Patent Publication Number: US-2019191814-A1

Title: System for retaining an upper on a sole structure

Description:
BACKGROUND 
     The inventive subject matter is generally directed to system for securing an upper on a sole structure for an article of footwear, and particularly a type of sandal known as thongs or flip-flops. More particularly, it is directed to a thong sandal having at least one strap attached to a sole structure of the sandal, and the strap has a retention element that helps prevents the strap from being pulled out of the sole structure when an upward tension is applied to the strap. 
     Thong sandals are a very popular type of footwear, and they may be preferred over other types of sandals for their simple design, ease of use, and comfort. A thong sandal typically includes an upper and a sole structure, wherein the sole structure is typically made of one or more layers of a foamed rubber material, unfoamed rubber, natural or synthetic leather, or a combination of such materials. The upper can include one or more straps attached to the sole structure. The sandal is held on a wearer&#39;s foot by the straps passing over the top or around the sides of the foot. The straps, which can be formed from a variety of materials (e.g., textiles, plastic, leather, synthetic leather, etc.) typically include a toe post or thong that fits between the first and second toes of a wearer. A generally “Y” shaped upper can be formed by joining the toe post with a pair of flexible straps, which respectively connect to the lateral and medial sides of the sole structure near the middle or rear region of sandal. 
     However, one disadvantage of the thong sandal is that under force the straps may become dislodged from the sole structure, particularly as the sole structure wears thin. This problem is particularly common for the toe post, which is frequently under upward lifting tension during activities (e.g., walking, running, etc.). As a result, the straps may be pulled out of the sole structure. 
     Previous attempts at solving one or more of the aforementioned problems have been made. For example, U.S. Pat. Nos. 9,259,048, 7,540,098, U.S. Publication No. 2009/0044423, and AU Patent No. 2013100142 disclose various mechanisms to help secure a toe post to a sandal&#39;s sole. The foregoing patent documents are hereby incorporated by reference in their entireties for all purposes. However, these methods have a number of shortcomings, including but are not limited to, inadequate protection, design complexity, and so on. 
     Therefore, there is a need for an improved system for retaining uppers on sole structures. There is particularly a need for an improved thong sandal that can be easily constructed, and effectively resist external tension so as to help prevent the straps from being pulled out of the sole structure. 
     SUMMARY 
     The innovations disclosed herein overcome problems in the prior art and address one or more of the aforementioned or other needs. 
     In some respects, the innovations disclosed here are generally directed to improved systems for retaining uppers on sole structures. 
     In some respects, the innovations disclosed herein are generally directed to an improved strap system for a sandal. According to some embodiments, the strap system includes a strap and a retention element. The strap can pass through a channel across a sole of the sandal, and the strap can have a plug end. The retention element can be disposed between the plug end and a bottom portion of the sole. The retention element can also include a base and one or more flanges disposed at an outer edge of the base projecting angularly upward and away from the base. 
     In some embodiments, the channel can terminate to a recess at the bottom portion of the sole. The retention element can be configured to engage with the sole by an interface between the flanges and an area surrounding a bottom opening of the channel in the recess when an upward tension is applied to the strap. 
     In some embodiments, the base has a generally planar surface. In certain embodiments, the base can have an aperture configured to allow the strap to pass through. The base can have a gap extending from the outer edge to the aperture, and the retention element can be configured to allow the strap to pass through the gap into the aperture. 
     In certain embodiments, the strap can be a toe post positioned at a front region of the sole. In certain embodiments, the strap can be positioned at a medial side or a lateral side of the sole. In the foregoing and other embodiments, the base and any of the flanges can form an angle between 20 degrees and 70 degrees. In certain embodiments, the angle is about 45 degrees. 
     According to some embodiments, the flanges can be made of a resiliently deformable material. Accordingly, the flanges can expand outwardly toward a plane that is tangent to the base when the flanges are urged against the area surrounding the bottom opening of the channel. In some other embodiments, the flanges can be made of a rigid material. According to certain embodiments, the retention element can be integrated with the strap in a unitary structure. 
     According to some embodiments, a widest width of the bottom opening of the channel is smaller than a distance between two opposing points on a peripheral edge of flanges. In some embodiments, any of the flanges can include one or more barbs on a peripheral edge of the flanges. 
     The inventive subject matter is also directed to an improved article of footwear. According to some embodiments, the article of footwear includes a sole which has a top portion and a bottom portion, as well as one or more straps. At least one of the straps can extend from the top portion to the bottom portion through a channel in the sole. The strap can have a plug end and a retention element. The retention element can be disposed between the plug end and the bottom portion of the sole. As well, the retention element can include a base and one or more flanges disposed at an outer edge of the base projecting angularly upward and away from the base. 
     In some embodiments, the channel can terminate to a recess at the bottom portion of the sole. The retention element can be configured to engage with the sole by an interference between the flanges and an area surrounding a bottom opening of the channel in the recess when an upward tension is applied to the strap. 
     In some embodiments, the base can have a generally planar surface. In certain embodiments, the base can have an aperture configured to allow the strap to pass through. The base can have a gap extending from the outer edge to the aperture, and the retention element can be configured to allow the strap to pass through the gap into the aperture. 
     In certain embodiments, the strap can be a toe post positioned at a front region of the sole. In certain embodiments, the strap can be positioned at a medial side or a lateral side of the sole. In the foregoing and other embodiments, the base and any of the flanges can form an angle between 20 degrees and 70 degrees. In certain embodiments, the angle is about 45 degrees. 
     According to some embodiments, the flanges can be made of a resiliently deformable material. Accordingly, the flanges can expand outwardly toward a plane that is tangent to the base when the flanges are urged against the area surrounding the bottom opening of the channel. In some other embodiments, the flanges can be made of a rigid material. According to certain embodiments, the retention element can be integrated with the strap in a unitary structure. 
     According to some embodiments, a widest width of the bottom opening of the channel is smaller than a distance between two opposing points on a peripheral edge of flanges. In certain embodiments, any of the flanges can include one or more barbs on a peripheral edge of the flange. 
     Related methods for constructing an article of footwear are also disclosed. For example, the methods include the acts of preparing a sole and attaching one or more straps to the sole. The sole can have a top portion and a bottom portion. At least one of the straps can extend from the top portion to the bottom portion through a channel in the sole. The strap can have a plug end and a retention element. The retention element can be disposed between the plug end and the bottom portion of the sole. As well, the retention element can include a base and one or more flanges disposed at an outer edge of the base projecting angularly upward and away from the base. 
     These and other embodiments are described in more detail in the following Detailed Description and the Figures. Other embodiments are contemplated in the Detailed Description below and in the appended Figures, and in the claims, as originally written or amended, the claims as such being incorporated by reference into this Summary. 
     The foregoing is not intended to be an exhaustive list of embodiments and features of the inventive subject matter. Persons skilled in the art are capable of appreciating other embodiments and features from the following detailed description in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The appended figures show embodiments according to the inventive subject matter, unless noted as showing prior art. 
         FIG. 1A  shows a top perspective view of a thong sandal according to one embodiment of the inventive subject matter. 
         FIG. 1B  shows a bottom view of the thong sandal illustrated in  FIG. 1A . 
         FIG. 2A  shows a top perspective view of a thong sandal according to another embodiment of the inventive subject matter. 
         FIG. 2B  shows a bottom view of the thong sandal illustrated in  FIG. 2A . 
         FIG. 3  shows the bottom view of a portion of a sandal&#39;s sole and a toe post passing through the sole. 
         FIG. 4  shows a top perspective view of a retention element. 
         FIG. 5A  illustrates a top view of a retention element disposed in a recess. 
         FIG. 5B  illustrates a cross-sectional view of the retention element shown in  FIG. 5A  together with a plug end of a toe post, disposed in a recess at the bottom portion of a sole. 
         FIG. 6  shows a top view of a retention element having a base, four flanges and a gap in the base. 
         FIG. 7  shows a top view of a retention element having a base, three flanges and a gap in the base. 
         FIG. 8  shows a top view of a retention element having a base, two flanges and a gap in the base. 
         FIG. 9  shows a top view of a retention element having a base, one flange and a gap in the base. 
         FIG. 10A  shows a cross-sectional view of the retention element shown in  FIG. 6  according to one embodiment. 
         FIG. 10B  shows the cross-section view of the retention element shown in  FIG. 10A  when an upward tension is applied to a toe strap passing through the retention element. 
         FIG. 11A  shows a cross-sectional view of the retention element shown in  FIG. 6  according to another embodiment. 
         FIG. 11B  shows the cross-section view of the retention element shown in  FIG. 11A  when an upward tension is applied to a toe strap passing through the retention element. 
         FIG. 12A  shows a cross-sectional view of the retention element shown in  FIG. 6  according to a third embodiment. 
         FIG. 12B  shows the cross-section view of the retention element shown in  FIG. 12A  when an upward tension is applied to a toe strap passing through the retention element. 
         FIG. 13  shows a top view of a retention element having a base, four flanges, wherein each flange has a number of barbs on a peripheral edge of the flange. 
         FIG. 14  shows a top view of a retention element having a base and four flanges, but has no gap in the base. 
         FIG. 15  shows a side view of a toe post with an integrated plug end and retention element according to one embodiment of the inventive subject matter. 
         FIG. 16  shows a side view of a toe post with an integrated plug end and retention element according to an alternative embodiment of the inventive subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     Representative embodiments according to the inventive subject matter are shown in  FIGS. 1-16 . 
     In some respects, the inventive subject matter is directed to an improved system for retaining an upper on a sole structure for an article of footwear. In a representative, non-limiting embodiment, the article of footwear is a thong sandal, which is a type of open-toed sandal. A thong sandal may or may not have a heel and/or heel strap. In some respects, the inventive subject matter is also directed to a toe post system for a thong sandal. Yet in other respects, the inventive subject matter is directed to a method of constructing an improved retention system for retaining an upper structure on an article of footwear. It is particularly suitable for retaining straps on a sole structure, especially a toe post on the sole structure for a thong sandal. 
     According to some embodiments, the thong sandal includes a sole and one or more straps. The sole structure can be made from any known or to be discovered material or materials, including one or more layers of a foamed rubber material, unfoamed rubber, natural or synthetic leather, or a combination of such materials. A popular material for thong sandals is ethylene-vinyl acetate (EVA). EVA is a polymer that approaches elastomeric materials in softness and flexibility, yet can be processed like other thermoplastics, thus providing for use of well-known injection and other molding and production techniques. The straps, which form part of an upper for the sandal, can be made with a variety of materials, such as molded rubber, plastic, leather, foam, fabric, etc. In certain embodiments, at least one of the straps is a toe post positioned at a front region of the sole. In certain embodiments, at least one of the straps is positioned at a medial side or a lateral side of the sole. 
     For example,  FIG. 1A  and  FIG. 1B  show a thong sandal  10  having a sole  19  and a plurality of straps ( 15 ,  15   a ,  15   b ). The sole  19  has a top portion  17  and a bottom portion  11 . The sole  19  can be held loosely on the foot by a Y-shaped strap system including a thong strap (or toe post)  15  connecting to a front region  12  of the sole  19 , a medial strap  15   a  connecting to a medial portion  14  of the sole  19 , and a lateral strap  15   b  connecting to a lateral portion  16  of the sole  19 . The straps ( 15 ,  15   a , and  15   b ) can be separate pieces that are coupled together, or can be constructed in a unitary piece. The toe post  15 , which passes between the first and second toes, can extend from the top portion  17  to the bottom portion  11  through a channel  13  in the sole  19 . The medial and lateral straps  15   a ,  15   b  can also extend from the top portion  17  to the bottom portion  11  through respective channels  13   a ,  13   b.    
       FIG. 2A  and  FIG. 2B  show another embodiment of a thong sandal  20  including a sole  29  and a plurality of straps ( 25 ,  25   a ,  25   b ). A toe post  25  is connected to a front region  22  of the sole  29 , extending from a top portion  27  to a bottom portion  21  through a channel  23  in the sole  29 . Unlike the embodiment shown in  FIGS. 1A-1B , the medial strap  25   a  and lateral strap  25   b  do not connect to the sole  29  via channels. Instead, the medial strap  25   a  is connected to a medial side  24  of the sole  29  at an attachment point  23   a , and the lateral strap  25   b  is connected to a lateral side  26  of the sole  29  at an attachment point  23   b . The connection of the medial and lateral straps  25   a ,  25   b  to the respective attachment points  23   a ,  23   b  can be implemented by gluing, screwing, buttoning, clasping, Velcro, or any known or to be discovered coupling mechanisms. 
     In a representative, non-limiting embodiment, a strap extending from a top portion to a bottom portion through a channel in the sole can be securely attached to the sole by a plug end and a retention element. By way of illustration and without any limitation, a toe post will be used hereafter to illustrate principals of the inventive subject matter. It should be understood that similar retention mechanism can also be applied to securely attach other straps (e.g., the medial strap and/or lateral strap) to a sandal&#39;s sole. Further, although the channels  13 ,  13 A,  13 B are shown running completely through the top to bottom of the sole, persons skilled in the art will appreciate that a strap plug end can be captured between layers of material in a sole so as not be exposed on the bottom side of the sole. 
     As an example of a typical toe post system, as improved by the inventive subject matter,  FIG. 3  shows the bottom view of a toe post  35  passing through a front region of a sole  31 . The toe post  35  can include a thong strap  36  passing through a channel  33  in the sole  31 , a plug end  37  and a retention element  30 . The retention element  30 , which will be described more fully in the following, can be disposed between the plug end  37  and the bottom portion of the sole  31 . 
     Attachment of the toe post  35  to the sole  31  can be accomplished by inserting the toe post&#39;s plug end  37  through the channel  33  in the sole  31  in a downward direction. Due to the deformable nature of the sole  31  and the plug end  37 , the widest width of the channel  33  can be smaller than the cross-sectional width of the plug end  37 . After the plug end  37  is passed through the channel  33  in the sole  31 , the retention element  30  can be inserted between the plug end  37  and the bottom portion of the sole  31 . The toe post  35  can also be attached to the sole  31  by inserting the thong strap  36  through the channel  33  in the sole  31  in an upward direction, thus leaving the plug end  37  at the bottom portion of the sole  31 . Then the retention element  30  can be inserted between the plug end  37  and the bottom portion of the sole  31 . 
     The width of channel  33  can be generally configured to match the width of the thong strap  36 , but the channel  33  can flare to a wider bottom opening to form a recess near the bottom portion of the sole. As described more fully below, the recess can be configured to receive the plug end  37  and the retention element  30 . Thus, when the toe post  35  is pulled upwards, the plug end  37  and the retention elements  30  are urged against (i.e., interference fit) the area surrounding the bottom opening of the channel  33  in the recess. The plug end  37  and the retention element  30  are retained because of the interference fit, thus helping prevent the toe post  35  from being pulled out of the sole  31 . 
       FIG. 4  shows a three-dimensional (3D) top perspective view of a representative, but non-limiting embodiment of a retention element  40 . In this example, the retention element  40  includes a base  49  and four flanges ( 41   a ,  41   b ,  41   c , and  41   d ) disposed at an outer edge  42  of the base  49 . The flanges ( 41   a ,  41   b ,  41   c , and  41   d ) can be arranged to project angularly upward and away from the base (i.e., the flanges protrude outward of the outer edge  42  and form a certain angle with the base  49 ). When coupled with a strap (e.g., a toe post) passing through a sole (not shown), the flanges are arranged to project generally toward a bottom surface of the sole. For example, in  FIG. 3 , the flanges project toward bottom portion of the sole  31 . In other embodiments (not illustrated), the plug and retention element can be sandwiched in sole material, with the flanges projecting upwardly towards the bottom surface of an intermediate layer of sole structure where a channel terminates. 
     In a representative, non-limiting embodiment, the base  49  can have a generally planar surface. In some embodiments, the base  49  can have an aperture  46  configured to allow a corresponding strap (not shown) to pass through. In an exemplary embodiment, the base  49  can have a gap  48  extending from the outer edge  42  to the aperture  46  in the base  49 , and the retention element  40  can be configured to allow a corresponding strap (not shown) to pass through the gap  48  into the aperture  46  in the base  49 . 
       FIG. 5A  illustrates a top view of a retention element  50  disposed in a recess  53  which is disposed in a bottom surface of the sole structure. For purposes of clarity, the toe post is not shown together with the retention element  50  in  FIG. 5A .  FIG. 5B  illustrates a cross-sectional view of the retention element  50  shown in  FIG. 5A  together with a toe post  55  having a thong strap  55   a  and a plug end  55   b , wherein the plug end  55   b  and the retention element  50  are disposed in the recess  53  at the bottom surface  57   b  of the sole  57 . 
     The cross section of the thong strap  55   a  can have a circular, eclipse, rectangular, hexagonal, or any other shape. The widest width measured in the cross section of the thong strap  55   a  can be labeled as Ds (i.e., Ds is the diameter of the cross section if the thong strap  55   a  has a generally cylinder shape). The plug end  55   b  is disposed at the distal end of the thong strap  55   a , and its top and bottom surfaces can have a circular, eclipse, rectangular, hexagonal, or any other shape. The widest width measured across the top and bottom surfaces of the plug end  55   b  can be labelled as Dp (i.e., Dp is the diameter of the surface if the plug end  55   b  has a generally circular shape). Dp is greater than Ds to allow the plug end  55   b  in combination with the retention element  50  to engage the sole structure  57  in an interference fit. 
     Similar to the example shown in  FIG. 4 , the retention element  50  has a base  59  and four flanges ( 51   a ,  51   b ,  51   c , and  51   d ) disposed at an outer edge  52  of the base  59  projecting angularly upward and away from the base  59 . Similarly, the base  59  can also have an aperture  56 , and a gap  58  extending from the outer edge  52  to the aperture  56 . The widest width Db of the aperture  56  (e.g., Db is the diameter of the aperture  56  if the aperture  56  has a circular shape) is generally larger than Ds (i.e., the widest width of the cross section of the thong strap  55   a ). The size of the gap  58  can be smaller than Ds. But since the thong strap  55   a  can be made of flexible materials and be deformable, the thong strap  55   a  can be squeezed though the gap  58  and into the aperture  56 . 
     Channel  54  starts at the top surface  57   a  of the sole  47  and terminates to a widened recess  53  at the bottom surface  57   b  of the sole  57 , for receiving the plug end  55   b  and the retention element  50 . The region of the recess  53  can be confined by an outer boundary  53   a . One or both of the plug end  55   b  and the retention element  50  can match the geometric shape of the recess  53 . For example, the widest width of the recess Dr (e.g., Dr is the diameter of the recess  53  if the recess  53  has a circular shape) can be similar to, or slightly larger than Dp (i.e. the widest width measured across the top and bottom surfaces of the plug end  55   b ). The depth of the recess  53  can be similar to, or slightly greater than the height of the plug end  55   b  plus the height of the base  59  of the retention element  50 . Thus, when the toe post  55  is drawn upwards, the plug end  55   b , as well as the retention element  50 , can be pulled into the recess  53 , and the plug end  55   b  can form a flush fit or generally smooth bottom surface of the thong sandal. 
     The toe post  55  passes through the sole  57  via the channel  54 , whose bottom opening  53   b  is disposed in the recess  53 . The cross section of the channel  54  may vary in size along its path. At least the widest width Da of the channel&#39;s bottom opening  53   b  (e.g., Da is the diameter of the bottom opening  53   b  if the channel  54  has a generally cylinder shape) is smaller than a distance De between two opposing points on a peripheral edge of the flanges. In some embodiments, when the retention element  50  is placed into the recess  53 , the base  59  of the retention element  50  generally covers the bottom opening  53   b  of the channel  54 . According to a representative, non-limiting embodiment, the size of the plug end  55   b  is generally bigger than the aperture  56  in the retention element  50 , so that the plug end  55   b  has an interference fit against the retention element  50 . In addition, the size of the retention element  50  is generally bigger than the bottom opening  53   b  of the channel  54 . Thus, at least the retention element  50  can be configured to engage with the sole  57  by an interference fit between the flanges ( 51   a ,  51   b ,  51   c , and  51   d ) and an area  53   c  surrounding the bottom opening  53   b  in the recess  53  (i.e., the area between the outer boundary  53   a  and the bottom opening  53   b ) when an upward tension is applied to a toe post having the retention element  50 . Accordingly, it will be difficult to pull the retention element  50  and the strap&#39;s plug end  55   b  away from the sole  57  through the channel  54 . 
     The retention element can have a variety of designs. For example, the number of flanges, the space between two adjacent flanges, the size and shape of the flanges, the size and shape of the base, the size and shape of the aperture in the base, the size and shape of the gap in the base (or no gap in the base), and/or other structural features of the retention element can be varied to achieve specific functional properties and/or ornamental characteristics. 
     As an example,  FIG. 6  shows a top view of a retention element  60  that has similar design as those shown in  FIG. 4  and  FIG. 5B . As illustrated in  FIG. 6 , the retention element  60  has a base  69  and four flanges ( 61   a ,  61   b ,  61   c  and  61   d ) disposed at an outer edge  62  of the base  69  projecting angularly and away from the base. Similarly, the base  69  can also have an aperture  66 , and a gap  68  extending from the outer edge  62  to the aperture  66 . The flanges ( 61   a ,  61   b ,  61   c  and  61   d ) can be disposed symmetrically, or asymmetrically along the outer edge  62 . Any of the flanges can have a variety of shapes and/or sizes, and the space between two adjacent flanges can also vary. 
     In another example,  FIG. 7  shows a top view of a retention element  70  having a base  79  and three flanges ( 71   a ,  71   b  and  71   c ) disposed at an outer edge  72  of the base  79  projecting angularly and away from the base. Similarly, the base  79  can also have an aperture  76 , and a gap  78  extending from the outer edge  72  to the aperture  76 . The flanges ( 71   a ,  71   b  and  71   c ) can be disposed symmetrically, or asymmetrically along the outer edge  72 . Any of the flanges can have a variety of shapes and/or sizes, and the space between two adjacent flanges can also vary. 
     In an alternative example,  FIG. 8  shows a top view of a retention element  80  having a base  89  and two flanges ( 81   a  and  81   b ) disposed at an outer edge  82  of the base  89  projecting angularly and away from the base. Similarly, the base  89  can also have an aperture  86 , and a gap  88  extending from the outer edge  82  to the aperture  86 . The flanges ( 81   a  and  81   b ) can be disposed symmetrically, or asymmetrically along the outer edge  82 . Any of the flanges can have a variety of shapes and/or sizes, and the space between the two flanges can also vary. 
     Yet in a further example,  FIG. 9  shows a top view of a retention element  90  having a base  99  and only one flange  91  disposed at an outer edge  92  of the base  99  projecting angularly and away from the base. Similarly, the base  99  can also have an aperture  96 , and a gap  98  extending from the outer edge  92  to the aperture  96 . The flange  91  can be disposed continuously along, or only a portion of the outer edge  82 . The flange  91  can also have a variety of shapes and/or sizes. 
       FIG. 10A  shows a cross-sectional view of the retention element shown in  FIG. 6  (along line B-B′) according to one exemplary embodiment. As shown, the retention element  100  has a base  109  and one or more flanges  101 . The base  109 , which has an aperture  106 , is generally planar, i.e., the base  109  is generally parallel to the plane  103 . The flanges  101 , which are disposed at the outer edge  102  of the base  109 , project angularly upward and away from the base  109 , when no tension is applied. For example, the flange  101  can have a tangential plane  104 A, which forms an angle α with the plane  103 . In a representative, non-limiting embodiment, the angle α is between about 20 degrees and about 70 degrees. In an exemplary embodiment, the angle is about 45 degrees, which can range between about 35 degrees and about 55 degrees. 
     According to some embodiments, the flanges  101  are made of a resiliently deformable material.  FIG. 10B  shows the cross-section view of the retention element  100  shown in  FIG. 10A  when an upward tension is applied to a toe strap (not shown) passing through the retention element  100 . The tension force can be transferred to the retention element  100  coupled to the toe strap when the retention element  100  is urged against a bottom portion of the sole (not shown). Accordingly, the flanges  101  can expand outwardly toward the plane  103  that is tangent to the base  109  when the flanges  101  are urged against the bottom portion of the sole. Thus, the plane  104 B of the expanded flange  101  can be pressed toward the base  109 , and the angle α′ between the plane  104 B and the base plane  103  is reduced compared to the original angle α. Yet according to an alternative embodiment, the flanges  101  can be made of a rigid material. When the flanges  101  are urged against the bottom portion of the sole, the flanges  101  do not deform and retain its original shape and orientation with respect to the base  109 . Since the sole is typically made of foamed rubber material, the flanges  101  can piece into and grip the sole. As the flanges  101 , either being made of deformable or rigid material, are pressed against the bottom portion of the sole, the associated toe post can be securely attached to the sole. 
       FIG. 11A  shows a cross-sectional view of the retention element shown in  FIG. 6  (along line B-B′) according to another embodiment. As shown, the retention element  110  has a base  119  and one or more flanges  111 . The base  119 , which has an aperture  116 , can have a convex shape. For example, the base  119  can curve upward in a region near the outer edge  112  relative to a region surrounding the aperture  116 . The aperture  116  at the bottom of the base  119  has a tangent plane  113 . The flanges  101 , which are disposed at the outer edge  112  of the base  119 , project angularly upward and away from the base  119 , when no tension is applied. For example, the flange  111  can have a tangential plane  114 A, which forms an angle α with the plane  113 . In a representative, non-limiting embodiment, the angle α is between about 20 degrees and about 70 degrees. In an exemplary embodiment, the angle is about 45 degrees, which can range between about 35 degrees and about 55 degrees. 
       FIG. 11B  shows the cross-section view of the retention element  110  shown in  FIG. 11A  when an upward tension is applied to a toe strap (not shown) passing through the retention element  110 . The tension force can be transferred to the retention element  110  coupled to the toe strap when the retention element  110  is urged against a bottom portion of the sole (not shown). Accordingly, the flanges  111  can expand outwardly toward the plane  113  that is tangent to the base  119  when the flanges  111  are urged against the bottom portion of the sole. Thus, the plane  114 B of the expanded flange  111  can be pressed toward the base  119 , and the angle α′ between the plane  114 B and the base plane  113  is reduced compared to the original angle α. Yet according to an alternative embodiment, the flanges  111  can be made of a rigid material. When the flanges  111  are urged against the bottom portion of the sole, the flanges  111  do not deform and retain its original shape and orientation with respect to the base  119 . Since the sole is typically made of foamed rubber material, the flanges  111  can piece into and grip the sole. As the flanges  111 , either being made of deformable or rigid material, are pressed against the bottom portion of the sole, the associated toe post can be securely attached to the sole. 
       FIG. 12A  shows a cross-sectional view of the retention element shown in  FIG. 6  (along line B-B′) according to an alternative embodiment. As shown, the retention element  120  has a base  129  and one or more flanges  121 . The base  129 , which has an aperture  126 , can have a corrugated shape. For example, the base  129  can have a plurality of ridges and furrows on its upper surface. The aperture  126  at the bottom of the base  129  has a tangent plane  123 . The flanges  121 , which are disposed at the outer edge  122  of the base  129 , project angularly upward and away from the base  129 , when no tension is applied. For example, the flange  121  can have a tangential plane  124 A, which forms an angle α with the plane  123 . In a representative, non-limiting embodiment, the angle α is between about 20 degrees and about 70 degrees. In an exemplary embodiment, the angle is about 45 degrees, which can range between about 35 degrees and about 55 degrees. 
       FIG. 12B  shows the cross-section view of the retention element  120  shown in  FIG. 12A  when an upward tension is applied to a toe strap (not shown) passing through the retention element  120 . The tension force can be transferred to the retention element  120  coupled to the toe strap when the retention element  120  is urged against a bottom portion of the sole (not shown). Accordingly, the flanges  121  can expand outwardly toward the plane  123  that is tangent to the base  129  when the flanges  121  are urged against the bottom portion of the sole. Thus, the plane  124 B of the expanded flange  121  can be pressed toward the base  129 , and the angle α′ between the plane  124 B and the base plane  123  is reduced compared to the original angle α. Yet according to an alternative embodiment, the flanges  121  can be made of a rigid material. When the flanges  121  are urged against the bottom portion of the sole, the flanges  121  do not deform and retain its original shape and orientation with respect to the base  129 . Since the sole is typically made of foamed rubber material, the flanges  121  can piece into and grip the sole. As the flanges  121 , either being made of deformable or rigid material, are pressed against the bottom portion of the sole, the associated toe post can be securely attached to the sole. 
     It should be understood that the examples shown in  FIGS. 10A-10B, 11A-11B , and  12 A- 12 B are not limiting. The base of the retention element can have other shapes without departing from the principles described above. 
       FIG. 13  shows another representative, non-limiting embodiment of a retention element  130 . As shown, the retention element  130  has a plurality of flanges  131   a ,  131   b ,  131   c  and  131   d , any of which can include one or more barbs  137   a ,  137   b ,  137   c  and  137   d , on a peripheral edge of the respective flange. When the flanges  131   a ,  131   b ,  131   c  and  131   d  are urged against the bottom portion of the sole, the barbs on the respective flanges ( 137   a ,  137   b ,  137   c  and  137   d ) can piece into and grip the sole, thus helping to securely attach the associated toe post to the sole. 
     While each of the retention elements described above has a gap in the base so that the retention element can be assembled over the strap (e.g., by sliding the strap through the gap into the aperture of the retention element), in other embodiments the retention element does not need to have a gap. For example,  FIG. 14  shows a retention element  140  having a base  149  and four flanges ( 141   a ,  141   b ,  141   c  and  141   d ) disposed at an outer edge  142  of the base  149  projecting angularly upward and away from the base  149 . Similarly, the base  149  can also have an aperture  146 . However, the base  149  has no gap extending from the outer edge  142  to the aperture  146 . 
     According to certain embodiments, the retention element  140  can be integrated with the corresponding strap in a unitary structure. For example,  FIG. 15  shows a toe post  150  having a plug end  155 , a retention element  159 , and a thong strap  152 , all integrated together to form a unitary structure. To assemble the sandal, the integrated toe post  150  can be inserted from the bottom portion  157   b  to the top portion  157   a  of the sole  157  via a channel  154 . As shown, the top opening  154   a  can be wider than the bottom opening  154   b  of the channel  154 . Channel  154  terminates to a recess  153 , which can receive the portion of integrated plug end  155  and the retention element  159 . The flanges  151  of the retention element  159  can form an interference fit against an area surrounding the bottom opening  154   b  of the channel  154  in the recess  153 , so that the toe post  150  can be securely attached to the sole  157 . The thong strap  152  can exit the top portion  157   a  of the sole  157  and be coupled to the medial and/or lateral straps to form a part of the sandal&#39;s upper. 
       FIG. 16  shows an alternative embodiment. In this example, the toe post  160  has a plug end  165 , a plurality of flanges  161 , and a thong strap  162 , all integrated together to form a unitary structure. Note that in this example, the plurality of flanges  161  are disposed directly on the plug end  165 . In other words, the plug end  165  itself functions as the base of a retention element. 
     To assemble the sandal, the integrated toe post  160  can be inserted from the bottom portion  167   b  to the top portion  167   a  of the sole  167  via a channel  164 . As shown, the top opening  164   a  can be wider than the bottom opening  164   b  of the channel  164 . Channel  164  terminates to a recess  163 , which can receive the portion of integrated plug end  165  and the plurality of flanges  161 . The flanges  161  can form an interference fit against an area surrounding the bottom opening  164   b  of the channel  164  in the recess  163 , so that the toe post  156  can be securely attached to the sole  167 . The thong strap  162  can exit the top portion  167   a  of the sole  167  and be coupled to the medial and/or lateral straps to form a part of the sandal&#39;s upper. 
     Any of the retention elements described herein, or a unitary retention element/plug end, such as plug end  165 , can have a variety of shapes, for example, a plate; disc; rectilinear; block, sphere, or other volumetric shape; ellipsoid; cylinder, etc. 
     Persons skilled in the art will recognize that many modifications and variations are possible in the details, materials, and arrangements of the parts and actions which have been described and illustrated in order to explain the nature of the inventive subject matter, and that such modifications and variations do not depart from the spirit and scope of the teachings and claims contained therein. 
     All patent and non-patent literature cited herein is hereby incorporated by references in its entirety for all purposes. 
     As used herein, “and/or” means “and” or “or”, as well as “and” and “or.” Moreover, any and all patent and non-patent literature cited herein is hereby incorporated by references in its entirety for all purposes. 
     The principles described above in connection with any particular example can be combined with the principles described in connection with any one or more of the other examples. Accordingly, this detailed description shall not be construed in a limiting sense, and following a review of this disclosure, those of ordinary skill in the art will appreciate the wide variety of systems that can be devised using the various concepts described herein. Moreover, those of ordinary skill in the art will appreciate that the exemplary embodiments disclosed herein can be adapted to various configurations without departing from the disclosed principles. 
     The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the disclosed innovations. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of this disclosure. Thus, the claimed inventions are not intended to be limited to the embodiments shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. 
     All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the features described and claimed herein. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as “a means plus function” claim under US patent law, unless the element is expressly recited using the phrase “means for” or “step for”. 
     The inventors reserve all rights to the subject matter disclosed herein, including the right to claim all that comes within the scope and spirit of the following claims: 
     The inventor(s) reserves the right to claim, without limitation, at least the following subject matter.