Patent Publication Number: US-9903117-B2

Title: Stiffness control in a structural member having an inflatable component

Description:
TECHNICAL FIELD 
     The present invention relates to inflatable structural members which may be stowed in a relatively compact, uninflated condition, and inflated to an end-use condition when required. 
     BACKGROUND 
     Inflatable structural members may be used for a variety of purposes. Such members may be stored in an uninflated, relatively compact condition until needed. The members may be inflated to an end-use shape when needed. However, when a structural member is inflated, it may be difficult for the member to maintain its desired shape under an applied load. Also, inflatable structural members designed for increased stiffness or resistance to deformation under load may be excessively bulky and/or difficult to fold and store compactly prior to deployment or use. 
     SUMMARY 
     In one aspect of the embodiments described herein, a structural member includes an inflatable member having an elastic, imperforate wall, an outer layer enclosing the inflatable member so as to define a cavity between the inflatable member and the outer layer, and at least one separator member positioned in the cavity so as to separate the outer layer from the inflatable member. The outer layer has at least one opening formed therealong and structured to enable fluid communication between the cavity and an exterior of the structural member. 
     In another aspect of the embodiments described herein, a structural member includes an inflatable member having an elastic, imperforate wall, and an outer layer enclosing the inflatable portion so as to define a cavity between the inflatable member and the outer layer. At least one separator member is positioned in the cavity between the inflatable member and the outer layer so as to separate the outer layer and the inflatable member. The at least one separator member is unattached to both the inflatable member and the outer layer, and is movable with respect to the inflatable member and the outer layer prior to inflation of the inflatable member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a structural member having an inflatable component, in accordance with an embodiment described herein and prior to inflation of the inflatable component. 
         FIG. 2  is a side cross-sectional view of a portion of the structural member embodiment shown in  FIG. 1 . 
         FIG. 3  is a schematic side view of the structural member of  FIG. 1  after inflation of the inflatable component. 
         FIG. 4  is the schematic side view of  FIG. 3  after application of an external load to the structural member. 
         FIG. 5  is a side cross-sectional view of a loaded portion of the structural member embodiment shown in  FIG. 4 . 
         FIG. 6  is a schematic side view of a structural member having an inflatable component, in accordance with another embodiment described herein and prior to inflation of the inflatable component. 
         FIG. 7  is a cross-sectional view of a portion of the structural member embodiment shown in  FIG. 6 , after inflation of the inflatable component of the structural member. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments described herein relate to a structural member with an inflatable component. The structural member has an innermost, inflatable member, an outer layer, and at least one separator member positioned between the inflatable member and the outer layer. When the inflatable component is uninflated, the layers forming the structural member may be spaced apart or lightly contacting each other, so that normal forces and the resulting frictional forces between the layers are minimized. In this state, the structural member may be relatively flexible and pliable. When the inflatable component is inflated, the constituent layers are forced against each other, thereby increasing the normal forces acting on the layers and the resultant friction between the layers. This acts to increase a stiffness of a composite wall of the structural member, formed by the combined thicknesses of the inflatable member, the at least one separator member, and the outer layer. 
       FIGS. 1-5  show views of one embodiment of a structural member  12  in accordance with an embodiment described herein. In the embodiment shown, structural member  12  includes an innermost, inflatable member  14  and an outer layer  16  enclosing the inflatable member  14  so as to define a cavity  15  between the inflatable member  14  and the outer layer  16 . At least one separator member  18  is positioned in the cavity  15  between the inflatable member  14  and the outer layer  16  so as to separate the outer layer and the inflatable member.  FIG. 1  shows the structural member  12  attached to an inflation nozzle  19  with the inflatable member  14  uninflated. Because the outer layer  16  is not inflated and is not designed to trap gases, the outer layer need not be necessarily attached to the nozzle  19 , or need not be attached to the nozzle so as to form an airtight seal. 
     Referring to  FIG. 2 , in some embodiments, inflatable member  14  has a gastight, elastic, imperforate wall  14   a . The inflatable member  14  may be in the form of an inflatable bladder or bag, for example. An exterior surface  14   b  of the wall  14   a  may have a relatively high roughness, to aid in preventing or inhibiting sliding between the surface  14   b  and separator member  18  when the inflatable member  14  is inflated to the extent that it presses against the separator member  18  and forces the separator member  18  against the outer layer  16 , as described herein. The inflatable member  14  may be formed from any material suitable for the purposes described herein. In particular embodiments, the inflatable member  14  is stretchable. The inflatable member  14  may be formed from an elastically stretchable material. For example, the inflatable member  14  may be formed from silicone rubber or a similar material. 
     The outer layer  16  has at least one opening  16   a  formed therealong and structured to enable fluid communication between the cavity  15  and an exterior of the structural member  12 . The opening  16   a  is structured and positioned to aid in preventing air or gasses from becoming trapped and forming pockets between the inflatable member  14  and the outer layer  16 . Such gas pockets may inhibit overall flexibility of the structural member prior to inflation of the inflatable member. 
     As shown in  FIGS. 1, 3, 4 and 6 , in some embodiments, the outer layer  16  may have a plurality of openings  16   a  formed therealong, where all of the openings  16   a  are structured to enable fluid communication between the cavity  15  and an exterior of the structural member  12 . The outer layer  16  may be formed from any material suitable for the purposes described herein. In some embodiments, the outer layer  16  is formed from an elastically or resiliently stretchable material. Alternatively, the outer layer  16  may be formed from a material with little or no stretchability responsive to inflation and expansion of the inflatable member  14 . In particular embodiments, the outer layer may be formed from a material having an elongation of up to about 20%. In particular embodiments, the outer layer may be formed from silicone rubber. In particular embodiments, the outer layer may be formed from a fiber-reinforced polymer. 
     Referring to  FIG. 2 , an interior surface  16   b  of the outer layer  16  may have a relatively high roughness, to aid in preventing or inhibiting sliding between the surface  16   b  and separator member  18  when the inflatable member  14  is inflated to the extent that it forces the separator member  18  against the outer layer interior surface  16   b , as described herein. 
     The separator member  18  is structured and positioned so as to space the outer layer  16  apart from the inflatable member  14 , and to facilitate relative movement of the outer layer with respect to the inflatable member  14  prior to inflation of the inflatable member. The separator member  18  aids in preventing an inner surface  16   b  of the outer layer  16  from contacting the exterior surface  14   b  of the inflatable member  14  prior to inflation. Since these surfaces  14   b  and  16   b  may be relatively rough, contact between these surfaces may cause friction between the surfaces, thereby inhibiting relative motion between the surfaces and reducing overall flexibility of the structural member prior to inflation of the inflatable member  14 . 
     The separator member  18  may be unattached to the inflatable member  14  and the outer layer  16 , and movable with respect to the inflatable member  14  and the outer layer  16  prior to inflation of the inflatable member  14 . The terms “unattached” and “movable” as applied to any of the separator members described herein mean that the entire separator member is capable of moving relative to an associated inflatable member  14  and relative to an associated outer layer  16 , and of shifting its position within the cavity  15  formed between the inflatable member  14  and the outer layer  16 . The separator member  18  is thus merely placed between the inflatable member  14  and the outer layer  16  and is not attached to these elements in any way (for example, using adhesives or mechanical fasteners). This enables the separator member  18  to move freely within the cavity  15 , subject only to contact forces between the separator member  18  and the inflatable member  14  and between the separator member and the outer layer  16 . 
     The separator member  18  may also be structured to facilitate sliding of the separator member  18  with respect to the inflatable member  14 , and also sliding of the outer layer  16  with respect to the separator member  18 , prior to inflation of the inflatable member. This may promote overall flexibility of the structural member  12  prior to inflation of the inflatable member  14 . For this purpose, the separator member  18  may have relatively smooth inner surfaces  18   a  and outer surfaces  18   b  facing the inflatable member  14  and the outer layer  16 , respectively. These surfaces of the separator member  18  may be structured such that coefficients of static and kinetic friction between the separator member  18  and the outer layer are relatively low. In some embodiments, the separator member  18  may be structured such that coefficients of static and kinetic friction between the separator member  18  and the outer layer  16  are less than coefficients of static and kinetic friction between inflatable member  14  and the outer layer  16 , and such that coefficients of static and kinetic friction between the separator member  18  and the inflatable member  14  are less than coefficients of static and kinetic friction between inflatable member  14  and the outer layer  16 . 
     A static friction force f s  may be defined as a force that must exerted to overcome static friction between two surfaces in contact before the surfaces can slide with respect to each other. Generally, the static friction f s  force may be expressed as a product of the coefficient of static friction μ s  and a normal force N between the surfaces, according to the relation f s =μ s ×N. Also, a kinetic friction force f k  may be defined as a force that must exerted to keep two surfaces in sliding motion with respect to each other. Generally, the kinetic friction f k  force may be expressed as a product of the coefficient of kinetic friction μ k  and a normal force N between the surfaces, according to the relation f k =μ k ×N. The friction coefficients μ s  and μ k  for a given interface between any two components (for example, between the separator member  18  and the outer layer  16 ) may be adjusted by appropriate selection of separator member materials and surface finishes. 
     The roughnesses of the separator member surfaces  18   a  and  18   b  contacting the inflatable member  14  and the outer layer  16  may be specified so as to balance the need for relatively low sliding friction between the surfaces prior to inflation, against the need for sufficient frictional force between the surfaces to prevent or greatly inhibit relative sliding between the surfaces when the inflatable portion is inflated. The thickness of the separator member and the area and/or distribution of coverage of the inflatable member  14  by the separator member  18  may also be specified for the purposes of maintaining separation between the inflatable member  14  and the outer layer  16  both prior to inflation and after inflation of the inflatable member. 
     The separator member  18  may be formed from any material suitable for the purposes described herein. In particular embodiments, the separator member  18  is formed from a polymer material. 
     In particular embodiments, and as shown in embodiment  112  of  FIGS. 6 and 7 , a plurality of discrete, individual separator members  118  may be positioned between the inflatable member  114  and the outer layer  116 , each separator member  118  being independently movable with respect to the inflatable member  114  and the outer layer  116  prior to inflation of the inflatable member  114 . Utilizing a plurality of smaller separate pieces as separator members may serve the purposes of preventing contact between the outer layer  116  and the inflatable member  114 , while effectively articulating and distributing the separator function and enhancing overall flexibility of the structural member  112  prior to inflatable member inflation.  FIG. 6  shows a side view of a structural member  112  containing a plurality of discrete separator members  118  positioned between an inflatable member  114  and an outer layer  116 , and prior to inflation of the inflatable member.  FIG. 7  shows the embodiment of  FIG. 6  after inflation of the inflatable member  114  as the multiple individual separator members  118  are pressed by inflatable member  114  into intimate contact with outer layer  116 , as previously described. 
     Prior to inflation of the inflatable member  14 , the structural member  12  may be loose or foldable, as shown in  FIGS. 1, 2, and 6 . Because portions of the various layers  14 ,  16 , and  18  may not be in contact with each other when the inflatable member  14  is uninflated, the distances between the inflatable member  14  and the separator member  18 , between the separator member  18  and the outer layer  16 , and between the inflatable member  14  and the outer layer  16  may vary along the extent of the structural member  12 . The room allowed for the layers to space apart when inflatable member  14  is uninflated and the structure of the separator member  18  may facilitate low-friction and/or no-contact movement of the layers  14 ,  18 , and  16  relative to each other when the inflatable member  14  is uninflated, thereby increasing pre-inflation flexibility and compactness. 
       FIGS. 3-5  show views of the structural member  12  after inflation of the inflatable member  14 .  FIG. 3  shows a schematic side view of the structural member  12  when the inflatable member has been fully inflated and prior to application of an external load.  FIGS. 4 and 5  show the inflatable member of  FIG. 3  during application of an external load F. The structural member  12  may be configured so that inflation of the inflatable member  14  forces the walls of the inflatable member  14 , the separator member  18 , and the outer layer  16  into pressurized intimate contact with each other, and also forces the structural member  12  into its desired end-use shape. The end-use shape shown in  FIGS. 3-5  is just one example of a possible end-use shape, presented here for illustrative purposes. Any of a variety of end-use shapes may be employed, to which the principles described herein are applicable. 
     As the inflatable member  14  is inflated, surface  14   b  of the inflatable member is brought into intimate contact with separator member surface  18   a  and the normal forces between surfaces  14   b  and  18   a  increase. Also, the separator member surface  18   b  is brought into intimate contact with outer layer surface  16   b  and the normal forces between surfaces  18   b  and  16   b  increase. Application of the external load F to the inflated structural member  12  further increases the normal forces between the various layers  14 ,  18 , and  16 . An increase in the normal forces between the contacting surfaces of adjacent layers will produce a corresponding increase in the static friction forces which must be overcome to make the surfaces slide with respect to each other. An increase in the normal forces between the contacting surfaces of adjacent layers will also produce a corresponding increase in the kinetic friction forces necessary to keep the surfaces sliding with respect to each other after they begin sliding. Thus, as the normal forces increase, sliding of the various structural member layers  14 ,  18 , and  16  with respect to each other may be prevented or greatly inhibited. 
     Due to the applied inflation pressure and resulting normal forces, an effective composite wall C is formed having a thickness t 1  equal to the combined thicknesses of the inflatable member  14 , separator member  18  and outer layer  16  after inflation of the inflatable member  14  to a desired or predetermined pressure or level. Further increases in inter-layer normal forces due to an applied load F will result in increased resistance to relative motion between the adjacent layers (or between portions of the layers) in contact. For example, the increases in inter-layer normal forces due to inflation of the inflatable member or to application of an applied load F may increase resistance to differential stretching of the surfaces in contact. That is, with first and second layers in intimate, pressurized contact, if a first layer may tend to stretch at a different rate than the second layer responsive to an applied load, this stretching may be inhibited or prevented by increased frictional forces operating at the contact interface between the layers. The increased resistance to relative motion between layers and/or portions thereof may be manifested in an increase in stiffness of the composite wall C. 
     The constituent materials and wall thicknesses of the inflatable member  14 , the separator member  18 , and the outer layer  16  may be adjusted or specified depending on the requirements of a particular application, so as to provide a balance between the overall flexibility of the structural member  12  prior to inflation, the desired stiffness of the composite wall thickness (formed by the combined inflatable member  14 , separator member  18  and outer layer  16 ) after inflation, and any desire to minimize the weight and/or bulk of the structural member  12  prior to inflation of the inflatable member. 
     Because the frictional forces preventing relative sliding of the layers increases as the pressure in the inflatable member  14  increases, the stiffness of the composite wall C of the structural member  12  just described may be controlled to some degree by correspondingly controlling the inflated pressure of the inflatable member  14 . In addition, the stiffness of the composite wall C may also be affected by varying the wall thicknesses of one or more of the inflatable member  14 , the separator member  18 , and the outer layer  16 . 
     It will be appreciated that the basic internal structure of the structural member described herein may be adapted to provide any of a variety of structural shapes when the inflatable member is inflated. For example, using fabrication techniques such as cutting the materials of the various layers to appropriate shapes and stitching the elements together, any of a variety of structural shapes may be provided. In addition, incorporation of the separator member(s) between the inflatable member and the outer layer may increase pliability of the structural member when the inflatable member is uninflated, and may also aid in increasing stiffness of the structural member in its inflated, final end-use condition. 
     The terms “a” and “an,” as used herein, are defined as one or more than one. The term “plurality,” as used herein, is defined as two or more than two. The term “another,” as used herein, is defined as at least a second or more. The terms “including” and/or “having,” as used herein, are defined as comprising (i.e. open language). The phrase “at least one of . . . and . . . ” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. As an example, the phrase “at least one of A, B and C” includes A only, B only, C only, or any combination thereof (e.g. AB, AC, BC or ABC). 
     In the preceding detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, figures, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. Accordingly, reference should be made to the following claims, rather than to the foregoing specification, as indicating the scope of the invention.