Abstract:
A multi-use safety syringe has a retractable needle that retracts only when the user wants to retract the needle. The safety syringe has an internal moveable carriage that locks to an end cap with releasable locking elements. The safety syringe guards against premature retraction of the needle by requiring the simultaneous release of two releasable locking elements by the user. When the locking elements are released, the carriage is released. The released carriage slides backward within the barrel, retracting the needle within the barrel.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a safety syringe with attached needle. 
   2. Description of the Prior Art 
   Used needles and syringes, especially extended needles, pose a risk of transmitting infectious diseases from accidental needle sticks. Contaminated needles and syringes can carry blood-borne infectious agents, such as gonorrhea and syphilis bacteria, as well as hepatitis and HIV viruses. While medical personnel and sanitation workers are at risk, the general population is also at risk from improper disposal of the used needle and syringe. 
   Prior art safety syringes with retractable needles have many problems. These problems relate to complexity, reliability, repeatability, cost and ease of use. Because syringes are mass produced at the rate of millions per day, cost is a significant factor in manufacture of the parts and the assembly of the device. Automated production of parts and assembly of parts is critical in order to have any hope of supplying a practical syringe to the market. 
   A major drawback of prior art single use syringes is that single use syringes cannot be used to clear air bubbles from the medicine, to inject fluid to mix medicine within a vial or to rinse the needle and syringe with a different medicine before filling with the desired medicine. In many of these devices once the plunger is plunger all the way forward, the plunger locks the needle and retracts the needle within the barrel to prevent a second use. 
   A need exists for a multiple use retractable syringe for health care and other workers. Health care workers typically push the plunger all the way forward before withdrawing fluid from a medicine vial. The worker then partially withdraws fluid from a vial into the syringe. The worker next flicks the syringe to free trapped air bubbles before plunging the air and at least some of the fluid back into the vial. This step clears air trapped within the barrel. After clearing out the air, the user withdraws the fluid for use. 
   Health care workers often first inject fluid into a vial of medicine in order to mix the medicine with the fluid. After mixing, the worker withdraws the mixed medicine from the vial for injection. Likewise, health care workers may first rinse the needle and vial with another medicine before inserting the needle into a medicine vial and withdrawing the medicine. After use, the worker can retract the needle into the syringe to prevent any risk of harm from the needle to others. 
   In a curious development, healthcare workers in the drug control field have expressed a need for a reusable retractable syringe to prevent the spread of blood borne diseases, such as AIDS and hepatitis. Such a syringe is preferably a full displacement syringe which will deliver essentially all of the contents without retracting and without limiting the ability of the user to draw a second dose. Hopefully the drug user will confine use to himself without sharing the needle but can retract the needle when finished and render the device inoperable. 
   The present invention is designed to accomplish these goals and more. 
   SUMMARY OF THE INVENTION 
   A multi-use safety syringe of the invention has a retractable needle that retracts when the user positively releases the needle. The safety syringe has a barrel with opposite plunger and end cap ends. Within the barrel is a carriage defined by a carriage wall extending axially from a radial base. An inward lip is located at one end of the carriage wall distal to the radial base. The needle attaches to the carriage and a spring abuts the carriage. 
   An end cap has a plug and a retainer adjacent to the plug. The plug engages the barrel at the end cap end and has a cylindrical sidewall. The retainer has a front wall opposite the plug and a pair of moveable locking elements located on opposite sides of the retainer. 
   Additional effects, features and advantages will be apparent in the written description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a syringe of the invention; 
       FIG. 2  is a perspective exploded view of a syringe of the invention; 
       FIG. 3  is a perspective view of a carriage of the invention; 
       FIG. 4  is a longitudinal sectional view of the carriage of  FIG. 3 ; 
       FIG. 5  is a perspective view of an end cap of the invention; 
       FIG. 6  is a top plan view of an end cap of the invention; 
       FIG. 7  is a partial side view of an unlocked carriage and end cap within the barrel of the invention and the needle retracted; 
       FIG. 8  is a partial side view of an locked carriage and end cap within the barrel of the invention; 
       FIG. 9  is a close-up partial view of the tab and lip of the invention during engagement; 
       FIG. 10  is a close-up partial view of the tab and lip of the invention when the needle and carriage are locked; and 
       FIG. 11  is a close-up partial view of the tab and lip of the invention during disengagement. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning to the Figures where like reference numerals refer to like structures, safety syringe  10  has barrel  12 , plunger  16 , end cap  26 , carriage  18  and needle  14 . Barrel  12  has an open plunger end  30  through which plunger  16  inserts. Opposite plunger end  30  of barrel  12  is an open end cap end  32  for receiving end cap  26 . Carriage  18  releasably locks to end cap  26  during use. 
   A moveable carriage  18  slides within syringe barrel  12 . Carriage  18  has a radial base  34  and carriage wall  52  extending axially from radial base  34 . Inward lip  20  of carriage wall  52  is distal to radial base  34 . While carriage wall  52  could be discontinuous, carriage wall  52  is preferably continuous and defines a chamber  54  and a mouth  56  located opposite radial base  34 . Inward lip  20  of carriage wall  52  preferably borders mouth  56 . A spring mount  28  can extend axially from the center of radial base  34  and is located within the carriage wall  52  and chamber  54 . 
   Needle  14  attaches to the center of carriage  18 , preferably attaching to spring mount  28 . Needle  14  can attach by matingly engaging a needle lock, such as a luer lock having an interlocking nub and receiver, or by extending through an opening  29  in spring mount  28 . 
   Seal  22  is located between carriage  18  and the interior wall of barrel  12 . Seal can be an O-ring, washer, gasket, and the like, and is preferably around carriage wall  52  adjacent radial base  34 . 
   The end cap  26  engages the barrel  12  at end cap end  32 , preferably by partially fitting within the barrel  12 . End cap  26  has plug  38  engaging barrel  12 , retainer  40  adjacent to plug  38  and nose  50  projecting from front wall  41  outside of the retainer  40  at an end opposite plug  38 . Retainer  40  has a pair of moveable locking elements  42  located on opposite sides of retainer  40  and which cooperatively engage lip  20  of carriage  18  when the syringe is in use. Each locking element  42  is part of retainer wall  46 . Retainer wall  46  connects to front wall  41  and can be cylindrical, partially cylindrical with opposing flat walls and opposing curved walls or have flat walls. Locking element  42  has a tab  58  with angled head  59  and preferably a button  60  extending outwardly. The distance between locking elements  42  is preferably less than the distance between the carriage walls  56  or the diameter of chamber  54 . 
   A nose hole  51  is in front wall  41  of retainer  40  and preferably is surrounded by nose  50 . A cap spring mount  48  projects radially from the nose hole  51  within the retainer and preferably surrounds nose hole  51  opposite nose  50 . Either cap spring mount  48  or nose  50  can have a pierceable membrane to seal the safety syringe  10  before use. 
   The plug  38  has cylindrical sidewall  64 , end walls  62  adjacent to retainer  40  and cylindrical sidewall  64 , and abutment ring  44  located on the exterior of cylindrical sidewalls  64 . The end walls  62  are preferably on a plane perpendicular to the cylindrical sidewall  64  and the retainer wall  46 , extending from an edge of the cylindrical sidewall  64  to the retainer  40 . Cylindrical sidewall  64  matingly engages barrel  12 . Cylindrical sidewall  64  preferably has a narrower diameter than barrel  12  and a wider diameter than carriage wall  52 . Each end wall  62  has an aperture  66  into which locking element  42  and preferably tab  58  at least partially extends. Abutment ring  44  projects from sidewall  64  and abuts barrel  12  at end cap end  32 . 
   A spring  24  is located between carriage  18  and end cap  26  and is preferably helical. Carriage end  36  of spring  24  abuts carriage  18 , while opposite cap end  37  abuts end cap  26 . Preferably, carriage end  36  surrounds spring mount  28  and cap end  37  surrounds cap spring mount  48  of end cap  26 . 
   To use the syringe  10 , the user pushes plunger  16  forward. The plunger  16  in turn pushes carriage  18  forward until lip  20  on carriage  18  engages tabs  58  of end cap  26 . As shown in FIGS.  8 - 11 , the design of lip  20  complements the design of head  59  of tab  58 , such as 45° angles. The complementary design allows lip  20  to slide past head  59  and force tab  58  inward ( FIG. 9 ). Once lip  20  reaches the end walls  62  of plug  38 , tab  58  returns to its initial position. The lower portion of lip  20  now locks against the upper part of head  59  and locks carriage  18 , needle  14  and compressed spring  24  into position. At this point, needle  14  extends through nose  50  of end cap  26 . If a pierceable material is used to make nose  50  or cap spring mount  48 , needle  14  pierces the membrane while carriage  18  moves forward. 
   Plunger  16  can now be drawn back to fill barrel  12  of the safety syringe  10 . To remove trapped air bubbles in the fluid or to mix the fluid within a vial, the user pushes plunger  16  forward to blow out air bubbles from the fluid in syringe barrel  12  and/or injects fluid into a vial. Carriage  18  remains locked to end cap  26 . 
   Once finished with the syringe, the user simultaneously pushes both buttons  60  on tabs  58  of locking elements  42  to unlock the end cap  26  and carriage  18 . This action pushes tabs  58  inwardly to disengage the heads  59  from lip  20 . Once disengaged, the compressed spring  24  releases and pushes carriage  18  and plunger  16  backward within barrel  12 . The retreating carriage  18  slides needle  14  through the nose  50 , end cap  26  and into the barrel  12  with it, where the needle  14  remains safety retracted within barrel  12 . 
   The safety syringe of the invention has a number of advantages. The syringe can be used for more than one use, thus allowing a user to clear air from the syringe before injection, mix medicine within a vial or pretreat the needle and syringe before drawing the desired medicine. 
   The syringe of the invention allows a one hand operation to retract the needle. This allows the user to have one hand free while retracting the needle. 
   Because the use of two tabs requires the user to simultaneously compress both tabs to retract the needle, this simultaneous operation prevents the premature retraction of the needle into the barrel if one tab is accidentally compressed. 
   If the carriage is color coded, such as green, the carriage shows through the aperture of the end cap, indicating that the carriage is securely locked into place and ready to use. This prevents the inadvertent use of the syringe before the needle is fully locked into position. 
   While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.