Abstract:
In an injection device a rotary indicator element ( 20 ) indexes angularly between a pre-firing position to an injection complete position to create a visual and audible/tactile signal as the drive plunger ( 28 ) arrives at or near its fired position. The indicator element ( 20 ) has a saw tooth profile which co-operates with respective abutments ( 34, 40 ) on the plunger and a housing part of the device to control and energise indicator movement.

Description:
BACKGROUND OF THE INVENTION 
     1. Field 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. 
     2. 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 desirable that at least some of the energy required to generate the audible signal is stored in an energy store associated with an indicator element so that a fast impact energetic movement can be released, that is essentially independent of the actual speed of plunger movement. Moreover it is desirable to provide an indicator arrangement which resets automatically for each injection cycle. 
     BRIEF 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 moveable in said housing between cocked and fired positions under the influence of a plunger drive source; 
     an indicator element biased towards an injection complete indicating position by an indicator bias; 
     a hold-release arrangement responsive to arrival of said plunger at or near its fired position to release said indicator element for movement under the influence of said indicator bias to move to said injection complete indicating position to impact a stop to create said kinetic impact. 
     By this arrangement, the energy to create the kinetic impact may be stored in the indicator bias which means that, once the indicator element is released its movement is generally independent of the plunger, which allows considerable flexibility in the design of the extent of movement, and energy delivered by the indicator. 
     Preferably said indicator element also provides a visual indication. 
     Conveniently, as said plunger moves towards its fired position, it energises said indicator bias. There are numerous ways which the bias may be energised, but in one arrangement, said plunger and said indicator element may have co-operating surfaces which engage to move the indicator element with the plunger during a part of the plunger stroke, thereby to energise said indicator bias. The hold-release arrangement may include a hold surface that co-operates with a complimentary surface on said indicator element to prevent movement thereof to said injection complete indicating position during energisation of said indicator bias. In this way, the energy tapped from the drive source is spread over a significant portion of the stroke of movement of the plunger so as to reduce the effect on the plunger movement. This allows an energy charging cycle in which charging is done slowly over an extended portion of the stroke, and discharging is done very quickly in a snap action. 
     In this arrangement, as said plunger arrives near or at its fired position, the plunger may move the complimentary surface on the indicator element out of co-operation with said hold surface, thereby releasing the indicator element for movement. 
     Preferably the indicator element moves angularly to its injection complete indicating position, optionally with an amount of longitudinal movement. 
     Preferably the indicator bias biases the indicator element linearly in a rearward direction generally opposed to that of the plunger as it moves towards its fired position and co-operating surfaces of said plunger and said indicator element are operable to act in a cammed manner to convert relative linear movement therebetween into angular movement of said indicator element upon release. 
     Preferably, the co-operating surfaces comprise an ear on said plunger and a repeating profile on said indicator element, the repeating profile comprising a plurality of ramp surfaces alternating with rising edge surfaces arranged such that a rising edge surface is adapted to impact a side of said ear as said indicator element reaches its injection complete indicating position. 
     Preferably said hold surface is provided on an element that includes a cam face that co-operates with one of said ramp surfaces on said indicator element to rotate the indicator element to a pre-firing position under the influence of said indicator bias as said drive plunger is returned to a cocked position. 
     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, upon 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. 
     Whilst the invention has been described above it extends to any combination of the inventive features disclosed herein or in the following description or drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be performed in various ways and, by way of example only, an embodiment thereof will now be described, reference being made to the accompanying drawings in which: 
         FIG. 1  is a general perspective view of an autoinjection device in accordance with this invention; 
         FIG. 2  is an exploded view of the rear body assembly with the syringe removed; 
         FIGS. 3  ( a ) to ( h ) are perspective views of the rear body assembly showing the configuration of various components in sequence through a firing and cocking operation, and 
         FIGS. 4(   a ) to ( h ) are corresponding side views of the rear body assembly during these operations. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , 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 assembly, cocking a drive mechanism contained in the rear body assembly, inserting or replacing a syringe  22  housed in the front body assembly and connecting the front and rear body assemblies together ready for use. This is similar to a well known Autoject® II device and as described in WO2004/108194. As in the arrangement of WO2004/108194, the cover is biased rearwardly to a position in which it interlocks with a trigger  16  to prevent actuation thereof. The cover  14  also has two diametrically opposed windows  18  through which an indicator sleeve  20  is visible and which moves to change colour on satisfactory completion of an injection. 
     In order to operate the device, the user grasps the cover  14  and presses the front end of the front body assembly  10  against the injection site, thus shifting the cover forwardly to release the mechanical interlock. On firing the trigger, the drive mechanism inside the rear body housing moves a drive plunger forwardly which is in contact with the syringe plunger  25  and this initially advances the syringe  22  so that its needle  24  penetrates the injection site, and thereafter the plunger moves the syringe piston  23  to expel a dose. Upon nearing or reaching the forward end of its stroke, the plunger releases the indicator sleeve  20  which rotates to change colour under the window  18  and to create an internal impact which provides an audible and tactile signal. On removing the device from the injection site the reaction force is removed and so the cover  14  shifts rearwardly on the rear body to interlock with the trigger  16 . 
     Because of the accumulated tolerances on the syringe (typically of glass) it is known that there is a variation in the forwardmost position of the plunger and so the injection complete position is usually determined to be a short distance behind the final, forwardmost position of the plunger. 
     Referring now to  FIGS. 2-4 , the rear body assembly will be described in more detail. In  FIGS. 3 and 4 , the rear body assembly  12  is shown in side and perspective views respectively, with a portion of the cover  14  cut away to reveal the inner workings of the assembly. In this arrangement, the cover  14  is slideably mounted around the outside of an inner body housing  22  of generally cylindrical form. At its rear end, the trigger  16  is secured by means of an integral fitting  24  which clips over the rear end of the inner body housing and supports the trigger for resilient rocking release movement. At the forward end of the inner body housing  22  is secured an externally threaded collar fitting  26  which screws into a threaded bore in the rear end of the front body assembly  10 . Slideably disposed within the inner body housing  22  is a drive plunger  28  which is urged forwardly by a main drive spring  30  acting between the plunger and a rear inner wall of the rear body assembly. The plunger  28  has a forward end face  32  (visible in  FIGS. 3(   b ) to ( h )) which is designed to engage the plunger  25  of a syringe  22 . The drive plunger  28  has at its rear end a latch surface  31  which latches with a corresponding latch surface (not shown) on the forward underside end of the trigger  16  which holds the plunger in its rearward, cocked position against the force of the main spring  30 . The drive plunger  28  has a pair of transverse ears  34  that extend through opposed longitudinal slots  36  in the wall of the inner body housing  22 . Each ear  34  has an inclined cam surface  37  and a longitudinally extending impact surface  38 . Towards the front end of the slot and angularly spaced therefrom in a counter-clockwise direction when viewed from the front end, are two diametrically opposed body stops  40  each of which defines a longitudinally extending hold surface  42  and a cam surface  44 . 
     The plunger ears  34  and the body stops  40  each co-operate with a circumferentially extending, rearwardly facing saw tooth profile on the rear of the indicator sleeve  20  which is slideably and rotatably mounted on the front end of the inner body housing  22 . The saw tooth profile in this example is made up of four linear ramp surfaces  41  each subtending an angle of 90°, and four axial rising edges  43 , with valleys  45  and peaks  47  being defined where the ramps meet the rising edges  43 . The indicator sleeve  20  is biased rearwardly by a compression spring  46  that acts between a forward facing inner shoulder of the indicator  20  and the rearward facing edge of the collar fitting  26 . The compression spring  46  is much weaker than the main spring  30 . The indicator sleeve carries coloured patches  21  equispaced at 90° around the sleeve which provide a visual indication of when the injection is complete. 
     In operation, assuming the rear body assembly has been cocked, the components of the assembly will be as in the configuration shown in  FIGS. 3(   a ) and  4 ( a ). In this condition, the plunger  28  is latched in its cocked position with the main spring  30  fully compressed. The plunger ears  34  are at the rear of the slot  36 . The indicator sleeve  20  is at its rearmost position urged by the spring  46  so that diametrically opposed valleys  45  of the saw tooth profile are urged into contact with the forward ends of the body stops  40 , with the holding surfaces  42  of the body stops effectively urged into contact with the rising edges  43  of the saw tooth, by virtue of the cam surfaces  44  of the body stops  40  being in camming contact with the ramp surfaces  41  of the indicator sleeve  20 . In this condition, the plain, uncoloured, surfaces of the indicator sleeve  20  are visible through windows  18 . 
     Having prepared the device for injection and offered it up to an injection site and pressed the outer cover  14  to release the interlock with the trigger, the trigger  16  is pressed thereby releasing the drive plunger  28  so that it can shoot forward under the influence of the main drive spring  30 , initially extending the syringe  22  so that its needle  24  projects from the front end of the front body assembly and thereafter moving the syringe piston  23  to expel a dose. 
       FIGS. 3(   b ) and  4 ( b ) show the plunger having moved forward to the point where the cam surfaces  37  on the ears  34  of the plunger have just contacted respective ramp surfaces  41  on the indicator sleeve  20 , but before any forward movement has been transmitted to the indicator sleeve. From this point, further forward movement of the plunger  28  shifts the indicator sleeve  20  against the bias of the spring  46 , with the sleeve being constrained against rotation by the sliding contact between the holding surface  42  of the body stops and rising edges  43  of the indicator  20 . 
     Beyond this point, as shown in  FIGS. 3(   d ) and  4 ( d ), the ramp surfaces  41  on the indicator  20  ride over the cam surfaces  37  and  44  on the plunger ears and body stops  40  respectively as the indicator sleeve  20  is now free to quickly rotate and move rearwardly under the influence of the expanding indicator spring  46  and the camming action of the ramps surfaces  41  on the cam surfaces  37 , until the rising edges  43  on the indicator sleeve  20  impact the impact surfaces  38  on the ears  36 , to generate an audible and tactile signal. At this point, the coloured region  21  on the indicator sleeve is now visible in the window  18  to indicate that the drive plunger  28  is at or near its forwardmost position. As noted above, due to the need to provide manufacturing tolerances due to the accumulated longitudinal tolerances in the syringe, the plunger continues moving forwardly a short distance to the position shown in  FIGS. 3(   e ) and  4 ( e ) which shifts the indicator sleeve  20  forwardly off the body stops  40 . 
     Referring now to the cocking sequence shown in  FIGS. 3 and 4(   e ) to ( h ), from a fully fired position, in order to cock the device, pressure is applied to the exposed end face  32  of the plunger to compress the main spring  30  e.g. using the forward end of the front body assembly  10  or other suitable tool and, as the plunger moves back, the indicator spring  46  expands to move the indicator sleeve  20  rearwardly with it. 
     When the indicator sleeve  20  reaches the position shown in  FIGS. 3(   f ) and  4 ( f ) the ramp surfaces  41  thereon engage the cam surfaces  44  on the body stops  40 , but rotational movement of the indicator sleeve  20  is prevented because of the sliding contact between the impact surface  38  of the ears  34  of the plunger and the rising edges  43  of the indicator sleeve  20 . However, as shown in  FIGS. 3(   g ) and  4 ( g ), once the sliding contact is lost, the indicator sleeve  20  is free to rotate and consequently move rearwardly under the influence of the indicator compression spring  46  as the ramp surfaces  43  slide over the cam surfaces  44  of the body stops  40 . This continues to the position shown in  FIGS. 3(   h ) and  4 ( h ), with the rising edges  43  of the indicator sleeve  20  abutting the holding surfaces  42  on the body stops  40 . In this position the sleeve is located with an uncoloured portion visible through the window  18 . Continued rearward movement of the plunger latches it against the trigger in the cocked position shown in  FIGS. 3(   a ) and  4 ( a ). 
     It will be noted that, in the embodiment described below, with each firing and cocking cycle, the indicator sleeve indexes through 90° (45° to move from the cocked, pre-firing state into the injection complete state and 45° in the same direction to move from the injection complete into the cocked state).