Abstract:
This syringe comprises a tubular piece surrounding the body of the syringe and driving the stem of the plunger of the syringe. During injection, the tubular piece slides forward on the body. At the end of injection the tubular piece detaches from the stem and, its front part can continue to slide in order to sheathe the needle.

Description:
TECHNICAL FIELD 
     The subject of the present invention is a safety syringe for medical use. 
     BACKGROUND OF THE INVENTION 
     A syringe comprises a tubular body made of glass or a synthetic substance, intended to contain the liquid that is to be injected, one end of which is equipped with an injection needle, and inside which is fitted a plunger seal that can be actuated by a stem protruding from the body at the opposite end to the end equipped with the needle. Prior to use, the needle is generally covered by a protective element, for example made of rubber. Once the liquid contained in the body of the syringe has been injected, by actuating the plunger using the stem, the needle remains bare, and this represents a risk of stick injury, which carries the risk of the transmission of certain diseases, such as hepatitis or AIDS. 
     As the selling price of a conventional syringe is very low, the invention aims to provide a safety syringe, the selling price of which is increased only a small amount by comparison with that of a conventional syringe, and which has a needle-protecting device which automatically covers this needle in the same movement as the injection movement so as to protect the needle after injection without the need for an additional and deliberate handling operation on the part of the user. 
     To this end, in the syringe to which it relates, which is of the aforementioned type, the syringe body is equipped, at its rear end, with at least one radial tab, a tubular piece of a length at least equal to the length of the syringe body increased by the length of the needle and having at least one axial slot extending from its rear end, each slot serving for the passage of one radial tab, this tubular piece being mounted so that it can slide along the body, and the stem of the plunger seal is equipped with means for axial immobilization inside the tubular piece, with this immobilization being freed at the end of the travel of the plunger seal, so as to allow the tubular piece to continue its axial movement, so that the front end of this tubular piece sheathes the needle. 
     Advantageously, the syringe body is equipped at its rear end with a sleeve secured to the body and coaxial therewith, to which it is connected directly or indirectly by at least one radial tab. 
     Prior to injection, the stem of the syringe and the tubular piece are secured one to the other. To carry out injection, the operator exerts pressure on the tubular piece. At the end of injection, the tubular piece detaches from the plunger stem and continues its forward movement, its front part then sheathing the needle, thus avoiding any risk of stick injury on this needle. 
     SUMMARY OF THE INVENTION 
     According to a first embodiment of this syringe, the means for axially immobilizing the stem of the plunger seal inside the tubular piece consist of flexible tabs secured to the end of the stem and extending the latter, these tabs facing from the inside outwards, and of which the free ends, which form a collar with a rib or a groove, collaborate respectively with a groove or annular rib formed on the inside of the tubular piece at a distance away from the rear end thereof which is at least equal to the length of the needle. At the end of injection, the tabs arranged at the rear end of the plunger stem engage in the body of the syringe, which moves the tabs closer together and allows them to detach from the tubular piece, which can thus continue its forward movement. 
     According to another embodiment, the means for axially immobilizing the stem of the plunger seal inside the tubular piece consist of a collar formed at the rear end of the stem of the plunger seal and projecting radially outwards, this collar being deformable by virtue of the presence of at least one axial slot open at the rear of the stem, this collar having a chamfered end edge and being intended to be engaged in an annular groove formed on the inside of the tubular piece at a distance away from the rear end thereof which is at least equal to the length of the needle. 
     In this case, at the end of the forward travel of the plunger, the stem is immobilized, and continued pressure exerted on the tubular piece allows the latter to detach from the rear end of the stem, given the flexibility afforded by the structure thereof. 
     Advantageously, the rear end of the tubular piece is closed by a cap which makes it more rigid. 
     The additional rigidity thus afforded is important, particularly in preventing undesired detachment between the rear end of the stem and the tubular piece. 
     To make the syringe easier to handle, the sleeve comprises, near its rear end, a complete or partial collar which projects outwards. 
     According to one possibility, the sleeve forms an integral part of the body of the syringe and is obtained by moulding a synthetic material at the same time as this body. 
     According to another possibility, the sleeve, produced independently of the syringe body, is secured to a bush of an inside diameter matched to the outside diameter of the syringe body. 
     According to one embodiment of this syringe, the tubular piece comprises, at its front end, a frangible extension intended to sheathe the needle before the syringe is used. 
     Before the syringe is used, the frangible extension may be separated from the tubular piece, for example by a twisting movement. 
     The tubular piece is short enough that, before injection, the front end of the body of the syringe is visible so as, for example, to allow the clarity of the liquid to be injected to be checked. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In any event, the invention will be clearly understood with the aid of the description which follows, with reference to the appended diagrammatic drawing which, by way of non-limiting examples, depict two embodiments of this syringe: 
     FIG. 1 is a view in exploded perspective of a first syringe; 
     FIG. 2 is a view thereof in longitudinal section and to a larger scale, prior to use; 
     FIG. 3 is a view thereof in cross section on the line III—III of FIG. 2; 
     FIGS. 4 and 5 are two views thereof in longitudinal section, one at the end of injection and the other after the needle has been withdrawn from the site of injection; 
     FIG. 6 is a detailed view in longitudinal section of an alternative form of the attachment of the plunger stem to the tubular piece; 
     FIGS. 7 and 8 are two views of an alternative form of the attachment of the stem to the tubular piece, one in the attached position and the other in the uncoupled position; 
     FIG. 9 is a view of an alternative form of this syringe, in which the body of the syringe is made of a synthetic material as a single piece with the sleeve surrounding the body. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The syringe depicted in FIGS. 1 to  5  comprises a glass syringe body  2 , one end of which is equipped with a separate injection needle  3  protected, prior to use, by a protector  4  depicted in chain line in FIG.  1 . This syringe body  2 , which is intended to contain a liquid  5  that is to be injected, is closed at its other end by a plunger seal  6 , actuated by a stem  7 . Mounted on the syringe body  2 , in the rear part thereof, is a sleeve  8  coaxial with the syringe body and secured to the latter by a bush  9  which bears against the syringe body  2  via longitudinal ribs  10 . The sleeve  8  is connected to the bush  9  by two radial tabs  12 . The sleeve  8  is equipped, at its rear end, with a partial collar  13  projecting outwards. 
     This syringe comprises a tubular piece  14 , the length of which is approximately equal to the length of the syringe body increased by the length of the needle  3  and which, starting from its rear end, has two longitudinal slots  15 , each serving for the passage of one tab  12  which connects the sleeve  8  and the bush  9 . The tubular piece  14  is intended to be engaged over the syringe body  2  and to slide relative to the latter inside the sleeve  8 . 
     In the embodiment depicted in FIGS. 1 to  5 , the stem  7  of the plunger  6  comprises, at its rear end, flexible tabs  16  extending the stem and facing from the inside outwards, and of which the free ends form a collar  17  facing outwards. This collar  17  is intended to be engaged in an annular groove  18  formed on the inside of the tubular piece  14 , at a distance from the rear end thereof that is at least equal to the length of the needle. The rear end of the tubular piece  14  may be closed off by a cap  19  which has a rim  20  which caps the tubular piece so as to prevent the possible opening thereof which may result from the presence of the slots  15 . 
     In the embodiment depicted in FIG. 2, the front part of the tubular piece  14  is equipped with an extension  22  which is frangible at a thinned zone  23 . This extension is intended to sheathe the needle before the syringe is used. Starting out with a syringe, as depicted in FIG. 2, the use of the syringe is as follows. 
     The operator removes the extension  23  of the tubular piece and the needle protector  4 . He may introduce the needle into the patient in an entirely normal way by holding the syringe by the sleeve  8 , between the index and middle fingers, and pressing the cap  20  of the tubular piece  14  with his thumb. The axial movement of the tubular piece  14  results in a corresponding driving of the stem  7  and of the plunger  6 , causing the liquid  5  contained in the syringe to be injected into the body of the patient. When, at the end of injection, the tabs  16  forming an elastic cone come into contact with the body of the syringe, the latter pushes the tabs  16  closer together and their collar  17  escapes from the groove  18  in the tubular piece  14 , as shown in FIG.  4 . 
     Throughout the injection phase, the front part of the tubular piece has gradually sheathed the syringe body  2  until, at the end of injection, it has come into contact with the skin of the patient. Continuing to push on the tubular piece  14  allows the needle to be completely sheathed by the front of the piece  14 , as shown in FIG. 5, as the needle is gradually pulled out of the skin. The complete syringe is retracted into the tubular piece  14  and can be disposed of without the risk of stick injury to the operator or to cleaning staff. 
     FIG. 6 depicts an alternative form of the attachment of the rear end of the stem  7  to the inside of the tubular piece  14 . In this case, the flexible tabs  16  at their free ends form a collar  17 , in the exterior face of which is formed a groove  25  in which an annular rib  26  formed on the inside of the tubular piece  14  is intended to engage. 
     The stem  7  is detached from the tubular piece  14  under the same conditions as hereinabove. 
     FIGS. 7 and 8 illustrate another embodiment of the invention, in which the same elements are denoted by the same references as previously. In this instance, the stem  7  is of constant cross section and has axial slots  27  opening into its rear edge. The stem  7  also has a peripheral collar  28 , interrupted by the slots  27 . This collar has a chamfered outer edge  29 . The collar  28  is intended to engage in an annular groove  30  in the tubular piece  14  so as to put together the stem and the tubular piece. When, at the end of injection, the stem  7  is axially immobilized, the rear part of the stem  7  can close up, by virtue of the presence of the slots  27 , the chamfered surfaces  29  allowing this closing-up movement and, consequently, the stem  7  can detach axially from the tubular piece  14 , the translational movement of which can be continued so as to sheathe the needle, as shown in FIG.  8 . 
     FIG. 9 depicts an alternative form of this syringe, in which the syringe body  2  is made of synthetic material and forms a single piece with the sleeve  8  to which it is connected by tabs  12 . In this instance, there is no intermediate bush  9  as there was before. 
     As is clear from the foregoing, the invention affords a great improvement to the existing art by providing a safety syringe equipped with an automatic device for protecting the needle at the end of injection, this protection being achieved without the operator having to perform a deliberate movement. Furthermore, the selling price of this syringe is not appreciably higher than that of a conventional syringe, insofar as the protective device consists merely of one additional component—the tubular piece—or two additional components, insofar as the sleeve does not form an integral part of the syringe body. 
     As goes without saying, the invention is not restricted simply to the embodiments of this syringe which have been described hereinabove by way of example; on the contrary, it encompasses all alternative forms thereof.