Trigger Mechanism and Drug Delivery Device herewith

Abstract

The present disclosure is generally directed to a trigger mechanism for initiating dispensing doses of a medicament from a drug delivery device. The trigger mechanism includes a trigger element movable in a first direction relative to a counter element. To provide a feedback to a user of the trigger mechanism, the trigger element includes a first interference member and the counter element includes a second interference member located with respect to the first interference member such that upon movement of the trigger element relative to the counter element the first interference member contacts and passes over the second interference member, thereby generating an audible and/or tactile feedback. Further, the disclosure includes a drug delivery device for selecting and dispensing a number of user variable doses of a medicament comprising such a trigger mechanism.

Claims

1. A trigger mechanism for initiating dispensing doses of a medicament from a drug delivery device, the trigger mechanism comprising: a trigger element movable in a first direction relative to a counter element, wherein the trigger element comprises a first interference member and the counter element comprises a second interference member, the second interference member being located with respect to the first interference member such that upon movement of the trigger element relative to the counter element the first interference member contacts and passes over the second interference member, thereby generating an audible and/or tactile feedback.

2. The trigger mechanism according to claim 1, wherein the first interference member and/or the second interference member is configured to be elastically deformed upon movement of the trigger element with respect to the counter element.

3. The trigger mechanism according to claim 1, wherein the trigger element comprises a button movable in a longitudinal direction of the drug delivery device.

4. The trigger mechanism according to claim 1, wherein the first interference member comprises a collar or a flange.

5. The trigger mechanism according to claim 1, wherein the counter element is immovable in the first direction.

6. The trigger mechanism according to claim 1, wherein the counter element comprises a rotatable number sleeve of a component part thereof.

7. The trigger mechanism according to claim 1, wherein the counter element comprises a housing.

8. The trigger mechanism according to claim 1, wherein the second interference member comprises a tooth or a spline.

9. The trigger mechanism according to claim 1, comprising a spring acting on the trigger element.

10. A drug delivery device for selecting and dispensing a number of user variable doses of a medicament, the device comprising: a trigger mechanism comprising a trigger element configured to be moved in a first direction relative to a counter element, wherein the trigger element comprises a first interference member and the counter element comprises a second interference member which is located with respect to the first interference member such that upon movement of the trigger element relative to the counter element the first interference member contacts and passes over the second interference member, thereby generating an audible and/or tactile feedback, a housing, a dose selector operable to set a dose by rotation relative to the housing, a number sleeve arranged within the housing such that at least a portion of the number sleeve is visible through a first aperture in the housing, a piston rod coupled to the housing and to a drive sleeve such that rotation of the drive sleeve relative to the housing causes the piston rod to translate relative to the housing, a clutch arranged between the number sleeve and the drive sleeve, a dispense clicker comprising a flexible arm and a toothed profile, and a button operable to effect dose dispensing.

11. The drug delivery device according to claim 10, wherein the clutch comprises a separate clutch element which is permanently rotationally constrained to the number sleeve wherein the flexible arm is provided on one of the button and the clutch element, and the toothed profile is provided on the other of the button and the clutch element.

12. The drug delivery device according to claim 10, wherein the toothed profile is a ring of radially inwardly directed ratchet teeth.

13. The drug delivery device according to claim 12, wherein the toothed profile comprises at least two differently shaped ratchet teeth.

14. The drug delivery device according to claim 10, wherein the button is axially displaceable between a dose setting position and a dose dispensing position, wherein the button is rotatable relative to the housing in its dose setting position and rotationally locked to the housing in its dose dispensing position.

15. The drug delivery device according to claim 10, comprising a cartridge containing a medicament.

16. The drug delivery device according to claim 15, wherein the medicament comprises a pharmaceutically active compound.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0084] Non-limiting, exemplary embodiments of the disclosure will now be described with reference to the accompanying drawings, in which:

[0085] FIG. 1 shows a top view of the drug delivery device of the present disclosure in the minimum dose position;

[0086] FIG. 2 shows an exploded view of the components of the device of FIG. 1;

[0087] FIG. 4a shows an enlarged sectional view of a detail of the device of FIG. 1 in the dose setting mode;

[0088] FIG. 4b shows an enlarged sectional view of a detail of the device of FIG. 1 in the dose dispensing mode;

[0089] FIG. 5 shows an interface between the clutch plate and the button of the device of FIG. 1; and

[0090] FIG. 6 shows an alternative interface between the clutch plate and the button.

DETAILED DESCRIPTION

[0091] FIG. 1 shows a drug delivery device in the form of an injection pen. The device has a distal end (left end in FIG. 1) and a proximal end (right end in FIG. 1). The component parts of the drug delivery device are shown in FIG. 2. The drug delivery device comprises a body or housing 10, a cartridge holder 20, a lead screw (piston rod) 30, a drive sleeve 40, a nut 50, a dose indicator (number sleeve) 60, a trigger element in the form of a button 70, a dial grip or dose selector 80, a torsion spring 90, a cartridge 100, a gauge element 110, a clutch plate 120, a clutch spring 130 and a bearing 140. A needle arrangement (not shown) with a needle hub and a needle cover may be provided as additional components, which can be exchanged as explained above. All components are located concentrically about a common principal axis I of the mechanism which is shown in FIG. 3.

[0092] The housing 10 or body is a generally tubular element having a proximal end with an enlarged diameter. The housing 10 provides location for the liquid medication cartridge 100 and cartridge holder 20, windows 11a, 11b for viewing the dose number on the number sleeve 60 and the gauge element 110, and a feature on its external surface, e.g. a circumferential groove, to axially retain the dose selector 80. A flange-like or cylindrical inner wall comprises an inner thread engaging the piston rod 30. The housing 10 further has at least one internal, axially orientated slot or the like for axially guiding the gauge element 110. In the embodiment shown in the Figures, the distal end is provided with an axially extending strip partly overlapping cartridge holder 20. The Figures depict the housing 10 as a single housing component. However, the housing 10 could comprise two or more housing components which may be permanently attached to each other during assembly of the device.

[0093] The cartridge holder 20 is located at the distal side of housing 10 and permanently attached thereto. The cartridge holder may be a transparent or translucent component which is tubular to receive cartridge 100. The distal end of cartridge holder 20 may be provided with means for attaching a needle arrangement. A removable cap (not shown) may be provided to fit over the cartridge holder 20 and may be retained via clip features on the housing 10.

[0094] The piston rod 30 is rotationally constrained to the drive sleeve 40 via a splined interface. When rotated, the piston rod 30 is forced to move axially relative to the drive sleeve 40, through its threaded interface with the inner wall of housing 10. The lead screw 30 is an elongate member with an outer thread (FIG. 3) engaging the corresponding thread of the inner wall of housing 10. The leadscrew thread may have a large lead-in, for example a wedge shape form, at its distal end to engage a corresponding housing thread form on the first rotation. The interface comprises at least one longitudinal groove or track and a corresponding protrusion or spline of the driver 40. At its distal end, the lead screw 30 is provided with an interface for clip attachment of the bearing 140.

[0095] The drive sleeve 40 is a hollow member surrounding the lead screw 30 and arranged within number sleeve 60. It extends from an interface with the clutch plate 120 to the contact with the clutch spring 130. The drive sleeve 40 is axially movable relative to the housing 10, the piston rod 30 and the number sleeve 60 in the distal direction against the bias of clutch spring 130 and in the opposite proximal direction under the bias of clutch spring 130.

[0096] A splined tooth interface with the housing 10 prevents rotation of the drive sleeve 40 during dose setting. This interface comprises for example a ring of radially extending outer teeth at the distal end of drive sleeve 40 and corresponding radially extending inner teeth of the housing component 10. When the button 70 is pressed, these drive sleeve 40 to housing 10 spline teeth are disengaged allowing the drive sleeve 40 to rotate relative to housing 10.

[0097] A further splined tooth interface with the number sleeve 60 is not engaged during dialing, but engages when the button 70 is pressed, preventing relative rotation between the drive sleeve 40 and number sleeve 60 during dispense. This interface may comprise inwardly directed splines on a flange on the inner surface of the number sleeve 60 and a ring of radially extending outer splines of drive sleeve 40. The corresponding splines are located on the number sleeve 60 and the drive sleeve 40, respectively, such that axial movement of the drive sleeve 40 relative to the (axially fixed) number sleeve 60 engages or disengages the splines to rotationally couple or decouple the drive sleeve 40 and the number sleeve 60. Preferably, the splines are arranged such that they are decoupled when teeth of drive sleeve 40 and inner teeth of housing component 10 mesh and engage when teeth and inner teeth disengage.

[0098] A further interface of the drive sleeve 40 comprises a ring of ratchet teeth located at the proximal end face of drive sleeve 40 and a ring of corresponding ratchet teeth of clutch plate 120.

[0099] The driver 40 has a threaded section providing a helical track for the nut 50. In addition, a last dose abutment or stop is provided which may be the end of the thread track or preferably a rotational hard stop for interaction with a corresponding last dose stop of nut 50, thus limiting movement of the nut 50 on the driver thread. At least one longitudinal spline engages a corresponding track of the lead screw 30. Further, the drive sleeve is provided with a ramp interacting with a clicker arm when the drive sleeve 40 is in its distal position during dose dispensing, i.e. when button 70 is depressed.

[0100] The last dose nut 50 is located between the number sleeve 60 and the drive sleeve 40. It is rotationally constrained to the number sleeve 60, via a splined interface. It moves along a helical path relative to the drive sleeve 40, via a threaded interface, when relative rotation occurs between the number sleeve 60 and drive sleeve 40 which is during dialing only. As an alternative, the nut 50 may be splined to the driver 40 and threaded to the number sleeve 60. A last dose stop is provided engaging a stop of drive sleeve 40 when a dose is set corresponding to the remaining dispensable amount of medicament in the cartridge 100.

[0101] The dose indicator or number sleeve 60 is a tubular element as shown in FIGS. 2 and 3. The number sleeve 60 is rotated during dose setting (via dose selector 80) and dose correction and during dose dispensing by torsion spring 90. Together with gauge element 110 the number sleeve 60 defines a zero position (at rest) and a maximum dose position. Thus, the number sleeve 60 may be seen as a dose setting member.

[0102] For manufacturing reasons the number sleeve 60 of the embodiment shown in the Figures comprises a number sleeve lower 60a which is rigidly fixed to a number sleeve upper 60b during assembly to form the number sleeve 60. Number sleeve lower 60a and number sleeve upper 60b are separate components only to simplify number sleeve 60 mould mold tooling and assembly. As an alternative, the number sleeve 60 may be a unitary component. The number sleeve 60 is constrained to the housing 10 by features towards the distal end to allow rotation but not translation. The number sleeve lower 60a is marked with a sequence of numbers, which are visible through the gauge element 110 and the openings 11a, 11b in the housing 10, to denote the dialed dose of medicament.

[0103] Further, the number sleeve lower 60a has a portion with an outer thread engaging the gauge element 110. End stops are provided at the opposite ends of this thread to limit relative movement with respect to the gauge element 110.

[0104] Clutch features which have the form of a ring of splines 61 are provided inwardly directed on number sleeve upper 60b for engagement with splines 71 of the button 70 during dose setting and dose correction. The splines 61 are located at the proximal end of number sleeve upper 60b. A clicker arm 62 is provided on the outer surface of number sleeve 60 which interacts with the drive sleeve 40 and the gauge member 110 for generating a feedback signal. In addition, the number sleeve lower 60a is rotationally constrained to the nut 50 and to the clutch plate 120 via a splined interface comprising at least one longitudinal spline.

[0105] The button 70 which forms the proximal end of the device is permanently splined to the dose selector 80. A central tubular stem extends distally from the proximal actuation face of the button 70. The tubular stem forms a skirt and is provided with splines 71 for engagement with splines 61 of the number sleeve upper 60b. Thus, it is splined via splines 61, 71 to the number sleeve upper 60b when the button 70 is not pressed (FIG. 4a), but this spline interface is disconnected when the button 70 is pressed (FIG. 4b). The button 70 has a discontinuous annular skirt with further splines. When the button 70 is pressed, these further splines on the button 70 engage with splines on the housing 10, preventing rotation of the button 70 (and hence the dose selector 80) during dispense. These further splines disengage when the button 70 is released, allowing a dose to be dialed.

[0106] As can be seen in FIGS. 4a and 4b, the tubular stem of the button 70 further comprises an annular detent 72 extending radially outwards. The detent 72 has angled distal and proximal sides in the form of ramps. The detent 72 is arranged such that it interferes with the number sleeve splines 61 when the button is moved axially from its dose setting position (FIG. 4a) to its dose dispensing position (FIG. 4b). Due to the angled sides of the detent 72 and due to some elasticity of the button 70 and the number sleeve upper 60b, the detent 72 passes over the splines 61 during this movement, thereby creating a tactile and/or audible feedback. For example, a user is able to sense an increase in force required for actuating button 70 when detent 72 contacts splines 61. In addition, a click and/or vibrations may be generated when detent 72 loses contact with splines 61.

[0107] The dose selector 80 is axially constrained to the housing 10. It is rotationally constrained, via the splined interface, to the button 70. This splined interface which includes grooves interacting with spline features formed by the annular skirt of button 70 remains engaged irrespective of the dose button 70 axial positions. The dose selector 80 or dose dial grip is a sleeve-like component with a serrated outer skirt.

[0108] The torsion spring 90 is attached at its distal end to the housing 10 and at the other end to the number sleeve 60. The torsion spring 90 is located inside the number sleeve 60 and surrounds a distal portion of the drive sleeve 40. The torsion spring 90 may be pre-wound upon assembly, such that it applies a torque to the number sleeve 60 when the mechanism is at zero units dialed. The action of rotating the dose selector 80, to set a dose, rotates the number sleeve 60 relative to the housing 10, and charges the torsion spring 90 further.

[0109] The torsion spring 90 is formed from a helical wire with at least two different pitches. Both ends are formed from closed coils, i.e. the pitch equals the wire diameter and each coil contacts the adjacent coil. The central portion has open coils, i.e. the coils do not contact each other.

[0110] The cartridge 100 is received in cartridge holder 20 (FIG. 3). The cartridge 100 may be a glass ampoule having a moveable rubber bung 101 at its proximal end. The distal end of cartridge 100 is provided with a pierceable rubber seal which is held in place by a crimped annular metal band. In the embodiment depicted in the Figures, the cartridge 100 is a standard 1.5 ml cartridge. The device is designed to be disposable in that the cartridge 100 cannot be replaced by the user or health care professional. However, a reusable variant of the device could be provided by making the cartridge holder 20 removable and allowing backwinding of the lead screw 30 and the resetting of nut 50.

[0111] The gauge element 110 is constrained to prevent rotation but allow translation relative to the housing 10 via a splined interface. The gauge element 110 has a helical feature on its inner surface which engages with the helical thread cut in the number sleeve 60 such that rotation of the number sleeve 60 causes axial translation of the gauge element 110. This helical feature on the gauge element 110 also creates stop abutments against the end of the helical cut in the number sleeve 60 to limit the minimum and maximum dose that can be set.

[0112] The gauge element 110 has a generally plate or band like component having a central aperture or window and two flanges extending on either side of the aperture. The flanges are preferably not transparent and thus shield or cover the number sleeve 60, whereas the aperture or window allows viewing a portion of the number sleeve lower 60a. Further, gauge element 110 has a cam and a recess interacting with clicker arm 62 of the number sleeve 60 at the end of dose dispensing.

[0113] As can be seen in FIG. 5, the clutch plate 120 is a ring-like component. The clutch plate 120 is splined to the number sleeve 60. It is also coupled to the drive sleeve 40 via a ratchet interface. The ratchet provides a detented position between the number sleeve 60 and drive sleeve 40 corresponding to each dose unit, and engages different ramped tooth angles during clockwise and anti-clockwise relative rotation. A clicker arm 121 is provided on the clutch plate 120 for interaction with ratchet features 73 of the button 70.

[0114] The clutch spring 130 is a compression spring. The axial position of the drive sleeve 40, clutch plate 120 and button 70 is defined by the action of the clutch spring 130, which applies a force on the drive sleeve 40 in the proximal direction. This spring force is reacted via the drive sleeve 40, clutch plate 120, and button 70, and when at rest it is further reacted through the dose selector 80 to the housing 10. The spring force ensures that the ratchet interface between driver and clutch plate is always engaged. In the at rest position, it also ensures that the button splines are engaged with the number sleeve splines, and the drive sleeve teeth are engaged with teeth of the housing 10. In addition, the force of the clutch spring 130 is sufficient to push button 70 back in the proximal direction after dose dispensing with detent 72 passing over splines 61. This may generate an additional feedback signal indicating to a user that dose dispensing is ended.

[0115] The bearing 140 is axially constrained to the piston rod 30 and acts on the bung 101 within the liquid medicament cartridge. It is axially clipped to the lead screw 30, but free to rotate.

[0116] With the device in the at rest condition as shown in FIG. 4a, the number sleeve 60 is positioned against its zero dose abutment with the gauge element 110 and the button 70 is not depressed. Dose marking 0 on the number sleeve 60 is visible through the windows of the housing 10 and gauge element 110, respectively. The torsion spring 90, which has a number of pre-wound turns applied to it during assembly of the device, applies a torque to the number sleeve 60 and is prevented from rotating by the zero dose abutment.

[0117] The user selects a variable dose of liquid medicament by rotating the dose selector 80 clockwise, which generates an identical rotation in the number sleeve 60. Rotation of the number sleeve 60 causes charging of the torsion spring 90, increasing the energy stored within it. As the number sleeve 60 rotates, the gauge element 110 translates axially due to its threaded engagement thereby showing the value of the dialed dose. The gauge element 110 has flanges either side of its window area which cover the numbers printed on the number sleeve 60 adjacent to the dialed dose to ensure only the set dose number is made visible to the user.

[0118] A specific feature of this disclosure is the inclusion of a visual feedback feature in addition to the discrete dose number display typical on devices of this type. The distal end (flange) of the gauge element 110 creates a sliding scale through the small window 11a in the housing 10. As an alternative, the sliding scale could be formed using a separate component engaged with the number sleeve 60 on a different helical track.

[0119] As a dose is set by the user, the gauge element 110 translates axially, the distance moved proportional to the magnitude of the dose set. This feature gives clear feedback to the user regarding the approximate size of the dose set. The dispense speed of an auto-injector mechanism may be higher than for a manual injector device, so it may not be possible to read the numerical dose display during dispense. The gauge feature provides feedback to the user during dispense regarding dispense progress without the need to read the dose number itself. For example, the gauge display may be formed by an opaque element on the gauge element 110 revealing a contrasting colored component underneath. Alternatively, the revealable element may be printed with coarse dose numbers or other indices to provide more precise resolution. In addition, the gauge display simulates a syringe action during dose set and dispense.

[0120] The openings 11a, 11 b in the housing 10 allow the user to view the gauge feature and number display. To reduce dust ingress and prevent the user from touching moving parts, these openings 11a, 11b are covered by translucent windows. These windows may be separate components, but in this embodiment they are incorporated into the housing 10 using twin-shot moulding molding technology.

[0121] The mechanism utilises a dose selector 80 with an increased diameter relative to the housing 10 which aids dialing although this is not a requirement of the mechanism. This feature is particularly useful (but not essential) for an auto-injector mechanism where a power supply is charged during dose setting and the torque required to turn the dose selector 80 may be higher than for a non-auto injector device.

[0122] The drive sleeve 40 is prevented from rotating as the dose is set and the number sleeve 60 rotated, due to the engagement of its splined teeth with teeth of the housing 10. Relative rotation must therefore occur between the clutch plate 120 and drive sleeve 40 via the ratchet interface.

[0123] The user torque required to rotate the dose selector 80 is a sum of the torque required to wind up the torsion spring 90, and the torque required to overhaul the ratchet interface. The clutch spring 130 is designed to provide an axial force to the ratchet interface and to bias the clutch plate 120 onto the drive sleeve 40. As the user rotates the dose selector 80 sufficiently to increment the mechanism by one increment, the number sleeve 60 rotates relative to the drive sleeve 40 by one ratchet tooth. At this point the ratchet teeth re-engage into the next detented position. An audible click is generated by the ratchet re-engagement, and tactile feedback is given by the change in torque input required.

[0124] Relative rotation of the number sleeve 60 and the drive sleeve 40 is allowed as splines are disengaged during dose setting. This relative rotation also causes the last dose nut 50 to travel along its threaded path, towards its last dose abutment on the drive sleeve 40. With no user torque applied to the dose selector 80, the number sleeve 60 is now prevented from rotating back under the torque applied by the torsion spring 90, solely by the ratchet interface between the clutch plate 120 and the drive sleeve 40. The user may now choose to increase the selected dose by continuing to rotate the dose selector 80 in the clockwise direction. If the user continues to increase the selected dose until the maximum dose limit is reached, the number sleeve 60 engages with its maximum dose abutment on the maximum dose abutment of gauge element 110. This prevents further rotation of the number sleeve 60, clutch plate 120 and dose selector 80.

[0125] Depending on how many increments have already been delivered by the mechanism, during selection of a dose, the last dose nut 50 may contact its last dose abutment with stop face of the drive sleeve 40. The abutment prevents further relative rotation between the number sleeve 60 and the drive sleeve 40, and therefore limits the dose that can be selected. The position of the last dose nut 50 is determined by the total number of relative rotations between the number sleeve 60 and drive sleeve 40, which have occurred each time the user sets a dose.

[0126] With the mechanism in a state in which a dose has been selected, the user is able to deselect any number of increments from this dose. Deselecting a dose is achieved by the user rotating the dose selector 80 anti-clockwise. The torque applied to the dose selector 80 by the user is sufficient, when combined with the torque applied by the torsion spring 90, to overhaul the ratchet interface between the clutch plate 120 and drive sleeve 40 in the anti-clockwise direction. When the ratchet is overhauled, anti-clockwise rotation occurs in the number sleeve 60 (via the clutch plate 120), which returns the number sleeve 60 towards the zero dose position, and unwinds the torsion spring 90. The relative rotation between the number sleeve 60 and drive sleeve 40 causes the last dose nut 50 to return along its helical path, away from the last dose abutment.

[0127] With the mechanism in a state in which a dose has been selected, the user is able to activate the mechanism to commence delivery of a dose. Delivery of a dose is initiated by the user depressing the button 70 axially in the distal direction. This requires detent 72 to pass over splines 61, thereby generating a feedback.

[0128] When the button 70 is depressed, splines between the button 70 and number sleeve 60 are disengaged, rotationally disconnecting the button 70 and dose selector 80 from the delivery mechanism, i.e. from number sleeve 60, gauge element 110 and torsion spring 90. Splines on the button 70 engage with splines on the housing 10, preventing rotation of the button 70 (and hence the dose selector 80) during dispense. As the button 70 is stationary during dispense, it can be used in the dispense clicker mechanism as shown in FIGS. 5 and 6. A stop feature in the housing 10 limits axial travel of the button 70 and reacts any axial abuse loads applied by the user, reducing the risk of damaging internal components.

[0129] The clutch plate 120 and drive sleeve 40 travel axially with the button 70. This engages the splined tooth interface between the drive sleeve 40 and number sleeve 60 preventing relative rotation between the drive sleeve 40 and number sleeve 60 during dispense. The splined tooth interface between the drive sleeve 40 and the housing 10 disengages, so the drive sleeve 40 can now rotate and is driven by the torsion spring 90 via the number sleeve 60, and clutch plate 120.

[0130] Rotation of the drive sleeve 40 causes the piston rod 30 to rotate due to their splined engagement, and the piston rod 30 then advances due to its threaded engagement to the housing 10. The number sleeve 60 rotation also causes the gauge element 110 to traverse axially back to its zero position whereby the zero dose abutment stops the mechanism.

[0131] Tactile feedback during dose dispensing is provided via the compliant cantilever clicker arm 121 integrated into the clutch plate 120. This arm 121 interfaces radially with ratchet features 73 on the inner surface of the button 70, whereby the ratchet tooth spacing corresponds to the number sleeve 60 rotation required for a single increment dispense (FIG. 5). During dispense, as the number sleeve 60 rotates and the button 70 is rotationally coupled to the housing 10, the ratchet features 73 engage with the clicker arm 121 to produce an identical audible click with each dose increment delivered. In the alternative embodiment of FIG. 6, the ratchet features 73 of the button have a different form. Compared with FIG. 5 every other tooth 73 is omitted in FIG. 6, thus generating a feedback only every other unit dispensed. As a further alternative, the size of the teeth 73 may vary, thereby generating different feedback signals depending which tooth 73 contacts clicker arm 121.

[0132] Delivery of a dose continues via the mechanical interactions described above while the user continues to depress the button 70. If the user releases the button 70, the clutch spring 130 returns the drive sleeve 40 to its at rest position (together with the clutch plate 120 and button 70), engaging the splines 14, 41 between the drive sleeve 40 and housing 10, preventing further rotation and stopping dose delivery.

[0133] During delivery of a dose, the drive sleeve 40 and number sleeve 60 rotate together, so that no relative motion in the last dose nut 50 occurs. The last dose nut 50 therefore travels axially relative to the drive sleeve 40 during dialing only.

[0134] Once the delivery of a dose is stopped, by the number sleeve 60 returning to the zero dose abutment, the user may release the button 70, which will re-engage the spline teeth between the drive sleeve 40 and housing 10 due to the bias of clutch spring 130. This proximal movement includes passing detent 72 back over splines 61. The mechanism is now returned to the at rest condition.

[0135] At the end of dose dispensing, additional audible feedback is provided in the form of a click, distinct from the clicks provided during dispense, to inform the user that the device has returned to its zero position via the interaction of clicker arm 62 on the number sleeve 60 with the ramp on the drive sleeve 40 and the cam and the recess on the gauge element 110. This embodiment allows feedback to only be created at the end of dose delivery and not created if the device is dialed back to, or away from, the zero position.

TABLE-US-00001 Reference Numerals: 10 housing 11a opening (window) 11b opening (window) 20 cartridge holder 30 lead screw (piston rod) 40 driver (axially movable drive sleeve) 50 nut 60 dose indicator (number sleeve) 60a number sleeve lower 60b number sleeve upper 61 spline (second interference member) 62 clicker arm 70 button 71 spline 72 detent (first interference member) 73 ratchet teeth 80 dose selector 90 torsion spring 100 cartridge 101 bung 110 gauge element 120 clutch plate 121 clicker arm 130 clutch spring 140 bearing I longitudinal axis