Abstract:
A safety hypodermic syringe is constructed to include a barrel, a needle assembly, a female connector, a plunger, and a male connector, wherein the female connector is disposed in the front end of the barrel and fastened to the needle assembly, having a rear retaining hole; the male connector is provided at the front side of the plunger and adapted to engage the rear retaining hole upon forward stroke of the plunger, for enabling the needle assembly to be pulled backwards with the plunger and received inside the barrel after the service of the hypodermis syringe.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a hypodermic syringe, and more particularly to a safety hypodermic syringe, which enables the needle assembly to be received inside the syringe barrel after the service of the syringe. 
     Regular safety hypodermic syringes are made for enabling the user (nurse or doctor) to pull the needle assembly backwards to the inside of the syringe barrel after injection, preventing possible contamination of bacteria or virus through the needle cannula. Taiwan Patent #356013 discloses a similar design of safety hypodermic syringe. However, this design of safety hypodermic syringe is still not satisfactory in function. When pushing the plunger into engagement with the needle assembly, a minor vibration occurs, causing the patient to feel uncomfortable. 
     SUMMARY OF THE INVENTION 
     The invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a safety hypodermic syringe, which enables the needle assembly to be pulled backwards and received inside the syringe barrel after the use of the syringe. It is another object of the present invention to provide a safety hypodermic syringe, which eliminates the occurrence of vibration during injection. It is still another object of the present invention to provide a safety hypodermic syringe, which saves much fabrication time, and reduces the manufacturing cost. According to the present invention, the safety hypodermic syringe comprises a barrel, a needle assembly, a female connector, a plunger, and a male connector. The needle assembly is disposed at the front side of the barrel, and connected to the front side of the female connector. The female connector has a rear retaining hole that can be radially reduced or expanded, and a rear side mounted with an elastic band. The elastic band imparts a radial compression force to the rear part of the female connector, causing the rear retaining hole to be reduced to the smallest status. The elastic band can be molded from rubber or other equivalent material. The male connector comprises a shank forwardly extended from the front side of the plunger, and a head at the front end of the shank. When pushing the plunger forwards in the barrel, the head of the male connector is forced to expand the rear retaining hole. After passed through the rear retaining hole, the rear retaining hole is reduced to stop the head of the male connector from backward movement, and therefore the needle assembly and the female connector are moved backwards with the male connector and received inside the barrel when pulling the plunger backwards to the rear end of the barrel. Because the opening status of the retaining hole is controlled by the elastic band, little vibration is produced when engaging the head of the male connector into the retaining hole of the female connector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a safety hypodermic syringe according the present invention. 
     FIG. 2 is an exploded view of a female connector according to a first embodiment of the present invention. 
     FIG. 3 is a perspective assembly view of the female connector shown in FIG.  2 . 
     FIG. 4 is a sectional view showing the status of the female connector before the insertion of the male connector. 
     FIG. 5 is a sectional view showing the head of the male connector inserted into the retaining hole of the female connector according to the present invention. 
     FIG. 6 is a sectional view showing the head of the male connector passed through the retaining hole into the chamber inside the female connector according to the present invention. 
     FIG. 7 is a sectional view of the safety hypodermic syringe according to the first embodiment of the present invention, showing the plunger pushed to the front limit position in the barrel. 
     FIG. 8 is another sectional view of the safety hypodermic syringe according to the first embodiment of the present invention, showing the plunger moved to the rear limit position in the barrel and the needle assembly received inside the barrel. 
     FIG. 9 is an exploded view of a female connector for a safety hypodermic syringe according to a second embodiment of the present invention. 
     FIG. 10 is a perspective assembly view of the female connector shown in FIG.  9 . 
     FIG. 11 is a sectional view of a part of the safety hypodermic syringe according to the second embodiment of the present invention, showing the head of the male connector inserted into the retaining hole of the female connector. 
     FIG. 12 is similar to FIG. 11 but showing the head of the male connector passed over the hooks of the stop blocks and engaged with the retaining hole of the female connector. 
     FIG. 13 is a sectional view of the second embodiment of the present invention, showing the plunger moved to the rear limit position in the barrel and the needle assembly received inside the barrel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. from  1  through  8 , a safety hypodermic syringe  10  is shown comprised of a barrel  20 , a needle assembly  30 , a female connector  50 , a plunger  60 , and a male connector  70 . 
     The barrel  20  comprises a cylindrical body  25 , and a finger flange  23  integral with the rear end  22  of the body  25 . The body  25  has a front opening  211  at the tapered front end  21  thereof, a rear opening  221  at the rear end  22  thereof, an inside receiving chamber  24  in communication between the front opening  211  and the rear opening  221 , and an annular inside stop flange  26  raised around the inside wall thereof within the inside receiving chamber  24  adjacent to the front opening  211 , and another annular inside step flange  27  raised around the inside wall of the rear end thereof within the inside receiving chamber  24  adjacent to the finger flange  23 . 
     The needle assembly  30  comprises a needle cannula  31  and a needle hub  32  holding the needle cannula  31 . The needle hub  32  has a locating flange  33  raised around the periphery of the rear end thereof. The diameter of the locating flange  33  is greater than the inner diameter of the annular inside stop flange  26 , so that the locating flange  33  can be positively stopped behind the annular inside stop flange  26  after installation of the needle assembly  30  in the front end  21  of the barrel  20 . The connection between the needle cannula  31  and the needle hub  32  can easily be achieved by conventional techniques. Further, any equivalent structural design can be employed instead of the matching of the annular inside stop flange  26  and the locating flange  33 . 
     The female connector  50  fits the inside wall of the barrel  20  around the receiving chamber  24 . According to the present preferred embodiment, the female connector  50  comprises a hollow connector body  51  defining a chamber  56 , and an elastic band  57  mounted on the connector body  51  (see FIGS.  2  and  3 ). The connector body  51  comprises a front needle hub support part  52  having a front hole  521 , and a rear male connector receiving part  54  having a retaining hole  541 . The front needle hub support part  52  is coupled to the rear side of the needle hub  32  of the needle assembly  30 . According to the present preferred embodiment, the front needle hub support part  52  is a hollow, stepped member fitted into the needle hub  32  from the rear side of the needle hub  32 , having a step  53  stopped at the locating flange  33  against the annular inside stop flange  26  to seal the gap and to prevent the fluid (medicine or blood) from leaking out of the hypodermic syringe. Alternatively, an O-ring may be used to seal the gap. The rear male connector receiving part  54  is disposed at the rear side of the front needle hub support part  52 . According to the present preferred embodiment, the rear male connector receiving part  54  and the rear side of the front needle hub support part  52  are made in integrity. The rear male connector receiving part  54  comprises two equiangularly spaced (spaced from each other at 180°) springy stop blocks  55 . The stop blocks  55  each have a part connected to the rear connector receiving part  54 . The elastic band  57  is mounted on the rear male connector receiving part  54  over the stop blocks  55  (see FIG.  3 ). After installation of the elastic band  57 , stop blocks  55  are forced inwards into the chamber  56 . The elastic band  57  is preferably molded from rubber. The number of the stop blocks  55  may be changed as desired. For example, three, four, five or more stop blocks  55  may be provided. However, the stop blocks  55  must be equiangularly spaced from one another. In case three stop blocks  55  are provided, the stop blocks  55  must be equally spaced at the internal of 120°. 
     The plunger  60  is inserted from the rear opening  221  into the body  25  of the barrel  20 , having a front end fixedly mounted with a stopper  61  and a rear end terminating in a thumb rest  62 . 
     The male connector  70  is installed in the front side of the plunger  60  and protruded over the front side of the stopper  61 . According to the present preferred embodiment, the male connector  70  is shaped like a parachute (mushroom), comprising a head  71  and a shank  72 . The head  71  is fixedly connected to one end, namely, the front end of the shank  72 , having a smaller front part and a greater rear part. The cross-sectional area of the rear part of the head  71  is greater than the retaining hole  541  defined after the stop blocks  55  has been forced into the chamber  56 . 
     During injection and before moving the male connector  70  into engagement with the female connector  50  (the male connector  70  can be made having a split for easy insertion into the female connector  50  with less insertion resistance), as shown in FIG. 4, the stop blocks  55  are forced by the compressive force of the elastic band  57  to project into the chamber  56 , defining the aforesaid retaining hole  541 . 
     When forcing the male connector  70  into the retaining hole  541 , as shown in FIG. 5, the stop blocks  55  are forced radially outwards by the greater rear part of the head  71  of the male connector  70  to expand the elastic band  57 . When the elastic band  57  expands, it buffers (smoothens) the radially outwardly displacement of the stop blocks  55 , preventing the occurrence of vibration. 
     After the head  71  of the male connector  70  passed the retaining hole  541 , as shown in FIG. 6, the elastic band  57  is released from pressure and returns to its former shape to force the stop blocks  55  back to their former positions smoothly, as shown in FIG. 7, eliminating possible shocks. 
     When the user pulls the plunger  60  backwards after injection, the female connector  50  and the needle assembly  30  are moved backwards with the male connector  70  and plunger  60  and received in the inside receiving chamber  24  inside the barrel  20  as shown in FIG. 8, and therefore the needle cannula  31  is well protected inside the barrel  20 . 
     FIGS. from  9  through  13  show a second embodiment of the present invention. The second embodiment has similar structure as the aforesaid first embodiment with the exception of the female connector. According to the second embodiment, the female connector, referenced by  40  comprises a hollow connector body  41  defining a chamber  46 , and an elastic band  47  mounted on the connector body  41 . The connector body  41  comprises a front needle hub support part  42  having a front hole  421 , and a rear male connector receiving part  44  having a retaining hole  441 . The front needle hub support part  42  is coupled to the rear side of the needle hub  32  of the needle assembly  30 . The front needle hub support part  42  is a hollow, stepped member fitted into the needle hub  32  from the rear side of the needle hub  32 , having a step  43  stopped at the locating flange  33  against the annular inside stop flange  26  to seal the gap. The rear male connector receiving part  44  comprises four equiangularly spaced springy stop blocks  45 . The stop blocks  45  each have an inward hook  451  facing the chamber  46 . Before engaging the head  71  of the male connector  70 , the cross-sectional area of the retaining hole  441  defined within the hooks  451  of the stop blocks  45  is smaller than the greatest cross-sectional area of the head  71  of the male connector  70 . 
     As illustrated in FIG. 11, when the head  71  is moved with the plunger  60  forwards to squeeze the hooks  451  of the stop blocks  45 , the stop blocks  45  are forced radially outwards to expand the elastic band  47  for enabling the head  71  of the male connector  70  to pass through the retaining hole  441  into the chamber  46 , as shown in FIG.  12 . When the user pulls the plunger  60  backwards after the service of the hypodermic syringe, the female connector  40  and the needle assembly  30  are moved backwards with the male connector  70  and plunger  60  and received in the inside receiving chamber  24  inside the barrel  20  as shown in FIG. 13, and therefore the needle cannula  31  is well protected inside the barrel  20 . 
     According to the second embodiment of the present invention, the elastic band  47  is preferably molded from natural rubber and then mounted on the rear male connector receiving part  44 . In order to save manufacturing cost and time, the elastic band  47  can be directly injection-molded on the outside of the rear male connector receiving part  44  after molding of the connector body  41 . 
     It is to be understood that the drawings are designed for purposes of illustration only, and are not intended for use as a definition of the limits and scope of the invention disclosed.