Injection devices for delivering liquid medications

Abstract

The present invention relates to a pre-filled injection device with a non-removable cartridge embedded in a housing structure and wherein a piston rod drive mechanism comprises a threaded piston rod which moves helically in a nut fixed to the housing structure. During assembly of the injection device, an air gap between the plunger in the cartridge and the piston rod means can be eliminated by axially moving a nut element of the drive mechanism during assembly. In an alternative solution, the piston rod comprises a telescopic element which can slide axially relative to the piston rod to obtain a zero position.

Description

Technical Field

[0001] The present invention relates to a prefilled injection device for delivering a liquid drug, preferably in the form of one or more doses of the liquid drug. The present invention particularly relates to such an injection device, wherein the distance between the piston rod that moves the plunger forward inside the container and the plunger itself has been minimized during assembly of the injection device.

[0002] In a second aspect, the invention relates to a method for assembling such an injection device.

[0003] Furthermore, the invention relates to an alternative solution and to a method for implementing the alternative solution. Background Art

[0004] Injection devices are widely known and used for treating many different diseases, in particular in the field of diabetes. A very popular type of injection device is the so-called disposable or prefilled injection device. This type of injection device usually comprises a cartridge which contains a predetermined amount of liquid medicament to be injected and which is non-replaceably embedded in the injection device. Therefore, after the contents contained in the packaged cartridge have been used, the user preferably discards the entire device for recycling. A very classic prefilled injection device is the It is described in further detail in WO 1999 / 38554 and disclosed in detail in Figures 11 to 17 thereof. The injection device comprises a housing structure including a cartridge holder which holds a cartridge containing 3 ml of liquid drug.

[0005] When producing such a pre-filled injection device, a relatively large number of different tolerances apply. There are various tolerances in the molding of the different components that make up the injection device. There are tolerances in the various snap and snap connections that permanently connect the various components, and there are also tolerances when filling the liquid drug into the cartridge.

[0006] Due to all these tolerances, the assembled injection device is usually delivered to the end user with a separate distance between the plunger and the piston rod inside the cartridge. This distance is called the air gap. Before starting to use the injection device to inject a dose of liquid drug, the user needs to remove this air gap, which is usually done by setting and ejecting a small dose, thus moving the piston rod forward without actually ejecting any liquid drug. This process is usually called initial priming of the injection device. Therefore, the first few empty dose ejections move the piston rod into abutment with the plunger, and the liquid drug is actually ejected only when physical contact between the plunger and the piston rod is established, and the set dose size is correctly ejected.

[0007] A new type of pre-filled injection device has recently been developed. These new injection devices are capable of discharging a limited and predetermined number of dose volumes, which are predetermined by the manufacturer of the injection device and are equal in volume. The new injection device is called a "multiple use fixed dose" injection device. When using such a fixed dose injection device, the user cannot set and eject small doses because all dose volumes are predetermined and preset by the manufacturer of the fixed dose device. An example of such a multiple use fixed dose device is provided in WO 2018 / 007259. Such an injection device is very suitable for injecting liquid GLP-1 drugs, which are usually injected in a fixed dose volume and are usually administered once a day or once a week.

[0008] In order to avoid the process of priming the injection device, different solutions have been proposed.

[0009] In WO 2009 / 095332 it has been suggested to provide a piston rod foot which can slide axially relative to the piston rod during assembly of the injection device and which is physically connected to the piston rod at a position where contact between the piston rod foot and the piston rod is established already during assembly. The publication also describes a method in which a housing structure comprises two parts which slide axially in a first state and are permanently fixed to each other in a second state. The first state is during assembly of the injection device, while the second state is the final, unused, delivery state of the injection device.

[0010] EP 2,968,777 describes a method in which an adjustment member threadedly connected to a piston rod is rotated relative to a housing structure during assembly of an injection device so that the piston rod is moved forward into contact with a plunger. Once contact has been established between the piston rod and the plunger, the adjustment member is physically fixed to the housing structure. When an injection is thereafter made, the adjustment member operates as a conventional nut element to helically advance the rotatable piston rod during rotation.

[0011] A similar approach is disclosed in WO 2017 / 001694, in which a nut element is moved into the correct position and physically fixed to the housing structure in that position. In this solution, the piston rod and the nut member are preassembled, after which the nut element together with the piston rod is axially positioned relative to the cartridge holder portion of the housing structure. When the piston rod is in the correct abutment position, the nut member is permanently connected to the cartridge holder portion, for example by welding.

[0012] However, these prior art methods are rather cumbersome and require a very specialized assembly process. Summary of the invention

[0013] It is an object of the present invention to provide an injection device in which the air gap can be minimized in a very simple manner suitable for large-scale production.

[0014] Therefore, in a first aspect of the present invention, there is provided a pre-filled injection device for delivering a liquid drug, preferably in doses. The pre-filled injection device comprises:

[0015] • A housing structure extending along a longitudinal axis defining a distal direction and a proximal direction and permanently embedded in the cartridge. The cartridge is also provided with a movable plunger.

[0016] A piston rod arrangement for advancing the movable plunger during dispensing. The piston rod arrangement has an external thread and a longitudinal track structure.

[0017] - A rotatable drive element engaging the longitudinal track structure of the piston rod arrangement such that a rotation of the drive element is converted into a rotation of the piston rod.

[0018] - A nut element having an internal thread for engaging the external thread of the piston rod arrangement.

[0019] The nut element has two different states;

[0020] a first state, in which the nut element is axially slidable relative to the housing structure, and

[0021] • A second state, wherein the nut element abuts the movable plunger and is permanently fixed to the housing structure.

[0022] In the first state, the nut element engages the housing structure via an elastic interface, which is capable of axially pushing the nut element and thereby the piston rod arrangement relative to the housing structure so that the piston rod arrangement abuts the movable plunger, and in the second state, the nut element is permanently fixed to the housing structure so that the piston rod moves helically relative to the nut member and the housing structure when rotating.

[0023] It is thus possible to first pre-assemble the nut element and the piston rod arrangement, after which the nut element is slid relative to the housing arrangement until the correct position is achieved and maintained.

[0024] In the correct position, ie the position in which the piston rod arrangement abuts the plunger inside the cartridge, the nut element is fixed to the housing.

[0025] Hereby it is ensured that the physical contact between the piston rod foot and the plunger is obtained individually for each individual injection device during assembly of the injection device.

[0026] The above principles may be used for any type of prefilled injection device in which a threaded piston rod is advanced inside a cartridge by rotating the piston rod relative to a threaded nut element carrying or otherwise associated with a housing structure.

[0027] It is particularly noted that, although many of the examples used throughout this application and especially in the more detailed parts of the description relate to so-called pre-loaded multiple-use fixed-dose injection devices, the general teaching of the present application is applicable to a wide variety of different pre-loaded injection devices and is in no way limited to the specific examples. More specifically, the invention claimed in the attached claims is in no way limited to the examples used.

[0028] Within the broad range of pre-filled injection devices covered by the appended claims, there are also pre-filled injection devices having a dose setting mechanism by which the user can set various individual dose sizes to be expelled in each expelling action.

[0029] The permanent connection between the nut element and the housing can be obtained in many different ways, but welding, in particular laser welding, is preferred.

[0030] The resilient interface preferably comprises one or more flexible arms which may be radially resilient and which are operable between the nut element and the housing structure.

[0031] The flexible arm is preferably provided on the nut element and abuts an inner surface of the housing structure.

[0032] Furthermore, the flexible arm abuts an inner surface in the housing structure, the inner surface comprising a plurality of grooves, wherein one or more of these grooves may be provided with an inclined bottom angled in the distal direction. The angle is preferably such that the piston rod means engaged by the internal thread inside the nut member is urged against the movable plunger inside the cartridge.

[0033] When the preassembled nut element and piston rod are pushed in the proximal direction, the resilience in the flexible arms, combined with the angled bottom surface in at least one of the grooves, pushes the nut element in the distal direction.

[0034] When contact with the plunger inside the cartridge is obtained, the flexible connection thus ensures that the nut element together with the piston rod arrangement is pushed in the distal direction such that the physical contact is maintained.

[0035] In the above it should be understood that the piston rod arrangement comprises in one example the actual piston rod and the piston rod foot. The piston rod can rotate relative to the piston rod, or it can be rotationally fixed to the piston rod so that they rotate in unison. The piston rod foot can therefore be a separate component or integrally molded with the piston rod.

[0036] The connection between the nut element and the housing structure is preferably a weld produced by directing a laser beam through an opening in the housing structure and onto the surface connecting the nut element and the housing structure.

[0037] The invention also relates to a method for assembling an injection device as defined herein.

[0038] The method comprises the following steps:

[0039] 1. threadingly engaging the nut member and the piston rod arrangement by rotating the nut member and the piston rod arrangement relative to each other,

[0040] 2. causing the nut member and the piston rod device to translate relative to the housing structure,

[0041] 3. inserting at least the proximal portion of the cartridge together with the plunger into the housing structure,

[0042] 4. moving the cartridge and the plunger together relative to the piston rod means to a position in which the plunger located inside the cartridge abuts the piston rod means, and

[0043] 5. Fix the nut element to the housing structure in this position.

[0044] In one example, the method further comprises welding, preferably by laser welding, at least one flexible arm of the nut element to the housing structure at a location where the plunger inside the cartridge abuts the piston rod arrangement.

[0045] The general concept of the method is therefore to slide the nut element into position in a first state and when in the correct position to permanently connect (eg by laser welding) the nut element to the housing structure.

[0046] In the second state, the nut member is thus permanently connected to the housing structure and operates as a well-known nut element for injection devices of this type.

[0047] In an alternative example, the pre-filled injection device comprises:

[0048] a housing structure extending along a longitudinal axis (X) defining a distal direction and a proximal direction and permanently embedding a cartridge with a movable plunger,

[0049] a piston rod with a piston rod foot for advancing the movable plunger during dispensing, the piston rod having an external thread and a longitudinal track structure,

[0050] a rotatable drive element engaging the longitudinal track structure of the piston rod such that a rotation of the rotatable drive element is converted into a rotation of the piston rod,

[0051] a nut element having an internal thread for engaging the external thread of the piston rod,

[0052] In this example, the piston rod foot is connected and axially fixed to a telescopic element, which operates in two different states;

[0053] - a first state, in which the telescopic element is arranged to be axially slidable relative to the piston rod, and

[0054] - a second state, in which the telescopic element is permanently fixed to the piston rod, and in which

[0055] The telescopic element non-rotatably engages a longitudinal channel in the piston rod extending along the longitudinal axis (X) in the first state, and the telescopic element is permanently fixed to the piston rod in the second state.

[0056] The piston rod foot is thus connected to the telescopic element, which slides axially relative to the piston rod and is permanently connected to the piston rod when physical contact has been established between the piston rod foot fixed to the telescopic element and the plunger inside the cartridge.

[0057] The permanent connection is preferably accomplished by welding (eg by laser welding) the telescopic element to the piston rod.

[0058] The present invention also includes a method for assembling such an injection device. The method comprises the following steps:

[0059] 1. Engaging the telescopic element and the piston rod foot in an axial coupling,

[0060] 2. Inserting the telescopic element into the longitudinal channel in the piston rod (60),

[0061] 3. Establishing physical contact between the plunger inside the cartridge and the piston rod foot, and

[0062] 4. Fix the telescopic element to the piston rod at this location, for example by welding.

[0063] definition:

[0064] An "injection pen" is typically an injection device having an oblong or elongated shape, somewhat like a pen used for writing. While such pens typically have a tubular cross-section, they can easily have a different cross-section, such as triangular, rectangular or square or any variation around these or other geometric shapes.

[0065] The term "needle cannula" is used to describe the actual catheter that performs the skin penetration during an injection. The needle cannula is typically made of a metallic material such as stainless steel and is preferably connected to a needle hub made of a suitable material such as a polymer. However, the needle cannula may also be made of a polymer material or a glass material. The needle cannula, for example installed in a hub, may be replaceable or permanently attached to the injection device.

[0066] As used herein, the term "liquid drug" is intended to encompass any flowable medicament containing a drug, such as a liquid, solution, gel, or fine suspension, that can be passed through a delivery device such as a hollow needle cannula in a controlled manner. Representative drugs may include drugs such as peptides, proteins (e.g., insulin, insulin analogs, and C-peptide), hormones, biologically derived or active agents, hormone- and gene-based agents, nutritional formulas, and other substances in solid (dispensed) or liquid form.

[0067] "Cartridge" is a term used to describe the main container that actually contains the liquid drug. Cartridges are usually made of glass, but can also be molded from any suitable polymer. The cartridge or ampoule is preferably sealed at one end by a pierceable membrane called a "septum", which can be pierced, for example, by the non-patient end of the needle cannula. Such a septum is usually self-sealing, which means that once the needle cannula is removed from the septum, the opening created during penetration is automatically sealed by inherent elasticity. The opposite end of the cartridge is usually closed by a plunger or piston made of a rubber composition or a suitable polymer. The plunger or piston can be slidably movable inside the cartridge. The space between the pierceable membrane and the movable plunger holds the liquid drug, and the liquid drug is pressed out when the plunger reduces the volume of the space holding the liquid drug.

[0068] Since the cartridge usually has a narrow distal neck into which the plunger cannot move, not all of the liquid drug contained in the cartridge can actually be discharged. The term "initial amount" or "substantially used" therefore refers to the injectable contents contained in the cartridge and therefore does not necessarily refer to the entire contents. The injectable contents in the cartridge must be at least equal to the volume constituting the multiple dose volumes of predetermined sizes to be discharged. In one example, if it is assumed that a multiple-use fixed-dose injection device contains three fixed doses, each having a volume of, for example, 0.3 ml, the injectable contents of the cartridge need to be at least 0.9 ml, and the entire volume of the cartridge must be larger to also include the volume that cannot be discharged due to the narrow neck portion.

[0069] The term "prefilled" injection device refers to an injection device in which a cartridge containing a liquid drug is permanently embedded in the injection device so that it cannot be removed without permanently destroying the injection device. Once a predetermined amount of liquid drug in the cartridge has been used, the user typically discards the entire injection device. Typically, a cartridge filled with a specific amount of liquid drug by the manufacturer is fixed in a cartridge holder, which is then permanently connected to the housing structure so that the cartridge cannot be replaced.

[0070] This is in contrast to a "durable" injection device, in which the user can replace the cartridge containing the liquid drug themselves when the cartridge is empty. Prefilled injection devices are typically sold in packages containing more than one injection device, while durable injection devices are typically sold one at a time. When using prefilled injection devices, the average user may need as many as 50 to 100 injection devices per year, while when using durable injection devices, a single injection device may last for several years, however, the average user may need 50 to 100 new cartridges per year.

[0071] A "multiple use fixed dose" injection device refers to a defined injection device that is capable of delivering a predetermined multiple (i.e., more than one) doses of substantially the same volume. Therefore, the liquid drug contained in the cartridge is discharged in a plurality of substantially the same dose volumes. In one example, the cartridge may, for example, contain 3 ml of liquid drug, which may, for example, be discharged in 6 identical doses (0.5 ml each). The number of doses of equal size is typically 2 to 8, preferably 4 to 6 identical dose volumes. The multiple use fixed dose injection device may be pre-assembled so that the entire injection device is discarded after a predetermined number of dose volumes have been discharged, or it may be a durable injection device so that the user can replace the cartridge and discharge a new series of equal-sized dose volumes from the new cartridge.

[0072] The term "automatic" used in conjunction with an injection device means that the injection device is capable of performing an injection without the user of the injection device delivering the force required to expel the liquid drug during administration. This force is usually delivered automatically by a motor or spring driver. The actual spring used for the spring driver is tensioned by the user during dose setting, for example, however, such a spring is usually pre-tensioned with a small force to avoid the problem of delivering very small doses. Alternatively, the manufacturer can fully pre-load the spring with a pre-load force sufficient to expel the entire initial content of the liquid drug contained in the cartridge (i.e., the entire injectable content) through multiple doses. Typically, the user activates a release mechanism provided on the surface of the housing or at the proximal end of the injection device to partially release some of the force accumulated in the spring when the injection is performed. Alternatively, the injection device can be shield-triggered so that the activation of the movable shield releases the force required to expel the dose.

[0073] The terms "permanently connected" or "permanently embedded" as used in this specification are intended to mean that components, in particular a cartridge, are permanently embedded in a housing structure, requiring the use of a tool in order to separate, and if the components are separated, at least one of the components will be permanently damaged, rendering the injection device inoperable.

[0074] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference in their entirety to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0075] All headings and sub-headings are used herein for convenience only and should not be construed as limiting the invention in any way.

[0076] Unless otherwise stated, the use of any and all examples or exemplary language (such as) provided herein is intended only to better illustrate the present invention, rather than to limit the scope of the present invention. Any language in this specification sheet should not be construed as indicating that any undeclared element is essential to the practice of the present invention.

[0077] The citation and incorporation of patent documents herein is for convenience only and does not reflect any view of the validity, patentability, and / or enforceability of such patent documents.

[0078] This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The present invention will be explained more fully below in conjunction with preferred embodiments and with reference to the accompanying drawings, in which:

[0080] Figure 1 An exploded view of a spring driven injection device according to an example of the present invention is shown.

[0081] Figure 2A -B shows Figure 1 Cross-sectional view of a spring-driven injection device. Figure 2B The view in is relative to Figure 2A Rotate 90°.

[0082] Figure 3 A cross-sectional view of the proximal portion of a spring driven injection device is shown with the piston rod in an initial position. Figure 3 The view in is relative to Figure 4 Rotate 90°.

[0083] Figure 4 A cross-sectional view of the proximal part of a spring driven injection device is shown with the piston rod in a parked position. Figure 4 The view in is relative to Figure 3Rotate 90°.

[0084] Figure 5A -B shows a more detailed cross-sectional view of the proximal portion of the spring driven injection device. Figure 5B The view in is relative to Figure 5A Rotate 90°.

[0085] Fig. 6A -B shows a perspective view of the drive tube from a different angle.

[0086] Fig. 7A -B shows a perspective view of the connector from the opposite end.

[0087] Figure 8 A perspective view of the piston rod is shown.

[0088] Fig. 9 A side view of the interface between the drive tube and the bridge structure inside the housing structure is shown.

[0089] Fig.10 A cut-away view of the interface between the drive tube and the housing structure is shown.

[0090] Fig.11A -C shows the attachment of the torsion spring to the spring base of the housing structure.

[0091] Fig.12 An exploded view of a piston rod and a nut member for zero point adjustment according to a first example is shown.

[0092] Fig.13 A diagram showing the zero point adjustment in a first example is shown.

[0093] Fig.14A -B shows a perspective view of the zero adjustment nut member from the opposite end.

[0094] Fig.15 A perspective view of a housing portion is shown.

[0095] Fig.16 A cutaway portion of a housing part for zero point adjustment is shown.

[0096] Fig.17A -B shows two cut-away images of the interface between the nut member and the housing portion for zero point adjustment.

[0097] Fig.18A -C shows a cross-sectional view of an alternative zero point adjustment.

[0098] FIG. 19 shows Fig.18A -C shows an alternative solution of the nut member.

[0099] Fig. 20An alternative piston rod is shown for a second alternative zero point adjustment.

[0100] Fig.21 A telescopic connection between the piston rod and the piston rod foot is shown for a second alternative zero point adjustment.

[0101] Fig.22A -B shows a cross-sectional view of a second alternative zero point adjustment. Fig. 22B The view in is relative to Fig.22A Rotate 90°.

[0102] For the sake of clarity, these figures are schematic and simplified, and they merely show details which are essential to the understanding of the invention, while other details are omitted. Throughout, the same reference numerals are used for the same or corresponding parts. DETAILED DESCRIPTION

[0103] When terms such as "upper" and "lower", "right" and "left", "horizontal" and "vertical", "clockwise" and "counterclockwise" or similar relative expressions are used in the following, these only refer to the drawings and not to actual usage. The drawings shown are schematic representations and therefore the configuration of the different structures as well as their relative sizes are for illustrative purposes only.

[0104] In this context, it may be convenient to define the term "distal end" in the drawings to mean the end of the injection device which holds the needle cannula during injection and which points towards the user, whereas the term "proximal end" refers to the opposite end, e.g. Figure 2A -B. Distal and proximal refer to axial orientations extending along the longitudinal axis (X) of the injection device, also shown in Figure 2A-2B In the public.

[0105] When referring to clockwise and counter- or anti-clockwise in the following examples, it is understood that the injection device is viewed from a distal position of the injection device. Thus, clockwise is a rotation to the right, like the arms on a clock, and anti-clockwise is a rotation to the left.

[0106] In order to explain the various movements that occur in the described injection device, the following terms are used in the following detailed description;

[0107] "Translational motion" refers to strictly linear motion without any rotation.

[0108] A "rotational movement" is any rotational movement about a center, which may be a central point, ie in one plane, or a central axis, ie having a longitudinal extension.

[0109] "Axial motion" means any motion in the axial direction. This motion may be strictly translational, or include rotation, making it a "helical motion", since this means a combination of axial and rotational motion.

[0110] "Telescopic" is intended to cover situations where the movable element moves out of and / or into the base element. The telescopic movement may be translational or include rotation, such that the movement is helical.

[0111] Figure 1 An exploded view of a spring injection device according to an example of the present invention is disclosed. In the disclosed example, the injection device is in the shape of a pen, also commonly referred to as an injection pen.

[0112] The liquid drug to be ejected is contained in a cartridge 5, which is typically a hollow glass ampoule, which is sealed at the distal end by a pierceable septum 6 and at the proximal end by a movable plunger 7. The movable plunger 7 is arranged to be moved in the distal direction by a piston rod 60. In order to properly distribute the force from the piston rod 60 to the plunger 7, a piston rod foot 85 may be provided between the piston rod 60 and the plunger 7, such as Fig.13 as shown in .

[0113] The cartridge 5 is typically filled with liquid drug by the manufacturer and is permanently and irreplaceably fixed in the housing structure of the injection device, making the injection device a pre-loaded injection device. The disclosed housing structure includes a housing portion 10, a cartridge holder 20, a spring base 25 and a shield guide 30. However, the housing structure may include any number of components, or alternatively be molded as a single housing unit.

[0114] The housing portion 10 (also Fig.15 ), the cartridge holder 20, the spring base 25 and the shield guide 30 are preferably permanently fixed to each other so that the cartridge 5 is permanently encapsulated in the housing structure, thereby constituting a pre-loaded injection device. On the proximal side, the housing part 10 is closed by the spring base 25, which is snap-fitted to the housing part 10 during assembly of the pre-loaded injection device. On the distal side, on the housing part 10, the shield guide 30 is also snap-fitted to the housing part 10. The cartridge holder 20 is preferably permanently fixed to the housing part 10 by a pair of resilient snap arms 21 or alternatively by being integrally molded with the housing part 10.

[0115] Although the drawings depict a pair of resilient snap arms 21, any number of arms may be provided. Since the examples herein refer to pen-shaped injection devices having a tubular cross-section, many of the various protrusions, arms, guide rails and other mechanical elements are provided in pairs of two. However, for many of these attributes, any random number may be provided.

[0116] The shield guide 30 guides the telescopically movable shield 40, and its function will be described later. On the far side, the shield guide 30 is provided with a peripheral track 31 with an axial opening 32 on the outer surface. The peripheral track 31 guides radially directed protrusions 36 located on the inner surface of the protective cap 35, such as Figure 2B in (and Figure 1 Thus, before the radially directed protrusions 36 can be axially moved out through the axial opening 32 and the protective cap 35 can be removed, the user needs to rotate the protective cap 35 in a counterclockwise direction (when viewed from a distal position) relative to the shield guide 30 and thus relative to the housing structure.

[0117] Distally, the cartridge holder 20 is provided, at least in use, with a needle hub 45 carrying a needle cannula 46. Alternatively, a needle magazine with a plurality of needle cannulas may be integrated into the injection device.

[0118] For example, in Figure 2A and 2B As disclosed in , the needle cannula 46 has a distal tip for penetrating the user's skin during injection and a proximal end 47 that penetrates through the septum 6 of the cartridge 5 so that liquid drug can be pressed out of the cartridge 5 and flow through the lumen of the needle cannula 46 and through the user's skin.

[0119] The needle hub 45 is fixed to the cartridge holder 20 by means of an interface that is activated during the activation process. During this activation process, the needle hub 45 is axially moved in the proximal direction so that the proximal end 47 of the needle cannula 46 penetrates through the septum 6 of the cartridge 5. Furthermore, in the sequence of moving the needle hub 45, the proximal locking arm 48 provided on the needle hub 45 is irreversibly engaged and locked to the distal hub 22 on the cartridge holder 20 so that the needle hub 45 is thereafter irreversibly locked to the cartridge holder 20.

[0120] The needle hub 45 is preferably moved in the proximal direction by rotation of the telescopically movable shield 40, which is able to move the needle hub 45 proximally by means of a spiral interface. Once the priming process has been completed, the locking arm 48 on the needle hub 45 is locked to the cartridge holder 20, and the snap arm 43 provided on the telescopically movable shield 40 engages the housing structure and prevents the user from rotating the telescopically movable shield 40 back to the previous position. The snap arm 43 preferably engages with the axial inner surface of the shield guide 30 fixed to the housing part 10. Thus, the priming process can only be performed once.

[0121] After the priming process has been completed, the injection device is in the Figure 2A-B, and the user can use the injection device to perform multiple injections, as will be explained. As further explained, the injection of the liquid drug is driven by a spring, which in the disclosed example is a torsion spring that transmits a torsional force. However, any type of spring can be used for the injection process.

[0122] The telescopically movable shield 40 carries a cleaning assembly 50 disclosed in further detail in WO 2019 / 101670. The cleaning assembly 50 keeps the distal end of the needle cannula 46 biologically clean between injections and is fixed to the telescopically movable shield 40 by a shield tip 55, which is snap-fitted to the telescopically movable shield 40 by engaging a resilient arm 56 of the telescopically movable shield 40, so that the cleaning assembly 50 follows all movements of the telescopically movable shield 40, i.e., rotational movement, translational movement, and spiral movement.

[0123] The cleaning component 50 preferably contains a liquid cleaning agent, which in one example can be the same preservative contained in the liquid drug in the cartridge 5. In a preferred example, the cleaning agent is the same preservative contained in the liquid drug in the cartridge 5 that is filled into the cleaning component 50 during activation of the injection device.

[0124] A torsion spring arrangement is provided to move the piston rod 60 in distal direction during dose expelling.The torsion spring arrangement comprises a torsion spring 65, a drive tube 70 and an inner nut member 11 for driving the piston rod 60 in distal direction, as will be explained.

[0125] In the disclosed example, the torsion spring 65 is a metal spring in which the wire is helically wound. In the longitudinal direction, the torsion spring 65 can be divided into different regions or zones. In some of these regions, the wires in the coils have no or only very small distances between the coils, while in other regions, the coils have significant longitudinal distances between the coils. These regions are referred to as compression regions 66 (see, e.g., Figure 1 ). Such a compression area 66 with a certain distance between the coils provides a compressive force so that the torsion spring 65 can apply a torsion force and a compressive force at the same time. When the two ends of the torsion spring 65 are compressed toward each other, the torsion spring 65 returns a force pointing in the longitudinal direction and urging the two ends away from each other.

[0126] Both ends of the torsion spring 65 are bent into hooks. One hook is attached to the housing structure via the spring base 25 at the proximal end of the injection device, and the other hook is attached to the drive tube 70 at the opposite and more distal end of the injection device. Therefore, a torsional force can be provided between the housing structure and the drive tube 70, which can be used to rotate the drive tube 70.

[0127] Preferably, the torsion spring 65 is installed by passing the hook through the axial opening in the corresponding part 25, 70, and then rotating the corresponding part 25, 70 and the torsion spring 65 relative to each other so that the hook is captured by the edge of the axial opening. The torsion spring 65 is preferably first engaged with the drive tube 70 and then engaged with the spring base 25 during the assembly process. In one example, both the drive tube and the spring base can be provided with snap projections, as will be explained.

[0128] Figure 8 The piston rod 60 disclosed in detail in FIG. 1 is provided with an external thread 61 on the outer surface and is also provided with a longitudinal track structure 62, which is open at the distal end but terminates at a stop surface 63 at the proximal end. The longitudinal track structure 62 has a free length referred to as "L". The free length "L" can be Figure 3 and 5A 62, and is the length measured from the engagement of the inwardly directed protrusion 75 on the drive tube 70 with the stop surface 63 at the proximal end of the track structure 62, as will be explained. Thus, the free length "L" is an expression of the axial length that the piston rod 60 is able to move in the distal direction before the stop surface 63 engages the inwardly directed protrusion 75. Thus, the free length "L" is shorter than the actual length of the track structure 62, as will be explained. Figure 3 As seen in.

[0129] The longitudinal track structure 62 refers to any type of structure provided in or on the piston rod 60 that is capable of defining a longitudinal free length "L". It may be, for example, any type of track, groove or similar indentation.

[0130] The internal nut member 11 is rotationally and axially fixed to the housing structure. In one example, the nut member 11 is an integral part of the housing part 10. Alternatively, the nut member 11 may be a separate part fixed to the housing part 10 during assembly of the injection device, for example by gluing or welding. The nut member 11 is provided with an internal thread 12 on an inner surface, which engages with an external thread 61 on the piston rod 60, so that the piston rod 60 moves helically when it rotates relative to the housing structure.

[0131] like Figures 12 to 17A -B, in another embodiment, the air gap may be eliminated by means of the nut member 11 during assembly of the injection device, as will be explained.

[0132] The longitudinal track structure 62 on the piston rod 60 is engaged by an inwardly directed protrusion 75 provided on the inner surface of the drive tube 70 so that whenever the drive tube 70 rotates, the piston rod 60 rotates simultaneously and thereby moves helically in the distal direction in the internal thread 12 of the nut member 11. Fig. 6AThe inwardly directed protrusions 75 disclosed in -B are preferably arranged in pairs, but may be arranged singly or in any random number.

[0133] The torsion spring 65 is enclosed between the housing structure and the drive tube 70, such that the torque stored in the torsion spring 65 can rotate the drive tube 70 relative to the housing structure. In the disclosed embodiment, the torsion spring 65 engages the drive tube 70 at its distal end and engages the spring base 25 at its proximal end. During the manufacture of the injection device, i.e. during the assembly of the injection device, the torsion spring 65 is tensioned, such that when the injection device is delivered to the user, a relatively high torque is stored in the torsion spring 65. The torque stored in the unused delivery state of the injection device is preferably sufficient to expel the entire initial content of the cartridge 5, which means that the torque is sufficient to drive the piston rod 60 and thus the plunger 7 to or close to the distal end of the cartridge 5. In a preferred example, such a multiple-use fixed-dose injection device will have a torsion spring 65 that is tensioned and ready to expel approximately 2 to 8 predetermined and equally sized dose volumes, such that the user does not need to tension the torsion spring 65 between each of these 2 to 8 injections.

[0134] like Fig. 6A The drive tube 70 disclosed in -B has a first helical shape 71 at its distal end, ie the distal end of the drive tube 70 is made of a sleeve that gradually recedes in the circumferential direction. The first helical shape 71 extends in the axial direction and terminates in a first axial drive flange 72 .

[0135] In addition, the distal-most portion of the drive tube 70 has an outer surface that is radially offset relative to the remainder of the drive tube 70. This radial recess in the outer surface of the drive tube 70 defines a second axial drive flange 78 that is parallel to the first axial drive flange 72 but rotationally offset by 180°, as shown in FIG. Fig. 6A The two axial flanges 72, 78 define stops for the rotation of the drive tube 70, as will be explained.

[0136] The radial recess leading to the second axial drive flange 78 has a helical structure which forms a helical surface to abut against a similar helical surface provided inside the housing structure. This helical surface has the same configuration as the housing helical shape 16, but is longitudinally offset in the proximal direction, such as Fig. 17B The interface between these two surfaces has the same effect as the interface between the first helical form 71 and the housing helical form 16, as will be explained. Having two such helical interfaces makes the operation of the injection device more stable.

[0137] Furthermore, two outwardly directed projections 73, 74 are provided on the outer surface of the drive tube 70. In the disclosed example, the two projections 73, 74 are also offset by 180° relative to each other and also by a certain distance in the longitudinal direction.

[0138] As explained, one or more inwardly directed protrusions 75 inside the drive tube 70 engage the longitudinal track structure 62 in the piston rod 60. On the outer surface, the drive tube 70 is provided with a helical flange 76, the use of which will be explained later.

[0139] The housing part 10 of the housing structure is internally molded with an internal bridge structure 15, which has an axial opening to allow the piston rod 60 to move through the opening. On the inner surface, the bridge structure 15 guides and supports the distal part of the drive tube 70. This guide Fig. 6A , where the outline of the bridge structure 15 is shown with dashed lines. In one example, the bridge structure 15, which also carries the nut member 11, can be molded separately and attached to the housing part 10. In both cases, the bridge part 15 is in contact with the housing part 10 only through the radial bearing part 19, which only has limited angular space so that there is an axial opening around the bridge part 15. This Fig.17A -B is best seen in.

[0140] The first helical shape 71 at the distal end of the drive tube 70 engages a similar helical shape 16 (see e.g. Fig.10 ), which also extends in the axial direction and is arranged in the bridge structure 15 inside the housing part 10 of the housing structure (hereinafter referred to as the housing spiral shape 16). The housing spiral shape 16, like the first spiral shape 71, is a sleeve that gradually fades in the circumferential direction and ends in a first axial housing flange 17, which can be engaged with the first axial drive flange 72 of the drive tube 70.

[0141] Fig. 9 The interface between the drive tube 70 and the bridge structure 15 located inside the housing part 10 is disclosed, ie the housing part 10 is visually cut away. Fig.10 The interface between the drive tube 70 and the housing structure including the bridge structure 15 is disclosed. Fig.10 In the view of FIG. 7 , the housing structure rather than the drive tube 70 is arranged along Figure 5A The cut is thus cut radially along the line "A" in FIG. 1 and viewed from a distal position. The cut thus passes through the first axial housing flange 17. The housing portion 10 is further visually cut in a longitudinal plane along the center line "X".

[0142] like Fig. 9 and Fig. 17BAs can be seen in FIG. 1 , the internal bridge structure 15 is also provided with a second axial housing flange 18, which is capable of abutting the second axial drive flange 78. Thus, the rotational engagement between the drive tube 70 and the housing structure is defined by the abutment of the first axial drive flange 72 and the first axial housing flange 17 and the second axial drive flange 78 and the second axial housing flange 18, as shown in FIG. Fig. 9 and 10 All four flanges 72, 17; 78, 18 are preferably parallel to each other and to the longitudinal center axis "X" of the injection device. In addition, the axial length ("dl", in Fig. 6A -B) as will be explained.

[0143] Since the torsion spring 65 constantly applies a torsional force to the drive tube 70, the drive tube 70 will rotate in a counterclockwise direction (in this example) when viewed from the distal end of the injection device. However, the engagement between the first axial drive flange 72 and the first axial housing flange 17 and between the second axial drive flange 78 and the second axial housing flange 18 prevents the drive tube 70 from rotating relative to the housing structure.

[0144] Furthermore, a plurality of ratchet arms 77 provided on the drive tube 70 engage the teeth 26 inside the spring base 25 so that the drive tube 70 can only be rotated in one direction, which in the disclosed example is counterclockwise when viewing the injection device from a distal position. Figure 5B Shown in.

[0145] The telescopically movable shield 40 is rotatable relative to the housing structure and can be rotated between a locked position and an unlocked position. Figure 1 As can be seen in FIG, the telescopically movable shield 40 is provided with a helical structure 41 on its outer surface, the helical structure terminating in radial ends 44a, b, which are located at an angular distance apart, so that these radial ends 44a, b together define an axial opening. An inwardly directed protrusion is provided on the inner surface of the housing part 10, which can slide through the axial opening of the helical structure 41 when the telescopically movable shield 40 has been rotated to the unlocked position. In any other position, if the telescopically movable shield 40 attempts to move in translation in the proximal direction, the inwardly directed protrusion will abut the helical structure 41, thus defining the locked position.

[0146] The spiral structure 41 further forces the needle shield 40 to move spirally when rotating. Therefore, the needle shield 40 can be moved to a certain position, in which the distal tip of the needle cannula 46 is just located outside the cleaning component 50 when the needle shield 40 is unlocked.

[0147] In the locked position, the telescopically movable shield 40 is blocked from translational movement, whereas in the unlocked position, the telescopically movable shield 40 is able to move in translation. In this context, translation is defined as an axial movement along the central axis "X" without any rotation.

[0148] The housing part 10 is provided with a pair of longitudinal windows 13. These longitudinal windows 13 are aligned with similar windows 23 provided in the cartridge holder 20, so that the user can visually check the contents of the cartridge 5. The telescopic movable shield 40, which is radially sandwiched between the housing part 10 and the cartridge holder 20, can be rotated between a locked position and an unlocked position, and is provided with another set of windows 49. These windows 49 are aligned with the other windows 13, 23, so that the user can only see the contents of the cartridge 5 when the telescopic movable shield 40 has been rotated to its unlocked position. When the telescopic movable shield 40 is in the locked position, the solid part of the telescopic movable shield 40 prevents the user from visually seeing the cartridge 5. Therefore, this rotation of a set of windows 49 in the telescopic movable shield 40 also indicates when the injection device is ready for injection.

[0149] In one example, a pair of longitudinal windows 13 provided in the housing portion 10 may be provided with graduations showing a number of doses in the injection device. Figure 1 and Fig.15 In the example of , the scale indicates four sections, each section representing one of the predetermined dose volumes. Thus, the user can visually see the physical position of the plunger 7 in the section of the window 13, and thus see how many doses have been used and how many doses are left in the cartridge 5.

[0150] The telescopically movable shield 40 is also used to release the torque stored in the torsion spring 65, thereby ejecting a predetermined dose volume when moving in translation in the proximal direction. During injection, the user presses the shield tip 55 and thus the telescopically movable shield 40 against the skin, thereby moving the telescopically movable shield 40 in the proximal direction.

[0151] In order to transmit the translational motion from the telescopically movable shield 40 to the drive tube 70, a Fig. 7A - A connector element 80 disclosed in B. This connector element 80 is guided in translation relative to the housing part 10, ie without any rotation, and is provided on its inner surface with two inwardly directed projections 81, 82 which are also rotationally and axially offset.

[0152] One of the two inwardly directed projections 81, 82 (indicated as "81") is not directly visible in the drawing, but is Figure 7B In the disclosed example, the two protrusions 81 , 82 are offset by 180° relative to each other.

[0153] Both the telescopically movable shield 40 and the connector element 80 are provided with hooks 42, 83. When the telescopically movable shield 40 rotates, the two hooks 42 on the telescopically movable shield 40 can be engaged with the two hooks 83 provided on the connector element 80.

[0154] The hooks 83 on the connector element 80 are disposed distally on a pair of axial extensions 84. These axial extensions 84 allow the connector portion 80 to surround the bridge portion 15 of the housing portion 10 and to operate through the axial opening between the radial bearings 19 in the connection between the bridge portion 15 and the housing portion 10, as shown in FIG. Figure 2A , 5A and Fig.17A Best seen in.

[0155] Spring attachment

[0156] like Figure 2A -B, the torsion spring 65 is located between the drive tube 70 and the spring base 25, so that the torsion spring 65 can rotate the drive tube 70 relative to the spring base 25 as part of the housing structure.

[0157] exist Fig.11A -C, the torsion spring 65 is provided with a hook 67 at the end of the torsion spring 65. To illustrate the spring attachment, Fig.11A -C shows only the proximal end of the torsion spring 65 and also only a portion of the replacement spring base 25. Nevertheless, Fig.11A -C discloses only one end of the torsion spring 65, and it is obvious that both ends may be provided with such a hook 67 and attached in the same manner.

[0158] To install the torsion spring 65, a hook 67 is first translated through the axial passage 26 in, for example, the spring base 25. This translation movement is caused by Fig.11A The arrow "A" in FIG. 1 indicates that the movement between the spring base 25 and the torsion spring 65 is a relative movement, that is, one or both of the elements may move in translation.

[0159] Once the hook 67 has axially passed through the axial passage 26, as Fig. 11B As disclosed in the invention, the torsion spring 65 and the spring base 25 are rotated relative to each other so that the hook 67 is caught on the shelf 27 formed in the spring base 25, as shown in FIG. Fig. 11C as shown in .

[0160] In order to irreversibly fix the torsion spring 65 to the spring seat 25 , a radial snap-in projection 28 is located on the spring seat 25 in the axial channel 26 .

[0161] When the torsion spring 65 and the spring base 25 rotate relative to each other, the hook 67 of the torsion spring 65 passes over the radial snap projection 28 and is thus irreversibly locked to the spring base 25. Fig. 11C as shown in .

[0162] The radial snap-fit ​​protrusion 28 has two sides arranged in the rotation direction. The side that first encounters the hook 67 during rotation has an inclined surface 29a to make it easier for the hook 67 of the torsion spring 65 to slide over the radial snap-fit ​​protrusion 28. The opposite side of the snap-fit ​​protrusion 28 is preferably provided with a steep surface 29b to prevent the hook 67 of the torsion spring 65 from rotating in the opposite direction after it is attached.

[0163] In one example, the inclined surface 29a is angled so that the hook 67 of the torsion spring 65 cannot pass through the radial snap projection 28 without being forced by an assembly tool. In such an example, it is not sufficient to simply rotate the spring base 25 and the torsion spring 65 relative to each other. This is particularly true if the torsion spring 65 has an open winding so that sufficient torque cannot be transmitted to the proximal end carrying the hook 67 when rotating the torsion spring 65. In this case, an assembly tool must be used that grasps the torsion spring 65 at the proximal end and forces the hook 67 through the radial projection.

[0164] In one example, the assembly tool may be a support element that is provided when the torsion spring 65 is in the Fig. 11B The position disclosed in the figure enters the axial channel and abuts the hook 67 at the rear side, thereby forcing the hook 67 to rotate over the radial snap projection 28 and enter Fig. 11C The location is disclosed in the .

[0165] Nevertheless, the radial snap projection 28 is disclosed in combination with the spring base 25, and such a radial snap projection 28 can also be provided on the drive tube 70 to fix the other end of the torsion spring 65. The snap projection 28 can therefore be provided on the spring base 25 or on the drive tube 70 or on both elements.

[0166] In one example, the torsion spring 65 is first attached to the spring base 25 or to the drive tube 70 by a pure rotational motion and, for example, by using a tool. This forms a preassembled unit including the spring base 25 or the drive tube 70 and the torsion spring 65. Since the torsion spring 65 is irreversibly attached due to the radial snap protrusions 28, this preassembled unit can be moved around during the assembly process without separating the torsion spring 65 from the spring base 25 or the drive tube 70.

[0167] At a later stage in the assembly process, the torsion spring 65 may also be attached to the spring base 25 or another portion of the drive tube 70 by rotating the torsion spring 65 relative to one another.

[0168] Preferably, the pre-assembled unit consists of the torsion spring 65 and the drive tube 70. During the pre-assembly process, the torsion spring 65 is irreversibly attached to the drive tube 70 as described above. Once the pre-assembled unit has been positioned inside the housing portion 10, the spring base 25 is rotated into engagement with the proximal hook 67 of the torsion spring 65 and axially fixed to the housing portion 10 (at the end of the housing portion 10) by engaging with a pair of flexible coupling arms 9 provided on the housing portion 10. Figure 15-16 In one example, the radial snap protrusion 28 is only provided on the drive tube 70 and not on the spring base 25.

[0169] injection

[0170] When the telescopically movable shield 40 has been rotated to its unlocked position, the user ejects a predetermined dose volume by pressing the distal shield tip 55 of the telescopically movable shield 40 against the skin, whereby the telescopically movable shield 40 is translated in the proximal direction. This translational movement is converted into a similar translational movement of the connector element 80.

[0171] Fig. 7A -B is guided in translation relative to the housing part 10 during administration, and the two inwardly directed protrusions 81, 82 abut against the outwardly directed protrusions 73, 74 on the outer surface of the drive tube 70, so that the drive tube 70 also moves in translation with the connector element 80. The compression area 66 on the torsion spring 65 allows the drive tube 70 to move in translation in the proximal direction, and the compression of the torsion spring 65 further applies an axial force to the drive tube 70, thereby pushing the drive tube 70 in the distal direction.

[0172] The translational movement of the drive tube 70 in the proximal direction causes the first axial drive flange 72 and the second axial drive flange 78 on the drive tube 70 to slide respectively along the first axial housing flange 17 and the second axial housing flange 18 in the housing part 10. At the same time, the inwardly directed protrusion 75 on the drive tube 70 slides a certain axial distance in the longitudinal track structure 62 on the piston rod 60.

[0173] The size of the predetermined dose volume prepared by this translational movement of the drive tube 70 is therefore related to the longitudinal distance moved by the drive tube 70 (i.e. the axial length of the engagement between the first axial drive flange 72 and the first axial housing flange 17 and the axial length of the engagement of the second axial drive flange 78 and the second axial housing flange 18) and the pitch of the threaded connection 12, 61 between the piston rod 60 and the nut member 11. The translational distance moved by the drive tube 70 when the predetermined dose volume is prepared is referred to as "dl" (activation distance).

[0174] Once the first axial drive flange 72 and the second axial drive flange 78 have been translated out of engagement with the first axial housing flange 17 and the second axial housing flange 18, the torque stored in the torsion spring 65 will force the drive tube 70 to rotate, so that the spiral shape 71 on the drive tube 70 rotates downward along the housing spiral shape 16 inside the housing portion 10 until the first axial drive flange 72 and the second axial drive flange 78 are again adjacent to the first axial housing flange 17 and the second axial housing flange 18. As previously described, the spiral motion can be supported by an additional spiral interface. The rotation is 360° in the disclosed example, that is, the drive tube 70 rotates a full circle each time the activation distance "dl" is translated in the proximal direction. Therefore, the piston rod 60 also rotates 360° and thus moves in the distal direction by the pitch of the thread 61 on the piston rod 60 and the pitch 12 in the engagement nut member 11.

[0175] Thus, each predetermined dose volume is prepared when the drive sleeve 70 translates an activation distance “dl” in the proximal direction, and is ejected when the drive sleeve 70 rotates in the distal direction and returns to its initial position.

[0176] A shield spring 90 in the form of a helically wound compression spring is arranged between the connector element 80 and the housing structure, preferably between the connector element 80 and the spring base 25, and exerts a compressive force on the connector element 80 when the connector element 80 has been translated proximally during dose preparation. The compression of the shield spring 90 pushes the connector element 80 in the distal direction.

[0177] Also like Fig. 6A -B, the drive tube 70 is provided with a helical flange 76 on the outer surface, which engages with inwardly directed projections 81, 82 inside the connector element 80 when the torsion spring 65 begins to rotate the drive tube 70. This engagement between the inwardly directed projections 81, 82 and the helical flange 76 supports the helical guidance of the drive tube 70.

[0178] The spiral flange 76 on the drive tube 70 is provided with two axial openings "d" ( Fig. 6A -B), when the opening "d" is rotationally aligned with the inwardly directed protrusions 81, 82, the inwardly directed protrusions 81, 82 inside the connector element 80 can slide translationally through said axial opening. This alignment occurs when the first axial drive flange 72 and the second axial drive flange 78 on the drive tube 70 are about to abut against the first axial housing flange 17 and the second axial housing flange 18 inside the housing part 10 again, i.e. when the predetermined dose volume has been discharged. Once the predetermined dose size has been discharged, i.e. after the drive tube 70 has rotated 360° (in this example) and reached its initial position, the shield spring 90 will therefore push the connector element 80 and the telescopically movable shield 40 in the distal direction.

[0179] Also in this state, the inwardly directed projections 81 , 82 will be aligned with the outwardly directed projections 73 , 74 , so that the next subsequent dose volume can be released by repeating the process described herein.

[0180] When the telescopically movable shield 40 moves back to its initial position, the cleaning assembly 50 carried by the telescopically movable shield 40 is brought back to its initial position, wherein the distal tip of the needle cannula 46 is positioned inside the cleaning chamber 50 .

[0181] During movement of the telescopic movable shield 40 in the distal direction, the spiral structure 41 on the telescopic movable shield 40 abuts against a similar spiral path 33 disposed inside the housing structure and preferably on the inner surface of the shield guide 30, and when the telescopic movable shield 40 moves back to its initial position, the spiral path forces the telescopic movable shield 40 to rotate to its locked position.

[0182] Termination of content

[0183] Therefore, the predetermined dose volume is prepared by pushing the telescopically movable shield 40 against the user's skin to move the drive tube 70 in the proximal direction. When the drive tube 70 moves the activation distance "dl" in the proximal direction, the first spiral shape 71 on the drive tube 70 is brought to its release position, wherein the axial drive flanges 72, 78 are released from the axial housing flanges 17, 18. In this release position, the drive tube 70 can rotate under the influence of the torque stored in the torsion spring 65. As explained, the drive tube 70 moves spirally in the distal direction during its rotation. In addition, during this rotation, due to the engagement between the longitudinal track structure 62 of the piston rod 60 and the inwardly directed protrusion 75 inside the drive tube 70, the drive tube 70 rotates the piston rod 60. Since the piston rod 60 thread (61, 12) is connected to the nut member 11 fixed in the housing structure, the piston rod 60 moves spirally in the distal direction during rotation.

[0184] Each time the drive tube 70 is moved in the proximal direction an activation distance "d1" and released, the piston rod 60 in this embodiment is forced to rotate 360°, i.e. one full turn, and thus move forward an axial distance given by the pitch of the thread between the piston rod 60 and the nut member 11. Once the remaining distance between the inwardly directed protrusion 75 on the drive tube 70 and the stop surface 63 on the piston rod 60 is less than the length "d1" of the axial flanges 72, 78, 17, 18, it is not possible to move the drive tube 70 to its release position to release another fixed dose.

[0185] When the injection device is delivered to the user, the stop surface 63 on the piston rod 60 is located at the proximal end of the injection device, such as Figure 3However, for each ejection of a predetermined dose size, the piston rod 60 moves in the distal direction until the stop surface 63 on the piston rod 60 is in a position where the drive tube 70 cannot move the entire activation distance "dl" in the proximal direction. When this happens, it is not possible to move the drive tube 70 to its release position, and therefore it is not possible to select another predetermined dose size, which prevents the user from expelling another predetermined dose.

[0186] In other words, when the remaining portion of the free length "L" of the track structure 62 of the piston rod 60 is shorter than the activation distance "dl", it is not possible to move the axial drive flanges 72, 78 out of engagement with the axial housing flanges 17, 18 and thereby release another fixed dose volume.

[0187] It is certain that each time the user prepares one of the predetermined dose volumes, the drive tube 70 is moved translationally in the proximal direction by the activation distance "d1" and rotated back to its initial position when the prepared and predetermined dose volume is expelled. In this rotational movement, the drive tube 70 preferably rotates about 360°. Once the cumulative number of times the drive tube 70 has moved the activation distance "d1" and the cumulative distance the piston rod 60 has moved in the distal direction leaves a length "d1" available that is less than the free length "L" of the track structure 62 of the piston rod 60, the stop surface 63 on the piston rod 60 prevents the dose tube 70 from moving in the proximal direction by the full fixed dose setting (i.e. the full activation distance "d1") and thus prevents the user from being able to select the full predetermined dose size.

[0188] In a different embodiment, the first helical shape 71 and the housing helical shape 16 may be divided into more than one surface, so that more than one axial flange abutment (72, 18; 78; 17) is provided. In such a case, the possible rotation of the drive tube 70 and the piston rod 60 for each translational movement may be different from 360°. If, for example, double the number of axial flange abutments is provided, the rotation will be 180°, so that the piston rod 60 rotates only half of a full rotation for each dose release.

[0189] Example of content termination

[0190] In one example, the free length "L" of the track structure 62 can be, for example, 43 mm, that is, the translation distance between the engagement of the inwardly directed protrusion 75 of the drive tube 70 with the piston rod 60 and the stop surface 63 in the piston rod 60 is set to 43 mm at the factory.

[0191] In order to release one of the fixed doses, the drive tube 70 moves an activation distance "dl" in the proximal direction. In this example, "dl" can be 5mm. Once the drive tube 70 has moved an activation distance "dl" = 5mm in the proximal direction, the torsion spring 65 will rotate the drive tube 70 back to its initial position by a full circle (i.e., 360°). During this rotation, the piston rod 60 is also forced to rotate the same degree, i.e., 360°. According to the pitch of the threaded connection between the piston rod 60 and the nut member 11, for each full circle, the piston rod 60 moves a given axial distance in the distal direction. The pitch can, for example, be such that for each complete rotation (360°) of the piston rod 60, the distance moved by the piston rod 60 is, for example, 10mm. This means that once four (4) fixed doses have been released (i.e. the drive tube 70 has moved the activation distance "dl" four times), the piston rod 60 has moved 40 mm in the distal direction, leaving only 3 mm of the free length "L" of the track structure 62 free before reaching the stop surface 63, and since the drive tube 70 requires an axial movement of "dl" = 5 mm in order to release another fixed dose volume, it is no longer possible to release another fixed dose volume despite the fact that the free length "L" of the track structure 62 still has 3 mm.

[0192] Zero point adjustment

[0193] In mainly Figures 12 to 17A -B, the nut member 11 can be a separate element fixed to the housing portion 10 of the housing structure during the assembly of the injection device. In such an embodiment, the nut member 11 can be fixed in the housing structure without the use of physical attachment means such as gluing or welding. By using a dedicated component, the nut member 11 in such an embodiment can also be used to completely eliminate or at least significantly minimize any air gap caused by different tolerances during the assembly process. Such air gap elimination is also commonly referred to as zero point adjustment. The zero point refers to the point where the piston rod 60 (or piston rod foot 85) abuts the plunger 7 inside the cartridge 5. When this abutment is completed during the manufacture of the injection device, there is no need for the user to perform an initial priming of the injection device before expelling the first dose volume.

[0194] The nut member 11 used for this purpose is Fig.14A -B, and comprises an internal thread 12 engaging an external thread 61 on a piston rod 60 and two external thread protrusions 95 disposed proximally on a nut member 11. The two angled thread protrusions 95 together form an external thread on the nut member 11. However, the external thread can be made of one or more flanges or any number of external thread protrusions 95.

[0195] The nut member 11 is further and also provided on the outer surface with a plurality of ratchet arms 96, the use of which will be explained. In the disclosed embodiment, two ratchet arms 96 are disclosed distally on the nut member 11, but any suitable number may be provided.

[0196] For example Fig.16 The bridge structure 15 inside the housing part 10 supporting the nut member 11 disclosed in the example is provided with axial teeth 97, which allow the nut member 11 to rotate in only one direction. The allowed rotation direction is clockwise; meaning that the ratchet arm 96 and the teeth 97 are connected so that rotation in the counterclockwise direction is prevented.

[0197] The bridge structure 15 inside the housing portion 10 is also provided with an internal thread 98 oriented so that the nut member 11 is screwed in the proximal direction when rotated in the permitted clockwise direction.

[0198] During assembly of the injection device, an important objective is to eliminate the distance (the so-called air gap) that exists between the piston rod 60 and the plunger 7 inside the cartridge 5. If the piston rod foot 85 is attached to the piston rod 60, such as Fig.13 As disclosed in , the purpose is to eliminate the physical distance between the distal surface of the piston rod foot 85 and the proximal surface of the plunger 7, so that the piston rod foot 85 and the plunger 7 are abutted when the injection device is delivered to the end user in an unused state.

[0199] When the nut member 11 is rotated relative to the housing structure during final assembly, the piston rod 60 is advanced in the distal direction until the piston rod 60 or the piston rod plunger 85 abuts the plunger 7 inside the cartridge 5 .

[0200] The rotation of the nut member 11 is preferably accomplished by using a dedicated tool in the production line that is capable of engaging the nut member 11 and transferring the rotation to the nut member 11. In a preferred example, the piston rod 60 is first positioned to engage the nut member 11 in the bridge structure 15 located in the housing portion 15. Thereafter, an electronic computerized device is used to detect the position of the plunger 7 in the cartridge 5 to be used for this particular injection device. When the position of the plunger 7 and the position of the piston rod 60 (or piston rod foot 85) are measured and known, the computer will be able to determine how much the nut member 11 needs to be rotated to bring the piston rod foot 85 or piston rod 60 in a particular injection device into abutment with the plunger 7 when the injection device is assembled.

[0201] Therefore, the position of the most proximal end of the piston rod 60 or the piston rod foot 85 is fine-tuned by rotating the nut member 11 in the one-way interface with the bridge structure 15. It is important here to allow the nut member 11 to rotate in a rotational direction that advances the piston rod 60 (or piston rod foot 85) into contact with the plunger 7.

[0202] The piston rod 60 is also provided with an axial track structure 62, which is engaged by an inwardly directed protrusion 75 on the drive tube 70, which is also provided with a plurality of ratchet arms 77, which engage the teeth 26 inside the spring base 25, thereby forming a one-way ratchet interface, so that the drive tube 70 can only be rotated in one direction, which in the disclosed example is counterclockwise when the injection device is viewed from a distal position. These ratchet arms 77 thus prevent the piston rod 60 from rotating in a clockwise direction.

[0203] Therefore, the engagement between the piston rod 60 and the drive tube 70 prevents the piston rod 60 from rotating in the clockwise direction. Therefore, when the nut member 11 rotates in the clockwise direction, the rotation is converted into a translation of the piston rod 60 in the distal direction because the piston rod 60 cannot follow the clockwise rotation of the nut member 11.

[0204] When a dose is discharged, the drive tube 70 and the piston rod 60 rotate in the counterclockwise direction. Since the one-way ratchet interface 96, 97 between the nut member 11 and the housing part 10 (via the bridge structure 15) prevents the nut member 11 from rotating in the counterclockwise direction, the nut member 11 does not rotate and thus supports the helical movement of the piston rod 60 in the distal direction.

[0205] To eliminate the air gap between the piston rod 11 (or the piston rod foot 85) and the plunger 7 inside the cartridge 5, the nut member 11 is rotated in a clockwise direction relative to the housing structure, thereby translating the piston rod 60 in a distal direction.

[0206] The nut member 11 cannot be rotated further in the clockwise direction when the piston rod 11 (or piston rod foot 85) abuts the plunger 7. However, in one example, this is accomplished by electronically measuring the position prior to final assembly so that the piston rod foot 85 is in the correct position when assembled with the cartridge holder part 20.

[0207] Due to the one-way interface 96 , 97 between the nut member 11 and the housing portion 10 , the nut member 11 cannot be rotated in a counter-clockwise direction (when viewed from a distal position).

[0208] As a result of the above operation, the nut member 11 is self-locking relative to the housing structure, and there is no need to physically fix the nut member 11 to the housing structure. Therefore, it is not necessary to weld or glue the nut member 11 to the housing structure as described in the prior art.

[0209] Self-locking here means that the nut member 11 cannot rotate in the clockwise direction due to the piston rod 60 (or foot 85) abutting the plunger 7 and the nut member 11 cannot rotate in the counterclockwise direction due to the one-way ratchet interfaces 96, 97.

[0210] When the piston rod 60 is rotated in the counterclockwise direction to expel the prepared dose volume, the nut member 11 is also unable to follow this rotation due to the one-way ratchet interfaces 96, 97, and when the nut member 11 is rotated clockwise during assembly to eliminate the air gap, the piston rod 60 is prevented from following this rotation by the engagement with the drive tube 70 (62, 75) and the engagement between the drive tube 70 and the housing structure (77, 26).

[0211] If the pitch of the first threaded connection 61, 12 between the piston rod 60 and the nut member 11 is large, that is, the piston rod 60 moves a long distance each time it rotates, it is wise to have a second threaded connection 95, 98 between the threaded protrusion 95 on the nut member 11 and the threaded flange 98 inside the housing part 10, so that the nut member 11 can be tightened in the proximal direction relative to the housing structure during rotation of the nut member 11.

[0212] like Fig. 17B As best seen in FIG. 1 , the protrusions 95 constituting the external threads on the nut member 11 are secured behind a threaded flange 98 inside the bridge structure 15 of the housing portion 10 so that the nut member 11 moves proximally when rotated relative to the housing structure. Fig.16 1 , the threaded flange 98 inside the bridge structure 15 is depicted as having an axial opening, thereby allowing the threaded protrusion 95 on the nut member 11 to engage proximally behind the threaded flange 98 .

[0213] This means that when the nut member 11 is rotated in a clockwise direction, the nut member 11 moves proximally while causing the piston rod 60 to move in a distal direction. Therefore, the pitch of the second threaded connection 95, 98 between the nut member 11 and the housing structure must be subtracted from the pitch of the first threaded connection 61, 12 between the piston rod 60 and the nut member 11 in order to find the effective zero adjustment pitch.

[0214] A low effective pitch in the zero adjustment makes it easier to fine tune the air gap elimination process. It is therefore beneficial to have a second threaded connection 95, 98 between the nut member 11 and the housing portion 10 when operating with a piston rod 60 having a large pitch, which is the case when a relatively large volume must be ejected for each rotation of the piston rod 60.

[0215] When the pitch of the first threaded connection 61 , 12 between the piston rod 60 and the nut member 11 is small, it is considered that the second threaded connection 95 , 98 is not required, so the nut member 11 only needs to rotate in one plane relative to the housing structure and cannot move axially.

[0216] Alternative zero adjustment

[0217] FIG. 18A to FIG. 19BAn alternative nut member for zero point adjustment is disclosed in . The alternative nut member is assigned reference numeral 111, and the various elements added in this embodiment are prefixed with "1". The remaining structural parts in this embodiment are numbered with the same numbers used in the previous embodiment.

[0218] The nut element 111 is provided with an internal thread 112 on an inner surface and with a pair of elastic arms 113 on an outer surface. Although only two elastic arms 113 are disclosed in this embodiment, any number of elastic arms 113 may be provided.

[0219] The axial opening in the bridge structure 15 of the housing structure guiding the nut element 111 is provided in this embodiment with at least one and preferably two axially extending grooves 115, which translationally guide the resilient arms 113. The engagement between the grooves 115 and the flexible arms 113 thus ensures that the nut element 111 can only slide in translation, i.e. without rotation relative to the housing structure.

[0220] The groove 115 is provided with an inclined bottom surface 116 (see Fig.18B ), the inclined bottom surface is inclined radially outwardly in the distal direction. This has the effect that the resilient arm 113 is exposed to an increasing radial force when moving in the proximal direction and is therefore pushed in the distal direction with an increasing force when the nut element 111 moves further proximally.

[0221] As shown, the flexible arm 113 is preferably inclined in a radial direction such that the flexible arm 113 follows an angle with respect to the central axis corresponding to the angle of the inclined bottom surface 116 .

[0222] To assemble the injection device, the nut element 111 and the piston rod 60 are first preassembled by rotating the nut element 111 and the piston rod 60 relative to each other so that the nut element 111 is threaded onto the piston rod 60. Thereafter, the preassembled piston rod 60 and nut element 111 are placed inside the opening of the bridge structure 15, as shown in FIG. Fig.18A In the public.

[0223] When the injection device is fully assembled, the piston rod 60 may abut directly against the plunger 7 inside the cartridge 5, or the piston rod foot 85 may be disposed between the piston rod 60 and the plunger 5 so that the abutment is located between the piston rod foot 85 and the plunger 7, such as Fig.18C In the public.

[0224] In one example, the piston rod foot 85 can be connected to the piston rod 60 before, simultaneously with, or after the piston rod 60 has been preassembled with the nut element 111, such as Fig.18B as shown in .

[0225] In one example, the piston rod foot 85 may be snap-fitted onto the piston rod 60 in a manner similar to a bearing connection, such that the piston rod foot 85 can rotate relative to the piston rod 60. In another example, the piston rod foot 85 is a separate or loose element located between the piston rod 60 and the plunger 7. Alternatively, the piston rod foot 85 may be rotationally connected to the piston rod 60 to rotate with the piston rod 60.

[0226] In the latter example, the piston rod foot 85 may comprise an electronic sensor capable of recording the number of rotations of the piston rod 60 relative to the cartridge 5 and thus the housing structure in order to determine the expelled volume.

[0227] Once the piston rod 60 and the nut element 111 are preassembled with or without the piston rod foot 85 , the nut element 111 is axially slid such that the flexible arms 113 engage the grooves 115 provided in the opening of the bridge section 15 of the housing structure.

[0228] In the final step of assembly, the cartridge 5 is placed inside the cartridge holder 20 and the cartridge holder 20 is moved together with the cartridge 5 in the proximal direction so that the plunger 7 inside the cartridge 5 comes into contact with the piston rod 60 (or foot 85) and the cartridge holder 20 snaps onto the housing portion 10 of the housing structure.

[0229] As a result, the plunger 7 inside the cartridge 5 abuts the piston rod 60 (or foot 85), forcing the nut element 111 to slide in translation in the proximal direction. When the flexible arm 113 pushes against the inclined bottom surface 116 of the groove 99, the elasticity in the flexible arm 113 will automatically push the nut element 111 and thus the piston rod 60 in the distal direction, so that the contact between the plunger 7 and the piston rod 60 (or foot 85) is maintained. Whenever the contact between the plunger 7 and the piston rod 60 (or foot 85) is obtained and maintained, the laser beam (at Fig.18C The bridge structure 15 is guided through the opening 14 in the shell structure and onto the outer surface of the bridge structure 15. Fig.18C As disclosed in , there may be two or more such openings 14 if desired.

[0230] The bridge structure 15 is preferably molded from a polymer that is more transparent to laser light than the polymer from which the flexible arms 113 of the nut element 111 are molded, so that the energy in the laser beam is converted into heat in the contact surface area between the bridge structure 15 and the flexible arms 113, i.e., on the inner surface of the bridge structure 15.

[0231] The injection device according to this embodiment thus has a nut element 111 that can be operated between two different states. A first state, in which the nut element 111 is axially movable and in which the nut element 111 is slightly moved in the proximal direction, preferably by collision with the plunger 7 in the cartridge 5. During this axial movement in the proximal direction, the elasticity of the nut element 111 rebounds the nut element 111 in the distal direction, thereby maintaining physical contact with the plunger 7.

[0232] In a position where physical contact between the plunger 7 and the piston rod 60 (or the foot 85 ) is achieved, the nut element 111 is welded or otherwise connected to the housing structure, thus defining a second state of the nut element 111 .

[0233] In this second state, the nut element 111 is axially fixed to the housing structure and the piston rod 60 thereafter moves helically when rotating relative to the nut element 111 and the housing structure.

[0234] The positioning of the pre-assembled nut element 111 and piston rod 60 may alternatively be determined electronically so that welding can be done before actually positioning the cartridge.

[0235] Second alternative zero adjustment

[0236] Figures 20 to 22B An alternative solution is disclosed, in which a telescopic element 100 is arranged between the piston rod foot 85 and the piston rod 60 .

[0237] Replacement piston rod 60 in Fig. 20 1 and are provided with two claws 105 at the distal end, which claws are able to grip around the telescopic element 100. Although only two such claws 105 are disclosed, any number of claws 105 may be provided.

[0238] The piston rod 60 is provided with an external thread 61 which engages with an internal thread 12 provided in the nut member 11 , which in this alternative embodiment is preferably an integral part of the housing structure. The piston rod 60 is also provided with a longitudinal track structure 62 which is engaged by the drive element 70 .

[0239] exist Fig.21 The telescopic element 100 shown in more detail in FIG. 1 is provided distally with a circular rib 101 behind which a snap arm 86 provided on the piston rod foot 85 engages so that the telescopic element 100 can be axially fixed to the piston rod foot 85. Due to this snap-fit ​​connection, the piston rod foot 85 can rotate relative to the telescopic element 100.

[0240] The telescopic element 100 is also provided with a plurality of outwardly directed surfaces 102, to which the claws 105 can abut, such as Fig.22AThe claws 105 are therefore adapted to slide on these outwardly directed surfaces 102 , so that the telescopic element 100 can slide relative to the piston rod 60 .

[0241] For this purpose, the telescopic element 100 is slidably arranged in an axial opening 106 in the piston rod 60 , so that the piston rod foot 85 together with the telescopic element 100 can slide axially relative to the piston rod 60 .

[0242] Once the piston rod foot 85 (connected to the telescopic element 100) has slid into contact with the plunger 7 inside the cartridge 5, as shown in FIG. Fig.22A -B, the telescopic element 100 is welded to the piston rod 60 by directing a laser beam “L” through an opening 14 in the housing structure onto the claws 105 of the piston rod 60 , whereby said claws are welded to the outwardly directed surface 102 of the telescopic element 100 .

[0243] The telescopic element 100 is preferably square, such that there are four outer surfaces 102 , and the axial opening 106 is preferably also square, such that the telescopic element 100 can only translate relative to the piston rod 60 in the first state.

[0244] Some preferred embodiments have been shown above, but it should be emphasized that the invention is not limited to these, but can be implemented in other ways within the subject matter defined in the following claims.

Claims

1. A prefilled injection device for delivering a liquid drug, comprising: a housing structure extending along a longitudinal axis (X) defining a distal direction and a proximal direction and permanently embedding a cartridge (5) having a movable plunger (7), a piston rod arrangement (60, 85) for advancing the movable plunger (7) during dispensing, the piston rod arrangement (60, 85) having an external thread (61) and a longitudinal track structure (62), a rotatable drive element (70) engaging the longitudinal track structure (62) of the piston rod arrangement (60, 85) such that a rotation of the drive element (70) is converted into a rotation of the piston rod (60), a nut element (111) having an internal thread (112) engaging an external thread (61) of the piston rod arrangement (60, 85), wherein the nut element (111) operates in two different states; a first state, wherein the nut element (111) is arranged to be axially slidable relative to the housing structure, and a second state in which the piston rod arrangement (60, 85) abuts the movable plunger and the nut element (111) is permanently fixed to the housing structure, It is characterized in that In the first state, the nut element (111) engages the housing structure via a resilient interface (113, 116) which is capable of axially pushing the nut element (111) relative to the housing structure such that the piston rod arrangement (60, 85) abuts the movable plunger (7), and In the second state, the nut element (111) is permanently fixed to the housing structure, so that the piston rod arrangement (60, 85) moves helically relative to the nut element (111) and the housing structure when rotating.

2. Injection device according to claim 1, wherein the nut element (111) is permanently fixed to the housing structure by welding.

3. The injection device according to claim 1 or 2, wherein the elastic interface (113, 102) comprises a plurality of flexible arms (113).

4. The injection device according to claim 3, wherein the flexible arm (113) has radial elasticity and is operable between the nut element (111) and the housing structure.

5. Injection device according to claim 4, wherein the flexible arm (113) is arranged on the nut element (111) and abuts an inner surface of the housing structure.

6. The injection device according to claim 5, wherein an inner surface adjacent to the flexible arm (113) is formed as a groove (116).

7. The injection device according to claim 6, wherein the groove (116) has an inclined bottom angled in the distal direction.

8. Injection device according to claim 7, wherein the piston rod arrangement (60, 85) comprises a piston rod (60) and a piston rod foot (85).

9. Injection device according to claim 8, wherein the housing structure has a passage (14) for a laser beam ("L").

10. A method for assembling an injection device according to any one of claims 1 to 9, the method comprising the steps of: threading the nut element (111) and the piston rod arrangement (60, 85) by rotating the nut element (111) and the piston rod arrangement (60, 85) relative to each other, causing the nut element (111) together with the piston rod arrangement (60, 85) to translate relative to the housing structure, inserting at least the proximal portion of the cartridge (5) together with the plunger (7) into the housing structure, moving the cartridge (5) and the plunger (7) together proximally to a position in which the plunger (7) inside the cartridge (5) abuts the piston rod means (60, 85), and In this position the nut element (111) is fixed to the housing structure.

11. A method for assembling an injection device according to claim 10, wherein At least one flexible arm (113) of the nut element (111) is welded to the housing structure at a location where the plunger (7) inside the cartridge (5) abuts the piston rod arrangement (60, 85).

12. A prefilled injection device for delivering a liquid drug, comprising: a housing structure extending along a longitudinal axis (X) defining a distal direction and a proximal direction and permanently embedding a cartridge (5) having a movable plunger (7), a piston rod (60) with a piston rod foot (85), the piston rod being used to advance the movable plunger (7) during dispensing, the piston rod (60) having an external thread (61) and a longitudinal track structure (62), a rotatable drive element (70) engaging the longitudinal track structure (62) of the piston rod (60) such that a rotation of the rotatable drive element (70) is converted into a rotation of the piston rod (60), a nut element (11) having an internal thread (12) for engaging an external thread (61) of the piston rod (60), It is characterized in that The piston rod foot (85) is connected and axially fixed to a telescopic element (100), which operates in two different states; a first state, in which the telescopic element (100) is arranged to be axially slidable relative to the piston rod (60), and a second state, wherein the telescopic element (100) is permanently fixed to the piston rod (60), and wherein The telescopic element (100) in the first state non-rotatably engages a longitudinal channel (106) in the piston rod (60) extending along the longitudinal axis (X), and The telescopic element (100) is permanently fixed to the piston rod (60) in the second state.

13. Injection device according to claim 12, wherein the telescopic element (100) is permanently fixed to the piston rod (60) by welding.

14. Injection device according to claim 13, wherein the telescopic element (100) is permanently fixed to the piston rod (60) by laser welding.

15. A method for assembling an injection device according to claim 12 or 13, the method comprising the steps of: engaging the telescopic element (100) and the piston rod foot (85) in an axial coupling, Inserting the telescopic element (100) into the longitudinal channel (106) in the piston rod (60), establishing physical contact between the plunger (7) inside the cartridge (5) and the piston rod foot (85), and The telescopic element (100) is fixed to the piston rod (60) at a position where physical contact is established between the plunger (7) inside the cartridge (5) and the piston rod foot (85).

16. A method for assembling an injection device according to claim 15, wherein A telescopic element (100) carrying the piston rod foot (85) is welded to the piston rod (60) at a location where the plunger (7) inside the cartridge (5) abuts the piston rod foot (85).

17. A method for assembling an injection device according to claim 16, wherein A telescopic element (100) carrying the piston rod foot (85) is laser welded to the piston rod (60).

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