Dose delivery device and method for operating a dose delivery device - Patents.com

Abstract

In a dose setting mode of the dose delivery device, the dose selection part 74 rotates the nut 16, which moves backwards a first axial distance d1 along the thread 8 of the piston rod 6. The gear mechanism transmits the axial movement of the nut 16 to the connector 20, which moves backwards a second axial distance d2 without rotating. In a dose delivery mode of the device, the dose selection part 74 is pushed forward, which drives the connector 20 to move forwards a second axial distance d2. The gear mechanism transmits the axial movement of the connector 20 to the nut 16, which pushes the piston rod 6 forwards a first axial distance d1 without rotating. The gear mechanism includes a first gear 28, which rotates without axial movement relative to the housing 4, and a second gear 30, which rotates without axial movement relative to the nut 16.

Description

[Technical field]

[0001] The present invention relates to a dose delivery device, also called a syringe pen, which provides a mechanism for setting a dose of medicament and then delivering the dose from a medicament cartridge to a patient. Typically, a dose is set by moving a dose selection to a position corresponding to the desired dose, and then the dose is delivered by pushing the dose selection a first distance back to its initial position. Typically, the medicament cartridge contains multiple doses of medicament in a chamber, and the dose delivery device includes a piston rod that advances to expel each dose from the chamber, the piston rod moving a second distance that determines the volume of the dose delivered. The present invention particularly relates to a geared dose delivery device in which the first distance is not equal to the second distance. [Background technology]

[0002] Geared dose delivery devices are known. The volume of medicament delivered from a cartridge is often rather small, so that to deliver a typical dose the piston rod needs to advance a small axial distance. The first advantage that gears offer is that the push button and / or dose selection part can be arranged to move a larger distance, which distance is generally proportional to the distance moved by the piston rod. This allows the user to set the desired dose more accurately. Gears also offer a second advantage, which stems from the improved mechanical advantage of the mechanism. In many circumstances, medicament delivery is easier and more controllable, by allowing the user to apply a smaller force over a longer distance rather than a larger force over a shorter distance. It is necessary to ensure that the additional friction caused by the gear mechanism does not outweigh this advantage.

[0003] In some dose delivery devices, the movement of the dose selection part in the drug delivery mode is not manually driven by pressure applied by the user, but is automatically driven by the energy of a spring. The user applies energy to the spring when moving the dose selection part during the dose setting mode. The advantages of the gears also apply to such automatic devices, which are not excluded from the scope of the present invention. Summary of the Invention

[0004] The present invention provides a fixed dose syringe pen as defined in claim 1.

[0005] Preferred but non-essential features of the invention are defined in the dependent claims.

[0006] The term "medicament" is used herein to describe any fluid substance to be delivered by the pen in a measured dose. A "medicament" would typically be a biologically active substance that is injected into the body of a human or animal subject, for example for medicinal or cosmetic purposes. However, the present invention may also be used in other applications where it is desired to dispense a fixed amount of a substance.

[0007] In this specification, terms such as "front" and "forwards" refer to the direction toward the needle-located end of the drug delivery device, which is shown at the bottom of the drawing, and terms such as "rear" and "backwards" refer to the opposite direction. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic diagram of a first gear mechanism according to the present invention; [Diagram 2] FIG. 4 is a schematic diagram of a second gear mechanism according to the present invention; [Diagram 3] FIG. 1 is a perspective view of a dose delivery device according to the present invention. [Figure 4] FIG. 4 is an exploded view of the dose delivery device of FIG. [Figure 4a] FIG. 5 is a partially enlarged view of FIG. [Figure 4b] FIG. 5 is a partially enlarged view of FIG. [Figure 4c] FIG. 5 is a partially enlarged view of FIG. [Figure 4d] FIG. 5 is a partially enlarged view of FIG. [Diagram 5] FIG. 4 is a longitudinal cross-sectional view of a portion of the dose delivery device of FIG. [Figure 6] FIG. 4 is an exploded perspective view of the components that make up the dose dial mechanism of the dose delivery device of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Figure 1 is a highly schematic view in cross section of the gear mechanism of a dose delivery device. In particular, the dimensions perpendicular to the axis 2 have been exaggerated to insert space and promote clarity. The gear mechanism is shown substantially only on one side of the axis 2, the other side being a mirror image except for the direction of winding of the threads.

[0010] A generally cylindrical housing 4 surrounds the shaft 2 and contains a gear mechanism. A piston rod 6 aligned with the shaft 2 includes a piston rod thread 8 on its outer surface. The piston rod 6 is configured to slide without rotation through a central opening 10 fixed relative to the housing 4. The piston rod thread 8 is interrupted by a pair of opposing flat surfaces or by two or more longitudinal tracks 12, thereby giving the piston rod 6 a non-circular cross-section that complements the shape of the opening 10 and prevents the piston rod 6 from rotating relative to the housing 4. At the front end of the piston rod 6, beyond the opening 10 and away from the gear mechanism, a bottom portion 14 is configured to engage a piston of a drug cartridge, not shown, which may be attached to the device. The front end of the drug cartridge may be pierced by a hollow needle, not shown. Forward movement of the piston rod 6 along the shaft 2 thereby advances the piston along the drug cartridge and expels a measured amount of drug from the cartridge through the needle.

[0011] The nut 16 includes internal threads that engage the piston rod threads 8 and are adapted to move along the threads 8 as the nut 16 rotates. A rigid tube 18 surrounds the piston rod 6 and extends rearwardly from the nut 16. The tube 8 is fixed to the nut 16 so as to follow the movement of the nut.

[0012] A generally cylindrical connector 20 surrounds the shaft 2 and is configured to move axially without rotation relative to the housing 4. The inner wall of the housing 4 may include one or more axial tracks 22, and the connector 20 may include a corresponding number of radially projecting lugs 24 that slide within each track 22.

[0013] A generally cylindrical dose dial sleeve 26 is concentric with the axis 2 and is radially nested between the housing 4 and the connector 20. The dose dial sleeve 26 engages the connector 20 such that it is constrained to move axially therewith but allows relative rotation therebetween. The dose dial sleeve 26 engages the housing via sleeve threads 27 such that any axial movement relative to the housing 4 causes the dose dial sleeve 26 to simultaneously rotate along the sleeve threads 27. The sleeve threads 27 have the same winding sense as the piston rod threads 8 but a larger pitch.

[0014] The operation of the gear mechanism will now be described, while the rest of the device will be described in more detail below with reference to the specific embodiment shown in Figures 3-6.

[0015] During a dose setting mode of operation, the tube 18 rotates, moving the nut 16 backwards according to the piston rod thread 8 a first axial distance d1 corresponding to the dose of medicament to be delivered. At the same time, the connector 20 moves axially backwards without rotating a second axial distance d2 greater than the first axial distance d1, thereby providing the advantages of a geared dose delivery device as described above. In the embodiment shown in FIG. 1, the second axial distance d2 is twice the first axial distance d1, but in other embodiments the gear ratio may be greater or less. During a dose delivery mode of operation, the connector 20 is pushed forwards back to its initial position. At the same time, the nut 16 moves forwards again, this time without rotating, the first axial distance d1, returning to its initial axial position, but not necessarily to its initial rotated position. This forward movement of the nut 16 advances the piston rod 6 forwards the first axial distance d1, thereby expelling a proportional dose of medicament from the medicament cartridge.

[0016] The differential motion between the nut 16 and the connector 20 is mediated by a first gear 28 and a second gear 30. The first and second gears 28, 30 are generally cylindrical and concentric with the shaft 2, and are nested between the tube 18 and the connector 20. The first gear 28 is connected to the housing 4 such that it is prevented from moving axially relative to the housing 4 but is free to rotate. The first gear 28 is connected to the connector 20 by a first helical thread 31 as a first engagement portion. The second gear 30 is connected to the nut 16 such that it is prevented from moving axially relative to the nut 16 but is free to rotate. The second gear 30 is connected to the connector 20 by a second engagement portion 32 and to the first gear by a third engagement portion 33.

[0017] In the gear mechanism shown in Fig. 1, the third engagement 33 between the first and second gears 28, 30 is a straight track, allowing relative axial movement between the two gears but preventing relative rotation. The second engagement between the second gear 30 and the connector 20 is a second helical thread 32 having the same winding sense as the first helical thread 31 but a smaller pitch than the first helical thread 31. The winding sense of the first and second helical threads 31, 32 may be the same as or opposite to the winding sense of the piston rod thread 8 and the sleeve thread 27.

[0018] During operation of the device, the first gear 28 is prevented from axial movement, the second gear 30 moves axially with the nut 16 a first axial distance d1, and the connector 20 moves axially a second axial distance d2. The connector 20 engages the first gear 28 via the first helical thread 31, so that axial movement of the connector 20 relative to the first gear 28 causes the first gear 28 to rotate at a speed determined by the pitch of the first helical thread 31. The first and second gears 28, 30 are connected by a linear track 33, so that the second gear 30 co-rotates with the first gear 28, which corresponds to the relative axial movement between the first and second gears 28, 30. Relative to the connector 20, the second gear 30 rotates at a speed determined by the first gear 28 and moves axially at a speed determined by the difference between d1 and d2. Therefore, the pitch of the second helical thread 32 must be able to accommodate these simultaneous relative axial and rotational movements. In practice, these values ​​are related by the following equation:

[0019]

number

[0020] The gear ratio R is also equal to the ratio of the pitch of the sleeve thread 27 to the pitch of the piston rod thread 8 .

[0021] The pitches p1 and p2 of the first and second helical threads 31, 32 can be selected to have any suitable value in this ratio, in particular both threads may have a high pitch to provide low frictional resistance when force is applied to the gear mechanism to drive the axial movement of the nut 16 during the dose delivery mode.

[0022] Figure 2 shows another gear mechanism from that of Figure 1. As most of the two mechanisms are the same, they are given the same reference numerals and their description will not be repeated here. In particular, the connection between the connector 120 and the housing 4, the connection between the first gear 128 and the housing 4, and the connection between the second gear 130 and the nut 16 are the same as those of Figure 1. The differences concern the first, second and third engagement parts 131, 132, 133 between the first gear 128, the second gear 130 and the connector 120. These are therefore given different reference numerals and will be described below.

[0023] The first gear 128 is connected to the connector 120 by a first helical thread 131 as a first engagement portion, as in the mechanism of FIG. 1. However, in the mechanism of FIG. 2, the second engagement portion 132 is a straight track, and the second gear 130 and the connector 120 are allowed to move axially relative to each other, but are prevented from rotating relative to each other. Meanwhile, the third engagement portion is a third helical thread 133 between the first and second gears 128, 130. (There is no "second helical thread" in the mechanism of FIG. 2.) The third helical thread 133 has the same winding direction as the first helical thread 131, but has a smaller pitch than the first helical thread 131.

[0024] During operation of the device of FIG. 2, the first gear 128 is prevented from axial movement, the second gear 130 moves axially with the nut 16 a first axial distance d1, and the connector 120 moves axially a second axial distance d2. The connector 120 engages the first gear 128 via a first helical thread 131, so that axial movement of the connector 120 relative to the first gear 128 causes the first gear 128 to rotate at a speed determined by the pitch of the first helical thread 131. The connector 120 and the second gear 130 are coupled by a linear track 132, so that the second gear 130 co-rotates with the connector 120, which corresponds to the relative axial movement between the connector 120 and the second gear 130. Relative to the first gear 128, the second gear 130 rotates at a speed determined by the connector 120 and moves axially at a speed determined by the movement of the nut 16. Therefore, the pitch of the third helical thread 133 must be able to accommodate these simultaneous relative axial and rotational movements. In practice, these values ​​are related by the following equation:

[0025]

number

[0026] The gear ratio R is also equal to the ratio of the pitch of the sleeve thread 27 to the pitch of the piston rod thread 8 .

[0027] The pitches p1 and p3 of the first and third helical threads 131, 133 may be selected to have any suitable value in this ratio.

[0028] In FIG. 1, the first engagement portion 31 is a helical thread, the second engagement portion 32 is a helical thread, and the third engagement portion 33 is a straight track. In FIG. 2, the first engagement portion 131 is a helical thread, the second engagement portion 132 is a straight track, and the third engagement portion 133 is a helical thread. In principle, all three engagement portions could be formed as helical threads, which would provide another degree of freedom in selecting the relative pitch of their threads. However, such benefits may be outweighed by the increased design complexity. The first engagement portion cannot be formed as a straight track, which would lock the first gear both axially and rotationally to the housing. In any arrangement, the second and third engagement portions cannot both be formed as straight tracks, which would cause the connector, first gear, and second gear to all be rotationally locked together and would not be able to accommodate axial differential movement between the connector and the nut 16.

[0029] In the present invention, when the engagement between two components is via a helical thread, generally only one component will have a complete thread and the other component will have one or more complementary short threaded sections. In general, the choice of which components will have a complete thread and which will have a threaded section is open, and the invention is not intended to be limited to the specific choices illustrated in the drawings. Similarly, when the engagement between two components is via a linear track with one or more projections running in complementary channels, generally the choice of which components will have a track and which will have a channel is open. Again, the invention is not intended to be limited to the specific choices illustrated in the drawings. It will be understood that configurations other than projections running in channels are possible to allow the two components to move axially without relative rotation. For example, one component may slide telescopically within the other, and the two components may have complementary non-circular cross sections.

[0030] Figures 3 to 6 show one embodiment of a dose delivery device according to the invention, which employs a gear mechanism of the type shown in Figure 1 and in which the same reference numbers are used.

[0031] A cartridge holder 40 is screwed into the front end of the housing 4. The cartridge holder 40 holds a drug cartridge 42, which contains a piston 44 that can move forward along an axis to expel the drug from the drug cartridge 42. The cartridge holder 40 further comprises a thread 46 for mounting a double-ended hollow needle (not shown). One end of the hollow needle is capable of penetrating the septum of the drug cartridge 42 and the other end is capable of delivering the drug expelled from the drug cartridge 42 to the skin of a patient.

[0032] The piston rod 6 is positioned along the axis 2 of the device such that the bottom 14 of the front end of the piston rod engages the piston 44 to urge the piston 44 along the drug cartridge 42. The piston rod 6 includes an external thread 8. The external thread 8 is interrupted by a pair of opposed flat surfaces, such that the piston rod 6 has a non-circular cross-section.

[0033] The piston rod guide 48 is fixed within the housing 4 such that the piston rod guide 48 cannot move relative to the housing 4, at least while the cartridge holder 40 is attached. The piston rod guide 48 defines a central opening 10 through which the piston rod 6 is slidable along the axis 2. The opening 10 has a non-circular shape complementary to the cross-section of the piston rod 6, thereby preventing the piston rod 6 from rotating relative to the housing 4.

[0034] The piston rod 6 passes through a hole in the nut 16, which includes an internal thread 49 at its forward end that engages with the external thread 8 of the piston rod 6. A rigid tube 18 extends rearward from the nut 16 and surrounds, but is not engaged with, the piston rod 6. The tube 18 is connected to the nut 16 such that it can move axially relative to the nut 16 but cannot rotate. Thus, any rotation of the tube 18 will necessarily rotate the nut 16. In the illustrated embodiment, an axial rib 50 on the tube 18 engages with an axial slot, not visible in the drawing, on the inside of the nut 16. Alternatively, the rib may be on the nut and the slot may be on the tube.

[0035] The dose dial sleeve 26 is nested within the housing 4 and includes a helical sleeve thread 27 on its outer surface. One or more threaded portions 51 on the inner wall of the housing 4 engage the sleeve thread 27, thereby allowing the dose dial sleeve 26 to move relative to the housing 4 following the helical path of the sleeve thread 27. A window 52 is provided in the housing 4 to allow indicia (not shown) on the dose dial sleeve 26 to be visible as the dose dial sleeve 26 rotates past the window 52, ​​thereby indicating to the user the dose that has been set. The dose dial sleeve 26 includes teeth 54 arranged side by side around the circumference of its rear end. The dose dial sleeve 26 further includes an internal flange 56 near its rear end.

[0036] A generally cylindrical connector 20 is concentrically disposed within the dose dial sleeve 26. At its forward end, the connector 20 includes an external flange 58 from which a number of lugs 24 project radially outward. In the illustrated embodiment, the number of lugs 24 is four, although other numbers are possible. The lugs 24 engage a corresponding number of axially aligned linear tracks 22 provided within the housing, such that the connector 20 is axially slidable but not rotatable relative to the housing 4. Towards its rearward end, the connector 20 is reduced in diameter via a step 62 to form a reduced diameter neck 60. The neck 60 is in sliding engagement with the outer surface of the tube 18. The step 62 of the connector 20 axially engages the front face of the internal flange 56 of the dose dial sleeve 26. A first ratchet portion 93, described below, is fixed to the neck 60 of the connector 20 and axially engages the rear face of the internal flange 56 of the dose dial sleeve 26. This constrains the dose dial sleeve 26 to move axially with the connector 20, but still allows relative rotation therebetween.

[0037] The first gear 28 is nested concentrically inside the connector 20 and outside the nut 16. The anchor piece 64 is fixed against axial or rotational movement inside the housing 4 and engages the front end of the first gear 28, thereby preventing the first gear 28 from moving axially but still allowing it to rotate freely about the axis 2. The front end of the first gear 28 is divided by a number of slots 66 to form a portion that is flexible enough to engage with the anchor piece 64 in a snap-fit ​​manner. The first gear 28 is connected to the connector 20 by a first threaded engagement portion that includes a helical thread 31 on the outside of the first gear 28 and is engaged by a threaded portion 68 on the inside of the connector 20. It will be recalled that since the connector 20 can only move axially and the first gear 28 can only move rotationally, the relative speed of these two movements is determined by the pitch p1 of the first helical thread 31.

[0038] The second gear 30 has substantially the same diameter as the nut 16. The second gear 30 is nested concentrically about the axis 2 between the first gear 28 and the tube 18 and is offset axially to the rear of the nut 16. The nut 16 and the second gear 30 abut each other such that as the nut 16 moves rearward, the second gear 30 is also driven rearward, but the second gear 30 is still free to rotate relative to the nut 16. The second gear 30 is connected to the connector 20 by a second engagement portion including a short threaded portion 70 on the outside of the second gear 30 that engages with a helical thread 32 on the inside of the connector 20. The second gear 30 is connected to the first gear 28 by a third engagement portion including an axial linear track 33 on the outside of the second gear 30 that engages with an inward projection 72 (see FIG. 5) on the inside of the first gear 28. This allows relative axial movement but not relative rotation between the first and second gears 28, 30. It will be understood that the relationship between the nut 16, the first gear 28, the second gear 30 and the connector 20 is the same as the gear mechanism described above in connection with FIG.

[0039] The dose selection portion 74 is located at the rear end of the device. A skirt 75 of the dose selection portion 74 is provided with a gripping portion 76 on its outer surface, which allows the user to rotate the dose selection portion 74 to set the desired dose. The dose selection portion 74 is attached to the rear end of the tube 18 such that the dose selection portion 74 can slide axially a short distance relative to the tube 18, but cannot rotate relative to the tube 18. In the illustrated embodiment, the inner sleeve 78 of the dose selection portion 74 includes an axial rib 79 that engages with an axial slot 80 in the tube 18. Alternatively, the rib may be provided on the tube and the slot may be provided on the dose selection portion.

[0040] The dose selection part 74 is held on the device by an arm 82 that extends forward and terminates in a hook 84 that snaps into place behind a corresponding hook 86 at the rear end of the dose dial sleeve 26. A compression spring 88 urges the dose selection part 74 rearward until it is stopped by engagement between the hooks 84,86. The skirt 75 of the dose selection part 74 includes a series of teeth 90 arranged along the inner circumference of its forward end. These teeth 90 are complementary to the teeth 54 on the outside of the dose dial sleeve 26 such that when the hooks 84,86 of the dose selection part 74 and the dose dial sleeve 76 are engaged, the respective sets of teeth 90,54 also engage with one another to prevent relative rotation between the dose selection part 74 and the dose dial sleeve 76.

[0041] The forward end of the compression spring 88 bears against a bidirectional rotating ratchet assembly 92 as a click mechanism including first, second and third ratchet sections 93, 94, 95. The first ratchet section 93 is rotationally fixed to the neck section 60 of the connector 20 and the third ratchet section 95 is rotationally fixed to the dose selection section 74. The second ratchet section 94 is formed as a rotating collar between the first and third ratchet sections 93, 95. The first set of ratchet teeth allows relative rotation between the first and second ratchet sections 93, 94 in a first angular direction but does not allow relative rotation in a second, opposite angular direction. The second set of ratchet teeth allows relative rotation between the second and third ratchet sections 94, 95 in a second angular direction but does not allow relative rotation in the first angular direction. Ratchet portions 93, 94, 95 are maintained in axial compression by compression spring 88 such that, in order for each set of ratchet teeth to pass each other, they must first move axially against the force of compression spring 88 before rebounding with an audible click. The angular spacing of the ratchet teeth may be selected so that each click corresponds to a unit added to or removed from the set dose.

[0042] The operation of the illustrated apparatus will now be described.

[0043] 5 shows the device in an initial configuration before a new dose (not necessarily the first dose) is set. The nut 16, connector 20, first gear 28, second gear 30 and dose dial sleeve 26 are all positioned as far forward as possible, with the dose dial sleeve 26 displaying a zero set dose through the window 52. In the dose set mode of operation, the compression spring 88 is extended to urge the dose selection portion 74 rearwardly against the dose dial sleeve 26 until further movement is prevented by engagement of the hooks 84, 86. This also engages the teeth 54, 90, rotationally locking the dose selection portion 74 against the dose dial sleeve. Because the dose selection portion 74 is displaced rearward, the tube 18 has some freedom to move axially, but remains rotationally locked against the dose selection portion 74 and the nut 16.

[0044] When the user rotates the dose selection portion 74 in a first angular direction to increase the set dose, the dose dial sleeve 26, which is rotationally locked to the dose selection portion 74, rotates the same angle and displays a series of indicia through the window 52 to indicate the new dose that has been set. The dose dial sleeve 26 simultaneously moves backwards in accordance with the sleeve thread 27 an axial distance (a "second axial distance" d2) determined by the pitch of the sleeve thread 27 relative to the housing. As previously described, the connector 20 is constrained to move axially together with the dose dial sleeve 26. Under the force of the compression spring 88, the hook 84 of the dose selection portion 74 remains engaged with the hook 86 of the dose dial sleeve 26, so that the dose selection portion 74 also moves the same axial distance d2 following the movement of the dose dial sleeve 26. Meanwhile, the third ratchet portion 95 rotates together with the dose selection portion 74. The second ratchet portion 94 cannot rotate in this direction relative to the first ratchet portion 93 and, as a result, remains rotationally locked to the connector 20 and thus to the housing. The third ratchet portion 95 therefore clicks over the second ratchet portion 94 providing further audible and tactile feedback to the user of the dose that has been set.

[0045] If the user turns the dose selection member 74 too far and wishes to reduce the set dose, they simply turn the dose selection member 74 in the opposite angular direction and the dose dial sleeve 26 screws back into the housing 4 according to the sleeve threads 27, displaying the new, reduced dose through the window 52. As the dose selection member 74 is turned in this second angular direction, the second and third ratchet portions 94, 95 rotate with the dose selection member 74 and the second ratchet portion 94 clicks over the non-rotating first ratchet portion 93, providing audible and tactile feedback of the change in the set dose.

[0046] The dose selection member 74 is rotationally locked to the rigid tube 18, which in turn is rotationally locked to the nut 16, so that rotation of the dose selection member 74 in either direction also rotates the nut 16 the same amount. The nut 16 travels an axial distance d1 along the piston rod threads 8. This axial distance d1 is determined by the pitch of the piston rod threads 8 and is less than the axial distance d2 traveled by the dose dial sleeve 26 and dose selection member 74. The axial differential movement is accommodated by the tube 18 sliding axially relative to the nut 16 and / or dose selection member 74.

[0047] Axial movement of the nut 16, forward or backward, is transmitted to the second gear 30, but rotational movement is not transmitted. This causes the gear mechanism described above in connection with Figure 1 to operate, adjusting the difference between the axial movement of the nut 16 and second gear 30, which moves an axial distance d1, and the movement of the connector 20, which moves a larger axial distance d2, by the co-rotation and relative axial movement of the first and second gears 28, 30.

[0048] Once the desired dose is set, the user pushes the dose selection portion 74 forward to inject the set dose. The dose selection portion 74 first moves axially relative to the dose dial sleeve 26 against the force of the compression spring 88, disengaging the teeth 90, 54 and allowing the dose selection portion 74 and dose dial sleeve 26 to rotate relative to each other. The axial movement of the dose selection portion 74 relative to the dose dial sleeve 26 continues until the end of the inner sleeve 78 of the dose selection portion 74 abuts the ratchet assembly 92 or until the compression spring 88 is fully compressed. Thus, the ratchet portions 93, 94, 95 are prevented from moving axially and therefore cannot click past each other, and the dose selection portion 74 is prevented from rotating relative to the connector 20. The device is now in dose delivery mode.

[0049] Any further force applied to the dose selection part 74 is directly transmitted (without rotation) to the neck 60 of the connector 20 via the ratchet assembly 92, sliding the connector 20 axially forward back to its initial position. The gear mechanism now works in reverse, whereby the forward axial movement of the connector 20, which moves a distance d2, is translated via the first gear 28 into a forward axial movement of the second gear 30, which moves a distance d1. The second gear 30 pushes the nut 16 forward the same distance back to its initial axial position. The piston rod thread 8 may be self-locking, whereby application of an axial force to the nut 16 prevents it from rotating along the thread 8. In any case, the nut 16 remains rotationally locked via the tube 18 to the dose selection part 74, which is not rotating in this dose delivery mode. The nut 16 thus moves forward without rotation, and the nut 16 also drives the piston rod 6, which moves forward without rotation an axial distance d1 proportional to the set dose.

[0050] The axial force applied to the dose selection portion 74 is also transmitted to the internal flange 56 of the dose dial sleeve 26 via the first ratchet portion 93, which drives the dose dial sleeve 26 to move forward by simultaneously rotating the dose dial sleeve 26 in accordance with the sleeve threads 27 until it returns to its initial position defined by the rotational stop of the sleeve threads 27.

[0051] Once the dose has been delivered and the nut 16, connector 20 and dose dial sleeve 26 have returned to their initial axial positions, pressure on the dose selection portion 74 may be released. The compression spring 88 then returns the dose selection portion 74 to the initial position shown in Figure 5. The device may be used to set and deliver further doses until the supply of drug in the drug cartridge 42 is exhausted.

[0052] The above described device can be modified in various ways without departing from the invention. For example, instead of the illustrated bidirectional ratchet 92, an alternative click mechanism may include two opposing rings of symmetrical triangular teeth. The two rings can move against the force of the compression spring 88 to click past each other when the dose selection portion 74 is rotated in either direction during the dose setting mode. During the dose delivery mode, the compression spring 88 is compressed and the teeth are clamped together preventing relative rotation between the dose selection portion 74 and the connector 20.

[0053] Means may be provided to prevent a dose being set that is greater than the amount of drug remaining in the drug cartridge 42. For example, the piston rod 6 may be provided with a head such that the axial distance between the head of the piston rod and the initial position of the nut thread 49 is a measure of the remaining drug. As the amount of drug remaining approaches zero, the axial distance between the head of the piston rod and the initial position of the nut thread 49 will also approach zero. During the next dose setting mode, the head prevents the nut 16 from retracting too far to set a dose greater than the amount of drug remaining.

[0054] If the device is intended to be reusable, such that an empty medicament cartridge 42 can be replaced with a full medicament cartridge, a reset mechanism may be provided to easily return the piston rod 6 to its initial position. For example, the reset mechanism may allow the piston rod guide 48 to be rotationally disengaged from the housing 4 when the cartridge holder 40 is removed, thereby allowing the piston rod 6 to be rotated relative to the nut 16, thereby threading the piston rod 6 back along the piston rod thread 8 and into position before delivering the first dose from the replacement cartridge.

Claims

1. A housing (4); a piston rod (6) including a piston rod thread (8) and configured to move axially without rotation relative to said housing (4); a nut (16) that engages the piston rod threads (8); a dose selection part (74) rotationally locked to said nut (16); a connector (20, 120) configured to move axially without rotation relative to the housing (4); a first gear (28, 128) configured to rotate relative to the housing (4) without axial movement, the first gear (28, 128) being coupled to the connector (20, 120) by a first engagement portion, the first engagement portion being a first helical thread (31, 131); a second gear (30, 130) configured to rotate without axial movement relative to the nut (16), the second gear (30, 130) being coupled to the connector (20, 120) by a second engagement portion and to the first gear (28, 128) by a third engagement portion; 13. A dose delivery device comprising:

2. The dose delivery device of claim 1, wherein the third engagement portion is a linear track (33) that allows relative axial movement between the first gear (28) and the second gear (30) but prevents relative rotation between them.

3. the second engagement portion being a second helical thread (32); 3. The dose delivery device of claim 2, wherein the first helical thread (31) and the second helical thread (32) have the same winding direction and the second helical thread (32) has a smaller pitch than the first helical thread (31).

4. The dose delivery device of claim 1, wherein the second engagement portion is a linear track (132) that allows relative axial movement between the second gear (130) and the connector (120) but prevents relative rotation between them.

5. the third engagement portion being a third helical thread (133); 5. The dose delivery device of claim 4, wherein the first helical thread (131) and the third helical thread (133) have the same winding direction, and the third helical thread (133) has a smaller pitch than the first helical thread (131).

6. A dose delivery device as described in any one of claims 1 to 5, further comprising a dose dial sleeve (26) configured to rotate without axial movement relative to the connector (20, 120), the dose dial sleeve (26) engaging with the housing via a sleeve thread (27).

7. The dose selection portion (74) is axially movable relative to the dose dial sleeve (26), whereby in a dose setting mode, the dose selection portion (74) is rotationally locked to the dose dial sleeve (26) but rotationally disengaged from the connector (20, 120); 7. The dose delivery device of claim 6, wherein in a dose delivery mode, the dose selection portion (74) is rotationally disengaged from the dose dial sleeve (26).

8. The dose delivery device of claim 7, further comprising a click mechanism (88, 92) acting between the dose selection portion (74) and the connector (20, 120), the click mechanism (88, 92) generating a click sound when the dose selection portion (74) rotates relative to the connector (20, 120) in the dose setting mode and rotationally locking the dose selection portion (74) relative to the connector (20, 120) in the dose delivery mode.

9. A method of operating a dose delivery device comprising a housing (4) and a piston rod (6) configured to move axially without rotation relative to the housing (4), comprising the steps of: In a dose setting mode, a dose selection portion (74) is rotated relative to the housing (4) and the dose selection portion (74) is rotationally locked to the nut (16), causing the nut (16) to move along the threads (8) of the piston rod (6) a first axial distance (d １ ) in the backward direction, The axial movement of the nut (16) is transmitted to a connector (20, 120) configured to move axially without rotating relative to the housing (4) via a gear mechanism, so that the connector (20, 120) moves from an initial position to the first axial distance (d １ A second axial distance (d ２ ) in the backward direction, Including, The gear mechanism comprises: a first gear (28, 128) that rotates without axial movement relative to the housing (4), the first gear (28, 128) being connected to the connector (20, 120) by a first engagement portion, the first engagement portion being a first helical thread (31, 131); a second gear (30, 130) that rotates without axial movement relative to the nut (16), the second gear (30, 130) being coupled to the connector (20, 120) by a second engagement portion and to the first gear (28, 128) by a third engagement portion; 23. A method of operating a dose delivery device comprising:

10. The dose selection portion (74) is spaced apart from the second axial distance (d ２ 10. The method of operating a dose delivery device according to claim 9, wherein the dose selection portion (74) is coupled to the connector (20, 120) so as to move by a distance of 10 mm.

11. In dose delivery mode: The connector (20, 120) is spaced apart from the second axial distance (d ２ ) forward to said initial position; The nut (16) and the piston rod (6) are spaced apart by the first axial distance (d １ transmitting axial movement of the connector (20, 120) through the gear mechanism so as to move the connector (20, 120) forward by 11. A method of operating a dose delivery device according to claim 9 or 10, further comprising:

12. The dose dial sleeve (26) rotates along the dose dial thread (27) between the dose dial sleeve (26) and the housing (4) while moving the second axial distance (d ２ 12. A method of operating a dose delivery device as claimed in claim 11, further comprising:

13. In the dose setting mode, the dose selection portion (74) is rotationally locked relative to the dose dial sleeve (26); A method of operating a dose delivery device according to claim 12, wherein in the dose delivery mode, the dose selection portion (74) is rotationally disengaged from the dose dial sleeve (26).

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