references to the device in the following detailed description are intended to refer to the device as referenced in the appended figures and not to when the device is in a use state . furthermore , the figures are intended to be schematic representations to highlight relevant functionality of the present invention and therefore unnecessary structures have been omitted from the device for clarity . the relative dimensions of the device are also illustratory only . reference to ‘ distal ’ and ‘ proximal ’ are intended to refer to the end of the device where medicament delivery occurs and the opposite end pointing away from the delivery site respectfully . the medicament delivery device 1 illustrated in fig1 comprises a housing 10 having a proximal end 10 a and a distal end 10 b . at the distal end 10 b , the housing is shaped to receive a removable end cap or cover ( not shown ). this end cap and the housing 10 ( at its proximal end ) are shaped to provide a form fit connection so that once the cap is slid onto the distal end 10 b of the housing 10 , the frictional fit between the cap and the housing 10 prevents the cap from inadvertently falling off the housing 10 . it will be understood that in other embodiments ( not shown ) other means of releasably securing the cap to the housing such as snap - fit may be employed . the interior surface of the cap and the outer surface of the housing 10 at its proximal end 10 b are shaped such that there is only one possible configuration in which the cap properly fits onto the distal end 10 b of the housing 10 . such an arrangement is preferable because it provides certainty in the alignment of components of the cap with components of the housing 10 , as will be explained below . the housing 10 contains a micro - processor control unit , pcb , an electro - mechanical drive train , a battery , and at least one medicament reservoir . a cartridge holder 14 can be removably attached to the housing 10 and may contain one or more cartridges of medicament . the cartridge holder 14 is configured so as allow the replacement of the medicament cartridges as necessary . the medicament delivery device 1 can be used to administer a computed dose of a medicament ( or medicaments ) through a needle assembly , such as a double ended needle assembly . it will be understood that the cap and housing arrangement described is equally applicable to needleless jet injectors . a control panel region is provided on one major face 16 of the housing 10 and comprises a digital oled display 18 towards the distal end 10 a of the housing 10 along with a plurality of human interface elements ( buttons 20 in the embodiment shown ) that can be manipulated by a user to set and inject a medicament dose . it will be understood that in other embodiments ( not shown ) different display technology such as lcd displays can be used . the buttons 20 also allow navigation through menu structures displayed on the oled display 18 . an eject button 21 described in greater detail below is provided at the distal end 10 b of the device 1 . a dose button 22 is provided in an end face of the housing 10 at its proximal end 10 a . in use , when the device is turned on , the digital display 18 shown in fig1 illuminates and provides the user certain device information , preferably information relating to the medicaments contained within the cartridge holder 14 . for example , the user is provided with certain information relating to both the contents of the cartridge and previous dose history . at the distal end 10 b of the housing is provided a dispense interface 30 . the dispense interface 30 is configured to receive a needle assembly or hub ( not shown ) via a screw - thread connector 31 . this needle hub can be configured to allow a dose dispenser , such as a conventional pen type injection needle assembly , to be removably mounted to the housing 10 . it will be understood that the attachment between the dispense interface 30 and a needle hub is preferably a screw fit to allow standard ‘ type a ’ needles to be fitted to the dispense interface 30 , although other attachment mechanisms as known in the art , such as luer lock attachments may be used in other embodiments ( not shown ). the dispense interface 30 is shown in greater detail in fig2 . the dispense interface 30 has spaced apart front and rear sidewalls 32 joined by spaced apart end sidewalls 34 to define a housing . the distal end 35 of the dispense interface 30 is closed save for an orifice or septum through the threaded connector 31 . the proximal end 36 of the dispense interface 30 is open and the sidewalls 32 , 34 define a cavity 38 . the front and rear sidewalls 32 are curved to define a pair of medicament cartridge receiving slots 40 within the cavity 38 . each of the front and rear sidewalls 32 has a cut away midsection 42 . received within the housing is an inner assembly 50 described in more detail with reference to fig3 . although the present embodiment shows two cartridge receiving slots 40 , embodiments may include a single receiving slot or multiple receiving slots . furthermore , in the present embodiment , the dispense interface 30 is symmetrical and therefore can receive the bezel of a cartridge in either receiving slot 40 . however , embodiments may provide size discrimination between cartridges to be made by , for example , only allowing a bezel of a particular size to be received within a specific cartridge receiving slot 40 . fig3 shows the inner assembly 50 of the dispense interface 30 . a platform 52 defines a base of the dispense interface housing and a seating surface for medicament cartridges in use . at each side 54 of the platform 52 a needle ( not shown ) extends upwardly into the dispense interface housing 32 , 34 , which needles pierce the septa of the medicament cartridges when the dispense interface 30 is mounted on the device housing 10 . below the platform 52 and mounted within the dispense interface housing 32 , 34 beneath its base is a valve assembly 56 comprising a pair of diaphragm valves 58 . mounted below the valves 58 is a septum 60 which is housed within the threaded connector 31 . it will be understood that when mounted on the device housing 10 , a valved flowpath exists from the medicament cartridge through the double ended needles , through the valve assembly and thereafter into an attached needle hub through the septum in the needle connector . extending upwardly from the platform 52 are a pair of spaced apart retaining arms 62 in the form of flexible tabs . a pair of spaced apart barbs 64 are integrally formed at the free ends of the tabs 62 . when mounted in the dispense interface housing 32 , 34 the tabs 62 are located within the cut outs 42 in the front and rear sidewalls 32 with the barbs 64 pointing away from the cavity 38 and extending above the sidewalls 32 , 34 . the barbs 64 have an outwardly tapering front surface 66 , a flat mid surface 68 and a rear surface 70 perpendicular to the tab 62 itself . the barbed tongues 62 , 64 constitute part of the attachment and release mechanism of the dispense interface 30 as will be described below . fig4 a shows a partial skeleton view of the dispense interface 30 both prior to connection with the distal end 10 b of the device 1 and after disconnection with the device 1 in its partially engaged position . as the dispense interface 30 is placed onto the device , the barbs 64 slide over inwardly facing main surfaces of a pair of mounting plates 72 a , 72 b . as the user continues to press the dispense interface 30 into the device , the interface 30 via hammer 74 compresses spring 76 until the fully operative engaged position of fig4 b is reached . as shown in fig4 b , one of the mounting plates 72 a has a rear blocking surface 78 which is perpendicular to its main surface , whereas the other mounting plate 72 b has a chamfered rear surface 80 . in the fully engaged position , the barbs 64 pass beyond the mounting surface 72 and flex outwardly ( due to the inherent flexibility of the tabs ). although biased away from the housing 10 by the spring 76 the dispense interface 30 is locked into its operative position by virtue of engagement of one pair of barbs 64 on one of the tabs 62 with the rear blocking surface 78 of the mounting plate 72 . the remaining pair of barbs 64 on the other tabs 62 are adjacent the chamfered rear surface 80 of the other mounting plate 72 b but are not locked therewith . the importance of this will become clear in the following paragraph . it will be understood that in the case of a symmetrical dispense interface 30 , the dispense interface can successfully be engaged with the housing of the device 1 in two orientations . to unlock the dispense interface 30 from the distal end 10 b of the device 1 , the user presses the eject button 21 on the lower portion of the front face 16 of the device 1 . the eject button 21 , via a peg ( not shown ) extending from the rear of the eject button 21 through opening 82 presses onto the tab 62 whose barbs 64 are engaged with the blocking surface 78 of the mounting plate 72 . by depressing the tab 62 , the rear surface disengages the blocking surface 78 and since the other barbs 64 are unconstrained by the chamfered surface 80 of the other mounting plate 72 b , the action of the compressed spring 76 now acts against the dispense interface 30 via the hammer 74 to force the dispense interface 30 away from the housing 10 . in this position the dispense interface 30 is partially engaged with respect to the housing 10 . the dispense interface 30 is prevented from fully disengaging with the device 10 due to the frictional engagement of the flat surfaces 68 of the barbs 64 with the mounting surface 72 . it will be understood to the skilled person that the biasing of the spring 76 and the frictional forces can be balanced by changing one or more of the strength of the spring 76 , the frictional coefficient of the barbs 64 and mounting plate 72 main surfaces , the area of contact between the barbs 64 and the mounting plate main surfaces or the flexibility of the tabs 62 . this frictional force holding the dispense interface 30 in the partially engaged position with respect to the housing 1 is then low enough to allow a user to easily and manually remove the dispense interface 30 from the device . furthermore , the dispense interface 30 release mechanism disengages the needles mounted within the dispense interface 30 from the cartridges mounted within the device 1 , breaking the fluid communication between the dispense interface 30 and the medicament contained within the device 1 when in the partially engaged position shown in fig4 b . by ensuring that the dispense interface 30 is not in fluid communication with the medicaments stored within the device 1 the risk of loss of medicament is eliminated . furthermore , the device is able to perform procedures that rely on the lack of fluid engagement such as detection of the position of the bung of the cartridges within the device without risk of loss of medicament or potential under or over dosing . embodiments of the present invention may include the use of the packaging of the dispense interface 30 in the engagement and disengagement process . for example , with a dispense interface 30 not attached to the distal end 10 b of the device 1 , a user may present the distal end of the device to the packaging containing the dispense interface 30 . it is envisaged that the dispense interface 30 is held within custom packaging , for example a plastic holder ( not shown ) and is open at the top of the housing such that the cavities 38 of the dispense interface 30 are accessible by the device 1 . a tear strip may be used to prevent contamination of the dispense interface 30 prior to use . in such embodiments , as the distal end 10 b of the device 1 is presented to the dispense interface 30 , the dispense interface 30 is received within the distal end 10 b of the device 1 such as shown in fig4 a . by continuing to bring the device 1 and the dispense interface 30 together , the dispense interface 30 engages with the device via the engagement of one pair of barbs 64 on one of the tabs 62 with the rear blocking surface 78 of the mounting plate 72 as described above to the position shown in fig4 b above . similarly , the dispense interface 30 may be removed from the device as described above , or in further alternative embodiments , the packaging of the dispense interface may unlock / disengage the dispense interface 30 from the device 1 automatically , for example by actuating the eject button of the device . alternatively , other unlock release mechanisms can be used such as a spring loaded push fit .
a medicament delivery device comprises a housing having a longitudinal axis , a medicament delivery mechanism within the housing , a dispense interface disengagement actuator and a detachable dispense interface . the interface is moveable between a first operative position in which the dispense interface is securely engaged and at least partially contained within the housing , and a second non - operative position in which the dispense interface is partially engaged and at least partially extending from the housing such that it can be detached from the housing manually . the travel of the dispense interface from the first position to the second position is along the longitudinal axis in a direction away from the housing and the movement from the first to the second position is actuated by the dispense interface disengagement actuator .