Abstract:
A device for administering a product dose, the device including a display drum for displaying a product dose, a housing, a first conveying member moveable relative to the housing in a conveying direction, a second conveying member moveable relative to the housing in and counter to the conveying direction, the second conveying member in a first threaded engagement with the first conveying member while being rotationally movable relative to the housing and the first conveying member and being translationally movable relative to the first conveying member counter to the conveying direction, a metering apparatus by which a product dose can be adjusted and which encompasses the display drum, the display drum being rotationally movable relative to the housing while being translationally movable in and counter to the conveying direction in a second threaded engagement, and a coupling element which interconnects the first conveying member and the display drum in a torsion-resistant manner in a coupling engagement which is releasable by actuating the administering device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/843,108 filed on Aug. 22, 2007, issued as U.S. Pat. No. 8,500,701 on Aug. 6, 2013, which is a continuation of International Application No. PCT/CH2006/000018 filed on Jan. 11, 2006, which claims priority to German Application No. DE 10 2005 008 280.7 filed on Feb. 23, 2005, the contents of all of which are incorporated in their entirety herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to devices for injecting, infusing, delivering, dispensing or administering substances, and to methods of making and using such devices. More particularly, the present invention relates to a device for administering a fluid product or substance which can be a medicine, a diagnostic agent or a cosmetic product. In some preferred embodiments, the invention is used in self-administering, although it is not limited to self-administration use, but can also be used in administering by medically trained staff. 
         [0003]    In therapies in which persons who are not medically trained administer an active agent, for example to themselves, the administering devices used have to be simple but still reliable to handle. In particular, it is necessary to ensure that in devices which allow selecting or setting the product dosage to be administered the dosage set is displayed accurately, conveniently and unequivocally. In diabetes therapy—a preferred area of use for the present invention—it should also be taken into account that the persons administering the insulin to themselves may be visually impaired and that the dosage set should therefore be particularly clearly and unambiguously legible on a dosage scale or display. It is conducive to good legibility if the dosage scale is disposed on a display drum which can be moved rotationally and translationally, since in this case, the dosage scale can extend along and in the rotational direction of the display drum. 
         [0004]    Devices of the type mentioned are known for example from WO 99/38554 A1. Typically, the devices are complex and require rotational blocks which allow a rotational movement by a piston rod in one rotational direction but prevent it in the other, and which additionally have to be adjusted to torques which are to be transferred or can only just still be transferred. 
         [0005]    A very simple device of the type mentioned is known from WO 03/075985 A1. As with the devices of WO 99/38554, however, it requires two spindle drives which are both formed to not be self-locking, such that when only a small dosage is set, only a short stroke of the display drum is provided. 
       SUMMARY 
       [0006]    It is an object of the present invention to provide an administering device of the type mentioned above, i.e. an administering device comprising a display drum and spindle drives, which is designed simply and can therefore be provided cheaply, but can still be flexibly adapted to administering needs with respect to gearing up or also, as applicable, gearing down between a delivery stroke of a conveying means and an adjusting movement of the display drum, when the product dosage is being set. 
         [0007]    In one embodiment, the present invention comprises a device for administering a product dose, the device including a display drum for displaying a product dose, a housing, a first conveying member moveable relative to the housing in a conveying direction, a second conveying member moveable relative to the housing in and counter to the conveying direction, the second conveying member in a first threaded engagement with the first conveying member while being rotationally movable relative to the housing and the first conveying member and being translationally movable relative to the first conveying member counter to the conveying direction, a metering apparatus by which a product dose can be adjusted and which encompasses the display drum, the display drum being rotationally movable relative to the housing while being translationally movable in and counter to the conveying direction in a second threaded engagement, and a coupling element which interconnects the first conveying member and the display drum in a torsion-resistant manner in a coupling engagement which is releasable by actuating the administering device. 
         [0008]    In one embodiment, the present invention comprises a device for administering a fluid product which comprises a casing comprising a receptacle for the product, a conveying means for conveying the product and a dosing means for setting a product dosage to be administered and displaying the product dosage set. The casing forms a receptacle for the product, in some preferred embodiments in the form of a receptacle for a container which is filled with the product. In principle, however, the receptacle could also itself directly form the product container. The conveying means comprises a first conveying member which can be moved in a conveying direction relative to the casing to deliver the a selected product dosage in a conveying stroke which is pre-set in accordance with the product dosage. In some embodiments, the conveying stroke is a translational movement by the first conveying member in the conveying direction, e.g. a linear movement along a conveying axis. The first conveying member can be formed as a piston rod which, in such an embodiment, is connected to a piston of the conveying means, for example formed in one piece with the piston, screwed or latched to the piston, or pressing loosely against a rear side of the piston during the conveying stroke. The conveying means also comprises a second conveying member which is in a first threaded engagement with the first conveying member, in which it can be rotated relative to the first conveying member and the casing to set the product dosage and can be moved translationally relative to the casing in the conveying direction to deliver the product dosage set. If the conveying means comprises an axially movable piston for conveying the product, as in some preferred embodiments, the first conveying member can be a piston rod. In such embodiments, the first conveying member can, however in principle be a transfer member which first transfers a conveying movement by the second conveying member onto a piston rod. 
         [0009]    In some preferred embodiments, the present invention comprises a display drum that can be rotated relative to the casing in a second threaded engagement, and moved translationally in and counter to the conveying direction. The display drum is in the second threaded engagement with the casing or with an intermediate structure connected to the casing. If the second threaded engagement is formed with an intermediate structure, the intermediate structure is connected to the casing such that it does not move relative to the casing either when the dosage is being set or during the conveying movement, or in both cases. 
         [0010]    In accordance with the present invention, in some embodiments the device also comprises a coupler which couples the display drum to the second conveying member, secured against rotation, wherein a coupler engagement formed by the coupler for the rotationally secure coupling is automatically released when the device is activated for administering. Advantageously, the coupler engagement is released before the conveying stroke of the second conveying member begins. Because the second conveying member can be moved relative to the casing in and counter to the conveying direction, it forms a first spindle drive with the first conveying member and is coupled to the display drum via a releasable coupler engagement while the product dosage is being set, the thread pitches of the two spindle drives, i.e. the first spindle drive formed with the second conveying member and the second spindle drive formed with the display drum, can be simply varied with respect to each other over a broad range. Thus, the spindle drive formed with the display drum can exhibit a large thread pitch and the spindle drive formed with the second conveying member can exhibit a small thread pitch. A small conveying stroke can thus be combined with a large display stroke. The thread pitch in the second threaded engagement can be, for example, three, four or five times as large as the thread pitch in the first threaded engagement. 
         [0011]    In some preferred embodiments, the threaded engagement between the conveying members is self-locking, which is advantageously achieved by making the pitch of the threads in the threaded engagement sufficiently small. Instead or additionally, a releasable locking engagement can prevent the second conveying member from performing an undesirable rotational movement during the conveying stroke. The angular distance of the rotational locking positions of such a locking engagement correspond to increasing or reducing the dosage by one settable unit. 
         [0012]    In preferred embodiments, the coupler is tensed into the coupler engagement by a spring and, for this purpose, comprises a first coupler member and a second coupler member, as well as the spring which tenses the coupler members together in the coupler engagement. At least in embodiments in which the force required for performing the conveying stroke is applied manually, it may be preferred if the coupler engagement is released by the force to be applied for the conveying stroke. The activating force generating the conveying stroke is advantageously exerted in the conveying direction, and the spring tenses one of the coupler members in or counter to the conveying direction, into the coupler engagement with the other. The coupler engagement, i.e. the rotational block established by the coupler members, can be based purely on a frictional lock, but may be based on a positive lock or at least comprises a positive-lock connection between the coupler members. The coupler engagement may be released by a movement in the conveying direction which one of the coupler members performs relative to the other. Advantageously, one of the coupler members can be moved relative to the other in the conveying direction along the conveying axis, out of the coupler engagement. 
         [0013]    For activating, the device comprises an activating element which, when activated, releases the coupler engagement. At least one of the display drum and the second conveying member, in some preferred embodiments, the display drum and the second conveying member as well, can be rotated relative to the activating element. The activating element is permanently connected to one of the two coupler members. It is connected to the relevant coupler member such that it cannot be moved in and counter to a direction in which the relevant coupler member is moved out of the coupler engagement. When activated, the activating element passes into contact against the other of the coupler members. The activating element and the other of the coupler members comprise low-friction contact areas for the contact, so that only small frictional forces oppose a relative rotation which may occur in the activating contact. 
         [0014]    In some embodiments, the spring of the coupler is a mechanical spring. It advantageously acts as a pressure spring. Alternatively, however, it can for example also act as a tension spring, the spring force of which draws the coupler members into the coupler engagement. In one preferred embodiment as a pressure spring, it acts on the one hand against one of the coupler members and on the other hand against the second conveying member. As a pressure spring, it can alternatively also be formed as a pressurized gas spring, for example a pressurized air spring. 
         [0015]    In some preferred embodiments, an equalizer or equalizing means is provided which is variable in length in the conveying direction and connects the second conveying member to the display drum, secured against rotation, when the coupler engagement exists. In some preferred embodiments, the equalizer comprises a spring arranged such that the length of the equalizer can only be reduced against a restoring elasticity force of the spring. The spring may be a mechanical spring, but could in principle also be a pneumatic spring. That which has been said with respect to the spring of the coupler applies similarly to the spring of the equalizer. The spring can be the spring described in connection with the coupler. In some embodiments, the spring serving to equalize the length can, however, be provided in addition to the spring of the coupler. 
         [0016]    In some preferred embodiments, the equalizer comprises at least two equalizing structures which overlap each other in the conveying direction and are guided, secured against rotation, relative to each other. The at least two equalizing structures are rotationally guided directly on each other. When the coupler engagement exists, one of the equalizing structures is connected, secured against rotation, to the display drum, and the other is connected, secured against rotation, to the second conveying member. In some preferred embodiments, the equalizing is formed as a telescope. In such embodiments, the equalizing structures each form a telescopic section extending in the conveying direction. In advantageous embodiments, the spring of the equalizer is supported on one of the equalizing structures in the conveying direction and on the other of the equalizing structures counter to the conveying direction, such that the spring force tends to drive or move the equalizing structures apart. In some preferred embodiments, the equalizer only comprises exactly two equalizing structures which can be moved relative to each other in the conveying direction. Advantageously, the equalizing structures are rigid in their own right in the conveying direction, but could also themselves exhibit an elasticity in the conveying direction, such that a separate spring could be omitted. The equalizer could thus perfectly well be formed as bellows which can also simultaneously be one of the coupler members. The equalizer is advantageous in combination with the coupler. Further, it is advantageous for maintaining the rotationally secure connection between the display drum and the second conveying member, but is also advantageous in its own right alone. 
         [0017]    In a preferred embodiment, the device comprises a guide for linearly guiding the first conveying member, secured against rotation, in the conveying direction. Advantageously, a torque cannot be transferred by such a first conveying member onto a conveying member, for example a piston, arranged subsequently in the conveying line. 
         [0018]    in some preferred embodiments, a retainer or retaining means is provided which, when in engagement with the first conveying member, prevents the first conveying member from moving counter to the conveying direction. The retainer and the first conveying member—as far as its co-operation with the retaining means is concerned—can be formed in the way known from injection devices comprising gear rack arrangements. Thus, the first conveying member can, for example, be formed as a gear rack comprising at least one row of serrated teeth, with which an elastically bending retaining tongue of the retaining means engages, to prevent the first conveying member from moving counter to the conveying direction but allow it to move in the conveying direction. 
         [0019]    In some preferred embodiments of the present invention, the administering device can be an injection device or apparatus, advantageously for subcutaneous administering by an injection needle or also for needle-free pressure injectors. The injection apparatus may be an injection pen. As already mentioned in connection with the retainer or retaining means, the device can be formed in the manner of a gear rack pen, wherein, however, the first conveying member is formed as a combined tooth-thread rack or at least comprises a corresponding section. Due to its simple design and therefore reasonable price, the device can also be provided as a disposable apparatus which is disposed of once the product container has been emptied. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  depicts a device in accordance with the present invention and a dosage display in the state of a zero dosage setting; 
           [0021]      FIG. 2  shows the device of  FIG. 1  in the state of a maximum dosage setting; 
           [0022]      FIG. 3  shows the device of  FIG. 1  in the state of the maximum dosage setting, in a longitudinal section; 
           [0023]      FIG. 4  shows the device in the state of the zero dosage setting, in the same sectional view as in  FIG. 3 ; and 
           [0024]      FIG. 5  shows a proximal portion of the device in the state of the maximum dosage setting, in the same longitudinal section as those of  FIGS. 3 and 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows a device for administering or injecting a fluid product—for example insulin, an osteoporosis preparation, or a growth hormone—in doses. The device is formed as a slim injection pen. It comprises a casing, a proximal casing section  2  of which can be seen. A cap  4  covers a distal casing section. The device is depicted in an initial state which it assumes before a product dosage which is to be administered is set or after the product has been administered. A dosing member  18  for setting the product dosage and a dosage display comprising a window  7  can be seen. The window  7  is formed as an aperture in the casing section  2  and is covered by a transparent cover, for example a magnifier; in principle, the window  7  can also simply be just an aperture through which the dosage set by means of the dosing member  18  is legible on a dosage scale. In the initial state in  FIG. 1 , the dosage display displays the dosage “zero”. A disc-shaped activating element  30  forms a proximal end of the device. 
         [0026]      FIG. 2  shows the device in the same view as  FIG. 1 , but after a product dosage has been set which is the maximum product dosage which can be administered per injection using the device. As can be read on the dosage display, the maximum product dosage corresponds for example to 80 dosage units of the product. The dosing member  18  is formed as a rotating knob. The dosage is set by a rotational dosing movement of the dosing member  18 . The rotational dosing movement rotates a display drum  17  out of the casing section  2  along a central longitudinal axis L of the device. The dosage scale is disposed, in a circumferential spiral, on the outer circumferential area of the display drum  17 . The display drum  17  is provided, in a circumferential spiral around the central longitudinal axis L, with a thread  19  which is in threaded engagement with a corresponding inner thread of the casing section  2 , such that the display drum  17  forms a spindle drive with the casing section  2 . The pitch of the threaded engagement with respect to the central longitudinal axis L is large enough that self-locking cannot occur if the display drum  17  is pressed into the casing section  2  by pressure against the activating element  30 . 
         [0027]      FIG. 3  shows the device in the state in  FIG. 2 , i.e. in the state of the maximum dosage setting, in a longitudinal section which includes the central longitudinal axis L of the device.  FIG. 4  shows the device in the state in  FIG. 1 , i.e. in the zero dosage setting, in the same longitudinal section.  FIG. 5  shows—in the same longitudinal section, but enlarged—the proximal portion of the device in the state of the maximum dosage setting. 
         [0028]    The distal casing section  1  and the proximal casing section  2  connected immovably to it form a casing or housing for the device. The distal casing section  1  forms a receptacle for a container  3  which is filled with the product and is formed by an ampoule such as is, for example, known for injection pens from diabetes therapy. A distal outlet of the ampoule is sealed by a septum. An injection cannula, arranged along the longitudinal axis L, protrudes through the septum. A piston is accommodated in the container  3  such that it can be moved along the longitudinal direction L in a conveying direction V towards the outlet. The longitudinal axis L also forms a conveying axis of the device and is also referred to as such in the following. 
         [0029]    A piston rod drives the piston along the conveying axis L in the conveying direction V. The piston rod forms a first conveying member  11  of the injection operational mechanism or conveying means which also comprises the piston and a second conveying member  12  which drives the first conveying member  11 . The first conveying member  11  is not visible in  FIGS. 3 ,  4  and  5 ; the reference sign “ 11 ” indicates its installed location. The first conveying member  11  is in threaded engagement with the second conveying member  12 , wherein the conveying axis L is the thread axis. The first conveying member  11  is also in engagement with a retainer or retaining means  5  connected to the casing section  2  such that it cannot be moved in or counter to the conveying direction V. The retainer  5  comprises two retaining tongues which engage with longitudinal grooves on the first conveying member  1  and block the first conveying member  1  from moving counter to the conveying direction V. For the retaining engagement with the two grooves, the first conveying member  1  is provided with a row of serrated teeth in each case. The co-operation between the first conveying member  1  and the retainer  5  corresponds to that of known gear rack pens. An example of such a pen is described in DE 102 32 411 A1, to which reference is made in this respect. 
         [0030]    The first conveying member  11  also cannot be rotated relative to the casing section  2  around the conveying axis L, wherein a rotational block formed for this purpose blocks a rotational movement in both rotational directions in all operational states of the device. The retainer  5  can also simultaneously form the rotational block, or a rotational block can also be additionally provided. 
         [0031]    The second conveying member  12  is sleeve-shaped, surrounds the first conveying member  1  and exhibits an inner thread  13  at its distal end which is in threaded engagement with an outer thread on the first conveying member  11 . The inner thread  13  and the outer thread on the first conveying member  11  are fine threads having a correspondingly small thread pitch. The second conveying member  12  also similarly forms a conveying stopper  14  in its distal end region which projects radially outwardly and, in co-operation with a counter stopper  6  formed by the retainer  5 , limits the conveying movement of the second conveying member  12  and therefore—because of the threaded engagement—also the conveying movement of the first conveying member  11  in the conveying direction V. The stopper  14  can be formed by a circumferential flange or a plurality of individual cams or as applicable also just one cam, if the counter stopper  6  encircles the conveying axis L. 
         [0032]    In addition to the threaded engagement between the conveying members  11  and  12 , another second threaded engagement is that formed between the display drum  17  and the casing section  2 , i.e. between the outer thread  19  on the display drum  17  and an inner thread  9  on the casing section  2 . The conveying axis L is also the threaded axis of the second threaded engagement. An annular gap remains between the second conveying member  12  and the casing section  2 , which the display drum  17  enters in the second threaded engagement when the product is being delivered and leaves when the dosage is being set. As it enters and leaves, it slides over the outer surface area of the second conveying member  12  which apart from the stopper  14  is smooth. The display drum  17  is thus radially guided on both sides, on the one hand in the second threaded engagement  9 ,  19  and on the other hand by the second conveying member  12 . Because the display drum  17  tightly surrounds the second conveying member  12 , the pen can be kept very slim. 
         [0033]    For setting the dosage, the second conveying member  12  is connected to the dosing member  18 , secured against rotation, via a coupler. The dosing member  18  and the display drum  17  are in turn formed in one piece as a sleeve body, with the display drum  17  as an elongated distal sleeve section and the dosing member  18  as a relatively wider but axially shorter proximal end section. 
         [0034]    The coupler comprises a first coupler member  21 , a second coupler member  22  and a spring  20  which is formed as a spiral spring and acts as a pressure spring to press the second coupler member  22  into coupler engagement with the first coupler member  21 . When engaged, the coupler members  21  and  22  are connected to each other in a positive lock, secured against rotation with respect to the conveying axis L. The first coupler member  21  is inserted into the sleeve section of the sleeve body which forms the dosing member  18 , and is connected to the sleeve body both secured against rotation and such that it cannot be moved axially. The first coupler member  21  is formed in the shape of a cup, with a base at the proximal end and a wall which circumferentially protrudes up from the base in the distal direction. It thus seals the sleeve body at its proximal end. For the coupler engagement, the first coupler member  21  is fitted with coupler ribs, cams, grooves  24  or the like, and the second coupler member  22  is fitted with corresponding counter grooves, ribs or cams  25  or the like, which engage with each other to prevent one of the coupler members  21  and  22  from rotating relative to the other. In some embodiments, one pair of coupler elements consisting, for example, of a coupler rib  24  and a coupler groove  25  as the engaging elements is sufficient for the coupler engagement. 
         [0035]    In a double function, the second coupler member  22  is also part of an equalizer or equalizing means which comprises the coupler member  22  as a first equalizing structure and a second equalizing structure  23  which co-operates with it. The spring  20  also fulfils a double function, on the one hand as a coupler spring of the coupler and on the other hand as an equalizing spring of the equalizer. The two equalizing structures  22  and  23  form a telescope, i.e. are telescopically coupled. They are linearly guided on each other, secured against rotation, in and counter to the conveying direction V along the conveying axis L, wherein the equalizing structure  22  forms an inner telescopic section and the equalizing structure  23  forms an outer telescopic section. For the rotational block, the equalizing structure  22  is provided with guiding elements  26  on its outer surface area, and the equalizing structure  23  is provided with guiding counter elements  27  on its inner surface area. The guiding elements  26  and  27  are formed in the manner of a groove and spring guide. In principle, the guide could also be formed by just one guiding element and one guiding counter element. 
         [0036]    As shown in  FIGS. 3 to 5 , the two equalizing structures  22  and  23  overlap each other almost completely in the state of the zero dosage setting, while the axial overlap is minimal in the state of the maximum dosage setting and still ensures the rotationally secured connection between the display drum  17  and the dosing member  18  on the one hand and the second conveying member  12  on the other. The equalizing structure  23  is cup-shaped, with a base at the distal end and a sleeve wall which circumferentially protrudes up from the base in the proximal direction. The spring  20  is supported in the conveying direction V on the base of the equalizing structure  23 . An axial guide for the spring  20  also protrudes centrally up from the base. The spring  20  presses the equalizing structure  23  in the conveying direction V until it abuts against the second conveying member  12 . The second conveying member  12  and the equalizing structure  23  are also in a rotationally secured engagement with each other with respect to the conveying axis L. For the rotationally secured engagement, the second conveying member  12  comprises axially short engaging elements on an inner surface area of its proximal end which are in the rotationally secured engagement with counter elements formed on the outer surface area of the equalizing structure  23 . The equalizing structure  23  is a separate component in this exemplary embodiment, but can alternatively be formed in one piece with the second conveying member  12 . Forming it as a separate component may be advantageous for production reasons. 
         [0037]    The activating element  30  forms a disc-shaped closing end of the device. A pin-shaped connecting section protrudes in the conveying direction V from the disc-shaped structure, through the base of the first coupler member  21 , into the interior of the dosing member  18 , where it is anchored in a base section of the second coupler member  22 , which is similarly cup-shaped, such that the coupler member  22  and the activating element  30  cannot be moved relative to each other in or counter to the conveying direction V. In some preferred embodiments, they can be rotated relative to each other around the conveying axis L; in principle, however, they can also be connected to each other, secured against rotation. The activating element  30  can be moved, together with the second coupler member  22 , in the conveying direction V relative to the first coupler member  21 , against the restoring elasticity force of the spring  20 . It can also be rotated around the conveying axis L at least relative to the first coupler member  21 . 
         [0038]    As can be seen most clearly in  FIG. 5 , a clearance “LH” remains axially between the activating element  30  and the first coupler member  21 , apart from the connecting section of the activating element  30 . The distance LH is between contact areas of the activating element  30  and coupler member  21  which axially oppose each other. The contact area of the activating element  30  is indicated as  31  and is formed centrally around the connecting section of the activating element  30  as a raised area protruding up in the distal direction. To form the counter contact area, a contact element  32  is incorporated into the coupler member  21 , complementarily to the contact area  31 . The contact area  31  and the counter area of the contact element  32  are formed to be low-friction and may be, for example, made of Teflon. 
         [0039]    How the device functions when the dosage is being set and administered is described below on the basis of  FIGS. 3 and 4 , wherein reference should also be made to  FIG. 5 . 
         [0040]    The device reaches the user in the state of the zero dosage setting, as shown in  FIG. 4 . The full container  3  is inserted in the receptacle of the distal casing section  1 . For a first injection, the user takes off the cap  4  and removes a needle protection which surrounds the injection needle. 
         [0041]    Before the desired dosage has been set, the cap  4  can be re-attached for safety reasons. To set the dosage, the user holds the device in the region of the casing or, if the cap  4  is attached, in the region of the casing section  2  and rotates the dosing member  18  until the desired dosage has been set. Due to the rotational dosing movement, the drum  17 —in the second threaded engagement—moves in the proximal direction, out of the casing section  2 . The dosage corresponding to the current dosing position is legible in the window  7 . The rotational dosing movement is performed in discrete steps between locking positions, wherein a distinct clicking sound can be perceived during each locking process. The maximum dosage setting is determined by a stopper on the display drum  17  and a counter stopper on the casing section  2 . Between the two extreme settings of the zero dosage and the maximum dosage, the dosing member  18  and together with it the display drum  17  can be rotated in both rotational directions from one locking position to the next, as desired, such that it is easily possible to correct a dosage. 
         [0042]    While the display drum  17  and the dosing member  18  are moved out, the second coupler member  22  is held permanently in coupler engagement with the first coupler member  21  by the spring  20 . During the rotational dosing movement, the coupler member  22  is also permanently in rotationally secured engagement with the equalizing structure  23 , which for its part is held in rotationally secured engagement with the second conveying member  12 . The rotational portion of the rotational dosing movement is thus transferred onto the second conveying member  12 . Since the first conveying member  11  cannot be rotated relative to the casing and is also prevented from moving counter to the conveying direction V by the retaining means  5 , the second conveying member  12 —in threaded engagement with the first conveying member  11 —is screwed counter to the conveying direction V, relative to the first conveying member  11 . During this dosing stroke which the second conveying member  12  performs relative to the first conveying member  11 , the axial distance between the stopper  14  and the counter stopper  6  is changed. This axial distance corresponds to the length of the dosing stroke and correspondingly also to the length of the conveying stroke. 
         [0043]    Since the thread pitch in the second threaded engagement (which may be referred to or thought of as the engagement of threads  9 ,  19 ) is larger than in the threaded engagement between the conveying members  11  and  12 —in the embodied apparatus, slightly over four times as large—the stroke completed by the display drum  17  when the dosage is being set is longer, over the same rotational angle, in accordance with the ratio between the pitches. The dosage values are correspondingly large and sufficiently spaced from each other on the dosage scale. 
         [0044]    The axial dosing stroke of the display drum  17  and dosing member  18 , i.e. the translational portion of the dosing movement, is longer than the dosing stroke of the second conveying member  12 . The equalizer, comprising structures  20 ,  22  and  23 , equalizes the difference in length, such that the rotationally secured connection between the display drum  17  and the dosing member  18  on the one hand and the second conveying member  12  on the other always exists, in the coupler engagement, between the extreme settings—the zero dosage setting and the maximum dosage setting—limited by stoppers. 
         [0045]    Once the desired dosage, for example the maximum dosage which in the exemplary embodiment measures 80 units ( FIG. 2 ), has been set, the user takes off the cap  4 , if it was still attached for safety reasons, injects the injection needle through the skin at the desired injection point and thus positions the needle tip in the subcutaneous tissue. 
         [0046]    While the injection needle is positioned subcutaneously, the user holds the device with one hand in the region of the casing and presses his/her thumb against the activating element  30  in the conveying direction V. In a first phase of the activating stroke, the pressure moves the second coupler member  22  in the conveying direction V relative to the first coupler member  21 , against the pressure of the spring  20 , out of the coupler engagement. The axial length of the engaging elements  24  and  25  mediating the coupler engagement is set such that the coupler engagement is released when the activating element  30  has traveled the idle stroke LH relative to the coupler member  21 . In the event of further pressure on the activating element  30 , the activating element  30  presses against the coupler member  22  via the contact element  32 , such that in the second phase of the activating stroke, the display drum  17 —in the second threaded engagement—is screwed into the casing section  2 , wherein the second coupler member  22  moves telescopically in the equalizing structure  23  up to an axial stopper which in the example embodiment is formed by the base of the equalizing structure  23 . As soon as the coupler member  22  abuts against the equalizing structure  23 , further pressure on the activating element  30  causes the second conveying member  22  to then be slaved in the final phase of the activating stroke due to the equalizing structure  23  pressing it, and to perform the conveying stroke. The conveying stroke is limited by the pair of stoppers  6 ,  14 . The activating stroke is functionally divided into phases, but is advantageously performed continuously. 
         [0047]    Once the conveying stroke has been completely performed, the pressure is taken off the activating element  30 , such that the spring  20  presses the coupler member  22  back into coupler engagement with the coupler member  21 . Once the injection needle has been drawn out of the tissue, the cap  4  is re-attached. The device is then back in the state in  FIG. 4 , only without the needle protection cap which is only present before the device is used for the first time. The device is stored in this state until the next injection. 
         [0048]    Embodiments of the present invention, including preferred embodiments, have been presented for the purpose of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms and steps disclosed. The embodiments were chosen and described to provide the best illustration of the principles of the invention and the practical application thereof, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth they are fairly, legally, and equitably entitled.