Abstract:
An injection device including a housing formed by two housing parts moveable in relation to each other, a drive element urged by a spring in an injection direction and releaseably held against movement, and a release element moveable from a lock position to an intermediate position due to the movement of the housing parts, the drive element remaining held against movement when the release element is in the intermediate position, the release element further moveable from the intermediate position to a release position in which the drive element is released.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]     This application is a continuation of International Application PCT/CH2004/000715, filed on Nov. 29, 2004, which claims priority to Swiss Application CH 2189/03, filed on Dec. 18, 2003 and German Application DE 203 19 648.1, filed on Dec. 18, 2003, the entire contents of all of which are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     The present invention relates to devices for delivering, administering, injecting or dispensing substances, and methods of making and using such devices. More particularly, it relates to an injection device for administering an injectable product, such as a liquid medicament such as insulin, a growth hormone, heparin, an osteoporosis preparation, etc. In some preferred embodiments, the injection device is an injection pen or an automatic injector.  
         [0003]     Injection devices of numerous designs are known. They are generally used for administering or delivering medicinal substances or medicaments, and, in many cases, are used by a patient to self-administer a substance.  
         [0004]     Automatic injection devices are one type of injection devices. Many automatic injectors have a release lock intended to prevent an injection procedure from being inadvertently triggered. An example of an automatic injector is described in document DE 4037418. This automatic injector has a housing for accommodating a container of active substance. The housing consists of two parts which can be displaced relative to one another from a first and a second position along an axis. The automatic injector also has a release mechanism, a dispensing mechanism for dispensing the active substance which is held by means of the release mechanism in a position into which it is urged or held by a spring, and a trigger device in the form of a push button, which can likewise be operated in the direction of said axis. In this instance, one housing part accommodates the trigger device and the other housing part accommodates the release mechanism. When the two housing parts are in the first position relative to one another, the release mechanism is disposed at a greater distance from the trigger device than in it is in the second position and operating the trigger device has no effect. When the housing parts are in the second position, the trigger device is closer to the release mechanism and is therefore in a position in which it can cause the release of the dispensing mechanism.  
       SUMMARY  
       [0005]     An object of the present invention is to provide an injection device which offers a high degree of safety against inadvertent triggering while requiring only a few components.  
         [0006]     In one embodiment, the present invention comprises an injection device comprising a housing formed by two housing parts moveable in relation to each other, a drive element urged by a spring in an injection direction and releaseably held against movement, and a release element moveable from a lock position to an intermediate position due to the movement of the housing parts, the drive element remaining held against movement when the release element is in the intermediate position, the release element further moveable from the intermediate position to a release position in which the drive element is released.  
         [0007]     In one embodiment, the present invention comprises a trigger-activatable injection device comprising a housing portion, a reservoir for an injectable product, an injection needle with a needle tip at one end, a needle guard moveable relative to the housing portion and to the injection needle from a protective position generally surrounding the needle to a retracted position, a drive mechanism for powering an injection, the drive mechanism releaseably held in a retaining engagement to prevent a driving movement, a switching element coupled to the needle guard so that the movement of the needle guard to the retracted position causes the switching element to move from a locked position to a coupled position, and an activatable trigger element for triggering the drive mechanism which, upon activation, is coupled with the switching element when the switching element assumes the coupled position and causes a movement of the switching element from the coupled position to a release position, wherein the retaining engagement of the drive mechanism is not released until the switching element is in the release position.  
         [0008]     In one embodiment, the present invention comprises an injection device comprising a housing portion, a reservoir for the product to be injected, namely the active ingredient, an injection needle, a needle guard, a drive mechanism for the injection and a trigger mechanism for triggering the drive mechanism. The housing portion, or another housing portion of the injection device connected to it, directly constitutes the reservoir. In some preferred embodiments, the reservoir is a container accommodated in the housing portion or the other housing portion. The injection device has a reservoir holder, which holds and centers the reservoir and is itself held and centered in a housing portion. The injection needle may be attached to the reservoir or to the reservoir holder. Accordingly, it projects axially forward, from the reservoir or the reservoir holder, and has a needle tip at its front, or distal end. The needle guard is joined to the housing portion so that it is able to move relative to the housing portion and relative to the injection needle from a protective position in which the injection needle is surrounded to a point beyond its needle tip, backwards, or proximally, axially relative to the housing portion and to the injection needle as far as a retracted position. The needle guard may be a purely visual guard which can be moved proximally against an elastic return force and pushed back in the distal direction again when the return force is released. Alternatively, however, it may also be locked in the protective position to prevent a return movement, in which case the locking action must be released prior to the injection, after which it may be releasable or non-releasable.  
         [0009]     The drive mechanism may comprise a dispensing drive with a conveyor element or drive element and a dispensing drive for the drive element, and the drive element acts on the product disposed in the reservoir in order to dispense the product. In preferred embodiments in which the injection device is an automatic injector, the drive mechanism not only has such a dispensing drive but also an injection drive for the injection needle. This being the case, the same force generator may be used to drive the dispensing drive and the injection drive. For example, a mechanical spring, e.g., a coil spring pre-stressed to a specific pressure, serves as the injection drive as well as the dispensing drive. However, separate force generators could also be provided for each of the two drives, for example a coil spring pre-stressed to a specific pressure. In some preferred embodiments, the injection drive is a force generator which assumes an elastically tensed state prior to an injection, from which it drives the injection needle so as to inject it in and/or through the skin in the distal, i.e. forward drive, direction. The drive mechanism may be designed so that it effects only a driving movement causing the dispensing action or a driving movement causing dispensing and prior injection, or it may effect one driving movement for initial injection and another driving movement for the dispensing process.  
         [0010]     When the injection device is in an initial state, the drive mechanism is held in a releasable retaining engagement so that it can not effect any driving movement and can not effect a driving movement causing the injection needle to be injected. If the injection device is not an automatic injector, but an injector with an injection needle by means of which the user must inject himself, only a dispensing drive is provided and it is on this which the retaining engagement therefore acts.  
         [0011]     In some embodiments, to trigger the drive mechanism, a moving housing part or the needle guard, trigger member or trigger element and a release element, e.g., a switching element, co-operate with one another. For example, the switching element and the needle guard may be coupled with one another so that the movement of the needle guard out of the protective position into the retracted position causes a movement of the switching element out of a latching or locking position into a coupled or intermediate position. Once the switching element assumes the coupled position, the trigger element can be moved into a coupled engagement with the switching element by operating the trigger element. In the coupled engagement, the triggering movement of the trigger element caused by activation is converted into a movement of the switching element out of the coupled position into a released position. As long as the switching element has not assumed the released position, it prevents the retaining engagement of the drive mechanism from being released. The retaining engagement exists directly, or via one or more intermediate elements, between the drive mechanism and the housing portion, which means that the drive mechanism is not able to effect any driving movement relative to the housing portion in the retained engagement. The driving movement is or includes a axial linear movement of the drive mechanism in a forward drive direction, for example in the distal direction. If the injection device is an automatic injector, the drive mechanism may be coupled with the injection needle so that it drives the injection needle in the drive direction, i.e. in the direction of its own driving movement.  
         [0012]     The switching element guides the movement from the locking position via the coupled position as far as the released position as a unit. As a result, the number of parts needed for the trigger system is kept low. The switching element may be made as a single piece, but may also be an assembled structure in principle, although the movement from the locked position as far as the released position is effected as a unit as if it were a single stiff body, at least as far as this movement is concerned.  
         [0013]     The movement of the switching element from the locked position into the released position is a movement in a single direction only, e.g., an axial movement in the proximal direction.  
         [0014]     The trigger element projects out from the housing portion so that it can be operated directly. In some embodiments, it is preferably a trigger button, i.e., a push button. The movement effected when the trigger element is operated is a movement transversely to a proximal-distal axis of the injection device.  
         [0015]     The coupled engagement between the trigger element and the switching element may be obtained on the basis of a sliding pressure or frictional contact. At least one of the switching element and trigger element acts as a switching cam and the other an engaging element sliding on the switching cam. The sliding pressure contact is established due to the trigger movement of the trigger element when the switching element assumes the coupled position. In the sliding pressure contact, the trigger element pushes the switching element out of the coupled position into the released position.  
         [0016]     In the positions which the switching element assumes during an injection prior to assuming the released position, it locks a blocking mechanism securing the retaining engagement between the drive mechanism and the housing portion, preventing the retaining engagement from being released. The blocking mechanism is elastically biased or urged towards a release of the retaining engagement but is prevented from releasing the engagement by the switching element. The switching element pushes a blocking element of the blocking mechanism into the retaining engagement. The switching member is designed so that it allows the blocking element to snap out of the retaining engagement in the released position, thereby automatically releasing the retaining engagement.  
         [0017]     In one embodiment of the present invention in the form of an automatic injector, the trigger element or trigger member can be moved in a plane disposed transversely to the longitudinal axis of the automatic injector and the release element can be moved parallel to the longitudinal axis of the automatic injector. The release element may, for example, be moved from the locked position into the intermediate position by moving the housing parts or portions relative to one another. In the intermediate position, the switching element in the form of a release element may co-operate with a locking device such as an injection blocking element, which secures the drive element and the forward-drive structure in a locked position. When the release element is in the intermediate position, it can be moved farther into the released position in which the drive element is released by means of the release element. To this end, the release can have a guide mechanism which co-operates with the release element so that it is moved into the released position. The guide mechanism may, for example, be in the form of a surface disposed at an angle relative to the longitudinal axis of the automatic injector on the release element, e.g., on the trigger element. When the trigger element is operated, an edge of the release element is moved so that it lies on the oblique surface of the trigger element and is pushed along the oblique surface into the released position when the trigger element is activated.  
         [0018]     As long as the release element is in the locked position, operating the release element will not trigger the automatic injector. The release element may be biased into a position projecting out of the automatic injector by means of a spring. With this type of embodiment, the automatic injector is triggered in two independent operating steps which are uncoupled form one another. It is therefore not possible to trigger the automatic injector inadvertently.  
         [0019]     The locking and unlocking mechanism and the trigger element do not move relative to one another in the longitudinal direction. They move in a plane disposed transversely to the longitudinal axis of the automatic injector, as a result of which no additional room for movement has to be provided for these components in the longitudinal direction of the automatic injector. This means that the automatic injector can be made shorter overall.  
         [0020]     In another embodiment of the present invention, the trigger element can be moved in the longitudinal direction of the automatic injector. This makes it easy to operate the trigger mechanism at one end of the automatic injector. In this embodiment, the release element, in its locked position, prevents the trigger element from moving along it. This ensures that the automatic injector has to be positioned first of all and then the operating element pressed. In one type of embodiment, the release element can be moved in a plane disposed transversely to the longitudinal axis or direction of the automatic injector. Consequently, in one variant, the release element may be guided so that it effects a translating movement from the locked position into the released position. This being the case, the release element has an orifice in the shape of a keyhole and an annular groove is provided on the drive element, in which the slim or narrow part of the keyhole orifice engages when the release element is in the locked position. In another variant, the release element is designed so that it effects a rotating movement from the locked position into the released position. In this instance, the release element has a non-rounded orifice and a head with a non-rounded cross-section is provided on the drive element which does not fit through the orifice except when the release element is in the released position. Both variants require only a few individual parts and enable an inexpensive automatic injector to be provided which is reliable in operation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  illustrates an exemplary embodiment of an automatic injector in accordance with the present invention in an initial state prior to injection,  
         [0022]      FIG. 2  shows a needle guard, a switching element and a trigger element of the automatic injector in the initial state,  
         [0023]      FIG. 3  shows cross-section A-A indicated in  FIG. 1 ,  
         [0024]      FIG. 4  illustrates the automatic injector of  FIG. 1  positioned at an injection point prior to triggering,  
         [0025]      FIG. 5  shows the needle guard, the switching element and the trigger element of the automatic injector in the state illustrated in  FIG. 4 ,  
         [0026]      FIG. 6  shows cross-section B-B indicated in  FIG. 4 ,  
         [0027]      FIG. 7  shows the automatic injector of  FIG. 1  positioned at an injection point in the triggered state,  
         [0028]      FIG. 8  shows the needle guard, the switching element and the trigger element in the triggered state,  
         [0029]      FIG. 9  shows cross-section C-C indicated in  FIG. 7 ,  
         [0030]      FIG. 10  illustrates a second exemplary embodiment of an automatic injector in accordance with the present invention in an initial state,  
         [0031]      FIG. 11  is a longitudinal section through an injection device in accordance with the invention in a state in which it may be supplied, and  
         [0032]      FIG. 12 , including  FIGS. 12   a  to  12   c , show, in cross section, three positions of a release element for the device illustrated in  FIG. 11 . 
     
    
     DETAILED DESCRIPTION  
       [0033]      FIG. 1  depicts an exemplary embodiment of an injection device in accordance with the present invention. The depicted embodiment is an automatic injector embodied in the form of an injection pen. It comprises a sleeve-shaped proximal or rear housing portion  1  serving as a gripping piece and a sleeve-shaped distal or front housing portion  2 , which forms a needle guard  2   a  at its distal end. Housing portion  2  is axially guided in housing portion  1 , linearly along a common longitudinal axis L.  
         [0034]     Housing portion  2  accommodates a reservoir  3 , which is filled with an injectable product, for example insulin. The reservoir  3  is a container and, in this example, is a standard ampoule, in which a drive element  4  in the form of a plunger is accommodated. Product is dispensed through an outlet of the reservoir  3  and an injection needle  5  connected to the reservoir  3  by moving the drive element  4  axially in a forward drive direction V. The injection needle  5  is attached to the distal end of the reservoir  3  and its free needle tip projects forward in the forward drive direction V. When the automatic injector is in the initial state illustrated in  FIG. 1 , the needle guard  2   a  surrounds the injection needle  5  as far as beyond its needle tip. This corresponds to an axial protective position of the needle guard  2   a . The reservoir  3  is held centred in a reservoir holder  6  and is supported by the reservoir holder  6  in the forward drive direction V. Housing portion  2  and hence its needle guard  2   a  is elastically biased in the forward drive direction V by means of a return spring  7 . It can be moved relative to the housing portion  2  against the force of the spring  7  in the direction opposite the forward drive direction V. In the embodiment illustrated as an example here, the spring  7  is directly supported on the housing portion  2  in the forward drive direction V and directly on the reservoir holder  6  in the direction opposite the forward drive direction V.  
         [0035]     A drive mechanism is accommodated in the housing portion  1  and is mounted or carried so as to be axially displaceable. The drive mechanism comprises a dispensing drive for dispensing the product and an injection drive for initially injecting the injection needle  5 . A dispensing spring  10  forms the dispensing drive. The dispensing spring  10  acts via a dispensing structure  11 , which is provided in the form of a dispensing sleeve for driving the product onto the drive element  4 . Due to the design of the drive element  4  in the form of a translating plunger, the dispensing structure  11  is a plunger rod. The dispensing spring  10  biases the dispensing structure  11  in the forward drive direction V. When the automatic injector is in the initial state, however, the dispensing structure  11  is in a retaining engagement which prevents the dispensing structure  11  from being moved forwards.  
         [0036]     The injection drive is also provided in the form of a spring, namely injection spring  13 . When the automatic injector is in the initial state, the injection spring  13  is also biased in the forward drive direction V. Due to its elastic force, it applies pressure to a forward drive structure  12 , which is held in a retaining engagement against the force of the injection spring  13  and is prevented from effecting a forward drive movement relative to the housing portion  1 . The forward drive structure  12  surrounds the dispensing structure  11 , providing a mount and linear guide for the latter in the axial direction. Both the dispensing spring  10  and the injection spring  13  are supported on the housing portion  1  in the direction opposite the forward drive direction V, the injection spring being directly supported on a bearing block  8  which is not able to move axially and radially and which does not turn, and in this sense is fixedly connected to the housing portion  1 . The bearing structure  8  also forms an axial linear guide for the forward drive structure  12 .  
         [0037]     The retaining engagement of the forward drive structure  12  comprises an injection blocking element  15  in the form of an elastic snapper and a projection, by means of which it projects into a recess  14  provided on an external surface of the sleeve-shaped forward drive structure  12 . The injection blocking element  15  is not able to move axially relative to the housing portion  1 . Several of the injection blocking elements  15  are disposed around the periphery of a sleeve body, each in the form of axial resilient tongues.  
         [0038]     To provide a retaining engagement for the dispensing structure  11 , the forward drive structure  12  also has several resilient tongues on its proximal end, which act as dispensing blocking elements  16  by each forming a forward drive stop for the dispensing structure  11 . The same sleeve body forming the injection blocking elements  15  pushes the dispensing blocking elements  16  radially inwards into the retaining engagement with the dispensing structure  11 .  
         [0039]     The injection blocking elements  15  are pushed radially inwards by means of a switching element  20  into the retaining engagement, i.e. into the recesses  14  or the recess  14  provided in the forward drive structure  12  in the form of a peripheral groove. To this end, the switching element  20  has a sleeve portion surrounding the forward drive structure  12  and the injection blocking elements  15  and pushes them into the recesses  15  or the peripherally extending recess  15 . The bearing structure  8  provides a mount for the switching element  20  so that it can be axially displaced. The bearing structure  8  and/or the sleeve body forming injection blocking elements  15  guide the switching element  20  linearly in the axial direction. The switching element  20  is in an axial pressure contact with the housing portion  2 , causing a movement of the housing portion  2  in the direction opposite the forward drive direction V and an identical movement of the switching element  20 . Finally, the switching element  20  is supported on the housing portion  1  by means of a return spring  23  in the direction opposite the forward drive direction V. In the initial state, the switching element  20  assumes an axial locking position in which it locks the injection blocking elements  15  in their retaining engagement with the forward drive structure  12 .  
         [0040]     In a proximal portion of the housing portion  1 , a trigger element  18  projects radially outwards from its external surface. The trigger element  18  can be pushed deeper into the housing portion  1 , e.g., by applying radial pressure, and, due to such an operation, moves in a direction disposed transversely, in this embodiment radially, with respect to a mid-longitudinal axis L of the automatic injector pointing in the forward drive direction V.  
         [0041]      FIG. 2  shows the housing portion  2  with the needle guard  2   a , the switching element  20  and trigger element  18  released from the automatic injector illustrated in  FIG. 1  in the relative positions which they assume when the automatic injector is in the initial state. Only the axial pressure contact exists between the housing portion  2  and the switching element  20 . The trigger element  18  and the switching element  20  are not engaged. As illustrated, however, a switching cam  19  is provided, which is inclined with respect to the forward drive direction V and with respect to the direction of the transverse movement of the trigger element  18 . The forward drive direction V and the direction of transverse movement, i.e. the direction of the triggering movement of the trigger element  18 , are oriented perpendicular to one another. The switching cam  19  points in the direction opposite the forward drive direction V. The switching element  20  is provided with a cam  21 , which forms an engaging element in a coupled engagement of the switching element  20  with the trigger element  18  and slides on the switching cam  19  as the trigger element  18  effects its triggering movement. The switching element  20  is also provided with a switching cam  22 , which in the embodiment illustrated as an example is provided on a rear surface of the cam  21 . The switching cam  22  may not fulfil any function in terms of triggering the automatic injector. It merely corrects the position of the trigger element  18  in the event that it is inadvertently pushed when the automatic injector is in the initial state. The two switching cams  19  and  22  extend in a straight line, i.e. are oblique. In principle, however, a non-linear contour would also be feasible.  
         [0042]      FIG. 3  specifically illustrates the trigger element  18  and the switching element  20  as well as their switching cams  19  and  22  through a cross-section A-A indicated in  FIG. 1 .  
         [0043]     Once the automatic injector has been positioned on or at the desired injection site on the skin, a first step of the injection involves applying pressure against the injection point so that the needle guard  2   a  and thus the entire housing portion  2  is moved proximally relative to the housing portion  1 , i.e. deeper into the housing portion  1 , until the distal end of the needle guard  2   a  and the distal end of the housing portion  1  are disposed at the same axial height.  
         [0044]      FIG. 4  illustrates the automatic injector at the end of this first phase of the injection. Due to the rearward movement of the needle guard  2   a  into the retracted position illustrated in  FIG. 4 , in which the needle tip sits directly above the skin, the needle guard  2   a  and the housing portion  2  have moved the switching element  20  back by the distance of their own rearward movement relative to the housing portion  1  and in particular relative to the trigger element  18 .  
         [0045]      FIG. 5  illustrates the relative position which the housing portion  2 , switching element  20  and trigger element  18  have now assumed. The axial position of the switching element  20  relative to the trigger element  18  is such that the switching cam  19  has effected a triggering movement of the trigger element  18 , i.e. when the trigger element  18  was depressed, to make a pressure sliding contact with the cam  21  and slides along the cam  21  in the pressure sliding contact. The axial position now assumed by the switching element  20  is therefore referred to as the coupled position.  
         [0046]     When the switching element  20  is in the coupled position and the injection is triggered by pressing the trigger element  18 , the latter moves relative to the housing portion  1  and in particular relative to the switching element  20  towards its cam  21 . It moves into said sliding pressure contact with the cam  21  and, because of the inclined contour of the switching cam  19 , pushes the cam  21  and thus with it the switching element  20  in the direction opposite the forward drive direction V, i.e. it pulls the switching element  20  in the proximal direction. The cam  21  forms an engagement member for this axial movement of the switching element  20 , which slides along the switching cam  19  when the trigger element  18  is pushed in. Since the trigger element  18  is guided and effects only the radial triggering movement but is unable to move axially relative to the housing portion  1 , the switching element  20  is pulled farther back in the direction opposite the forward drive direction V by means of its cam  21  into an axial end position.  
         [0047]      FIG. 7  illustrates the exemplary automatic injector after triggering, i.e. the trigger element  18  has effected its triggering movement and the switching element  20  has assumed its proximal end position relative to the trigger element  18  and relative to the injection blocking elements  15 . In its sleeve portion, by means of which it has so far pushed the injection blocking elements  15  into the retaining engagement with the forward drive structure  12 , the switching element  20  has a recess  24 . In the embodiment illustrated as an example, this is provided in the form of a wider region extending round the internal surface of the sleeve portion of the switching element  20 , terminating the switching element at the distal end. When the switching element  20  is in the proximal end position, the injection blocking elements  15  snap radially outwards, out of the retaining engagement with the forward drive structure  12  into the recess  24  due to their natural elastic rebound forces. The retaining engagement of the forward drive structure  12  is therefore released and the forward drive structure  20  is driven forwards in the forward drive direction V by the tensed injection spring  13 . As it is driven forwards, it pushes against the reservoir holder  6 , which is moved together with the reservoir  3  accommodated in it in the forward drive direction V. During the forward driving movement, the injection needle  5  is moved forwards out of the housing portions  1  and  2  and into and through the skin. The forward driving movement of the forward drive structure  12  is restricted by a stop.  
         [0048]     As soon as the forward driving movement of the forward drive structure  12  and, thus, the forward injection movement of the injection needle  5  has ended, the dispensing blocking elements  16  move into a recess  17  of the sleeve body, which also forms injection blocking elements  15 , and snap into the recess  17 . Due to the forward snapping action of the dispensing blocking elements  16 , the retaining engagement of the dispensing structure  11  is released and it now slides relative to the forward drive structure  12  in the forward drive direction V. The dispensing structure  11  thus comes into contact with the drive element  4  and pushes it forwards in the reservoir  3  towards its outlet. As a result, the product is dispensed from the reservoir  3  and through the injection needle  5  and is administered.  
         [0049]      FIG. 8  provides another detailed illustration of the housing portion  2 , the switching element  20  and the trigger element  18  in the axial positions which they assume relative to one another after triggering.  FIG. 9  illustrates the same state but in a cross-section through C-C indicated in  FIG. 7 .  
         [0050]      FIG. 10  depicts a second exemplary embodiment of an injection device. The automatic injector of the second embodiment differs from the embodiment described as a first example in terms of its injection blocking elements, which are denoted by reference  25  in the embodiment illustrated as a second example. The blocking elements  25  are ball bearings or cylindrical pins, which are also biased radially outwardly and are locked by the switching element  20  to prevent them from moving out of the retaining engagement. To this extent, the switching element  20  of the second embodiment corresponds to that of the embodiment described as a first example. There are also no differences as regards the co-operation with the needle guard  2   a  and the trigger element  18 . The differences relate to another aspect and have nothing to do with the trigger mechanism formed by the needle guard  2   a  or housing portion  2 , the switching element  20  and the trigger element  18 . In this respect, the explanations given with reference to the first embodiment apply.  
         [0051]     The trigger element  18  is displaceable in a plane disposed transversely to the longitudinal direction of the automatic injector and the release element  20  is displaceable in the longitudinal direction of the automatic injector. The release element  20  is provided in the form of a sleeve, which is axially displaceable relative to the front, distal and rear proximal housing parts  1  and  2  and is disposed inside these housing parts. The trigger element  18  is formed by a button projecting out from the side of the automatic injector. In  FIGS. 1 and 2 , the release element  20  is in the locked position or protective position, i.e. in a position at a distance from the trigger element  18  and is biased forwards in this locking position by means the cone spring  23 . This being the case, the release element  20  co-operates with a locking mechanism in the form of two oppositely lying locking arms  15  which are biased and engage in a recess  14  on the drive element  12 , thereby locking it so that it can not be pushed forwards. Naturally, it would also be possible to provide only one locking arm or more than two locking arms. The locking arms  15  are biased forward by means of the internal surface of the sleeve of the release element  20  into the recesses  14  of the drive element  12 . The locking mechanism could also be provided in the form of ball bearings or a forward-biased annular element, for example, co-operating with the drive element in a locking relationship.  
         [0052]     In  FIGS. 4 and 5 , the release element  20  is shown in an intermediate or coupled position. The front housing part  2  is pushed inside the automatic injector relative to the rear housing part  1 , for example when placed on the injection site on the skin of a patient. The release element  20  adjoins the front housing part  2  and is pushed together with it relative to the rear housing part  3  into the intermediate position. The locking arms  15  slide along the internal surface of the sleeve of the release element  20  and are pushed ever further into the recesses on the drive element  12  by the sleeve of the release element  20  so that they prevent said drive element  12  from moving forwards. When the automatic injector is removed from the injection site, the release element  20  is pushed backwards by the cone spring  23  back into the locked position.  
         [0053]     The release element  20  has reached the intermediate position within the movement range of the trigger element  18  and can now only co-operate with a guide mechanism on the trigger element  18  and be moved by the latter into a released position. In the embodiment illustrated as an example here, the guide mechanism is provided in the form of the surface  22  on the trigger element  18  extending at an angle with respect to the longitudinal axis of the automatic injector, forming a switching cam. Alternatively, a similar surface or a guide mechanism could also be provided on the release element  20 . Provided on the sleeve of the release element  20  is an extension in the direction of the trigger element  18 , which has a lug or a cam  21  which, when the oblique surface  22  of the trigger element  18  is in the immediate position, moves in a radial direction towards the longitudinal axis of the automatic injector, as may best be seen from  FIG. 5 .  
         [0054]      FIGS. 7 and 8  illustrate the release element  20  in a released position. When the release element  20  is in the intermediate position, the trigger element  18  may interact with the release element  20 . When the trigger element  18  is operated, the oblique surface  22  is moved toward the lug  21  of the release element  20 . The lug  21  moves so that it lies on the oblique surface  22  and, as the trigger element  18  is pushed farther in, slides along the oblique surface so that the release element  20  is pulled or pushed in the direction of the trigger element  18  due to the angled geometry until the release element  20  is in the released position. In the released position, a region with a wider cross-section of the sleeve of the release element  20  moves so that it lies opposite the locking arms  15  so that they move radially outwards out of the recesses  14  of the drive element  12  due to their forward bias and release the drive element  12 . The drive element can now act on the container  3  of active substance and the injection needle  5  and push them out beyond the front end of the housing parts  1  and  2 , resulting in an injection at the injection site.  
         [0055]     In this embodiment, triggering can only take place if the front sleeve  2  is pushed back into the rear sleeve  1  and the trigger button  18  is simultaneously depressed.  
         [0056]      FIGS. 11 and 12   a  to  12   c  illustrate another embodiment of an injection device in accordance with the present invention.  
         [0057]     The injector illustrated in longitudinal section in  FIG. 11  is designed for one-off use only and has a housing comprising a rear housing part  1  and a front housing part  2 , which can be moved towards one another from the position illustrated in  FIG. 11  against the force of a spring  109 . A container  3  filled with an active substance is accommodated in a housing sleeve  110  in the interior of the automatic injector. At its front end, the container  3  supports an injection needle  5  and can be displaced axially in the housing in conjunction with the housing sleeve  110  by the force of a drive spring  107  in order to inject the injection needle  5  in the skin of a patient. The injection needle  5  is not essential to the invention and the trigger mechanism described here may also be used with a needle-less automatic injector. A forward drive structure comprising a rod-shaped drive element  12  engages by means of its front end facing the injection needle  5  in the container  3 , where it is connected to a plunger  4 , the purpose of which is to dispense the active substance contained in the container  3 . Between the two ends of the drive element  12 , the latter is connected to a transmission part  114 , by means of which the force of the drive spring  107  is transmitted to the drive element  12 . At its rear end remote from the injection needle  5 , the drive element  12  has an annular groove  115 , the purpose of which will be described below.  
         [0058]     The injector is illustrated in the tensed and ready-to-use state in  FIG. 11 . Biased forwards in the direction towards the container  3  by the force of the compressed drive spring  107 , the drive element  12  is locked at its rear end by a release element  20 , which engages in the annular groove  115 . The release element  20  sits on a retaining plate  130  and is able to move transversely to the longitudinal axis of the automatic injector, against the force of a spring, although this is not illustrated. Accordingly, the drive element  12  projects with its rear end through an orifice  129  in this retaining plate  130 . A trigger element  18  is provided in the form of a cover, which fits onto the rear end of the automatic injector and which can be activated in its axial direction, against the force of a spring, although this is not illustrated. As clearly illustrated in  FIG. 11 , the trigger element  18  can not be operated when the automatic injector is in the illustrated operating position because it sits against the flat surface  138  of the release element  20 .  
         [0059]     In order to use the injector, the needle guard cap  132  which keeps the injection needle  5  sterile must first be removed. The automatic injector is then gripped by the rear housing part  1 , placed so that the front housing part  2  sits on the skin of the patient and pushed lightly, whereupon the front housing part  2  pushes against the force of the spring  109  relative to the rear housing part  1 . As this happens, a tongue  119  formed on the front housing part  2  moves into abutment with an oblique surface  122  of the release element  20  and moves the release element transversely to the longitudinal direction of the automatic injector into an intermediate position. The distance covered by the release element  20  is not enough to release the drive element  12 . However, an edge  139  on the release element  20  moves into the region of an oblique surface  140  provided on the trigger element  18  so that the trigger element  18  can now be activated in the axial direction of the automatic injector. Due to the contact of the oblique surface  140  with the edge  139 , the release element is moved further until it reaches its released position, in which it releases the drive element  12 , triggering an injection.  
         [0060]      FIGS. 12   a  to  12   c  illustrate a cross-section along line II-II indicated in  FIG. 11  showing how the release element  20  operates.  FIG. 12   a  illustrates the release element  20  in the same position as that shown in  FIG. 11 , namely in a locked position. An orifice  121  is provided in the release element  20 , which has the shape of a keyhole. In the locked position illustrated in  FIG. 12   a , the narrower part of the orifice  121  engages in the annular groove  115  of the drive element  12  and holds it locked as a result.  FIG. 12   b  illustrates the intermediate position in which the tongue  119  has pushed the release element  20  into its intermediate position. A head  141  of the drive element axially adjoining the annular groove  115  is now disposed at the transition between the narrow part and the wide part of the orifice  121  in the release element, as a result of which the drive element  12  is still held locked in its position biased by the spring  107 . Finally,  FIG. 12   c  shows the released position of the release element  20 . The wider part of the orifice  121  has been pushed into the region of the annular groove  115  so that the head  141  can now enter the wider part of the orifice  121  and the injection is triggered.  
         [0061]     The type of embodiment of the invention described above and illustrated in the drawings is based on a translating movement of the release element  20 . In another type of embodiment, the release element  20  can be moved in rotation. In an embodiment of this type, the tongue  119  is bevelled at its end directed towards the release element  20  so that the tongue  119  rotates the release element  20  about the longitudinal axis of the automatic injector when the housing parts  1 ,  2  are moved relative to one another. In this instance, the oblique surface  140  of the trigger element  18  is not oriented radially as illustrated in  FIG. 11  but in the circumferential direction. In this embodiment too, the release element has three positions and is moved by the tongue  119  from the locked position into the intermediate position and by the trigger element  18  from the intermediate position into the released position. The orifice in the release element and the head  141  of the drive element  12  in this embodiment are of a non-circular shape. In the locked position and in the intermediate position, the head does not fit through the orifice, whereas it fits through the orifice in the released position.  
         [0062]     When the housing parts are pushed towards one another, the release element can be moved from its locked position into an intermediate position in which it holds the drive element locked and the trigger element is capable of moving the release element out of the intermediate position into the released position.  
         [0063]     In view of the fact that neither the movement of the housing parts nor activation of the trigger element alone can lead to an injection being triggered, the system is particularly safe in terms of preventing unintentional triggering. In addition, this solution ensures that the automatic injector has to be placed on the skin of a patient before the trigger element can be activated.  
         [0064]     Embodiments of the present invention, including preferred embodiments, have been presented for the purpose of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms and steps disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments were chosen and described to provide the best illustration of the principles of the invention and the practical application thereof, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth they are fairly, legally, and equitably entitled.