric unit cells when the structure is expanded, and the height and the width of the structure when expanded are both greater than the height and the width of the structure when collapsed. In certain embodiments the structures have unit cells based upon triangles or bowtie shapes.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Provisional Patent Application Ser. No. 61/546,834, filed Oct. 13, 2011, the entire content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to negative Poisson&#39;s ratio (NPR) auxetic structures and, in particular, to rapidly deployable apparatus, devices and systems based upon these structures. 
       BACKGROUND OF THE INVENTION 
       [0003]    People have long been fascinated with structures and forms which are easily collapsible and/or readily expandable. A pioneer in this field is Chuck Hoberman, now affiliated with Hoberman Associates. Hoberman holds several U.S. patents relating to ‘reversibly expandable structures,’ including radially expanding trusses. Hoberman&#39;s initial patents dealt with transformability in structures. In 2008, Hoberman founded Adaptive Building Initiative with Buro Happold to design rapidly transformable buildings, which led to the construction of the POLA Ginza Building&#39;s adaptive façade in 2009. Three more of Hoberman&#39;s adaptive shading installations were constructed in 2010, including the Aldar Central Market, the Wyss Institute at Harvard, and the Simons Center at Stony Brook University. 
         [0004]    Johnson Outdoors of Racine, Wis., a manufacturer of tents for both government and consumer markets, approached Hoberman Associates in 2005 to develop a new line of large shelters for military use and crisis relief. This led to the development of Rapidly Deployable Shelters (RDS) under Johnson&#39;s Eureka brand. With easier deployment and minimal time-consuming secondary connections, the RDS system uses fewer, larger, and more robust parts than competitive products. The RDS comes in several sizes, the largest of which deploys to 750 square feet, and folds down to a 3 foot by 3½ foot by 6 foot compact bundle. 
         [0005]    U.S. Pat. No. 7,644,721 to Hoberman et al. is directed to tents and the provision of temporary shelter. The particular problem addressed in the patent relates to extensible tong linkages, sometimes referred to as scissor linkages which are used to construct transformable truss-structures in a variety of shapes. While such scissor linkages are effective in creating structures that deploy or transform, once the structure is deployed, they are less effective in providing an optimum structural system. This is due to the fact that the “structural depth” of a scissor linkage varies widely. In some places, there is significant distance between its links while in other places, both links overlap such that there is no depth provided beyond the individual link dimensions. This results in a basic structural inefficiency. Such inefficiency can limit the structural span, lead to increased weight, and prevent efficient packaging. 
         [0006]    The &#39;721 patent describes a system based on parallel, four-bar linkages. The invention relates to means of connecting series of four-bar linkages together such that they provide a structural truss in their extended state, provide a compact package in their retracted state, and move together in a synchronized fashion. The mechanism is comprised of two or more four-bar linkages wherein each linkage shares a common link with each adjacent linkage and the movement of said two or more linkages is synchronized by mechanical means such that said mechanism may move between a collapsed and an extended state. The mechanical means may be in the form of additional links or geared connections. The patent further discloses means to cause the mechanism, when in its extended state, to become stiff and structural. Fabric elements may be attached to these mechanisms to form rapidly deployable shelters. 
         [0007]    Another commercially available rapidly deployable shelter is called DRASH (Deployable Rapid Assembly Shelter), a portable, geodesic shelter that can be set up within minutes of arriving on site with no special tools. The system is manufactured and sold by DHS Systems LLC (Orangeburg, N.Y.). The structures, which are supported by composite struts, have footprints from 109 sq ft (10.1 m 2 ) up to 1,250 sq ft (116 m 2 ). Each DRASH shelter comes with flooring and ground covers manufactured from polyester and nylon to U.S. military standards. DRASH also provides generators and trailers plus various accessories for the shelters themselves. For transport or storage, the shelters pack down to less than 2% of its deployed size into a transport bag that can be stowed on a trailer or HMMWV. Teams of four to six can easily erect a shelter simply by pulling on the sides of the shelter and raising the shelter in designated “push points” on the shelter. 
         [0008]    The above examples are only a few of many more in the field of rapidly deployable structures, shelters, tents and other temporary or emergency dwellings. Other examples include, for example, inflatable components. 
         [0009]    Commonly assigned U.S. Pat. No. 7,910,193, relates to negative Poisson&#39;s ratio (NPR) or auxetic structures and, in particular, to three-dimensional auxetic structures and applications thereof. Poisson&#39;s ratio (ν), named after Simeon Poisson, is the ratio of the relative contraction strain, or transverse strain (normal to the applied load), divided by the relative extension strain, or axial strain (in the direction of the applied load). Some materials, called auxetic materials, have a negative Poisson&#39;s ratio (NPR). If such materials are stretched (or compressed) in one direction, they become thicker (or thinner) in perpendicular directions. 
         [0010]    NPR structures can react differently under applied loads. One possibility is a reactive shrinking mechanism, obtained through a topology optimization process. The unique property of this structure is that it will shrink in two directions if compressed in one direction. Auxetic and NPR structures have been used in a variety of applications. Heretofore, however, such structures have not been exploited for use in rapidly deployable shelters and components used in such structures. 
       SUMMARY OF THE INVENTION 
       [0011]    This invention relates generally to negative Poisson&#39;s ratio (NPR) auxetic structures and, in particular, to rapidly deployable apparatus, devices and systems based upon these structures. An expandable-collapsible structure constructed in accordance with the invention includes a plurality of joint bodies, each joint body having a plurality of connection features. A plurality of interconnecting link members are provided with opposing ends, each end including connection features that engage with the connection features of the joint bodies such that the link members pivot about different axes relative to the joint bodies, thereby forming an expandable and collapsible structure having a height and a width. The link members form an array of geometric unit cells when the structure is expanded, and the height and the width of the structure when expanded are both greater than the height and the width of the structure when collapsed. 
         [0012]    In preferred embodiments, some of the interconnecting link members form parallel, straight lines when the structure is expanded. For example, structures having unit cells based upon triangles or bowtie shapes for substantially straight, parallel lines when expanded. In such embodiments, the interconnecting link members have side edges which are proximate to one another or touching only when the structure is collapsed. 
         [0013]    The interconnecting link members may be rigid or flexible; straight or curved, and may have uniform or varied cross sections. The joint bodies with connection features and pivot axes may be arranged on different levels or planes. The structure may further include a flexible sheet of material adhered to the joint bodies, link members, or both, thereby forming a covered panel when the structure is expanded. The material may be waterproof or weather-resistant, and the panels may be configured to form a building, tent, shelter, storage unit, mobile house, vehicle body or other enclosure. 
         [0014]    A joint in general may have one or multiple layers refer to different levels or planes. Possible examples include one-layer, two-layer, three-layer and four-layer joints with the understanding that additional levels are possible with sufficient stepped outer profiling. Each layer of the joint may have multiple axles with different (including same) axial directions defined by the axis angles. Each of the joint bodies may utilize any number of different joint types; for example, joint types having male-female, female-female, female-male and male-male interconnection configurations, various clicking joints, and different types of pin connections. 
         [0015]    The connection features may include posts or projections, with holes or recesses being configured to receive the posts or projections. Alternatively, the connection features may comprise pins disposed along the pivot axes. The ends of the link members may include two arms with connection features, enabling the arms are temporarily spread apart to engage with the connection features on the joint bodies, resulting in “snap-in” connections. 
         [0016]    The link members form an array of geometric unit cells having a periodicity when the structure is expanded, and the periodicity may vary in one or more dimensions. The number of unit cells within a layer of unit cells may define a height of that layer, with the height being the same or different with respect to different layers. The unit cells may also define a width when the structure is expanded, with the width being uniform or variable in one or more dimensions. The link members may be constructed from metals, ceramics, fiber-reinforced composite materials, polymer matrix materials, plastics, or fibers. The structure may further include foam or other filler material surrounding the link members. The structure has an outermost surface when expanded, and the outermost surface may be cylindrical or curved in one or more dimensions. The link members have cross sections, and the cross sections may define solid or hollow rods or tubes, flat or curved plates or strips, or U-shaped, T-shaped, V-shaped or I-shaped beams. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  illustrates a collapsible panel based upon a “nested-V” auxetic structure in and expanded form; 
           [0018]      FIG. 2  show the panel of  FIG. 1  in a collapsed state; 
           [0019]      FIG. 3  is a detailed diagram which better illustrates the way in which unit cells according to the invention are constructed and how they interact; 
           [0020]      FIG. 4A  is a detailed, oblique drawing of a joint body; 
           [0021]      FIG. 4B  illustrates the way in which connecting members attach to a joint body; 
           [0022]      FIG. 4C  shows a plurality of interconnecting members coupled to the joint body of  FIG. 4A ; 
           [0023]      FIG. 5  depicts the way in which interconnecting members may snap into a joint body; 
           [0024]      FIG. 6  illustrates the progressive expansion of a V-type auxetic panel; 
           [0025]      FIG. 7  shows an auxetic panel based upon a X- or “bowtie”-shape type of unit cell; 
           [0026]      FIG. 8  depicts the nested-V cell used in a cylindrical configuration to construct a honeycomb auxetic beam; 
           [0027]      FIG. 9A  shows an expanded auxetic beam having a square cross section; 
           [0028]      FIG. 9B  shows an expanded auxetic beam having a hexagonal or honeycomb cross section; 
           [0029]      FIG. 9C  shows an expanded auxetic beam having an octagonal cross section; 
           [0030]      FIG. 9D  shows an expanded auxetic beam having a 10-sided cross section; 
           [0031]      FIGS. 10A-10C  illustrate a mean unfolding mechanism that may be used to form curved beams to construct a tent or other structure; 
           [0032]      FIG. 11  illustrates the unfolding of an X-type auxetic beam; 
           [0033]      FIG. 12  shows a curved expandable beam with variable NPR cells along a circular cross section; 
           [0034]      FIG. 13  depicts how a curved tube may be achieved by distributing variable NPR cells around a form having a circular cross section; 
           [0035]      FIG. 14A  is a top view of an alternative N-axle joint body; 
           [0036]      FIG. 14B  is a side view of the joint body of  FIG. 14A  showing how M layers may be provided; 
           [0037]      FIG. 15  shows joint types having male-female, female-female, female-male and male-male interconnection configurations; 
           [0038]      FIG. 16  illustrates a first set of possible clicking joints; 
           [0039]      FIG. 17  illustrates a second set of possible clicking joints; 
           [0040]      FIG. 18  illustrates different types of pin connection features; 
           [0041]      FIG. 19  shows examples of one-layer joints; 
           [0042]      FIG. 20  shows examples of two-layer joints; 
           [0043]      FIG. 21  depicts joint bodies having 1 to 4 layers; 
           [0044]      FIG. 22  illustrates a variety of fabricated joints and interconnecting members; 
           [0045]      FIG. 23  depicts an expandable panel based upon a two-layer, eight-axle joint bodies; 
           [0046]      FIG. 24  shows how the structure of  FIG. 25  have be formed into an arch configuration; 
           [0047]      FIG. 25  depicts expandable beams based upon two-layer, four-axle joint bodies; 
           [0048]      FIG. 26  shows a multi-layered expandable panel based upon two-layer, eight-axle joint bodies; 
           [0049]      FIG. 27  depicts typical expandable structures; 
           [0050]      FIGS. 28A-D  shows possible toy configurations constructed in accordance with the invention; and 
           [0051]      FIG. 29  illustrates a collapsible-expandable panel based upon X-type auxetic unit cells. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0052]    This invention improves upon rapidly deployable structures by providing components based upon negative Poisson&#39;s ratio (NPR) auxetic designs.  FIGS. 1 and 2  illustrate a first such design based upon a “nested-V” configuration.  FIG. 1  shows the structure in an expanded form, whereas  FIG. 2  shows the structure in a collapsed state. In the collapsed state of  FIG. 2 , the structure assumes a width (W) reduction on the order of 70%. Being an auxetic in nature, a height (H) reduction is also evident from the diagrams. 
         [0053]    The configuration of  FIGS. 1 ,  2  is based upon an array of unit cells, each of which includes two shorter members (i.e., A, B) connected by joint bodies  102  forming a smaller V-shape and two longer members (i.e., C, D), also connected by joints, forming a larger V-shape. In the preferred embodiments members A, B are substantially the same length, as are members C, D, and all of the members are straight. However, in alternative embodiments the members may be of different lengths and may be curved or otherwise ‘non-straight.’ Note in the expanded state of  FIG. 1  that the nested V-shapes are nearly triangular, while in the collapsed state of  FIG. 2  the members associated with each unit cell assume a more parallel arrangement wherein the sides of the members are proximate to one another, if not touching in some cases. It is also worth noting that in this and other designs, some of the members form substantially parallel lines  150 ,  152 ,  154 ,  156  in the expanded state. 
         [0054]    To provide a structural building element such as a wall component, a fabric  104  or other cover may be attached to the V-shapes, preferably at the joints  102 , so as to realize a panel structure that may readily expand and collapse. Alternatively, the fabric material may be bonded to the sides of the various members. Although only one fabric sheet is depicted in  FIGS. 1 and 2 , a second sheet may be provided on the opposing side, thereby creating a trapped air space which may be filled with insulative material(s). As seen in  FIG. 1 , in the expanded state the flexible sheet is substantially unfolded, whereas in the collapsed states of  FIG. 2 , the sheet is folded along with the structure itself. 
         [0055]    The members and joint bodies may be made out of any suitable material such as plastics, metals or wood. The members may be solid or hollow. Any type of fabric may be used, including canvas, nylon, and so forth. In lightweight implementations for shelters, tents, and the like, one preferred combination comprises aluminum interconnecting members, aluminum or plastic joint bodies, and rip-stop nylon fabric. 
         [0056]      FIG. 3  is a more detailed diagram which better illustrates the way in which the unit cells are constructed and how they interact. Note that while this description may use terms such as upper, lower, right, left, lateral, vertical, inverted, forward, rear, etc., the reader should understand that these are for description only and that all of the structures disclosed herein may be oriented in any direction. Unit cell  10 , in the middle of  FIG. 3 , includes upper members A, B and lower members C, D. Members A, B are connected with joint  112 , members C, D are connected with joint  132 , members A, C are connected with joint  102 , and members B, D are connected with joint  122 . In this case, all of the joint bodies  102 ,  112 ,  122 ,  132  may be the same. 
         [0057]    Each member is pivotally coupled to two joints, one at each respective end of each member. Using joint  102  as an example, the joint includes two opposing connection points  104 ,  106  for shorter members and two connection points  108 ,  110  for longer members. These connections may be made in any appropriate manner, including nuts and bolts, rivets, spring pins or, as shown in subsequent Figures, with spring-action, clip-on arrangements. 
         [0058]    Note that in  FIG. 3 , unit cell  10  shares its two longer members with inverted cells  90 ,  50  on either side. Unit cell  10  further shares its shorter member A with member A of cell  20 , and shares its shorter member B with member B of cell  40 . Unit cell  10  further shares its shorter member A with member A of invented cell  20 , and shares its shorter member B with member B of inverted cell  40 . In addition, joint  112  is shared by cells  10 ,  20 ,  30 ,  40 ; joint  132  is shared by cells  10 ,  50 ,  70 ,  90 , and so on. 
         [0059]      FIG. 4A  is an oblique drawing of a body  102 ′ similar to that shown in  FIG. 3 , but with additional connection points to achieve additional structural arrangements. The body, which may be made of any hard, durable material such as metal or plastic, includes an upper portion  109  with connection points  108 ,  110 , and two side extensions  103 ,  105  with connection points  104 ,  106 . Forward and rear extensions  405 ,  407  allow the connections with the members to be flush as shown in the top-down and oblique views of  FIGS. 4B and 4C . 
         [0060]      FIG. 5  depicts the way in which an interconnecting member  502  may snap into a joint body  504 . In this case the ends of the member  502  are temporarily spread apart enabling projections, posts or pins  506 ,  508  to be received by opposing openings in the body  504  represented by the axis  510  of a hole through the body. Note that the hole need not penetrate entirely through the body so long as appropriate corresponding depressions, recesses, or cavitations are provided. 
         [0061]    As mentioned, for larger structures, geometries may be adjusted to suit different applications. For example, as shown in  FIG. 6 , an auxetic panel measuring just 1 foot by 4 feet may be expanded into a wall panel measuring 10 feet by 8 feet. Once expanded, the panels may be joined through any appropriate edge connections to produce walls for buildings, ceilings, and so forth. 
         [0062]      FIG. 7  shows an auxetic panel based upon a different type of unit cell, in this case an X- or “bowtie” shape. The figure shows the panel in the contract and expanded conditions. As in  FIG. 6 , such a panel measuring just 1 foot by 4 feet may be expanded into a wall panel measuring 10 feet by 8 feet. Further, as with the array of V-shapes, some of the members of the bowtie configuration form substantially parallel lines  702 ,  704 , etc. upon assuming the expanded configuration. 
         [0063]      FIG. 8  depicts the nested-V cell used in a cylindrical configuration to construct a honeycomb auxetic beam, in this case having a generally hexagonal cross section. Such beams may be used in conjunction with the panels described herein to hold up roof structures, for example. As with the panel structures, the outside and/or inside surfaces of such beams may be fabric-covered. 
         [0064]    As shown in  FIG. 9 , square, octagonal and other cross-sectional shapes are possible for beam constructions.  FIG. 9A  shows an expanded auxetic beam having a square cross section;  FIG. 9B  shows an expanded auxetic beam having a hexagonal or honeycomb cross section;  FIG. 9C  shows an expanded auxetic beam having an octagonal cross section; and  FIG. 9D  shows an expanded auxetic beam having a 10-sided cross section; 
         [0065]      FIGS. 10A-10C  illustrate a beam unfolding mechanism. In  FIG. 10A , in the folded mode the beam may only be a foot long. The structure undergoes expansion in all directions in  FIG. 10B , leading to a fully expanded shape in  FIG. 10C  that may be used for Quonset-type huts, tents, and other such structures.  FIG. 11  illustrates the unfolding of an X-type auxetic beam. 
         [0066]      FIG. 12  shows a curved expandable beam with variable NPR cells along the circle. With this transition in differently sized unit cells, either a straight beam may be constructed, as shown in  FIG. 12 , as illustrated in  FIG. 13 , the beam may form a curved shape by properly distributing variable NPR cells around a circle. 
         [0067]      FIG. 14  illustrates the general concept for the joint. In particular,  FIG. 14A  is a top view of an alternative N-axle joint body, and  FIG. 14B  is a side view of the joint body of  FIG. 14A  showing how M layers may be provided. In this context, M layers refers to different levels or planes which, in the preferred embodiments are substantially parallel to one another. Each of the joint bodies shown in  FIG. 14  may utilize any number of different joint types as shown in the diagram of  FIG. 15 ; for example, joint types having male-female, female-female, female-male and male-male interconnection configurations. 
         [0068]      FIGS. 16 and 17  illustrate various possible clicking joints constructed in accordance with the invention, while  FIG. 18  illustrates different types of pin connection features.  FIG. 19  shows examples of possible one-layer joints, and  FIG. 20  shows examples of possible two-layer joints.  FIG. 21  depicts joint bodies having up to 4 layers with the understanding that additional level are possible with sufficient stepped outer profiling. 
         [0069]    In terms of specific structures,  FIG. 23  depicts an expandable panel based upon a two-layer, eight-axle joint bodies, and  FIG. 24  shows how the structure of  FIG. 23  may be formed into an arch configuration.  FIG. 25  depicts expandable beams based upon two-layer, four-axle joint bodies, and  FIG. 26  shows a multi-layered expandable panel based upon two-layer, eight-axle joint bodies.  FIG. 27  illustrates typical expandable structures.  FIG. 28A-D  show a variety of expandable, collapsible and reconfigurable toy configurations constructed in accordance with the invention which may or may not be auxetic in nature. 
         [0070]    It will be appreciated that multiple variations are possible beyond the structures so far described. As previously described,  FIG. 29  illustrates a collapsible-expandable panel based upon X-type auxetic unit cells. The members defining the expandable structure linkages may use different for “stuffer” members and “tensor” members, with dimensions, shapes, topologies, cross-sections, and material usages being defined by the intended application. The members defining the expandable structure may be made of ‘active’ materials, including shape-memory alloys such as Nitinol. Further, the members defining the expandable structure may include actuators and mechanical or electronic locking provisions associated with the joints and/or linkages.