Abstract:
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.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 11/765,789 filed on Jun. 20, 2007, which is a continuation of application Ser. No. 10/667,040 filed on Sep. 22, 2003, which is a continuation of application Ser. No. 09/882,536 filed on Jun. 14, 2001 and claims priority under 35 U.S.C. 119 of Danish application nos. PA 2000 00932 and PA 2001 00372 filed on Jun. 16, 2000 and Mar. 7, 2001 respectively, and U.S. provisional application Nos. 60/214,470 and 60/275,790 filed on Jun. 27, 2000 and Mar. 14, 2001 respectively. The benefit of application Ser. No. 11/765,789 filed on Jun. 20, 2007; Ser. No. 10/667,040 filed on Sep. 22, 2003; Ser. No. 09/882,536 filed on Jun. 14, 2001 in the U.S. is claimed under 35 U.S.C. 120, the contents of which are fully incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to syringes by which a dose can be set by rotating a dose setting member and by which an injection button elevates from an end of the syringe a distance proportional to the set dose and wherein the set dose can be injected by pressing home the injection button to its not elevated position. 
     An almost classic pen of this type is described in EP 327 910. 
     By setting a dose on this pen a tubular member forming an injection button is screwed up along a threaded piston rod a distance corresponding to the distance said piston rod must be moved to inject the set dose. The tubular member simply forms a nut which is during the dose setting screwed away form a stop and which is during the injection pressed back to abutment with said stop and the force exerted on the button is directly transmitted to the a piston closing one end of an ampoule in the syringe which ampoule contains the medicament to be injected. When the piston is pressed into the ampoule the medicament is pressed out through a needle mounted through a closure at the other end of the ampoule. 
     By time it has been wanted to store larger amount in the ampoules, typically 3 ml instead of 1.5 ml. As it has not been appropriate to make the syringe longer the ampoule is instead given a larger diameter, i.e. the area of the piston facing the medicament in the ampoule has been doubled and consequently the force which has to be exerted on the piston to provide the same pressure as previously inside the ampoule has been doubled. Further the distance the piston has to be moved to inject one unit of the medicament has been halved. 
     This development is not quite favourable, as especially users having reduced finger strength have their difficulties in pressing the injection button, a problem that is further increased when still thinner needles are used to reduce the pain by injection. Also with quite small movements of the button it is difficult to feel whether the button is moved at all and by injection of one unit from a 3 ml ampoule the piston and consequently the injection button has to be moved only about 0.1 mm. 
     Consequently a wish for a gearing between the injection button and the piston has occurred so that the button has a larger stroke than has the piston. By such a gearing the movement of the injection button is made larger and the force, which has to be exerted on the injection button, is correspondingly reduced. 
     In EP 608 343 a gearing is obtained by the fact that a dose setting element is screwed up along a spindle having a thread with a high pitch. When said dose setting element is pressed back in its axial direction the thread will induce a rotation of said dose setting element, which rotation is via a coupling transmitted to a driver nut with a fine pitch which driver nut will force a threaded not rotatable piston rod forward. 
     A similar gearing is provided in WO 99/38554 wherein the thread with the high pitch is cut in the outer surface of a dose setting drum and is engaged by a mating thread on the inner side of the cylindrical housing. However, by this kind of gearing relative large surfaces are sliding over each other so that most of the transformed force is lost due to friction between the sliding surfaces. Therefore a traditional gearing using mutual engaging gear wheels and racks is preferred. 
     From WO 96/26754 is known an injection device wherein two integrated gear wheels engages a rack fixed in the housing and a rack inside a plunger, respectively. When the plunger is moved axially in the housing the rack inside this plunger can drive the first gear wheel to make the other integral gear wheel move along the fixed rack in the housing. Thereby the gear wheel is moved in the direction of the plunger movement but a shorter distance than is this plunger and this axial movement of the integrated gear wheels is via a housing encompassing said gear wheels transmitted to a piston rod which presses the piston of an ampoule further into this ampoule. However, the rack inside the plunger is one of a number axial racks provided inside said plunger. These racks alternates with untoothed recesses, which allow axial movement of the plunger without the first gear wheel being in engagement with a rack in this plunger. This arrangement is provided to allow the plunger to be moved in a direction out of the housing when a dose is set. When the plunger is rotated to set a dose it is moved outward a distance corresponding to one unit during the part of the rotation where the first gear wheel passes the untoothed recess, thereafter the first gear wheel engages one of the racks so the set unit can be injected, or the rotation can be continued to make the first gear wheel pass the next recess during which passing the set dose is increased by one more unit and so on until a dose with the wanted number of units is set. 
     A disadvantage by this construction is that the teeth of the racks and gearwheels alternating have to be brought in and out of engagement with each other with the inherit danger of clashing. As only a few racks separated by intermediary untoothed recess can be placed along the inner surface of the plunger only few increments can be made during a 360 degree rotation. 
     SUMMARY OF THE INVENTION 
     It is an objective of the invention to provide an injection device, which combines the advantages of the devices according to the prior art without adopting their disadvantages and to provide a device wherein is established a direct gearing, i.e. a gearing by which more transformations of rotational movement to linear movement and linear movement to rotational movement are avoided, between the injection button and the piston rod. 
     This can be obtained by an injection device comprising a housing wherein a piston rod threaded with a first pitch is non rotatable but longitudinally displaceable guided, a nut engaging the thread of the piston rod which nut can be screwed along the threaded piston rod away from a defined position in the housing to set a dose and can be pressed back to said defined position carrying the piston rod with it when the set dose is injected, a dose setting drum which can be screwed outward in the housing along a thread with a second pitch to lift an injection button with it up from the proximal end of the housing, which injection device is according to the invention characterised in that a gearbox is provided which provides a gearing between the axial movements of the injection button and the nut relative to the housing which gearing has a gearing ratio corresponding to the ratio of said second and first pitch. 
     In a preferred embodiment the gearing between the movements of the injection button and the nut is obtained by the gearbox comprising at least one gear wheel carried by a connector which projects from the gear box longitudinally displaceable but non rotatable relative to said gearbox and is integral with the nut, a first rack integral with a first element of the gearbox, which element is rotational but not longitudinally displaceable relative to the housing, and second element carrying a second rack projecting from said gearbox longitudinally displaceable but non rotatable relative to said first element and being coupled to the injection button to follow longitudinal movements of said button, the at least one gear wheel engaging the first and the second rack, respectively, and being dimensioned to provide a gearing by which a longitudinal movement of the second rack is transformed to a longitudinal movement of the connector with a gearing ratio for the mentioned longitudinal movements of the second rack and the connector relative to the housing, which gearing ratio corresponds to the ratio of said second to said first pitch. 
     In such a device only the forces necessary to drive the dose setting drum are transformed by a thread with a high pitch whereas the forces necessary to move the piston by injection is transmitted to said piston through a conventional gear with constantly engaging gears and racks. 
     The piston rod is provided with a stop for the movement of the nut along the thread of said piston rod. This way a dose setting limiter is provided in the classic way, which involves no additional members to prevent setting of a dose exceeding the amount of liquid left in the ampoule. 
    
    
     
       In the following the invention is described in further details with references to the drawing, wherein 
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically shows a sectional view of an injection device according to the invention, and 
         FIG. 2  shows schematically a sectional view of the gear box along the line I-I in  FIG. 1 , 
         FIG. 3  shows a longitudinal sectional view in the dose setting part of another embodiment of an injection device according to the invention, 
         FIG. 4  shows a longitudinal sectional view perpendicular to the view in  FIG. 3 , and 
         FIG. 5  shows an exploded picture of the of the device shown in  FIGS. 3 and 4 . 
     
    
    
     DETAILED DESCRIPTION 
     In the device shown in  FIG. 1  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  FIG. 2  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. 
       FIGS. 3 and 4  shows a preferred embodiment wherein only one size gear wheel is used and wherein elements corresponding to elements in  FIGS. 1 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  FIG. 1 . The bearing is shown as a radial bearing but can be replaced by an axial bearing