fig1 a and 1 b show an injection device 110 , having an injection device housing 112 . the injection device 110 has a removable cap 190 . with the cap 190 removed , as shown in fig2 , the end of the housing 112 can be seen to have an exit aperture 128 , through which the end of a sleeve 119 can emerge . the injection device 110 also has a trigger 180 . as shown in fig2 a and 2 b , the housing 112 contains a hypodermic syringe 114 of conventional type , including a syringe body 116 defining a reservoir and terminating at one end in a hypodermic needle ( not shown ) and at the other in a flange 120 . the hypodermic needle is covered by a needle shield 118 . the needle shield 118 is fixed inside the cap 190 . the syringe body 116 is of substantially constant diameter along the length of the reservoir , and is of significantly smaller diameter close to the end of the syringe which terminates in the hypodermic needle . a drive element 134 ( syringe piston ) acts through the bung of the syringe to discharge the contents of the syringe 114 through the needle 118 . this drive element 134 constrains a drug ( contained in the syringe ) to be administered within the reservoir defined by syringe body 116 . whilst the syringe illustrated is of hypodermic type , this need not necessarily be so . transcutaneous or ballistic dermal and subcutaneous syringes may also be used with the injection device of the present invention . the housing 112 comprises a case nose 113 which is integrally formed with a sleeve 160 . the sleeve 160 surrounds a syringe carrier 150 which is moveable within the sleeve 160 along its longitudinal axis . as illustrated , the syringe 114 is housed within the syringe carrier 150 . the syringe carrier 150 has a first end 151 and a reduced diameter section 151 a . the section 151 a of the syringe carrier supports the end of the syringe 114 nearest to the hypodermic needle . the syringe carrier 150 comprises a bearing surface 153 on which an end of a return spring 126 is located . the return spring 126 , via the syringe carrier 150 biases the syringe 114 from an extended position in which the needle 118 extends from the aperture 128 in the housing 112 to a retracted position in which the needle 118 is contained within the housing 112 . if the syringe were to fail or break , the syringe carrier 150 , which substantially surrounds the syringe 114 along its length , would contain the broken pieces of syringe and reduce the likelihood of them from escaping from the injection device . the housing 112 also includes a trigger 180 , and a drive which here takes the form of a compression drive spring 130 . drive from the drive spring 130 is transmitted via a multi - component drive ( 118 a ) to the drive element 134 of the syringe 114 to advance the syringe from its retracted position to its extended position and discharge its contents through the needle 118 . the drive accomplishes this task by acting directly on the syringe 114 and the drug in the syringe . static friction between the drive element 134 and the syringe body 116 initially ensures that both the syringe 114 and bung advance together , until the return spring 126 bottoms out when the bearing surface 153 on the syringe carrier 150 comes up against an opposing bearing surface 161 on the sleeve 160 . the trigger 180 is provided on the housing 112 remote from the exit aperture 128 . the trigger , when operated , serves to decouple a drive sleeve 131 on which the drive spring 130 acts from the housing 112 , allowing it to move relative to the housing 112 under the influence of the drive spring 130 . the operation of the device is then as follows . the cap 190 can be removed by a user with a twist and pull action or simply by pulling the cap . the exact action required depends on the type of syringe 114 being used . in one embodiment , the syringe 114 will comprise a rigid needle shield 118 containing a rubber boot ( not shown ) in which the needle is contained . in this embodiment , the needle shield 118 simply needs to be removed by pulling the cap 190 along the longitudinal axis of the device 110 . in an alternative embodiment , the syringe 114 comprises a plastic needle shield 118 which is held to the syringe 114 by a frangible connection . in order to break the frangible connection , the cap 190 must be first twisted and then pulled along the longitudinal axis of the device 110 . a guiding element 191 on the end cap 113 serves to guide the removal of the cap 190 in the way that is required to remove the needle shield 118 . since the needle shield 118 is held inside the cap 190 , removal of the cap 190 , causes the needle shield to be removed , thereby exposing the needle of the syringe 114 within the injection device . at this time , the needle is still enclosed by the housing 112 . initially , the syringe carrier 150 and syringe 114 , are prevented from movement by a resilient latch member 162 . by moving the sleeve 119 in a direction into the housing 112 , the latch member 162 moves outwards disengaging from the syringe carrier 150 . once the latch member 162 has disengaged from the syringe carrier 150 , the syringe 114 and syringe carrier 150 are free to move . the trigger 180 can then be depressed by a user and the drive spring 130 is released . the drive spring 130 moves the drive sleeve 131 , the piston 134 and , by virtue of static friction and hydrostatic forces acting through the drug to be administered , moves the syringe body 114 against the action of the return spring 126 . the syringe body 114 moves the syringe carrier 150 , which compresses the return spring 126 . the hypodermic needle 118 emerges from the exit aperture 128 of the housing 112 . this continues until the return spring 126 bottoms out or the syringe body 116 meets some other obstruction ( not shown ) that retards its motion . because the static friction between the second drive element 134 and the syringe body 116 and the hydrostatic forces acting through the drug 124 to be administered are not sufficient to resist the full drive force developed by the drive spring 130 , at this point the second drive element 134 begins to move within the syringe body 116 and the drug begins to be discharged . one embodiment of the present invention is depicted in fig3 a and 3 b . the syringe carrier is shown with two arms 172 extending from a second end 158 of the syringe carrier 150 , opposite its first end 151 . as shown in fig3 b , the syringe 114 has a flange 120 on its rear end attached to the syringe body 116 . an underside 175 of the flange 120 is in juxtaposition with one or more supporting lugs 170 located on the arms 172 , wherein each supporting lug provides a supporting interface for the underside 175 of the flange 120 to prevent forward movement of the syringe during device operation . each arm 172 also includes means for restricting movement of the syringe relative to the syringe carrier in a direction from the first end of the syringe carrier to the second end of the syringe carrier which are restraining lugs 172 which are dimensioned and shaped with a restraining surface 173 to prevent movement in a rearwards direction r ( i . e . movement in a direction from the first end 151 to the second end 158 of the syringe carrier 150 ) of the syringe 114 relative to the syringe carrier 150 . each restraining surface 173 prevents rearward movement by interfacing with an upper surface 176 of the flange . following insertion of the syringe 114 into the syringe carrier 150 during manufacture , there may be a nominal separation between the restraining surface 173 and the upper surface 176 of the flange 120 . this nominal separation allows some movement of the syringe 114 in a rearwards direction r to buffer the impact of the discharge nozzle as it becomes fully extended during use , thereby reducing pain to a user of the device . during manufacture of the device 110 , the syringe 114 is inserted into the syringe carrier 150 by first inserting its discharge nozzle through the opening at the second end 158 of the syringe carrier 150 . the underside 175 of the flange 120 is nominally prevented from passing over the lugs 171 . the lugs 171 are sloped on their top surface which means that , as the underside 175 of the flange 120 is pushed over the lugs 171 , the arms 172 move apart so that , eventually , the lugs 171 no longer hinder movement of the syringe 114 into the syringe carrier 150 and the restraining surface 173 of the lugs hinders rearward movement of the syringe 114 in the syringe carrier 150 . an alternative embodiment of the invention is shown in fig4 a and 4 b . in this embodiment , the syringe carrier 150 includes arms 172 and supporting lugs 170 as described above . the syringe carrier also includes a release mechanism 250 that acts to release the drive sleeve 131 from the piston 134 when the drive sleeve 131 moves over the release mechanism 250 when the syringe 114 reaches its extended position . in this way , the force of the drive spring 130 on the syringe 114 is released when it reaches its extended position so that the syringe 114 can then be retracted . the release mechanism 250 is attached to the arms 172 of the syringe carrier 150 by protrusions 260 which engage with openings ( not shown ) on the arms 172 . the release mechanism 260 includes two damping elements 270 which are each in the form of an arc of material connected at each end of the arc to the release mechanism 250 at pivot points p . the damping elements 270 are on opposing sides of the release mechanism 250 . the damping elements 270 can each resiliently pivot about points p as a result of the resilience of the material and the lever arm formed at the points p . the damping elements 270 can resiliently pivot in a direction r towards the body of the release mechanism 250 , providing bias in the opposite direction . in this way , when the release mechanism 250 is rigidly connected via protrusions 260 to the arms 172 , following insertion of the syringe 114 during manufacture , a convex section c of each arc is in juxtaposition with the upper surface 176 of the flange 120 . thus , movement of the syringe 114 within the syringe carrier 150 in direction r is damped . in this way , sudden movement of the syringe 114 caused by an impact force is absorbed by the damping elements 270 . since the damping elements 270 absorb such syringe movement gradually , there is reduced likelihood that the flange 120 can fracture . moreover , the needle shield 118 remains in place on the discharge nozzle , whilst the integrity seal of the discharge nozzle connecting to the syringe does not get disturbed because sudden rearward movement of the syringe 114 is damped . it will of course be understood that the present invention has been described above purely by way of example and modifications of detail can be made within the scope of the invention .
an injection device 110 is described having a housing 112 that receives a syringe 114 having a needle 118 , wherein the syringe is supported in a syringe carrier 150 . the syringe 114 and syringe carrier 150 are biased by a return spring 126 from an extended position in which the needle 118 extends from the housing 112 through an exit aperture 128 to a retracted position in which it does not . a drive spring 130 acts via a drive to advance the syringe 114 from its retracted position to its extended position and discharge its contents through the needle 118 and a return spring 126 , brought into play when the drive has reached a nominal return position , restores the syringe 114 to its retracted position . the syringe carrier 150 is designed to restrict rearward movement of the syringe so that the injection device is less prone to failure and damage to is components than prior art devices .