Spring strain mechanism for torsion spring based devices

Abstract

The present invention relates to a drug delivery device (1), comprising: a housing (2) extending along a main axis; a torsion spring (5), the torsion spring comprising a first spring end (4) fixedly arranged relative to the housing (2) and a second spring end (6) rotatable about the main axis; a rotatable shaft (80) extending along the main axis, the rotatable shaft (80) having a non-self-locking thread (81) and axially fixed relative to the housing (2); a spring end retainer (82), the second spring end (6) being attached to the spring end retainer, the spring end retainer (82) being rotationally fixed relative to the rotatable shaft (80); and a nut member (45) engaged with the non-self-locking thread (81), the nut member (45) being axially movable by translation relative to the housing (2), thereby causing the non-self-locking thread (81) to travel between a first position in which the torsion spring (5) is in a relaxed state and a second position in which the torsion spring (5) is in a strained state.

Description

Technical Field

[0001] The present invention relates generally to medical devices and, more particularly, to an automatic drug delivery device including a torsion spring powered drug expelling mechanism. Background Art

[0002] Drug delivery devices such as injection devices are widely used to administer liquid drugs to people who need therapeutic treatment. Many injection devices are capable of repeatedly setting and injecting fixed or variable volumes of drugs when operating the corresponding dose setting and drug expelling mechanism in the device. Some injection devices are suitable for loading pre-filled drug reservoirs containing a certain volume of drug sufficient to provide multiple injectable doses. When the reservoir becomes empty, the user will replace it with a new reservoir, so that the injection device can be used again and again. Other injection devices are pre-filled when delivered to the user and can only be used after the drug reservoir has been emptied, after which the device is discarded. Various injection devices include a drug expelling mechanism, which usually discharges the drug by using a motion-controlled piston rod to advance a piston in the reservoir.

[0003] Some injection devices require the user to press a button a certain distance towards the housing, thereby manually causing the piston rod to pressurize the reservoir and advance the piston therein to expel the dose. The force that must be applied to the button to perform such an operation is generally not large and may cause operational problems for people with reduced finger strength and / or dexterity.

[0004] Automatic injection devices that provide automatic expulsion of a dose of drug in response to the release of a cocked spring are popular because the spring, once released, provides all the energy required to complete the injection. Such devices typically require only a small, short-duration force to be applied by the user to trigger the injection. The spring may be arranged to be strained prior to each injection, or it may be pre-strained, for example by the manufacturer, to store energy sufficient to cause the drug reservoir to empty in one or more injections.

[0005] However, such energy storage can be challenging because large parts of the injection device components are typically plastic and therefore risk being overloaded by the heavy strain springs. If the injection device has a long shelf life and / or is used over a long period of time, this can lead to creep. This problem can be addressed by designing the components that bear the load with larger dimensions or by using more expensive materials, but this would contrast with the general desire to provide a small and inexpensive injection device that can be carried discreetly.

[0006] In view of this, it is sometimes preferred to provide automatic drug delivery devices of the foregoing type in which the majority of the spring-induced loading of the bearing component is achieved within a relatively short period of time, even though these devices require an additional user handling step in the form of a spring straining action.

[0007] In WO 2009 / 092807 (Novo Nordisk A / S), it is shown how a spring straining action can be incorporated as part of a treatment procedure that is normally performed by the user in any manner. Specifically, WO 2009 / 092807 teaches a pen injection device in which a drive spring is axially compressed during installation and / or removal from a protective capped pen housing.

[0008] US 8,343,103 (TecPharma Licensing AG) discloses a dual chamber mixing and injection device in which the expulsion spring is compressed during the introduction of the ampoule into the device. In this case, in order to compress the spring, the user is required to perform repeated rotational actions to screw the ampoule holder into the device housing. This appears cumbersome and some users may find this ergonomically challenging.

[0009] Even though WO 2009 / 092807 discloses the use of a torsionally pre-strained spring, the spring is essentially a compression spring, as disclosed in US 8,343, 103. Both documents do not relate to a solution for easily straining a torsion spring in a drug delivery device. Summary of the invention

[0010] It is an object of the present invention to obviate or mitigate at least one disadvantage of the prior art, or to provide a useful alternative to prior art solutions.

[0011] In particular, it is an object of the present invention to provide a drug delivery device based on a torsion spring, wherein straining of the torsion spring can be easily performed, which can also be easily performed by persons with reduced dexterity.

[0012] Another object of the present invention is to provide a device in which the straining of the torsion spring does not require a separate handling step by the user.

[0013] In the disclosure of the present invention, various aspects and embodiments will be described that will address one or more of the above objectives and / or will address objectives that will be apparent from the following text.

[0014] A drug delivery device, such as a drug injection device, embodying the principles of the present invention comprises: a housing extending along a main axis; a torsion spring comprising a first spring end fixedly arranged relative to the housing and a second spring end rotatable about the main axis; a rotatable shaft extending along the main axis, the rotatable shaft having a non-self-locking thread and axially fixed relative to the housing; a spring end retainer to which the second spring end is attached, the spring end retainer being rotationally fixed relative to the rotatable shaft; and a nut member engaged with the non-self-locking thread. The nut member can be axially moved between a first position on the non-self-locking thread in which the torsion spring is in a relaxed state and a second position on the non-self-locking thread in which the torsion spring is in a strained state by translation relative to the housing.

[0015] Such a mechanism converts translational motion of the nut member into rotational motion of the rotatable shaft and spring end retainer, thereby causing angular displacement of the second spring end relative to the first spring end, ie, the mechanism provides strain in the torsion spring based on a purely linear input.

[0016] The nut member may be coupled to a user interface structure that is accessible from the outside of the housing, such as a button that can slide along the housing surface, or it may itself be accessible from the outside of the housing, allowing the user to manipulate it directly. In any case, a simple linear motion by the user is sufficient to store energy in the torsion spring.

[0017] The drug delivery device inherently comprises a drug expelling mechanism, and the torsion spring may be adapted to power the drug expelling mechanism.Alternatively, the torsion spring may be adapted to power another mechanism in the drug delivery device.

[0018] In one aspect, the present invention provides a drug delivery device as defined in claim 1 .

[0019] Therefore, a drug delivery device is provided, comprising: a housing extending along a main axis or reference axis; a drug expelling mechanism; and a torsion spring adapted to provide power to the drug expelling mechanism. The torsion spring comprises a first spring end fixedly arranged relative to the housing and a second spring end rotatable about the main axis.

[0020] The drug delivery device also includes a rotatable shaft, which extends along the main axis and is axially fixed relative to the housing. The rotatable shaft is provided with a non-self-locking thread and a load-bearing spring end retainer, the spring end retainer is rotationally fixed relative to the rotatable shaft, and the second spring end is attached to the rotatable shaft. In addition, a nut member engages with the non-self-locking thread. The nut member can be axially moved by translation relative to the housing, that is, the nut member is rotationally locked relative to the housing. Thus, due to the non-self-locking thread, the rotatable shaft rotates in response to the translation movement of the nut member, and vice versa. The nut member is therefore configured to allow the non-self-locking thread to travel between a first position where the torsion spring is in a first energy state (e.g., a relaxed state) and a second position where the torsion spring is in a second energy state (e.g., a strained state).

[0021] The drug delivery device also includes an input structure for straining the torsion spring. The input structure is axially movable by translation relative to the housing and includes an interface portion accessible to be operated from the outside of the housing (i.e., mechanically contactable), allowing a user to cause translation of the input structure by interacting with the interface portion. The nut member is axially fixed relative to the input structure, and as the nut member advances the non-self-locking thread, the rotatable shaft rotates in response to the translational movement of the interface portion.

[0022] The nut member can be translated by the user immediately before initiating the drug expelling action, whereby the nut member will cause the non-self-locking thread to move from the first position to the second position to strain the torsion spring and then release it, whereby the torsion spring will release its stored energy and push the nut member to cause the non-self-locking thread to move from the second position back to the first position.

[0023] The nut member may be separated from the drug expelling mechanism during the translation of the nut member toward the second position along the first axial direction, and may be operably coupled to the drug expelling mechanism during the translation of the nut member toward the first position along the second axial direction (i.e., opposite to the first axial direction). Therefore, the translation of the nut member along the first axial direction has no effect on the drug expelling mechanism, while the translation of the nut member along the second axial direction causes the activation of the drug expelling mechanism. For example, the drug expelling mechanism may include a piston rod configured to be axially advanced relative to the housing by rotation relative to the housing, i.e., distal movement (i.e., helical movement), and the nut member may be rotationally separated from the piston rod during translation along the first axial direction, and may be rotationally coupled to the piston rod during translation along the second axial direction.

[0024] Thus, when the drug expelling mechanism is powered, when the drug delivery device is ready to deliver a drug dose, and when the drug delivery device expel a prepared dose, the torsion spring exhibits a shift between a relaxed state and a strained state. It is worth noting that in the relaxed state, the torsion spring is not completely relaxed, as the manufacturer slightly pre-strains the torsion spring during assembly of the drug delivery device to ensure that there is always enough energy to deliver the entire intended dose, regardless of its size.

[0025] The drug delivery device may also include a releasable retaining mechanism for holding the torsion spring in a strained state. For example, the releasable retaining mechanism may include a one-way ratchet mechanism, wherein a ratchet arm is rotationally locked relative to the spring end retainer and is axially movable between a holding position and a release position, in which the ratchet arm engages with a ratchet surface that is rotationally locked relative to the housing, thereby preventing the spring end retainer from rotating in the spring deployment direction, and in the release position, the ratchet arm disengages from the ratchet surface, thereby allowing the spring end retainer to rotate in the spring deployment direction. The ratchet arm may be biased toward the holding position, for example, by a compression spring.

[0026] The torsion spring and the rotatable shaft can be arranged so that the nut member moves relative to the proximal side of the housing so that the spring end retainer rotates in the direction of the spring strain. Alternatively, the torsion spring and the rotatable shaft can be arranged so that the nut member moves relative to the distal side of the housing so that the spring end retainer rotates in the direction of the spring strain. Therefore, the drug delivery device can be designed according to the most suitable way found about the translation direction of the nut member that strains the torsion spring. For example, if the drug delivery device also includes a detachable cover for protecting a drug reservoir connected to the distal end portion of the housing, the nut member can be operably connected to the cover and is configured to move distally relative to the spring strain of the housing in response to the cover being removed from the housing. Remove the cover, and the drug reservoir is exposed as a result, for example, allowing the injection needle assembly to be attached to the drug reservoir, thus triggering the strain of the torsion spring, thereby automatically preparing the drug discharge mechanism.

[0027] The input structure may comprise an axially extending rod member, and the interface portion may be arranged at an end portion of the axially extending rod member, axially spaced from the nut member. This will allow the nut member to be operated at an axial distance away from the nut member.

[0028] In a particular embodiment of the invention, the nut member forms part of the input structure, thereby minimising the number of components in the device whilst providing a rigid and stable construction for the spring straining mechanism.

[0029] The drug delivery device may further comprise a reservoir holder for holding at least one drug reservoir. The reservoir holder may be axially fixed to the distal end portion of the housing and may comprise an axially extending track, e.g. a slot or groove, which is preferably straight or linear, in which the interface portion is slidably arranged. This allows, for example, the nut member to be operated from the distal end of the drug delivery device.

[0030] The drug delivery device may also include an injection needle device, the injection needle device including an injection needle unit, which is configured to be attached to the distal portion of the reservoir holder by relative translational movement. An axially extending track may extend from the distal portion of the reservoir holder, and a portion of the injection needle device may be configured to interact with the interface portion during attachment of the injection needle unit. Thus, for example, proximal movement of the injection needle device above the reservoir holder may push the interface portion proximally in the axially extending track, and the torsion spring is therefore automatically strained during attachment of the injection needle unit to the reservoir holder.

[0031] The injection needle device may further comprise a removable needle container for housing and protecting the injection needle unit in a pre-use state, and a part of the injection needle device configured to interact with the interface part during attachment of the injection needle unit may be or may comprise a part of said removable needle container.

[0032] The injection needle unit may include an injection needle member and a needle shield which may be axially movable relative to the injection needle member between an extended position in which the skin-insertable portion of the injection needle member is covered, and a retracted position in which the skin-insertable portion of the injection needle member is uncovered.

[0033] In a specific embodiment of the present invention, for example, the embodiment mentioned above, the injection needle assembly is a needle manifold, which includes: a needle hub; a front needle for insertion into the skin, the front needle extending distally from the needle hub; and two rear needles extending proximally from the needle hub, each rear needle being fluidly connected to the front needle and configured to establish fluid communication with a drug reservoir, and the needle cover can be moved between an extended position and a retracted position to cover and expose the front needle, respectively.

[0034] In certain embodiments of the invention, for example, the embodiments mentioned above, the one-way ratchet is configured to move from the retaining position to the releasing position in response to the needle shield moving from the extended position to the retracted position. Thus, a drug delivery device is provided, wherein the action of attaching the injection needle unit to the drug delivery device automatically stores energy in the torsion spring, thereby preparing the device for drug delivery, and wherein the action of inserting the skin-insertable portion of the injection needle unit into the skin automatically releases the stored energy and performs drug delivery.

[0035] It is often recommended that injection needle units be discarded after a single use, i.e., to avoid skin contamination incidents. However, this recommendation is sometimes ignored by users because it involves an unnecessary additional handling step. A drug delivery device that provides automatic dose preparation in response to each installation of an injection needle unit may support a disposal mode that includes removing the used injection needle unit and replacing it with a new one. This is particularly true if the injection needle unit is designed as a single-use unit with a needle shield that locks after the skin-insertable portion of the injection needle member is pulled out of the injection site.

[0036] In certain embodiments of the invention, such as those mentioned above, the axially extending track extends a distance corresponding to the axial extent of the non-self-locking thread. Thus, the interface portion can be configured to travel from end to end in the axially extending track while the nut member travels from end to end on the non-self-locking thread, thereby optimizing the axial dimensions of the drug delivery device.

[0037] An axially extending track may be arranged in the outer surface of the reservoir holder, whereby movement of the interface part will be visible to the user, allowing for example visual monitoring of dose progression during drug expulsion.

[0038] The spring end retainer may be a separate component rotationally fixed relative to the rotatable shaft, or it may alternatively form part of the rotatable shaft, in which case the number of components in the device may be reduced and a particularly stable interface with the torsion spring may be provided.

[0039] In the present context, the terms "distal" and "proximal" refer to positions at or along the drug delivery device or needle unit, wherein "distal" refers to the drug outlet end and "proximal" refers to the end opposite to the drug outlet end.

[0040] In this specification, reference to an aspect or an embodiment (e.g., "an aspect", "a first aspect", "an embodiment", "an exemplary embodiment", etc.) indicates that a particular feature, structure or characteristic described in conjunction with the corresponding aspect or embodiment is included in at least one aspect or embodiment of the invention, or is inherent thereto, but is not necessarily included in / inherent in all aspects or embodiments of the invention. However, it is emphasized that any combination of the various features, structures and / or characteristics described with respect to the present invention is covered by the present invention, unless explicitly described herein or clearly contradicted by the context.

[0041] Unless otherwise stated, the use of any and all examples or exemplary language (e.g., such as, etc.) herein is intended only to illustrate the present invention, rather than to limit the scope of the present invention. In addition, any language or wording in this specification should not be construed as indicating that any unclaimed element is essential to the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Hereinafter, the present invention will be further described with reference to the accompanying drawings, in which

[0043] Figure 1 is an exploded perspective view of a drug delivery device according to an exemplary embodiment of the present invention,

[0044] Figure 2 is a perspective view of the assembled drug delivery device,

[0045] Figure 3 is a perspective view of an injection needle device including a needle container and an injection needle unit for attachment to a drug delivery device,

[0046] Figure 4 is a longitudinal cross-sectional view of the drug delivery device before use,

[0047] Figure 5a is a longitudinal cross-sectional view of the drug delivery device after the injection needle device is attached, Figure 5b is a cross-sectional view through section BB,

[0048] Figure 6a is a longitudinal cross-sectional view of a drug delivery device in a ready-to-use state, Figure 6b is a cross-sectional view through its section CC, and

[0049] Figure 7a is a longitudinal cross-sectional view of the proximal portion of the drug delivery device when the torsion spring is released, Figure 7b is a cross-sectional view through its section CC.

[0050] In the drawings, similar structures are mainly identified by similar reference numerals. DETAILED DESCRIPTION

[0051] When / if relative expressions are used in the following text, for example, "upper" and "lower", "left" and "right", "horizontal" and "vertical", "clockwise" and "counterclockwise", etc., these relative expressions are with reference to the drawings and not necessarily to actual use. The drawings shown are schematic representations and for this reason the configuration of the different structures and their relative dimensions are intended for illustrative purposes only.

[0052] Figure 11 is an exploded view of a drug delivery device 1 according to an exemplary embodiment of the present invention. The drug delivery device 1 is a dual chamber device in the sense that it can deliver substances from two parallel reservoirs through a single needle / skin interface. The basic component is an elongated housing 2 of elliptical cross section, which extends along a general axis. The housing 2 accommodates the drug delivery mechanism and is fixedly connected to a cartridge holder 10, which has a cartridge holder body 11, which accommodates a first cartridge 30 containing a first substance and a second cartridge 34 containing a second substance arranged side by side.

[0053] The barrel holder body 11 has a transverse end face with a first opening 12, a second opening 13 and a third opening 14, wherein the first opening provides access to a first permeable septum 31, which seals the first barrel 30 at the distal end; the second opening provides access to a second permeable septum 35, which seals the second barrel 34 at the distal end; the third opening provides an interface with a trigger mechanism for a drug delivery mechanism, which will be explained below. In addition, an axial slot 15 is provided in the upper side wall of the barrel holder body 11, extending from the transverse end face to the proximal side. The first barrel 30 is sealed at the proximal side by a first slidable piston (not visible), and the second barrel 34 is sealed at the proximal side by a second slidable piston (not visible).

[0054] The drug delivery mechanism includes: a first piston rod 60, which advances the first slidable piston in the first barrel 30 through a first piston gasket 61; a second piston rod 65, which advances the second slidable piston in the second barrel 34 through a second piston gasket 66. The two piston rods 60, 65 are carried by a base 50 fixed in the housing 2. The first piston rod 60 is threadedly connected to a first nut 53 in the base 50, and the second piston rod 65 is threadedly connected to a second nut 54 in the base 50. An activation rod 70 extends through a hole in the base 50 between the two nuts 53, 54.

[0055] The base 50 carries on its proximal side a first bearing 51 for a first piston rod drive sleeve 55 (see Figure 6b ) and a second bearing 52 for a second piston rod drive sleeve 56 (see Figure 6b ). Clutch 75 (see Figure 4 ) is arranged to be axially fixed but freely rotatable between the two bearings 51, 52. The clutch 75 has external teeth 76, which are permanently engaged with the corresponding toothed outer surfaces of the first piston rod drive sleeve 55 and the second piston rod drive sleeve 56.

[0056] The spindle 80 carrying the non-self-locking thread 81 is axially fixed relative to the clutch 75 and relative to the spring seat 90, which is axially and rotationally locked to the housing 2. The spring seat 90 accommodates the drive spring 5 (see Figure 4), the drive spring is a torsion spring capable of storing and releasing rotational energy for activating the two piston rods 60, 65. The spring base 90 is provided with a collar 91 at its proximal end. The collar 91 has a proximal edge that provides an abutment interface for a cup 8 supporting a return spring 9 in the form of a compression spring.

[0057] The activator plate 38 is axially slidably arranged in the cartridge holder body 11 between the two cartridges 30, 34. The activator plate 38 includes an axially projecting pin 39 and is biased by an activator biasing spring 7 (see Figure 4 ) is biased towards a distal position in which the pin 39 is flush with the lateral end surface in the third opening 14.

[0058] The loader 40 extends within both the housing 2 and the cartridge holder body 11 and includes a rod 41 terminating distally in a rod end portion 42 and a loader nut 45. The loader nut 45 has a threaded section 46 that engages with the non-self-locking thread 81, and the rod end portion 42 is slidably disposed in the axial slot 15, thereby providing a well-defined axial movement of the loader 40 relative to the housing 2 and the cartridge holder 10.

[0059] Figure 2 is a perspective view of the drug delivery device 1 in an assembled state, wherein the rod end portion 42 is positioned in the axial slot 15 at the lateral end face of the cartridge holder body 11 .

[0060] Figure 3 2 is a perspective view of a needle device 20 for use with a drug delivery device 1. The needle device 20 is composed of a needle manifold 25 configured to establish fluid communication with a first cartridge 30 and a second cartridge 34 and to deliver a first substance and a second substance to a single outlet, and a needle container 21 for accommodating the needle manifold 25 at least in its pre-use state. The needle container 21 includes a proximal abutment surface 22 adapted to interface with a rod end portion 42 during mounting of the needle manifold 25 to the cartridge holder body 11.

[0061] The needle manifold 25 comprises a manifold body 24 and a needle shield 23 which is axially displaceable between an extended position and a retracted position relative to the manifold body 24. The needle shield 23 has a circumferentially closed side wall and a transverse end wall with a central aperture 23o.

[0062] Figure 4is a longitudinal cross-sectional view of the drug delivery device 1 in a pre-use state before the needle manifold 25 is attached. It is noteworthy that the cross section is orthogonal to the plane in which the two barrels 30, 34 lie. The drive spring 5 has a proximal spring end 4 attached to the spring base 90 and a distal spring end 6 attached to the spring end retainer 82. The rod end portion 42 is positioned at the distal end of the axial slot 15, and the loader nut 45 is positioned at the distal end of the non-self-locking thread 81. In this pre-use state of the drug delivery device 1, the drive spring 5 is in a relaxed state in which it exhibits only a small pre-tension introduced by the manufacturer during the assembly process.

[0063] The activation rod 70 extends axially from the collar 91 through the base 50 within the housing 2. Axial splines (not visible) are provided along the outer surface of the activation rod 70 so that the activation rod 70 and the spindle 80 are rotationally interlocked. The activation rod 70 has a pair of ratchet arms 73 at its proximal end, which engage with the collar 91 in the axial position of the activation rod 70 shown and prevent the activation rod 70 from rotating clockwise relative to the spring base 90 (as seen from the distal end of the drug delivery device 1). The activation rod 70 is provided with a head portion 72 near its distal end, which interfaces with a narrowed portion 71 arranged within the clutch 75. The head portion 72 has a toothed outer surface that is configured to be slidingly received by internal teeth (not visible) in the clutch 75. The activation rod 70 is axially biased by the return spring 9 towards the shown distal position in the housing 2, thereby providing a downward force to the cup 8.

[0064] Figure 5a The drug delivery device 1 is shown after the needle manifold 25 is attached to the cartridge holder body 11. The attachment of the needle manifold 25 is achieved by axially mounting the needle container 21 on the distal portion of the cartridge holder body 11. It is noteworthy that by this action, the abutment surface 22 abuts the rod end portion 42 and pushes the rod 41 proximally relative to the housing 2. As a result, the loader nut 45 is pushed proximally within the housing 2, which causes the threaded segment 46 to advance the non-self-locking thread 81 when the spindle 80 rotates due to the application of axial force. The resulting rotation of the spring end retainer 82 causes an angular displacement of the distal spring end 6 relative to the proximal spring end 4, thereby straining the drive spring 5. When the needle manifold 25 is properly attached to the cartridge holder body 11, the rod end portion 42 is positioned at the proximal end of the axial slot 15, and the threaded segment 46 is positioned at the proximal end of the non-self-locking thread 81. The drive spring 5 is now in a strained state in which it stores rotational energy which can be released to activate the two piston rods 60 , 65 .

[0065] The proximal displacement of the loader nut 45 that rotates the spindle 80 also causes the activation rod 70 to rotate due to the spline connection between the two. However, since the narrowed portion 71 is located within the clutch 75 at the distal position of the activation rod 70, the rotation is not transmitted to the clutch 75, and the two piston rods 60, 65 are therefore not activated.

[0066] The figure also shows that when the needle manifold 25 is attached to the barrel holder body 11, the pusher 23p axially connected to the needle shield 23 is aligned with the third opening 14 and is positioned just distal to the pin 39. The needle hub 26 in the manifold body 24 carries two parallel rear needles (not visible in this section) and fluidly connects them with a single front needle 27, which is suitable for insertion into the skin portion of the user. One of the rear needles extends through the first opening 12 and the first permeable septum 31 into the interior of the first barrel 30, while the other rear needle extends through the second opening 13 and the second permeable septum 35 into the interior of the second barrel 34.

[0067] Figure 5b It passes through Figure 5a BB, which reveals a one-way ratchet interface between the activation rod 70 and the collar 91, which includes a pair of opposing radial protrusions 92 on the inner surface portion of the collar 91, acting as stop surfaces for the pair of ratchet arms 73. In the strained state of the drive spring 5, the radial protrusions 92 prevent clockwise rotation of the activation rod 70 and thereby prevent clockwise rotation of the spring end retainer 82 relative to the housing 2, whereby the drive spring 5 is in a fired state.

[0068] Figure 6a The drug delivery device 1 is shown after the needle container 21 has been removed. The drug delivery device 1 is now ready for use, and the user can grasp the housing 2, place the needle shield 23 at the desired location on the skin, and press the entire drug delivery device 1 against the skin. This will cause the needle shield 23 to be axially displaced from an extended position to a retracted position relative to the manifold body 24, whereby the front needle 27 will be exposed as it protrudes through the central aperture 23o and into the subcutaneous tissue of the user.

[0069] The axial movement of the needle shield 23 causes the pusher 23p to abut the pin 39 and push the activator plate 38 proximally against the biasing force from the activator bias spring 7. At a certain point, the proximal surface of the activator plate 38 reaches the activation rod 70 and pushes the activation rod 70 proximally, thereby compressing the return spring 9. By the proximal displacement of the activation rod 70 during the last part of the movement of the needle shield 23 to the retracted position, the toothed outer surface of the head portion 72 slides into engagement with the internal teeth of the clutch 75, thereby rotationally interlocking the activation rod 70 and the clutch 75. In addition, the ratchet arm 73 slides axially relative to the radial protrusion 92 and disengages from the collar 91, thereby releasing the drive spring 5. Figure 7aThe proximal portion of the drug delivery device 1 is shown in a momentary activated state when the needle shield 23 reaches the retracted position.

[0070] Since the proximal spring end 4 is attached to a spring base 90 fixed in the housing 2, the rotational energy released by the drive spring 5 will cause the distal spring end 6 and the spring end retainer 82 to rotate relative to the housing 2. Therefore, when the main shaft 80 undergoes a rotary rotation, the activation rod 70 also undergoes a rotary rotation. However, the activation rod 70 is now rotationally coupled to the clutch 75, which means that the clutch 75 rotates accordingly. The engagement between the toothed edge 76 and the corresponding toothed outer surfaces of the first piston rod drive sleeve 55 and the second piston rod drive sleeve 56 thus causes the first piston rod drive sleeve 55 to rotate in the first bearing 51 and the second piston rod drive sleeve 56 to rotate in the second bearing 52.

[0071] Figure 6b and Figure 7b Passing through Figure 6a , Figure 7a FIG. 1 is a cross-sectional view of section CC showing the difference between two states of the drug delivery device 1 , wherein in the ready-to-use state ( Figure 6b ) The clutch 75 surrounds the narrowing portion 71, and in the excited state ( Figure 7b ) The clutch 75 surrounds the head portion 72. In addition, both figures show that the first piston rod drive sleeve 55 has an inner surface configuration corresponding to the cross-sectional profile of the first piston rod 60, and the second piston rod drive sleeve 56 has an inner surface configuration corresponding to the cross-sectional profile of the second piston rod 65. Thus, the first piston rod 60 is rotationally interlocked with the first piston rod drive sleeve 55, and the second piston rod 65 is rotationally interlocked with the second piston rod drive sleeve 56.

[0072] The rotation of the clutch 75 caused in the activated state of the drug delivery device 1 thus essentially causes a rotation of the first piston rod 60, which is thus screwed into the first barrel 30 due to the threaded engagement with the first nut 53, and causes a rotation of the second piston rod 65, which is thus screwed into the second barrel 34 due to the threaded engagement with the second nut 54. The corresponding movement of the two piston rods 60, 65 causes a dose of the first substance from the first barrel 30 and a dose of the second substance from the second barrel 34 to be discharged into the user's body through the respective rear needle and front needle 27.

[0073] When the drive spring 5 is expanded and the spindle 80 is rotated, the loader nut 45 is pushed axially in the distal direction, causing the non-self-locking thread 81 to travel back to its distal end. During this return movement of the loader nut 45, the rod 41 and the rod end portion 42 are displaced accordingly, whereby the rod end portion 42 travels the axial slot 15 back to its distal end. The movement of the rod end portion 42 in the axial slot 15 during the expansion of the drive spring 5 serves to signal the user that the drug expulsion is proceeding correctly.

Claims

1. A drug delivery device (1), comprising: - a housing (2) extending along a main axis, - drug discharge mechanism, - a torsion spring (5) adapted to provide power to the drug expelling mechanism, the torsion spring (5) comprising a first spring end (4) arranged fixedly relative to the housing (2) and a second spring end (6) rotatable about the main axis, - a rotatable shaft (80) extending along the main axis, the rotatable shaft (80) having a non-self-locking thread (81) and being axially fixed relative to the housing (2), a spring end holder (82) to which the second spring end (6) is attached, the spring end holder (82) being rotationally fixed relative to the rotatable shaft (80), - a nut member (45) engaged with the non-self-locking thread (81), the nut member (45) being axially movable by translation relative to the housing (2) so as to cause the non-self-locking thread (81) to travel between a first position in which the torsion spring (5) is in a relaxed state and a second position in which the torsion spring (5) is in a strained state, and - an input structure (40) operable to strain the torsion spring (5), the input structure (40) being axially movable by translation relative to the housing (2) and comprising an interface portion (42) accessible for operation from outside the housing (2), the nut member (45) being axially fixed relative to the input structure (40), whereby the rotatable shaft (80) rotates in response to translational movement of the interface portion (42).

2. A drug delivery device according to claim 1, wherein the torsion spring (5) and the rotatable shaft (80) are arranged so that proximal movement of the nut member (45) relative to the housing (2) causes the spring end retainer (82) to rotate in the direction of spring strain.

3. The drug delivery device according to claim 1 or claim 2, further comprising a releasable retaining mechanism for retaining the torsion spring (5) in the strained state, the releasable retaining mechanism comprising a ratchet arm (73), the ratchet arm being rotationally locked relative to the spring end retainer (82) and being axially movable between a retaining position and a release position, wherein in the retaining position, the ratchet arm (73) engages with a ratchet surface (92) rotationally locked relative to the housing (2), thereby preventing the spring end retainer (82) from rotating in the spring expansion direction, and in the release position, the ratchet arm (73) disengages from the ratchet surface (92), thereby allowing the spring end retainer (82) to rotate in the spring expansion direction.

4. A drug delivery device according to claim 1 or claim 2, wherein the nut member (45) forms part of the input structure (40).

5. The drug delivery device according to claim 1 or claim 2, further comprising a reservoir holder (10) for holding at least one drug reservoir (30, 34), wherein the reservoir holder (10) is axially fixed to the distal end portion of the housing (2) and comprises an axially extending linear track (15), wherein the interface portion (42) is slidably arranged in the axially extending linear track.

6. The drug delivery device according to claim 5, further comprising an injection needle device (20), the injection needle device comprising an injection needle unit (25) configured to be attached to the distal end portion of the reservoir holder (10) by relative translational movement, wherein The axially extending linear track (15) extends from a distal portion of the reservoir holder (10), and wherein a portion of the injection needle device (20) is configured to interact with the interface portion (42) during attachment of the injection needle unit (25).

7. A drug delivery device according to claim 6, wherein the injection needle device (20) further comprises a removable needle container (21) for accommodating and protecting the injection needle unit (25) in a pre-use state, and wherein a portion of the injection needle device (20) configured to interact with the interface portion (42) during attachment of the injection needle unit (25) comprises an adjacent portion (22) of the removable needle container (21).

8. A drug delivery device according to claim 6 or claim 7, wherein the axially extending linear track (15) extends a distance corresponding to the axial extent of the non-self-locking thread (81).

9. The drug delivery device according to claim 5, wherein the axially extending linear track (15) is arranged in an outer surface of the reservoir holder (10).

10. A drug delivery device according to claim 1 or claim 2, wherein the spring end retainer (82) forms part of the rotatable shaft (80).

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