Abstract:
The invention refers to an auto-injector for administering a medicament (M), comprising of a chassis, a syringe with a hollow needle and a stopper; a drive spring capable of, upon activation: advancing the needle ( 3 ), injecting the medicament (M), and retracting the syringe with the needle after delivering the medicament (M); and; activating means arranged to lock and release the drive spring, wherein the drive spring is a compression spring arranged to be grounded at a distal end in the chassis for advancing the needle and for injecting the dose of medicament (M) via a plunger and wherein the drive spring is arranged to have its ground in the chassis switched to its proximal end for retracting the syringe. A refraction sleeve is axially movable arranged around the syringe, wherein the retraction sleeve is fixable in a maximum proximal position for providing ground at the distal end of the drive spring, wherein the retraction sleeve is arranged to take the syringe with it when released and translated in distal direction (D), wherein the compression spring is wrapped over the retraction sleeve with its distal end bearing against a thrust face on the retraction sleeve and with its proximal end bearing against a thrust collar arranged to be coupled to the plunger for joint axial translation for advancing the needle and for injecting the dose of medicament (M) and to decouple from the plunger for retraction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. National Phase Application pursuant to 35 U.S.C. §371 of International Application No. PCT/EP2011/067502 filed Oct. 6, 2011, which claims priority to European Patent Application No. 10187008.7 filed Oct. 8, 2010 and U.S. Provisional Patent Application No. 61/432,257 filed Jan. 13, 2011. The entire disclosure contents of these applications are herewith incorporated by reference into the present application. 
    
    
     TECHNICAL FIELD 
     The invention relates to an auto-injector for administering a dose of a liquid medicament according to the preamble of claim  1 . 
     BACKGROUND 
     Administering an injection is a process which presents a number of risks and challenges for users and healthcare professionals, both mental and physical. 
     Injection devices (i.e. devices capable of delivering medicaments from a medication container) typically fall into two categories—manual devices and auto-injectors. 
     In a manual device—the user must provide the mechanical energy to drive the fluid through the needle. This is typically done by some form of button/plunger that has to be continuously pressed by the user during the injection. There are numerous disadvantages to the user from this approach. If the user stops pressing the button/plunger then the injection will also stop. This means that the user can deliver an underdose if the device is not used properly (i.e. the plunger is not fully pressed to its end position). Injection forces may be too high for the user, in particular if the patient is elderly or has dexterity problems. 
     The extension of the button/plunger may be too great. Thus it can be inconvenient for the user to reach a fully extended button. The combination of injection force and button extension can cause trembling/shaking of the hand which in turn increases discomfort as the inserted needle moves. 
     Auto-injector devices aim to make self-administration of injected therapies easier for patients. Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and newer GLP-1 class drugs), migraine, hormone therapies, anticoagulants etc. 
     Auto-injectors are devices which completely or partially replace activities involved in parenteral drug delivery from standard syringes. These activities may include removal of a protective syringe cap, insertion of a needle into a patient&#39;s skin, injection of the medicament, removal of the needle, shielding of the needle and preventing reuse of the device. This overcomes many of the disadvantages of manual devices. Injection forces/button extension, hand-shaking and the likelihood of delivering an incomplete dose are reduced. Triggering may be performed by numerous means, for example a trigger button or the action of the needle reaching its injection depth. In some devices the energy to deliver the fluid is provided by a spring. 
     U.S. 2002/0095120 A1 discloses an automatic injection device which automatically injects a pre-measured quantity of fluid medicine when a tension spring is released. The tension spring moves an ampoule and the injection needle from a storage position to a deployed position when it is released. The content of the ampoule is thereafter expelled by the tension spring forcing a piston forward inside the ampoule. After the fluid medicine has been injected, torsion stored in the tension spring is released and the injection needle is automatically retracted back to its original storage position. 
     The European patent application EP 10153999.7 discloses an auto-injector for administering a dose of a liquid medicament, comprising:
         an elongate housing arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, the housing having a distal end and a proximal end with an orifice intended to be applied against an injection site, wherein the syringe is slidably arranged with respect to the housing,   spring means capable of, upon activation:   pushing the needle from a covered position inside the housing into an advanced position through the orifice and past the proximal end,   operating the syringe to supply the dose of medicament, and   retracting the syringe with the needle into the covered position after delivering the medicament,   activating means arranged to lock the spring means in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring means for injection.       

     The spring means is a single compression spring arranged to be grounded at a distal end in the housing for advancing the needle and for injecting the dose of medicament via a plunger and wherein the compression spring is arranged to have its ground in the housing switched to its proximal end for retracting the syringe. 
     SUMMARY 
     It is an object of the present invention to provide an improved auto-injector. 
     The object is achieved by an auto-injector according to claim  1 . 
     Preferred embodiments of the invention are given in the dependent claims. 
     In the context of this specification the term proximal refers to the direction pointing towards the patient during an injection while the term distal refers to the opposite direction pointing away from the patient. 
     According to the invention an auto-injector for administering a dose of a liquid medicament has a distal end and a proximal end with an orifice intended to be applied against an injection site. The auto-injector comprises:
         a chassis arranged to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament, wherein the syringe is slidably arranged with respect to the chassis,   a drive spring capable of, upon activation:
           pushing the needle from a covered position inside the chassis into an advanced position through the orifice and past the proximal end,   operating the syringe to supply the dose of medicament, and   retracting the syringe with the needle into the covered position after delivering the medicament,   activating means arranged to lock the drive spring in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the drive spring for injection.   
               

     The drive spring is a compression spring arranged to be grounded at a distal end in the chassis for advancing the needle and for injecting the dose of medicament via a plunger. The drive spring is arranged to have its ground in the chassis switched to its proximal end for retracting the syringe. 
     The single compression spring is used for inserting the needle, fully emptying the syringe and retracting the syringe and needle to a safe position after injection. Thus a second spring for withdrawing the syringe and needle, which is a motion with an opposite sense compared to advancing the syringe and injecting the dose, is not required. While the distal end of the compression spring is grounded the proximal end moves the syringe forward for inserting the needle and carries on to the injection by pushing on the stopper. When the injection is at least nearly finished the compression spring bottoms out at its proximal end, resulting in the proximal end being grounded in the chassis. The distal end of the compression spring may now be released from its ground in the chassis. The compression spring is now pulling the syringe in the opposite direction. 
     According to the invention a retraction sleeve is axially movable arranged around the syringe. The retraction sleeve is fixable to the chassis in a maximum proximal position for providing ground at the distal end of the drive spring. The retraction sleeve is arranged to take the syringe with it when released and translated in distal direction. The compression spring is wrapped over the retraction sleeve with its distal end, bearing against a thrust face on the retraction sleeve and with its proximal end bearing against a thrust collar arranged to be coupled to the plunger for joint axial translation for advancing the needle and for injecting the dose of medicament. The thrust collar is arranged to be decoupled from the plunger for refraction. 
     Due to the drive spring wrapped over the plunger and the retraction sleeve its length is not added to the overall length of the auto-injector. Consequently, the auto-injector according to the invention can be made shorter. 
     The auto-injector according to the invention has a particularly low part count compared to most conventional auto-injectors. The use of just one compression spring reduces the amount of metal needed and thus consequently reduces weight and manufacturing costs. 
     In one embodiment of the invention the activating means is arranged as a trigger button in the shape of a wrap-over sleeve button arranged over the distal end of the auto-injector. The trigger button extends at least almost over the whole length of the auto-injector. The trigger button is arranged to release the drive spring upon translation in proximal direction. The trigger button is arranged to release the drive spring upon translation in proximal direction. In order to trigger an injection the auto-injector has to be pressed against an injection site, e.g. a patient&#39;s skin. A user, e.g. the patient or a caregiver, grabs the wrap-over sleeve button with their whole hand and pushes against the injection site. Consequently, the trigger button translates in proximal direction and releases the drive spring for starting the injection cycle. This embodiment is particularly well suited for people with dexterity problems since triggering does not require operation of small buttons by single fingers. Instead, the whole hand is used. 
     An interlock sleeve may be telescoped with the proximal end of the chassis and with the trigger button. The interlock sleeve is translatable in longitudinal direction between a proximal position relative to the trigger button and a distal position relative to the chassis and biased towards the proximal position, e. g. by an interlock spring. The interlock sleeve is arranged to release the retraction sleeve when in the proximal position and with the trigger button translated in proximal direction, i.e. when the injection has been triggered by actuating the trigger button followed by removal of the auto-injector from the injection site and consequent translation of the interlock sleeve into a final proximal position. The interlock sleeve is arranged to block the translation of the retraction sleeve otherwise, so the syringe is only retracted if an injection cycle has been started before and if the user removes the auto-injector from the injection site. As the proximal position of the interlock sleeve is limited by the trigger button or a component attached to the trigger button the final proximal position of the interlock sleeve after actuation of the trigger button is further advanced with respect to the chassis as an initial proximal position before actuation of the trigger button. 
     In order to hold or release the retraction sleeve the interlock sleeve may comprise at least one leg arranged distally. At least one third resilient clip is arranged on the proximal end of the retraction sleeve, wherein a respective protrusion for each third resilient clip is arranged on the chassis. The third resilient clip and/or the protrusion exhibit a ramp for flexing the third resilient clip away from the protrusion for disengaging them under load of the drive spring thus releasing the retraction sleeve. The leg is arranged to allow this disengagement only when the interlock sleeve is in the final proximal position with the trigger button translated in proximal direction. Otherwise the leg is arranged to support the third resilient clip in a manner to prevent it from flexing away from the protrusion thus keeping them engaged and blocking the retraction sleeve in a manner to prevent it from translating. 
     The retraction sleeve may exhibit at least one moving shutter and the chassis may comprises a fixed shutter, the shutters forming a shuttering mechanism for controlling translation of the plunger. The moving shutter and the fixed shutter respectively comprise a number of regularly spaced castellation. The castellations of the moving shutter are out of phase with the castellations of the fixed shutter when the retraction sleeve is fixed in the maximum proximal position thus creating a surface of alternating castellations of both shutters for a respective first clip to travel along. The first clip is connected to the plunger and arranged to keep the thrust collar coupled to the plunger when being held on the level of that surface. On translation of the retraction sleeve in distal direction the moving shutter gets in phase with the fixed shutter in a manner to regularly interrupting the surface by gaps between consecutive castellation allowing the first clip to be flexed inwards into the gaps or proximally behind the most proximal castellations. The first clip is flexed inwards by at least one ramp on the first clip and/or on the thrust collar under load of the drive spring. By the first clip flexing inwards the thrust collar is decoupled from the plunger. Consequently the plunger is no longer pushed in proximal direction and does not prevent retraction of the syringe and needle, so they can be retracted along with the plunger. 
     A decoupling sleeve may be arranged around the retraction sleeve inside the drive spring. The decoupling sleeve is attached to the plunger at a distal end. The decoupling sleeve may therefore be considered part of the plunger. However, having two different parts is preferred for assembly purposes. Prior to manual operation of the activating means the thrust collar is coupled through the first clip and the decoupling sleeve to the retraction sleeve. The activating means is arranged to prevent decoupling of the decoupling sleeve from the retraction sleeve prior to actuation and to allow decoupling on actuation. Since the retraction sleeve is coupled to the chassis in this situation the injection cannot start before actuation of the activating means. 
     For interacting with the activating means, e.g. the trigger button, the decoupling sleeve may exhibit a resilient arm protruding in distal direction, the resilient arm having a wedge arranged to be held between a ramp on the retraction sleeve and a bar protruding in proximal direction from a distal end face of the trigger button prior to actuation of the trigger button. Upon actuation of the trigger button the bar is translated so as to allow the wedge to be flexed into a recess in the bar by the ramp on the retraction sleeve under load of the drive spring. 
     The trigger button does not have to be pushed against the force of the drive spring thus allowing for a drive spring with a high spring force suitably for thin needles and highly viscous medicaments without the user having to exert too high an activation force. 
     Usually the hollow needle is equipped with a protective needle shield for keeping the needle sterile and preventing it from being mechanically damaged. The protective needle shield is attached to the needle when the auto-injector or the syringe is assembled. 
     Preferably a cap is provided at the proximal end of the auto-injector. A sheet metal clip is attached to the cap for joint axial movement and independent rotation. The sheet metal clip is arranged to extend through an orifice into the chassis when the cap is attached to the auto-injector. The sheet metal clip may comprise at least two barbs snapped into a circumferential notch or behind a shoulder of the protective needle shield. This allows for automatically engaging the sheet metal clip with the protective needle shield during assembly. When the cap is removed from the auto-injector in preparation of an injection the protective needle shield is reliably removed without exposing the user to too high a risk to injure themselves. 
     The cap may be attachable to the auto-injector by a screw connection. This allows for a low force removal of the protective needle shield. 
     Since the orifice has to be wide enough for the protective needle shield and the parts of the cap for removing it, the needle may become accessible for users with small fingers after removal of the protective needle shield. 
     In order to address this problem a spring wire may be attached at the orifice on the chassis. The spring wire has an arcuate transversal section biased inwardly so as to essentially obstruct the orifice for finger access when released by roughly bisecting the orifice. The spring wire is arranged to stay far enough off-centre in this situation to allow the needle to advance through the orifice without touching the spring wire. The spring wire allows the needle to be as near as possible to the proximal end prior to actuation thus reducing travel of the syringe and the overall length of the auto-injector but still preventing needle stick injuries. 
     A notch may be arranged in a proximal face of the chassis near the orifice for catching the arcuate transversal section when it is released and allowed to flex inwards. This prevents the spring wire from being easily pushed aside by the user and hence increases needle safety. Furthermore, the cap is kept from being reattached to the auto-injector after removal thus preventing damage and blunting to the needle before injection. 
     The cap may comprise an inner cylinder arranged to extend into the orifice for removing the protective needle shield. The inner cylinder may be arranged for keeping the arcuate transversal section from flexing inwards when the cap is attached to the auto-injector. 
     The interlock sleeve may be telescoped in the sleeve trigger button or in a head part attached to the proximal end of the sleeve trigger button. A force required to translate the interlock sleeve in distal direction is preferably lower than a force required to translate the trigger button in proximal direction thus providing a two stage operation with a step in the force felt by the user when pushing the auto-injector against the injection site. 
     A decoupling carrier may be slidably arranged in the retraction sleeve and coupled to the syringe for joint axial translation. The decoupling carrier comprises at least one second resilient clip engageable in a detent in or behind a shoulder on the plunger in a manner to lock the decoupling carrier to the plunger for joint axial translation. The retraction sleeve is arranged for outwardly supporting the second resilient clip prior to the syringe reaching an injection depth during needle insertion. A respective aperture for each second resilient clip is arranged in the retraction sleeve allowing the second resilient clip to be flexed outwards and disengage from the detent upon the syringe reaching the injection depth thus coupling the plunger to the stopper. Consequently, a so called wet injection is avoided, i.e. the liquid medicament is not leaking out of the hollow needle before the needle is inserted. 
     The sleeve trigger button may have at least one viewing window for inspecting the syringe. 
     The auto-injector may preferably be used for subcutaneous or intra-muscular injection, particularly for delivering one of an analgetic, an anticoagulant, insulin, an insulin derivate, heparin, Lovenox, a vaccine, a growth hormone, a peptide hormone, a proteine, antibodies and complex carbohydrates. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION 
       The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
         FIGS. 1A and 1B  are longitudinal sections of an auto-injector in an as delivered, initial state with a cap, 
         FIG. 2  is an isometric sectional view of the auto-injector, 
         FIG. 3  is another isometric sectional view of the auto-injector, 
         FIG. 4  is an isometric view of a proximal end of the auto-injector during removal of a cap, 
         FIG. 5  is an isometric view of the cap with a protective needle shield and a syringe, 
         FIG. 6  is an isometric view of the proximal end of the auto-injector before removal of the cap, 
         FIG. 7  is an isometric view of the proximal end of the auto-injector after removal of the cap with an activated finger guard, 
         FIG. 8  is an isometric view of a chassis of the auto-injector with the activated finger guard, 
         FIG. 9  is a detail view of a first alternative embodiment of a shuttering mechanism in an auto-injector, 
         FIG. 10  is a schematic view of the shuttering mechanism of  FIG. 9  with a moving shutter arm with ramped moving protrusions, 
         FIG. 11  is a schematic view of a second alternative embodiment of the shuttering mechanism, 
         FIG. 12  is a schematic view of a third alternative embodiment of the shuttering mechanism, 
         FIG. 13  is a schematic view of a fourth alternative embodiment of the shuttering mechanism, 
         FIG. 14  is a schematic view of a fifth alternative embodiment of the shuttering mechanism, 
         FIG. 15  is a schematic view of a sixth alternative embodiment of the shuttering mechanism, 
         FIG. 16   a  is a schematic view of a seventh alternative embodiment of the shuttering mechanism prior to actuation, 
         FIG. 16   b  is a schematic view of the seventh alternative embodiment of the shuttering mechanism during translation, 
         FIG. 17  is a schematic view of an eighth alternative embodiment of the shuttering mechanism, 
         FIG. 18  is a schematic view of a ninth alternative embodiment of the shuttering mechanism, 
         FIG. 19  is a schematic view of a tenth alternative embodiment of the shuttering mechanism, 
         FIGS. 20A ,  20 B,  20 C and  20 D are schematic views of an eleventh alternative embodiment of the shuttering mechanism, 
         FIGS. 21A and 21B  are schematic views of a twelfth alternative embodiment of the shuttering mechanism, and 
         FIGS. 22A and 22B  are schematic views of thirteenth alternative embodiment of the shuttering mechanism. 
     
    
    
     Corresponding parts are marked with the same reference symbols in all figures. 
     DETAILED DESCRIPTION 
       FIGS. 1A and 1B  show two longitudinal sections in different section planes of an auto-injector  1 , the different section planes approximately 90° rotated to each other. The auto-injector  1  comprises a chassis  2 . A syringe  3 , e.g. a Hypak syringe, with a hollow needle  4  is arranged in a proximal part of the auto-injector  1 . When the auto-injector  1  or the syringe  3  is assembled a protective needle shield  36  is attached to the needle  4 . A stopper  6  is arranged for sealing the syringe  3  distally and for displacing a liquid medicament M through the hollow needle  4 . The syringe  3  is held in a tubular syringe carrier  7  and supported at its proximal end therein. The syringe carrier  7  is slidably arranged in the chassis  2 . A single drive spring  8  in the shape of a compression spring is arranged in a distal part of the auto-injector  1 . 
     The drive spring  8  is loaded between a retraction sleeve  10  and a thrust collar  37 . A plunger  9  for forwarding the spring force of the drive spring  8  to the syringe  3  and/or the stopper  6  is mechanically linked to a decoupling sleeve  38  at a distal end of the plunger  9 . The plunger  9  and the decoupling sleeve  38  are slidable in longitudinal direction. The drive spring  8  is wrapped over the decoupling sleeve  38 . The thrust collar  37  is coupled with the decoupling sleeve  38  for joint axial translation by a pair of first clips  39  arranged proximally at the decoupling sleeve  38 . Inside the thrust collar  37  and the decoupling sleeve  38  the retraction sleeve  10  is slidably arranged. The retraction sleeve  10  comprises a thrust face  13  extending through apertures in the decoupling sleeve  38  so as to bear against the distal end of the drive spring  8 . Inside the refraction sleeve  10  a decoupling carrier  41  is slidably arranged. The decoupling carrier  41  is coupled to the syringe carrier  7  for joint axial translation. The decoupling carrier  41  comprises two resilient second clips  42  engageable in a detent  43  in the plunger  9  in a manner to lock the decoupling carrier  41  to the plunger  9  for joint axial translation. At least in an initial state prior to actuation the second resilient clips  42  are engaged in the detent  43  and outwardly supported by the retraction sleeve  10  and thus prevented from flexing outwards and disengaging from the detent  43 . 
     A trigger button  20  is arranged in the shape of a wrap-over sleeve button over the distal end D of the auto-injector  1  extending almost over the whole length of the auto-injector  1 . A head part  50  is attached at the proximal end P of the trigger button  20 . The trigger button  20  and the head part  50  are slidable in longitudinal direction with respect to the chassis  2 . 
     A skin interlock sleeve  25  is arranged at the proximal end P and telescoped with the chassis  2 . The interlock sleeve  25  is telescoped in the head part  50  of the wrap-over trigger button  20 . An interlock spring  26  for biasing the interlock sleeve  25  in proximal direction P against the chassis  2  is arranged inside the head part  50 . The head part  50  provides a first abutment  5  limiting translation of the interlock sleeve  25  in proximal direction P. 
       FIG. 2  is an isometric sectional view of the auto-injector  1  without the cap  44  and the head part  50  for better recognisability of interior parts. 
     The skin interlock sleeve  25  comprises two legs  51  arranged distally (see  FIG. 2 , only one leg shown, the other one is on the opposite side). In the initial state the legs  51  are arranged between two third resilient clips  52  on the proximal end of the retraction sleeve  10  thus keeping them from flexing inwards. Outwardly, the third clips  52  are held behind protrusions  53  (one of them illustrated, the other one masked in  FIG. 2 ) in the chassis  2  in a manner to prevent translation of the retraction sleeve  10  in distal direction D. Thus, the distal end of the compression spring  8  is grounded in the chassis  2 . The retraction sleeve  10  exhibits a number of moving shutters  61  and the chassis  2  comprises a fixed shutter  62 . The moving shutter  61  and the fixed shutter  62  respectively comprise a number of regularly spaced castellations. In the initial state the castellations of the moving shutters  61  are out of phase with the castellations of the fixed shutter  62  (cf.  FIGS. 1 and 2 ) thus creating a surface of alternating castellations of both shutters  61 ,  62  for the first clip  39  to travel along without allowing the first clip  39  to flex inwards. If the retraction sleeve  10  is translated so as to bring the moving shutter  61  in phase with the fixed shutter  62  (not illustrated) the surface is regularly interrupted by gaps allowing the first clip  39  to flex inwards by ramps on the first clip  39  interacting with ramps on the thrust collar  37  under load of the drive spring  8  thus decoupling the thrust collar  37  from the decoupling sleeve  38 . 
     Initially the drive spring  8  is grounded to the thrust face  13  of the retraction sleeve  10  and bears against the thrust collar  37 . The retraction sleeve  10  is prevented from translating in distal direction D because of the engagement of the third clips  52  to the chassis  2  and the legs  51 . The thrust collar  37  is kept from translating in proximal direction P by engagement to the retraction sleeve  10  through the first clips  39  and the decoupling sleeve  38 . The decoupling sleeve  38  exhibits a resilient arm  54  protruding in distal direction D with a wedge  55  held between a ramp  56  on the retraction sleeve  10  and a bar  57  protruding in proximal direction P from a distal end face  58  of the trigger button  20  (see  FIG. 2 ). In the initial position under load of the drive spring  8  the ramp  56  tries to flex the wedge  55  aside but is kept from doing so by the bar  57  supporting the wedge  55  from opposite the ramp  56 . 
     A cap  44  is arrangeable at the proximal end of the auto-injector  1 . The cap  44  comprises an inner cylinder  45  arranged to extend into an orifice  46  (see  FIGS. 6 ,  7 ,  8 ) in the proximal end of the chassis  2 . The orifice  46  needs to be considerably wider than the needle  4  because of the space required for the protective needle shield  36  and the inner cylinder  45 . In an initial state prior to use the inner cylinder  45  grips the protective needle shield  36  which is arranged on the needle  4 . 
     In order to prepare for an injection the cap  44  has to be removed.  FIG. 5  is an isometric view of the cap  44  with the protective needle shield  36  and the syringe  3 . On removal of the cap  44  the protective needle shield  36  is removed, too. The force required to pull the protective needle shield  36  off the syringe  3  is relatively high. In order to avoid the syringe  3  being pulled in proximal direction P during removal of the protective needle shield  36  the syringe  3  has to be held firmly in position. This is achieved by the syringe  3  being supported at its proximal end in the syringe carrier  7 , the syringe carrier  7  being coupled to the decoupling carrier  41 , the decoupling carrier  41  being engaged to the plunger  9 , the plunger  9  attached to the decoupling sleeve  38 , the decoupling sleeve  38  prevented from advancing by the wedge  55  held between the ramp  56  on the retraction sleeve  10  and the bar  57  and by the retraction sleeve  10 . 
     After removal of the protective needle shield  36  the needle  4  is no longer protected but still a small distance back in the orifice  46 . However, the orifice  46  would be wide enough to allow a user, at least a child to touch it with their fingers. In order to prevent finger access a spring wire  48  is arranged at the orifice  46 . The spring wire  48  is attached to the chassis  2  and comprises an arcuate transversal section  48 . 1  biased in a manner to flex inwards so as to essentially obstruct the orifice  46  for finger access even for very small fingers while staying just enough off-centre to allow the needle  4  to advance without touching the spring wire  48  (cf.  FIGS. 7 and 8 ). A notch  49  is arranged in a proximal face of the chassis  2  near the orifice  46  in a manner to lock the transversal section  48 . 1  in that position so it cannot easily be pushed aside by a user&#39;s finger. As long as the cap  44  is attached to the proximal end P the inner cylinder  45  keeps the arcuate transversal section  48 . 1  from flexing inwards (cf.  FIGS. 4 and 6 ).  FIG. 6  shows the situation when the cap  44  is in place without showing the cap  44  itself.  FIG. 4  shows the proximal end of the auto-injector  1  without the interlock sleeve  25  during removal of the cap  44 . 
     The spring wire  48  allows the needle  4  to be as near as possible to the proximal end P prior to actuation thus reducing travel of the syringe  3  and the overall length of the auto-injector  1  but still preventing needle stick injuries. 
     In the illustrated embodiment the cap  44  is held on the proximal end P by two fourth resilient clips  47 . It could likewise be attached to the auto-injector  1  by a screw connection. 
     After removal of the cap  44  and the protective needle shield  36  the proximal end P of the auto-injector  1  is pressed against an injection site, e.g. a patient&#39;s skin. Thereby the skin interlock sleeve  25  is translated from a proximal position into a distal position against the bias of the interlock spring  26 . When the pressure against the injection site is maintained or increased the sleeve trigger button  20  starts translating in proximal direction P. Typically, the auto-injector  1  is arranged to require a higher force for the trigger button  20  to translate than for the interlock sleeve  25  thus providing a two stage operation with a step in the force felt by the user when pushing the auto-injector  1  against the skin. As the trigger button  20  translates with respect to the chassis  2  the bar  57  is also translated until the wedge  55  can flex into a recess  59  in the bar  57  thus releasing the resilient arm  54 , the decoupling sleeve  38 , the thrust collar  37  and the plunger  9  in a manner to allow the drive spring  8  to translate them in proximal direction P. 
     The drive spring  8  now pushes the thrust collar  37  in proximal direction P taking with it the decoupling sleeve  38 , the plunger  9 , the decoupling carrier  41 , the syringe carrier  9  and the syringe  3  with the needle  4  while no load is exerted onto the stopper  6 . The hollow needle  4  appears from the proximal end P and is inserted into the injection site, e.g. the patient&#39;s skin. 
     The forward movement continues until the syringe carrier  9  bottoms out at a second abutment  32  in the chassis  2 . The travel from the initial position up to this point defines an injection depth, i.e. needle insertion depth. 
     At the same time the decoupling carrier  41 , moving relative to the retraction sleeve  10 , reaches an aperture  60  in the retraction sleeve  10 . The second resilient clips  42  of the decoupling carrier  41  are no longer outwardly supported by the retraction sleeve  10 . As the drive spring  8  keeps pushing the plunger  9  the second resilient clips  42  are pushed out of the detent  43  by ramps or rounded edges at the distal sides of the detent  43  and the second clips  42 . The plunger  9 , no longer coupled to the decoupling carrier  41  and the syringe  3 , keeps advancing and starts pushing against the stopper  6  for expelling the medicament M from the syringe  3  and injecting it into or through the patient&#39;s skin. 
     As the thrust collar  37 , the decoupling sleeve  38  and the first clips  39  travel in proximal direction P the first clip  39  slides along the surface created by the out of phase castellations of the moving shutters  61  and fixed shutter  62 . 
     When the auto-injector  1  is taken away from the injection site during the injection or at the end of injection the interlock sleeve  25  translates in proximal direction P under load of the interlock spring  26 . Since the trigger button  20  and the head part  50  have translated in proximal direction P when the auto-injector  1  was triggered, the first abutment  5  in the head part  50  limiting travel of the interlock sleeve  25  is further in proximal direction P than in the initial state. Hence, the interlock sleeve  25  translates in proximal direction P beyond its initial proximal position into a final proximal position in which the leg  51  is removed from between the two resilient third clips  52  on the proximal end of the refraction sleeve  10  thus allowing them to flex inwards due to their ramped engagement to the protrusions  53  in the chassis  2  and due to the drive spring  8  pushing against the thrust face  13  of the retraction sleeve  10 . The retraction sleeve  10  is now decoupled from the chassis  2  so the drive spring  8  is no longer grounded at its distal end. The refraction sleeve  10  translates in distal direction D until a first shoulder  63  in the retraction sleeve  10  hits a second shoulder  64  on the syringe carrier  7  under load of the drive spring  8  thus bringing the moving shutters  61  in phase with the fixed shutter  62  and creating a number of consecutive gaps between the aligned castellations. 
     If the retraction sleeve  25  is released mid injection the injection continues until the first clip  39  meets the next gap between the aligned castellations in proximal direction P. The first clip  39  is flexed inwards into the gap due to its ramped engagement to the thrust collar  37 . Consequently, the thrust collar  37  and the decoupling sleeve  38  decouple and the plunger  9  stops advancing. The thrust collar  37 , still under the force of the drive spring  8  continues travelling until it hits a stop on the chassis (not illustrated) giving the drive spring  8  a new ground at its proximal end. The retraction sleeve  10 , still under the opposite force of the drive spring  8  and pushing with its first shoulder  63  against the second shoulder  64  of the syringe carrier  7  can now drag the whole assembly of syringe carrier  7 , syringe  3 , plunger  9  and decoupling sleeve  38  into the auto-injector  1  in distal direction D. The needle  4  is now a safe distance back in the auto-injector  1  thus preventing post injection needle stick injuries. 
     If the retraction sleeve  25  is released at the end of injection the first clip  39  has already travelled until the most proximal castellation of the moving shutter  61  which is now removed thus allowing the first clip  39  to flex inwards proximally from the aligned shutters  61 ,  62 . The thrust collar  37  and the decoupling sleeve  38  decouple. The thrust collar  37 , still under the force of the drive spring  8  continues travelling a short distance until it hits a stop on the chassis (not illustrated) giving the drive spring  8  a new ground at its proximal end and allowing the first clip  39  to dive through under the thrust collar  37  so the first clip  39  is not prevented from translating in distal direction D by the castellations. The refraction sleeve  10  under the opposite force of the drive spring  8  can now drag the whole assembly of syringe carrier  7 , syringe  3 , needle  4 , plunger  9  and decoupling sleeve  38  into the auto-injector  1  in distal direction D. The needle  4  is now a safe distance back in the auto-injector  1  thus preventing post injection needle stick injuries. 
     The spring wire  48  serving as a finger guard may be applied with any auto-injector or other injection device. 
     The fixed shutter  62  and the moving shutter  61  form one embodiment of a shuttering mechanism for controlling translation of the plunger  9  relative to the chassis  2 . 
       FIGS. 9 to 22B  illustrate alternative embodiments of shuttering mechanisms. 
       FIG. 9  shows a shuttering mechanism  101  for controlling translation of a longitudinally moveable component  102 . The shuttering mechanism  101  comprises at least one fixed shutter  103  having a set of fixed protrusions  103 . 1  to  103 . 6  in the shape of castellations  103 . 1  to  103 . 6 , the fixed shutter  103  preferably being part of a housing  104  or chassis. The shuttering mechanism  101  furthermore comprises at least one resilient arm  105  associated with the longitudinally moveable component  102 . At a proximal tip of the resilient arm  105  a dog  106  is resiliently biased towards the castellations  103 . 1  to  103 . 6  so as to engage between or behind the castellations  103 . 1  to  103 . 6  and block the translation of the longitudinally moveable component  102 . A respective moving shutter arm  107  is arranged alongside the fixed shutter  103 , the moving shutter arm  107  having a number of consecutive ramped moving protrusions  107 . 1  to  107 . 6  spaced from each other, their ramps facing in distal direction D. The castellations  103 . 1  to  103 . 6  and the ramped protrusions  107 . 1  to  107 . 6  have the same pitch and form a profiled surface. The moving shutter arm  107  is moveable in longitudinal direction with respect to the fixed shutter  103 . The moving shutter arm  107  has at least one locking position with its ramped protrusions  107 . 1  to  107 . 6  essentially in phase with the castellations  103 . 1  to  103 . 6  thus allowing the dog  106  of the resilient arm  105  to catch between or behind the castellations  103 . 1  to  103 . 6 . The moving shutter arm  107  has at least one unlocking position with its ramped protrusions  107 . 1  to  107 . 6  out of phase with the castellations  103 . 1  to  103 . 6  in such a manner that the ramped protrusions  107 . 1  to  107 . 6  prevent the dog  106  from engaging with the castellations  103 . 1  to  103 . 6  or disengage them thus allowing translation of the longitudinally moveable component  102 . 
     The longitudinally moveable component  102  is preferably a plunger  102  for transmitting a driving force of a drive means, e.g. a spring to a syringe  108  or to a stopper  109  for sealing the syringe  108  and displacing a liquid medicament from the syringe  108 . The syringe  108 , the shuttering mechanism  101 , the plunger  102  and the drive means may be part of an auto-injector for delivering the medicament. 
       FIG. 9  shows the shuttering mechanism  101  during an injection. 
     Prior to use the plunger  102  resolves the driving force acting in proximal direction P into the fixed shutter  103 . The moving shutter arm  107  is in phase with the fixed shutter  103  and hence carries no load. The plunger  102  cannot be pushed in proximal direction P because of the dog  106  caught behind the most distal castellation  103 . 1 . 
     To allow translation of the plunger  102  in proximal direction P, the moving shutter arm  107  must be translated in distal direction D relative to the fixed shutter  103 , such that they are out of phase. The ramp of the most distal moving protrusion  107 . 1  of the moving shutter arm  107  cams the dog  106  out of engagement with the fixed shutter  103 , to the same level as the top of the first castellation  103 . 1 . At this point the plunger  102  is free to move in proximal direction P under the driving force. If the relative position of the shutters  103 ,  107  is held constant, the dog  106  will continue to ride up the surface formed by the out of phase fixed shutter  103  and moving shutter arm  107  in proximal direction P as shown in  FIG. 9 . 
     In the embodiment shown in  FIGS. 9 and 10  the dog  106  running along the surface will produce a sound each time it snaps off the top of the fixed shutter  103  castellation  103 . 1  to  103 . 6  and will alternately apply a force to the moving shutter arm  107  as it rides up the ramps of the moving protrusions  107 . 1  to  107 . 6 . This will provide both audible and tactile feedback that the injection is taking place. Once these stop, the injection is complete. 
     If the moving shutter arm  107  is translated back in phase with the fixed shutter  103  during the injection (either by moving it further in distal direction D, or moving it towards the position it was prior to firing), the dog  106  will catch on the next fixed shutter  103  castellation  103 . 1  to  103 . 6  and stop the injection. The injection can then be restarted by translating the moving shutter arm  107  in phase with the fixed shutter  103  again. Alternatively the moving shutter arm  107  may be latched or disconnected from the user&#39;s control, preventing any further dose from being delivered. 
       FIG. 11  shows an alternative embodiment of the shuttering mechanism  101 . The moving shutter arm  107  has only one ramped moving protrusion  107 . 1  while the other moving protrusions  107 . 2  to  107 . 6  are castellations. If the moving shutter arm  107  is translated in phase with the fixed shutter  103  during translation of the plunger  102 , the dog  106  will flex into the next space between the castellations  103 . 1  to  103 . 5 ,  107 . 1  to  107 . 6  and remain there since it cannot be ramped out by the moving shutter arm  107 , again. Hence, the injection, once stopped cannot be restarted. The embodiment of  FIG. 11  does not produce an audible or tactile feedback during the translation of the plunger  102 , e.g. during injection. 
       FIG. 12  shows another embodiment of the shuttering mechanism  101  wherein only one fixed castellation  103 . 1  is provided on the fixed shutter  103  and only one ramped moving protrusion  107 . 1  on the moving shutter arm  107 . To allow translation of the plunger  102  in proximal direction P, the moving shutter arm  107  must be translated in distal direction D relative to the fixed shutter  103 , such that they are out of phase as in  FIG. 12 . The ramp of the moving protrusion  107 . 1  cams the dog  106  out of engagement with the fixed shutter  103 , to the same level as the top of the fixed castellation  103 . 1 . At this point the plunger  102  is free to move in proximal direction P under the driving force. From this point on the injection continues without the user being able to pause or stop it. The embodiment of  FIG. 12  does not produce an audible or tactile feedback during the translation of the plunger  102 , e.g. during injection. 
       FIG. 13  is an embodiment of the shuttering mechanism wherein a set of castellations  103 . 1  to  103 . 5  is provided on the fixed shutter  103  and only one ramp  107 . 1  on the moving shutter arm  107 . Proximally from that ramp  107 . 1  the moving shutter arm  107  remains on the top level of the ramp  107 . 1 . To allow translation of the plunger  102  in proximal direction P, the moving shutter arm  107  must be translated in distal direction D relative to the fixed shutter  103 , such that they are out of phase as in  FIG. 13 . The ramp  107 . 1  of the moving shutter arm  107  cams the dog  106  out of engagement with the fixed shutter  103 , to the same level as the top of the castellation  103 . 1 . At this point the plunger  102  is free to move in proximal direction P under the driving force. From this point on the injection continues without the user being able to pause or stop it. The embodiment of  FIG. 13  does not produce an audible or tactile feedback during the translation of the plunger  102 , e.g. during injection. This embodiment allows for using the same housing  104  with the integrated fixed shutter  103  as in the embodiment of  FIGS. 9 and 10 . The functionality is changed just by applying the modified moving shutter arm  107 . This allows for creating a platform of auto-injectors with a number of common parts, where only some parts have to be exchanged in order to change the functionality. 
       FIG. 14  is yet another embodiment of the shuttering mechanism  101 . The shuttering mechanism  101  comprises at least one fixed shutter  103  in the shape of a set of ramped moving protrusions  103 . 1  to  103 . 5 . The ramps of the ramped fixed protrusions  103 . 1  to  103 . 5  of the fixed shutter  103  face in proximal direction P. A respective moving shutter arm  107  is arranged alongside the fixed shutter  103 , the moving shutter arm  107  having a number of consecutive ramped fixed protrusions  107 . 1  to  107 . 6  spaced from each other, their ramps facing in distal direction D. The ramped fixed protrusions  103 . 1  to  103 . 5  of the fixed shutter  103  and the ramped moving protrusions  107 . 1  to  107 . 6  of the moving shutter arm  107  have the same pitch and form a profiled surface. The moving shutter arm  107  is moveable in longitudinal direction with respect to the fixed shutter  103 . The moving shutter arm  107  has at least one locking position with its ramped moving protrusions  107 . 1  to  107 . 6  essentially in phase with the ramped fixed protrusions  103 . 1  to  103 . 5  of the fixed shutter  103  thus allowing the dog  106  of the resilient arm  105  to catch between or behind the ramped fixed protrusions  103 . 1  to  103 . 5  of the fixed shutter  103 . The moving shutter arm  107  has at least one unlocking position with its ramped moving protrusions  107 . 1  to  107 . 6  out of phase with the ramped fixed protrusions  103 . 1  to  103 . 5  in such a manner that the ramped moving protrusions  107 . 1  to  107 . 6  prevent the dog  106  from engaging with the ramped fixed protrusions  103 . 1  to  103 . 5  or disengage them thus allowing translation of the longitudinally moveable component  102 . 
     Prior to use the plunger  102  resolves the driving force acting in proximal direction P into the fixed shutter  103 . The moving shutter arm  107  is in phase with the fixed shutter  103  and hence carries no load. The plunger  102  cannot be pushed in proximal direction P because of the dog  106  caught behind the most distal ramped fixed protrusion  103 . 1  of the fixed shutter  103 . 
     To allow translation of the plunger  102  in proximal direction P, the moving shutter arm  107  must be translated in distal direction D relative to the fixed shutter  103 , such that they are out of phase. The ramp of the most distal ramped fixed protrusion  107 . 1  of the moving shutter arm  107  cams the dog  106  out of engagement with the fixed shutter  103 , to the same level as the top of the ramped fixed protrusion  103 . 1 . At this point the plunger  102  is free to move in proximal direction P under the driving force. If the relative position of the shutters  103 ,  107  is held constant, the dog  106  will continue to ride up and down the surface formed by the out of phase fixed shutter  103  and moving shutter arm  107 . 
     In the embodiment shown in  FIG. 15  the dog  106  running along the surface will provide both audible and tactile feedback that the injection is taking place, but muffled in comparison to the embodiment of  FIG. 9 . 
     As in the embodiment of  FIG. 9  the injection can be interrupted and restarted. Furthermore, the ramped fixed protrusions  103 . 1  to  103 . 5  of the fixed shutter  103  in place of the castellations allow for implementing a retraction of the plunger  102  and consequently retraction of the syringe  108  and needle, since as the fixed shutter  103  and the moving shutter arm  107  are out of phase as in  FIG. 14 , the dog  106  can run in distal direction D as well without catching between the ramped protrusions  103 . 1  to  103 . 5 ,  107 . 1  to  107 . 6  of either shutter  103 ,  107 . 
       FIG. 15  is another embodiment of the shuttering mechanism  101 . The shuttering mechanism  101  comprises at least one fixed shutter  103  with a set of fixed protrusions  103 . 1  to  103 . 5 , the most distal one of them in the shape of a castellation  103 . 1  and the other protrusions  103 . 2  to  103 . 5  ramped with their ramps facing in distal direction D. A moving shutter arm  107  is arranged alongside the fixed shutter  103 , the moving shutter arm  107  having one ramped protrusion  107 . 1  with its ramp facing in distal direction D. The moving shutter arm  107  is moveable in longitudinal direction with respect to the fixed shutter  103 . 
     Prior to use the plunger  102  resolves the driving force acting in proximal direction P into the fixed castellation  103 . 1  of the fixed shutter  103 . The ramped moving protrusion  107 . 1  of the moving shutter arm  107  is in phase with the fixed castellation  103 . 1  of the fixed shutter  103 . The plunger  102  cannot be pushed in proximal direction P because of dog  106  caught behind the fixed castellation  103 . 1  of the fixed shutter  103 . 
     To allow translation of the plunger  102  in proximal direction P, the moving shutter arm  107  must be translated in distal direction D relative to the fixed shutter  103 , such that they are out of phase. The ramp of the ramped moving protrusion  107 . 1  cams the dog  106  out of engagement with the fixed shutter  103 , to the same level as the top of the first fixed protrusion  103 . 1 . At this point the plunger  102  is free to move in proximal direction P under the driving force. From this point on the injection continues without the user being able to pause or stop it. The dog  106  will continue to ride up and down the surface formed by the fixed protrusions  103 . 2  to  103 . 5 . 
     In the embodiment shown in  FIG. 15  the dog  106  running along the surface will provide only an audible feedback that the injection is taking place. If the moving shutter  107  had ramped protrusions  107 . 2  to  107 . 6  and the fixed shutter  103  had none, the shuttering mechanism  101  could also provide a tactile feedback. 
       FIGS. 16   a  and  16   b  show yet another embodiment of the shuttering mechanism  101 . 
     The shuttering mechanism  101  comprises at least one fixed shutter  103  with a set of fixed protrusions  103 . 1  to  103 . 5  in the shape of castellations protruding to one side. A moving shutter arm  107  is arranged alongside the fixed shutter  103 , the moving shutter arm  107  having ramped moving protrusions  107 . 1  to  107 . 7  protruding to the opposite side with their ramps facing in distal direction D and engaged with mating ramps  110 . 1  to  110 . 7  in the fixed shutter  103 . The moving shutter arm  107  is moveable in longitudinal direction with respect to the fixed shutter  103 . 
     Prior to use (see  FIG. 16   a ) the plunger  102  resolves the driving force acting in proximal direction P into the fixed castellation  103 . 1  of the fixed shutter  103 . The ramped moving protrusions  107 . 1  to  107 . 7  of the moving shutter arm  107  are fully engaged with the mating ramps  110 . 1  to  110 . 7  of the fixed shutter  103 . The plunger  102  cannot be pushed in proximal direction P because of dog  106  caught behind the fixed castellation  103 . 1  of the fixed shutter  103 . 
     To allow translation of the plunger  102  in proximal direction P, the moving shutter arm  107  must be translated in distal direction D relative to the fixed shutter  103 . The engaged ramped moving protrusions  107 . 1  to  107 . 7  and the mating ramps  110 . 1  to  110 . 7  push the moving shutter arm  107  away from the fixed shutter  103  so that a backside of the moving shutter arm  107  opposite the protrusions  107 . 1  to  107 . 7  becomes flush with the top of the fixed protrusions  103 . 1  to  103 . 5  thus disengaging the dog  106  from the fixed shutter  103  (see  FIG. 16   b ). At this point the plunger  102  is free to move in proximal direction P under the driving force. If the relative position of the shutters  103 ,  107  is held constant, the dog  106  will continue to ride up the surface formed by the fixed shutter  103  and moving shutter arm  107  in proximal direction P. 
     If the moving shutter arm  107  is translated back in proximal direction P, the moving shutter  107  is no longer forced away from the fixed shutter  103  and the ramped moving protrusions  107 . 1  to  107 . 7  and the mating ramps  110 . 1  to  110 . 7  fully re-engage. The dog  106  will catch on the next fixed shutter  103  castellation  103 . 1  to  103 . 6  and stop the injection. The injection can then be restarted by translating the moving shutter arm  107  in distal direction D again. 
     In the embodiment of  FIGS. 16   a  and  16   b  the number of moving protrusions  107 . 1  to  107 . 7  and their pitch relative to the pitch of the fixed protrusions  103 . 1  to  103 . 5  is insignificant other than to define the amount of distal movement of moving shutter arm  107  required to start or stop the proximal movement of plunger  102 . It would be sufficient to have one moving protrusion  107 . 1  and one mating ramp  110 . 1 . However, at least two moving protrusions  107 . 1  to  107 . 7  and two mating ramps  110 . 1  to  110 . 7  will be more robust. 
     The embodiment of  FIGS. 16   a  and  16   b  does not provide audio or tactile feedback. Because there is no requirement for phasing between the fixed shutter  103  and the moving shutter  107 , the fixed protrusions  103 . 1  to  103 . 5  can be thin and close together resulting in a better resolution of stopping positions. Other than in the previously described embodiments, where the distance between the fixed protrusions  103 . 1  to  103 . 5  is driven by the length of the ramps, which is driven by the force/displacement specified to release the dog  106 , in the embodiment of  FIGS. 16   a  and  16   b  the ramps of the moving protrusions  107 . 1  to  107 . 7  are independent of the fixed protrusions  103 . 1  to  103 . 5 . Hence, more, closely spaced fixed protrusions  103 . 1  to  103 . n  can be used for improving the resolution of stopping positions. 
       FIGS. 17 ,  18  and  19  show variants of the embodiment of  FIGS. 9 and 10 . 
     In  FIG. 17 , the level of the moving shutter arm  107  distally from the most distal ramped moving protrusion  107 . 1  as well as the level of the fixed shutter  103  distally from the most distal fixed protrusion  103 . 1  is below the level between the protrusions  103 . 1  to  103 . 5 ,  107 . 1  to  107 . 6 . Consequently, the ramp of the ramped moving protrusion  107 . 1  is longer and camming the dog  106  from its position prior to use (distally from the protrusions  103 . 1 ,  107 . 1 ) requires more travel of the moving shutter  107  than for restarting the injection. This reduces the sensitivity of the arrangement to initial movement of the moving shutter arm  107 , thereby reducing the chance of accidental triggering at the start of injection, yet maintains the ability to stop quickly. A good resolution between stopping points is provided. 
     In  FIG. 18 , the ramp of the most distal ramped moving protrusion  107 . 1  is steeper than the ramps of the other ramped moving protrusions  107 . 2  to  107 . 6 . Consequently, camming the dog  106  from its position prior to use (distally from the protrusions  103 . 1 ,  107 . 1 ) requires more increased force on the moving shutter  107  than for restarting the injection. This reduces the chance of unintended triggering at the start of injection. 
     In the embodiments which allow stopping and/restarting the injection, there will always be an amount of liquid medicament dispensed before the injection actually stops since the dog  106  has to travel until the distal edge of the next fixed protrusion  103 . 1  to  103 . 5 . In order to reduce this amount of medicament the auto-injector may have at least two shuttering mechanisms  101  (e.g. one on either side of the auto-injector) which are out of phase with each other. Thus, the effective pitch of the shutter mechanism  101  would be halved and the dispensed dose of medicament until the stop would be significantly reduced. 
     In  FIG. 19 , the fixed protrusions  103 . 1  to  103 . 6  and the moving protrusions  107 . 1  to  107 . 7  have different length. In order to control translation of the plunger  102  it is sufficient to cover the proximal edge of the moving protrusions  107 . 1  to  107 . 7  by the fixed protrusions  103 . 1  to  103 . 6 . Complete overlap is not required. This allows the pitch of the shutters to be reduced so less medicament will be dispensed when the injection is interrupted. In this arrangement, the width of dog  106  in the axial direction needs to be sufficiently short that it will engage between the proximal edge of moving protrusion  107 . 1  to  107 . 7  and the distal edge of fixed protrusion  103 . 1  to  103 . 6  when the moving shutter arm  107  is moved out of phase with the fixed shutter  103 . 
     The shuttering mechanism  101  may likewise be applied in other environments requiring control of translation of a longitudinally moveable component  102  other than a plunger  102 . 
     The numbers of fixed protrusions  103 . 1  to  103 . 6  and moving protrusions  107 . 1  to  107 . 7  can differ from the numbers given in the embodiments. 
     Preferably, motion of the moving shutter arm  107  can be actuated by pressing a proximal end of an auto-injector against an injection site, e.g. a user&#39;s skin thereby pushing a sleeve or bar protruding from the proximal end of the auto-injector in distal direction. The motion may likewise be actuated by pushing an end button or indirectly through a cam or other mechanism linked to a side button or end button. 
     In addition, the auto-injector could be triggered by a secondary mechanism and the shuttering mechanism  101  could simply be used as a control mechanism. In this implementation, the moving shutter&#39;s  107  position would be controlled by a ‘pause’ button. This would separate the mechanisms to fire and pause the auto-injector, improving usability. 
     The ‘pause’ button could be designed to be ‘press to inject’ or ‘press to pause’. The trigger could be combined with the pause button if the mechanism were ‘press to inject’. 
     In an alternative embodiment the moving shutter  107  may be arranged to rotate or translate in the direction perpendicular to the shutters into the gaps between the fixed protrusions  103 . 1  to  103 . 5  rather than translated longitudinally as in the illustrated embodiments. 
     In yet another alternative embodiment, shown in  FIGS. 20A ,  20 B,  20 C and  20 D, the shutters  103 ,  107  could be facing each other and the plunger  102  could navigate a gap created between the shutters  103 ,  107 . For this arrangement, the distal faces of the fixed protrusions  103 . 1  to  103 . 5  and moving protrusions  107 . 1  to  107 . 6  both need to be ramped in order to allow the dog  106  to pass along the passage formed when the protrusions are moved out of phase. 
     In yet another embodiment the dog  106  could oscillate through a continuous sinusoidal path cut into the two shutters  103 ,  107  (see  FIGS. 21A ,  21 B,  22 A and  22 B). The sinusoidal path would be broken by shifting the moving shutter  107  into the locking position thus preventing the dog  106  from advancing beyond the next change-over between the shutters  103 ,  107 .