Simplified retractable needle syringe

Abstract: A simplified retractable needle hypodermic syringe is provided which includes a barrel (10) having a needle carrier (20) mounted therein with a cannula (90) attached thereto. A slidable plunger (50) is mounted within the barrel (10) which includes a shaft (80) and hub (81) for locking to the carrier (20) by engagement in an enlarged bore (23) in the carrier. A plunger seal (60) is conveniently mounted about the shaft (80) between the plunger (50) and the hub (81). The shaft (80) may be shearable above the hub (81) to allow the hub to be broken off and left in the carrier (20) after use.

Description: BACKGROUND OF THE INVENTION Due to the recent advent of the AIDS virus, which may be contracted by contaminated hypodermic syringes, there have been several retractable needle hypodermic syringes invented and patented. The retraction of the needle into the barrel of the syringe after use reduces the risk of "needle prick", or the accidental pricking of the person giving the injection after the syringe has been used. Some of the recently patented retractable needle syringes include U.S. patents 4,692,156 (Haller); 4,675,005 (DeLucia); 4,747,830 (Gloyer, et al); and my own patent 4,790,822. While each of the patents disclose devices which would be suitable for use, none appears of simple enough construction for mass production at competitive costs. Generally each discloses a sophisticated locking or sealing mechanism for locking the needle carrier to the plunger or sealing the carrier in the barrel. With the practical thought in mind that the hypodermic syringe is disposable and made for only one use, I have developed a simplified version of my earlier patented syringe which can be manufactured inexpensively and performs satisfactorily. SUMMARY OF THE INVENTION The simplified retractable needle hypodermic syringe of the present invention is designed to include the minimum number of parts and to utilize as much as possible from currently available syringe parts. According to this invention, there is provided a hypodermic syringe having a retractable needle, comprising: a hollow cylindrical barrel open at both ends and having an inwardly projecting lip at the lower end and finger flanges at the upper end; a rigid cylindrical needle carrier mounted within said barrel and seated on said lip, said needle carrier having an extension protruding through the opening at the lower end of said barrel; a hypodermic needle mounted on said extension; a plunger slidably mounted in said barrel through the upper open end and defining a fluid chamber between said carrier and said plunger; a central bore through said carrier and extension for fluid communication between said needle and said chamber; and a shaft extending from the lower end of said plunger; a hub on the lower end of said shaft; and a seal member between said plunger and said hub; characterised in that: said needle carrier is retained in place within said barrel solely by frictional sealing engagement between the outer diameter of said needle carrier and the inner wall of said barrel; said needle carrier has an enlarged bore intermediate the upper and lower surfaces of said carrier co-axial with said central bore; said hub on the lower end of said shaft is adapted to lock into said enlarged bore; and said seal member is secured about said shaft. The projection of the needle carrier is designed for attachment of a standard hypodermic needle or cannula (the words are used interchangeably herein). The hub on the shaft of the plunger locks into the needle carrier after use, allowing the carrier and needle to be retracted into the barrel. In accordance with a preferred feature of the invention, the hub may be broken off in the carrier blocking the fluid channel and preventing any further use of the syringe. While the friction seal between the carrier and the barrel may lose its integrity after repeated movement in the barrel, it does provide a good seal for at least one use. It is the simplicity of the locking mechanism and the absence of any special sealing mechanism for the carrier which distinguishes the present invention from the prior art. The invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIG.1 is an exploded perspective view showing all of the parts of the retractable needle syringe of the present invention. FIG.2 is a side elevational view in partial cross section of the lower end of the assembled syringe of the present invention. FIG.3 is a side elevational view in partial cross section of the upper end of the assembled syringe with the needle retracted and hub broken. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT For a detailed description of the preferred embodiment the reader is directed to the accompanying figures in which like components are given like numerals for ease of reference. In figure 1 the simplicity of the present retractable needle hypodermic syringe is illustrated in an exploded view showing all of the components. The syringe is shown to comprise a hollow cylindrical barrel 10 with standard finger flanges 12 on one end and inwardly projecting lip 11 on the opposite end. A needle carrier 20 is inserted into the barrel 10 through the flanged end opening and is seated on the lip 11 such that the extension 24 protrudes out of the barrel 10. A cannula 90 is attached to extension 24 by friction fit through sleeve 30 integral with cannula 90. The cannula is provided with protective sheath 40 for protection before use. Plunger 50 with shaft 80 about which is secured a rubber seal 60 is inserted into the barrel 10 and the syringe is ready for use. The entire syringe thus consists of only six distinct parts. Only the carrier and plunger are different from standard syringes once the needle mounting extension has been removed from the lower end of the barrel to provide lip 11. In one embodiment which has been made from an existing syringe, even the plunger seal has been reused. Referring now to figure 2 details of the new parts are illustrated. The carrier 20 is shown seated on the lip 11 with extension 24 protruding out of the barrel. The outer diameter of the carrier is sized to provide a snug friction seal with the inner walls of the barrel 10. Clearances may have to be adjusted for different material of construction to provide the seal while allowing the carrier to be retracted with minimum force. The integral sleeve 30 of cannula 90 is secured to extension 24 normally by a tight friction fit also. However additional securing means, such as an approved glue, may be used. A central bore 21 extends through the carrier 20 to provide fluid communication between the cannula 90 and fluid chamber 100. Near the upper end of central bore 21 is a hollow chamber 22 which includes an enlarged bore 23. Plunger 50 is slidably mounted within barrel 10. Shaft 80 extends from the lower end 52 of the plunger 50. At the lower end of shaft 80 is a hub 81 which is adapted to fit and lock into enlarged bore 23 in carrier 20. Widened shoulders 82 and 83 are provided along shaft 80 to secure rubber seal 60 to the shaft between the plunger end 52 and hub 81. Referring now to figure 3 the cannula 90 is shown retracted into the barrel 10. The hub is shown engaged within enlarged bore 23 with shoulder 84 in locking engagement with the upper inner surface 25 of enlarged bore 23. The shaft 80 is shearable above hub 81 so that the hub nay be broken off inside the enlarged bore 23 effectively blocking fluid channel 21. Preformed perforations (not shown) may be provided to allow the shearing while still providing sufficient tensile strength to pull the carrier with cannula into the barrel. In use the plunger 50 is depressed in the barrel 10 until solid resistance is met between the hub 81 and carrier 20 as shown in figure 2. The cannula 90 may then be inserted into the fluid to be injected and the fluid drawn into the chamber 100 by retraction of the plunger 50. Any air drawn in with the fluid may be removed in the usual manner--by inverting the syringe and thumping it until the bubble rises to the cannula end and depressing the plunger until fluid exits the cannula. The fluid may then be injected. As soon as the cannula is withdrawn from the recipient, the user may then further depress the plunger 50 until the hub 81 to engages the carrier 20. After the hub 81 has engaged the carrier 20 the needle carrier 20 with cannula 90 may then be retracted into the barrel 10. Finally, the hub 81 may be broken off of shaft 80 and left with the carrier 20 to prevent any further use of the syringe.

Claims: A hypodermic syringe having a retractable needle, comprising: a hollow cylindrical barrel (10) open at both ends and having an inwardly projecting lip (11) at the lower end and finger flanges (12) at the upper end; a rigid cylindrical needle carrier (20) mounted within said barrel (10) and seated on said lip (11), said needle carrier (20) having an extension (24) protruding through the opening at the lower end of said barrel (10); a hypodermic needle (90) mounted on said extension (24); a plunger (50) slidably mounted in said barrel (10) through the upper open end and defining a fluid chamber (100) between said carrier (20) and said plunger (50); a central bore (21) through said carrier (20) and extension (24) for fluid communication between said needle (90) and said chamber (100); a shaft (80) extending from the lower end of said plunger (50); a hub (81) on the lower end of said shaft (80); and a seal member (60) between said plunger (50) and said hub (81); characterised in that: said needle carrier (20) is retained in place within said barrel (10) solely by frictional sealing engagement between the outer diameter of said needle carrier (20) and the inner wall of said barrel (10); said needle carrier (20) has an enlarged bore (23) intermediate the upper and lower surfaces of said carrier (20) co-axial with said central bore (21); said hub (81) on the lower end of said shaft (80) is adapted to lock into said enlarged bore (23); and said seal member (60) is secured about said shaft (80). The hypodermic syringe of claim 1 wherein said shaft (80) is shearable above said hub (81) to allow said hub (81) to be broken off and left in enlarged bore (23) after use. The hypodermic syringe of claim 1 or claim 2 further comprising at least one shoulder (82, 83) about said shaft (80) to retain said seal member (60) about said shaft (80).

Inventors: HAINING MICHAEL LYNN, HAINING, MICHAEL LYNN
Applicants: HAINING MICHAEL L, HAINING, MICHAEL LYNN
Application year: 1990
Main classification: A61M5
IPC codes: A61M5