Abstract:
An injection device includes an injection complete indicator which includes its own bias and which is latched into a retracted position as the injection device is cocked. Upon firing the injection device, the injection complete indicator is kept in its retracted position until towards the end of the forward stroke of the drive mechanism, whereupon the injection complete indicator is unlatched and shoots forwardly under the influence of the bias to impact an abutment to generate an audible/tactile indication along with a visual indication.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to injection devices and in particular, but not exclusively, to reusable autoinjector devices comprising a housing into which a disposable syringe may be inserted to effect the injection and then removed and replaced as required for the next injection. 
     DESCRIPTION OF THE RELATED ART 
     It is a common requirement that autoinjectors signal to the user when the injection is complete by means of an ‘injection complete’ signal. The term ‘injection complete’ is used to refer to a condition in which a satisfactory delivery of the drug has been achieved. It is also desirable that this indication is not only visual but also audible and/or tactile, to provide confirmation to the user when injection site is out of sight, or would require some straining to see, for example in the buttocks or upper arm. 
     It is also desirable that the energy required to generate the audible or tactile signal does not subtract significant energy from the main drive source of the device as this might impair efficient sequencing and delivery. We have designed an injection device which provides an audible and/or tactile indication to the user as well as a visual indication, without taking significant energy from the main drive source. It is additionally desirable to provide an arrangement in which the indicator is reset automatically for each injection cycle. 
     SUMMARY OF THE INVENTION 
     Accordingly, in one aspect, this invention provides an injection device including an injection complete indicator for providing a kinetic impact indication, the device including: 
     a housing; 
     a plunger movable in said housing between cocked and fired positions under the influence of a plunger drive source; 
     an indicator element movable between an extended position and a retracted position and being biased towards said extended position by an indicator bias; 
     an indicator latch arrangement for latching said indicator element in a retracted position; 
     a motion transfer arrangement between the plunger and the indicator element for retracting said indicator element to said retracted position as said plunger is moved to its cocked position but allowing forward movement of said plunger relative to the indicator element; 
     the device being arranged such that, after firing, as the plunger nears or reaches the end of its operating stroke, it enables release of the indicator latch arrangement to cause the indicator element to move to its extended position under the influence of said bias to impact a stop surface to create said kinetic impact. 
     Preferably, said indicator element also provides a visual indication upon approaching or reaching its extended position. 
     It will be noted that the indicator element is provided with its own bias and that the motive force for moving the indicator forward after the indicator latch arrangement has been released may be provided by the indicator bias. Conveniently said motion transfer arrangement comprises an abutment surface associated with one of said plunger and said indicator element and a cooperating projection associated with the other thereof. 
     Preferably said indicator latch arrangement includes a flexible latch finger associated with said housing and having a latching tooth past which a flexible finger on the indicator element may snap as the indicator element is moved to its retracted position. The latch finger associated with the housing is advantageously resiliently deflectable to allow said indicator finger to move forwardly, with the deflection being prevented except when the plunger is at or near the end of its stroke. Once deflection is possible the indicator may be released for forward movement. 
     In many configurations the plunger is movable longitudinally between its cocked and fired positions, and the body finger preferably extends generally longitudinally, with the plunger having a support surface which underlies the body finger, until the plunger nears or reaches the end of its stroke. 
     Concurrently the latch tooth comprises respective ramp surfaces facing in the cocking and firing directions respectively, with the ramp surfaces providing a profile in which the inclination of the ramp face first contacted by the indicator finger when moving to its retracted position is shallower than the other face, whereby the indicator finger can snap past the latch tooth when moving in the direction of retraction, but not in the opposite direction. 
     In another aspect, this invention provides an injection device including an injection complete indicator, the device including: 
     a housing; 
     a plunger movable in said housing between cocked and fired positions under the influence of a plunger drive source; 
     an indicator element movable between a pre-firing position and an injection complete position; 
     the device being arranged such that, after firing, as the plunger nears or reaches the end of its operating stroke, the indicator element is caused to move to its injection complete position and wherein subsequent re-cocking of the plunger returns said indicator element to its pre-firing position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Whilst the invention has been described above, it extends to any novel combination of the features set out above, or in the following description or drawings. Whilst the invention may be performed in various ways, an embodiment thereof will now be described by way of example only, reference being made to the accompanying drawings in which: 
         FIGS. 1( a ) to ( e )  are perspective views of an autoinjection device in accordance with this invention showing various stages in operation prior to, during and after firing; 
         FIG. 2  is an exploded view of the rear body assembly excluding the cover; 
         FIG. 3  is a view of the rear body assembly of the embodiment of  FIG. 1 , with the cover removed; 
         FIG. 4  is a perspective view of the rear body housing of the rear body assembly; 
         FIG. 5  is a perspective view of the indicator and forward end of the rear body housing; 
         FIG. 6  is a perspective view of the plunger and part of the drive spring of the rear body assembly; 
         FIGS. 7( a ) to ( h )  are perspective views of the rear body assembly showing the configuration of the various components in sequence through a cocking and firing operation, and 
         FIGS. 8( a ) to ( h )  are corresponding side views of the rear assembly during these operations. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIGS. 1( a ) to ( e ) , a preferred embodiment of autoinjector comprises a separable body comprising a front body assembly  10  screwed or otherwise releasably coupled to a rear body  12  having an outer slideable cover  14 . The device is designed to be reusable with the user separating the front and rear body assemblies, inserting or replacing a syringe  22  housed in the front body assembly, priming or cocking a drive mechanism contained in the rear body assembly, and connecting the front and rear body assemblies together. This is similar to our well known Autoject® II device and as described in WO2004/108194. As in the arrangement of WO2004/108194, the cover  14  is biased rearwardly to a position where it interlocks with a trigger  16  to prevent actuation thereof. The cover  14  also has a window  18  through which an indicator sleeve  20  becomes visible upon satisfactory completion of an injection (see  FIG. 1( d ) ). In order to operate the device, the operator grasps the cover  14  and presses the front end of the front body assembly  10  against the injection site, thus shifting the cover  14  forwardly to release the mechanical interlock. On pressing the trigger  16 , the drive mechanism inside the rear body housing moves a plunger forwardly which initially advances the syringe  22  so that its needle  24  penetrates the injection site and thereafter the plunger moves the syringe piston to expel a dose. Upon nearing or reaching the forward end of its stroke, the plunger releases the indicator sleeve  20  which shoots forward to become visible to give a visual indication in window  18  and also to impact an internal surface to create an audible and tactile signal ( FIG. 1( d ) ). On removing the device from the injection site the reaction force is removed and so the cover  14  again shifts rearwardly on the rear body to interlock with the trigger  16 . 
     Referring initially to  FIGS. 2 to 6 , the rear body assembly  12  comprises a rear body housing  26  of generally cylindrical form cut away on its upper surface to provide an open wide slot  28  bridged at its forward end by a bridge  30  and supporting the trigger  16  at its rear end by means of live hinges  32 . About half way down the slot  28  extends a parallel axial finger  34  hinged at its rear end by a live hinge  36  so that it can deflect resiliently into the bore of the rear body housing  26 . The axial finger  34  has an asymmetric latch tooth  38  having a shallowly inclined forward ramp face  40  and a steeper rear ramp face  42 . In the base of the rear body housing  26 , opposite the wide slot  28  is a narrow slot  44  which allows a lost motion connection between the indicator sleeve  20  and the plunger  45  as to be described below. At 90° to the slots  28  and  44  are disposed internal guide grooves  46  that constrain the plunger so that it moves longitudinally without rotational movement. The bridge  30  includes an anchorage  48  for one end of an indicator spring  50 . 
     The plunger is generally of stepped cylindrical form having a flat front end face  52  for engaging the syringe plunger (not shown) and open at its rear end to receive the front end of a drive spring  54 . Side ribs  53  run in the guide grooves  46  of the rear body housing. Extending rearwardly from the upper side of the plunger as viewed is a tab  56  having a latch rib  58  which cooperates with a complementary latch rib  60  on the trigger  16  when the plunger is in its cocked position. A stop  62  upstands from a forward region of the tab  56  and cooperates with the bridge  30  on the rear body housing  26  to limit forward movement of the plunger. Extending along the entire length of the main plunger body  45  is a part cylindrical support surface  65  which cooperates with the latch finger  34  to prevent inward resilient deflection of the axial finger  34  until the plunger is at or near its forwardmost position. 
     The indicator sleeve  20  is slideably mounted around the outside of the rear body housing  26  for movement between the forwardmost, indicating, position shown in  FIGS. 7( a ) and 8( a )  to the retracted position shown in  FIGS. 7( d ) and 8( d ) . The indicator  20  is biased forwardly by means of the indicator spring  50  which is a tension spring. The indicator spring  50  is connected to the indicator  20  at a spring anchorage  64 . 
     A collar fitting  66  clips to the front end of the rear body housing  26  by means of sprung arms  68  which clip around the bridge  30 . The collar fitting provides an annular stop surface  69  (see  FIG. 3 ) which limits forward movement of the indicator sleeve  20  and also acts as an impact surface to generate an audible/tactile signal. The collar fitting  66  also includes a thread  67  to allow the rear body assembly to be screwed to the front body assembly  10 . 
     The indicator sleeve  20  is cut away on its upper surface to leave a cutaway region at the forward end of which is a circumferential finger  70  resiliently attached by a live hinge  72  to the indicator sleeve  20 . The circumferential finger  70  cooperates with the latch tooth  38  on the axial finger  34  of the rear body assembly in a manner to be described below. Opposite the cutaway region and projecting inwardly from the inner wall of the indicator is a projection  74  which extends through the narrow slot  44  in the base of the rear body assembly  26  to project into the path of the rear of the plunger as it is moved rearwardly to cock the device. 
     Referring now more particularly to the sequence shown in  FIGS. 7( a ) to ( h ) and 8( a ) to ( h ) ,  FIG. 7( a )  shows the various components of the rear body assembly in the configuration prior to cocking. The indicator sleeve  20  and the plunger  45  are at their forwardmost positions with the indicator spring  50  and main drive springs  54  in relatively relaxed conditions. In order to cock the device, the front end of the front body assembly  10  (or any other suitable tool) is placed against the front end face  52  of the plunger to urge the plunger rearwardly. As the plunger moves rearwardly, the main drive spring  54  is compressed ( FIGS. 7( b ) and 8( b ) ). After a small amount of rearward movement, the rearward surface of the plunger contacts the projection  74  on the indicator sleeve  20  so that the two move rearwardly together ( FIGS. 7( c ) and 8( c ) ). At this point, the support surface  65  on the plunger  45  is underlying the axial finger  34  thereby preventing it from resilient inward movement. Further rearward movement of the plunger  45  carries the indicator sleeve  20  with it so that the circumferential finger  70  engages the shallow inclined forward facing ramp surface  40  on the latch tooth  38  so as to snap past it ( FIGS. 7( d ) and 8( d ) ). The force of the extended indicator spring  50 , the ramp angle of the steep rearward ramp face  42  and the flexibility of the live hinge  72  are selected such that the tension spring is not strong enough to pull the circumferential finger  70  back past the latch tooth  38  when the axial finger  34  is held against inward deflection. 
     In this position, the latch rib  58  on the plunger has snapped past the latch rib  60  on the trigger  16  thereby cocking the plunger and restraining it against movement, with the drive spring  54  compressed. 
     The rear assembly is now in a cocked position ready for firing and the device can be assembled by loading a syringe into the front body portion and screwing it onto the rear body portion. To fire the device, the trigger  16  is depressed, releasing the plunger  45  for forward movement ( FIGS. 7( e ) and 8( e ) ). The plunger  45  then moves forwardly to extend the syringe and, during all but the last part of the stroke of movement of the piston, the support surface  65  thereon underlies the axial finger  34  and prevents it from displacing inwardly and so the indicator sleeve  20  is held in its rearmost position (see  FIGS. 7( f ) and ( g ) ). But in the final part of the stroke the plunger  45  is in a position where the support surface  62  is forwardly of the axial finger, no longer supporting it, so that the circumferential finger  70  on the indicator sleeve may cam the axial finger  34  downwardly, releasing the indicator sleeve to shoot forwards to impact the collar fitting  66 , emitting an audible and tactile signal as the forward facing circumferential edge on the indicator element strikes a corresponding rearward surface on the collar fitting  66 , and also making the indicator visible behind window  18  of the cover  14 . 
     In this manner, audible, visual and tactile indications of end of dose are provided for the user without significantly diverting the energy of the main drive spring  54 . Also the indicator is reset automatically each time the device is locked.