Abstract:
An injection device ( 210 ) is described. A housing ( 212 ) receives a syringe and includes a return spring ( 226 ) for biasing the syringe from an extended position in which its needle ( 218 ) extends from the housing ( 212 ) to a retracted position in which the it does not. A drive spring ( 230 ) acts on a first drive element ( 232 ) and a second drive element ( 234 ) acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the needle. The first drive element ( 232 ) is capable of movement relative to the second ( 234 ) once a nominal decoupling position has been reached. A release mechanism is activated when the first drive element ( 234 ) is further advanced to a nominal release position, to release the syringe ( 214 ) from the action of the drive spring ( 230 ), whereupon the return spring ( 226 ) restores the syringe ( 214 ) to its retracted position. A locking mechanism ( 337, 375 ) confines the returned syringe in its retracted position.

Description:
The present application claims the benefit and priority to and is a U.S. National Phase of PCT International Application Number PCT/GB2005/002137, filed on May 27, 2005, which claims priority to United Kingdom Application No. 0412061.4, filed May 28, 2004, both of which are expressly incorporated by reference in their entirety. 
     BACKGROUND TECHNOLOGY 
     The present invention relates to an injection device of the type that receives a syringe, extends it, discharges its contents and then retracts it automatically. Devices of this general description are shown in WO 95/35126 and EP-A-0 516 473 and tend to employ a drive spring and some form of release mechanism that releases the syringe from the influence of the drive spring once its contents are supposed to have been discharged, to allow it to be retracted by a return spring. 
     In devices of this nature, it is desirable for the return spring to be sufficiently strong that it can retract the syringe quickly. However, it is then possible for the syringe to be retracted so forcefully that it escapes from those elements of the device that are supposed to hold it during the extension and retraction phases. The syringe may then be free to move around within the body of the device. This gives rise to a number of undesirable effect. Firstly, the syringe will rattle around in the body of the device, giving an impression of poor quality. Secondly, shaking the device, which may be encouraged in those patients of a certain disposition by the rattling noise made by the syringe, might break the syringe, allowing broken glass to escape. Moreover, if the device has a viewing window, through which the discharged syringe may be inspected, the syringe will no longer be correctly positioned relative to it. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide an improved injection device that does not suffer from these shortcomings. 
     Accordingly, the present invention provides an injection device comprising:
         a housing adapted to receive a syringe having a discharge nozzle and including means for biasing the syringe from an extended position in which the discharge nozzle of the syringe extends from the housing to a retracted position in which the discharge nozzle is contained within the housing;   an actuator;   a drive acted upon by the actuator and in turn acting on the syringe to advance it from its retracted position to its extended position and discharge its contents through the discharge nozzle;   a release mechanism, activated when the drive has been advanced to a nominal release position, to release the syringe from the action of the actuator, whereupon the biasing means restores the syringe to its retracted position; and   a locking mechanism that confines the returned syringe in its retracted position.       

     By confining the syringe in its retracted position, rather than permitting it to break free, the present invention overcomes the disadvantages discussed above. Preferably, the locking mechanism is activated when the drive has been advanced to a locking position that is no more advanced than the said nominal release position. 
     In a preferred implementation of the present invention, the housing includes a syringe carrier adapted to receive the syringe and the biasing means is adapted to bias the syringe carrier from an extended position to a retracted position. In that case, the locking mechanism can prevent the drive from retracting relative to the syringe carrier, thus confining the syringe between the drive and the syringe carrier in preparation for the activation of the release mechanism. 
     Con convenience of manufacture and simplicity of operation, the drive may include a flexible latch that rides over a detent as the drive is advanced and thereafter engages beyond it. For example, the syringe carrier may include a detent and the flexible latch may ride over the detent as the drive is advanced and thereafter engage beyond it. The flexible latch may comprises a flexible barb, for increased security of latching. 
     A plurality of such flexible latches may be present, and they can be substantially equidistantly spaced around the circumference of the drive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is an illustration of a comparative injection device as discussed above; and 
         FIGS. 2-4  show an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an injection device  210  in which a housing  212  contains a hypodermic syringe  214 . The syringe  214  is again of conventional type, including a syringe body  216  terminating at one end in a hypodermic needle  218  and at the other in a flange  220 , and a rubber bung  222  that constraints a drug  224  to be administered within the syringe body  216 . The conventional plunger that would normally be connected to the bung  222  and used to discharge the contents of the syringe  214  manually, has been removed and replaced with a multi-component drive element as will be described below. Whilst the syringe illustrated is again of hypodermic type, this need not necessarily be so. As illustrated, the housing includes a return spring  226  that biases the syringe  214  from an extended position in which the needle  218  extends from aperture  228  in the housing  212 , to a retracted position in which the hypodermic needle  218  is contained within the housing  212 . The return spring  226  acts on the syringe  214  via a sleeve  227 . 
     At the other end of the housing is a compression drive spring  230 . Drive from the drive spring  230  this transmitted via the multi-component drive to the syringe  214  to advance it from its retracted position to its extended position and discharge its contents through the needle  218 . The drive accomplishes this task by acting directly on the drug  224  and the syringe  214 . Hydrostatic forces acting through the drug  224  and, to a lesser extent, static friction between the bung  222  and the syringe body  216  initially ensures that they advance together, until the return spring  226  bottoms out or the syringe body  216  meets some other obstruction that retards its motion. 
     The multi component drive between the drive spring  230  and the syringe  214  again consists of three principal components. The drive sleeve  231  takes drive from the drive spring  230  and transmits it to flexible latch arms  233  on a first drive element  232 . These elements are shown in detail “A”. The first drive element  232  in turn transmits drive via flexible latch arms  235  to a second drive element  234 . These elements are shown in detail “B”. As before, the first drive element  232  includes a hollow stem  240 , the inner cavity of which forms a collection chamber  242 . The second drive element  234  includes a blind for  246  that is open at one end to receive the stem  240  and closed at the other. As can be seen, the bore  246  and the stem  240  define a fluid reservoir  248 , within which a damping fluid is contained. 
     A trigger (not shown) is provided at the middle of the housing  212  and, one operated, serves to decouple the drive sleeve  231  from the housing  212  allowing it to move relative to the housing  212  under the influence of the drive spring  230 . The operation of the device is then as follows. 
     Initially, the drive spring  230  moves the drive sleeve  231 , the drive sleeve  231  moves the first drive element  232  and the first drive element  232  moves the second drive element  234 , in each case by acting through the flexible matching arms  233 ,  235 . The second drive element  234  moves and, by virtue of static friction and hydrostatic forces acting through the drug  224  to be administered, moves the syringe body  216  against the action of the return spring  226 . The return spring  226  compresses and the hypodermic needle  218  emerges from the exit aperture  228  of the housing  212 . This continues until the return spring  226  bottoms out or the syringe body  216  meets some other obstruction that retards its motion. Because the static friction between the bung  222  and the syringe body  216  and the hydrostatic forces acting through the drug  224  to be administered are not sufficient to resist the full drive force developed by the drive spring  230 , at this point the second drive element  234  begins to move within the syringe body  216  and the drug  224  begins to be discharged. Dynamic friction between the bung  222  and the syringe body  216  and hydrostatic forces acting through the drug  224  to be administered are, however, sufficient to retain the return spring  226  in its compressed state, so the hypodermic needle  218  remains extended. 
     Before the second drive element  234  reaches the end of its travel within the syringe body  216 , so before the contents of the syringe have fully discharged, the flexible latch arms  235  linking the first and second drive elements  232 ,  234  reach a constriction  237 . The constriction  237  is formed by a component  262  that is initially free to move relative to all other components, but that is constrained between the syringe flange  220  and additional flexible arms  247  on the second drive element  234 . These additional flexible arms  247  overlie the flexible arms  235  on the first drive element  232 , by means of which drive is transmitted to the second drive element  234 .  FIG. 1  illustrates the injection device  210  at the position where the additional flexible arms  247  are just making contact with the constriction  237  in the component  262 . 
     The constriction  237  moves the additional flexible arms  247  inwards, aided by the bevelled surfaces on both, and the additional flexible arms  247  in turn move the flexible arms  235 , by means of which drive is transmitted from the first drive element  232  to the second drive element  234 , inwards from the position shown to a position at which they no longer couple the first and second drive elements together. Once this happens, the first drive element  232  acts no longer on the second drive element  234 , allowing the first drive element  232  to move relative to the second drive element  234 . 
     Because the damping fluid is contained within a reservoir  248  defined between the end of the first drive element  232  and the blind bore  246  in the second drive element  234 , the volume of the reservoir  248  will tend to decrease as the first drive element  232  moves relative to the second drive element  234  when the former is acted upon by the drive spring  230 . As the reservoir  248  collapses, damping fluid is forced into the collection chamber  242 . Thus, once the flexible latch arms  235  have been released, the force exerted by the drive spring  230  does work on the damping fluid, causing it to flow into the collection chamber  242 , and also acts hydrostatically through the fluid and through friction between the first and second drive elements  232 ,  234 , thence via the second drive element  234 . Losses associated with the flow of the damping fluid do not attenuate the force acting on the body of the syringe to a great extent. Thus, the return spring  226  remains compressed and the hypodermic needle remains extended. 
     After a time, the second drive element  234  completes its travel within the syringe body  216  and can go no further. At this point, the contents of the syringe  214  are completely discharged and the force exerted by the drive spring  230  acts to retain the second drive element  234  in its terminal position and to continue to cause the damping fluid to flow into the collection chamber  242 , allowing the first drive element  232  to continue its movement. 
     A flange  270  on the rear of the second drive element  234  normally retains the flexible arms  233  in engagement with the drive sleeve  231 . However, before the reservoir  248  of fluid is exhausted, the flexible latch arms  233  linking the drive sleeve  231  with the first drive element  232  move sufficiently far forward relative to the second drive element  234  that the flange  270  is brought to register with a rebate  272  in the flexible arms  233 , whereupon it ceases to be effective in retaining the flexible arms  233  in engagement with the drive sleeve  231 . Now, the drive sleeve  231  moves the flexible latch arms  233  inwards from the position shown to a position at which they no longer couple the drive sleeve  231  to the first drive element  232 , aided by the bevelled latching surfaces  274  on the flexible arms  233 . Once this happens, the drive sleeve  231  acts no longer on the first drive element  232 , allowing them to move relative to each other. At this point, of course, the syringe  214  is released, because the forces developed by the drive spring  230  are no longer being transmitted to the syringe  214 , and the only force acting on the syringe will be the return force from the return spring  226 . Thus, the syringe  214  now returns to its retracted position and the injection cycle is complete. 
     However, in this example, it may be possible for the syringe to return beyond its retracted position, or in other words to come free of the syringe carrier and then rattle around within the body of the injection device. Although there is of course no possibility of the syringe falling out of the injection device altogether, the various undesirable consequences that have already been discussed may follow. 
       FIGS. 2-4  show an injection device  310  in which this problem is neatly overcome. Again, a housing  312  contains a hypodermic syringe  314 . The syringe  314  is again of conventional type, including a syringe body  316  terminating at one end in a hypodermic needle  318  and at the other in a flange  320 , and a rubber bung  322  that constraints a drug  324  to be administered within the syringe body  316 . Whilst the syringe illustrated is again of hypodermic type, this need not necessarily be so. As illustrated, the housing includes a return spring  326  that biases the syringe  314  from an extended position in which the needle  318  extends from an aperture  328  in the housing  312 , to a retracted position in which the hypodermic needle  318  is contained within the housing  312 . The return spring  326  acts on the syringe  314  via a sleeve  327 . The extended position of the syringe  314  is shown in  FIG. 3 ; and the retracted position, after the injection cycle is complete is shown in  FIG. 4 . 
     At the other end of the housing is a compression drive spring  330 . Drive from the drive spring  330  this transmitted via the multi-component drive to the syringe  314  to advance it from its retracted position to its extended position and discharge its contents through the needle  318 . The drive accomplishes this task by acting directly on the drug  324  and the syringe  314 . Hydrostatic forces acting through the drug and, to a lesser extent, static friction between the bung  322  and the syringe body  316  initially ensures that they advance together, until the return spring  326  bottoms out or the syringe body  316  meets some other obstruction that retards its motion. 
     The multi component drive between the drive spring  330  and the syringe  314  again consists of three principal components. The drive sleeve  331  takes drive from the drive spring  330  and transmits it to flexible latch arms  333  on a first drive element  332 . The first drive element  332  in turn transmits drive via flexible latch arms (not shown) to a second drive element  334 . As before, the first drive element  332  includes a hollow stem  340 , the inner cavity of which forms a collection chamber  342 . The second drive element  334  includes a blind bore  346  that is open at one end to receive the stem  340  and closed at the other. As can be seen, the bore  346  and the stem  340  define a fluid reservoir  348 , within which a damping fluid is contained. 
     A trigger  349  is provided in the housing  312 . The trigger  349 , one operated, serves to decouple the drive sleeve  331  from the housing  312  allowing it to move relative to the housing  312  under the influence of the drive spring  330 . The operation of the device is then as follows. 
     Initially, the drive spring  330  moves the drive sleeve  331 , the drive sleeve  331  moves the first drive element  332  and the first drive element  332  moves the second drive element  334 , in each case by acting through the flexible matching arms (not shown). The second drive element  334  moves and, by virtue of static friction and hydrostatic forces acting through the drug  324  to be administered, moves the syringe body  316  and hence the sleeve  327  against the action of the return spring  326 . The return spring  326  compresses and the hypodermic needle  318  emerges from the exit aperture  328  of the housing  312 . This continues until the return spring  326  bottoms out or the sleeve  327  meets some other obstruction that retards its motion. Because the static friction between the bung  322  and the syringe body  316  and the hydrostatic forces acting through the drug  324  to be administered are not sufficient to resist the full drive force developed by the drive spring  330 , at this point the second drive element  334  begins to move within the syringe body  316  and the drug  324  begins to be discharged. Dynamic friction between the bung  322  and the syringe body  316  and hydrostatic forces acting through the drug  324  to be administered are, however, sufficient to retain the return spring  326  in its compressed state, so the hypodermic needle  318  remains extended. 
     Before the second drive element  334  reaches the end of its travel within the syringe body  316 , so before the contents of the syringe have fully discharged, the flexible latch arms (not shown) linking the first and second drive elements  332 ,  334  reach a constriction  337 . The constriction  337  is formed by a component  362  that is formed integrally with the syringe carrier. As before, additional flexible arms (not shown) on the second drive element  334  overlie the flexible arms (not shown) on the first drive element  332 , by means of which drive is transmitted to the second drive element  334 . 
     In the same way as for  FIG. 1 , the constriction  337  causes the first and second drive elements  332 ,  334  to disengage. In addition, the constriction  337  serves a second purpose. To this end, the second drive element  334  is provided with a pair of oblique flexible barbs  375 . In their rest position, the barbs extend from the second drive element  334  to a diameter that is larger than the inner diameter of the constriction  337 . As the second drive element advances, oblique flexible barbs  375  are pressed down against the second drive element  334 , and pass thought the constriction  337 . Once they have passed through it, they spring back to their rest position. Because, in that position, they extend from the second drive element  334  to a diameter that is larger than the inner diameter of the constriction  337 , any attempt to move the second drive element  334  backwards through the constriction  337  will result in the flexible barbs  375  being splayed outwards, preventing the backward motion. Thus, the flexible barbs  375  and the constriction  337  together form a non-return mechanism. 
     Because the damping fluid is contained within a reservoir  348  defined between the end of the first drive element  332  and the blind bore  346  in the second drive element  334 , the volume of the reservoir  348  will tend to decrease as the first drive element  332  moves relative to the second drive element  334  when the former is acted upon by the drive spring  330 . As the reservoir  348  collapses, damping fluid is forced into the collection chamber  342 . Thus, once the flexible latch arms (not shown) have been released, of the force exerted by the drive spring  330  does work on the damping fluid, causing it to flow into the collection chamber  342 , and also acts hydrostatically through the fluid and through friction between the first and second drive elements  332 ,  334 , thence via the second drive element  334 . Losses associated with the flow of the damping fluid do not attenuate the force acting on the body of the syringe to a great extent. Thus, the return spring  326  remains compressed and the hypodermic needle remains extended. 
     After a time, the second drive element  334  completes its travel within the syringe body  316  and can go no further. At this point, the contents of the syringe  314  are completely discharged and the force exerted by the drive spring  330  acts to retain the second drive element  334  in its terminal position and to continue to cause the damping fluid to flow into the collection chamber  342 , allowing the first drive element  332  to continue its movement. 
     A flange  370  on the rear of the second drive element  334  normally retains the flexible arms  333  in engagement with the drive sleeve  331 . However, before the reservoir  348  of fluid is exhausted, the flexible latch arms  333  linking the drive sleeve  331  with the first drive element  332  move sufficiently far forward relative to the second drive element  334  that the flange  370  is brought to register with a rebate  372  in the flexible arms  333 , whereupon it ceases to be effective in retaining the flexible arms  333  in engagement with the drive sleeve  331 . Now, the drive sleeve  331  moves the flexible latch arms  333  inwards from the position shown to a position at which they no longer couple the drive sleeve  331  to the first drive element  332 , aided by the bevelled latching surfaces  374  on the flexible arms  333 . Once this happens, the drive sleeve  331  acts no longer on the first drive element  332 , allowing them to move relative to each other. At this point, of course, the syringe  314  is released, because the forces developed by the drive spring  330  are no longer being transmitted to the syringe  314 , and the only force acting on the syringe will be the return force from the return spring  326 . Thus, the syringe  314  now returns to its retracted position and the injection cycle is complete. 
     The non-return mechanism formed by the barbs  375  and the constriction  337  at all times constrains the syringe between the drive and the syringe carrier, thus preventing it from coming loose within the body of the injection device.