Patent Abstract:
A combination of an inner frame and at least two blades for a plug is provided. The combination includes an inner frame and at least two blades. The inner frame includes at least two positioning holes and at least two hook members respectively located adjacent to the positioning holes. Each blade extends through an associated one of the positioning holes of the inner frame. Each blade includes a portion engaged with an associated one of the hook members, thereby retaining the blades in the inner frame during formation of a housing of a plug by injection molding.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a structure for engaging blades with an inner frame of a plug. 
   2. Description of the Related Art 
   A typical plug includes two or three blades. In manufacture, an end of a wire is placed into a wire-receiving groove in an end of a respective blade. The end of the respective blade is then pressed to securely clamp the end of the wire. Referring to  FIG. 1  of the drawings, after the clamping procedure, the blades  1  are disposed in an inner frame  12  which is then placed into a mold for forming a housing of the plug by means of injection molding. However, it was found that the blades  1  could not be reliably positioned in the inner frame  12  during the injection molding procedure such that disqualified products were produced frequently. Further, undesired contact between the blades  1  extending through holes (not labeled) of the inner frame  12  occurred easily. As a result, a short circuit was apt to occur when the blades  1  were in a conductive state. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a structure for engaging blades with an inner frame of a plug, thereby securely positioning the blades during an injection molding procedure for forming a housing of the plug. 
   In accordance with an aspect of the invention, a combination of an inner frame and at least two blades for a plug is provided. The combination includes an inner frame and at least two blades. The inner frame includes at least two positioning holes and at least two hook members respectively located adjacent to the positioning holes. Each blade extends through an associated one of the positioning holes of the inner frame. Each blade includes a portion engaged with an associated one of the hook members, thereby retaining the blades in the inner frame during formation of a housing of a plug by injection molding. 
   In an embodiment of the invention, the blades include a positive blade and a negative blade. Each blade includes an insulating layer formed on a rear section thereof. The insulating layer includes a flange that is engaged with the associated one of the hook members. 
   In another embodiment, the blades further include a grounding blade having an engaging hole for engaging with an associated one of the hook members. 
   In a further embodiment, the insulating layer of each blade includes a protruded portion, thereby forming a recessed portion on an outer side of the inner frame. The inner frame includes a plurality of through-holes extending through a bottom wall of the recessed portion and thus communicating with the recessed portion. Molten plastic material for forming the housing of the plug fills the recessed portion via the through-holes, thereby improving the bonding strength of the housing and the inner frame. Preferably, the through-holes include two rectangular through-holes. 
   A separation wall is formed between two positioning holes to eliminate the risk of short circuit resulting from a contact between the blades when in a conductive state. 
   Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of two blades and an inner frame of a conventional plug. 
       FIG. 2  is an exploded perspective view of a first embodiment of a structure for engaging blades with an inner frame of a plug in accordance with the present invention. 
       FIG. 3  is a sectional view of the blades and the inner frame in  FIG. 2 . 
       FIG. 4  is a plug made from the blades and the inner frame in  FIG. 3 . 
       FIG. 5  is an exploded perspective view of a modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention. 
       FIG. 6  is a perspective view of the blades and the inner frame in  FIG. 5 . 
       FIG. 7  is a plug made from the blades and the inner frame in  FIG. 6 . 
       FIG. 8  is an exploded perspective view of another modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention. 
       FIG. 9  is a sectional view of the blades and the inner frame in  FIG. 8 . 
       FIG. 10  is a plug made from the blades and the inner frame in  FIG. 9 . 
       FIG. 11  is an exploded perspective view of a further modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention. 
       FIG. 12  is a perspective view of the blades and the inner frame in  FIG. 11 . 
       FIG. 13  is a plug made from the blades and the inner frame in  FIG. 12 . 
       FIG. 14  is an exploded perspective view of still another modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention. 
       FIG. 15  is a sectional view of the blades and the inner frame in  FIG. 14 . 
       FIG. 16  is a plug made from the blades and the inner frame in  FIG. 15 . 
       FIG. 17  is an exploded perspective view of yet another modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention. 
       FIG. 18  is a perspective view of the blades and the inner fame in  FIG. 17 . 
       FIG. 19  is a plug made from the blades and the inner frame in  FIG. 18 . 
       FIG. 20  is a sectional view similar to  FIG. 3 , illustrating still another modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2  is an exploded perspective view of a first embodiment of a structure for engaging blades with an inner frame of a plug in accordance with the present invention.  FIG. 3  is a sectional view of the blades and the inner frame in  FIG. 2 .  FIG. 4  is a plug made from the blades and the inner frame in  FIG. 3 . 
   The inner fame  2  includes two positioning holes  21  through which two blades  31  (a positive blade and a negative blade) extend, respectively. Two resilient hook members  23  are provided on the inner frame  2  and respectively located adjacent to the positioning holes  21  of the inner frame  2 . Further, a separation wall  25  is formed between the positioning holes  21 . 
   Each blade  31  includes an insulating layer  33  formed on a rear section thereof. The insulating layer  33  is made of plastics and formed on the rear section of the blade  31  by injection molding. The insulating layer  33  further includes a flange  331  on a rear end thereof. 
   Referring to  FIG. 3 , when the respective blade  31  is disposed in the inner frame  2  and extends through the respective positioning hole  21  of the inner frame  2 , the respective resilient hook member  23  bends away from the respective blade  31  and then returns to its original position after the flange  331  of the insulating layer  33  of the respective blade  31  has passed through a hook end  230  of the respective resilient hook member  23 . The respective blade  31  is thus retained in place, as the insulating layer  33  of the respective blade  31  is reliably positioned by the respective resilient hook member  23 , best shown in  FIG. 3 . Next, the inner frame  2  together with the blades  31  are placed into a mold for forming a housing  4  by means of injection molding, thereby providing a plug with two blades, as shown in  FIG. 4 . It is noted that formation of the housing  4  is performed after clamping of an end of a respective wire in a wire-receiving groove  332  ( FIG. 2 ) of the respective blade  31 . Further, provision of the separation wall  25  between the positioning holes  21  of the inner frame  2  eliminates the risk of short circuit resulting from a contact between the blades  31  when in a conductive state. 
     FIG. 5  is an exploded perspective view of a modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention.  FIG. 6  is a perspective view of the blades and the inner frame in  FIG. 5 .  FIG. 7  is a plug made from the blades and the inner frame in  FIG. 6 . 
   In this embodiment, in addition to the two positioning holes  21 , the inner frame  2  includes a positioning hole  22  through which an additional blade  32  (a grounding prong or blade) extends. Further, an additional resilient hook member  24  is provided on the inner frame  2  and located adjacent to the positioning hole  22  of the inner frame  2 . 
   The grounding blade  32  includes an engaging hole  321  for engaging with the resilient hook member  24  of the inner frame  2  when the grounding blade  32  is disposed in the inner frame  2 . 
   Similar to the above embodiment, each blade  31  includes an insulating layer  33  formed on a rear section thereof. The insulating layer  33  is made of plastics and formed on the rear section of the blade  31  by injection molding. The insulating layer  33  further includes a flange  331  on a rear end thereof. 
   Formation of a housing  5  of the plug is substantially the same as that of the first embodiment. 
     FIG. 8  is an exploded perspective view of another modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention  FIG. 9  is a sectional view of the blades and the inner frame in  FIG. 8 .  FIG. 10  is a plug made from the blades and the inner frame in  FIG. 9 . 
   The only difference between this embodiment and the embodiment of  FIGS. 2 through 4  is that the insulating layer  33  of the respective blade  31  includes two opposite sides  33 A that are flush with two lateral sides of the respective blade  31 . 
     FIG. 11  is an exploded perspective view of a further modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention.  FIG. 12  is a perspective view of the blades and the inner frame in  FIG. 11 .  FIG. 13  is a plug made from the blades and the inner frame in  FIG. 12 . 
   The only difference between this embodiment and the embodiment of  FIGS. 5 through 7  is that the insulating layer  33  of the respective blade  31  includes two opposite sides  33 A that are flush with two lateral sides of the respective blade  31 . 
     FIG. 14  is an exploded perspective view of still another modified embodiment of the structure for engaging blades with an inner flame of a plug in accordance with the present invention.  FIG. 15  is a sectional view of the blades and the inner frame in  FIG. 14 .  FIG. 16  is a plug made from the blades and the inner frame in  FIG. 15 . 
   The only difference between this embodiment and the embodiment of  FIGS. 2 through 4  is that the insulating layer  33  of the respective blade  31  includes four sides  33 B that are respectively flush with four sides of the respective blade  31 . 
     FIG. 17  is an exploded perspective view of yet another modified embodiment of the structure for engaging blades with an inner fire of a plug in accordance with the present invention.  FIG. 18  is a perspective view of the blades and the inner frame in  FIG. 17 .  FIG. 19  is a plug made from the blades and the inner frame in  FIG. 18 . 
   The only difference between this embodiment and the embodiment of  FIGS. 5 through 7  is that the insulating layer  33  of the respective blade  31  includes four sides  33 B that are respectively flush with four sides of the respective blade  31 . 
     FIG. 20  is a sectional view similar to  FIG. 3 , illustrating still another modified embodiment of the structure for engaging blades with an inner frame of a plug in accordance with the present invention. In this embodiment, the inner frame  2 C includes a protruded portion  26 , thereby forming a recessed portion  27  in an outer side of the inner frame (now designated by  2 C). The inner frame  2 C has a plurality of through-holes  271  (preferably two rectangular through-holes in this embodiment) extending through a bottom wall of the recessed portion  27  and thus communicating with the recessed portion  27 . The through-holes  271  provide a passage through which air passes during the injection molding procedure for forming the housing  4 ,  5  of the plug. Further, the molten plastic material may rapidly fill the recessed portion  27  via the through-holes  271 . After hardening of the plastic material, the bonding strength between the inner frame  2 C and the housing  4 ,  5  of the plug is improved. 
   Conclusively, the blades  31  and  32  are reliably positioned when they are disposed in the inner frame  2 ,  2 C through provision of the flange  331  of the insulating layer  33  of the respective blade  31 , the engaging hole  321  of the blade  32 , and the resilient hook members  23 ,  24  of the inner frame  2 . Further, provision of the separation wall  25  between the positioning holes  21  of the inner frame  2  eliminates the risk of short circuit resulting from a contact between the blades  31  when in a conductive state. Further, the inner frame  2 C may include a recessed portion  27  having a plurality of through-holes  271  allowing passage of air during the injection molding procedure for forming a housing  4 ,  5  of the plug. The through-holes  271  also allow molten plastic material to rapidly fill the recessed portion  27  via the through-holes  271 . The bonding strength between the inner frame  2 C and the housing  4 ,  5  of the plug is improved after hardening of the plastic material. 
   Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.

Technology Classification (CPC): 7