Abstract:
A safety hypodermic syringe in which the plunger is detachably connected to the stopper by a hook joint so that when the user pulled the plunger backwards to carry the stopper and the needle assembly backwards to the inside of the barrel after the service of the syringe, the plunger is automatically disconnected from the stopper, leaving the stopper and the needle assembly inside the barrel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a hypodermic syringe and, more particularly, to a safety hypodermic syringe, which enables the plunger to be automatically disconnected from the stopper after the service of the syringe, leaving the stopper and the needle assembly inside the barrel. 
     2. Description of the Related Art 
     When disposing of a disposable hypodermic syringe after its service, the person handling the disposable hypodermic syringe may be injured by the protruding needle cannula accidentally. In order to eliminate this problem, safety hypodermic syringes are developed. These safety hypodermic syringes enable the needle assembly to be pulled backwards with the plunger and received inside the barrel after the service. Exemplars of these safety hypodermic syringes are seen in Taiwan Patent Application Nos. 189436; 356013; 463639; 414085; 384709; 359621; 492328; 467752; 475449; 480185; 497976; 430565; 471322; 332433; 394027; and 447310, and U.S. Pat. Nos. 5,385,557; 4,747,830; 4,677,980; 5,242,400; 4,986,813; 4,947,863; 5,533,975; 5,171,300; 4,944,723, . . . etc. These safety hypodermic syringes still have drawbacks. When the needle assembly received inside the barrel after the service of the hypodermic syringe, the plunger is still maintained secured to the stopper and the barrel. If the person disposing of the hypodermic syringe pushes the plunger accidentally, the needle cannula may be forced out of the barrel to injure the person disposing of the hypodermic syringe or a nearby person. In order to eliminate this problem, safety hypodermic syringes with a disconnectable plunger are developed. FIG. 1 shows a safety hypodermic syringe according to the prior art. According to this design, the plunger  11  has a neck  111  near the front side. When the needle assembly  13  and the stopper  12  received inside the barrel  14  upon a return stroke of the plunger  11 , the user can twist the plunger  11  to break the neck  111 . U.S. Pat. No. 4,944,723 shows a similar design. FIG. 2 shows a safety hypodermic syringe according to Taiwan Patent Publication NO. 492328. According to this design, a breaking groove  112  is provided in the connecting area between the plunger  11  and the stopper  12 . When the needle assembly  13  and the stopper  12  received inside the barrel  14  upon a return stroke of the plunger  11 , the user can disconnect the plunger  11  from the stopper  12  by biasing the plunger  11 . U.S. Pat. No. 5,242,400 shows a similar design. FIG. 3 shows a safety hypodermic syringe according to Taiwan Patent Publication No. 378541. According to this design, the stopper  12  has a T-block  121  invertedly suspended at the bottom side, and the plunger  11  has a front coupling hole  113  detachably coupled to the T-block  121 . When disconnecting the plunger  11  from the stopper  12 , the user must twist the plunger  11  with force. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a safety hypodermic syringe, which enables the plunger to be automatically disconnected from the stopper after the service of the syringe, leaving the stopper and the needle assembly inside the barrel. 
     To achieve this and other object of the present invention, the safety hypodermic syringe comprises a barrel, the barrel comprising a body and a socket at a front side of the body; a needle assembly, the needle assembly comprising a needle hub mounted in the front socket of the barrel, the needle hub having a bottom retaining hole, and a needle cannula forwardly extended from the needle hub outside the barrel; and a plunger and stopper unit, the plunger and stopper unit comprising a stopper fitted into the body of the barrel, and an elongated plunger adapted to reciprocate the stopper in the body of the barrel, the stopper having an arrowhead-like front hook engageable into a bottom retaining hole of the needle hub for enabling the needle assembly to be pulled backwards with the plunger and stopper unit and received inside the body of the barrel; wherein the barrel has a stop device in a rear side of the body and adapted to stop the stopper from falling out of the body; the plunger comprises a plurality of equiangularly spaced and radially extended springy front wings, the front wings each having a crevice longitudinally extended to a front side thereof, the front wings including two opposite front wings, the opposite front wings each having a plurality of retaining blocks; the stopper has a plurality of locating blocks protruded from a bottom sidewall thereof and defining a receiving space adapted to receive the front wings of the plunger, the locating blocks each having a protruded engagement portion adapted to engage the retaining blocks of the opposite front wings of the plunger and to secure the plunger to said stopper. dr 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional side view of a safety hypodermic syringe according to the prior art. 
     FIG. 2 is a sectional side view of another design of safety hypodermic syringe according to the prior art. 
     FIG. 3 is a sectional side view of still another design of safety hypodermic syringe according to the prior art. 
     FIG. 4 is an exploded view of a safety hypodermic syringe according to the present invention. 
     FIG. 5 is an exploded view of the plunger and stopper unit of the safety hypodermic syringe according to the present invention. 
     FIG. 6 is a bottom view of the stopper of the plunger and stopper unit of the safety hypodermic syringe according to the present invention. 
     FIG. 7 is a schematic side view of the plunger and stopper unit of the safety hypodermic syringe according to the present invention, showing the front wings compressed and inserted into the crossed receiving space in the bottom side of the stopper. 
     FIG. 8 is a schematic side view of the plunger and stopper unit of the safety hypodermic syringe according to the present invention, showing the plunger fastened to the stopper. 
     FIG. 9 is a schematic side view of the present invention, showing a status of use of the safety hypodermic syringe. 
     FIG. 10 is a sectional view taken along line  10 — 10  of FIG.  9 . 
     FIG. 11 is similar to FIG. 10 but showing an alternate form of the stop device. 
     FIG. 12 is a schematic side view of the present invention, showing the return stroke of the plunger and stopper unit. 
     FIG. 13 is similar to FIG. 12 but showing the plunger disconnected from the stopper. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 4, a safety hypodermic syringe in accordance with the present invention is shown comprised of a barrel  2 , which comprises a body  21  and a socket  22  at the front side of the body  21 , a needle assembly  3 , which comprises a needle hub  31  mounted in the front socket  22  of the barrel  2  and a needle cannula  32  forwardly extended from the needle hub  31  outside the barrel  2 , a plunger and stopper unit  4 , which comprises a stopper  42  fitted into the body  21  of the barrel  2  and an elongated plunger  41  adapted to reciprocate the stopper  42  in the body  21  of the barrel  2 , and a cap  5  adapted to protect the needle assembly  3 . The stopper  42  has an arrowhead-like front hook  421  that can be hooked in a bottom retaining hole (not shown) in the needle hub  31  for enabling the needle assembly  3  to be pulled backwards with the plunger and stopper unit  4  and received inside the body  21  of the barrel  2 . 
     FIG. 5 is an exploded view of the aforesaid plunger and stopper unit  4 . The plunger  41  comprises four equiangularly spaced and radially extended springy front wings  41   a ,  41   b ,  41   c , and  41   d , each having a crevice  411  longitudinally extended to the front side. The front wings  41   a ,  41   b ,  41   c , and  41   d  are arranged in two pairs each including two opposite wings. Two opposite wings  41   a  and  41   b  each have two reversely protruded retaining blocks  412   a  and  412   c ;  412   b  and  412   d . The stopper  42  has four locating blocks  42   a ,  42   b ,  42   c , and  42   d  protruded from the bottom sidewall and defining a crossed receiving space  423  for receiving the front wings  41   a ,  41   b ,  41   c , and  41   d  of the plunger  41 . The locating blocks  42   a ,  42   b ,  42   c , and  42   d  each have a protruded engagement portion  422   a ,  422   b ,  422   c , or  422   d  adapted to engage the retaining blocks  412   a  and  412   c ,  412   b , and  412   d  of the plunger  41 . 
     FIG. 6 is a bottom view of the stopper  42  in which the imaginary lines indicate the positioning of the front wings  41   a ,  41   b ,  41   c , and  41   d  of the plunger  41  relative to the locating blocks  42   a ,  42   b ,  42   c , and  42   d.    
     FIG. 7 is a plain view of the plunger  4 . The left and right front wings  41   a  and  41   b  are radially compressed inwards to close the respective crevices  411  for enabling the four front wings  41   a ,  41   b ,  41   c , and  41   d  of the plunger  41  to be inserted into the crossed receiving space  423  in the bottom side of the stopper  42 . After insertion of the four front wings  41   a ,  41   b ,  41   c , and  41   d  into the crossed receiving space  423  and release of radial compressive force from the left and right front wings  41   a  and  41   b , the left and right front wings  41   a  and  41   b  are returned to their former shape to force the respective retaining blocks  412   a  and  412   c ,  412   b , and  412   d  into engagement with the corresponding protruded engagement portions  422   a ,  422   b ,  422   c , or  422   d  of the locating blocks  42   a ,  42   b ,  42   c , and  42   d , and therefore the plunger  41  is secured to the stopper  42  (see FIG.  8 ). 
     FIG. 9 is a schematic sectional view, showing a status of use of the safety hypodermic syringe. As illustrated, the plunger and stopper unit  4  is pushed forwards to force liquid medicine L out of the needle cannula  32 . When the plunger and stopper unit  4  moved to the upper limit position, the arrowhead-like hook  421  of the stopper  42  is forced into engagement with the bottom retaining hole  311  of the needle hub  31  for enabling the needle assembly  3  to be received inside the barrel  2  upon a back stroke of the plunger and stopper unit  4 . 
     Referring to FIGS. 10 and 11 and FIG. 9 again, the body  21  of the barrel  2  has a stop device  23  at the rear side adapted to stop the stopper  42  from falling out of the barrel  2  upon a backstroke of the plunger and stopper unit  4 . The stop device  23  may be variously embodied. For example, the stop device  23  can be an inside annular flange protruded from the inside wall of the body  21  of the barrel  2  as shown in FIG. 10, or comprised of a plurality of blocks protruded from the inside wall of the body  21  of the barrel  2  as shown in FIG.  11 . The body  21  of the barrel  2  can be made having small raised portions  24  on the inside above the stop device  23 . The small raised portions  24  are not requisite. The effect of the small raised portions  24  will be explained latter. 
     FIG. 12 illustrates a status of use of the safety hypodermic syringe after return stroke of the plunger and stopper unit  4 . When the plunger  41  pulled backwards to the rear side of the barrel  2 , the front wings  41   a ,  41   b ,  41   c , and  41   d  are radially inwardly forced by the stop device  23  to close the respective crevices  411 , thereby causing the respective retaining blocks  412   a  and  412   c ,  412   b , and  412   d  to be disengaged from the corresponding protruded engagement portions  422   a ,  422   b ,  422   c , and  422   d  of the locating blocks  42   a ,  42   b ,  42   c , and  42   d , and therefore the plunger  41  is disconnected from the stopper  42 , leaving the stopper  42  and the needle assembly  3  inside the barrel  2  (see FIG.  13 ). 
     Referring to FIG. 13 again, after removal of the plunger  41  from the stopper  42 , the cap  5  is covered on the front socket  22  to close the barrel  2 . At this time, the stopper  42  is retained inside the body  21  of the barrel  2  between the small raised portions  24  and the stop device  23 , holding the needle assembly  3  inside the barrel  2 . Because the stopper  42  is an elastic member, it can be deformed to pass over the raised portions  24  when pulled backwards by the plunger  41 . After removal of the plunger  41  from the stopper  42 , the stopper  42  is firmly stopped between the small raised portions  24  and the stop device  23 . 
     A prototype of safety hypodermic syringe has been constructed within the features of FIGS.  4 ˜ 13 . The safety hypodermic syringe functions smoothly to provide all the features discussed earlier. 
     Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.