Patent Abstract:
The present invention relates to a polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes. More particularly, to a shock absorbing polygonal rib structure. In a polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes, a thickened central portion located at a substantially central portion in the longitudinal direction of each side of the polygonal rib is bisected. The opposed parting surfaces formed upon the bisection are spaced from each other to form an opening portion, and each side of the polygonal rib is so shaped that the cross-sectional area of the opening portion is reduced as one goes from the opening end toward the depth. Thus, an opened polygonal rib structure is formed.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2004-278543 filed on Sep. 24, 2004 the entire contents of which are hereby incorporated by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes, and particularly a shock absorbing polygonal rib structure. 
   DESCRIPTION OF BACKGROUND ART 
   A honeycomb structure having a hexagonal cross-sectional shape is disclosed in Japanese Patent Laid-Open No. Hei 9-105013. 
   The honeycomb structure disclosed in Japanese Patent Laid-Open No. Hei 9-105013 has a structure in which a surface formed by connecting end edges of ribs arranged in a honeycomb shape is a curved surface, and it has been attempted to apply the honeycomb structure to a shock absorbing member for helmets. 
   In manufacturing this honeycomb structure, as shown in  FIGS. 20 and 21  of the drawings, a band-like blank material  01  that is directed rectilinearly in one direction and has a rectangular cross-sectional shape is fed between a pair of truncated conical rolls  02 , and is rolled to have an elongate trapezoidal cross-sectional shape as shown in  FIG. 21 . Thus, a band-like blank material  01 A is obtained in which the band-like blank material  01  directed rectilinearly in one direction is spirally wound. 
   The band-like blank material  01 A that is spirally wound is divided into a plurality of portions, for example, three portions evenly over the winding direction, as shown in  FIG. 23 . The surface of the arcuate band-like blank material  01 B is divided at regular angular intervals from the spiral center O into sections (X 1 , X 2 , X 3 , X 2 ) (X 1 , X 2 , X 3 , X 2 ) . . . , as shown in  FIG. 22 . In the surface of one of the adjacent arcuate band-like blank materials  01 B, an adhesive is applied to the sections X 1  intermediated by the three sections X 2 , X 3 , X 2 . In the surface of the other of the adjacent arcuate band-like blank materials  01 A, an adhesive is applied to the central section X 3  located at an intermediate position between the adhesive-coated sections X 1 . After curing of the adhesives, both upper and lower end portions of the band-like blank materials  01 B that are divided into arcuate forms are broadened from each other as shown in  FIG. 24 , whereby a honeycomb structure as shown in  FIG. 14  can be manufactured. 
   In order to manufacture the honeycomb structure disclosed in Japanese Patent Laid-Open No. Hei 9-105013, a process is used in which the rectangular band-like blank material  01  having a cross-sectional shape with a fixed thickness over the longitudinal direction is formed into the band-like blank material  01 A having an elongate trapezoidal cross-sectional shape. It is necessary to prepare a band-like blank material  01  which is free of dispersions in the width direction and in the thickness over the longitudinal direction thereof. At the same time, it is necessary that the accuracy of the outer peripheral surfaces of the pair of truncated conical rolls  02  and the accuracy of the parallelism and size between the roll axes should be high. Moreover, a large number of working steps is required. As a result, productivity is low, and it is impossible to obviate a high cost. 
   In addition, it has been difficult to apply the structure disclosed in Japanese Patent Laid-Open No. Hei 9-105013 to polygonal rib structures other than the honeycomb structure. 
   SUMMARY AND OBJECTS OF THE INVENTION 
   The present invention pertains to an improvement in a polygonal rib structure which overcomes the above-mentioned difficulties. In one embodiment of the present invention a polygonal rib structure is provided which is rich in mass-producibility and is low in cost. 
   An embodiment of the present invention resides in an opened polygonal rib structure having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes. A thickened central portion located at a substantially central portion in the longitudinal direction of each side of the polygonal rib is bisected, and the opposed parting surfaces formed upon the bisection are spaced from each other to form an opening portion. Each side of the polygonal rib is shaped so that the cross-sectional area of each opening portion is reduced along the direction from the opening end toward the depth. 
   An embodiment of the present invention resides in an opened polygonal rib structure, wherein the shape and size of the rhombic opening portions of the polygonal rib are varied as one goes in one direction or a plurality of directions in the one plane. 
   An embodiment of the present invention resides in an opened polygonal rib structure wherein the opening portion is closed, and the outer peripheral surface of the opening portion is in contact with a rib edge on the side where the opening area is wider and is formed as a projectingly curved surface. 
   An embodiment of the present invention resides in a polygonal rib structure wherein the cross-sectional shape of the polygonal rib is a set of connected regular hexagons or rectangles. 
   An embodiment of the present invention resides in a polygonal rib structure wherein the polygonal rib structure is a shock absorbing member. 
   An embodiment of the present invention resides in a polygonal rib structure wherein the polygonal rib structure is a shock absorbing member for a helmet. 
   An embodiment of the present invention resides in a mold for molding an opened polygonal rib structure, comprised of an upper-lower pair of molds, wherein one of the molds has a structure in which a tapered tetragonal pyramidal male mold being rhombic in cross-sectional shape and tapered toward the tip end thereof is located at the center of each outer peripheral surface of a virtual regular polygonal columnar surface, and the longitudinal section of the tapered tetragonal pyramidal male mold is disposed along the virtual regular polygonal columnar surface. The other of the molds has a structure in which a regular polygonal groove with a fixed width is formed, with the virtual regular polygonal columnar surface as a center. A V-shaped recessed portion that is gradually reduced toward the groove depth is formed at the center in the longitudinal direction of the regular polygonal groove. 
   An embodiment of the present invention resides in a method of molding a polygonal rib structure, including the steps of charging the space between the pair of molds with a molding material and thereafter bringing the opposed wall surfaces of the tetragonal pyramidal opening portion formed by the tapered tetragonal pyramidal male mold into contact with each other to constitute a polygonal rib structure. 
   According to an embodiment of the present invention, an opened polygonal rib structure is provided having ribs directed orthogonal to one plane and intersecting each other to form polygonal shapes wherein a tapered tetragonal pyramidal opening portion having a rhombic sectional shape is formed in a thickened central portion located at substantially a central portion in the longitudinal direction of each side of the polygonal rib that can be mass-produced at low cost. 
   According to an embodiment of the present invention, the outer peripheral surface in contact with the rib edges of the polygonal rib can be so varied that the radius of curvature varies from location to location. 
   According to an embodiment of the present invention, by closing the rhombic tapered tetragonal pyramidal opening portions a polygonal rib structure is formed wherein the outer peripheral surface of the opening portion is in contact with the rib edge on the side where the opening area is broader that is formed as a projectingly curved surface that can be easily produced. 
   According to an embodiment of the present invention, a polygonal rib structure wherein the cross-sectional shape of the polygonal rib is a set of connected regular hexagons or rectangles can be easily produced. 
   According to an embodiment of the present invention, a polygonal rib structure that is light in weight and high in shock absorbing property can be obtained. 
   According to an embodiment of the present invention, by adding the polygonal rib structure to the inner peripheral surface of a helmet, a helmet is obtained that is light in weight and high in shock absorbing property and inexpensively to manufacture. 
   By using the mold according to the present invention, the polygonal rib structure can be easily obtained inexpensively. 
   By applying the method of molding according to the present invention, the polygonal rib structure can be easily mass-produced at a low cost. 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1  is a plan view of an opened hexagonal rib structure according to one embodiment of the present invention; 
       FIG. 2  is an enlarged view of a major part of  FIG. 1 ; 
       FIG. 3  is a vertical sectional view taken along line III-III of  FIG. 2 ; 
       FIG. 4  is a vertical sectional view taken along line IV-IV of  FIG. 2 ; 
       FIG. 5  is an exploded perspective view of a mold; 
       FIG. 6  is a bottom view, as viewed upwards from the lower side, of an upper mold; 
       FIG. 7  is a plan view of a lower mold; 
       FIG. 8  is an enlarged plan view of a major part of  FIG. 7 ; 
       FIG. 9  is a sectional view taken along line IX-IX of  FIG. 5 ; 
       FIG. 10  is a sectional view taken along line X-X of  FIG. 5 ; 
       FIG. 11  is a plan view of a hexagonal rib structure; 
       FIG. 12  is a sectional view taken along line XII-XII of  FIG. 11 ; 
       FIG. 13  is a sectional view taken along line XIII-XIII of  FIG. 11 ; 
       FIG. 14  is an overall perspective view of the hexagonal rib structure; 
       FIG. 15  is an enlarged plan view of a major part of an opened rib structure in which the shapes of rhombuses of opening portions are different; 
       FIG. 16  is a sectional view taken along line XVI-XVI of  FIG. 15 ; 
       FIG. 17  is a plan view of a square rib structure according to another embodiment of the present invention; 
       FIG. 18  is a plan view of a regular triangular rib structure according to a further embodiment of the present invention; 
       FIG. 19  is a plan view of a combined square-octagonal rib structure according to yet another embodiment of the present invention; 
       FIG. 20  is a perspective view showing a part of the process of manufacturing a hexagonal rib structure in the related art; 
       FIG. 21  is a horizontal sectional view along line XXI-XXI of  FIG. 20 ; 
       FIG. 22  is an illustration of the condition where an adhesive is applied to a band-like blank material obtained in  FIG. 20 ; 
       FIG. 23  is a perspective view of an arcuate blank material obtained by dividing the band-like blank material obtained in  FIG. 20 ; and 
       FIG. 24  is an illustration of the last step, after the adhesive shown in  FIG. 22  is applied and cured. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now, one embodiment of the present invention shown in  FIGS. 1 to 14  will be described. 
   An opened hexagonal rib structure  2  according to one embodiment of the invention is shown in  FIG. 1 .  FIG. 2  is an enlarged plan view of a major part of this embodiment of the present invention. 
   In the opened hexagonal rib structure  2 , end portions of ribs  3  are integrally joined to each other at angular intervals of 120°, a thickened central portion is located at a substantially central portion in the longitudinal direction of each of the ribs  3  that is bisected to form a rhombic opening portion  4 . The rhombic opening portion  4  is rhombic in cross-sectional shape, and is so shaped that the cross-sectional area thereof is reduced as one goes downwardly from the upper opening end. 
   The outside surfaces of the ribs  3  adjacent, respectively, to a longitudinal valley line  6  directed in the longitudinal direction of the rib  3  in the opening inside surface  5  and a widthwise valley line  7  directed in the width direction of the rib  3  are provided, respectively, with a notch  8  and a notch  9  which are V-shaped in section. 
   In order to manufacture the opened hexagonal rib structure  2  shown in  FIGS. 1 and 2 , a mold  20  consisting of an upper mold  21  and a lower mold  30  is used which constitute an upper-lower pair shown in  FIG. 5 . 
   As shown in  FIGS. 5 and 6 , the upper mold  21  has a structure in which truncated tetragonal pyramidal male molds  23  project downwardly from the lower surface of an upper base  22  of the upper mold  21  so that the longitudinal edge lines  26  of the truncated tetragonal pyramidal male molds  23  coincide with the sides of a virtual regular hexagon  24  indicated by dot-dash line. In addition, the truncated tetragonal pyramidal male molds  23  are located at the centers of the sides of the virtual regular hexagon  24 . 
   In addition, the lower mold  30  has a structure in which a mold thick plate (not shown) is provided with regular hexagonal grooves  34  having a width equal to the thickness of the opened hexagonal rib structure  2  shown in  FIG. 2 , along virtual regular hexagons  33  indicated by dot-dash line having the same shape as the virtual regular hexagons  24  of the upper mold  21 . A truncated tetragonal pyramidal recessed portion  35  having the same shape as the outside surface  25  of the truncated tetragonal pyramidal male mold  23  of the upper mold  21  is formed at a central portion of each side of the regular hexagonal grooves  34 . A projected beam  36  that is triangular in section is directed in the vertical direction and is formed at the groove bottom of the truncated tetragonal pyramidal recessed portion  35 . End edges of the truncated tetragonal pyramidal recessed portion  35  are provided with projecting beams  37  along the end edges, whereby the lower mold  30  has a structure in which deformed hexagonal columnar male molds  32  are integrally joined to a lower base  31 . 
   In the condition where the truncated tetragonal pyramidal male molds  23  of the upper mold  21  are loosely fitted in the truncated tetragonal pyramidal recessed portions  35  of the lower mold  30  so that the center line of the truncated tetragonal pyramidal male mold  23  of the upper mold  21  is set coinciding with the center line of the truncated tetragonal pyramidal recessed portion  35  located at the central portion of each side of the regular hexagonal groove  34  of the lower mold  30 , a thermoplastic resin is injected into the cavities between the upper mold  21  and the lower mold  30 . Thus, the opened hexagonal rib structure  2  shown in  FIGS. 1 to 4  can be injection molded. 
   When an adhesive is applied to the opening inside surfaces  5  of the injection-molded opened hexagonal rib structure  2  shown in  FIGS. 1 to 4 , and then both side surfaces of each of the rhombic opening portions  4  are pressed so as to bring the opposed widthwise valley lines  7  into contact with each other, the rhombic opening portions  4  are closed and the hexagonal rib structure  1  shown in  FIG. 11  is formed. 
   In the rib top face  10  of the opened hexagonal rib structure  2 , as shown at a right lower portion of  FIG. 2 , the distance S 1  between the rib top face intersection center point  11  where three ribs  3  intersect and the adjacent rib top face intersection center point  11  is the sum of the interval  2 A 1  of the longitudinal valley line top points  12  of both longitudinal valley lines  6  and the double  2 C of the distance C between the rib top face intersection center point  11  and the longitudinal valley line top point  12 , that is:
 
 S   1 =2( A   1   +C ).
 
   In the rib bottom face  14  of the opened hexagonal rib structure  2 , as shown at a left lower portion of  FIG. 2 , the distance T 1  between the rib bottom face intersection center point  15  where three ribs  3  intersect and the adjacent rib bottom face intersection center point  15  is the sum of the distance  2 B 1  between both longitudinal valley line bottom points  16  and the double  2 D of the distance D between the rib bottom face intersection center point  15  and the longitudinal valley line bottom point  16 , that is:
 
 T   1 =2( B   1   +D )= S   1 .
 
   When the rhombic opening portions  4  of the opened hexagonal rib structure  2  are closed, the widthwise valley line top points  13  of the widthwise valley lines  7  in the hexagonal rib structure  1  come into contact with each other. Therefore, as shown in  FIG. 12 , the distance S 2  between the longitudinal valley line top point  12  in the rib top face  10  and the adjacent longitudinal valley line top point  12  is the sum of the double  2 A 2  of the distance A 2  between the longitudinal valley line top point  12  and the widthwise valley line top point  13  and the double  2 C of the distance C between the rib bottom face intersection center point  15  and the longitudinal valley line bottom point  16 , that is:
 
 S   2 =2( A   2   +C ).
 
   In the rib bottom face  14  of the hexagonal rib structure  1  in the condition where the rhombic opening portions  4  of the opened hexagonal rib structure  2  are closed, the distance T 2  between the rib bottom face intersection center point  15  and the adjacent rib bottom face intersection center point  15  is the sum of the double  2 B 2  of the distance B 2  between the longitudinal valley line bottom point  16  and the widthwise valley line bottom point  17  and the double  2 D of the distance D between the rib bottom face intersection center point  15  and the longitudinal valley line bottom point  16 , that is:
 
 T   2 =2( B   2   +D ).
 
   In the rib top face  10 , when the rhombic opening portions  4  are closed, the distance S 1  between the adjacent rib top face intersection center points  11  of the opened hexagonal rib structure  2  becomes the distance S 2  between the adjacent rib top face intersection center points  11  of the hexagonal rib structure  1 , and the difference between the two kinds of distances is:
 
 S   2   −S   1 =2( A   2   −A   1 ).
 
   Here, as is clear from  FIG. 2 , A 2  is the length of the oblique line  12 - 13  of the right-angled triangle having the longitudinal valley line top point  12 , the widthwise valley line top point  13  and the opening center point  18  as apexes, and is longer than the base  12 - 18  of the triangle. Therefore, when the rhombic opening portions  4  are closed, the distance between both rib top face intersection center points  11  is increased by 2(A 2 −A 1 ). 
   Similarly, in the rib bottom face  14  also, the distance T 2  between both rib bottom intersection center points  15  in the condition where the rhombic opening portions  4  are closed and the distance T 1  between both rib bottom face intersection center points  15  in the condition where the rhombic opening portions  4  are formed are in the relationship of:
 
 T   2   −T   1 =2( B   2   −B   1 ).
 
   Thus, when the rhombic opening portions  4  are closed, the distance between both rib bottom face intersection center points  15  is increased by 2(B 2 −B 1 ). However, this elongation amount is small, since B 1  and B 2  are shorter as compared with A 1  and A 2 . Therefore, the surface formed by joining the rib top faces  10  is an upwardly projecting curved surface as shown in  FIG. 14 , which makes it possible to apply the hexagonal rib structure  1  to a helmet shock absorbing member (not shown). 
   According to the embodiment shown in  FIGS. 1 to 14 , the opened hexagonal rib structure  2  can be efficiently injection molded in a short time, by only using the mold  20  composed of the upper mold  21  and the lower mold  30  constituting an upper-lower pair and injecting a thermoplastic resin or thermosetting resin into the cavities formed between the upper mold  21  and the lower mold  30 . Therefore, productivity can be enhanced, and the opened hexagonal rib structure  2  can be mass-produced at a low cost. 
   In addition, by integrally joining the opposed opening inside surfaces  5  in the molded opened hexagonal rib structure  2  by use of an adhesive, the rhombic opening portions  4  can be closed, and the hexagonal rib structure  1  curved to the upper side as shown in  FIG. 14  can be produced. 
   Further, when a material comparatively low in shock breakage strength is used as the material for constituting the opened hexagonal rib structure  2 , a structure can be obtained that is light in weight and favorable in shock absorbing property. 
   With the size and shape of the rhombic opening portions  4  in the opened hexagonal rib structure  2  appropriately varied depending on the location in the opened hexagonal rib structure  2 , the curved surface shape of the hexagonal rib structure  1  can be conformed to the shape of a helmet, and the hexagonal rib structure can be easily applied to a shock absorbing member for helmets. 
   While the opposed opening inside surfaces  5  in the opened hexagonal rib structure  2  have been integrally joined by use of an adhesive, the opposed opening inside surfaces  5  in the opened hexagonal rib structure  2  may be integrally joined by fusing (welding) in the case where a thermoplastic resin is used as the material for constituting the hexagonal rib structure  1 . 
   While the rhombus of the upper opening of the rhombic opening portion  4  and the rhombus of the lower opening of the rhombic opening portion  4  have been different in size and substantially analogous in shape in the embodiment shown in  FIGS. 1 to 14 , there may be adopted a configuration in which, as shown in  FIGS. 15 and 16 , the size in the longitudinal direction of the upper opening  4   a  of the rhombic opening portion  4 X is equal to the size in the longitudinal direction of the lower opening  4   b  of the rhombic opening portion  4 X. However, the size in the width direction of the upper opening  4   a  is larger than the size in the width direction of the lower opening  4   b , and the shape of the upper opening  4   a  is conspicuously different from the shape of the lower opening  4   b.    
   While the polygon has been a regular hexagon in the embodiment shown in  FIGS. 1 to 14 , the present invention naturally is applicable also to a square rib structure  40  as shown in  FIG. 17  and to a regular triangular rib structure  41  as shown in  FIG. 18 . 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Technology Classification (CPC): 0