FIELD OF THE INVENTION

The present invention relates generally to devices for delivering medicine to a subject, and more specifically to injection devices capable of setting and expelling one or more doses of drug from a drug reservoir.

BACKGROUND OF THE INVENTION

In the diabetes care segment parenteral drug administration carried out using a traditional vial and syringe system is increasingly being substituted by administration using a pen injec- tion device. Pen injection devices are particularly convenient in that they allow the user to perform a dosed injection from a prefilled drug reservoir without first having to manually transfer the particular dose from one reservoir (the vial) to another (the syringe).

Predominantly, two types of pen injection devices are available, durable injection devices being capable of delivering one or more doses of drug from a prefilled drug cartridge which can be loaded into the device before use and replaced after exhaustion, and disposable in- jection devices being capable of delivering one or more doses of drug from a prefilled and non-exchangeable drug cartridge. Each of these types of pen injection devices are, or may in principle be, realised in various sub-types, such as e.g. single shot devices adapted to deliver only one dose from a drug cartridge, multi-shot devices capable of delivering a plural ity of doses from a drug cartridge, manual devices, where the user provides the force need- ed for injection, automatic devices having a built-in energy source releasable to occasion the injection, fixed dose devices adapted to deliver a predetermined dose of drug, variable dose devices offering delivery of different doses of drug, settable by the user, etc.

As the labels suggest a durable injection device is intended for use over a considerable pe- riod of time during which multiple drug cartridges are exhausted and replaced, whereas a disposable injection device is intended for use until its dedicated drug cartridge is exhausted, after which the entire injection device is discarded.

In the treatment of diabetes, it is advisable to keep a log of the administered doses of a par- ticular drug (e.g. insulin or glp-1 ), as well as the respective times of dose administration. Some injection devices accordingly offer electronic dose capturing and the opportunity to review dose related information on a digital display. Until recently, the use of electronic features like the ones above has been limited to durable injection devices, as the additional cost connected with an inclusion of such features in a disposable injection device has been considered to lead to an economically unviable end- product. However, the advances within less expensive electronics, such as printed electron- ics, are promising vis-a-vis the possibility of producing disposable injection devices with in- tegrated electronic components at a reasonable cost.

WO 2015/071354 A1 discloses a drug delivery device having a flexible sheet mounted at least in part to the exterior of its housing, the flexible sheet carrying e.g. printed electronic components such as a display, a processor, an energy source, and input means actuatable by an action performed on or by the device. The display is configured to visually indicate e.g. the size of a set dose, the size of an expelled dose, and/or a time parameter in response to actuation of the input means. The input means are exemplified by various switch structures, each adapted to provide connection to an interior device component through an opening in the housing. WO 2016/180873 A1 discloses a drug delivery device having a switch assembly comprising a flexible sheet metal member and a flexible printed substrate. The flexible sheet metal member provides a plurality of individual flexible contact fingers, wherein the flexible sheet metal member is mounted on the flexible printed substrate on which a plurality of contact pads are formed. The flexible contact fingers of the flexible sheet metal member protrude through openings in the flexible printed substrate and operates by engaging an indicator structure of the drug delivery device.

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 drug injection device having means for enabling detection of a change of state of the drug injection device.

It is a further object of the invention to provide a drug injection device having means for providing electronic monitoring of a state and/or a change of state of the drug injection de vice. It is a further object of the invention to provide a drug injection device with a switch arrange- ment providing a space-saving design.

It is an even further object of the invention to provide such a drug injection device which is relatively inexpensive to produce.

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.

A drug injection device embodying the principles of the present invention comprises:

- a housing portion extending along a central longitudinal axis,

- an activation element configured to undergo rotational movement around an axis cor- responding to one of a dose setting action and a dose expelling action performed on or by the drug injection device, the activation element comprising at least one protru- sion extending radially outwards from a surface of the activation element,

- a switch arrangement mounted relative to the housing portion, and configured to co- operate with the activation element to detect positional information of the activation element,

- a processor electrically connected with the switch arrangement, and

- an energy source coupled to the processor,

wherein said rotational movement of the activation element brings one of said at least one protrusion into an activating position detectable by the switch arrangement,

wherein the switch arrangement is configured as a multi-layer substrate having a dimension extending in parallel with the central longitudinal axis, the multi-layer substrate exhibiting either a planar or curved configuration, the switch arrangement comprises:

a first sheet having a radially outwards facing surface that includes a first electrode carrying surface portion, the first sheet being provided as a thin flexible sheet, and a second sheet arranged in general parallelism with the first sheet, the second sheet having a radially inwards facing surface opposing the radially outwards facing sur- face of the first sheet, the radially inwards facing surface including a second elec- trode carrying surface portion, wherein one or more pair(s) of switch electrodes is defined by respective electrodes of the first electrode carrying surface portion and the second electrode carrying surface portion,

wherein each one or more pairs of switch electrodes of the switch arrangement is configured to assume an inactive state where the first and the second electrode carrying surface por- tions are spaced apart and an active state where the first and the second electrode carrying surface portions are in contact,

wherein when the one of said at least one protrusion assumes the activating position it acts on the first sheet to deflect the first electrode carrying surface portion located at the respec- tive pair of switch electrodes into contact with the second electrode carrying surface portion to shift the respective pair of switch electrodes from the inactive state to the active state thereby establishing electrical contact between the electrodes of said pair of switch elec- trodes, and

wherein the processor is configured to detect the shift of the switch arrangement from the inactive state to the active state and/or to detect the shift of the switch arrangement from the active state into the inactive state.

One of the advantages of forming such switch arrangement, in particular for a disposable injection device, i.e. a device which irreplaceably holds a pre-filled reservoir (i.e. a so-called pre-filled injection device), is that a rotational switch arrangement can be made particularly inexpensive, yet sufficiently robust since no transversal abrasive movement relative to elec- trode portions will take place. Hence, the requirement for using gold-plated electrodes for the switch arrangement can be avoided. By forming the switch arrangement in a configuration as a multi-layer substrate having a dimension extending in parallel with the central longitudi nal axis the switch arrangement can be provided as a common substrate that, for monitoring purposes, cooperates with a multitude of individual components in the device to monitor po- sitional information of the individual components. Hence, a particular cost-effective solution can be provided. Furthermore, assembly of the mechanical system with the electronic com- ponents can be made particularly simple and fast since a simple interface is enabled for coupling the mechanical parts and the electronic components. A further advantage of form- ing such switch arrangement is that it only takes up very little space as the sandwich formed by the first sheet and the second sheet can be made with a very low profile. A still further advantage is that the suggested switch arrangement is that conductive electrodes of the first sheet are formed on the side of the first sheet facing away from the activation element, thereby not being subject to wear and tear by directly engaging with the protrusion(s). In some embodiments, when the one of said at least one protrusion assumes the activating position it engages directly with the first sheet to deflect the first electrode carrying surface portion radially outwards to make contact with the radially inwards facing surface of the sec- ond electrode carrying surface portion of the second sheet.

In some embodiments, the switch arrangement further comprises one or more spacer ge- ometries arranged between the first sheet and the second sheet, the one or more spacer geometries arranged adjacent the one or more pair(s) of switch electrodes to urge the elec- trodes of each pair of switch electrodes away from each other. In some embodiments, the one or more spacer geometries are formed as a common spacer sheet with apertures locat- ed at the one or more pair(s) of switch electrodes to provide for the first sheet being locally deformed to deflect into contact with the second sheet in alternative embodiments, the one or more spacer geometries are geometries or components that are disposed on either the first sheet and/or the second sheet, for example disposed thereon by a printing or adhering process. In still other embodiments, the one or more spacer geometries are formed by the first sheet and/or the second sheet, for example by an embossing process of the respective sheet(s) to provide elevated geometries that protrude from the base layer of the sheet, e.g. the first sheet and/or the second sheet.

The first sheet may be formed so that it provides inherent rigidity to maintain the one or more pair(s) of switch electrodes to assume the inactive state when no protrusions of the activa- tion element is rotationally aligned with the respective pair of switch electrodes. In configura- tions that include one or more spacer geometries, the said spacer geometries aid in separat- ing the first sheet from the second sheet when no protrusions of the activation elements are positioned rotationally aligned with the respective pair of switch electrodes. In some embod- iments, the first sheet is formed so that at least the portion of the sheet that defines the first electrode carrying surface portion is formed as a continuous sheet of material that contains no holes or apertures, and optionally not having any discontinuations in the form of cuts or slits. In some embodiments, the entire first sheet is formed with no holes, apertures, cuts or slits. Also, in some embodiments, the entire second sheet is formed with no holes, aper- tures, cuts or slits. Either the first sheet and/or the second sheet may be formed or comprise one or more film materials selected from a polymeric material, such as made of polyethylene terephthalate (PET), a metallic material or similar. In some forms of the switch arrangement, the first sheet and the second sheet are laminated together. In particular forms, the first sheet and second sheet form a sealed switch arrange- ment wherein one or more of the pairs of switch electrodes define a sealed compartment for the respective switch. Such configurations provide for a robust switch arrangement which prevents liquid ingress, and which provide superior performance even when operating in ambient conditions having high relative humidity.

In some embodiments, each of the at least one protrusion on the activation element is dis- posed at and end portion of a flexible tab that is able to flex radially while urging the protru- sion towards the first sheet. When the activation element comprises a plurality of protru- sions, the protrusions may be located on respective individual flexible tabs. The flexible tabs supporting the individual protrusions provide a springing effect for the protrusions to ensure a suitable contact pressure for deflecting the first sheet towards the second sheet.

In some embodiments, the at least one protrusion of the first activation element is moved in sliding engagement along the first surface of the first sheet into the activation position while the at least one protrusion deflects the first electrode carrying surface portion in a direction substantially transversal to the first surface.

In some embodiments, the housing portion comprises a first radial aperture, wherein the switch arrangement is mounted relative to the housing portion and arranged so that the switch arrangement covers the first radial aperture and wherein when the one of said at least one protrusion assumes the activating position it protrudes radially through or into the first radial aperture of the housing portion.

In some embodiments, the at least one protrusion of the activation element is provided as a plurality of protrusions distributed around the axis to protrude from a surface of the first acti vation element. Some embodiments further comprise a drug expelling mechanism for expelling a volume of drug from a reservoir, wherein the activation element forms part of the drug expelling mech- anism and is adapted to rotate unidirectionally about the longitudinal axis during a drug ex pelling action in accordance with an expelled dose. In some embodiments, the at least one protrusion of the activation element is provided as a plurality of protrusions, and wherein the protrusions are configured to sequentially deflect the first electrode carrying surface portion into contact with the second electrode carrying sur- face portion to shift the switch arrangement from the inactive state to the active state in re- sponse to the activation element undergoing a predetermined angular displacement relative to the housing, the predetermined angular displacement correlating with a predefined amount of drug expelled from the reservoir.

The drug injection device may further comprise:

a second activation element configured to undergo movement relative to the housing portion corresponding to an action performed on or by the drug injection device, the second activation element comprising at least one protrusion extending radially out- wards, wherein the switch arrangement is further configured to cooperate with the second activation element to detect positional information of the second activation element,

wherein the switch arrangement further defines:

- one or more pairs of switch electrodes dedicated for cooperation with the second ac- tivation element, and being defined by respective electrodes of the first electrical conducting electrode configuration and the second electrical electrode configuration, wherein, when the one of said at least one protrusion of the second activation element as- sumes the activating position at a selected one of the one or more pairs of switch electrodes dedicated for cooperation with the second activation element, it acts on the first sheet to deflect the first electrode carrying surface portion located at the selected one of the one or more pairs of switch electrodes into contact with the second electrode carrying surface por- tion to shift the respective pair of switch electrodes from the inactive state to the active state thereby establishing electrical contact between the electrodes of said pair of switch elec- trodes, and

wherein the processor is configured to detect the deflection registered by the selected one of the one or more pairs of switch electrodes dedicated for cooperation with the second activa- tion element.

In some embodiments, the movement of the second activation element relative to the hous- ing is a rotational movement about the central longitudinal axis, and wherein the at least one protrusion of the second activation element is provided as a plurality of protrusions distribut- ed around the central longitudinal axis.

Some embodiments further comprising a dose setting mechanism for setting a dose of drug to be expelled, wherein the second activation element forms part of the dose setting mecha- nism and is adapted to rotate about the longitudinal axis during a dose setting action in ac- cordance with the setting of a dose.

In further embodiments, the first or the second activation element forms a dosing member, such as a dose setting member, that is rotatable in increments away from a zero-dose set- ting position in a helical movement towards a max-dose setting position, wherein the dosing member is rotatable more than 360 degrees, such as 2, 3 or more full rotations and/or full and partial rotations. The helical movement may in some embodiments be provided as de- termined by a threaded coupling relative to a component associated with the switch ar- rangement, such as the housing portion that the switch arrangement is mounted relative to, or any intermediary component. The dosing member is formed having said at least one pro- trusion provided as a plurality of protrusions distributed around the dosing member. The switch arrangement comprises a pair of switch electrodes that provides a zero-dose setting switch being rotationally and axially positioned such that the zero-dose setting switch exclu- sively cooperates with one protrusion of the plurality of protrusions dedicated the zero-dose setting position, whereas, for any other rotational position the dosing member assumes other than the zero-dose setting position, no protrusions of the plurality of protrusions will be able to rotationally and axially align with the zero-dose setting switch. The switch arrangement further comprises one or more additional pairs of switch electrodes providing additional dose setting switches which sequentially cooperates with the plurality of protrusions as the dosing member is rotated. When the dosing member assumes a rotational position that is nx360 degrees from the zero-dose setting position, where n is an integer, or where the dosing member assumes a rotational position within 1 increment therefrom, the protrusion dedicat- ed the zero-dose setting position aligns rotationally and axially with the one or more addi- tional pairs of switch electrodes providing the additional dose setting switches. In this way, the protrusion dedicated the zero-dose setting position operates the zero-dose setting switch only when the dosing member assumes the zero-dose setting position, whereas this protru- sion operates the additional dose setting switches in the same manner as the remaining protrusions of the dosing member, as the dosing member is turned away from the zero-dose setting position. In some embodiments, the processor and conductors connecting the processor with the re- spective pairs of electrodes are disposed on one of the first surface of the second sheet and the second surface of the first sheet.

In some embodiments the energy source is arranged on the same sheet as the processor. The processor may in some embodiments be electrically connected with the said electrodes by respective printed conductors.

Some embodiments further comprise an electronic storage configured to log an expelled dose of drug, or a multitude of expelled doses of a drug.

The drug injection device may in further embodiments also comprise an antenna and a communication unit, wherein the drug injection device is configured for communicating stored entries of the electronic storage to an external device. In some embodiments, the antenna and/or the communication unit is disposed on at least one of the first surface of the second sheet and the second surface of the first sheet, such as by being disposed by a printing process. In some embodiments, the drug injection device forms a pre-filled device irreplaceably ac- commodating one or more drug reservoirs, whereas in other embodiments, the drug injec- tion device forms a reusable device which replaceably accommodates one or more drug reservoirs.

As used herein the term "drug injection device" covers all types of devices for administering drug transcutaneously, i.e. including devices which are conventionally labelled injection de- vices (with or without an injection needle), where the drug is delivered over a relatively short time span, and devices which are conventionally labelled infusion devices, where the drug is delivered continuously over a longer period of time.

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. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be further described with references to the drawings, wherein

Fig. 1 is a longitudinal section view of a proximal portion of a state of the art automatic injec- tion device 1’,

Fig. 2 is a perspective view of an automatic injection device 1 according to an embodiment of the invention,

Fig. 3 is a perspective view of a piston rod guide 70, a scale drum 60, and a switch ar- rangement 100 of the automatic injection device 1 shown in fig. 2, Fig. 4 is a magnified perspective view of the switch arrangement 100 shown in fig. 3,

Fig. 5 is an exploded perspective view of the switch arrangement 100 shown in fig. 3,

Fig. 6 is a detailed perspective view of the piston rod guide 70 shown in fig. 3, and

Fig. 7 is a detailed perspective view of the scale drum 60 shown in fig. 3.

In the figures like structures are mainly identified by like reference numerals. DESCRIPTION OF EXEMPLARY EMBODIMENTS

When in the following relative expressions, such as "clockwise" and "counter-clockwise", are used, 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 pur- poses only.

Fig. 1 is a longitudinal section view of a proximal portion of a state of the art automatic injec- tion device T which corresponds to the automatic injection device disclosed in WO 2017/055492. In fig. 1 only a proximal portion of the injection device T is shown. The undis- closed distal portion may be realised as such are conventionally in the art of pen-type injec- tion devices. The injection device T has a generally circular-cylindrical housing 2 which accommodates a portion of a drug containing cartridge 30, being sealed by, respectively, a slidable piston 31 and a needle-penetrable rubber septum (not shown), as well as a drive mechanism for ad- vancing the piston 31 through the cartridge 30. A rotatable, 2K moulded, dose dial 3 is ar- ranged at the proximal end of the housing 2 for allowing a user to select a dose to be deliv- ered from the cartridge 30.

A piston rod 9 extends longitudinally within the housing 2 and is in threaded engagement with a nut member 7 thereof. The piston rod 9 has a distal end face which during use of the injection device T abuts a piston washer 8 serving as a force distributor for the piston 31. The piston rod 9 further has a longitudinally extending groove (not visible) providing for rota- tional interlocking engagement with a piston rod guide 70, a key 71 of the latter being slida- bly received in the groove.

The piston rod guide 70 is axially fixed in, but capable of unidirectional rotation relative to, the housing 2. On an interior surface the piston rod guide 70 is provided with teeth 72 adapted for disengageable engagement with mating teeth 19 on an exterior portion of a drive tube 10.

The drive tube 10 is a unitary structure which extends axially in the housing 2 and is ar- ranged about a portion of the piston rod 9. A distal portion of the drive tube 10 has longitudi nal slits (not visible) to allow an otherwise exteriorly arranged scale drum 60 to extend radial ly through the drive tube 10 and threadedly engage with the piston rod 9 via an interior nut member 61. In addition to coupling the scale drum 60 directly to the piston rod 9 this pro- vides a rotational interlocking connection between the drive tube 10 and the scale drum 60. The scale drum 60 serves as a dose setting member.

A proximal portion 15 of the drive tube 10 comprises a circumferential toothing 18 adapted for disengageable engagement with an interior toothed collar 4 of the dose dial 3, and a ra- dially inwardly extending catch portion 17 firmly gripping a harpoon member 6 of a proximal injection button 5, thereby providing a translational interlocking connection between the drive tube 10 and the injection button 5. The injection button 5 is axially movable between an inac- tive position (shown in Fig. 5), in which the injection device T is in a dose setting state, and an active position, in which the injection device T is in a dose delivery state. A compression spring 50 arranged to act between an interior surface of the injection button 5 and an upper transversal surface of the toothed collar 4 biases the injection button 5 towards the inactive position. The proximal most position of the injection button 5 relative to the housing 2 is de- fined by a flange 14 provided on the proximal portion 15 of the drive tube 10, which flange 14 serves to limit proximal movement of the drive tube 10 relative to a spring base 40 being axially and rotationally fixed with respect to the housing 2.

The drive mechanism is powered by the torsion spring 20. A hook (not shown) of the proxi- mal end portion 22 is rotationally anchored to the spring base 40, in a manner conventionally known in the art, and the spring base 40 thus provides a stationary reference point for the torsion spring 20. The distal end portion 23 is wrapped around a spring receiving portion 11 of the drive tube 10 so as to establish a rotational interlocking connection between the distal end portion 23 and the drive tube 10. The spring receiving portion 11 has an outer diameter, D, which is larger than the inner diameter, d, of the torsion spring 20, which means that the distal end portion 23 is elastically expanded over the spring receiving portion 11 and thus exerts a compressional force there onto. In the shown embodiment three windings of the torsion spring 20 overlap the spring receiving portion 11 and thus ensure a sticking friction engagement with the drive tube 10.

The spring base 40 has a proximally facing serrated surface 44 capable of slipping engage- ment with a distally facing serrated interior surface 84 of the dose dial 3, thereby providing a ratchet mechanism for preventing relaxation of the torsion spring 20 during dose setting.

In the following a situation of use of the injection device 1’ will be described.

The injection device T is prefilled in the sense that it carries the cartridge 30 when delivered from the manufacturer, and the basic user steps required to administer a dose of the con- tained drug (e.g. insulin, glp-1 or a mixture thereof) are simple and relatively fast to execute: 1 ) attach an injection needle assembly (not shown) to the distal end of the cartridge 30, 2) dial a desired dose, 3) insert the injection needle at a suitable injection site, and 4) initiate an expelling of the set dose by releasing the torsion spring 20. Steps 1 ) and 3) may be per- formed in accordance with common ways of attaching an injection needle assembly to a pen-type injection device and subsequently inserting the injection needle into the skin, and since these steps are irrelevant to the description of the present invention they will not be discussed any further in this text.

So, in order to set a dose to be administered the user may hold the housing 2 in one hand and use the other hand to rotate the dose dial 3 relative to the housing 2, about a longitudi- nal axis of the injection device T. The injection button 5 is in its inactive position, i.e. its prox- imal most position relative to the housing 2, due to the biasing force from the compression spring 50. Due to the engagement between the harpoon member 6 and the catch portion 17 the drive tube 10 is accordingly situated in a proximal most position. In the proximal most position of the drive tube 10 the circumferential toothing 18 is radially aligned with the interior toothed collar 4, thereby rotationally interlocking the drive tube 10 and the dose dial 3. A rotation of the dose dial 3 about the longitudinal axis, in either direction, thus results in a corresponding rotation of the drive tube 10.

The rotation of the drive tube 10 occasions both a helical travel of the scale drum 60 within the housing 2 and a twisting of the torsion spring 20. Due to the rotational interlocking con- nection between the drive tube 10 and the scale drum 60 the scale drum 60 is forced to ro- tate in accordance with the rotation of the drive tube 10, and as the piston rod 9 is held sta- tionary by the piston rod guide 70, the threaded engagement between the piston rod 9 and the nut member 61 causes the scale drum 60 to move helically about the piston rod 9. The scale drum 60 carries a plurality of dose related indicia (not shown), and a window (not visi ble) in the housing 2 allows the user to see a subset of these dose related indicia pass by as the scale drum 60 moves and to determine the size of the set dose from the current position of the scale drum 60. Furthermore, as the spring receiving portion 11 of the drive tube 10 is rotated relative to the spring base 40 the wrapped distal spring end portion 23 is angularly displaced relative to the proximal spring end portion 22, an amount corresponding to the angular displacement of the spring receiving portion 11 due to the sticking friction engage- ment between the two, whereby rotational energy is stored in the torsion spring 20. The ratchet connection between the proximally facing serrated surface 44 of the spring base 40 and the distally facing serrated interior surface 84 of the dose dial 3 allows the user to set the desired dose by rotating the dose dial 3 relative to the housing 2 in discrete steps, and to reduce a set dose by rotating the dose dial 3 in the reverse direction.

In order to expel a set dose from the cartridge 30 the injection button 5 is depressed, where- by the compression spring 50 is compressed and the drive tube 10 is moved distally in the housing 2. The distal movement of the drive tube 10 causes the circumferential toothing 18 to slide out of engagement with the interior toothed collar 4 and the teeth 19 to slide into engagement with the mating teeth 72 on the interior surface of the piston rod guide 70. No- tably, the resulting rotational interlocking of the drive tube 10 with the piston rod guide 70 takes effect before complete disengagement of the circumferential toothing 18 from the inte- rior toothed collar 4. At some point during the depression of the injection button 5 the circumferential toothing 18 disengages completely from the interior toothed collar 4, whereby the energy stored in the torsion spring 20 is released and the distal end portion 23 is returned to its pre-dose setting position. The rotation of the distal end portion 23 causes a corresponding rotation of the drive tube 10 due to the sticking friction engagement between the wrapped spring windings and the spring receiving portion 1 1.

Due to the established rotational interlocking engagement between the drive tube 10 and the piston rod guide 70 the piston rod guide 70 is forced to rotate, whereby the key 71 , being engaged in the longitudinally extending groove of the piston rod 9, causes a corresponding rotation of the piston rod 9, which is then helically advanced through the nut member 7 to displace the piston washer 8 and the piston 31 distally in the cartridge 30.

Simultaneously, the scale drum 60 rotates along with the drive tube 10, and is thereby heli cally displaced in the distal direction along with the piston rod 9, until a portion of the scale drum 60 meets a rotational stop surface (not visible) in the housing 2. At this stop surface the scale drum 60 is in an end-of-dose position in the housing 2.

As the rotation of the scale drum 60 stops, so does the rotation of the drive tube 10 and thereby also the rotation of the piston rod guide 70 and the piston rod 9 is resultantly halted in the nut member 7. When the user discontinues her force on the injection button 5 the compression spring 50 expands and returns the injection button 5 to the inactive position. The drive tube 10 is thereby moved proximally in the housing 2 until the flange 14 meets a stop surface (not visible) on the spring base 40. In this position of the drive tube 10 the cir- cumferential toothing 18 has re-engaged with the interior toothed collar 4 and the teeth 19 have disengaged from the teeth 72, rotationally decoupling the drive tube 10 and the piston rod guide 70. The injection device 1’ is now ready for the setting of a new dose.

Fig. 2 is an exploded view of a pen injection device 1 according to an exemplary embodi- ment of the invention. The pen injection device 1 comprises a generally cylindrical housing 2 having a slightly less curved exterior switch carrier surface onto which a switch arrangement 100 is disposed. The housing 2 accommodates a drug containing cartridge at a distal end thereof. The cartridge, which is closed at its distal end by a penetrable self-sealing septum and at its proximal end by a slidable piston (not visible), is held within the housing 2 by a cartridge holding section. The cartridge holding section further has a needle mount and thereby serves as an attachment interface for an injection needle unit (not shown). The housing 2 is provided with a longitudinal window for inspection of the cartridge contents.

The pen injection device 1 further includes a dose setting and expelling mechanism which generally corresponds to the dose setting and expelling mechanism described in connection with the automatic injection device T shown in fig. 1. However, in particular for some com- ponents, such as the housing 2, the piston rod guide 70 and the scale drum 60, these com- ponents have been redesigned and restructured to enable inclusion of electronics for elec- tronic sensing component movement for providing an electronic logging function for expelled and/or set doses. It is to be noted that the dose setting and expelling mechanism described in connection with automatic injection device T only provides an exemplary embodiment, and that the claimed invention may be embodied to include mechanisms that are structured differently than the one described.

With respect to the housing 2, radially below the switch arrangement 100, some wall materi- al has been removed to provide a radial aperture, such as one or more openings, located on a side portion of housing 2 to enable the piston rod guide 70 and the scale drum 60 to cooperate and engage with respective areas of the switch arrangement 100.

In the shown embodiment, the switch arrangement 100 is provided as a multi-layer foil as- sembly comprising at least one flexible sheet arranged in parallel with at least one other sheet which can be provided either as a flexible sheet or a substantially rigid sheet. The sheets are arranged as a layered stack where the sheets are fixedly attached to each other, for example at an outer periphery of switch arrangement 100. One or more of the sheets carry electronic components, such as printed electronics, which may include a processor 120, an electronic storage, one or more of electrodes, one or more contact pads and various conductive traces electrically interconnecting the processor and the remaining other of the electronic components with each other. Optionally, the electronics provided on the one or more sheets may additionally include components, such as one or more of a battery, anten- na wirings for enabling wireless communication, an electronic controlled display, or other kinds of electronics. In the shown embodiment, the switch arrangement does not carry an electronic display, but carries a communication unit which is connected to antenna wirings 140 as well as a flat battery 1 10, cf. fig .4. In other embodiments, other types of energy sources may be incorporated, such as a capacitor, which may be charged by an energy har- vesting process. In the shown embodiment, the switch arrangement 100 is mounted by adhering the switch arrangement onto a slightly curved platform on housing 2, i.e. the above-mentioned switch carrier surface.

Fig. 3 is a schematic perspective view of a piston rod guide 70, a scale drum 60, and a switch arrangement 100 of the automatic injection device 1 shown in fig. 2, providing an overview on how the piston rod guide 70 and scale drum 60 orient relative to switch ar- rangement 100, and in particular relative to electrode configurations provided thereon.

Fig. 4 is a magnified perspective view of the switch arrangement 100 shown in fig. 3. Apart from the electronic components discussed above the switch arrangement 100 include areas defining pairs of switch electrodes to cooperate with geometries provided on piston rod guide 70 and scale drum 60. A first electrode pair 160.1 , a second electrode pair 160.2 and a third electrode pair 160.3 are arranged to cooperate with the geometries provided on scale drum 60. A fourth electrode pair 170.1 is configured to cooperate with the geometries pro- vided on piston rod guide 70. Reference 130 refers to a contact pad which is used for per- manently making contact between the above mentioned at least one flexible sheet arranged in parallel with said at least one other sheet.

Reference is made to fig. 6 which is a detailed perspective view of the piston rod guide 70. The piston rod guide is provided as a tubular formed element having a plurality of outwards protruding protrusions 70.1 distributed evenly around the circumference, e.g. 12 protrusions in this embodiment. Each protrusion is arranged at the proximal end of an individually radial ly inwards flexible tab, each tab having a distal end that connects to a distal rigid cylindrical portion of piston rod guide 70. The protrusions are in this embodiment arranged at the same axial position of piston rod guide 70.

The scale drum 60 is shown on fig. 7 which depicts the component in a detailed perspective view. The scale drum 60 is provided as a tubular formed element having a plurality of out- wards protruding protrusions 60.0, 60.1 distributed evenly around the circumference, e.g. 12 protrusions in this embodiment. Each protrusion is arranged at the proximal end of an indi vidually radially inwards flexible tab, each tab having a distal end that connects to a distal rigid cylindrical portion of scale drum 60. All but one of the protrusions 60.0, 60.1 are in this embodiment arranged at the same axial position of scale drum 60. The single protrusion 60.0 is not positioned at the same axial position as the remaining protrusions 60.1 , the latter protrusions being arranged more proximally on scale drum 60, i.e. the protrusion 60.0 is dis posed on a flexible tab that is positioned more distally than the remaining other flexible tabs.

Scale drum 60 further comprises a threaded coupling with the piston rod. Hence, as the scale drum 60 is dialled up by rotating, e.g. away from the“0” setting, the scale drum moves proximally until a maximum dose stop position is reached, in this example an“80” setting. Rotating the scale drum 60 in the opposite direction, to dial down an initially set dose, the scale drum moves distally towards the minimum dose stop position, i.e. the“0” setting. The scale drum is movable rotationally in incremental steps of 1 unit both when dialling up and when dialling down. The scale drum furthermore includes a series of dose indications 60.5 provided along a helical path in agreement with the lead of the threaded engagement. A window opening (non-referenced) in the housing 2 enables the dose indication 60.5 of a current dose setting to be viewed through the window opening by visual inspection.

Fig. 5 is an exploded perspective view of the switch arrangement 100 shown in figs. 3 and 4. A first sheet 100.1 , provided as a thin flexible sheet, has first and second surfaces oriented away from each other, wherein the second surface includes a first electrode carrying surface portion.

A second sheet 100.2, which also may be provided as a thin flexible sheet, is arranged in general parallelism with the first sheet 100.1 , the second sheet 100.2 having first and sec- ond surfaces oriented away from each other. The first surface of the second sheet 100.2 is arranged facing the second surface of the first sheet and includes a second electrode carry- ing surface portion. When the first sheet 100.1 and the second sheet 100.2 are stacked to- gether a plurality of pairs of switch electrodes are defined by respective electrodes of the first electrode carrying surface portion and the second electrode carrying surface portion, i.e. the first electrode pair 160.1 , the second electrode pair 160.2, the third electrode pair 160.3, and the fourth electrode pair 170.1. An electrode pair is also provided for the above- mentioned contact pad 130.

In the shown embodiment, the first sheet 100.1 is provided as a continuous electrical con- ductive sheet which does not form dedicated isolated islands and conductive traces between islands. Furthermore, in this embodiment, the first sheet is formed without apertures or other discontinuations, such as cuts or slits. In the shown embodiment, the first sheet serves as a ground layer which defines logic low. Apart from this, in this embodiment, a spacer layer is provided as a third layer 100.3 being positioned between the first sheet 100.1 and the sec- ond sheet 100.2, the third layer 100.3 forming an electrically insulating layer having material openings at the respective electrode pairs 160.1 , 160.2, 160.3, 170.1 , and further at the con- tact pad 130. The spacer layer 100.3 serves to separate and urge the first sheet 100.1 and the second sheet 100.2 away from each other at the respective electrode pairs, except for the electrode pair provided at the contact pad 130 where permanent electrical conductive connection is provided, i.e. serving to connect the ground layer with the battery and the pro- cessor.

In other not shown alternative configurations, the first sheet may be formed with dedicated isolated islands and conductive traces between islands whereas the second sheet may be formed without dedicated isolated islands and conductive traces between islands. Also, in alternative embodiments, no dedicated spacer layer is provided between the first sheet 100.1 and the second sheet 100.2, but spacer areas may be provided as a plurality of sepa- rate components arranged between the first sheet 100.1 and the second sheet 100.2, i.e. around or in the vicinity of the electrode pairs 160.1 , 160.2, 160.3, 170.1. Still alternatively, spacer geometries or components may be added to either of the first sheet 100.1 and/or the second sheet 100.2, for example by printing or adhering. Still alternatively, spacer geome- tries may be formed by the first sheet 100.1 and/or the second sheet 100.2, for example by embossing of the respective sheet(s) to provide elevated geometries that protrude from the base layer of the sheet, e.g. the first sheet and/or the second sheet.

Each of the pairs of switch electrodes of the switch arrangement 100 is configured to as- sume an inactive state where the first and the second electrode carrying surface portions are spaced apart and an active state where the first and the second electrode carrying surface portions are in contact. When one of said protrusions of the piston rod guide 70 and the scale drum 60 assumes the activating position where it locates below the corresponding electrode pair the“active” protrusion acts on the first sheet to deflect the first electrode car- rying surface portion into contact with the second electrode carrying surface portion to shift the switch in question from the inactive state to the active state thereby establishing electri cal contact between the electrodes of said pair of switch electrodes. As soon as the“active” protrusion leaves the corresponding electrode pair, the spacer will act to separate the first sheet and the second sheet to thereby break the contact, until another protrusion starts to engage the first sheet to initialize a renewed activation of the electrode pair in question. The flexible tabs which supports the independent protrusions on the scale drum 60 and the pis- ton rod guide 70 provide a springing effect for the protrusion to ensure a suitable contact pressure for deflecting the first sheet towards the second sheet. The processor 120 is configured to detect the shift of the electrode pairs 160.1 , 160.2, 160.3,

170.1 of the switch arrangement 100 from the inactive state to the active state, and from the active state to the inactive state. The processor will typically provide or connect to pull-up or pull-down resistors that further connect to the respective electrode pairs. Hence, the proces- sor is able to monitor all movements that is provided by the scale drum 60 and the piston rod guide 70. The processor 120 is configured to count and calculate the adjusted dose as set by means of the dose dial 3 by receiving signals from the electrode pairs 160.1 , 160.2, 160.3, but also count and calculate expelled doses by signals received from electrode pair

170.1. In a particular embodiment, the processor is configured to only count expelled doses for storing the information of the expelled dose in combination with timing information.

The scale drum 60 and the electrode pairs 160.1 , 160.2 are configured as a quadrature en- coder to enable detection of rotational movement, and also the direction of rotation, i.e. both for dialling up a dose and for dialling down a dose. The two electrode pairs 160.1 and 160.2 are so configured that these electrode pairs provide pulsed signals signifying 24 counts for each revolution from the 12 protrusions of the scale drum 60. The electrode pairs 160.1 ,

160.2 are configured as longitudinally extending electrodes running in parallel with the axis so that the protrusions of the scale drum 60 will be able to cooperate with the electrode pairs

160.1 , 160.2 irrespective of the axial displacement of the scale drum 60.

The electrode pair 160.3 is configured as a“0” setting detector. A particular protrusion 60.0 on the scale drum 60 is dedicated the“0” setting. This particular protrusion 60.0 exclusively aligns axially and rotationally with the electrode pair 160.3 in the“0” setting. After dialling up a few units, the particular protrusion 60.0 moves away from axial alignment with the elec- trode pair 160.3 and will, when further increasing the dose, and when the particular protru- sion 60.0 rotationally aligns with the electrode pairs 160.1 , 160.2, cooperate with the latter two electrode pairs - similarly to the remaining protrusions 60.1.

The electrode pair 170.1 cooperates with the twelve protrusions 70.1 of the piston rod guide 70 to provide a pulse for each protrusion that passes into engagement with the electrode pair 170.1. The electrode pair 170.1 is used for detecting movement of the piston rod guide 70 which only occurs during expelling of a set dose. During dose expelling, the piston rod guide 70 moves as the scale drum 60 moves. During dose setting, e.g. during dialling down of a set dose said simultaneous movement will not occur as the piston rod guide is kept sta- tionary. Hence, the comparison between signals from the electrode pair cooperating with the piston rod guide 70 and the electrode pairs cooperating with the scale drum 60 provides information as to whether the device is in dose setting mode or in dose expelling mode, i.e. whether the scale drum is returned towards the“0” setting in a dialling down operation, or whether the scale drum is returned towards the“0” setting in a dose expelling operation. In this way, the number of expelled units in an administered dose is determined using simple means yet operating in a failsafe manner.

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 sub- ject matter defined in the following claims.