CARTRIDGE SYSTEM FOR RECEIVING A DOSE SENSING MODULE

The present invention provides a cartridge system (30) for a drug delivery device, comprising a drug cartridge (20) comprising a cartridge body (21) extending along a reference axis between a distal outlet end portion and a proximal rim (21.2), and a displaceable piston (22) arranged in the cartridge body (21) an axial distance from the proximal rim (21.2), an outer cavity (29) thus being formed between the displaceable piston (22) and the proximal rim (21.2), and a guide element (60, 90) comprising a main guide body (61, 91), and a rim interface member (62, 92) adapted to abut or engage the proximal rim (21.2) and thereby cover the proximal rim (21.2) at least partially. The main guide body (61, 91) extends between a first main guide body end (61.1) bordering the rim interface member (62, 92) and a second main guide body end (61.2) and defines a passage for a sensor unit.

FIELD OF THE INVENTION

The present invention relates generally to drug delivery devices having integrated dose capturing means, and more specifically to cartridge systems for such drug delivery devices.

BACKGROUND OF THE INVENTION

Injection devices, such as injection pens, are widely used for self-administration of liquid drugs by people in need of therapeutic treatment. Many injection devices are capable of repeatedly setting and injecting either a fixed or a variable volume of drug upon operation of respective dose setting and dose expelling mechanisms in the device. Some injection devices are adapted to be loaded with a prefilled drug reservoir containing a volume of drug which is sufficient to provide for a number of injectable doses. When the reservoir is empty, the user replaces it with a new one and the injection device can thus be used again and again. Other injection devices are prefilled when delivered to the user and can only be used until the drug reservoir has been emptied, after which the whole injection device is discarded. The various injection devices typically expel the drug by advancing a piston in the reservoir using a motion-controlled piston rod.

Within some therapy areas the tendency of a patient to adhere to the prescribed therapy is dependent on the simplicity of the specific treatment regimen. For example, many people with type 2 diabetes are diagnosed with the disease at a relatively high age where they are less prone to accept a treatment that intervenes too much with their normal way of living. Most of these people do not like to be constantly reminded of their disease and, as a consequence, they do not want to be entangled in complex treatment patterns or waste time on learning to operate cumbersome delivery systems. In essence, many are of the opinion that the less manual involvement the better.

For a person with diabetes it is important to timely administer one or more glucose regulating agents to maximise the time spent in normoglycemia. In that connection, in order to establish an overview of one's adherence to a particular treatment regimen, it is significant to keep track of both when such a regulating agent is administered and how much is administered. Accordingly, it is recommended that the person keeps a log of administered dose sizes and times of administration.

Previously, the establishment and maintenance of such a log would require manually noting down the data, e.g. on paper or a pc. However, as this would entail frequent active involvement many people neglected the importance of establishing the overview. In recognition of this undesirable situation various solutions have been suggested for automatic capturing of the relevant information from the individual injection devices.

For example, WO 2018/078178 (Novo Nordisk A/S) discloses a pen type injection device having a sensor arranged on a deflectable exterior surface of the injection device housing. The deflectable exterior surface is configured to undergo a deflection at a specific angular displacement of an interior component rotationally locked to the piston rod, and the sensor is adapted to output a signal in response to a detected deflection, the signal thus being representative of the angular displacement of the piston rod. Since the amount of drug expelled by the disclosed injection device correlates with the total angular displacement of the piston rod relative to the housing the output signals are automatically captured by a processor in the injection device and used as a basis for an estimation of the administered dose. In addition, the processor may establish a time for reception of the output signals and provide a time stamp for the dose expelling event. The data may then be retrieved via an electronic display on the injection device or by wireless transmission to an external device e.g. having, or being connectable to, a display.

An alternative dose detection solution is presented in WO 2014/128155 (Novo Nordisk A/S) which discloses a pen-type drug delivery device with a fully integrated sensor unit in the form of a piston washer module arranged between the piston rod of the dose expelling mechanism and the cartridge piston. The sensor unit operates like a rotary encoder and comprises a first sensor part which is engaged with the piston rod and a second sensor part which is engaged with the cartridge piston. The relative angular displacement between the two sensor parts exhibited during a dose expelling event, when the piston rod rotates relative to the drug delivery device housing and the cartridge, is detected galvanically and translated to an estimate of the size of the administered dose.

Conventionally, the cartridges used for such drug delivery devices comprise a hollow cartridge body made of glass and having a generally cylindrical main body portion with a proximal rim forming a proximal opening, and a distal narrowing forming an outlet end portion, which is sealed by a penetrable septum. In a drug-filled cartridge the cartridge piston is arranged sealingly in the main body portion, typically a short distance from the proximal opening, whereby an outer cavity is formed between the piston and the proximal opening.

During manufacturing of the drug delivery device disclosed in WO 2014/128155 the sensor unit will be placed in the outer cavity. However, as the proximal rim constitutes the most fragile portion of the cartridge structure and is the part of the cartridge which most frequently exhibits crack formation, it is important, in order to avoid fracture, that it is not accidentally impacted by a hard surface when the distal most portion of the sensor unit is lead through the proximal opening. This places severe demands on the radial alignment of the sensor unit with the proximal opening and, resultantly, on the tolerances in the assembly setup.

SUMMARY OF THE INVENTION

It is an object of the invention to eliminate or reduce at least one drawback of the prior art, or to provide a useful alternative to prior art solutions.

In particular, it is an object of the invention to provide a solution which prevents a potentially damaging collision between the sensor unit and the proximal rim of the cartridge during assembly.

It is another object of the invention to provide a solution which allows for some degree of slack in the assembly line without increasing the risk of the sensor unit impacting the proximal rim of the cartridge.

In the disclosure of the present invention, aspects and embodiments will be described which will address one or more of the above objects and/or which will address objects apparent from the following text.

In one aspect the invention provides a cartridge system as defined in claim1.

Accordingly, a cartridge system for use in a drug delivery device is provided, comprising a drug cartridge and a guide element adapted to be arranged in axial extension of one another. The drug cartridge, which is suitable for holding a volume of e.g. liquid drug, comprises a cartridge body having a main body portion, a distal outlet end portion and a proximal rim. A displaceable piston is arranged in the cartridge body an axial distance from the proximal rim, whereby an outer cavity is formed between the displaceable piston and the proximal rim. This outer cavity is destined to become deeper as the displaceable piston is displaced axially in the drug cartridge during use. The guide element, which may be formed, e.g. moulded, as a single piece component or composed of two separately produced parts, comprises a main guide body, and a rim interface member which is adapted to abut or engage the proximal rim and thereby cover the proximal rim at least partially. The main guide body extends between a first main guide body end bordering the rim interface member and a second main guide body end and defines a passage for a sensor unit.

By arranging the guide element such that the rim interface member covers the proximal rim at least partially the guide element allows for insertion of the sensor unit into the outer cavity without the risk of a damaging impact to the proximal rim. The risk of cartridge fracture during assembly of the drug delivery device is thus markedly reduced.

The main guide body may comprise an interior guide surface configured to guide the sensor unit into the outer cavity. In particular embodiments of the invention the interior guide surface tapers radially towards the first main guide body end. Thereby, the main guide body exhibits an interior funnel shape, where the second main guide body end has a larger transversal interior dimension than the first main guide body end. The sensor unit does thus not need to be strictly aligned with the proximal opening initially during insertion into the outer cavity, because the funnel shaped guide surface will guide a radially offset sensor unit into the right radial position as the sensor unit approaches the cartridge. This solution can thus accommodate a certain degree of slack in the assembly setup. p For example, the first main guide body end may exhibit an internal first end diameter which corresponds, at least substantially, to the internal diameter of the proximal rim, and the second main guide body end may exhibit an internal second end diameter which is 5-20% larger, such as 10-15% larger, than the internal first end diameter.

The sensor unit may comprise a distal module part having one or more radially outwardly projecting studs adapted to interface with an interior surface of the cartridge body for impeding relative rotation between the distal module part and the cartridge. The diameter of the distal module part may be only slightly smaller than the internal diameter of the proximal rim, and the radially outwardly projecting studs may be radially inwardly displaceable against a bias force to allow passage through the proximal opening. Hence, the radially outwardly projecting studs may be adapted to transition from an unstrained state to a strained state as the distal module part enters the outer cavity.

The main guide body may, alternatively or additionally, comprise a plurality of splines extending axially between the first main guide body end and the second main guide body end, and a plurality of intermediate keyways formed by the plurality of splines, where each of the plurality of splines comprises a radially facing surface for guiding the sensor unit into the outer cavity.

The splines will thus serve to lead the distal module part axially into the outer cavity, while the keyways provide room for the radially outwardly projecting studs.

In particular embodiments of the invention each of the plurality of splines tapers radially towards the second main guide body end. The radially facing surfaces of the plurality of splines thus together provide a funnel shape for guiding even a radially offset sensor unit securely into the outer cavity, similarly to what is described above.

Each of the plurality of splines may, alternatively or additionally, taper circumferentially towards the second main guide body end, i.e. each intermediate keyway may be wider at the second main guide body end than at the first main guide body end. This allows for greater flexibility in the initial positioning of the sensor unit, as the angular orientation of the distal module part relative to the guide element when the sensor unit is to be inserted into the main guide body is less critical. The main guide body simply accepts the distal module part in a larger number of relative angular positions of the guide element and the sensor unit because the wide keyways at the second main guide body end provide wider entrance sections for the one or more radially outwardly projecting studs.

The rim interface member may comprise a circumferential collar adapted to surround a proximal exterior end portion of the cartridge body. The circumferential collar may have alternating convexly and concavely shaped sections. The convexly shaped sections may follow the contour of the cartridge body and the concavely shaped sections may comprise contact areas which abut the cartridge body to provide for firm attachment of the rim interface member to the drug cartridge.

The circumferential collar may, alternatively or additionally, comprise a plurality of collar partitions, and each collar partition may be circumferentially spaced apart from a neighbouring collar partition to thereby provide respective collar openings therebetween. The collar openings may allow for reception of e.g. radial protrusions of a non-rotatable component to thereby ensure complete rotational fixation of the guide element in the drug delivery device.

Since the drug delivery device may end up shelved for a significant period of time before being taken into use it may be undesirable to install the sensor unit in a position where the radially outwardly projecting studs are in the strained state, as this could lead to a gradual reduction of the contact force applied to the interior surface of the cartridge body over time and resultantly to a gradual loss of friction in the interface between the cartridge body and the distal module part. Consequently, the sensor unit may be installed in a pre-use position where the radially outwardly projecting studs are in the unstrained state, e.g. within the main guide body just outside the proximal opening. In that case the splines furthermore serve to prevent rotation of the distal module part in a pre-use state of the drug delivery device, and thereby to prevent erroneous sensor readings resulting from the drug delivery device e.g. being dropped or otherwise subjected to jolting motion. The sensor unit is then adapted to be moved axially before the first dose expelling, from the pre-use position in which each of the one or more radially outwardly projecting studs is accommodated between two splines to an in-use position in which the one or more radially outwardly projecting studs are in contact with the interior surface of the cartridge wall.

In particular embodiments of the invention the cartridge system further comprises a cartridge holder for accommodating the drug cartridge, and the cartridge holder comprises a radially inwardly extending protrusion adapted to be received in one of the collar openings, thereby rotationally interlocking the cartridge holder and the guide element. In these embodiments a complete rotational fixation of the guide element in the drug delivery device can be ensured by rotational fixation of the cartridge holder to a housing of the drug delivery device.

Each collar partition may comprise at least one convexly shaped section and at least one concavely shaped section. A symmetrical contact interface between the rim interface member and the cartridge body can thereby be established, reinforcing the attachment of the guide element to the drug cartridge. Further, the resulting curved shape of each collar partition will serve as a shock-absorber, protecting the proximal exterior end portion of the cartridge body, including the proximal rim, in case the drug delivery device is dropped to one side. In particular embodiments thereof, each collar partition comprises two convexly shaped sections separated by one concavely shaped section.

The sensor unit is gradually advanced in the drug cartridge as a dose is expelled. Thus, the small radial dimensions of the cartridge body, and the drug delivery device itself, demands a small-sized sensor unit. The constituent mechanical and electrical components do, however, take up some space, and the incorporation of the sensor unit between the piston rod and the displaceable piston accordingly results in the proximal rim taking up a different axial position in the drug delivery device than it would otherwise do.

The guide element may further comprise a plurality of axially compressible flange members extending axially, specifically proximally, from the second main guide body end. These flange members may, by virtue of their shape and/or the material they are made of, act as compression springs in response to an axial impact to the guide element. Accordingly, the flange members may protect the cartridge body in case the drug delivery device is dropped and lands on either end.

In particular embodiments of the invention the plurality of axially compressible flange members constitutes two axially compressible flange members arranged diametrically opposite one another. Free space is thereby provided between them for allowing radially inwards deflection of portions of the cartridge holder during assembly of the cartridge holder and the housing. Such deflections could e.g. occur in connection with a snap fitting of the cartridge holder to the housing as flexible portions of the cartridge holder pass respective snap geometries on interior surface portions of the housing.

In another aspect the invention provides a guide element for use in a cartridge system as described above.

In a further aspect the invention provides a drug delivery device comprising a cartridge system as described above.

The drug delivery device may further comprise a housing, a dose expelling mechanism comprising an axially advanceable piston rod, and a sensor unit for determining a size of an expelled dose, arranged at least partially in the outer cavity and comprising a proximal module part rotationally locked with respect to the axially advanceable piston rod and a distal module part abutting the displaceable piston.

In particular embodiments of the invention the drug delivery device comprises a cartridge system as described above, in which the guide element comprises a plurality of axially compressible flange members, e.g. exactly two axially compressible flange members arranged diametrically opposite one another, extending axially from the second main guide body end, a housing, a dose expelling mechanism comprising an axially advanceable piston rod, and a sensor unit for determining a size of an expelled dose, arranged at least partially in the outer cavity and comprising a proximal module part rotationally locked with respect to the axially advanceable piston rod and a distal module part abutting the displaceable piston,

wherein each of the plurality of axially compressible flange members abuts a transversally extending interior portion of the housing, or a transversally extending structure axially fixed with respect to the housing.

The drug cartridge is thus elastically supported at its proximal end and thereby protected in case the drug delivery device is accidentally dropped and lands on either end.

In other embodiments of the invention the drug delivery device comprises a cartridge system as described above, including the cartridge holder comprising the radially inwardly extending protrusion adapted to be received in one of the collar openings, thereby rotationally interlocking the cartridge holder and the guide element, a housing, a dose expelling mechanism comprising an axially advanceable piston rod, and a sensor unit for determining a size of an expelled dose, arranged at least partially in the outer cavity and comprising a proximal module part rotationally locked with respect to the axially advanceable piston rod and a distal module part abutting the displaceable piston, wherein the cartridge holder further comprises a radially outwardly extending protrusion adapted to engage with the housing, thereby rotationally interlocking the cartridge holder and the housing.

For the avoidance of any doubt, in the present context the term “drug” designates a medium which is used in the treatment, prevention or diagnosis of a condition, i.e. including a medium having a therapeutic or metabolic effect in the body. Further, the terms “distal” and “proximal” denote positions at or directions along a drug delivery device, or a needle unit, where “distal” refers to the drug outlet end and “proximal” refers to the end opposite the drug outlet end.

In the present specification, reference to a certain aspect or a certain embodiment (e.g. “an aspect”, “a first aspect”, “one embodiment”, “an exemplary embodiment”, or the like) signifies that a particular feature, structure, or characteristic described in connection with the respective aspect or embodiment is included in, or inherent of, at least that one aspect or embodiment of the invention, but not necessarily in/of all aspects or embodiments of the invention. It is emphasized, however, that any combination of the various features, structures and/or characteristics described in relation to the invention is encompassed by the invention unless expressly stated herein or clearly contradicted by context.

The use of any and all examples, or exemplary language (e.g., such as, etc.), in the text is intended to merely illuminate the invention and does not pose a limitation on the scope of the same, unless otherwise claimed. Further, no language or wording in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

In the figures like structures are mainly identified by like reference numerals.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

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

FIG. 1shows a rotary sensor module according to the prior art, arranged between a distal end of a piston rod1015and a proximal end of a piston1022sealing a drug containing cartridge1020close to a proximal rim1021.2thereof. The sensor module, which is powered by a coin cell type battery1075, comprises a first sensor part1070in the form of a flexible printed circuit board sheet having a proximally directed sensor surface1071on which 24 individual electrically conductive sensor areas1072are disposed circumferentially about a centre axis, and a second sensor part1060mounted on a distal end portion of the piston rod1015opposite the first sensor part1070and having contact structures in the form of two electrically connected flexible arms1061, each terminating in a contact point1062.

The first sensor part1070is adapted to engage, directly or indirectly, the piston1022such that no relative rotation therebetween is possible. The second sensor part1060is rotationally fixed to the piston rod1015, and the contact points1062are adapted to engage and electrically connect various individual electrically conductive sensor areas1072upon relative rotational motion between the first sensor part1070and the second sensor part1060, experienced as the piston rod1015rotates during a dose expelling action. This allows for an estimation of a total angular displacement exhibited by the piston rod1015during the dose expelling action and thereby of the amount of drug expelled.

As can be seen, even though the rotary sensor module is small-sized the transversal dimension of the first sensor part1070corresponds approximately to the internal diameter of the drug containing cartridge1020. During assembly of the injection device incorporating the rotary sensor module, unless the individual components are completely aligned there is a significant risk that the first sensor part1070impacts the proximal rim1021.2of the drug containing cartridge1020, causing fracture thereof. Obviously, if that happens the drug containing cartridge1020cannot be used and must be scrapped. This places severe demands on the tolerances in the assembly setup.

FIG. 2is a perspective longitudinal section view of an injection device1having an integrated sensor module50for estimation of the size of an expelled dose of drug. The injection device1is of the prefilled autopen injector type, with an elongated housing2extending along a reference axis and accommodating a dose expelling mechanism. A cartridge holder3, holding a cartridge20with an interior chamber25defined by a cartridge wall21, a distal penetrable septum23and a proximal piston22, is permanently fixed to the housing2. The chamber25is at least substantially filled with a liquid substance (not visible). In the depicted state of the injection device1a needle assembly40is attached to a needle mount portion of the cartridge holder3in such a manner that an injection needle45has penetrated the septum23to establish fluid communication to the chamber25.

A user operable dose dial4is arranged at a proximal end portion of the housing2for selective setting of a dose to be ejected from the cartridge20. The dose dial4is operatively coupled with a scale drum8which displays a selected dose through a window9. An injection button5is axially depressible to release a windable torsion spring10. The release of the torsion spring10will cause a helical advancement of a piston rod15through a nut member7fixed in the housing2and thereby result in an execution of a dose expelling action.

Details of the dose setting and the dose expelling mechanisms are irrelevant to the present invention and will accordingly not be provided in the present text. For an example of how such mechanisms may be constructed reference is made to WO 2015/071354, particularly p. 10, I. 21-p. 15, I. 13. What is important is that the rotational movement of the piston rod15during dose expelling is correlated with the prompted movement of the piston22through the design of the piston rod thread and the nut member7such that a predetermined angular displacement of the piston rod15relative to the housing2corresponds to a predetermined axial displacement of the piston22relative to the cartridge wall21. This relationship may in principle be chosen arbitrarily by the manufacturer, with a view to the dimensions of the cartridge20. In the present example a15° angular displacement of the piston rod corresponds to a specific axial displacement of the piston22which results in the expelling of1IU of the contained substance through the injection needle45.

It is noted that the injection device1includes a guide element90having a funnel shaped guide body91and a circumferential seat92. The circumferential seat92abuts a proximal rim21.2of the cartridge wall21defining a proximal opening of the cartridge20. The guide element90and the cartridge20together constitute a cartridge system according to an embodiment of the present invention. By employing the whole cartridge system instead of just the cartridge20the strict requirements to radial alignment of the sensor module50with the proximal opening of the cartridge20are eased because the funnel shaped guide body91directs the sensor module50towards the proximal opening of the cartridge20during relative axial converging motion between the sensor module50and the cartridge20if the position of the sensor module50initially is somewhat radially offset. This will be discussed further below in connection with another exemplary embodiment of the invention.

FIG. 3is an exploded view highlighting the individual elements of the present sensor module50. The sensor module50comprises a first sensor part in the form of a PCB assembly52with a rigid support sheet52.4having a proximal surface52.1carrying various electronic components52.5, including a processor, and a distal surface52.2carrying a plurality of electrically conductive sensor areas (not visible), the configuration of which will be described below. The support sheet52.4has an overall circular periphery, but is provided with several notches, some of which resulting in a pair of diametrically opposite radial protrusions52.3. Furthermore, the support sheet52.4has a central through-going bore52.6.

The first sensor part is complemented by a second sensor part in the form of a wiper53being fixedly mounted to a piston rod connector54to ensure joint rotation therewith. The piston rod connector54extends axially through the through-going bore52.6and is adapted for press-fit engagement with a cavity in a distal end portion of the piston rod15, as shown onFIG. 2. This provides for a joint movement of the piston rod15and the piston rod connector54. The wiper53comprises one ground contact53.1and two code contacts53.2arranged on respective flexible arms53.5and adapted to galvanically connect with the electrically conductive sensor areas on the distal surface52.2of the support sheet52.4, as described in more detail below. Notably, the ground contact53.1and the code contacts53.2are all proximally directed.

The two sensor parts, forming a rotary encoder system, are accommodated in a module housing51which also accommodates a power source in the form of a battery55, a retainer56also functioning as a positive battery connector, and a rigid (negative) battery connector57. The retainer56has a transversal support surface56.1for carrying the battery55and two axially extending opposite retainer arms56.2. Each retainer arm56.2is provided with a proximal cut-out56.3shaped to receive one of the radial protrusions52.3, thereby rotationally interlocking the retainer56and the PCB assembly52and axially restricting the support sheet52.4. The module housing51has a pair of diametrically opposite side openings51.2shaped to receive the retainer arms56.2so as to rotationally interlock, or at least substantially rotationally interlock, the retainer56and the module housing51, and a plurality of antirotation tabs51.1spaced apart along its circumference, each anti-rotation tab51.1comprising a contact surface51.8for interaction with an interior surface of the cartridge wall21. The PCB assembly52is thus at least substantially rotationally locked with respect to the module housing51, which in turn is rotationally frictionally fitted in the cartridge20, which is rotationally fixed in the cartridge holder3. The PCB assembly52is thereby at least substantially rotationally fixed with respect to the housing2and accordingly suitable as reference component for measuring angular displacements of the piston rod15.

FIG. 4is a perspective longitudinal section view of the sensor module50in an assembled state. As can be seen the piston rod connector54extends through the through-going bore52.6in the support sheet52.4and is press-fitted with a sleeve53.6on the wiper53. The module housing51has a foot51.3which rests against the piston22(cf.FIG. 2). Furthermore, the figure shows the position of the retainer arms56.2in the side openings51.2and the arrangement of the radial protrusions52.3in the cut-outs56.3. During a dose expelling action with the injection device1the rotation of the piston rod15is transferred to the piston rod connector54and further on to the wiper53. The ground contact53.1and the code contacts53.2thus sweep the sensor areas of the distal surface52.2which remains, at least substantially, rotationally stationary due to the engagement between the radial protrusions52.3and the cut-outs56.3, the fitting of the retainer arms56.2in the side openings51.2, the frictional interface between the foot51.3and the piston22, and the frictional interface between the anti-rotation tabs51.1and the cartridge wall21.

FIG. 5is a side view of the two sensor parts showing the connection between the ground contact53.1and the code contacts53.2and the distal surface52.2of the support sheet52.4, andFIG. 6is a perspective distal view of the same. In the shown exemplary embodiment the aforementioned plurality of electrically conductive sensor areas on the distal surface52.2are arranged such that a single circular ground track52.7provides a ground connection for the ground contact53.1and36individual code fields52.8together constitute a code track52.9which the code contacts53.2are adapted to sweep. A secondary ground connection is provided through a spherical end54.1of the piston rod connector54contacting the (negative) battery connector57. The secondary ground connection may be relevant to stabilise the signal output in case the dynamics of the dose expelling mechanism generates vibrations in the sensor module50.

As the piston rod connector54rotates jointly with the piston rod15during a dose expelling action the two code contacts53.2, which are circumferentially separated by 45°, respectively sweep the code track52.9, generating signals representative of the angular position of the wiper53as different code fields52.8get connected to ground. The two sensor parts output a 4-bit Gray code, i.e. eight different codes which for a 360° rotation of the wiper53are repeated nine times, giving72distinguishing codes. This output thus forms the basis for an estimation, by one or more of the electronic components52.5including the processor, of the total angular displacement of the piston rod15during a dose expelling action, and thereby for an estimation of the expelled dose.

FIG. 7is a perspective distal view of two sensor parts of an alternative rotary encoder system which may be employed in lieu of the one described above. The sensor parts comprise a wiper153and a PCB assembly152held in mutual position by the piston rod connector54in a manner similar to that disclosed in connection with the previous embodiment. The geometrical configuration of the PCB assembly152as well as its interaction with other components of the sensor module is identical to that of the formerly described PCB assembly52. Particularly, the PCB assembly152comprises a rigid support sheet152.4having a proximal surface152.1which carries various electronic components152.5, including a processor, and a distal surface152.2on which is disposed a plurality of electrically conductive code fields152.8arranged side by side to thereby provide a circular code track. However, contrary to the former embodiment the distal surface152.2does not comprise a dedicated ground track. Instead, the ground connection is supplied via the spherical end54.1of the piston rod connector54being in contact with the (negative) battery connector57, similarly to the above described.

The wiper153comprises a sleeve153.6press-fitted onto the piston rod connector54, to ensure joint rotation of the piston rod15and the wiper153, and two code contacts153.2, each arranged at an end portion of a flexible arm153.5capable of axial deflection. The code contacts153.2are angularly separated by 45° and will when rotated relative to the distal surface152.2sweep the code fields152.8and produce a 4-bit Gray code, similarly to the previous embodiment.

FIG. 8is a perspective distal view of two sensor parts of another alternative rotary encoder system. Similarly to the previous embodiments the sensor parts comprise a wiper253and a PCB assembly252held in mutual position by the piston rod connector54. The geometrical configuration of the PCB assembly252as well as its interaction with other components of the sensor module is identical to that of the formerly described PCB assembly52. Particularly, the PCB assembly252comprises a rigid support sheet252.4having a proximal surface252.1which carries various electronic components252.5, including a processor, and a distal surface252.2on which is disposed a plurality of electrically conductive sensor areas.

However, contrary to the former embodiments the distal surface252.2carries 40 electrically conductive sensor areas arranged in a circular track pattern where every other sensor area constitutes a ground field252.7and every other sensor area constitutes a code field252.8. A secondary ground connection is supplied via the spherical end54.1of the piston rod connector54being in contact with the (negative) battery connector57, as described above in connection with the first embodiment of the invention.

A wiper253is attached to the piston rod connector54and is adapted to sweep the 40 electrically conductive sensor areas as the piston rod15rotates during a dose expelling action (as described above). The wiper253has three flexible arms253.5, each terminating in a contact point253.2which is adapted to galvanically connect with a ground field252.7or a code field252.8, depending on the angular position of the wiper253relative to the PCB assembly252. The three contact points253.2are separated 120° from each other such that one contact point253.2is always connected to a ground field252.7and two contact points253.2are always connected to a code field253.8. The two sensor parts output a 4-bit Gray code and offer a higher resolution than the former two embodiments of the invention, enabling an even more accurate estimation of the total relative angular displacement between the PCB assembly252and the wiper253, and thereby of the total angular displacement of the piston rod15relative to the housing2, during a dose expelling event.

FIG. 9is an exploded view of a cartridge system30according to another exemplary embodiment of the invention together with the cartridge holder3. The cartridge system30comprises the drug cartridge20which is sealed by the piston22an axial distance from the proximal rim21.2, whereby an outer cavity29is formed between the piston22and the proximal rim21.2, and a guide element60. The cartridge holder3is configured to receive the drug cartridge20, as shown inFIG. 2, and comprises openings3.9for fixation to the housing2of the injection device1.

InFIG. 10a proximal portion of the cartridge system30is depicted. The guide element60is a single piece component made of low-density polyethylene (LDPE) and comprises a main guide body61, and a guide collar62configured to engage the proximal rim21.2of the cartridge20. The main guide body61extends axially between a distal guide body end61.1and a proximal guide body end61.2, and the distal guide body end61.1borders the guide collar62. A pair of diametrically opposite flanges66extend proximally from the proximal guide body end61.2. The purpose of these flanges66will be clear from the below.

FIG. 11is a perspective view of the guide element60, revealing several constructional details. Firstly, the guide collar62is divided into four identical collar partitions63, each of which is circumferentially spaced apart from a neighbouring collar partition, thereby providing four evenly distributed collar openings69along the guide collar circumference. Each collar partition63comprises two convex flank sections63.1separated by a concave central section63.2.

Secondly, the main guide body61has an interior surface which is provided with a plurality of evenly distributed axially extending splines61.3having respective radially facing surfaces61.6for guiding a sensor module. The splines61.3taper both radially and circumferentially towards the proximal guide body end61.2. Two neighbouring splines61.3define an intermediate keyway61.9which accordingly tapers circumferentially towards the distal guide body end61.1.

Finally, each flange66has a shape which resembles a handle, with a central hole65and an obtuse apex66.1. This particular shape of the flanges66along with the relatively soft polymer material render them axially elastically compressible.

FIG. 12is a longitudinal section view of the proximal portion of the cartridge system30, from which it can be seen that each spline61.3extends between a distal spline end61.4at the distal guide body end61.1and a proximal spline end61.5at the proximal guide body end61.2, and that the distal spline end61.4is markedly wider circumferentially than the proximal spline end61.5. Also, the radially facing surfaces61.6of the splines61.3together constitute a funnel-shaped internal guide surface which tapers radially towards the distal guide body end61.1. A wider inlet68for the sensor module is thus provided at the proximal guide body end61.2. Furthermore, the guide collar62surrounds a proximal end portion of the cartridge wall21, including the proximal rim21.2.

For the sake of clarity,FIGS. 13-15are simplistic section views in the sense that only the material present in the specific sections is visible.

Hence,FIG. 13is a simplistic longitudinal section view of the proximal portion of the cartridge system30, illustrating some important radial dimensions. The section is cut through a pair of opposite splines61.3and therefore shows the diameter of the funnel-shaped internal guide surface of the main guide body61, which decreases gradually towards the proximal opening of the cartridge20from a proximal guide diameter, dguide, proximal, at the proximal guide body end61.2to a distal guide diameter, dguide, distal, at the proximal guide body end61.1. The distal guide diameter, dguide, distal, corresponds to the diameter of the proximal opening of the cartridge20, dopening.

FIG. 14is a simplistic section view of a sensor module350in a pre-assembly position outside the cartridge system30. The structure of the sensor module350resembles that of the previously described sensor module50. Accordingly, the sensor module350comprises a module housing351with a foot for engagement with the piston22, and a piston rod connector354for engagement with the piston rod (not shown). The main difference vis-à-vis the former sensor module50is that the module housing351comprises a pair of anti-rotation tabs351.1which are arranged more proximally than the anti-rotation tabs51.1of the module housing51. The anti-rotation tabs351.1are radially inwardly deflectable against a radial restoration force to allow passage through the proximal opening of the cartridge20and subsequent firm connection with the cartridge wall21.

Contrary to the section inFIG. 13the section inFIG. 14is cut through a pair of opposite keyways61.9, and the taper of the main guide body61accordingly appears smaller in this view, just as the guide collar62does not seem to cover the proximal rim21.2entirely. This section is presented to illustrate the relative angular orientations of the sensor module350and the cartridge system30during assembly, where the anti-rotation tabs351.1are aligned with respective keyways61.9for sliding reception therein.

As is indicated by the arrows inFIG. 14the tapering internal guide surface of the main guide body61allows for some play in the assembly setup in that minor radial misalignments of the sensor module350with the proximal opening of the cartridge20will be compensated during the relative axial converging motion between the sensor module350and the cartridge20such that the sensor module350eventually enters the outer cavity29safely without impacting the proximal rim21.2.

In fact, because of the circumferential tapering of the splines61.3forming keyways61.9that are wider at the proximal guide body end61.2than at the distal guide body end61.1the sensor module350need not even initially be in strict angular alignment with the guide element60, as the keyways61.9will receive the anti-rotation tabs351.1at a wider angle on entry into the main guide body61and subsequently guide the anti-rotation tabs351.1into a proper angular orientation as the sensor module350approaches the outer cavity29.

FIG. 15shows the sensor module350in an assembled pre-use position in the cartridge system30. In this pre-use position the module housing351is axially spaced apart from the piston22and each anti-rotation tab351.1is unstrained and rests in a narrow section of a keyway61.9.

FIG. 16, which is a cross-sectional view through section A-A, shows that at this point the antirotation tabs351.1are firmly engaged with the respective keyways61.9, and the module housing351is accordingly rotationally locked with respect to the guide element60.

In the pre-use position of the sensor module350the piston rod connector354is prevented from rotating about the longitudinal axis, because the piston rod15(seeFIG. 17) is rotationally fixed with respect to the housing2in a pre-use state of the injection device1. Furthermore, the module housing351is prevented from rotating because the anti-rotation tabs351.1engage with the keyways61.9, and the guide element60is rotationally fixed with respect to the housing2(which will be explained further below).

The sensor module350is thus rotationally fixed in a pre-use state of the injection device1, so even if the injection device1is dropped on the ground or otherwise exhibits jolting movements, e.g. in connection with transportation or general handling, there is no risk of prematurely wakening the sensor electronics and thereby draining the battery.

The sensor module350is adapted to be displaced axially, during the first use of the injection device, from the pre-use position to an in-use position in the outer cavity29. During this displacement from the pre-use position to the in-use position the anti-rotation tabs351.1will be deflected radially inwardly against the radial restoration force provided by the structure of the module housing351, and the sensor module350accordingly transitions from an unstrained state to a strained state. Once the anti-rotation tabs351.1have passed the proximal rim21.2they will apply a radially outwardly directed force to, and thus increase friction in the interface with, the cartridge wall21, thereby impeding rotation of the module housing351relative to the cartridge20. It is advantageous to shelve the injection device1with the sensor module350in the unstrained state to avoid the risk of strained anti-rotation tabs351.1losing tension over time, as this would lead to a reduction of the contact force, and resultantly loss of friction, in the interface with the cartridge wall21.

FIG. 17is a longitudinal section view of a central portion of the injection device1with the cartridge system30and the sensor module350incorporated. The injection device is shown in a pre-use state where the sensor module350is in the pre-use position and a protective cap19is attached to the cartridge holder3. Notably, the guide element60is located between the cartridge20and a transversal nut portion7.1of the nut member7, the apex66.1of each flange66abutting a distally facing surface of the transversal nut portion7.1. The cartridge20is thus elastically supported between the cartridge holder3and the nut member7due to the axial compressibility of the flanges66. Thereby, the cartridge wall21is protected from shock damages resulting from the injection device1being dropped or otherwise roughly handled, as the flanges66will cushion any axial displacement of the cartridge20relative to the housing2and the nut member7.

FIGS. 18aand 18bare longitudinal section views of the guide element60illustrating the cushioning effect as the flanges66deform during an axial impact. The flanges66exhibit an initial axial height, h, in an undeformed state of the guide element60, shown inFIG. 18a, and a smaller axial height, hdef, in a deformed state of the guide element60, shown inFIG. 18b, where the cartridge system30is transiently exposed to a significant axial force. The flanges66deform elastically in response to the proximal rim21.2applying an axial compressive force to the guide collar62, whereby the respective central holes65are temporarily flattened. Immediately after the impact the flanges66recover to the initial axial height, h, and thereby return the cartridge20to the position shown inFIG. 17.

FIG. 19depicts the central portion of the injection device1in a different longitudinal section view, from which it is seen that a top portion3.2of the cartridge holder3is positioned proximally of a pair of opposite radially inwardly projecting snaps7.2of the nut member7. During assembly of the injection device1the top portion3.2, which possesses a certain radial flexibility, is urged past the snaps7.2, whereby the snaps7.2respectively enter the openings3.9(seeFIG. 9) to provide a both translationally and rotationally interlocked connection between the housing2and the cartridge holder3.

FIG. 20is a cross-sectional view through section B-B, albeit (for the sake of clarity) not showing the housing2. This figure shows the collar openings69occupied by respective internal protrusions3.8on the cartridge holder3, providing a rotationally interlocked connection between the guide element60and the cartridge holder3. As a consequence, since the cartridge holder3, as explained above, is rotationally fixed with respect to the housing2, so is the guide element60. The guide element60thus provides rotational fixation of the module housing351relative to the housing2in the shown pre-use position of the sensor module350.

The respective collar partitions63offer an additional shock absorption in connection with potential radial impacts to the injection device1, such as if the injection device1is dropped to one side. The alternating convex flank sections63.1and concave central section63.2of each collar partition63together with the air gaps resultantly formed between the convex flank sections63.1and the cartridge20and between the concave central section63.2and the cartridge holder3provoke a spring-like action and thereby a cushioning effect which protects the proximal end portion of the cartridge wall61, including the proximal rim21.2.