Abstract:
An injection device  110  is described having a housing  112  that receives a syringe  114 . The syringe  114  is biased by a return spring  126  from an extended position in which the needle  118  extends from the housing  112  through an exit aperture  128  to a retracted position in which it does not. A drive spring  130  acts via a drive to advance the syringe  114  from its retracted position to its extended position and discharge its contents through the needle  118  and a return spring  126 , brought into play when the drive has reached a nominal return position, restores the syringe  114  to its retracted position. A releasable locking mechanism retains the syringe  114  in its retracted position. A sleeve  119  projects from the exit aperture  128  and can be depressed to release the locking mechanism. A trigger  300  has a rest position, in which it engages the drive, retaining it in a position corresponding to the retracted position of the syringe  114 , and a depressed position, in which it no longer causes the drive to be so retained. The sleeve  119  normally locks the trigger  300  in its rest position. However, depression of the sleeve  119  into the exit aperture  128 , allows the trigger to be depressed. Thereafter, the trigger  300  is retained in its active position.

Description:
BACKGROUND TECHNOLOGY 
       [0001]    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. The initial action of the drive spring is typically controlled by means of a trigger. Depression of the trigger causes the drive spring to become operative. 
         [0002]    It is not uncommon for the operation of the trigger to be dependent upon the operation of a safety interlock, to prevent accidental operation. First the safety interlock must be operated, and then the trigger. 
         [0003]    Market research has shown that it is beneficial for an injector device to provide some form of visual indication that the device is either ready to use or has been used. As ever, the simplest and cheapest way of achieving this is sought. 
       SUMMARY OF THE INVENTION 
       [0004]    The injection devices of the present invention are designed to do this. 
         [0005]    An injection device according to the present invention comprises:
       a housing adapted to receive a syringe having a discharge nozzle so that the syringe is movable between a retracted position in which the discharge nozzle is contained within the housing and an extended position in which the discharge nozzle extends from the housing;   a drive that is acted upon and in turn acts upon the syringe;   a trigger movable from a rest position, in which it causes the drive to be retained in a position corresponding to the retracted position of the syringe, to an active position, in which it no longer causes the drive to be so retained, thus allowing it to be advanced and in turn to advance the syringe from its retracted position to its extended position and discharge its contents through the discharge nozzle; and   an interlock member movable between a locking position, at which it prevents movement of the trigger from its rest position to its active position, and a releasing position, at which it allows movement of the trigger from its rest position to its active position, the device having a visual indicator activating upon said trigger moving to an active position.       
 
         [0010]    Thus, a device according to this invention provides a visual indication that it is either ready to use or has been used. 
         [0011]    Preferably, the said visual indicator is provided by the trigger being retained in its active position. If such a device is ready for use, the trigger will be in its rest position. If it has been used, the trigger will be in its active position. These positions can be discriminated by the user. Moreover, the device incorporates the mechanism for achieving this result into a safety interlock mechanism, in the interests of simplicity. The trigger may comprise a locking member that, in the rest position of the trigger, engages a locking surface of the drive and, in the active position, does not. 
         [0012]    The interlock member may comprises a primary member, the locking position of the interlock member being one in which the primary member projects from the discharge opening and the releasing position being one in which the primary member does not project from the discharge opening or projects from it to a lesser extent. This means that the interlock member may be moved from its locking position to its releasing position by bringing the end of the injection device into contact with the skin at the injection site. Apart from anything else, this ensures that the injection device is optimally positioned relative to the injection site before the injection cycle can begin. A primary member in the form of a sleeve allows a relatively large area to contact the skin and allows the discharge nozzle of the syringe to be advanced and retracted within it. In the case of a hypodermic syringe, the sleeve will shroud the needle from view, which is a good idea for the squeamish, particularly those who have to administer to themselves. 
         [0013]    The locking of the trigger in its rest position may be achieved as follows. The trigger and the interlock member include a projection and an aperture, the projection being in register with the aperture when the interlock member is in its releasing position, but not otherwise. This allows the trigger to move from its rest position to its active position by movement of the projection into the aperture. The projection may be on the trigger and the aperture is in the interlock member. 
         [0014]    The retention of the trigger in its active position may be achieved as follows. The trigger and another component of the device include a latching projection and a corresponding latching surface against which the latching projection latches when the trigger is in its active position. The latching projection may be on the trigger. This other component of the device is preferably the interlock member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention will now be described by way of example with reference to the accompanying drawings, in which: 
           [0016]      FIG. 1  shows in section an injection device of the type to which the present invention is applicable; 
           [0017]      FIG. 2  shows in sectional schematic how that device may be modified in accordance with the invention; 
           [0018]      FIG. 3  is a cut-away view of the modified injection device; and 
           [0019]      FIG. 4  shows in section a preferred injection device. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  shows an injection device  110  having a housing  112  that contains a hypodermic syringe  114  of conventional type, including a syringe body  116  terminating at one end in a hypodermic needle  118  and at the other in a flange  120 . The conventional plunger that would normally be used to discharge the contents of the syringe  114  manually have been removed and replaced with a drive element  134 , terminating in a bung  122 . The bung  122  constrains a drug  124  to be administered within the syringe body  116 . Whilst the syringe illustrated is of hypodermic type, this need not necessarily be so. Transcutaneous or ballistic dermal and subcutaneous syringes may also be used with the injection device of the present invention. As illustrated, the housing includes a return spring  126  that biases the syringe  114  from an extended position in which the needle  118  extends from an aperture  128  in the housing  112  to a retracted position in which the discharge nozzle  118  is contained within the housing  112 . The return spring  126  acts on the syringe  114  via a syringe carrier  127 . 
         [0021]    At the other end of the housing is an actuator, which here takes the form of a compression drive spring  130 . Drive from the drive spring  130  is transmitted via a multi-component drive to the syringe  114  to advance it from its retracted position to its extended position and discharge its contents through the needle  118 . The drive accomplishes this task by acting directly on the drug  124  and the syringe  114 . Hydrostatic forces acting through the drug and, to a lesser extent, static friction between the drive element  134  and the syringe body  116  initially ensure that they advance together, until the return spring  126  bottoms out or the syringe body  116  meets some other obstruction (not shown) that retards its motion. 
         [0022]    The multi-component drive between the drive spring  130  and the syringe  114  consists of three principal components. A drive sleeve  131  takes drive from the drive spring  130  and transmits it to flexible latch arms  133  on a first drive element  132 . This in turn transmits drive via flexible latch arms  135  to a second drive element, the drive element  134  already mentioned. 
         [0023]    The first drive element  132  includes a hollow stem  140 , the inner cavity of which forms a collection chamber  142  in communication with a vent  144  that extends from the collection chamber through the end of the stem  140 . The second drive element  134  includes a blind bore  146  that is open at one end to receive the stem  140  and closed at the other. As can be seen, the bore  146  and the stem  140  defining a fluid reservoir  148 , within which a damping fluid is contained. 
         [0024]    A trigger (not shown) is provided that, when operated, serves to decouple the drive sleeve  131  from the housing  112 , allowing it to move relative to the housing  112  under the influence of the drive spring  130 . The operation of the device is then as follows. 
         [0025]    Initially, the drive spring  130  moves the drive sleeve  131 , the drive sleeve  131  moves the first drive element  32  and the first drive element  132  moves the second drive element  134 , in each case by acting through the flexible latch arms  133 ,  135 . The second drive element  134  moves and, by virtue of static friction and hydrostatic forces acting through the drug  124  to be administered, moves the syringe body  116  against the action of the return spring  126 . The return spring  126  compresses and the hypodermic needle  118  emerges from the exit aperture  128  of the housing  112 . This continues until the return spring  126  bottoms out or the syringe body  116  meets some other obstruction (not shown) that retards its motion. Because the static friction between the second drive element  134  and the syringe body  116  and the hydrostatic forces acting through the drug  124  to be administered are not sufficient to resist the full drive force developed by the drive spring  130 , at this point the second drive element  134  begins to move within the syringe body  116  and the drug  124  begins to be discharged. Dynamic friction between the second drive element  134  and the syringe body  116  and hydrostatic forces acting through the drug  124  to be administered are, however, sufficient to retain the return spring  126  in its compressed state, so the hypodermic needle  118  remains extended. 
         [0026]    Before the second drive element  134  reaches the end of its travel within the syringe body  116 , so before the contents of the syringe have fully discharged, the flexible latch arms  135  linking the first and second drive elements  132 ,  134  reach a constriction  137  within the housing  112 . The constriction  137  moves the flexible latch arms  135  inwards from the position shown to a position at which they no longer couple the first drive element  136  to the second drive element  134 , aided by the bevelled surfaces on the constriction  137 . Once this happens, the first drive element  136  acts no longer on the second drive element  134 , allowing the first drive element  132  to move relative to the second drive element  134 . 
         [0027]    Because the damping fluid is contained within a reservoir  148  defined between the end of the first drive element  132  and the blind bore  146  in the second drive element  134 , the volume of the reservoir  146  will tend to decrease as the first drive element  132  moves relative to the second drive element  134  when the former is acted upon by the drive spring  130 . As the reservoir  148  collapses, damping fluid is forced through the vent  144  into the collection chamber  142 . Thus, once the flexible latch arms  135  have been released, the force exerted by the drive spring  130  does work on the damping fluid, causing it to flow though the constriction formed by the vent  144  and also acts hydrostatically through the fluid and through friction between the first and second drive elements  132 ,  134 , thence via the second drive element  134 . 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  126  remains compressed and the hypodermic needle remains extended. 
         [0028]    After a time, the second drive element  134  completes its travel within the syringe body  116  and can go no further. At this point, the contents of the syringe  114  are completely discharged and the force exerted by the drive spring  130  acts to retain the second drive element  134  in its terminal position and to continue to cause the damping fluid to flow though the vent  144 , allowing the first drive element  132  to continue its movement. 
         [0029]    Before the reservoir  148  of fluid is exhausted, the flexible latch arms  133  linking the drive sleeve  131  with the first drive element  132  reach another constriction  139  within the housing  112 . The constriction  139  moves the flexible latch arms  133  inwards from the position shown to a position at which they no longer couple the drive sleeve  131  to the first drive element  132 , aided by the bevelled surfaces on the constriction  139 . Once this happens, the drive sleeve  131  acts no longer on the first drive element  132 , allowing them to move relative each other. At this point, of course, the syringe  114  is released, because the forces developed by the drive spring  130  are no longer being transmitted to the syringe  114 , and the only force acting on the syringe will be the return force from the return spring  126 . Thus, the syringe  114  is now returned to its retracted position and the injection cycle is complete. 
         [0030]    All this takes place, of course, only once the cap  111  has been removed from the end of the housing  112 . As can be seen from  FIG. 3 , the end of the syringe is sealed with a boot  123 . The central boss  121  of the cap that fits within the sleeve  119  when the cap  111  is installed on the housing  112 , is hollow at the end and the lip  125  of the hollow end is bevelled on its leading edge  157 , but not its trailing edge. Thus, as the cap  111  is installed, the leading edge  157  of the lip  125  rides over a shoulder  159  on the boot  123 . However, as the cap  111  is removed, the trailing edge of the lip  125  will not ride over the shoulder  159 , which means that the boot  123  is pulled off the syringe  114  as the cap  111  is removed. 
         [0031]      FIGS. 2 and 3  show the device may be further modified. Although  FIGS. 2 and 3  differ from  FIG. 1  in some details, the principles now discussed are applicable to the device shown in  FIG. 1 . As can be seen, the device includes a trigger  300  having a button  302  at one end and a pair of lugs  304  that cooperate with pins (not shown) on the inside of the housing  112  to allow the trigger to pivot about an axis through the two lugs  304 . The main body portion of the trigger  300 , to which both the button  302  and the lugs  304  are affixed, forms a locking member  306 . In the position shown, the end of the locking member  306  remote from the button  302  engages the end of the drive sleeve  131 , against which the drive spring  130  acts and which in turn acts upon the multi-component drive previously discussed. This prevents the drive sleeve  131  from moving under the influence of the drive spring  130 . When the button  302  is depressed, the trigger  300  pivots about the lugs  304 , which lifts the end of the locking member  306  from its engagement with the drive sleeve  131 , now allowing the drive sleeve  131  to move under the influence of the drive spring  130 . 
         [0032]      FIG. 3  shows the exit aperture  128  in the end of the housing  112 , from which the end of the sleeve  119  can again be seen to emerge. As is shown in  FIG. 2 , the sleeve  119  is coupled to a button lock  310  which moves together with the sleeve  119 . The trigger includes a stop pin  312  and the button lock  310  includes an stop aperture  314  which, as shown in  FIG. 2 , are out of register. They can, however, be brought into register by inward movement of the sleeve  119 , which results in a corresponding movement of the button lock  310 . Whilst the stop pin  312  and the stop aperture  314  are out of register, the button  302  may not be depressed; once they are in register, it may. The trigger  300  also includes a flexible, barbed latching projection  316  and the button lock  310  also includes a latching surface  318  with which the latching projection  316  engages when the button is depressed. Once the latching projection  316  has latched with the latching surface  318 , the trigger  300  is permanently retained with the button  302  in its depressed position. 
         [0033]    Thus, movement of the sleeve  119  in a direction into the housing  112 , or in other words depression of the projecting end of the sleeve, brings the stop pin  312  into register with the stop aperture  314 , allowing the trigger button  302  to be depressed, whereupon it is retained in its depressed position by the latching projection  316  and the latching surface  318 . The sleeve  119  may be depressed by bringing the end of the injection device into contact with the skin at an injection site which, apart from anything else, ensures it is properly positioned before the injection cycle begins. 
         [0034]      FIG. 4  shows a preferred injection device  210  to which the improvements described above with reference to  FIGS. 2 and 3  are applied. Again, 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 . 
         [0035]    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 ensure that they advance together, until the return spring  226  bottoms out or the syringe body  216  meets some other obstruction that retards its motion. 
         [0036]    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. 
         [0037]    A trigger as described above with reference to  FIGS. 6 and 7  is provided in the middle of the housing  212 . The trigger, 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. 
         [0038]    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. 
         [0039]    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. 3  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 . 
         [0040]    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 . 
         [0041]    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. 
         [0042]    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  142 , allowing the first drive element  232  to continue its movement. 
         [0043]    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 damping 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.