in the device shown in fig1 an elongated cylindrical housing 1 has a partitioning wall 2 which divides the housing in a compartment containing a dose setting mechanism and a compartment 3 designed for the accommodation of a not shown ampoule . a threaded piston rod 4 has a not round cross section by which it fits through a central opening in the wall 2 so that the piston rod 4 can be displaced longitudinally through the central opening in the wall 2 but not rotated relative to this wall . concentrically with the housing 1 the wall 2 carries on its side turning away from the compartment 3 a tubular element 5 which is at a part of it adjacent to the wall 2 provided with an outer thread 6 and which has at its free end a circumferential recess 7 . a ring shaped coupling element 8 on a gear box 9 engages the recess 7 . by this coupling the gearbox is fixed in the housing 1 in a way that allows the gearbox 9 to rotate in the housing but not to be axially displaced relative to said housing . in the gearbox 9 a gear wheel assembly comprising two integral gear wheels is journaled on a shaft 11 , which runs perpendicular to the longitudinal axis of the device between two axial connection bars 12 . the connection bars 12 project from the gear box towards the partition wall 2 and are connected to a nut 13 which adjacent to the wall 2 engages the thread of the piston rod 4 . the gear wheel assembly comprises a gear wheel 14 with a large diameter engaging the teeth of a rack 15 which is guided in the gear box to be displaced in the longitudinal direction of the device , and a gear wheel 16 with a small diameter engaging a rack 10 in fig2 extending in the longitudinal direction of the device on the inner wall of the gearbox 9 . the gear wheel 16 with the small diameter may be divided into two gear wheels placed on each side of the of the gear wheel 14 , and the rack on the inner wall of the gearbox 9 may have a longitudinal recess without any teeth to make room for the gear wheel 14 . a tubular dose setting drum 17 fitting into the housing 2 is at an end provided with an internal thread mating and engaging the outer thread 6 of the tubular element 5 and has at its other end a part with enlarged diameter forming a dose setting button 18 . due to the engagement with the thread 6 the dose setting drum 17 may be screwed in and out of the housing to show a number on a not shown helical scale on its outer surface in a not shown window in the housing 1 . a bottom 19 in a deep cup shaped element , which has a tubular part 20 fitting into the dose setting drum 17 and encompassing the gearbox 9 , forms an injection button . coupling means between the dose setting drum 17 and the cup shaped element ensures that rotation of the dose setting drum 17 is transmitted to the cup shaped element . further the inner wall of the tubular part 20 has longitudinal recesses 22 engaged by protrusions 23 on the gearbox 9 so that rotation of the dose setting drum 17 via the cup shaped element is transmitted to the gearbox 9 . at the edge of the open end of the cup shaped element a rosette of v - shaped teeth are provided , which teeth engage a corresponding rosette of v - shaped teeth 24 on a ring 25 which is pressed against the edge of the cup shaped element by a spring 26 which is compressed between a not toothed side of the ring 25 and a round going shoulder 27 on the inner wall of the dose setting drum 17 at an inner end of the inner thread of this drum . the ring is provided with an inner recess , which is engaged by a longitudinal rib 28 on the tubular element 5 so that the ring 25 can be displaced in the axial direction of the device but cannot be rotated relative to the housing 1 . thereby a click coupling is established which makes a click noise when the v - shaped teeth at the edge of the cup shaped element by rotation of this element rides over the v - shaped teeth of the ring 25 . a head 29 on the projecting end of the rack 15 is with a play fixed at the bottom of the cup shaped element between the bottom 19 forming the injection button and an inner wall 30 near this bottom . the rack is fixed in a position with its head pressed against the wall 30 by a spring 31 between the bottom 19 and the head 29 . to set a dose the dose setting button 18 is rotated to screw the dose - setting drum 17 up along the thread 6 . due to the coupling 21 the cup shaped element will follow the rotation of the dose - setting drum 17 and will be lifted with this drum up from the end of the housing 1 . by the rotation of the cup shaped element the v - shaped teeth 24 at the edge of its open end will ride over the v - shaped teeth of the non rotatable ring 25 to make a click sound for each unit the dose is changed . a too high set dose can be reduced by rotating the dose setting button 18 in the opposite direction of the direction for increasing the dose . when the dose setting drum is screwed up along the thread 6 on the tubular element 5 the ring 25 will follow the dose setting drum in its axial movement as the spring 26 is supported on the shoulder 27 . the spring will keep the v - shaped teeth of the ring 25 and the cup shaped element in engagement and maintain in engagement the coupling 21 , which may comprise a - shaped protrusions 32 on the cup shaped element engaging a - shaped recesses in an inner ring 33 in the dose setting button 18 . the rotation of the dose setting button 18 and the cup shaped element is further transmitted to the gearbox 9 through the protrusions 23 on this gearbox engaging the longitudinal recesses 22 in the inner wall of the tubular part 20 of said cup shaped element . the rotation of the gearbox 25 is through the connection bars 12 transmitted to the nut 13 , which is this way screwed up along the thread of the piston rod 4 and lifted away from its abutment with the wall 2 when a dose it set . as the dose is set by moving the nut 13 on the very piston rod which operates the piston in the not shown ampoule in the compartment 3 a dose setting limiter , which ensures that the size of the set dose does not exceed the amount of medicament left in the ampoule , can easily be established by providing the piston rod 4 with a stop 35 which limits the movement of the nut 13 up along the piston rod 4 . due to the confinement of the head 29 in the space between the bottom 19 and the wall 30 of the cup shaped element , the rack 15 is drawn with the injection button outward . also the axial movement of the nut 13 relative to the housing 1 will be transmitted to the gear wheel assembly through the connection bars 12 and this movement will through the gearbox induce an outward movement of the rack 15 . this induced outward movement have to be the same as the outward movement induced by outward movement of the injection button . this is obtained by dimensioning the gear wheels of the gearbox 9 so that the gear ratio for the movements of the connection bars 12 and the rack 15 relative to the housing corresponds to the ratio of the pitches for the thread on the piston rod and for the thread 6 for the longitudinal movement of the dose setting drum 17 . to inject a set dose the injection button is pressed by pressing on the bottom 19 . in the initial phase of the pressing the spring 31 is compressed where after the pressing force is directly transmitted to the head 29 of the rack 15 and this way to the rack 15 itself . through the gear box 9 the force is transformed and is transmitted through the connection bars 12 to the nut 13 which will press the piston rod 4 into the compartment 3 until the dose - setting drum 17 abuts the wall 2 . during the initial phase of the movement of the injection button the a - shaped protrusions 32 on the cup shaped element will be drawn out of their engagement with the a - shaped recesses in the ring 33 . the dose - setting drum 17 can now rotate relative to the injection button and will do so when the a - shaped protrusions 32 press against a shoulder 34 at the bottom of the dose setting button 18 . only a force sufficient to make the dose setting drum rotate to screw itself downward along the thread 6 is necessary as the force necessary to make the injection is transmitted to the piston rod 4 through the gearbox 9 . a helical reset spring 36 concentric with the dose setting drum can be mounted at the lower end of this drum and can have one end anchored in the dose setting drum 17 and the other end anchored in the wall 2 . during setting of a dose this spring may be tighter coiled so that on the dose setting drum it exerts a torque approximately corresponding to the torque necessary to overcome the friction in the movement of the dose setting drum along the thread 6 so that the force which the user have to exert on the injection button is only the force necessary to drive the piston rod into an ampoule to inject the set dose . it shall be noticed that use of only one size gear wheel which engages as well the rack 15 , which is movable relative to the gear box 9 , as the rack 10 , which is unmovable relative to the gear box , provides a gearing ratio of 2 : 1 for the longitudinal movement relative to the syringe housing 1 for the movable rack 15 and the connector 12 , which carries the shaft 11 of the gear wheel . fig3 and 4 shows a preferred embodiment wherein only one size gear wheel is used and wherein elements corresponding to elements in fig1 and 2 are given the same references as these elements with a prefixed “ 1 ”. for manufacturing reasons minor changes are made . so the partitioning wall 102 and the tubular element 105 are made as two parts which are by the assembling of the device connected to each other to make the assembled parts act as one integral part . the same way the dose setting drum 117 and the dose setting button 118 are made as two parts , which are fixed firmly together . a circumferential recess 107 is provided as an outer recess at the free end of the tubular part 105 and a ring shaped coupling element is provided as an inner bead 108 on the gearbox element 109 which bead engages the recess 107 to provide a rotatable but not axially displaceable connection between the tubular part 105 and the gearbox . a tubular element 120 having ridges 122 which engages recesses 123 on the gearbox is at its upper end closed by a button 119 from which a force provided by pressing this button is transmitted to the tubular element 120 . the gearbox is formed by two shells , which together form a cylinder fitting into the tubular element where the shells are guided by the engagement between the ridges 122 and the recesses 123 . racks 110 and 115 are provided along edges of the shells facing each other . one shell forming the gearbox part 109 is provided with the inner bead 108 , which engages the circumferential recess 107 at the end of the central tubular part 105 and carries the rack 110 . the other shell is axially displaceable in the tubular element 120 and forms the rack 115 . at its outer end projecting from the gearbox the shell carrying the rack 115 is provided with a flange 140 which is positioned in a cut out 141 in the end of the tubular element 120 carrying the button 119 so that this button and the tubular element 120 can be moved so far inward in the device that the engagement of the teeth 132 and 133 can be released before the button 119 abuts the flange 140 . a tubular connection element 112 connects the threaded piston rod 104 with the gearbox . at its end engaging the piston rod 104 the connection element has a nut 113 with an internal thread mating the external thread of the piston rod . at its end engaging the gear box the connection element is provided with two pins 111 projecting perpendicular to the longitudinal axis of the connection element 112 at each side of this element . each pin 111 carries a gear wheel 114 which is placed between and engages the two racks 110 and 115 . this way the connection element 112 will be rotated with the gear box but can be displaced axially relative to said gear box when the racks 110 and 115 are moved relative to each other . in practice it will be the rack 115 , which is moved relative to the gearbox element 109 and the housing and will by the shown construction result in a movement of the connection element 112 relative to housing a distance which is half the distance which the rack 115 is moved . a ring 125 which is at its periphery provided with a rosette of teeth 124 and has a central bore fitting over the central tube in the housing 101 so that this ring 125 can be axially displaced along said central tube 105 , but internal ridges 128 in the central bore of the ring 125 engages longitudinal recesses 137 in the central tube to make the ring non rotatable in the housing so that a rosette of teeth at the edge of the tubular element 120 can click over the teeth 124 of the ring when said tubular element is rotated together with the dose setting drum 117 . a spring 126 working between the ring 125 and an internal shoulder 127 provided in the dose setting drum 117 makes the ring follow the tubular element 120 when this element with the dose setting drum is moved longitudinally in the housing . to make the dose setting drum easy rotatable , especially when said dose setting drum is pressed inward in the housing , a roller bearing having an outer ring 142 supported by the shoulder 127 and an inner ring 143 supporting a pressure bushing 144 which supports the spring 126 . by the provision of this smooth running support only very small axial forces are needed to rotate the dose setting drum 117 back to its zero position when a set dose is injected . this solution replaces the provision of a reset spring as the spring 36 in fig1 . the bearing is shown as a radial bearing but can be replaced by an axial bearing
a medication dispensing device with a housing and a member wherein the member is moveable in a distal direction is useful in delivering medication to a patient . a fluid container can be used with the device and often has a moveable piston at one end and an outlet at the other . the member receives a force from a user and drives the piston in the distal direction to expel medication . a intermediate system is disposed between the member and the piston including a gear set that has a pinion in meshed engagement with a rack . the system allows the member to move a greater distance than the piston moves thereby increasing the force on the piston .