Safety syringe

Abstract

A safety syringe ( 100; 700; 1200 ) comprising: a barrel ( 104; 704; 1204 ) having an opening at an end thereof; a syringe plunger ( 108; 708; 1208 ) configured to move within the barrel such that an inward stroke of the syringe plunger causes a substance within the barrel to be expelled from the opening; and a sheath ( 112; 712; 1212 ) configured to cover at least partially the opening in the barrel after use of the syringe, wherein the sheath is coupled to the syringe plunger and is configured to decouple from the syringe plunger at a point on the inward stroke such that the sheath is moveable independently of the syringe plunger and further movement of the sheath after decoupling at least partially covers the opening in the barrel.

1 . A safety syringe comprising:
 a barrel having an opening at an end thereof;   a syringe plunger configured to move axially within the barrel to cause a substance within the barrel to be expelled from the opening;   a safety plunger coupled to the syringe plunger such that an inward stroke of the safety plunger causes the syringe plunger to move axially within the barrel; and   a sheath configured to cover at least partially the opening in the barrel after use of the syringe,   wherein the safety plunger is configured to be coupled to the sheath at a first point on the inward stroke and is configured to decouple from the syringe plunger at a second point on the inward stroke, the second point being substantially the point at which the syringe plunger has reached the end of the barrel, such that the safety plunger is axially moveable independently of the syringe plunger,   and wherein further axial movement of the safety plunger after the first and second points on the inward stroke causes the sheath at least partially to cover the opening in the barrel,   the syringe plunger further comprising a lost motion device configured to compress, if needed, to account for manufacturing tolerances and ensure decoupling of the safety plunger from the syringe plunger only after a tip of the syringe plunger has reached the end of the barrel.   
     
     
         2 . A safety syringe according to  claim 1 , wherein the first point on the inward stroke is the outermost point on the inward stroke, such that the safety plunger is coupled to the syringe plunger at the beginning of the inward stroke. 
     
     
         3 . A safety syringe according to  claim 2 , wherein the sheath is fixedly coupled to the safety plunger. 
     
     
         4 . A safety syringe according to  claim 1 , wherein the safety plunger is configured to move along an exterior of the barrel during its inward stroke and to decouple from the syringe plunger at or before a point at which the sheath passes the opening in the barrel. 
     
     
         5 . A safety syringe according to  claim 1 , further comprising a decoupling mechanism configured to decouple the safety plunger and the syringe plunger. 
     
     
         6 . A safety syringe according to  claim 5 , wherein the decoupling mechanism is configured to decouple the safety plunger and the syringe plunger under rotation of the syringe plunger relative to the safety plunger. 
     
     
         7 . A safety plunger according to  claim 5 , wherein the decoupling mechanism is configured to decouple the safety plunger and the syringe plunger by way of the force applied to the safety plunger on its inward stroke. 
     
     
         8 . A safety syringe according to  claim 5 , wherein the decoupling mechanism comprises a lug on the syringe plunger configured to move between engagement and disengagement with a coupling recess in the safety plunger. 
     
     
         9 . A safety syringe according to  claim 8 , wherein the lug of the syringe plunger is configured to disengage from the coupling recess of the safety plunger by rotation of the syringe plunger relative to the safety plunger. 
     
     
         10 . A safety syringe according to  claim 9 , wherein a body of the syringe plunger comprises a rotation surface configured to engage with a reaction surface to rotate the plunger, wherein the reaction surface is fixed with respect to the barrel. 
     
     
         11 . A safety syringe according to  claim 1 , further comprising a locking mechanism configured to lock the sheath in a position at least partially covering the opening of the barrel. 
     
     
         12 . A safety syringe according to  claim 11 , wherein the decoupling mechanism is configured to decouple the safety plunger and the syringe plunger under rotation of the syringe plunger relative to the safety plunger, and comprises a lug on the syringe plunger configured to move between engagement and disengagement with a coupling recess in the safety plunger, wherein the locking mechanism comprises the lug and a return recess in the safety plunger, wherein the lug is configured to engage with the return recess at the end of the inward stroke of the safety plunger. 
     
     
         13 . A safety syringe according to  claim 12 , wherein the locking mechanism is a biased locking mechanism, the safety syringe further comprising a biasing member configured to provide a biasing force causing outward movement and reverse rotation of the syringe plunger to move the lug into the return recess. 
     
     
         14 . A safety syringe according to  claim 13 , wherein the biasing member comprises a resiliently deformable syringe plunger tip configured to compress against an internal surface of the barrel proximal an end comprising the opening. 
     
     
         15 . A safety syringe according to  claim 13 , wherein the lateral extent of the return recess is less than the lateral extent of the coupling recess, for preventing full reverse rotation of the syringe plunger. 
     
     
         16 . A safety syringe according to  claim 13 , wherein the safety syringe comprises a locking channel comprising the coupling recess and the return recess connected by a substantially longitudinal channel, and wherein the locking channel is configured to guide the lug during activation of the biased locking mechanism. 
     
     
         17 . A safety syringe according to  claim 16 , wherein the lug is configured to meet an end of the substantially longitudinal channel after the end of the inward stroke of the safety plunger, thereby compressing the resiliently deformable tip of the syringe plunger. 
     
     
         18 . A safety syringe according to  claim 11 , wherein the locking mechanism comprises a projection configured to enter a locking recess, wherein one of the projection and the locking recess is fixed in relation to the barrel and the other of the projection and the locking recess is located on the safety plunger or the sheath such that when the projection is located within the locking recess, the sheath is locked in a position at least partially covering the opening of the barrel. 
     
     
         19 . A safety syringe according to  claim 18 , wherein the projection is biased towards the locking recess such that the projection is urged into the locking recess upon alignment of the projection and the locking recess. 
     
     
         20 . A safety syringe according to  claim 19 , wherein during at least part of the inward stroke of the safety plunger, the projection is configured to ride over a surface until the projection and the locking recess are aligned, and wherein the biasing of the projection towards the locking recess exerts a frictional force on the safety plunger during the inward stroke. 
     
     
         21 . A safety syringe according to  claim 18 , wherein the projection comprises a resiliently deformable prong. 
     
     
         22 . A safety syringe according to  claim 1 , comprising a rate controlling means is for limiting and/or controlling a rate of travel of the safety plunger after the second point on the inward stroke. 
     
     
         23 . A safety syringe according to  claim 22 , wherein the rate controlling means comprises a rate limiting member, coupled to the safety plunger and configured to engage with the syringe plunger after the second point on the inward stroke. 
     
     
         24 . A safety syringe according to  claim 23 , wherein the rate limiting member comprises a first screw thread and the syringe plunger comprises a second screw thread that is configured to engage with the first screw thread to rotate the syringe plunger on further movement of the safety plunger after the second point on the inward stroke. 
     
     
         25 . A safety syringe according to  claim 24 , further comprising a rotation prevention member configured to prevent rotation of the syringe plunger from the first to the second points on the inward stroke. 
     
     
         26 . A safety syringe according to  claim 25 , wherein the rotation prevention member comprises an aperture through which the syringe plunger passes, wherein the aperture comprises first keying features configured to correspond to second keying features on the syringe plunger. 
     
     
         27 . A safety syringe according to  claim 26 , wherein the syringe plunger is configured such that the second keying features disengage from the first keying features at the second point along the inward stroke. 
     
     
         28 . A safety syringe according to  claim 27 , wherein the syringe plunger is configured to pass through the aperture completely at the second point on the inward stroke. 
     
     
         29 . A safety syringe according to  claim 23 , further comprising a resiliently deformable bung within the barrel. 
     
     
         30 . A safety syringe according to  claim 29 , wherein the resiliently deformable bung is configured to rotate when the syringe plunger rotates, and wherein the bung has a diameter greater than an inner diameter of the barrel, such that a friction force resists rotation of the bung and the syringe plunger. 
     
     
         31 . A safety syringe according to  claim 29 , wherein the resiliently deformable bung is configured to allow relative rotation between the resiliently deformable bung and the syringe plunger, and wherein a friction force between the syringe plunger and the resiliently deformable bung resists rotation of the bung and the syringe plunger. 
     
     
         32 . A safety syringe according to  claim 23 , wherein the rate controlling means comprises a resiliently deformable rate controlling projection configured to be deformed by a deforming surface after the second point on the inward stroke, thereby generating a friction force resisting further movement of the safety plunger. 
     
     
         33 . A safety syringe according to  claim 32 , wherein the resiliently deformable rate controlling projection projects radially inwardly towards a longitudinal axis of the safety syringe, and wherein the deforming surface is located on the safety plunger and comprises a tab extending outwardly away from the longitudinal axis of the safety syringe. 
     
     
         34 . A safety syringe according to  claim 1 , wherein the safety plunger extends beyond a head of the syringe plunger, and wherein a head of the safety plunger comprises at least one arm, the head of the safety plunger for applying force by a user to cause the inward stroke of the safety plunger. 
     
     
         35 . A safety syringe according to  claim 34 , further comprising a guard positioned between the head of the syringe plunger and the head of the safety plunger. 
     
     
         36 . A safety syringe according to  claim 35 , wherein the guard comprises a rod extending between the head of the safety plunger and the head of the syringe plunger, wherein the rod is configured to enter the syringe plunger after decoupling of the safety plunger and the syringe plunger. 
     
     
         37 . A safety syringe according to  claim 1 , further comprising a hypodermic needle connected to the opening in the barrel, and wherein the sheath is configured to cover at least partially the hypodermic needle after use of the syringe. 
     
     
         38 . A safety syringe apparatus for use with a syringe, the syringe comprising a barrel having an opening at an end thereof and a syringe plunger configured to move axially within the barrel to cause a substance within the barrel to be expelled from the opening, wherein the safety syringe apparatus comprises:
 a safety plunger configured to be coupled to the syringe plunger such that an inward stroke of the safety plunger causes the syringe plunger to move axially within the barrel; and   a sheath configured to cover at least partially the opening in the barrel after use of the syringe,   wherein the safety plunger is configured to be coupled to the sheath at a first point on the inward stroke and is configured to decouple from the syringe plunger at a second point on the inward stroke, the second point being substantially the point at which the syringe plunger has reached the end of the barrel, such that the safety plunger is axially moveable independently of the syringe plunger,   and wherein further axial movement of the safety plunger after the first and second points on the inward stroke causes the sheath at least partially to cover the opening in the barrel,   the syringe plunger further comprising a lost motion device configured to compress, if needed, to account for manufacturing tolerances and ensure decoupling of the safety plunger from the syringe plunger only after a tip of the syringe plunger has reached the end of the barrel.   
     
     
         39 . A kit of parts comprising:
 a safety plunger configured to be coupled to a syringe plunger of a syringe such that an inward stroke of the safety plunger causes the syringe plunger to move axially within the barrel; and   a sheath configured to cover at least partially an opening in a barrel of the syringe after use of the syringe,   wherein the safety plunger is configured to couple to the sheath at a first point on the inward stroke and is configured to decouple from the syringe plunger at a second point on the inward stroke, the second point being substantially the point at which the syringe plunger has reached the end of the barrel, such that the safety plunger is axially moveable independently of the syringe plunger,   and wherein further axial movement of the safety plunger after the first and second points on the inward stroke causes the sheath at least partially to cover the opening in the barrel,   the syringe plunger further comprising a lost motion device configured to compress, if needed, to account for manufacturing tolerances and ensure decoupling of the safety plunger from the syringe plunger only after a tip of the syringe plunger has reached the end of the barrel.   
     
     
         40 . A kit of parts according to  claim 39  further comprising a handle portion configured to be coupled to the barrel and to receive the safety plunger, such that the safety plunger is able to pass through the handle portion. 
     
     
         41 . A kit of parts according to  claim 39 , further comprising a syringe.