Patent Publication Number: US-2021178077-A1

Title: Drive mechanism

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to European Patent Application No. 19215189.2 filed Dec. 11, 2019, which is herewith incorporated by reference into the present application. 
     TECHNICAL AREA 
     The present application relates to a drive mechanism for a medicament delivery device. 
     BACKGROUND 
     Medicament delivery devices such as auto-injectors, safety syringes, pen-injectors, inhalers, on-body devices are generally known for the self administration of a medicament by patients without formal medical training occurs. As just one example, those patients suffering from diabetes may require repeated injections of insulin. Other patients may require regular injections of other types of medicaments, such as a growth hormone or biological medicaments. Therefore, to facilitate for the patients, there is a demand to design medicament delivery devices with multiple automatic functions, predetermined dosage and assembled a medicament container. 
     To simplify the medicament delivery operation sequence, most of medicament delivery devices in the market are designed with multiple functions related to the medicament delivery operation can be achieved by one or two simple actions from end users. 
     The document FR 2767479 discloses an injection device comprising a syringe a rod configured to empty a medicament contained in the syringe. The rod comprises a tongue and a tab selectively engaging with the body of the syringe; the rod further comprises a set of racks configured to engage with a pinion. The injection device further comprises a pusher comprising another two sets of racks configured to rotate the pinion when the pusher is axially displaced, such that the rod will therefore be axially displaced. When the first set of racks of the pusher interacts with the pinion and the tongue of the rod engages with the body of the syringe, the axially displacement of the rod moves the syringe forward and protruding from a housing of the injection device; when the second set of racks of the pusher interacts with the pinion, the axial displacement of the pusher oppositely rotates the pinion, the rod is therefore moved rearward. Until the tab of the rod engages with the body of the syringe, the rod engages and therefore moves the syringe retracting together with the rearward movement of the rod. Such that the sequence of needle penetration on the injection site, medicament delivery and the needle retraction from the injection site can be all done by one axial displacement of the pusher that initiated by the end user. 
     However, the arrangement as disclosed in FR 2767479 requires both the rod and the pusher to be longitudinally arranged with sets of racks which causes the injection device to become longer. It also requires two radially opposite arranged sets of racks on the pusher which causes the pusher to become wider, so as the injection device will then become wider. Further, the injector in FR 2767479 uses the rod to move forward the medicament container, so there might be a risk that the medicament starts to be delivered before the medicament delivery member reaches a proper position. 
     SUMMARY 
     The aim of the present disclosure is to solve or at least mitigate the problems of the prior art. 
     In the present disclosure, when the term “distal direction” is used, this refers to the direction pointing away from the dose delivery site during use of the medicament delivery device. When the term “distal part/end” is used, this refers to the part/end of the delivery device, or the parts/ends of the members thereof, which under use of the medicament delivery device is/are located furthest away from the dose delivery site. Correspondingly, when the term “proximal direction” is used, this refers to the direction pointing towards the dose delivery site during use of the medicament delivery device. When the term “proximal part/end” is used, this refers to the part/end of the delivery device, or the parts/ends of the members thereof, which under use of the medicament delivery device is/are located closest to the dose delivery site. 
     Further, the terms “longitudinal”, “longitudinally”, “axially” and “axial” refer to a direction extending from the proximal end to the distal end and along the device or components thereof, typically in the direction of the longest extension of the device and/or component. 
     Similarly, the terms “transverse”, “transversal” and “transversally” refer to a direction generally perpendicular to the longitudinal direction. 
     An object of this disclosure is to provide a simple and reliable way of accidental activation prevention mechanism for a medicament delivery device. 
     According to an aspect of the disclosure, the object is achieved by a robust and reliable drive mechanism according to claim  1 . 
     There is hence provided a drive mechanism for a medicament delivery device, comprising: a housing having a proximal end and a distal end; a container carrier arranged within the housing and being axially movable in relation to the housing; a drive assembly partially arranged within the housing and being axially movable in relation to the housing; and wherein the drive assembly comprises a proximally extended rack arm; a cogwheel arranged within the housing and being rotatable but axially fixed in relation to the housing; wherein the cogwheel is selectively coupled to the rack arm through a tangential engagement with a first set of rack teeth or a second set of rack teeth which are arranged on the rack arm; wherein the first set of rack teeth or the second set of rack teeth forces the cogwheel to rotate when the drive assembly is axially moved towards the proximal end in relation to the housing; wherein the cogwheel further comprises a connecting member configured to connect to a counter connecting member which is fixed to the container carrier; such that a rotational movement of the cogwheel is converted into a linear movement of the container carrier. 
     According to one embodiment, the drive assembly is rotationally fixed in relation to the housing. 
     According to one embodiment, the container carrier is moved towards the proximal end in relation to the housing when the cog wheel is rotated by the first set of rack teeth and is moved towards the distal end in relation to the housing when the cog wheel is rotated by the second set of rack teeth while the drive assembly is moved towards the proximal end in relation to the housing. 
     According to one embodiment, the connecting member is a protruded pin perpendicularly arranged in relation to the edge of the cogwheel; wherein the counter connecting member is a traverse recess; and wherein the protruded pin is arranged in the traverse recess. 
     According to one embodiment, the first set of rack teeth is discrete proximally arranged in relation to the second set of rack teeth. 
     According to one embodiment, the drive assembly further comprises a user accessible pushing element; such that the proximally axial movement of the drive assembly is created by a manually proximal pushing action applied onto the pushing element by the user. 
     According to one embodiment, the drive assembly is axially biased in the proximal direction by a drive unit. 
     According to one embodiment, the first set of rack teeth and the second set of rack teeth are arranged to rotate the cogwheel in the same rotation direction. 
     According to one embodiment, the drive mechanism is included in a medicament delivery device. 
     According to one embodiment, the medicament delivery device comprises a medicament container arranged with a medicament delivery member on its proximal end and contained a medicament therein; wherein the medicament container is axially fixed to the container carrier; and wherein the medicament container comprises a plunger configured to be moved towards the proximal end to expel the contained medicament through the medicament delivery member. 
     According to one embodiment, the drive assembly further comprises a plunger holder associated with the stopper of the medicament container; wherein the proximal movement of the drive assembly moves the plunger towards the proximal end through the plunger holder. 
     According to one embodiment, the proximal movement of the drive assembly sequentially causes the first set of rack teeth rotate the cogwheel, the plunger moves proximally to expel the medicament and the second set of rack teeth rotate the cogwheel. 
     According to one embodiment, the rack arm, the user accessible pushing element and the plunger holder arranged on the drive assembly can be all formed as one single component, or as all separate components or some are integral together and some are separate components. 
     According to one embodiment, the medicament container can be a syringe arranged with a needle or a delivery nozzle; or a cartridge that can be attached with a needle or a delivery nozzle by an end user. 
     According to one embodiment, the medicament delivery device can be a safety syringe, an auto injector, a pen injector, an inhalation device, an on-body device or a medical sprayer. 
     Other aspects, features, and advantages will be apparent from the summary above, as well as from the description that follows, including the figures and the claims. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc.”, unless explicitly stated otherwise. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  displays a drive mechanism of the disclosure for a medicament delivery device. 
         FIG. 2  displays an exploded view of the drive mechanism of  FIG. 1 . 
         FIG. 3A  displays the front and back view of a cogwheel of the drive mechanism of  FIG. 1 . 
         FIG. 3B  displays the front and back view of a cogwheel of the drive mechanism of  FIG. 1 . 
         FIG. 4A  displays a housing of the drive mechanism of  FIG. 1 . 
         FIG. 4B  displays the housing arranged with the cogwheel of the drive mechanism of  FIG. 1 . 
         FIG. 5  displays the perspective view of the drive mechanism of  FIG. 1 . 
         FIG. 6  displays a side view of the drive mechanism of  FIG. 1 . arranged with the medicament container and without the housing. 
         FIG. 7  displays a container carrier arranged with the cogwheel of the drive mechanism of  FIG. 1 . 
         FIG. 8  displays a medicament container arranged with the container carrier of the drive mechanism of  FIG. 1 . 
         FIG. 9A  displays the operation sequence of the drive mechanism of  FIG. 1  without the housing. 
         FIG. 9B  displays the operation sequence of the drive mechanism of  FIG. 1  without the housing. 
         FIG. 9C  displays the operation sequence of the drive mechanism of  FIG. 1  without the housing. 
         FIG. 10A  displays a plunger rod of the drive mechanism of  FIG. 1 . 
         FIG. 10B  displays a plunger rod of the drive mechanism of  FIG. 1 . 
         FIG. 11  displays a drive assembly of the drive mechanism of  FIG. 1  and the plunger rod. 
         FIG. 12A  displays the operation sequence of the drive mechanism of  FIG. 1 . 
         FIG. 12B  displays the operation sequence of the drive mechanism of  FIG. 1 . 
         FIG. 12C  displays the operation sequence of the drive mechanism of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. 
       FIG. 1  illustrates a drive mechanism for a medicament delivery device comprising: a housing  1  having a proximal end and a distal end; and a drive assembly  2  partially arranged within the housing  1 . The housing  1  extends along a longitudinal axis L from the proximal end to the distal end. The drive assembly  2  is axially movable in relation to the housing  1  and along the longitudinal axis L. As shown in  FIG. 2 , the drive assembly  2  comprises a proximally extended rack arm  21 , a user accessible pushing element  22  and a plunger holder  23 . The proximally extended rack arm  21  comprises a first set of rack teeth  21   a  discrete proximally arranged in relation to a second set of rack teeth  21   b . The drive mechanism further comprises a container carrier  3  and a cogwheel  4 . 
       FIG. 3A-3B  illustrate a front surface  42  and a back surface  43  of the cogwheel  4 . The cogwheel  4  comprises a fixture  41  configured to axially fix but rotatably attached the cogwheel  4  to the housing  1 , the fixture can be a central through opening or a backward protruded pin. The front surface  42  is arranged with a connecting member  44 , preferably, it can be a front protruded pin radial inwardly protruding towards a central cavity of the housing  1 . The back surface  43  of the cogwheel  4  is circularly arranged with plurality cogs  45 . Each cog of the plurality cogs  45  comprises a thickness at least partially occupied the space defined by the back surface  43  of the cogwheel and the inner surface of the housing  1 . Each cog of the plurality cogs  45  further comprises an engaging end  45   a  and a connecting end  45   b . The connecting end  45   b  of each cog of the plurality cogs  45  is configured to couple to each other in a central portion of the back surface  43  of the cogwheel  4 . The engaging end  45   a  of each cog of the plurality cogs  45  is configured to radial outwardly extend towards the outer edge of the back surface  43  of the cogwheel  4 . The cogwheel  4  is selectively coupled to the rack arm  21  through a tangential engagement between the plurality cogs  45 , more specifically the engaging end  45   a  of each cog of the plurality cogs  45 , with the first set of rack teeth  21   a  or the second set of rack teeth  21   b.    
     Further, the cogwheel  4  may optionally comprise a smooth portion  46 . The smooth portion  46  is arranged between two cogs of the plurality cogs  45  and is configured to define a start and an end rotation position of the cogwheel  4 , such that the cogwheel  4  is configured to be rotated by the rack arm  21  from one cog adjacent to the smooth portion  46 , through the rest of the plurality cogs  45  to another cog adjacent to the smooth portion  46 . 
       FIG. 4A-4B  illustrate the attachment between the housing  1  and the cogwheel  4 . The housing  1  comprises a counter fixture  11 , configured to engage with the fixture  41  of the cogwheel  4 , preferably, the counter fixture  11  is an inwardly radial extending protrusion, as shown in  FIG. 4A . When the cogwheel  4  is attached to the housing  1  as shown in the  FIG. 4B , the front surface  42  of the cogwheel  4  faces the central cavity of the housing  1  which is configured to receive a medicament container  5 . 
     The rack arm  21  is configured to extend between the housing  1  and the back surface  43  of the cogwheel, as shown in  FIG. 5 . The first set of rack teeth  21   a  or the second set of rack teeth  21   b  are selectively engaged with the plurality cogs  45 , such that an axial movement of the drive assembly  2  in relation to the housing  1  causes the first set of rack teeth  21   a  or the second set of rack teeth  21   b  to rotate the cogwheel  4  when the first set of rack teeth  21   a  or the second set of rack teeth  21   b  are engaged with the plurality cogs  45 , as shown in  FIG. 6 . 
     The connecting member  44  of the cogwheel  4  is configured to connect to a counter connecting member  32 , which is arranged on the container carrier  3 , as shown in  FIG. 7 , preferably, the counter connecting member  32  is a transverse recess in relation to the longitudinal axis L. The container carrier  3  further comprises a retainer  31 , which is configured to receive and hold a flange  51  of the medicament container  5 , as shown in  FIG. 8 . The housing  1  may optionally comprise an inner support  12  and an inner wall  13 , as shown in  FIG. 4A . The inner wall  13  is configured to prevent the radial movement and the rotation movement of the container carrier  3 . The inner support  12  is radial inwardly extending from the inner wall towards the central cavity of the housing  1 . The inner support  12  defines a central passage with a dimension that is larger than the radial dimension of the medicament container but smaller than the radial dimension of the container carrier  3 , such that the medicament container  5  is able to at least partially pass through the central passage, and the container carrier  3  is configured to be supported by the inner support  12  at its proximal position. 
     It should be noted that, alternatively, the connecting member  44  can be a transverse recess or a transverse curve recess in relation to the longitudinal axis L; and the counter connecting member  32  can be a radial outwardly protruding pin configured to engage with the transverse recess or the transverse curve recess of the connecting member  44 . Further, the retainer  31  can be arranged to receive the flange of the medicament container  5 , a distal portion of the medicament container or to receive a tubular main body of the medicament container  5 . 
     Since the counter connecting member  32  is the transverse recess, when the cogwheel  4  rotates, the connecting member  44  will gradually press on an edge of the transverse recess, such that the container carrier  3  is moved axially by the connecting member  44 . A rotational movement of the cogwheel  4  is therefore converted into a linear movement of the container carrier  3 . 
     The operation sequence of the drive mechanism of the disclosure is shown in  FIG. 9A-9C . The dash line acts as a reference that indicates the position of the fixture  41  of the cogwheel  4  in  FIG. 9A-9C .  FIG. 9A  illustrates the medicament container  5  in an axial initial position. To move the medicament container  5  in the proximal direction in relation to the housing  1 , the drive assembly  2  is axially moved to the proximal direction in relation to the housing  1 . When the first set of rack teeth  21   a  on the rack arm  21  is moved into an engagement with the plurality cogs  45 , the axial movement of the first set of rack teeth  21   a  rotates the cogwheel  4 . Due to the connection between the connecting member  44  of the cogwheel  4  and the counter connecting member  32  of the container carrier  3 , the rotation movement of the cogwheel  4  turns into the axial movement of the container carrier  3  and the medicament container  5 , such that the medicament container is moved to its proximal position as shown in  FIG. 9B . The axial moving distance of the medicament container  5  may be defined by the diameter of the cogwheel  4  or the diameter of the circular moving path of the connecting member  44  associated with the inner support  12  of the housing  1 . When the medicament container  5  has been moved into its proximal position, a medicament delivery operation may start. During the medicament delivery operation, the rack arm  21  is decoupled from the cogwheel  4  as none of the first set of rack teeth  21   a  or the second set of rack teeth  21   b  is engaged with the plurality cogs  45 ; the rack arm  21  is therefore prevented to rotate the cogwheel  4  with its axial movement. 
     After the medicament delivery operation is completed, the continuously axial movement of the drive assembly  2  causes the second set of rack teeth  21   b  to rotate the cogwheel  4 . The rotation direction of the cogwheel  4  caused by the first set of rack teeth  21   a  is preferably the same as the rotation direction of the cogwheel  4  that is caused by the second set of rack teeth  21   b ; therefore, the cogwheel  4  would be rotated about one complete circle by the first set of rack teeth  21   a  and the second set of rack teeth  21   b . The connecting member  44  of the cogwheel  4  is thereby rotated with the cogwheel  4  from its most distal position to its most proximal position by the axial movement of first set of rack teeth  21   a ; and rotated with the cogwheel  4  from its most proximal position back to its most distal position by the axial movement of second set of tack teeth  21   b . Due to the connection between the connecting member  44  and the counter connecting member  32  as mentioned above, the rotation of the cogwheel  4  by the second set of rack teeth  21   b  axially moved the container carrier  3  so as the medicament container  5  back to its initial position, as shown in  FIG. 9C  at the end of the medicament delivery operation. 
     The drive mechanism may further comprises a plunger rod  6 , as shown in  FIG. 10A . The plunger rod  6  is configured to apply an axial biasing force on the stopper of the medicament container  5  in the proximal direction in relation to the medicament container  5 . Such that the medicament contained within the medicament container  5  can thereby be delivered to the user of the medicament delivery device. 
     The drive assembly  2  may further comprises a plunger holder  23 , configured to transfer the axial force applied on the drive assembly  2  to the stopper of the medicament container  5 , the stopper of the medicament container  5  is thereby being axially moved toward the proximal direction in relation to the medicament container  5  during the medicament delivery operation of the medicament delivery device. Such arrangement is achieved by a releasable engagement between the plunger holder  23  and the plunger rod  6 . 
     The plunger holder  23  is configured to engage with the plunger rod  6  in the initial position of the medicament delivery device and during the medicament delivery operation of the medicament delivery device. During the medicament delivery operation, the drive assembly  2  is moved axially towards the proximal direction of the housing  1 . The force applied on the drive assembly  2  transfer to the stopper of the medicament container, therefore proximally moves the stopper of the medicament container to deliver the contained medicament. Once the stopper of the medicament container  5  has been moved into its end position, the plunger rod  6  is disengaged from the plunger holder  23 , such that the drive assembly  2  can continuously move to the proximal direction in relation to the housing  1  without transferring the force to the stopper of the medicament container. The continuously proximal movement of the drive assembly  2  moves the container carrier  3  and the medicament container  5  back to its initial position by the mechanism as mentioned above. Such engagement and disengagement between the plunger rod  6  and the plunger holder  23  can be achieved by an engaging element  61  on the plunger rod  6  and a counter engaging element  23   a  on the plunger holder  23 , as shown in  FIG. 11 ; and by a guide track  62  on the plunger rod and a guide pin on the inner surface of the container carrier  3  (not shown); and will be explained in detail later. 
     The plunger rod  6  comprises a hollow and longitudinally extending central cavity in which the plunger holder  23  is partially positioned. The counter engaging element  23   a  is configured to releasably engage with the engaging element  61  of the plunger rod  6  from the interior of the plunger rod  6 . As shown in  FIG. 10B , the engaging element  61 , preferably a recess, comprises a proximal end edge  61   a  configured to axially align and engage with the counter engaging element  23   a  when the counter engaging element  23   a  is engaged with the counter engaging element  23   a ; and a disengaging edge  61   b  angularly offsets in relation to the proximal end edge  61   a . Preferably, the counter engaging element  23   a  is a radially outwards extending protruding rib arranged on the outer surface of the plunger holder  23 . The proximal end edge  61   a  is a radially inwards extending ledge. The radially inwards extending length of the disengaging edge  61   b  is less than the radially inwards extending length of proximal end edge  61   a.    
     The counter engaging element  23   a  comprises a radially outwards extending length which is overlapping the radially inwards extending length of the proximal end edge  61   a ; and is free from overlapping with the radially inwards extending length of the disengaging edge  61   b . Therefore, once the counter engaging element  23   a  is aligned with the proximal end edge  61   a , the counter engaging element  23   a  is able to rest on the proximal end edge  61   a , such that the plunger holder  23  and the plunger rod  6  is releasably engaged and are able to move together in the proximal direction in relation to the housing  1 . Once the counter engaging element  23   a  is aligned with the disengaging edge  61   b , the counter engaging element  23   a  will be free from being axially supported in the proximal direction of the plunger rod  6 , such that the plunger holder  23  is axially movable in relation to the plunger rod  6 . 
     The guide track  62  on the plunger rod  6  comprises a first linear groove  62   a , a second linear groove  62   c , which is distally positioned and linearly offset in relation to the first linear groove  62   a , and a ramp turning groove  62   b  connecting the first linear groove  62   a  and the second linear groove  62   c.    
     It should be noted that, alternatively, the second linear groove  62   c  can be removed and the ramp turning groove  62   b  can extend to the distal end edge of the outer surface of the plunger rod  6 . 
     In the initial position of the medicament delivery device, which is the position before a medicament delivery operation is initiated and the medicament delivery member is hidden within the housing  1 , the guide pin on the inner surface of the container carrier  3  is positioned within the first linear groove  62   a  of the plunger rod  6 , and the counter engaging element  23   a  of the plunger holder  23  is rest on the proximal end edge  61   a  of the plunger rod  6 , such that the proximally axially movement of the drive assembly  2  also causes the plunger rod  6  to move axially in the proximal direction in relation to the housing  1 , as shown in  FIG. 12A . To initiate the whole operation sequence of the medicament delivery device, the user needs to aim the proximal end of the housing  1  to the medicament delivery site, and apply an axial proximal force on the pushing element  22 . The axial proximal force applied on the pushing element  22  turns into the axial movement of the drive assembly  2 . With the proximal axial movement of the drive assembly  2 , the rack arm  21  of the drive assembly  2  rotates the cogwheel  4  through the engagement between the first set of rack teeth  21   a  and the plurality cogs  45  of the cogwheel  4  as mentioned above, the container carrier  3  and the medicament container  5  are also moved towards the proximal direction in relation to the housing  1 , since both the plunger rod  6  and the medicament container  5  are axially moved in the proximal direction in relation to the housing  1 , the plunger rod  6  is free from applying the axial biasing force on the stopper of the medicament container  5 . Once the medicament container  5  and the container carrier  3  reaches their most proximal position, which may be defined by the diameter of the cogwheel or the circular moving path of the connecting member  44  associated with the inner support  12  of the housing  1 , a medicament delivery member  52  is properly exposed, as shown in  FIG. 12B . The medicament delivery device now is ready for initiating the medicament delivery operation. Since the counter connecting member  32  of the container carrier  3  is connected to the connecting member  44 , once the connecting member  44  reaches to its most proximal position, and/or the container carrier  3  is supported by the inner support  12  of the housing, the further proximal movement of the container carrier  3  is prevented. 
     Since the container carrier  3  and the medicament container  5  is no longer movable in the proximal direction in relation to the housing  1 , the continuous axial movement of the drive assembly  2  and the plunger rod  6  in the proximal direction in relation to the housing  1  causes the plunger rod  6  to apply an axial biasing force on the stopper of the medicament container  5  and moves the stopper of the medicament container  5  towards the proximal direction in relation to the medicament container  5 . The medicament contained within the medicament container  5  is thereby delivered to the user of the medicament delivery device. 
     The axial travel length of the guide pin on the first linear groove  62   a  and the ramp turning groove  62   b  may be designed depending on the volume of the contained medicament The further axial movement of the drive assembly  2  causes the plunger rod  6  to rotate when the guide pin of the container carrier  3  passes ramp turning groove  62   b , such that the disengaging edge  61   b  is aligned with counter engaging element  23   a , allowing the plunger holder  23  to disengage from the plunger rod  6 . 
     Once the plunger holder  23  is disengaged from the plunger rod  6 , the drive assembly  2  continuously moves to the proximal direction in relation to the housing  1  without axially moving the plunger rod  6 . The axial continuously movement of the drive assembly  2  and the rack arm  21  rotates the cogwheel  4  through the engagement between the second set of rack teeth  21   b  and the plurality cogs  45  of the cogwheel  4 , since the counter connecting member  32  of the container carrier  3  is connected to the connecting member  44 , when the connecting member  44  rotates together with the cogwheel  4  from its most proximal position to its most distal position, the connecting member  44  moves the container carrier  3  and the medicament container  5  back to the initial position. As shown in  FIG. 12C , the medicament delivery member is thereby moved back into the housing  1  with the medicament container  5  and the container carrier  3 , such that access to the medicament delivery member  52  by the user is prevented and thereby the injury or infection caused by accessing the used medicament delivery member can be prevented. When the pushing element  22  moved to couple with the housing  1  by the user, the user is aware that the whole operation sequence of the medicament delivery device is completed and the medicament delivery device can be removed from the medicament delivery site. 
     It should be noted that, the drive assembly can also be used with a medicament container with a plunger and a plunger rod. In this embodiment, the plunger rod  6  of the drive mechanism can be rearranged with a larger diameter and a shorter axial length, such that the plunger rod  6  of the drive mechanism can be distance from the stopper of the medicament container. The plunger rod of the medicament container can be arranged within the plunger rod  6  of the drive mechanism, and axially fixed to each other. 
     When the second set of rack teeth  21   b  reach to the smooth portion  46  of the cogwheel, the second set of rack teeth  21   b  can no longer rotate the cogwheel  4 . Since both second set of rack teeth  21   b  or the first set of rack teeth  21   a  can now only pass through the smooth portion  46  of the cogwheel, the backward or forward linear movement of the rack arm  21  can no longer cause the rotation of the cogwheel, the rack arm  21  is thereby decoupled from the cogwheel. Such that reusing of the medicament delivery device is prevented. Further, the drive assembly  2  may further comprises a final position locking member configured to interact with a counter final position locking member arranged on the inner surface of the housing  1 , such that the drive assembly  2  can be axially fixed to the housing  1  with the distal surface of the pushing element  22  exposed from the housing  1 , as shown in  FIG. 12C . The engagement between the final position locking member and the counter final position locking member can be arranged as snap fitting structure, form fitting structure or force fitting structure, to prevent the medicament delivery device being reused. 
     It should be noted that, the smooth portion  46  of the cogwheel  4  and the final position locking mechanism performed by the final position locking member and the counter final position locking member can be both implemented in the medicament delivery device or only using one of them as the reusing prevention mechanism in the medicament delivery device. 
     It should be noted that, the drive assembly can be arranged to associate with a power source, such as spring, gas canister or electric motor. In this embodiment, the pushing element  22  can completely arranged within the housing  1 , such that the user cannot access to the pushing element  22 ; and the pushing element  22  be connected to the power source. Further, the rack arm  21 , the user accessible pushing element  22  and the plunger holder  23  arranged on the drive assembly  2  can be all formed as one single component, or as all separate components or some are integral together and some are separate components. 
     The inventive concept has been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.