The present invention relates to devices, assemblies and systems adapted for capturing information. In a specific aspect the invention addresses issues relating to electronic dose data capturing in and for a drug delivery device.

BACKGROUND OF THE INVENTION

In the disclosure of the present invention reference is mostly made to the treatment of diabetes by delivery of insulin using a drug delivery device, however, this is only an exemplary use of the present invention.

Drug injection devices have greatly improved the lives of patients who must self-administer drugs and biological agents. Drug injection devices may take many forms, including simple disposable devices that are little more than an ampoule with an injection means or they may be durable devices adapted to be used with pre-filled cartridges. Regardless of their form and type, they have proven to be great aids in assisting patients to self-administer injectable drugs and biological agents. They also greatly assist care givers in administering injectable medicines to those incapable of performing self-injections.

Performing the necessary insulin injection at the right time and in the right size is essential for managing diabetes, i.e. compliance with the specified insulin regimen is important. In order to make it possible for medical personnel to determine the effectiveness of a prescribed dosage pattern, diabetes patients are encouraged to keep a log of the size and time of each injection. However, such logs are normally kept in handwritten notebooks, from the logged information may not be easily uploaded to a computer for data processing. Furthermore, as only events, which are noted by the patient, are logged, the note book system requires that the patient remembers to log each injection, if the logged information is to have any value in the treatment of the patient's disease. A missing or erroneous record in the log results in a misleading picture of the injection history and thus a misleading basis for the medical personnel's decision making with respect to future medication. Accordingly, it may be desirable to automate the logging of ejection information from medication delivery systems.

Correspondingly, a number of injection devices with a dose monitoring/acquisition feature have been suggested, see e.g. US 2009/0318865, WO 2010/052275, WO 2014/128156, US 7,008,399 and WO 2013/083715, the latter comprising a rotational dose setting member and an axially moveable release button. However, most devices of today are without it. Having regard to the above, it is an object of the present invention to provide a drug delivery device as well as components and assemblies therefore which cost-effectively and reliably allows detection and storage of dose data related to use of a drug delivery device. DISCLOSURE OF THE INVENTION

In the disclosure of the present invention, embodiments and aspects will be described which will address one or more of the above objects or which will address objects apparent from the below disclosure as well as from the description of exemplary embodiments. Thus, in a first aspect of the invention a drug delivery device is provided, comprising a housing, an expelling mechanism adapted to expel a user set dose of drug from a distal end of the drug delivery device and comprising an indicator member rotating corresponding to a reference axis during drug expelling, as well as a button member arranged rotatable relative to the housing and corresponding to the reference axis to thereby set a dose of drug to be ex- pelled. The button member is further axially moveable between a proximal state in which the button member can be rotated by a user to set a dose of drug to be expelled, an intermediate state in which the button member is rotationally locked relative to the housing, and a distal state in which the button member is rotationally locked relative to the housing and the expelling mechanism is allowed to expel a set dose. The drug delivery device further comprises dose logging circuitry comprising a first rotary sensor part coupled non-rotationally to the button member, a second rotary sensor part coupled non-rotationally to the indicator member, and axial switch circuitry adapted to detect the axial state of the button member. The dose logging circuitry is adapted to determine an amount of expelled drug, the determination comprising the steps of determining a first rotational position between the first and second rotary sensor parts when the axial switch circuitry detects that the axial state shifts from the proximal to the intermediate state, and determining a second rotational position between the first and second rotary sensor parts when the axial switch circuitry detects that the axial state shifts from the distal to the intermediate state. By such an arrangement the rotational position of the rotary sensor can be precisely determined both before and after a dose expelling event and thus rotational movement has taken place.

The term button member encompasses embodiments in which the button member comprises a number of components, i.e. forming an assembly, which then is arranged to both rotate and move axially. The means providing the rotational lock between the different components corresponding to the different states may be of any suitable design, e.g. inter-engaging splines or teeth being moved into and out of engagement with each other. The first and second rotary sensor por- tions form in combination a sensor assembly allowing a rotational position or movement between the two rotary sensor parts to be determined. The determination may be based on any suitable sensor technology, e.g. relying on galvanic, optical or magnetic sensing means. The axial switch circuitry adapted to detect the axial state of the button member may correspondingly be of any suitable design allowing an axial position or state between two components to be determined, e.g. relying on galvanic, optical or magnetic sensing means. The indicator member may be any suitable member performing a rotational movement corresponding to a reference axis during drug expelling. For a spring-driven device the indicator member may be the transmission member on which the drive spring acts or a member coupled directly or indirectly thereto.

In an exemplary embodiment at least a portion of the dose logging circuitry is housed in the button member and moves axially and rotationally therewith. The first rotary sensor part may be axially locked to the button member. Also the second sensor portion may be axially locked to the button member. In an alternative embodiment the dose setting and dose release means may be in the form of separate dose setting and dose release members. In such an embodiment the dose release member would be the axially moveable member controlling the rotationally movability of the dose setting member.

In an exemplary embodiment the axial switch circuity comprises a first axial switch portion and a second axial switch portion, the first axial switch portion being axially locked to the housing during axial movement of the button member, and the second axial switch portion being coupled axially non-moveable to the button member. The first axial switch portion may be axially locked to the housing during both rotational and axial movement of the button member. The first and second axial switch portions may be rotationally coupled to and rotate together with the button member.

The drug delivery device may comprise a mounting structure coupled axially locked but rotationally free to the housing, e.g. in the form of a ring member, as well as axially free but rotationally locked to the button member, wherein the first axial switch portion is mounted to the mounting structure. The second axial switch portion may be coupled to the button member and move therewith during both rotational and axial movement of the button member. In an exemplary embodiment the drug expelling mechanism comprises an axially displacea- ble piston rod, a rotatable drive member for driving the piston rod in the distal direction, a drive spring for rotating the drive member, the drive spring being strained when a dose is be- ing set by rotation of the button member, wherein the indicator member is formed by or coupled non-rotationally to the drive member.

The electronic circuitry may be provided with logging means adapted to create a log for determined dose amounts of drug. The electronic circuitry may further comprise a display con- trolled by the electronic circuitry and adapted to display dose related data. The electronic circuitry may further comprise transmitter means adapted to transmit stored data to an external receiver.

The drug delivery device may be of the pre-filled type comprising a cartridge with an axially displaceable piston, or it may be of the durable type being adapted to receive a cartridge. In case the drug delivery device is of the pre-filled and thus disposable type, the button member may comprise the electronic circuitry and be releasably coupled to the disposable portion of the device, this allowing the button member to be transferred to a new disposable device adapted to receive the button member.

In the present context the term "axial state" indicates that a(n indefinite) number of actual axial positions correspond to a given state.

In a specific aspect of the invention a drug delivery device is provided, comprising or being adapted to receive a cartridge with an axially displaceable piston. The drug delivery device comprises a housing comprising a distal end and a proximal end, a drug expelling mechanism and a sensor system. The drug expelling mechanism comprises an axially displaceable piston rod adapted to move the piston of a cartridge in a distal direction to thereby expel drug from the cartridge, a rotatable drive member for driving the piston rod in the distal direction, a drive spring for rotating the drive member, a rotatable dose setting member allowing a user to set a dose of drug to be expelled and strain the drive spring correspondingly, an indicator member adapted to rotate corresponding to a reference axis during drug expelling and a user actuated release member for releasing the strained drive spring to thereby move the piston rod in the distal direction corresponding to the set dose. The sensor system comprises a ro- tary sensor adapted to detect a relative rotational position between the indicator member and the housing, the rotary sensor comprising a first sensor part coupled rotationally locked to the dose setting member and a second sensor part coupled rotationally locked to the indicator member, a state switch, and electronic circuitry adapted to receive input from the state switch and the rotary sensor and determine the size of an expelled dose based on the received input. The release member can be moved axially relative to the housing from a dose setting state through a secure state to a dosing state, the state switch being adapted to detect the state, the setting member can be rotated to set a dose when the release member is in the initial position, the dose setting member and thereby the first sensor part is rotationally locked relative to the housing when the release member is in the intermediate state, and the drive spring is released to thereby rotate the drive member and the indicator member when the release member is in the dosing state. A first rotational position between the first and second sensor parts is determined when the state switch detects that the release member is moved from the dose setting state to the secure state, and a second rotational position between the first and second sensor parts is determined when the state switch detects that the release member is moved from the dosing state to the secure state.

As appears, in contrast to the device of the first aspect, the rotational locking of the dose setting member as well as actuation of the state switch is controlled by the axially moved release member. The device of the specific aspect may be modified as described above for the device of the first aspect.

As used herein, the term "drug" is meant to encompass any flowable medicine formulation capable of being passed through a delivery means such as a cannula or hollow needle in a controlled manner, such as a liquid, solution, gel or fine suspension, and containing one or more drug agents. The drug may be a single drug compound or a premixed or co-formulated multiple drug compounds drug agent from a single reservoir. Representative drugs include pharmaceuticals such as peptides (e.g. insulins, insulin containing drugs, GLP-1 containing drugs as well as derivatives thereof), proteins, and hormones, biologically derived or active agents, hormonal and gene based agents, nutritional formulas and other substances in both solid (dispensed) or liquid form. In the description of the exemplary embodiments reference will be made to the use of insulin and GLP-1 containing drugs, this including analogues thereof as well as combinations with one or more other drugs.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following exemplary embodiments of the invention will be described with reference to the drawings, wherein figs. 1 and 2 show a front-loaded drug delivery device with respectively without a drug cartridge mounted,

fig. 3 shows in part a cross-sectional view of a drug delivery device,

fig. 4 shows a switch disc incorporated in the device of fig. 3,

fig. 5 shows a logging module, and

figs. 6A-6F illustrate different positions of the dose button during an actuation stroke.

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

When in the following terms such as "upper" and "lower", "right" and "left", "horizontal" and "vertical" or similar relative expressions are used, these only 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. When the term member or element is used for a given component it generally indicates that in the described embodiment the component is a unitary component, however, the same member or element may alternatively comprise a number of sub-components just as two or more of the described components could be provided as unitary components, e.g. manufactured as a single injection moulded part. The terms "assembly" and "subassembly" do not imply that the described components necessarily can be assembled to provide a unitary or functional assembly or subassembly during a given assembly procedure but is merely used to describe components grouped together as being functionally more closely related. Referring to fig. 1 a pen-formed drug delivery device 100 will be described. The device represents a "generic" drug delivery device providing an example of a device in combination with which embodiments of the present invention is intended to be used, such a device comprising a rotational member adapted to rotate corresponding to a set and/or expelled dose of drug.

More specifically, the pen device comprises a cap part (not shown) and a main part having a proximal body or drive assembly portion 120 with a housing 121 defining a general axis and in which a drug expelling mechanism is arranged or integrated, and a distal cartridge holder portion in which a drug-filled transparent cartridge 180 with a distal needle-penetrable sep- turn can be arranged and retained in place by a cartridge holder 1 10 attached to the proximal portion, the cartridge holder having openings allowing a portion of the cartridge to be in- spected. The cartridge may for example contain an insulin, GLP-1 or growth hormone formulation. The shown device is of the front-loaded type and is designed to be loaded by the user with a new cartridge through a distal receiving opening in the cartridge holder, the cartridge being provided with a piston driven by a piston rod 128 forming part of the expelling mecha- nism.

The mechanism comprises a scale drum member provided with a plurality of dose size indices (not shown), the scale drum member being arranged rotationally corresponding to the general axis. The housing comprises a display opening (or window) 126 arranged to show a scale member dose size indicia corresponding to a set dose.

A proximal-most rotatable dose ring member 125 serves to manually set a desired dose of drug shown in display window 126 and which can then be expelled when the release button 127 is actuated. The dose member and release button may be in the form of a combined dose setting and release button (. Depending on the type of expelling mechanism embodied in the drug delivery device, the expelling mechanism may comprise a spring which is strained during dose setting and then released to drive the piston rod when the release button is actuated. Alternatively the expelling mechanism may be fully manual in which case the dose ring member and the release button moves proximally during dose setting corresponding to the set dose size, and then moved distally by the user to expel the set dose. In such an embodiment the release button could be considered a "drive button". The cartridge is provided with distal coupling means in the form of a needle hub mount 182 having, in the shown example, an external thread 185 adapted to engage an inner thread of a corresponding hub of a needle assembly. In alternative embodiments the thread may be combined with or replaced by other connection means, e.g. a bayonet coupling.

The cartridge holder comprises a distal opening adapted to receive a cartridge. More specifically, the cartridge holder comprises an outer rotatable tube member 170 operated by the user to control movement of gripping means to thereby open and close gripping shoulders 145 configured to grip and hold a cartridge. Fig. 2 shows the device with the cartridge removed and the gripping shoulders in their un-locked "open" position in which a cartridge can be removed and a new inserted.

As appears, fig. 1 shows a drug delivery device of the front-loaded type in which a cartridge is inserted through a distal opening in the cartridge holder which in non-removable attached to the main part of the device, however, the drug delivery device may alternatively be of the rear-loaded type and comprise a cartridge holder adapted to be removed from the device main portion and in which a cartridge is received and removed through the proximal opening.

The drug delivery device 100 is provided with sensor means and electronic circuitry adapted to create a log for dose amounts of drug expelled from a cartridge by the drug expelling means, wherein the dose amounts are calculated based on relative movement between sensor parts during setting and/or expelling of a dose of drug. The sensor means may be in the form of a rotary sensor adapted to detect rotational movement between two sensor parts, typically a stationary sensor part and a sensor part which rotates during setting and/or expel- ling of a dose of drug, e.g. as disclosed in WO 2014/128156 which is hereby incorporated by reference.

Before turning to an embodiment of the present invention an example of a spring-driven pen- device comprising a dose logging module arranged in a combined dose setting and release button will be described, the pen device forming a basis for an implementation of aspects of the present invention. The description will primarily focus on the incorporation of a dose logging module and to a lesser degree on the pen mechanism as such.

Fig. 3 shows the proximal portion of a drug delivery device 400 in a dose setting state, the device comprising an inner housing member 420 in which a scale drum 410 is helically guided, a protective outer housing member 425, a piston rod 465, a tubular transmission member 460, a double-wound helical torsion drive spring 459 arranged between the housing and the transmission member, a carrier member 450 with outer splines 451 , a ratchet member 470 with inner splines 471 , a ratchet release member ("lifter") 480, a combined dose setting and release member (dose button) 430, and a dose button return spring 439. The shown embodiment also comprises a trigger member 440 and a trigger spring 449 which are described in greater detail in WO 2017/009102 which is hereby incorporated by reference, however, these components are not relevant in the context of the present invention. In the interior of the dose button 430 a logging module 490 is arranged, the module comprising a folded flexible printed circuit board (PCB) 498 on which are mounted or formed a distal- ly facing disc-formed sensor portion 491 , an electric cell 492, electronic circuitry 493, and a display 494. The module components are mounted in a module inner housing structure 499 which is arranged non-rotationally in the dose button 430 thus serving as a module outer housing. A transparent window 495 forms the proximal end surface of the dose button. A proximally-facing switch disc 455 is non-rotationally attached to the carrier member 450 (see fig. 4) by e.g. heat stalking as shown, the disc comprising a pair of long-travel mode switch arms 456, a pair of EoD switch arms 457, and a number of encoder switch arms 458 each having a switch point "dimple" 454 adapted to cooperate with corresponding contact structures on the disc-formed sensor portion 491. The latter two structures 458, 491 together form a rotary sensor assembly whereas the additional switch structures 456, 457 are specific for the embodiment of a switch disc shown in figs. 3 and 4. In alternative embodiments the additional switch functionality may not be necessary or it may be incorporated in other structures of the drug delivery device.

The carrier member 450 is mounted axially and rotationally locked to the tubular transmission member 460 and in releasable splined 451 , 471 engagement with the ratchet member 470, which is in splined rotationally locked engagement with a circumferential array of dose button splines 431. A uni-directional ratchet interface is provided between the ratchet member 470 and the housing member 420, however, the ratchet release member 480 provides that the ratchet member can be lifted out of engagement with the housing whereby a set dose can be reduced incrementally. As is relevant for the below-described embodiment of fig. 5, the ratchet release member 480 rotates together with the dose button 430 via splines but is axially fixed relative to the housing. The entire ratchet arrangement is described in greater detail in WO 2016/135237 which is hereby incorporated by reference.

The drive spring 459 is coupled between the housing and the transmission member at its ends, the dose button return spring 439 is supported between the dose button 430 and the ratchet member 470, and the scale drum is rotationally coupled to the transmission member at the distal end (not shown).

When setting a dose the dose button 430 is rotated clock-wise whereby the thereto coupled ratchet member 470, carrier member 450, transmission member 460 and the scale drum rotate therewith, this straining the drive spring 459. Due to the ratchet interface between the ratchet member 470 and the housing member 420 the rotated components are held in the set position. As the dose button 430 and the carrier member 450 rotate together no relative rotational movement takes place between the switch disc and the contact disc.

When a dose has been set and the dose button 430 is actuated, the dose button, the carrier member 450 and the drive spring is moved distally. During the initial axial movement the dose button splines 431 engage an outer array of housing splines 421 whereby the dose but- ton is rotationally locked to the housing. At the same time the mode switch arms 456 engage the proximal end of the ratchet member to thereby switch the mode switch in its actuated (closed) mode, i.e. indicating an out-dosing state. At the distal end of the expelling mechanism (not shown) a drive clutch provides that the transmission member 460 is rotationally coupled to a piston rod driver. When the dose button is moved further distally the carrier member 450 disengages the ratchet member, this allowing the strained spring to rotate the transmission member 460 counter-clock-wise, the transmission member thereby transmitting the rotational force of the drive spring whereby the piston rod driver causes the piston rod 465 to rotate and move distally to expel drug. As the carrier member 450 rotates with the transmission member the rotary sensor detects rotational movement corresponding to the dose amount being expelled. At the same time the scale drum 410 is rotated helically back towards its initial zero position. In the shown embodiment, when the scale drum reaches the zero position an EoD switch is actuated, this indicating to the logging circuitry that a set dose has been fully expelled, the dose size corresponding to the detected rotational movement between the carrier member and the dose button.

When pressure on the dose button is released the return spring 439 returns the dose button to its initial proximal position, whereby the EoD switch re-opens, the carrier member 450 reengages the ratchet member splines 471 , the drive clutch disengages, the mode switch re- opens and the dose button disengages the housing member.

Having described the general working principle of a "generic" drug delivery device in which a logging module with a rotary sensor assembly is incorporated, an exemplary embodiment of a switch arrangement for a rotary sensor assembly in accordance with aspects of the present invention will be described.

Fig. 5 shows a logging module 590 similar to the logging module 490 of fig. 3 in combination with a stationary mode switch member 510 to form a switch assembly. Also shown in fig. 5 are a ratchet release member 580 with outer splines 581 for a dose button, and a ratchet member 570 with inner splines 571 , these components generally corresponding to the ratchet release member 480 and ratchet member 470 of the above-described embodiment.

The mode switch member 510 comprises a mounting portion 51 1 mounted on the ratchet release member and thus rotating together with the dose button (not shown) but being axially non-moveable relative to the housing (not shown). The mode switch member further comprises a pair of flexible switch arms 512, 513 extending proximally and having a free end adapted to be in sliding engagement with corresponding contact areas on the logging module as the latter is moved axially between its proximal-most and distal-most positions, one switch arm being a ground switch arm 512 and the other being a state switch arm 513. As also described above the logging module comprises a housing structure (not shown) in which a folded flexible PCB 598 with mounted or thereon formed components is arranged. In fig. 5 a disc-formed rotary sensor portion 591 , an electric cell 592 and a proximally-facing switch disc 555 can be seen. The switch disc engages the disc-formed rotary sensor portion 591 and is non-rotationally attached to a carrier member (not shown) rotating with a trans- mission member during an expelling event, this as described above. Corresponding to a laterally facing portion of the folded PCB a switch contact array 532 for the module electronic circuitry is arranged. The switch array comprises a ground contact area 533, a distal dial state switch segment 534, an intermediate secure state switch segment 535, and a proximal dose state switch segment 536. A gap is provided between the dial state and intermediate state switch segments, as well as between the intermediate state and dose state switch segments.

The ground switch arm 512 is permanently in contact with the ground contact area 533, whereas the state switch arm is in contact with the dial state switch segment 534 when the dose button (and thus the logging module) is in a proximal dose setting position, in contact with the secure state switch segment 535 when the dose button is in an intermediate position having engaged the housing to become rotationally locked (but is not in a dose release position), and in contact with the dose state switch segment 536 when the dose button is in a distal dose expelling position.

The above-described gaps between the switch segments ensure that the switch is positively either in a dial state, in a secure state or in a dose state.

By the described switch arrangement the rotational position of the rotary sensor can be pre- cisely determined both before and after a dose expelling event and thus rotational movement has taken place. The secure state provides that the sensor system has sufficient time to determine a well-defined, rotationally locked position both when the expelling system is activated and de-activated. A detailed description of the fig. 5 switch assembly in the form of a self-contained logging module assembly incorporated in a spring-driven drug delivery device can be found in EP application 16201777.6 which is hereby incorporated by reference. Every mechanical system is manufactured with given tolerances for each component and thus for the combined system. In the present case the axial length and position of the individual switch segments are calculated such that when the switch is in the secure state the dose button (and thus the logging module) will, given that all components are within their respective tolerances, be rotationally locked and the expelling system will be in a non-dosing state. This relationship between the switch state and the axial position of the different release- and locking structures will be described in greater detail with reference to fig. 6.

Figs. 6A-6F illustrate, corresponding to six different positions of the dose button during an actuation stroke, how the different coupling systems engage and disengage in relation to the position of the state switch as defined by the "axial state" of the state switch. In the shown embodiment each coupling system comprises pointed spline structures which engage and dis-engage as the dose button is actuated. In the following the couplings are denoted "dose button coupling", "ratchet coupling" and "clutch coupling". The figures are drafted to primarily show the axial relationship between the different components during actuation of the dose button. More specifically, each fig. 6 shows a system 600 comprising a dose button 630 with splines 631 , a mode switch member 610, a housing (or a member axially locked to the housing) 620 with splines 621 , a ratchet member 670 with splines 671 , a transmission member 660 with proximal splines 651 and distal splines 666, and a clutch member 665 with splines 667. Corresponding to the above-described fig. 5 embodiment the mode switch member 610 is axially stationary relative to the housing 620 and comprises a ground switch arm 612 and a state switch arm 613. The switch contact array 632 moves with the dose button 630 and comprises a ground contact area 633, a distal dial state switch segment 634, an intermediate secure state switch segment 635, and a proximal dose state switch segment 636. As appears, the dose button coupling is formed by cooperating splines 621 , 631 , the ratchet coupling is formed by cooperating splines 651 , 671 and the clutch coupling is formed by cooperating splines 666, 667. The proximal-most position of the dose button is represented by a bold reference line 601 . Figs. 6A-6F also illustrate how the switch arrangement is designed and dimensioned to correctly detect the actual state also for "worst case" tolerance scenarios. For that purpose the switch arms are shown as "long" in figs. 6A and 6B to illustrate the proximal-most position of the switch arm contact points relative to the dose button, and as "short" in figs. 6C-6F to illustrate the distal-most position of the switch arm contact points relative to the dose button. In position A the system is in the dialling state with the dose button 630 in the proximal-most position, with the ratchet coupling 651 , 671 fully engaged, the dose button coupling 621 , 631 and the clutch coupling 666, 667 fully disengaged, and the state switch arm 613 fully positioned on the dial state switch segment 634. In position B the dose button 630 has been moved distally to a position in which the dose button coupling 621 , 631 is beginning to engage. The shown position corresponds, given the tolerances of the system, to the latest possible secure lock between the dose button and the housing as well as the earliest allowed contact between the state switch arm 613 and the secure state switch segment 635.

In position C the dose button has been moved further distally to a position representing the latest possible beginning engagement of the clutch coupling 666, 667, the state switch arm 613 being positioned in contact with the secure state switch segment 635 also in its "short" form (see above).

In position D the dose button has been moved further distally to a position representing the earliest possible start of dis-engagement of the ratchet coupling 651 , 671 , the state switch arm 613 just leaving the secure state switch segment 635. In position E the dose button has been moved further distally to a position representing an "intermediate" dis-engagement of the ratchet coupling, the state switch arm 613 just entering the dose state switch segment 636.

In position F the dose button has been moved fully to the distal-most position in which the ratchet coupling 651 , 671 has been fully dis-engaged with the state switch arm 613 being positioned fully on the dose state switch segment 636.

When the user releases the dose button the above-described sequence is reversed with the difference that "at the latest" becomes "at the earliest" and vice versa. As appears, the above-described arrangement addresses how to correctly and reliably detect the rotational start and end positions of the rotary sensor for an expelling event. However, most drug delivery devices of the above-described general type will have a rotational indicator being able to rotate more than 360 degrees. To correctly determine the expelled size sensor system will have to either count increments during expelling or be designed to detect rotational positions during expelling. An example of a suitable arrangement for that purpose is described in greater detail in EP2016/082513 which is hereby incorporated by reference.

In the above description of exemplary embodiments, the different structures and means providing the described functionality for the different components have been described to a degree to which the concept of the present invention will be apparent to the skilled reader. The detailed construction and specification for the different components are considered the object of a normal design procedure performed by the skilled person along the lines set out in the present specification.