Abstract:
The present invention relates to an infusion device comprising a housing ( 10, 12 ); a compartment inside said housing for positioning a medicament container ( 78 ), an infusion needle ( 124 ) arranged to said housing, being connectable to said medicament container for delivering a dose of medicament, a piston plunger ( 72 ) arranged in said housing capable of acting on said medicament container for delivering a dose of medicament, mechanical drive means capable of acting on said piston plunger for delivering a dose of medicament. The invention is characterised in that said piston plunger comprises a number of distinct segments ( 82 ) being inter-connectable to each other for forming an elongated piston plunger.

Description:
TECHNICAL AREA 
       [0001]    The present invention relates to an infusion device and in particular to a compact and easy to use mechanical driven infuser. 
       BACKGROUND OF INVENTION 
       [0002]    For a number of years infusers have been used that provides the patient or user with the means of administering a drug in an easy way without the need for a medically trained person, such as a physician or nurse to handle the device. 
         [0003]    One drawback with these infusers is that they have a medicament container of a certain length as well as a plunger rod acting on said medicament container for delivering a dose of medicament, also having a certain length, whereby the total length of a device has to be at least the length of the medicament container and the plunger rod. If a drive member is used, such as for instance a drive spring, the length of the device is further increased. 
         [0004]    One way of handling this is to make at least the plunger rod shorter or not adding so much to the overall length. One solution to this is to have a flexible plunger rod, which is disclosed for example in EP 1 583 573 where the plunger rod may be bent or formed as a circle. Another solution is disclosed in EP 1 276 529 having a bendable plunger rod with a ratchet on a side surface, where the plunger rod is bent around a cogwheel, for driving the plunger rod. 
         [0005]    The drawback with these solutions is that the length may not be increased by the whole length of the plunger rod, but at least by some amount because the circle formed by the bent plunger rod also adds to the length. Further, the dimensions of the device in other directions are increased considerably by these solutions, providing a rather bulky device. 
         [0006]    The above mentioned solutions utilize some sort of power spring wound around a shaft or the like positioned in the centre of the circle formed by the curved plunger rod. These power springs often act directly or almost directly on the curved plunger rod, such as with the device of EP 1 276 529 where the power spring acts on the cog wheel. 
         [0007]    The drawback with this drive solution is that it complicates the addition of functions such as activation mechanisms, constant infusion speed mechanism, automatic stop mechanisms, just to mention a few. This is mainly because the plunger rod surrounds and thereby blocks access to the plunger drive spring without enlarging the device. 
         [0008]    Regarding the infusion speed control aspect, some solutions have been device, such as for example in EP 1 326 659 where an electric motor is utilized for driving the flexible plunger rod. Also document WO 2010/112377 discloses a device utilizing electric motors for driving and controlling the movement and speed of the plunger rod. 
         [0009]    The drawback with this is that the device has to rely on electric power in order to deliver a dose of medicament. If any batteries used are depleted, the device cannot be used at all, which may be critical for some types of drugs. 
       BRIEF DESCRIPTION OF INVENTION 
       [0010]    The aim of the present invention is to remedy the above drawbacks with the state of the art devices. 
         [0011]    According to one major aspect of the invention the piston plunger preferably comprises a number of distinct segments being inter-connectable to each other for forming an elongated piston plunger. In this aspect it is to be noted that the segments are not connected to each other beforehand. They are each distinct separate components that can be positioned inside the device in many ways. 
         [0012]    The segments have members that provide a connection between the successive segments such that adding and connecting of segments forms an elongated piston plunger. This provides an advantage in that the space required for the plunger rod segments is much lesser than the space required for a flexible piston plunger. The interconnection of the segments preferably provides a locking in the longitudinal direction of the piston plunger, thereby acting as if it was a solid plunger rod. 
         [0013]    The segments may be interconnected successively during delivery of a dose of medicament, whereby a subsequent segment is put in position and inter-connected with a previous segment as the piston plunger advances during infusion. This provides the possibility of arranging the segments in a pile or stack, in turn providing as very compact and space-saving design of the piston plunger. It is of course feasible to have more than one pile or stack of segments. 
         [0014]    In order to advance and position subsequent segments of the piston plunger, especially when placed in a stack, a force member may be provided, capable of acting on said stack of piston plunger segments for successively interconnecting piston plunger segments. The force member may then act on the whole stack or pile, pushing on the last segment to be inter-connected so that each subsequent segment is pushed into place in relation to a previous segment. The force member may be a spring member or the like being in a tensioned state before activation of the infusion and the inter-connection of the segments. 
         [0015]    Preferably the piston plunger is threaded and cooperates with a drive nut for the advancement of the piston plunger during infusion. In this aspect, the piston plunger segments are arranged with threads, designed to interact with the drive nut connected to said mechanical drive means. 
         [0016]    An advantageous design of the piston plunger segments regarding both piling in stacks and interacting with a drive nut, the segments have a generally rectangular cross-section and having thread segments on the corners of the rectangles. 
         [0017]    Further, in order to have a compact mechanical drive means, it may comprise a flat spiral spring preferably arranged in a rotatable spring housing. Thereby the length of the device is not affected by the mechanical drive means acting on the piston plunger. Rather, when a rotating spring housing is provided, a compact a drive member arranged between said spring housing and said drive nut may be arranged. 
         [0018]    The device may further comprise an infusion speed control mechanism operatively connected to said mechanical drive means if that is a requirement. Preferably the infusion speed control mechanism comprises a centrifugal brake. The advantage with this is that a purely mechanical speed control may be obtained, thereby avoiding any electrically driven solutions. A mechanical centrifugal brake is also not so space-consuming and may be made very compact. In order to provide a proper function of the centrifugal brake, a transmission may be arranged between said mechanical drive means and said centrifugal brake. 
         [0019]    Preferably the device may further comprise a penetration mechanism, capable of extending said infusion needle into an infusion site. Thereby the user does not necessarily have to perform the penetration manually, which is an advantage for some users who do not like the concept of needles and the penetration thereof. Then a penetration performed by the device is preferable. In addition to the penetration the penetration mechanism may further be capable of retracting said infusion needle upon completion of dose delivery. Then the device is harmless after performed infusion and the risk of unintentional needle sticks is removed. 
         [0020]    The device may further be arranged with a manually operable operation mechanism, for activating delivery of a dose of medicament, such as a turnable knob, wherein turning of the knob a certain rotational distance activates the penetration mechanism. A turnable knob is an intuitive component that a user has no problems as how to handle. The turning motion of the knob may also be advantageous in that it may easily be transferred to other components of the device for initiating and/or performing additional functions, such as activating of infusion and withdrawal of the infusion needle. 
         [0021]    These and other aspects of, and advantages with, the present invention will become apparent from the following detailed description of the invention and from the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]    In the following detailed description of the invention, reference will be made to the accompanying drawings, of which 
           [0023]      FIG. 1  is a side view of an embodiment of the present invention, 
           [0024]      FIG. 2  is a side view of the device of  FIG. 1  turned 180 degrees, 
           [0025]      FIG. 3  is an exploded view of the device of  FIG. 1 , 
           [0026]      FIG. 4  is a partly exploded view of the device of  FIG. 1  with the proximal housing part removed for clarity, 
           [0027]      FIG. 5  is a partly exploded view of the device of  FIG. 1  with the distal housing part removed for clarity, 
           [0028]      FIG. 6   a  is a detailed view of the piston plunger comprised in the present invention, 
           [0029]      FIG. 6   b  is a detailed view of a piston plunger segment comprised in the piston plunger according to the present invention, 
           [0030]      FIG. 7   a  is a detailed view of the piston plunger according to the invention with a spring unit and follower, 
           [0031]      FIG. 7   b  is a detailed view of a magazine to house the piston plunger, 
           [0032]      FIG. 8  shows a partly exploded view of the device according to  FIG. 1 , 
           [0033]      FIG. 9  shows a partly exploded view according to  FIG. 8  and turned 180 degrees, 
           [0034]      FIG. 10  shows a partly exploded view of a penetration mechanism according to one aspect of the invention, 
           [0035]      FIG. 11  shows a further partly exploded view of the penetration mechanism, 
           [0036]      FIG. 12  show a perspective view of the device of  FIG. 1  with the distal housing part removed for clarity, 
           [0037]      FIG. 13  shows a perspective view of the device of  FIG. 1  with the proximal housing part removed for clarity, 
           [0038]      FIG. 14  shows a view of the distal housing part and a part of an operation mechanism, 
           [0039]      FIGS. 15   a, b  show details views of a knob comprised in the present invention, 
           [0040]      FIG. 16  shows a detailed view of a component comprised in an auto-stop mechanism, 
           [0041]      FIGS. 17 to 29  show different functional positions of the device during use. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0042]    The embodiment of an infusion device shown in the drawings comprises a housing, which may be in two housing parts  10 ,  12 . It is of course feasible that it comprises more than two housing parts. Preferably, the complete housing has a generally rectangular shape having a measure or thickness as seen along a proximal-distal axis  14  that is much less than the dimensions in the other two directions, vertical  16  and horizontal  18 . The housing is arranged with an operating means,  20  in the embodiment shown as a turnable knob on the distally directed housing surface. 
         [0043]    On the proximally directed housing surface, an opening is arranged, through which an Allen keyhole  22  is accessible,  FIG. 2 . The Allen keyhole  22  is arranged on a shaft  24 ,  FIG. 4 , rotatably arranged inside the housing and journalled with a distal end in a seat  26  on the inner surface of the distal housing part  10 . A proximal end of the shaft  24  is arranged with a number of arms  28  that extend from a hub  30  in a generally circumferential direction. The free ends of the arms  28  are arranged with radially outwardly directed edges  32 . The hub  30  with the arms  28  is intended to fit into a seat  34 ,  FIG. 5 , on the inner surface of the proximal housing part  10 . The seat  34  is surrounded by an annular ledge  36  having radially inwardly directed teeth  38  of a certain configuration. The teeth  38  are intended to cooperate with the free ends of the arms  28  as will be described. 
         [0044]    The shaft  24  is further arranged with a slit  40 ,  FIGS. 4 and 5 , along its length. Further, around the shaft  24  is a flat spiral spring  42 ,  FIG. 4 , wound, wherein the inner end of the spiral spring  42  fits into the slit  40 , thereby locking the spring  42  to the shaft  24 . The spring  42  is further arranged inside a spring housing  44  designed as a generally tubular part. The inner surface of the tubular part is arranged with a locking segment  46 ,  FIG. 4 , into which an outer end of the spiral spring  42  fits, thereby locking the spiral spring  42  to the spring housing  44 . The spring housing  44  is further arranged with a sidewall  48 ,  FIG. 5 , having a central opening  50 , through which the shaft  24  can extend. On the outer circumferential surface of the spring housing  44  a ratchet  52  is arranged. The ratchet  52  is intended to cooperate with a cogwheel  54  of a drive member  56 , where the cogwheel  54  preferably is bevelled. The drive member  56  comprises a shaft  56  where the cogwheel  54  is attached to one end such that the shaft  56  extends generally in the radial direction of the spring housing  44  as seen in  FIG. 4  along line  58 . The shaft  56  is journalled in the proximal housing part  10  by support members  60 ,  FIG. 5 . A second cogwheel  62  is arranged at the second end of the shaft  56 ,  FIG. 5 . The second cogwheel  62  is arranged to be in contact with teeth  64  of a drive nut  66 , where the teeth  64  extend around the circumference of the drive nut  66 . The drive nut  66  is further arranged with a central opening  68 ,  FIG. 4 , which opening  68  is arranged with threads  70 . The threads  70  of the drive nut  66  are intended to interact with a threaded piston plunger  72 . The spring housing  44  is further arranged with indicia or markings  73 ,  FIG. 5 , in the embodiment shown a series of curved lines on the outer surface of the sidewall  48 . These markings  73  are visible in a window or opening  75  on the distal housing part  FIG. 1 , as will be explained below. 
         [0045]    In the embodiment shown the piston plunger is of a certain configuration,  FIG. 6   a, b . The piston plunger generally has a rectangular configuration as seen in a cross-sectional view. Each corner of the rectangular piston plunger  72  is arranged with thread segments  74 . Further the piston plunger is divided up into a number of piston plunger segments. The end of the first piston plunger segment  76  that is to be in contact with a medicament container  78 ,  FIG. 3 , is arranged with a generally circular pusher plate  80  having a diameter somewhat less than the inner diameter of the medicament container. The first piston plunger segment  76  has a certain length. The following piston plunger segments  82 ,  FIG. 6   a,  are somewhat shorter. All piston plunger segments are arranged with connection members that comprise generally vertically arranged cut-outs  84  at their distal ends. The side walls  86  of the cut-outs  84  are arranged with generally vertically directed grooves  88 , having a certain configuration. Further, each piston plunger segment apart from the first segment, is arranged with a proximally directed nose  90  designed to fit into the cut-out  84  of a previous plunger segment  82 . Further the nose  90  is arranged with generally vertically extending ledges  92  having similar configuration as the grooves  88  of the cut-out  84 , whereby the ledges  92  may fit into the grooves  88  as seen in  FIG. 6   b.    
         [0046]    The piston plunger segments  82  are arranged in a generally vertical stack on top of each other and directed such that the corners with the thread segments extend generally horizontally,  FIG. 7   a . The stack of piston plunger segments is held in place inside the housing by a magazine  94  providing side supports on three sides. The fourth side is arranged with an elongated slit  96 ,  FIG. 7   b . In the slit a flat band spring  98  is arranged having a first upper end attached to a fixture post  100  on the magazine  94 ,  FIG. 7   a . The second lower end is attached to a piston plunger follower  102  inside that magazine  94 ,  FIG. 7   a . The function of the described components will be explained below. 
         [0047]    The proximal end of the piston plunger  72  extends into a space in the device intended to accommodate the medicament container  78 ,  FIG. 8 . The space is accessible via a hingedly attached lid  104 ,  FIG. 1 , on an upper area of the housing. Inside the space a holder or cartridge retainer  106 ,  FIG. 3 ,  11 , is arranged, on which the medicament container may be placed. The cartridge retainer  106  is arranged slidable in a longitudinal direction inside the housing guided by its longitudinal edges  108 ,  FIGS. 8 and 9 , fitting into guides  110  on each housing part,  FIG. 8 . Further a cogwheel segment  111  of a cartridge cam  112 , is turnably attached to posts  114 ,  FIG. 9 , on the proximal housing part  12 . An upper surface of the cartridge cam  112  is arranged with a curved ridge  116 ,  FIG. 9 , which ridge cooperates with downwardly directed protrusions  118  on the underside of the cartridge retainer  106 . The cogwheel segment  111  of the cartridge cam  112  is further connected to a ratchet segment  120 ,  FIG. 9 , arranged on an outer surface of the operation member  20 , in the embodiment shown a turnable knob. The function of the knob and the cartridge cam will be explained in detail below. 
         [0048]    The cartridge retainer  106  is further arranged with an end piece  122 ,  FIG. 9 , which is intended to be in contact with an end of the container  78 , comprising a septum (not shown). The end piece  122  is further arranged with a hollow needle piece  124 ,  FIG. 9 , intended to pierce the septum of the container, as will be described. The needle piece  124  extends through the end piece and is further provided with a bend of generally ninety degrees. At the lower end of the needle piece, a first end of a flexible tube  126  (not shown) is attached. Further, a second end of the flexible tube is attached to a distal end of an infusion needle  128 ,  FIG. 10 . The infusion needle is attached to a generally cylindrical needle hub  130 , which in turn is positioned inside a generally cylindrical needle plunger  132 . The needle plunger  132  is in turn positioned inside a generally tubular guide piece  134 , being a part of the proximal housing part  10 . A lower end of the guide piece is open towards the proximal direction and the opening is arranged with a ruptable membrane  136 . The needle plunger  132  is further arranged with transversally extending arms  138 ,  FIGS. 10 and 11 . Each arm is arranged with a chamfered side surface  140 , which chamfered surfaces  140  are intended to cooperate with ledges  142 ,  FIG. 5 , on an inner surface of the knob  20 . The needle plunger  132  is urged in the distal direction by a spiral spring  143  acting between the transversal arms  138  and the inner surface of the proximal housing part,  FIG. 10 . 
         [0049]    The device is further arranged with an infusion speed control mechanism  144 , that preferably is capable of providing a constant infusion speed during the infusion. It comprises a transmission,  FIGS. 12 and 13 , with a first cogwheel  146 ,  FIG. 12 , with a small diameter acting on the ratchet  52  on the outer surface of the spring housing  44 . The first cogwheel  146  is attached to a second cogwheel  148  having a larger diameter, wherein the first and second cogwheels  146 ,  148  are rotatably arranged to a first shaft  150 . The second cogwheel  148  is in engagement with a third cogwheel  152  having a smaller diameter. The third cogwheel  152  is attached to a fourth cogwheel  154  having a larger diameter. The third and the fourth cogwheel  152 ,  154  are rotatably arranged to a second shaft  156 . The fourth cogwheel is then in engagement with a fifth  158  cogwheel having a smaller diameter,  FIG. 13 . The fifth cogwheel  158  is attached to a sixth cogwheel  160  having a larger diameter. The fifth and the sixth cogwheels  158 ,  160  are rotatably arranged to a third shaft  162 . The sixth cogwheel  160  is in engagement with a seventh cogwheel  164 . The seventh cogwheel  164  is attached to a centrifugal brake  166 , comprising a number of arms  168  attached to a hub  170 ,  FIG. 12 , where the seventh cogwheel  164  and the hub  170  are rotatably arranged to a fourth shaft  172 . The arms  168  of the centrifugal brake  166  extend generally in circumferential direction, having their free ends becoming trailing ends when the hub rotates. The outer surfaces of the arms  168  are arranged with ledges  174 . The hub  170  with its arms  168  is positioned in a generally tubular piece  176  attached to the inner surface of the distal housing part  12 . The diameter of the tubular piece  176  is chosen such that there is a small gap between the ledges  174  of the arms  168  and the inner surface of the tubular piece  176  when the hub  170  is not rotating. The centrifugal brake  166  is further arranged with transversally extending arms  178  attached to the hub  170 . The free ends of the arms  178  are arranged with end pieces  180 ,  FIG. 14 , extending generally perpendicular to the extension of the arms  178 . 
         [0050]    The device is further arranged with an operation mechanism  182 . The operation mechanism  182  comprises the previously mentioned knob  20 ,  FIG. 14 . Further, it comprises a start linkage  184  designed with an arm  186  attached to a cylindrical hinge  188  fitting into a post  190  in the proximal housing part  10 . The arm  186  extends towards and into the knob  20 . At the end of the arm a contact surface  192  is arranged, which is intended to interact with a protrusion  194  inside the knob  20 , as will be explained. Further the arm  186  of the start linkage  184  is arranged with a branch  196  extending towards the centrifugal brake  166 , and intended to interact with the end pieces  180  of the transversal arms  178  of the hub  170 . At an inner end of the arm  186  a spring element  198  is arranged. 
         [0051]    The operation mechanism is further arranged with a movement member arranged as a spring  200  provided with two arms  202 ,  204 , each in turn arranged with an end piece  206 ,  208  directed generally perpendicular to the arms  202 ,  204 . The first end piece  206  of the spring is attached to the distal housing part,  FIG. 12 . The second end piece is in an initial position held by a hook  210 ,  FIG. 12 , adjacent the opening in the distal housing part intended for the knob  20 . When the knob is operated during use, as will be described, the second end piece will fit into a seat  212  in a generally radially protruding ledge  214  attached to the knob,  FIG. 15 . 
         [0052]    The device is further arranged with an auto-stop mechanism  216 ,  FIG. 11 . It comprises a beam  218  provided with a proximal end  220 ,  FIG. 15 . The proximal end  220  is arranged with a downwardly directed ledge  222 , intended to be in sliding contact with a curved surface  224 ,  FIG. 12 , on the inner surface of the proximal housing part  10 . Further a flexible arm  226  is arranged on a side surface of the beam  218 , the arm  226  being flexible in the proximal-distal direction  14 . The arm  226  is arranged with a distally directed ledge  228 , the ledge being provided with a bevelled surface  230 . The arm  226  and the ledge  230  are arranged to come in contact with a proximally directed protrusion  232  on the knob  20 ,  FIG. 15 . The protrusion of the knob is also arranged with a bevelled surface  234 , intended to interact with the bevelled surface  230  of the arm  210  of the beam  202 , as will be explained. Further, the proximal part of the beam  218  is arranged with an arm  236  extending from the underside of the beam  218  and towards the spring housing  44  as seen in  FIG. 13 . The free end of the arm  236  is arranged with a downwardly directed protrusion  238 , which protrusion  238  is intended to interact with a groove  240 ,  FIGS. 4 and 13 , arranged on the outer surface of the spring housing  44 , as will be explained. 
         [0053]    The beam  218  is arranged with a distal part  242  being directed more upwards than the proximal part as seen in  FIG. 12 , giving the beam a curved shape as seen in the proximal direction of the device. The upper end  244  of the distal end of the beam  218  is positioned adjacent the drive nut  66  and the piston plunger  72 ,  FIG. 12 , for reasons that will be explained below. 
         [0054]    Intended Function of the Device 
         [0055]    The device is usually delivered without a medicament container. Thus, before use, a medicament container  78  has to be inserted into the device. The lid  104  at the upper end of the device is then opened,  FIG. 17 , whereby the space and the cartridge retainer  106  are accessible. The medicament container  78  is then inserted with a neck portion towards the end piece  122  of the cartridge retainer  106 . The lid is then closed. 
         [0056]    The device is now made ready. This may be done by inserting an alien key into the hole  22  on the proximal surface of the device and turning the shaft  24  in the anti-clockwise direction. This causes the arms  28  of the hub  30  to slide over the teeth  38  because of the direction of the arms in relation to the teeth. Because the inner end of the spiral spring is attached to the turning shaft  24  the spiral spring is tensioned. When the user stops turning the shaft, it is locked against rotating back because of the edges  32  of the arms now locking against the teeth  38 . The device is now ready for delivering a dose of medicament. 
         [0057]    In the initial position, the knob is in the rest or delivery position as seen in  FIG. 17 . In this position, as seen in  FIG. 128 , the ratchet segment  120  of the knob  20  is not yet in engagement with the cartridge cam. The contact surface  192  of the operation mechanism  182  is on the inner surface of the knob, unaffected. As seen in  FIG. 19 , this position of the operation mechanism causes the branch  196  to be in the path of the end pieces  180  of the arms  178  of the hub  170 , whereby rotation of the hub  170  of the constant speed control mechanism  144  is prevented. The process up to this point may be done without the device being in contact with the patient. In order to be able to deliver a dose of medicament to the patient, the proximal surface of the device has to be in contact with some part of the body of the patient, i.e. to releasibly attach the device to the body. This may be performed in many ways, by straps, by merely pressing it manually, but preferably the proximal surface is arranged with some sort of adhesive, like sticky tape, with which the device may be fastened to the body. One variant is to have double-sided sticky tape on the proximal surface with an outer protective layer that is peeled off before attachment. 
         [0058]    When the device is activated, the user initially turns the knob to the first position, as seen in  FIG. 1 , displaying the pause sign. This turning of the knob causes its ratchet segment  120  to engage the cogwheel segment  111  of the cartridge cam, whereby the cartridge cam is turned around its contact point with the proximal housing part. The turning of the cartridge cam causes in turn the curved ridge  116  to act on the protrusions  118  of the cartridge retainer  106 , causing the cartridge container  106  to be moved linearly, guided by the guides for the cartridge retainer  110 , such that the end piece  122  is moved towards, and in contact with, the neck portion of the medicament container  78 . The medicament container  78  is in turn held in longitudinal position by the proximal end of the piston plunger  72  with the pusher plate  80  being in contact with the stopper of the medicament container. The movement of the end piece causes the needle piece  124  to penetrate the septum of the medicament container, thereby creating a passage for the medicament through the septum. The medicament can now flow into the flexible tube and to the infusion needle. 
         [0059]    The turning of the knob also initiates the penetration by the infusion needle. The ledges  142  on the inner surface are inclined, as seen in  FIG. 20  and in  FIG. 15 , and the chamfered surfaces  140  of the transversal arms  138  of the needle plunger  132 , will slide on these inclined surfaces, whereby the needle plunger  132  is pushed in the proximal direction against the force of the needle plunger spring  143 . The infusion needle will rupture the membrane  136  and extend out of the device as shown in  FIG. 20 . 
         [0060]    Initiation of Infusion 
         [0061]    In order to start the infusion, the user turns the knob a step further to the position indicated by a “play” arrow,  FIG. 21 . This causes the protrusion  194  inside the knob  20 ,  FIG. 22 , to come in contact with the contact surface of the start linkage  184 , whereby it will turn around its hinge  188 . The turning of the start linkage will cause the branch  196  to move out of contact with the end pieces  180  of the arms  178  of the hub, whereby the hub is free to rotate,  FIG. 23 . Because of the chain of cogwheels of the transmission of the speed control mechanism, the spring housing  44  is free to rotate due to the force of the tensioned flat spiral spring  42 . The knob is held in this position in that the end piece of  208  of the spring during rotation is moved from the hook  210  to the seat  212  of the ledge  214  of the knob  20 ,  FIG. 22 . This new position of the spring will urge the knob to turn in this direction. However, the knob is prevented from turning further because the protrusion  232  of the knob  20  with its bevelled surface  234  is in contact with the bevelled surface  230  of the ledge  228  of the flexible arm  226 ,  FIG. 24 . 
         [0062]    Infusion Operation 
         [0063]    The rotation of the spring housing  44  will cause its ratchet  52  to move around the circumference, thereby acting on the cogwheel  54  of the drive member. The rotation of the second cogwheel  62  of the drive member  54  will, due to the engagement with the drive nut  66 , cause the latter to rotate. In turn, the rotation of the drive nut  66  will cause the piston plunger  72  to move in the proximal direction by the engagement between the drive nut and the thread segments  74 . When the first piston plunger segment  76  has moved a distance in the proximal direction, the space behind the first segment is so large that a subsequent piston plunger segment  82  may be pushed in the vertical direction by the flat band spring  98  acting on the lowermost positioned piston plunger follower  102 . When the following piston plunger segments are pushed upwards in the vertical direction, they are connected to a previous piston plunger segment in that the ledges  92  of the nose  90  of the subsequent segment fit into the grooves  88  of the cut-out  84  of the previous segment, thereby sequentially “building” a continuous piston plunger  72  with the segments. The process of the infusion sequence is also visible in the opening  75  where the indicia  73  on the spring housing  44  pass. 
         [0064]    Speed Control of Infusion 
         [0065]    The movement of the piston plunger  72  in the proximal direction will cause the stopper of the medicament container to move inside the container, whereby medicament is pushed through the needle piece  124 , the flexible tube  126  and the infusion needle  128 . A constant speed of the piston plunger  72  is ascertained by the constant speed control mechanism in that the rotation of the spring housing  44  is transmitted to the hub  170  of the centrifugal brake  166  via the transmission of cogwheels  146 ,  148 ,  152 ,  154 ,  158 ,  160  and  164 . The rotation of the hub  170  will cause the arms  168  to move in the radial direction if the speed is increased over a pre-set level. The movement in the radial direction will cause the ledges  174  of the arms  168  to be moved in contact with the tubular piece  176 , causing a contact friction between the ledges of the arms and the tubular piece that will reduce the speed. In this manner the speed will be kept more or less constant when the arms are moved in and out of contact with the tubular piece during rotation. 
         [0066]    Pausing of the Infusion 
         [0067]    The user may pause the infusion by turning the knob  20  back to the “pause” position against the force of the spring  200 . This will cause the contact surface  192  of the start linkage  184  to move out of contact with the protrusion  194  of the knob, which in turn will cause the start linkage to swing back to its initial position by the spring element  198 . This in turn will cause the branch  196  to move in the path of the end pieces  180  of the arms  178  of the hub  170 , whereby the rotation of the hub is blocked. This in turn will stop the rotation of the spring housing  44  via the transmission, and also the rotation of the drive nut, thereby stopping the movement of the piston plunger  72 . 
         [0068]    Auto-Stop Function 
         [0069]    When the infusion sequence is about to end when the medicament container has been emptied, there will be a space  246  behind the last of the piston plunger segments  82 ,  FIG. 25 . Because the upper end  244  of the beam constantly has been in contact with and underside of the piston plunger, it is now free to move upwards into the space. Due to this and the form of the beam, the arm  236  is moved towards the spring housing, whereby the protrusion  238  of the arm  236  comes in contact with the outer surface of the spring housing  44  and when the groove  240  of the spring housing comes in position in relation to the protrusion, the latter will be forced into the groove and the rotation of the spring housing is blocked,  FIG. 26 . 
         [0070]    When the protrusion  238  enters the groove  240  the force of the spiral spring on the spring housing will cause the beam to be lifted somewhat in the vertical direction. This movement of the beam will cause the flexible arm  226  and its ledge to be moved out of contact with the protrusion of the knob  232   FIG. 27 . Due to the force of the spring  200  acting on the knob  20  and urging it in the clock-wise direction, the knob will be turned in this direction. On the inner surface of the knob, the ledge that the transversal arm is resting on is terminated at  246 ,  FIGS. 27 and 15   b , whereby the needle plunger is free to be moved in the distal direction by the needle plunger spring  143 . This now causes the infusion needle to be withdrawn from the infusion site. The device may now be removed and discarded. 
         [0071]    Manual Stop 
         [0072]    Instead of the automatic stopping of the device, it may be stopped manually by turning the knob further,  FIG. 1 , against the force between the flexible arm  226  and the protrusion  232  of the knob,  FIG. 28 . This will cause the flexible arm  226  to move in the proximal direction such that the protrusion  232  of the knob can pass. The arm will then flex back whereby the ledge  228  of the arm  226  prevents the user from turning back the knob. At the same time, the contact surface  192  of the start linkage  184  is moved out of contact with the protrusion  194  of the knob, which will stop the rotation of the spring housing  44  via the transmission in the same manner as when the infusion is paused as described above. However, in this position, the knob may not be turned back, thereby avoiding unintentional activation of the device again. 
         [0073]    Further, in this position, the ledge that the transversal arm is resting on is terminated, whereby the needle plunger is free to be moved in the distal direction by the needle plunger spring, in the same manner as with the auto-stop function. This now causes the infusion needle to be withdrawn from the infusion site. The device may now be removed and discarded. 
         [0074]    It is to be understood that the embodiment described above and shown in the drawings is to be regarded only as a non-limiting example of the invention and that it may be modified in many ways within the scope of the patent claims. 
       COMPONENT LIST 
       [0075]      10  proximal housing part 
         [0076]      12  distal housing part 
         [0077]      14  proximal-distal direction 
         [0078]      16  vertical direction 
         [0079]      18  horizontal direction 
         [0080]      20  knob 
         [0081]      22  alien key hole 
         [0082]      24  shaft 
         [0083]      26  seat 
         [0084]      28  arms 
         [0085]      30  hub 
         [0086]      32  edge 
         [0087]      34  seat 
         [0088]      36  annular ledge 
         [0089]      38  teeth 
         [0090]      40  slit 
         [0091]      42  flat spiral spring 
         [0092]      44  spring housing 
         [0093]      46  locking segment 
         [0094]      48  sidewall 
         [0095]      50  central opening 
         [0096]      52  ratchet 
         [0097]      54  cogwheel 
         [0098]      56  drive member, shaft 
         [0099]      58  line 
         [0100]      60  support member for shaft 
         [0101]      62  second cogwheel 
         [0102]      64  teeth 
         [0103]      66  drive nut 
         [0104]      68  central opening of drive nut 
         [0105]      70  threads of central opening 
         [0106]      72  piston plunger 
         [0107]      74  thread segments 
         [0108]      76  first piston plunger segment 
         [0109]      78  medicament container 
         [0110]      80  pusher plate 
         [0111]      82  following piston plunger segments 
         [0112]      84  cut-out of piston plunger segment 
         [0113]      86  side walls of cut-out 
         [0114]      88  groove 
         [0115]      90  nose 
         [0116]      92  ledge 
         [0117]      94  magazine 
         [0118]      96  slit 
         [0119]      98  flat band spring 
         [0120]      100  fixture post on magazine 
         [0121]      102  piston plunger follower 
         [0122]      104  lid 
         [0123]      106  cartridge retainer 
         [0124]      108  longitudinal edge of cartridge retainer 
         [0125]      110  guides for cartridge retainer 
         [0126]      111  cogwheel segment 
         [0127]      112  cartridge cam 
         [0128]      114  posts for cartridge cam 
         [0129]      116  curved ridge 
         [0130]      118  protrusions on cartridge retainer 
         [0131]      120  ratchet segment 
         [0132]      122  end piece 
         [0133]      124  needle piece 
         [0134]      126  flexible tube (not shown) 
         [0135]      128  infusion needle 
         [0136]      130  needle hub 
         [0137]      132  needle plunger 
         [0138]      134  guide piece 
         [0139]      136  membrane 
         [0140]      138  transversal arms 
         [0141]      140  chamfered surface of the arms 
         [0142]      142  ledges of the knob 
         [0143]      143  needle plunger spring 
         [0144]      144  constant speed control mechanism 
         [0145]      146  1&#39;st cogwheel 
         [0146]      148  2&#39;nd cogwheel 
         [0147]      150  1&#39;st shaft 
         [0148]      152  3&#39;rd cogwheel 
         [0149]      154  4&#39;th cogwheel 
         [0150]      156  2&#39;nd shaft 
         [0151]      158  5&#39;th cogwheel 
         [0152]      160  6&#39;th cogwheel 
         [0153]      162  3&#39;rd shaft 
         [0154]      164  7&#39;th cogwheel 
         [0155]      166  centrifugal brake 
         [0156]      168  arms of centrifugal brake 
         [0157]      170  hub 
         [0158]      172  4&#39;th shaft 
         [0159]      174  ledges of arms 
         [0160]      176  tubular piece of centrifugal brake 
         [0161]      178  arms of the hub 
         [0162]      180  end pieces 
         [0163]      182  operation mechanism 
         [0164]      184  start linkage 
         [0165]      186  arm of start linkage 
         [0166]      188  hinge 
         [0167]      190  post 
         [0168]      192  contact surface 
         [0169]      194  protrusion of knob 
         [0170]      196  branch 
         [0171]      198  spring element 
         [0172]      200  spring as movement member 
         [0173]      202 ,  204  arms of spring 
         [0174]      206 ,  208  end pieces of arms 
         [0175]      210  hook for spring 
         [0176]      212  seat 
         [0177]      214  ledge of knob 
         [0178]      216  auto-stop mechanism 
         [0179]      218  beam 
         [0180]      220  proximal end 
         [0181]      222  ledge 
         [0182]      224  curved surface 
         [0183]      226  flexible arm 
         [0184]      228  ledge of arm 
         [0185]      230  bevelled surface of ledge 
         [0186]      232  protrusion of knob 
         [0187]      234  bevelled surface of protrusion 
         [0188]      236  arm 
         [0189]      238  protrusion 
         [0190]      240  groove of spring housing 
         [0191]      242  distal part of beam 
         [0192]      244  upper end of distal part 
         [0193]      246  space 
         [0194]      248  termination of ledge of knob