Pen-shaped torsion spring driven injection device

The invention relates to a pen-shaped torsion spring driven injection device for apportioning set dose of a liquid drug. A piston rod having an external thread is driven forward by a rotatable piston rod guide engaging the piston rod. The piston rod guide is rotated by a torsion spring encompassed between the housing and the piston rod guide. A scale drum having a thread engaging the external thread of the piston rod is provided, and the scale drum is rotated up and down the piston rod by a proximal located rotatable dose setting member cooperating with the scale drum. The scale drum thus move helically when rotated as the piston rod is held inrotatable during dose setting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 National Stage application of International Application PCT/EP2015/064131 (published as WO 2015/197629), filed Jun. 23, 2015, which claims priority to European Patent Application 14174108.2, filed Jun. 26, 2014; the contents of which are incorporated herein by reference.

THE TECHNICAL FIELD OF THE INVENTION

The invention relates to a pen-shaped injection device, such as a purely mechanical pen-shaped injection device in which the expelling of the individually set doses is driven by a torsion spring.

DESCRIPTION OF RELATED ART

Spring operated injection devices wherein the injection is driven by a torsion spring has been known for decades. An example of such early torsion spring injection device is provided in U.S. Pat. No. 5,104,380. However, this automatic injection device has no separate scale drum and the set dose is visualized only by the rotational position of the dose setting button in relation to the housing. This strongly reduces the number of possible settings since a user, even with impaired sight, must be able to visually see the indicia indicating the dose sizes.

For more modern injection devices it is almost a requirement that the injection device can display a high number of different dose settings. It has therefore become state-of-art to implement a helical movable scale drum in the injection device. Due to the helical movement of the scale drum it has been possible to display a high number of different dose sizes. However, the presence of such helical movable scale drum makes the injection device rather thick and bulky.

Examples of spring operated injection devices having a helical movable scale drum for indicating the set doses are provided in US 2011/0054412 and in WO 2002/053214.

US 2011/0054412 disclose a spring driven injection device in which the torsion spring is a so-called clock spring encompassed between the housing and a drive shaft. The clock spring is torsional strained when a dose is set and released during dosing to drive the drive shaft which via a dose mechanism moves a piston rod forward inside the cartridge.

It can be seen from this reference that a clock spring is meant to be a wounded spring where all the windings are provided consecutively upon each other without any helical extension. Such clock springs are usually wounded from a steel tape and the width of such clock spring is therefore the same as the width of the steel tape from which the spring is wounded. Common for clock spring is further that they operate as torsion springs thus applying a rotational torque. Clock springs are also often referred to as constant force spring since they tend to deliver a constant force when they recoil.

The injection device disclosed in US 2011/0054412 is a tubular pen-shaped device which seems to be the shape preferred by many users. Such injection device usually comprises several constructional layers which often makes such pen shaped injection devices rather thick and bulky. As disclosed the outer layer (not considering the housing itself) is a scale drum which is helically guided in a thread provided on the inner surface of the housing.

In the injection device disclosed in WO 2002/053214, the scale drum is driven directly on the piston rod which makes it possible to avoid threads on the inside surface of the housing. However, the spring used is a helical wounded compression spring providing an axial force which requires additional constructional elements inside the injection device to transform this axial force to a rotation of the piston rod, and such additional elements adds to the overall diameter of the injection device.

DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a pen-shaped injection having the ability to display a high number of different dose sizes and in which the numbers of constructional layers have been reduced thereby reducing the outside diameter of the injection device.

The invention is defined in the attached claim1followed by a number of embodiments. The individual claims are explained in details in the following.

Accordingly, in one aspect of the present invention a pen-shaped torsion spring driven injection device for apportioning set doses of a liquid drug is provided. The torsion spring driven injection device comprises the following main components:A housing which is provided with a window,A piston rod having an external thread and preferably a non-circular cross section,A rotatable piston rod guide which engages and drives the piston rod at least during dose expelling,A torsion spring for rotating the piston rod guide at least during dose expelling,A rotatable scale drum with a thread engaging the external thread of the piston rod and which scale drum carries a plurality of indicia wherein at least a subset of the plurality of indicia is viewable through the window,A proximally located rotatable dose setting member which cooperates with the scale drum such that rotation of the dose setting member at least during dose setting is transformed to a rotation of the scale drum.

Further, when setting a dose, the piston rod is held inrotatable whereby the scale drum rotates helically on the external thread of the piston rod.

The operable connection between the dose setting member and the scale drum can be geared such that the rotational modus is different for the dose setting button and for the scale drum. The scale drum thus travels axially and rotates on the piston rod at the same time whenever the dose setting button is rotated. During this helical movement, the scale drum passes by the window in the housing such that the user visibly can inspect the indicia provided on the scale drum as the dose is being set. The window can be covered by a transparent material which in one example is shaped as a magnifier, alternatively the window can be any kind of opening in the housing through which a user can visibly inspect the indicia.

During dose setting, the scale drum rotates helically whereas the piston rod is held inrotatable. This can in one example be done by securing the piston rod guide rotational to the housing at least in one rotational direction and to have the piston rod guide engage with the non-circular cross-section of the piston rod. The prevented rotational direction being one that would move the piston rod proximally, thus the mechanism only allows the piston rod to move distally.

The indicia are also successively viewable during expelling of the dose as the scale drum rotates back to its initial position. During expelling of the dose the rotation of the scale drum back to its initial position is accompanied by a movement of the piston rod in the distal direction thus moving the piston rod further into the cartridge to thereby expel the set dose.

In a further example, the torsion spring for driving out the set dose is operable between a driver element and a part of the housing. A part of the housing can be either a part stationary coupled to the housing or it can be an integral part of the housing.

The driver element is coupled to the dose setting button at least during dose setting meaning that the driver element can be de-coupled from the dose setting button when the set dose is injected. This has the effect that when the driver element rotates during dose expelling, the dose setting button is de-coupled and thus do not rotate.

Further, the torsion spring which at one end is connected to the driver element to rotate this has the opposite end connected to the housing, or at least to a part of the housing. The torsion spring thus delivers a torque between the housing of the injection device and the driver element.

In one example, the part connected to the housing could be a proximal located separate part which closes the housing and e.g. functions as a base for the torsion spring. This separate part could be connected to the housing by welding, by gluing or simply by being click-fitted or press-fitted to the housing. However many other assembly methods can be utilized.

In a further aspect the scale drum has at least a part which extends through the driver element to engage the piston rod. The scale drum has an outer surface which carries the indicia and which outer surface is visible through the window in the housing as it rotates pass the window. At the centre of the scale drum a thread traveling on the thread of the piston rod is provided. This thread can be connected to the outer surface in multiple ways.

In one example, the thread surrounding the piston rod is created in an element which is connected to the outer surface through one or more arms. Both the element carrying the thread, the arms and the outer surface can be manufactured as separate elements which are then connected to form an assembly. They parts can alternatively be made as one unison scale drum element e.g. through injection moulding.

In a further example, the driver element is provided with a longitudinal opening through which at least the part of the scale drum extends to engage the piston rod. The longitudinal opening allows for relative axial motion between the driver element and the scale drum.

The part extending through the longitudinal opening of the scale drum is preferably a number of radial arms connecting the outer surface and the element carrying the thread. Rotation of the driver element is thus conveyed to the scale drum which thus rotates together with the driver element at least during dose setting.

In a further example, the driver element rotates back to its initial position during expelling of the set dose. Since the arms of the scale drum extend through the driver element this backwards rotation is also conveyed to the scale drum which thus rotates also during expelling of the set dose.

In such example, the scale drum thus rotates helically on the piston rod during dose setting since the piston rod is held inrotatable during dose setting. During expelling of the set dose, the piston rod screws forward in a helical movement which thus also brings along the scale drum in a helical movement back to its initial position.

Since the scale drum moves helically, the radial arms of the scale drum travels axially inside the injection device, this movement being accommodated by the longitudinal opening in the driver element.

When rotating the drive element in either rotational direction, the force is thus transformed to the scale drum by the abutment between the radial arms on the scale drum and the sidewalls of the longitudinal opening or slit in the driver element.

In a further aspect, the driver element is axially movable between a first position and a second position by the user activating an injection button which is coupled to the driver element.

An injection button which is preferably located at a proximal end of the pen-shaped injection is stiffly connected to the driver element such that the driver element moves in the distal direction when a pressure is applied to the injection button.

In one example a compression spring is provided which urges the injection button, and the driver element, back to the initial position when no pressure is applied to the injection button.

The driver element thus shifts between two different positions;

A first position wherein the driver element engages the dose setting member to rotate with the dose setting member. In this first position the driver element is rotationally de-coupled from the piston rod guide. By rotational de-coupled means that the driver element and the piston rod guide is able to rotate independently of each other, however, there can be some degree of physical overlapping of the elements without transferring rotation, and

A second position in which the driver element is rotationally decoupled from the dose setting member. In this second position the driver element is rotational coupled to the piston rod guide such that the rotation of the driver element caused by the torsion spring is transformed to a rotation of the piston rod guide thereby driving the piston rod forward.

The piston rod guide is internally provided with a non-circular opening which engages the non-circular cross section of the piston rod such that the piston rod rotates whenever the piston rod guide is rotated. The piston rod further has a thread on the outside engaging a similar thread provided in the housing of the injection device (or in an element coupled to the housing) such that the piston rod is rotated forward whenever the piston rod guide is rotated.

The non-circular cross section of the piston rod can be shaped in many different ways. It can e.g. be a longitudinal groove or a track, or it can be provided by cutting away part of the circular cross section thus providing a flat longitudinal surface.

In the first position of the driver element (the dose setting mode) rotation of the dose setting member introduces a torque in the torsion spring which is operable and preferably also physical encompassed between, the driver element and the housing. The introduced torque is further released to drive an ejection upon movement of the driver element axially into the second position.

In the second position, the driver element has been moved axially to rotationally engage the piston rod guide such that the piston rod guide and the driver element rotate in unison.

The torsion spring can be pre-strained with a predetermined torque. If the user only dials a small dose, the torque introduced in the torsion spring during dose setting can in one example be too small to overcome the friction between the different rotatable elements in the injection device. It is therefore often seen that such torsion springs are pre-strained such that the spring characteristic in the zero position of the injection device lies above the zero point of the spring force. Or in other words that torque is always present in the torsion spring even when the scale drum is in its zero position. When the prestrained torque overcomes the friction it is thus possible to eject even very small doses.

In the first position of the driver element, when the dose setting button and the driver element are rotated together, a torque is thus build up in the torsion spring. This torque needs to be maintained in the torsion spring also when the user removes the fingers from the dose setting button. A mechanism holding the torque of the strained torsion spring may thus be provided between the dose setting member and the housing, since the dose setting member is rotationally coupled to the driver element. The term housing is also meant to encompass a part connected to the housing.

The mechanism can be materialized in many different ways both axially or radially. It can be one or more radial ratchet arms being locked in one rotational direction against a toothed ring or it can be axially provided by opposed saw-teeth in an engagement e.g. established by a resilient force which can be delivered by a compression spring.

The torsion spring used can either be a helically wounded torsion spring or it can be a non-helical wounded clock spring. A non-helical spring requires only very little axial space inside the housing, whereas a helical spring does not require much radial space.

In a different aspect, the housing of the pen-shaped injection device is formed as a unitary tubular housing element which surrounds at least the scale drum, the torsion spring and a majority of the cartridge. The unitary housing thus has an axial length such that both the dose mechanism and the majority of the cartridge are contained inside the unitary housing. This makes the assembly of the injection device very simple. The dose mechanism can be loaded into the unitary housing element from one end and the cartridge can be loaded into the other end of the unitary housing element. The compartment of the unitary housing containing the cartridge can be separated from the compartment holding the dose mechanism by a partition which is only penetrated by the piston rod.

By the majority of the cartridge is meant that more than 50% and preferably more than 80% of the cartridge.

In one example, the unitary housing part is sealed at the distal end by a capsule-formed element carrying the interface for holding the injection needle. In such example nearly the entire cartridge must be contained in the unitary housing such that the capsule-formed part can be connected to the unitary housing part. The connection can be established by a click-fit, a press-fit or the capsule-formed part can be glued or welded to the unitary housing part. In one example, a capsule-formed part extends only to the shoulders of the cartridge.

Definitions

An “injection pen” is typically an injection apparatus having an oblong or elongated shape somewhat like a pen for writing. Although such pens usually have a tubular cross-section, they could easily have a different cross-section such as triangular, rectangular or square or any variation around these geometries.

The term “Injection Needle” is used to describe an assembly made form a hub holding the actual conduit performing the penetration of the skin during injection. The actual conduit is often referred to as the “Needle Cannula” and is usually made from a metallic material such as e.g. stainless steel. A needle cannula could however also be made from a polymeric material or a glass material. The hub also carries the connecting means for connecting the injection needle to an injection apparatus and is usually moulded from a suitable thermoplastic material. The “connection means” could as examples be a luer coupling, a bayonet coupling, a threaded connection or any combination thereof e.g. a combination as described in EP 1,536,854.

As used herein, the term “drug” is meant to encompass any drug-containing flowable medicine capable of being passed through a delivery means such as a hollow needle in a controlled manner, such as a liquid, solution, gel or fine suspension. Representative drugs includes pharmaceuticals such as peptides, proteins (e.g. insulin, insulin analogues and C-peptide), and hormones, biologically derived or active agents, hormonal and gene based agents, nutritional formulas and other substances in both solid (dispensed) or liquid form.

“Cartridge” is the term used to describe the container actually containing the drug. Cartridges are usually made from glass but could also be moulded from any suitable polymer. A cartridge or ampoule is preferably sealed at one end by a pierceable membrane referred to as the “septum” which can be pierced e.g. by the non-patient end of a needle cannula. Such septum is usually self-sealing which means that the opening created during penetration seals automatically by the inherent resiliency once the needle cannula is removed from the septum. The opposite end is typically closed by a plunger or piston made from rubber or a suitable polymer. The plunger or piston can be slidable moved inside the cartridge. The space between the pierceable membrane and the movable plunger holds the drug which is pressed out as the plunger decreased the volume of the space holding the drug. However, any kind of container—rigid or flexible—can be used to contain the drug.

Since a cartridge usually has a narrower distal neck portion into which the plunger cannot be moved not all of the liquid drug contained inside the cartridge can actually be expelled. The term “initial quantum” or “substantially used” therefore refers to the injectable content contained in the cartridge and thus not necessarily to the entire content.

By the term “Pre-filled” injection device is meant an injection device in which the cartridge containing the liquid drug is permanently embedded in the injection device such that it cannot be removed without permanent destruction of the injection device. Once the pre-filled amount of liquid drug in the cartridge is used, the user normally discards the entire injection device. This is in opposition to a “Durable” injection device in which the user can himself change the cartridge containing the liquid drug whenever it is empty. Pre-filled injection devices are usually sold in packages containing more than one injection device whereas durable injection devices are usually sold one at a time. When using pre-filled injection devices an average user might require as many as 50 to 100 injection devices per year whereas when using durable injection devices one single injection device could last for several years, however, the average user would require 50 to 100 new cartridges per year.

“Scale drum” is meant to be a cylinder shaped element carrying indicia indicating the size of the selected dose to the user of the injection pen. The cylinder shaped element making up the scale drum can be either solid or hollow. “Indicia” is meant to incorporate any kind of printing or otherwise provided symbols e.g. engraved or adhered symbols. These symbols are preferably, but not exclusively, Arabian numbers from “0” to “9”. In a traditional injection pen configuration the indicia is viewable through a window provided in the housing.

Using the term “Automatic” in conjunction with injection device means that, the injection device is able to perform the injection without the user of the injection device delivering the force needed to expel the drug during dosing. The force is typically delivered—automatically—by an electric motor or by a spring drive. The spring for the spring drive is usually strained by the user during dose setting, however, such springs are usually prestrained in order to avoid problems of delivering very small doses. Alternatively, the spring can be fully preloaded by the manufacturer with a preload sufficient to empty the entire drug cartridge though a number of doses. Typically, the user activates a latch mechanism e.g. in the form of a button on, e.g. on the proximal end, of the injection device to release—fully or partially—the force accumulated in the spring when carrying out the injection.

All references, including publications, patent applications, and patents, cited herein are incorporated by reference in their entirety and 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.

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

The use of any and all examples, or exemplary language (e.g. such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. The citation and incorporation of patent documents herein is done for convenience only and does not reflect any view of the validity, patentability, and/or enforceability of such patent documents.

This invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law.

The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts.

DETAILED DESCRIPTION OF EMBODIMENT

When in the following terms as “upper” and “lower”, “right” and “left”, “horizontal” and “vertical”, “clockwise” and “counter clockwise” or similar relative expressions are used, these only refer to the appended figures and not to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as there relative dimensions are intended to serve illustrative purposes only.

In that context it may be convenient to define that the term “distal end” in the appended figures is meant to refer to the end of the injection device which usually carries the injection needle whereas the term “proximal end” is meant to refer to the opposite end pointing away from the injection needle and usually carrying the dose dial button.

Distal and proximal are meant to be along an axial orientation extending along the longitudinal axis of the injection device and is further indicated in the figures.

First Embodiment—FIGS.1to3

FIG. 1depicts an exploded view of the torsion spring operated and pen-shaped injection device1according to a first embodiment. The outer shell is made up from a housing10which is divided into a distal housing part10A and a proximal housing part10B. The distal housing part10A is attached to a cartridge holder20which holds the cartridge25containing the liquid drug.

A cartridge holder20is preferably irreversible connected to the distal housing part10A thus making the injection device a so-called pre-filled injection device. The cartridge holder20is distally provided with a thread21(or a similar connection mean) for attaching an injection needle5to the injection device. Further, the cartridge holder20is equipped with a window22through which the liquid drug contained in the cartridge25can be inspected.

In order to protect the liquid drug from exposure to daylight during storing of the injection device1, a removable cap23is mounted on the outside of the cartridge holder20thus covering the window22.

The cartridge25is further provided with a movable plunger26which is moved forward by a piston rod30. This piston rod30is provided with an outside thread31and a longitudinal groove32. In order to equally distribute the force from the piston rod30to the plunger26a piston rod foot33is provided between the piston rod30and the plunger26.

The outside thread31of the piston rod30is threaded to a similar thread36provided internally in a nut member35. This nut member35is rotational secured to the distal housing part10A, or alternatively moulded as an integral part of the distal housing part10A. In order to secure the depicted nut member35to the housing10, the nut member35is provided with a longitudinal tongue37which engages a longitudinal slit11in the distal housing part10A.

Whenever the piston rod30is rotated it moves forward due to the engagement between the outside thread31of the piston rod30and the internal thread36of the nut member35.

In order to rotate the piston rod30, a piston rod guide40is provided. This piston rod guide40is internally and distally provided with at least one key41engaging the longitudinal track32of the piston rod30such that the piston rod30rotates whenever the piston rod guide40is rotated. Proximally, the piston rod guide40is internally provided with a toothed ring42and on the outside surface a number of longitudinal tongues43are provided the purpose of which will be explained later.

The piston rod guide40is urged in the proximal direction by a first compression spring2which is encompassed between the nut member35and the piston rod guide40. In the first position depicted inFIG. 2which is the situation during dose setting, the piston rod guide40is positioned in its most proximal position and the longitudinal tongues43are rotational locked in similar tracks14(seeFIG. 3) provided internally in the distal housing part10A.

At the proximal end of the injection device1, the proximal housing part10B carries a dose setting button45. This dose setting button45has a rim46engaging a groove12provided externally on the proximal housing part10B. Further, the dose setting button45is provided with an extension47which extend on the inside surface of the second housing part10B. Distally this extension47is provided with an inwardly pointing part48which carries a number of balls49.

This inwardly pointing part48is on its inside surface provided with means such as teeth to engages with the toothed ring64on the drive element60whenever the injection device1is in its first position as seen inFIG. 2.

As can be best seen inFIG. 1, the proximal housing part10B has a number of slits13which internally supports the balls49.

The balls49are secured to the inwardly pointing part48of the dose setting button45such that whenever the user rotates the dose setting button45to set a dose, the balls49also rotate against the slits13. The dose setting button45is thus rotatable in one direction to set a dose and in the opposite direction to decrease a set dose.

The dose setting button45is further provided with a proximal opening through which the injection button50extends. The injection button50is via a flexible grip51secured to the drive member60. Further, a second compression spring3is provided between the injection button50and the inwardly pointing part48of the dose setting button45urging the injection button50in the proximal direction.

When the injection button50is not activated as inFIG. 2, i.e. during dose setting, the second compression spring3via the injection button50urges the driver element60in the proximal direction.

The driver element60which is best viewed inFIG. 1is distally provided with a toothed interface61. Further, the distal part of the driver element60has an open longitudinal slit62. The centre part of the driver element60is provided with a longitudinal groove63and proximal to the centre part, the driver element60is provided with a toothed ring64and a proximal extension65.

In the dose setting mode as depicted inFIG. 2, the driver element60is moved in the proximal direction by the second compression spring3such that the toothed interface61is located proximal to the toothed ring42of the piston rod guide40. The driver element60is thus rotatably independently of the piston rod guide40. In this first position, the piston rod guide40is rotational locked to the housing10by having its external tongues43engage the tracks14provided in the distal housing part10B.

Further, in the dose setting mode (first position), the inwardly pointing part48of the dose setting button45engages the toothed ring64such that rotation of the dose setting button45is conveyed to a simultaneous rotation of the driver element60.

A clock spring70dedicated to drive the driver element60is depicted inFIG. 1. This clock spring70is a torsion spring embodied in this embodiment as a clock-spring70, which is a wounded spring not having any particular axial extension but wounded in one dimension only i.e. having no helical coils. Such clock-springs are usually wounded from a metal strip having a certain width. The number of wounds and the width are important factors determining the torque applied by such clock spring70.

The inner winding has an inwardly pointing flange71securing the clock spring70to a spring base75, and the outer winding has a similar fold72securing the spring70to the proximal housing part10B by being inserted into a longitudinal groove15in the housing wall.

The spring base75is on its inside surface provided with a tongue76which engages the longitudinal groove63of the driver element60such that the spring base75and the driver element60rotate together. However, the driver element60is able to slide relatively to the spring base75such that the driver element60can be moved axially during dosing.

When setting a dose to be injected, the user holds the device as inFIG. 2, i.e. without pressing the injection button50. In this position, the user rotates the dose setting button45. Due to engagement between the inwardly pointing part48of the dose setting button45and the toothed ring64of the driver element60, the driver element60is also rotated.

The spring base75follows the rotation of the driver element60thus straining the torsion spring70. The engagement between the balls49(secured to dose setting button45) and the slits13of the housing10prevents the torque of the torsion spring70from rotating the driver element60back to its initiate position, i.e. the torque is held by this engagement.

At the same time the piston rod30is secured against rotation by the engagement of the piston rod guide40with the housing via the engagement between the tracks14of the distal housing part10A and the longitudinal tongues43provided externally on the piston rod guide40.

As the driver element60is rotated, this rotation is conveyed to the scale drum80by the engagement between the open slit62on the driver element60and an inwardly pointing part81provided on the scale drum80as here explained.

The scale drum80is, as depicted e.g. inFIG. 2, provided with a part81pointing inwardly. This part81carries a thread82which mates the thread31of the piston rod30such that the scale drum80moves helically when rotated in relation to the piston rod30.

As a result, whenever the driver element60is rotated the scale drum80also rotates and is forced to move helically such that indicia85printed, or otherwise provided, on the scale drum80passes by a window16in the housing10. This window16is preferably provided with a magnifying lens magnifying the indicia85.

To inject the set dose, the user activates the injection button50as indicated by the arrow “P” inFIG. 3. This movement also shots the driver element60axially forward such that the toothed interface61at the distal end of the driver element60engages the toothed ring42inside the piston rod guide40. As the piston rod guide40is moved forward against the force of the first compression spring2and into the position depicted inFIG. 3, the longitudinal tongues43on the piston rod guide40moves out of engagement with the tracks14of the housing10and the piston rod guide40is thus set free to rotate. At the same time, the toothed ring64on the driver element60moves out of engagement with the inwardly pointing part48of the dose setting button45. In this position, the clock spring70rotates the driver element60which in turn also rotate the piston rod guide40which again rotate the piston rod30. Whenever the piston rod30is rotated it is screwed forward in the thread36fixed in relation to the housing10and is thus moved further into the cartridge25.

The sequence is thus that the driver element60is moved into engagement with the piston rod guide40which is at the same time is moved axially out of its engagement with the tracks14of the housing10. At the same time, the driver element60is moved out of its engagement with the dose setting button45by moving the toothed ring64of the driver element60out of engagement with the inwardly pointing part48of the dose setting button45.

During dose setting; the dose setting button45, the drive element60and the scale drum80rotate together while the clock spring70is being strained.

During injection, the driver element60, the piston rod guide40, the scale drum80and the piston rod30is rotated together by the force accumulated in the clock spring70. As the piston rod30is screwed forward in the thread36, the scale drum80threadedly engaging the piston rod30returns to its initial position.

A second embodiment is disclosed in theFIGS. 4 to 8.FIG. 4disclose an exploded view of this second embodiment wherein similar elements are numbered by the same reference number as in the first embodiment, however with a “1” in front.

The housing110is in this second embodiment divided into a main housing part110C and a distal housing part110D. The distal housing part110D is secured to the main housing part110C after a cartridge125has been placed inside the main housing part110C.

The distal housing part110D carries a thread121securing the injection needle105and the main housing part110C holds both the cartridge125and the dose mechanism. The main housing part110C is further provided with a longitudinal window122through which a user can inspect the liquid drug contained inside the cartridge125.

The main housing part110C has a length such that it can contain both the dose mechanism and at least the majority of the cartridge125. In fact, the distal housing part110D is shaped as a capsule that it clicked onto the main housing part110C during assembly of the injection device101.

The distal part of the injection device101including the longitudinal window122is, when not in use, covered by a removable cap123as e.g. disclosed inFIG. 5A.

The cartridge125is a well-known glass cartridge125which proximally is provided with a plunger126which can be moved in the distal direction by a piston rod130.

The longitudinal groove132of the piston rod130is further engaged by a piston rod guide140which internally is provided with a key141to engage the longitudinal groove132of the piston rod130. Rotation of the piston rod guide140is thus transferred to rotation of the piston rod130which again is screwed forward in a thread136provided in the main housing part110C. The thread136could also be provided in a nut member coupled to the main housing part as in the first embodiment.

Internally the piston rod guide140is provided with teeth142engageable to the driver element160. Externally the piston rod guide140is provided with one or more ratchet arms144which engage a toothed interior118of the main housing part110C such that the piston rod guide140can only rotate in one rotational direction. It is thus not possible to move the piston rod130in the proximal direction.

The main housing part110C is further provided with a window116through which a user is able to view indicia185provided on the scale drum180. This window116can in one aspect be an opening in the main housing part110C or alternatively it can be covered by a transparent element. As in the first embodiment, this transparent element can be a magnifying lens for magnifying the indicia85.

The scale drum180is internally provided with a number of inwardly pointing arms181(seeFIG. 7-8) which carries a thread182mating the outside thread131of the piston rod130. Externally the scale drum180can be provided with circumferential ridges183which slide on an internal surface of the main housing part110C to reduce friction.

The inwardly pointing arms181of the scale drum180protrude through a pair of open slits162provided in the driver element160. Distally the drive element160is provided with a toothed interface161whereas the proximal half is provided with a toothed ring164. Most proximal the driver element160is provided with a plurality of flexible arms165securing the injection button150.

The injection button150is urged in the proximal direction by a second compression spring103which is encompassed between the injection button150and the dose setting button145.

The dose setting button145is internally provided with radially pointing teeth148for engaging the toothed ring164of the driver element160as explained later. On the outside surface, the dose setting button145is provided with a soft rubber layer190which is preferably moulded onto the dose setting button145using a 2K moulding technic.

The main housing part110C is proximally closed by a spring base175which has a plurality of longitudinal notches177engaging longitudinal slits117provided on the inside surface of the main housing part110C. The spring base175thus operational functions as an integral part of the main housing part110C and could in an alternative be moulded as an integral part of the main housing part110C.

The spring base175is further proximally provided with internally pointing flange parts179which rest against an outwardly pointing flange166provided on the driver element160. This engagement prevents the driver element160from moving proximally and also helps transferring the force of the second compression spring103onto the dose setting button145.

The spring base175secures the proximal end of a torsion spring170having its distal end secured to the driver element160to drive an injection. The torsion spring170disclosed in this embodiment is a well-known helically wounded torsion spring170.

The toothed ring164of the driver element160engages the radial teeth148of the dose setting button145such that rotation of the dose setting button145is transferred to a rotation of driver element160, which rotation strains the torsion spring170. As best seen inFIG. 4, the radial teeth148are provided on a bridge which also functions as a torque limiter allowing the dose setting button145to continue rotation even if the driver element160comes to a stop.

In order to maintain the torque in the torsion spring170when the dose setting button145is not rotated, a plurality of axially pointing teeth149provided internally in the dose setting button145is urged axially against a toothed ring178provided proximally on the spring base175.

When a dose is to be set, the injection device101is held in the first position as depicted inFIG. 5whereFIG. 5Adepict the full injection in the first position andFIG. 5Bdiscloses a partial enlarged view of the dose mechanism ofFIG. 5A.

In the first position rotation of the dose setting button145is transferred to rotation of the drive element160which is positioned in its proximal position due to force of the second compression spring103.

The driver element160is coupled to the dose setting button145by the toothed engagement between the internal radial teeth148of the dose setting button145and the toothed ring164on the driver element160. The toothed interface161is at the same time axially removed from the internal teeth142of the piston rod guide140by the second compression spring103pulling the driver element160in the proximal direction.

When the driver element160is rotated in the dose setting direction, the torsion spring170is strained, and when rotated in the opposite direction, the torsion spring170is released. The engagement between the axially pointing teeth149and toothed ring178secures that the torque is maintained in the torsion spring170also when the user removes the fingers from the dose setting button145.

When the correct dose has been dialed, the user releases the set dose by pushing the injection button150in the distal direction against the force of the second compression spring103.

This second position is depicted inFIG. 6, whereFIG. 6Ais a full picture of the injection device101andFIG. 6Bis a partial end enlarged view of the dose mechanism ofFIG. 6A.

Movement of the injection button150in the distal direction as indicated by the arrow “P” inFIG. 6Bis immediately transferred to an axial movement of the driver element160. When the driver element160is moved in the distal direction the toothed ring164slides out of engagement with the radial teeth148of the dose setting button145where after the driver element160is forced to rotate by the torque present in the torsion spring170.

At the same time the toothed interface161distally on the driver element160is moved into engagement with the teeth142of the piston rod guide140such that the piston rod guide140is forced to rotate together with the driver element160.

Rotation of the piston rod guide140translates to rotation of the piston rod130which henceforth moves in the distal direction while pressing the plunger deeper into the cartridge125.

FIG. 5andFIG. 6both disclose the injection device101with the scale drum180in the maximum position i.e. the maximum dose of the injection device101is set. In this maximum position a stop flange184on the scale drum180abut a similar stop provided on the spring base175.

FIG. 7discloses the scale drum180when it has returned to the zero position after having expelled the set dose. In this position a distal stop flange on the scale drum180abut a stop119provided internally in the housing110as seen inFIG. 8.

InFIG. 7, the injection button150is not activated, and the driver element160is thus positioned in the proximal position i.e. not coupled to the piston rod guide140.

The sequence in this embodiment thus being that the piston rod guide140does not move axially at all, but the driver element160is moved axially into contact with the piston rod guide145as the drive element160is moved out of engagement with the dose setting button145. With the driver element160in the first position (FIG. 5), the piston rod guide140is able to rotate in one direction since the piston rod guide140is not locked to the housing110. However, the piston rod guide140is prevented from rotation in a rotational direction that would cause the piston rod130to move in the proximal direction i.e. the piston rod130can only move in the distal direction (the dose expelling direction). The one-way rotational lock is due to the engagement between the ratchet arms144on the piston rod guide140and the toothed interior118of the housing110.

When setting a dose in the first position, rotational force is transmitted from the driver element160to the scale drum180by the engagement of the open slit162with the inwardly pointing part181of the scale drum180. The internal thread182of the scale drum180secures that the scale drum180engages the outer thread131of the piston rod130such that the scale drum180is moved helically up and down the piston rod130.

When the set dose is expelled, the driver element160rotate in the opposite direction, however the engagement between the open slit162of the driver element160and the inwardly pointing part181of the scale drum180secures that the scale drum180move helically back to its initial position.

Yet another embodiment is disclosed in theFIGS. 9 to 13whereFIG. 9Adisclose an exploded view of the third embodiment wherein similar elements are numbered by the same reference number, however with a “2” in front.

As can be seen from the figures, the cartridge225is secured in a housing210which in this third embodiment is divided into a main housing part210C and a distal housing part210D. The distal housing part210D is secured to the main housing part210C after the cartridge225has been placed inside the main housing part210C e.g. by gluing the two parts210C-D together.

The distal housing part210D carries the thread221securing the injection needle205and the main housing part210C holds both the cartridge225and the dose mechanism. The distal part of the injection device201is, when not in use, covered by a removable cap223as disclosed inFIG. 10A.

In the third embodiment, the driver element260is divided into a distal driver part260A and a proximal driver part260B. These two driver parts260A-B are secured to each other such that they both rotate and translate axially together as one unison driver element260. Distally, this driver element260is connected to the torsion spring270which again proximally is connected to the spring base275.

The spring base275is coupled to the housing210or alternatively moulded as an integral part of the housing260. The result being that whenever, the driver element260is rotated to set a dose, the torsion spring270is strained.

In order to rotate the driver element260during dose setting, the driver element260is coupled to the dose dial button245. This coupling is in the third embodiment an axial coupling between a toothed ring264on the driver element260and axially placed internal teeth248provided inside the dose setting button145. A second compression spring203urges the internal teeth248against the toothed ring264. The force of the second compression spring203together with the coupling also functions as a torque limiter since the coupling (264/248) is able to slide if a user keeps rotating the dose setting button245after the driver element260has come to a stop. However, if the torque is not surpassed, the driver element260rotates together with the dose setting button245during dose setting.

To stabilize the driver element260a stabilizer ring267is surrounding the driver element260. At its distal end, the driver element260(the distal driver part260A) is further provided with an axially pointing toothed interface261which engages a drive assembly255.

The drive assembly255comprises the piston rod guide240, a spring256and a toothed drive ring257. The teeth242on this toothed drive ring257points in an axial direction. Both the spring256and the toothed driver ring257are coupled to the piston rod guide240to rotate with the piston rod guide240. The toothed drive ring257is internally provided with a shape configured to rotational lock to a similar shape provided in the piston rod guide240and the spring256is further provided with bended arms258which lie against a surface of the piston rod guide240. The result being that both the toothed driver ring257and the spring256rotate together with the piston rod guide240which again is secured to the driver element260by a number of hooks259engaging the driver element260such that the drive assembly255including the piston rod guide240moves axially together with the driver element260as will be explained later.

The bended arms258of the spring256further engages a toothed interior218of the housing210such that the drive assembly255can only rotate in one rotational direction, however in the first position depicted inFIG. 10, the piston rod guide240(and thus the drive assembly255) is prevented from rotation also in the opposite direction by the engagement between the external teeth243on the piston rod guide240and the tracks214provided internally in the housing210.

The first position is disclosed inFIG. 10whereFIG. 10Adisclose the entire injection device201andFIG. 10Bdisclose an enlarged view of the dose mechanism. In operation, the user selects a dose to be injected by rotating the dose setting button245. This rotation is conveyed to a similar rotation of the driver element260thus straining the torsion spring270.

The piston rod guide240is secured against rotation by the external teeth243being rotational locked to the internal tracks214inside the housing210. Since the piston rod guide240is prevented form rotation so is the toothed driver ring257and the toothing242provided on the toothed driver ring257clicks over the distal toothing261on the driver element260thus providing the user with a clicking sound during dose setting.

As the user rotates the dose setting button245and the driver element260during dose setting, the torsion spring270encompassed there between is strained and the scale drum280move helically in the proximal direction.

Since the spring256urges the toothed drive ring257in the proximal direction, the engagement between the teeth242on the toothed drive ring257and the axial pointing teeth161on the driver element160secure that the torque is maintained in the torsion spring270until the torsion spring270is released to drive the driver element.

The connection between the driver element260and the scale drum280is disclosed in details inFIG. 7andFIG. 8which disclose the scale drum280returned to its zero position. The scale drum280carries an internal thread282threaded to the thread231of the piston rod230. The part281of the scale drum280connecting the outer surface of the scale drum280and the thread282is engaged by the longitudinal slit262in the distal part260A of the driver element260. Henceforth when the driver element260is rotated, the scale drum280is also rotated.

During dose setting the external teeth243of the piston rod guide240is locked by the tracks214provided inside the housing210thus the drive assembly255is not rotated.

During dose expelling, the user pushes the injection button250in the distal direction as indicated by the arrow “P” in theFIGS. 11A-BwhereFIG. 11Bis an enlarged view of the dose mechanism ofFIG. 11A.

Proximally in the injection device201this movement moves the toothed ring264out of engagement with the internal teeth248such that the driver element260is able to rotate independently of the dose setting button245.

Distally in the injection device, the external teeth243are moved out of the engagement with the internal tracks214inside the housing210. Further, the toothed interface261is pressed against the teeth242on the toothed driver ring257whereby rotation of the driver element260is transformed to rotation of the toothed driver ring257and thus rotation of the piston rod guide240since the toothed driver ring257internally is shaped to fit the piston rod guide240.

As in the previous embodiment, the piston rod guide240is internally provided with a key241which engages the longitudinal groove232in the piston rod230such that rotation of the drive assembly255and thus the piston rod guide240is transferred to a rotation of the piston rod230.

A partition provided internally in the housing210is provided with a thread236such that rotation of the threaded piston rod230screws the piston rod230forward inside the cartridge225thus moving the plunger226distally.

When the user removes the finger from the injection button250, the second compression spring203moves the driver element260in the proximal direction thus also pulling the piston rod guide240into its locked position. This proximal movement of the driver element260also removes some pressure from the spring256such that the toothed interface261rides over the teeth242of the toothed driver ring257whenever a new dose is set by rotation of the driver element260.

In the third embodiment, the piston rod guide240is thus moved axially in and out of engagement with the housing210by its connection to the axially movable driver element260.

In the first position, the dose setting button245, the driver element260and the scale drum280rotate together and since the piston rod230is kept inrotatable the scale drum280climbs helically inside the injection device201.

In the second position, the driver element260, the scale drum280and the drive assembly255all rotate together under influence of the released torsion spring270such that the piston rod230is moved in the distal direction.

Generally speaking for all embodiments, the scale drum80,180,280is coupled to rotate together with the driver element60,160,260and the engagement between the scale drum80,180,280and the driver element60,160,260comprises a part81,181,281on the scale drum80,180,280extending through an open slit62,162,262provided in the driver element60,160,260such that a thread82,182,282internally on the scale drum80,180,280engages the piston rod30,130,230which is held inrotatable during dose setting.

The scale drum80,180,280and the part81,181,281connecting the outer surface of the scale drum80,180,280with the internal thread82,182,282are together with the internal thread82,182,282preferably made as an integral element e.g. through injection moulding. However, it could also be an assembly made from individual components which are connected together by welding, gluing or by another method.

FIG. 12discloses the scale drum280when it has returned to the zero position after having expelled the set dose. In this position a distal stop flange on the scale drum280abut a stop219provided internally in the housing210as seen inFIG. 13.

FIG. 12further depicts the abutment between the part281of the scale drum280and the slit262of the driver element260(the part260A). Since this slit262has a longitudinal extension, the scale drum280is able to move axially while being rotated by the driver element260. The resulting movement thus being helical due to the threaded engagement with the piston rod230being held inrotatable during dose setting. During expelling the driver element260, the scale drum280and the piston rod230rotate in unison while the piston rod230is being moved axially forward. The movement of the scale drum280during dose expelling thus also being helical.

Further in all embodiments, the piston rod30,130,230is held inrotatable at least in the first position (dose setting mode);

In the first embodiment, the piston rod guide40is locked to the housing10during dose setting by having the longitudinal tongues43locked in tracks14inside the housing10in the first position thus preventing rotation of the piston rod guide40and henceforth the piston rod30.

In the second embodiment, the piston rod guide140is secured to the housing by one or more way ratchet arms144which prevent rotation of the piston rod guide140in a direction which would course the piston rod130to travel in the proximal direction.

In the third embodiment, the piston rod230is locked to the housing by having the teeth243provided on the piston rod guide240to engage tracks214provided in the housing210in the first position such that the piston rod guide240and thus the piston rod230is unable to rotate in the first position.

Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject matter defined in the following claims.