Dosing device with a drive

Abstract

In the dose setting mode of the dose delivery device, the dose selector (74) rotates to turn the nut (16) so that the nut moves backward along the thread (8) of the piston rod (6) by a first axial distance (d<subgt;1< / subgt>). The gearing mechanism transfers the axial movement of the nut (16) to the connector (20), which moves backward by a second axial distance (d<subgt;2< / subgt>) without rotating. In the dose delivery mode of the device, the dose selector (74) is pushed forward and drives the connector (20) to move forward by the second axial distance (d<subgt;2< / subgt>). The gearing mechanism transfers the axial movement of the connector (20) to the nut (16), which pushes the piston rod (6) forward by the first axial distance (d<subgt;1< / subgt>) without rotating. The gearing mechanism includes a first gear (28) that rotates relative to the housing (4) without axial movement and a second gear (30) that rotates relative to the nut (16) without axial movement.

Description

Field of the Invention

[0001] The present invention relates to a dose delivery device, also known as a syringe pen, which provides means for setting a dose of a drug and then delivering that dose from a cartridge to a patient. The dose is typically set by moving a dose selector to a position corresponding to the desired dose, and then delivered by pushing the dose selector back to its initial position through a first distance. The cartridge typically contains a plurality of doses of the drug in a chamber, and the dose delivery device includes a piston rod that is advanced to eject each dose from the chamber, the piston rod moving through a second distance that determines the volume of the dose delivered. The present invention particularly relates to a gear-driven dose delivery device in which the first distance is not equal to the second distance. Background Art

[0002] Gear-driven dose delivery devices are known. Since the volume of the drug delivered from the cartridge is typically very small, the piston rod only needs to be advanced through a small axial distance to deliver a typical dose. The gearing provides a first benefit in that the button and / or dose selector can be arranged to move through a larger distance, which is typically proportional to the distance the piston rod moves. This allows the user to more precisely set the desired dose. The gearing also provides a second benefit resulting from the improved mechanical advantage of the mechanism. In many cases, it enables the user to apply a small force over a longer distance rather than a large force over a shorter distance, making drug delivery easier and more controllable. It must be ensured that this benefit is not outweighed by the additional friction introduced by the gearing mechanism.

[0003] In some dose delivery devices, the movement of the dose selector in the drug delivery mode is automatically driven by the energy of a spring rather than manually by the pressure applied by the user. When the dose selector is moved during the dose setting mode, the user adds energy to the spring. The benefits of the gearing 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 present invention are defined in the dependent claims.

[0006] In this specification, the word "drug" is used to describe any fluid substance that will be delivered by the pen in a measured dose. It is typically a bioactive substance that is injected into a human or animal subject, for example, for medical or cosmetic purposes. However, the present invention can be used in other applications where it is desired to dispense a fixed amount of a substance.

[0007] In the present specification, terms such as "front" and "forward" indicate the direction towards the end of the drug delivery device where the needle is located, which is shown at the bottom of the drawings. Terms such as "rear" and "backward" indicate the opposite direction. Description of the Drawings

[0008] Figure 1 is a schematic view of a first drive mechanism according to the present invention.

[0009] Figure 2 is a schematic view of a second drive mechanism according to the present invention.

[0010] Figure 3 is a perspective view of a dose delivery device according to the present invention.

[0011] Figure 4 is Figure 3 an exploded view of the dose delivery device.

[0012] Figures 4a to 4d is Figure 4 an enlarged view of a part of.

[0013] Figure 5 is Figure 3 a longitudinal section of a part of the dose delivery device.

[0014] Figure 6 is Figure 3 an exploded perspective view of the components of the dose scale mechanism of the dose delivery device. Detailed Description of the Invention

[0015] Figure 1 is a highly schematic cross-sectional view of the drive mechanism of the dose delivery device. Specifically, the dimension perpendicular to axis 2 is enlarged to introduce space and improve clarity. The mechanism is shown substantially only on one side of axis 2. The other side is a mirror image except for the helix direction of the threads.

[0016] A generally cylindrical housing 4 surrounds axis 2 and houses the drive mechanism. A piston rod 6 aligned with axis 2 includes a piston rod thread 8 on its outer surface. The piston rod 6 is configured to slide non-rotatably through a central hole 10 fixed relative to the housing 4. The piston rod thread 8 is interrupted by a pair of opposing planes or by two or more longitudinal tracks 12, thereby providing a non-circular cross-section of the piston rod 6 complementary to the shape of the hole 10 and preventing the piston rod 6 from rotating relative to the housing 4. At the front end of the piston rod 6, beyond the hole 10 and away from the drive mechanism, a foot 14 is configured to engage a piston of a cartridge (not shown) that can be attached to the device. The front end of the cartridge can be pierced by a hollow needle (not shown), whereby forward movement of the piston rod 6 along axis 2 causes the piston to advance along the cartridge and discharge a measured amount of drug from the cartridge through the needle.

[0017] The nut 16 includes an internal thread by which it engages with the piston rod thread 8 such that rotation of the nut 16 causes it to travel along the thread 8. The rigid tube 18 surrounds the piston rod 6 and extends rearwardly from the nut 16. The tube 18 is fixed to the nut 16 such that it follows the movement of the nut.

[0018] The generally cylindrical connector 20 surrounds the axis 2 and is configured to move axially relative to the housing 4 without rotation. The inner wall of the housing 4 may be provided with one or more axial tracks 22 and the connector 20 may include a corresponding number of radially projecting lugs 24 that slide in the respective tracks 22.

[0019] The generally cylindrical dose scale sleeve 26 is concentric with the axis 2 and is radially nested between the housing 4 and the connector 20. It engages the connector 20 in such a way that the dose scale sleeve 26 is restricted to move axially with the connector 20 but allows relative rotation therebetween. The dose scale sleeve 26 engages with the housing via a sleeve thread 27 such that any axial movement of the dose scale sleeve 26 relative to the housing 4 must be accompanied by simultaneous rotation of the dose scale sleeve 26 along the sleeve thread 27. The sleeve thread 27 has the same hand of helix as the piston rod thread 8 but has a larger pitch.

[0020] We now describe the operation of the gearing mechanism; more details of other parts of the device will be provided below in relation to the specific embodiments shown below Figures 3 to 6 in connection with the specific embodiments shown below.

[0021] During the dose setting operation mode, the tube 18 rotates and causes the nut 16 to move rearwardly along the piston rod thread 8 through a first axial distance d1, which corresponds to the dose of the drug to be delivered. At the same time, the connector 20 moves axially rearwardly through a second axial distance d2 that is greater than the first axial distance d1 without rotation, thereby providing the aforementioned benefits of a gear-driven dose delivery device. In Figure 1 the example shown, the second axial distance d2 is twice as large as the first axial distance d1, but in other examples the gear ratio can be greater or smaller. During the dose delivery operation mode, the connector 20 is pushed forward to return to its initial position. The nut 16 moves forward simultaneously through the first axial distance d1, this time without rotation, to return to its initial axial position but does not necessarily return to its initial rotational position. This forward movement of the nut 16 advances the piston rod 6 through the first axial distance d1, thereby expelling a proportional dose of the drug from the cartridge.

[0022] The differential movement between the nut 16 and the connector 20 is mediated by the first gear 28 and the second gear 30. The first and second gears 28, 30 are generally cylindrical and concentric with the axis 2, nested between the tube 18 and the connector 20. The first gear 28 is coupled to the housing 4, thereby preventing its axial movement relative to the housing 4, but being free to rotate. The first gear 28 is coupled to the connector 20 by a first engagement portion in the form of a first helical thread 31. The second gear 30 is coupled to the nut 16, thereby preventing its axial movement relative to the nut 16, but being free to rotate. The second gear 30 is coupled to the connector 20 by a second engagement portion 32 and to the first gear by a third engagement portion 33.

[0023] In Figure 1 the shown gearing mechanism, the third engagement portion 33 between the first and second gears 28, 30 is a straight track which allows relative axial movement but prevents relative rotation between the gears. The second engagement portion between the second gear 30 and the connector 20 is a second helical thread 32 which has the same hand as the first helical thread 31, but has a smaller pitch. The hands of the first and second helical threads 31, 32 may be the same or opposite to the hands of the piston rod thread 8 and the sleeve thread 27.

[0024] During operation of the device, the first gear 28 is prevented from axial movement, the second gear 30 moves axially together with the nut 16 through a first axial distance d1, and the connector 20 moves axially through a second axial distance d2. The connector 20 engages with the first gear 28 via the first helical thread 31, so the 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. Since the first and second gears 28, 30 are coupled by the straight track 33, the second gear 30 rotates together with the first gear 28, while the straight track 33 accommodates 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 such that it can accommodate these simultaneous relative axial and rotational movements. In fact, these values are related by the following equation:

[0025]

[0026] where:

[0027] p1 is the pitch of the first helical thread 31,

[0028] p2 is the pitch of the second helical thread 32, and

[0029] R is the transmission ratio, R = d2 / d1

[0030] The transmission ratio R is also equal to the ratio between the pitch of the sleeve thread 27 and the pitch of the piston rod thread 8.

[0031] The pitches p1 and p2 of the first and second helical threads 31, 32 can be chosen to have any suitable values, provided they are in that ratio. Specifically, the two threads can have large pitches so that during the dose delivery mode, when a force is applied to the drive mechanism to drive the axial movement of the nut 16, they should provide low frictional resistance.

[0032] Figure 2 is shown Figure 1 an alternative drive mechanism of the transfer device mechanism, most of the two mechanisms being the same, so they are given the same reference numerals and their description will not be repeated here. Specifically, the couplings between the connector 120 and the housing 4, between the first gear 128 and the housing 4, and between the second gear 130 and the nut 16 are the same as Figure 1 in. The differences relate to the first, second and third joints 131, 132, 133 between the first gear 128, the second gear 130 and the connector 120, so they are given different reference numerals and will now be described.

[0033] The first gear 128 is again coupled to the connector 120 by a first joint in the form of a first helical thread 131. However, in this mechanism, the second joint 132 is a straight track which allows relative axial movement but prevents relative rotation between the second gear 130 and the connector 120. On the other hand, the third joint is a third helical thread 133 between the first and second gears 128, 130. (In this mechanism, there is no "second helical thread"), and the third helical thread 133 has the same hand of helix as the first helical thread 131 but has a smaller pitch.

[0034] In Figure 2During operation of the device, axial movement of the first gear 128 is prevented, the second gear 130 axially moves together with the nut 16 through a first axial distance d1, and the connector 120 axially moves through 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 rate determined by the pitch of the first helical thread 131. Since the connector 120 and the second gear 130 are coupled by a straight track 132, the second gear 130 rotates together with the connector 120, while the straight track 132 accommodates the relative axial movement between the connector 120 and the second gear 130. The second gear 130 rotates relative to the first gear 128 at a speed determined by the connector 120 and axially moves at a speed determined by the movement of the nut 16. Therefore, the pitch of the third helical thread 133 must be such that it can accommodate these simultaneous relative axial and rotational movements. In fact, these values are related by the following equation:

[0035]

[0036] where:

[0037] p1 is the pitch of the first helical thread 131,

[0038] p3 is the pitch of the third helical thread 133, and

[0039] R is the transmission ratio, R = d2 / d1

[0040] The transmission ratio R is also equal to the ratio between the pitch of the sleeve thread 27 and the pitch of the piston rod thread 8.

[0041] The pitches p1 and p3 of the first and third helical threads 131, 133 can be chosen to have any suitable values, as long as they are in that ratio.

[0042] In Figure 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 Figure 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 can be formed as helical threads, which would provide another degree of freedom in choosing the relative pitches of these threads. However, the additional complexity of the design may outweigh any benefits that can be provided. The first engagement portion cannot be formed as a straight track because the first gear would be axially and rotationally locked to the housing. In any given device, the second and third engagement portions cannot both be formed as straight tracks because then the connector, the first gear, and the second gear would all be rotationally locked together and would not be able to accommodate the differential axial movement between the connector and the nut 16.

[0043] In the present invention, when the engagement between two components is via a helical thread, it is generally sufficient that only one of the two components includes a full thread while the other component includes one or more short thread sections complementary thereto. It is generally freely selectable which component should include the full thread and which component should include the thread sections, and the present invention is not to be limited to the specific selection shown in the drawings. Similarly, when the engagement between two components is via a straight track including one or more protrusions extending in complementary channels, it is generally freely selectable which component should include the track and which should include the channel. Again, the present invention is not to be limited to the specific selection shown in the drawings. It should be understood that arrangements other than the protrusions extending in the channels are also possible to allow axial movement of the two components without relative rotation. For example, one component may slide telescopically within the other component, the two components having complementary non-circular cross-sections.

[0044] Figures 3 to 6 An embodiment of a dose delivery device according to the present invention is shown. This embodiment employs a Figure 1 transmission mechanism of the type shown and will use the same reference numerals.

[0045] The cartridge holder 40 is screwed into the front end of the housing 4. The cartridge holder 40 holds a cartridge 42 which in turn contains a piston 44 which can be moved forward along the axis to expel the drug from the cartridge 42. The cartridge holder 40 also includes a thread 46 for attaching a double-ended hollow needle (not shown), one end of which is able to pierce the septum of the cartridge 42 and the other end of which is able to deliver the drug expelled from the cartridge 42 into the skin of a patient.

[0046] The piston rod 6 is arranged along the axis 2 of the device such that the foot 14 at the front end of the piston rod engages the piston 44 to push the piston along the cartridge 42. The piston rod 6 includes an external thread 8 which is interrupted by a pair of opposing flats so that the piston rod 6 has a non-circular cross-section.

[0047] The piston rod guide 48 is fixed in the housing 4 such that at least when the cartridge holder 40 is attached, the piston rod guide 48 cannot move relative to the housing 4. The piston rod guide 48 defines a central hole 10 through which the piston rod 6 can slide along the axis 2. The hole 10 has a non-circular shape complementary to the cross-section of the piston rod 6 which prevents the piston rod 6 from rotating relative to the housing 4.

[0048] The piston rod 6 passes through a hole in the nut 16 which includes an internal thread 49 at its front end that engages the external thread 8 of the piston rod 6. A rigid tube 18 extends rearwardly from the nut 16 and surrounds the piston rod 6 without engaging it. The tube 18 is coupled to the nut 16 such that the tube 18 can move axially but cannot move rotationally relative to the nut 16. Thus, when the tube 18 rotates, the nut 16 must also rotate. In the illustrated embodiment, axial ribs 50 on the tube 18 engage internal axial slots (not visible in the drawing) in the nut 16. Alternatively, the ribs can be provided on the nut and the slots can be provided on the tube.

[0049] The dose scale sleeve 26 is nested within the housing 4 and includes a helical sleeve thread 27 on its outer surface. One or more threaded segments 51 on the inner wall of the housing 4 engage the sleeve thread 27 such that the dose scale sleeve 26 can move relative to the housing 4 by following a helical path of the sleeve thread 27. A window 52 is provided in the housing 4 to permit viewing of markings (not shown) on the dose scale sleeve 26 when the sleeve rotates past the window 52, thereby indicating to the user the dose that has been set. The dose scale sleeve 26 includes an array of teeth 54 disposed around the outer circumference of its rear end. The dose scale sleeve 26 also includes an inner flange 56 near its rear end.

[0050] The generally cylindrical connector 20 is concentrically located within the dose scale sleeve 26. At its front end, the connector 20 includes an outer flange 58 from which a plurality of lugs 24 project radially outwardly. In the illustrated embodiment, the number of lugs 24 is four, but other numbers are possible. The lugs 24 engage a corresponding number of axially aligned straight tracks 22 in the interior of the housing such that the connector 20 can slide axially but cannot rotate relative to the housing 4. Towards the rear end of the connector 20, its diameter is gradually reduced via a shoulder 62 to form a reduced-diameter neck 60 that slidably engages the outer surface of the tube 18. The shoulder 62 of the connector 20 axially engages the front of the inner flange 56 of the dose scale sleeve 26. A first ratchet member 93 (described below) is fixed to the neck 60 of the connector 20 and axially engages the rear of the inner flange 56 of the dose scale sleeve 26. Thereby the dose scale sleeve 26 is restricted to move axially with the connector 20, but relative rotation between them is still possible.

[0051] The first gear 28 is concentrically nested within the connector 20 and outside the nut 16. The anchor 64 is fixed within the housing 4 to prevent axial or rotational movement and engages the front end of the first gear 28 such that the first gear 28 is prevented from moving axially but remains free to rotate about the axis 2. The front end of the first gear 28 is separated by a plurality of slots 66 to form segments having sufficient flexibility to engage the anchor 64 in a hook - and - latch fit. The first gear 28 is coupled to the connector 20 by a first threaded engagement that includes a helical thread 31 on the exterior of the first gear 28 that is engaged by a threaded segment 68 on the interior of the connector 20. It will be recalled that the connector 20 is only capable of axial movement and the first gear 28 is only capable of rotational movement, so the relative speed of these two movements is determined by the pitch p1 of the first helical thread 31.

[0052] The second gear 30 has a diameter substantially the same as the nut 16. It is disposed concentrically about the axis 2, nested between the first gear 28 and the tube 18, and axially offset to the rear of the nut 16. The nut 16 and the second gear 30 are adjacent to each other such that if the nut 16 moves rearward, it also drives the second gear 30 rearward, but the second gear 30 remains free to rotate relative to the nut 16. The second gear 30 is coupled to the connector 20 by a second engagement that includes a short threaded segment 70 on the exterior of the second gear 30 that engages the internal helical thread 32 of the connector 20. The second gear 30 is coupled to the first gear 28 by a third engagement that includes a straight axial track 33 on the exterior of the second gear 30 that is engaged by an inward projection 72 on the interior of the first gear 28 (see Figure 5 ). Thus, the first and second gears 28, 30 are able to move axially relative to each other but not rotationally relative to each other. It can now be appreciated that the relationship between the nut 16, the first gear 28, the second gear 30, and the connector 20 is the same as that of the transmission mechanism described previously with respect to Figure 1 the described transmission mechanism.

[0053] The dose selector 74 is provided at the rear end of the device. The skirt 75 of the dose selector 74 provides a grip 76 on its outer surface by which the user can rotate the dose selector 74 to set the desired dose. The dose selector 74 is mounted on the rear end of the tube 18 such that the dose selector 74 can axially slide a short distance relative to the tube 18 but cannot rotate relative to it. In the illustrated embodiment, the inner sleeve 78 of the dose selector 74 includes axial ribs 79 that engage axial slots 80 in the tube 18. Alternatively, the ribs can be provided on the tube and the slots can be provided in the dose selector.

[0054] The dose selector 74 is held on the device by a forwardly extending arm 82 terminating in a hook 84 which snap-fits behind a corresponding hook 86 at the rear end of the dose scale sleeve 26. A compression spring 88 urges the dose selector 74 rearwardly until its movement is arrested by the engagement between the corresponding hooks 84, 86. The skirt 75 of the dose selector 74 includes an array of teeth 90 disposed around the inner circumference of its front end. These teeth 90 are complementary to the external teeth 54 on the dose scale sleeve 26 such that when the corresponding hooks 84, 86 of the dose selector 74 and the dose scale sleeve 26 are engaged, the sets of corresponding teeth 90, 54 also engage one another and prevent relative rotation between the dose selector 74 and the dose scale sleeve 26.

[0055] The front end of the compression spring 88 abuts a click mechanism in the form of a bi-directional rotary ratchet assembly 92 which includes first, second and third ratchet members 93, 94, 95. The first ratchet member 93 is rotationally fixed to the neck 60 of the connector 20 and the third ratchet member 95 is rotationally fixed to the dose selector 74. The second ratchet member 94 is formed as a rotary collar between the first and third ratchet members 93, 95. A set of first ratchet teeth permits relative rotation between the first and second ratchet members 93, 94 in a first angular direction but not in the opposite second angular direction. A set of second ratchet teeth permits relative rotation between the second and third ratchet members 94, 95 in the second angular direction but not in the first angular direction. The ratchet members 93, 94, 95 are held in axial compression by the spring 88 such that in order for the corresponding ratchet teeth of each set to pass one another, they must first move axially against the force of the spring 88 before springing back with a click. The angular pitch of the ratchet teeth can be selected such that each click corresponds to a unit added to or removed from the set dose.

[0056] The operation of the illustrated device will now be described.

[0057] Figure 5 The device is shown in its initial configuration prior to setting a new dose (which need not be the first dose). The nut 16, the connector 20, the first gear 28, the second gear 30 and the dose scale sleeve 26 are all positioned as far forward as possible and the dose scale sleeve 26 displays a set dose of zero through the window 52. In the dose setting operation mode, the compression spring 88 extends to urge the dose selector 74 rearwardly relative to the dose scale sleeve 26 until further movement is prevented by the engagement of the corresponding hooks 84, 86. The corresponding teeth 54, 90 thus also engage to rotationally lock the dose selector 74 to the dose scale sleeve. Since the dose selector 74 is displaced rearwardly, the tube 18 has some freedom of axial movement but it remains rotationally locked to the dose selector 74 and to the nut 16.

[0058] When the user rotates the dose selector 74 in the first angular direction to increase the set dose, the dose scale sleeve 26, which is rotationally locked to the dose selector 74, rotates by the same angle and displays a series of markings through the window 52 to indicate the new dose that has been set. The dose scale sleeve 26 simultaneously follows the sleeve thread 27 and moves axially backward relative to the housing by an axial distance (“second axial distance” d2) determined by the pitch of the sleeve thread 27. As previously described, the connector 20 is restricted to move axially with the dose scale sleeve 26. Under the force of the compression spring 88, the hook 84 of the dose selector 74 remains engaged with the hook 86 of the dose scale sleeve 26, so the dose selector 74 also follows the dose scale sleeve 26 and moves through the same axial distance d2. At the same time, the third ratchet member 95 rotates with the dose selector 74. The second ratchet member 94 cannot rotate relative to the first ratchet member 93 in this direction, and the first ratchet member 93 is in turn rotationally locked to the connector 20 and thus to the housing. Therefore, the third ratchet member 95 clicks on the second ratchet member 94 to provide further audible and tactile feedback to the user setting the dose.

[0059] If the user rotates the dose selector 74 too far and wishes to decrease the set dose, the dose selector 74 can simply be rotated in the opposite angular direction, and the dose scale sleeve 26 will screw back into the housing 4 along the sleeve thread 27 to indicate the new decreased dose through the window 52. When the dose selector 74 is rotated in this second angular direction, the second and third ratchet members 94, 95 rotate with it, while the second ratchet member 94 clicks on the non-rotating first ratchet member 93 to provide audible and tactile feedback of the change in the set dose.

[0060] Since the dose selector 74 is rotationally locked to the rigid tube 18, which in turn is rotationally locked to the nut 16, rotation of the dose selector 74 in either direction causes the nut 16 to rotate by the same angle. The nut 16 moves axially along the piston rod thread 8 by an axial distance d1, which is determined by the pitch of the piston rod thread 8 and is less than the axial distance d2 moved by the dose scale sleeve 26 and the dose selector 74. The different axial movements are accommodated by the tube 18 that slides axially relative to the nut 16 and / or the dose selector 74.

[0061] The forward or backward axial movement of the nut 16, rather than its rotational movement, is transmitted to the second gear 30. This initiates the gearing mechanism previously described with respect to Figure 1 which the co-rotation and relative axial movement of the first gear 28 and the second gear 30 accommodate the difference between the axial movement of the nut 16 and the second gear 30 through the axial distance d1 and the movement of the connector 20 through the greater axial distance d2.

[0062] When the desired dose has been set, the user pushes the dose selector 74 forward to inject the set dose. The dose selector 74 first axially moves relative to the dose scale sleeve 26 against the force of the spring 88 to disengage the corresponding teeth 90, 54, so that the dose selector 74 and the dose scale sleeve 26 are free to rotate relative to each other. The axial movement of the dose selector 74 relative to the dose scale sleeve 26 continues until the end of the inner sleeve 78 of the dose selector 74 abuts against the ratchet assembly 92 or until the spring 88 is fully compressed. Thereby, the corresponding ratchet members 93, 94, 95 are prevented from axially moving so that they cannot click past each other, and the dose selector 74 is prevented from rotating relative to the connector 20. The device is now in the dose delivery mode.

[0063] The further force applied to the dose selector 74 is directly transmitted through the ratchet assembly 92 (without any rotation) to the neck 60 of the connector 20, and causes the connector 20 to axially slide forward to return to its initial position. Now, the transmission mechanism works in reverse, whereby the forward axial movement of the connector 20 by a distance d2 is converted via the first gear 28 into the forward axial movement of the second gear 30 by a distance d1. The second gear 30 pushes the nut 16 forward by the same distance to return to its initial axial position. The piston rod thread 8 can be self-locking so that applying an axial force to the nut 16 does not cause it to rotate along the thread 8. In any case, the nut 16 remains rotationally locked to the dose selector 74 via the tube 18, which does not rotate in this dose delivery mode. Thus, the nut 16 moves forward without rotating, and it also drives the piston rod 6 forward by an axial distance d1 without rotation, which axial distance is proportional to the set dose.

[0064] The axial force applied to the dose selector 74 is also transmitted to the inner flange 56 of the dose scale sleeve 26 through the first ratchet member 93. This drives the dose scale sleeve 26 to move forward, which can be achieved by simultaneously rotating to follow the sleeve thread 27 until it returns to its initial position defined by the rotation stop in the sleeve thread 27.

[0065] Once the dose has been delivered and the nut 16, the connector 20 and the dose scale sleeve 26 have returned to their initial axial positions, the pressure on the dose selector 74 can be released. Then, the compressed spring 88 returns the dose selector 74 to Figure 5 the initial position shown. The device can now be used to set and deliver additional doses until the drug supply in the cartridge 42 is exhausted.

[0066] The device may be varied in various ways without departing from the invention. For example, instead of the illustrated two-way ratchet 92, an alternative click mechanism may include two facing rings of symmetric triangular teeth that may move against the force of spring 88 to click past each other when the dose selector 74 is rotated in either direction during the dose setting mode. During the dose delivery mode, spring 88 is compressed and the teeth are held together to prevent relative rotation between the dose selector 74 and the connector 20.

[0067] Means may be provided to prevent the setting of a dose greater than the amount of drug remaining in the 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 amount of drug remaining. Then, 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 a subsequent dose setting mode, the head will prevent the nut 16 from retracting far enough to set a dose greater than the amount of drug remaining.

[0068] If the device is intended for reuse such that an empty cartridge 42 may be replaced by a full cartridge, a reset mechanism may also be provided to facilitate returning the piston rod 6 to its initial position. For example, when the cartridge holder 40 is removed, the reset mechanism may allow the piston rod guide 48 to be rotationally disengaged from the housing 4 such that the piston rod 6 can rotate relative to the nut 16 and thereby be screwed back along the piston rod thread 8 to return to its desired position prior to delivering the first dose from the replacement cartridge.

Claims

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

2. The dose delivery device according to claim 1, wherein, The third engagement portion is a straight track that allows relative axial movement between the first and second gears but prevents relative rotation between the first and second gears.

3. The dose delivery device according to claim 2, wherein: the second engagement portion is a second helical thread (32); the first and second helical threads have the same hand of helix; and the second helical thread (32) has a smaller pitch than the first helical thread (31).

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

5. The dose delivery device according to claim 4, wherein: the third engagement portion is a third helical thread (133); the first and third helical threads have the same hand of helix; and the third helical thread (133) has a smaller pitch than the first helical thread (131).

6. The dose delivery device according to any one of the preceding claims, further comprising a dose scale sleeve (26) configured to rotate relative to the connector (20, 120) without axial movement, the dose scale sleeve (26) engaging the housing via a sleeve thread (27).

7. The dose delivery device according to claim 6, wherein, The dose selector (74) is axially movable relative to the dose scale sleeve (26) such that: in the dose setting mode, the dose selector (74) is rotatably locked to the dose scale sleeve (26) but is rotationally disengaged from the connector (20, 120); and in the dose delivery mode, the dose selector (74) is rotationally disengaged from the dose scale sleeve (26).

8. The dose delivery device according to claim 7 further comprises a click mechanism which acts between the dose selector (74) and the connector (20, 120) to produce a click sound when the dose selector (74) rotates relative to the connector (20, 120) in the dose setting mode; and rotationally locks the dose selector (74) to the connector (20, 120) in the dose delivery mode.

9. A method of operating a dose delivery device, the dose delivery device comprising a housing (4) and a piston rod (6) configured to axially move relative to the housing (4) without rotation; the method comprising: In the dose setting mode, rotating a dose selector (74) relative to the housing (4), the dose selector (74) being rotationally locked to a nut (16) which thereby moves axially backward along a thread (8) of the piston rod (6) by a first axial distance (d1); and Transmitting the axial movement of the nut (16) to a connector (20, 120) configured to axially move relative to the housing (4) without rotation in the dose setting mode and the dose delivery mode, such that the connector (20, 120) moves backward from an initial position by a second axial distance (d2) greater than the first axial distance (d1); Wherein the transmission mechanism comprises: A first gear (28, 128) which rotates 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 which is a first helical thread (31, 131); and A second gear (30, 130) which rotates relative to the nut (16) without axial movement, 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.

10. The method according to claim 9, wherein The dose selector (74) is coupled to the connector (20, 120) such that the dose selector (74) also moves by the second axial distance (d2).

Images