Patent ID: 12239826

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 term “assembly” does not imply that the described components necessarily can be assembled to provide a unitary or functional assembly during a given assembly procedure but is merely used to describe components grouped together as being functionally more closely related.

Before turning to embodiments of the present invention per se, an example of a prefilled drug delivery will be described, such a device providing the basis for the exemplary embodiments of the present invention. Although the pen-formed drug delivery device100shown inFIGS.1-3may represent a “generic” drug delivery device, the actually shown device is a FlexTouch® prefilled drug delivery pen as manufactured and sold by Novo Nordisk A/S, Bagsværd, Denmark.

The pen device100comprises a cap part107and a main part having a proximal body or drive assembly portion with a housing101in which a drug expelling mechanism is arranged or integrated, and a distal cartridge holder portion in which a drug-filled transparent cartridge113with a distal needle-penetrable septum is arranged and retained in place by a non-removable cartridge holder attached to the proximal portion, the cartridge holder having openings allowing a portion of the cartridge to be inspected as well as distal coupling means115allowing a needle assembly to be releasably mounted. The cartridge is provided with a piston driven by a piston rod forming part of the expelling mechanism and may for example contain an insulin, GLP-1 or growth hormone formulation. A proximal-most rotatable dose setting member180with a number of axially oriented grooves182serves to manually set a desired dose of drug shown in display window102and which can then be expelled when the button190is actuated. As will be apparent from the below description, the shown axially oriented grooves182may be termed “drive grooves”. The dose setting member180has a generally cylindrical outer surface181(i.e. the dose setting member may be slightly tapered) which in the shown embodiment is textured by comprising a plurality of axially oriented fine grooves to improve finger grip during dose setting. The window is in the form of an opening in the housing surrounded by a chamfered edge portion109and a dose pointer109P, the window allowing a portion of a helically rotatable indicator member170(scale drum) to be observed. Depending on the type of expelling mechanism embodied in the drug delivery device, the expelling mechanism may comprise a spring as in the shown embodiment 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 member and the actuation button moves proximally during dose setting corresponding to the set dose size, and then is moved distally by the user to expel the set dose, e.g. as in a FlexPen® manufactured and sold by Novo Nordisk A/S.

AlthoughFIG.1shows a drug delivery device of the prefilled type, i.e. it is supplied with a premounted cartridge and is to be discarded when the cartridge has been emptied, in alternative embodiments the drug delivery device may be designed to allow a loaded cartridge to be replaced, e.g. in the form of a “rear-loaded” drug delivery device in which the cartridge holder is adapted to be removed from the device main portion, or alternatively in the form of a “front-loaded” device in which a cartridge is inserted through a distal opening in the cartridge holder which is non-removable attached to the main part of the device.

As the invention relates to electronic circuitry adapted to interact with a drug delivery device, an exemplary embodiment of such a device will be described for better understanding of the invention.

FIG.2shows an exploded view of the pen-formed drug delivery device100shown inFIG.1. More specifically, the pen comprises a tubular housing101with a window opening102and onto which a cartridge holder110is fixedly mounted, a drug-filled cartridge113being arranged in the cartridge holder. The cartridge holder is provided with distal coupling means115allowing a needle assembly116to be releasable mounted, proximal coupling means in the form of two opposed protrusions111allowing a cap107to be releasable mounted covering the cartridge holder and a mounted needle assembly, as well as a protrusion112preventing the pen from rolling on e.g. a table top. In the housing distal end a nut element125is fixedly mounted, the nut element comprising a central threaded bore126, and in the housing proximal end a spring base member108with a central opening is fixedly mounted. A drive system comprises a threaded piston rod120having two opposed longitudinal grooves and being received in the nut element threaded bore, a ring-formed piston rod drive element130rotationally arranged in the housing, and a ring-formed clutch element140which is in rotational engagement with the drive element (see below), the engagement allowing axial movement of the clutch element.

The clutch element is provided with outer spline elements141adapted to engage corresponding splines104(seeFIG.3B) on the housing inner surface, this allowing the clutch element to be moved between a rotationally locked proximal position, in which the splines are in engagement, and a rotationally free distal position in which the splines are out of engagement. As just mentioned, in both positions the clutch element is rotationally locked to the drive element. The drive element comprises a central bore with two opposed protrusions131in engagement with the grooves on the piston rod whereby rotation of the drive element results in rotation and thereby distal axial movement of the piston rod due to the threaded engagement between the piston rod and the nut element. The drive element further comprises a pair of opposed circumferentially extending flexible ratchet arms135adapted to engage corresponding ratchet teeth105arranged on the housing inner surface. The drive element and the clutch element comprise cooperating coupling structures rotationally locking them together but allowing the clutch element to be moved axially, this allowing the clutch element to be moved axially to its distal position in which it is allowed to rotate, thereby transmitting rotational movement from the dial system (see below) to the drive system. The interaction between the clutch element, the drive element and the housing will be shown and described in greater detail with reference toFIGS.3A and3B.

On the piston rod an end-of-content (EOC) member128is threadedly mounted and on the distal end a washer127is rotationally mounted. The EOC member comprises a pair of opposed radial projections129for engagement with the reset tube (see below).

The dial system comprises a ratchet tube150, a reset tube160, a scale drum170with an outer helically arranged pattern forming a row of dose indicia, a user-operated dial member180for setting a dose of drug to be expelled, a release button190and a torque drive spring155(seeFIG.3). The dial member is provided with a circumferential inner teeth structure181engaging a number of corresponding outer teeth161arranged on the reset tube, this providing a dial coupling which is in an engaged state when the reset tube is in a proximal position during dose setting and in a disengaged state when the reset tube is moved distally during expelling of a dose. The reset tube is mounted axially locked inside the ratchet tube but is allowed to rotate a few degrees (see below). The reset tube comprises on its inner surface two opposed longitudinal grooves169adapted to engage the radial projections129of the EOC member, whereby the EOC can be rotated by the reset tube but is allowed to move axially. The clutch element is mounted axially locked on the outer distal end portion of the ratchet tube150, this providing that the ratchet tube can be moved axially in and out of rotational engagement with the housing via the clutch element. The dial member180is mounted axially locked but rotationally free on the housing proximal end, the dial ring being under normal operation rotationally locked to the reset tube (see below), whereby rotation of the dial ring results in a corresponding rotation of the reset tube160and thereby the ratchet tube. The release button190is axially locked to the reset tube but is free to rotate. A return spring195provides a proximally directed force on the button and the thereto mounted reset tube. The scale drum170is arranged in the circumferential space between the ratchet tube and the housing, the drum being rotationally locked to the ratchet tube via cooperating longitudinal splines151,171and being in rotational threaded engagement with the inner surface of the housing via cooperating thread structures103,173, whereby the row of numerals passes the window opening102in the housing when the drum is rotated relative to the housing by the ratchet tube. The torque spring is arranged in the circumferential space between the ratchet tube and the reset tube and is at its proximal end secured to the spring base member108and at its distal end to the ratchet tube, whereby the spring is strained when the ratchet tube is rotated relative to the housing by rotation of the dial member. A ratchet mechanism with a flexible ratchet arm152is provided between the ratchet tube and the clutch element, the latter being provided with an inner circumferential teeth structures142, each tooth providing a ratchet stop such that the ratchet tube is held in the position to which it is rotated by a user via the reset tube when a dose is set. In order to allow a set dose to be reduced a ratchet release mechanism162is provided on the reset tube and acting on the ratchet tube, this allowing a set dose to be reduced by one or more ratchet increments by turning the dial member in the opposite direction, the release mechanism being actuated when the reset tube is rotated the above-described few degrees relative to the ratchet tube.

Having described the different components of the expelling mechanism and their functional relationship, operation of the mechanism will be described next with reference mainly toFIGS.3A and3B.

The pen mechanism can be considered as two interacting systems, a dose system and a dial system, this as described above. During dose setting the dial mechanism rotates and the torsion spring is loaded. The dose mechanism is locked to the housing and cannot move. When the push button is pushed down, the dose mechanism is released from the housing and due to the engagement to the dial system the torsion spring will now rotate back the dial system to the starting point and rotate the dose system along with it.

The central part of the dose mechanism is the piston rod120, the actual displacement of the piston being performed by the piston rod. During dose delivery, the piston rod is rotated by the drive element130and due to the threaded interaction with the nut element125which is fixed to the housing, the piston rod moves forward in the distal direction. Between the rubber piston and the piston rod, the piston washer127is placed which serves as an axial bearing for the rotating piston rod and evens out the pressure on the rubber piston. As the piston rod has a non-circular cross section where the piston rod drive element engages with the piston rod, the drive element is locked rotationally to the piston rod, but free to move along the piston rod axis. Consequently, rotation of the drive element results in a linear forwards movement of the piston. The drive element is provided with small ratchet arms134which prevent the drive element from rotating clockwise (seen from the push button end). Due to the engagement with the drive element, the piston rod can thus only move forwards. During dose delivery, the drive element rotates anti-clockwise and the ratchet arms135provide the user with small clicks due to the engagement with the ratchet teeth105, e.g. one click per unit of insulin expelled.

Turning to the dial system, the dose is set and reset by turning the dial member180. When turning the dial, the reset tube160, the EOC member128, the ratchet tube150and the scale drum170all turn with it due to the dial coupling being in the engaged state. As the ratchet tube is connected to the distal end of the torque drive spring155, the spring is loaded. During dose setting, the arm152of the ratchet performs a dial click for each unit dialed due to the interaction with the inner teeth structure142of the clutch element. In the shown embodiment the clutch element is provided with 24 ratchet stops providing 24 clicks (increments) for a full 360 degrees rotation relative to the housing. The spring is preloaded during assembly which enables the mechanism to deliver both small and large doses within an acceptable speed interval. As the scale drum is rotationally engaged with the ratchet tube, but movable in the axial direction and the scale drum is in threaded engagement with the housing, the scale drum will move in a helical pattern when the dial system is turned, the number corresponding to the set dose being shown in the housing window102.

The ratchet152,142between the ratchet tube and the clutch element140prevents the spring from turning back the parts. During resetting, the reset tube moves the ratchet arm152, thereby releasing the ratchet click by click, one click corresponding to one unit IU of insulin in the described embodiment. More specifically, when the dial member is turned clockwise, the reset tube simply rotates the ratchet tube allowing the arm of the ratchet to freely interact with the teeth structures142in the clutch element. When the dial member is turned counter-clockwise, the reset tube interacts directly with the ratchet click arm forcing the click arm towards the centre of the pen away from the teeth in the clutch, thus allowing the click arm on the ratchet to move “one click” backwards due to torque caused by the loaded spring.

To deliver a set dose, the push button190is pushed in the distal direction by the user as shown inFIG.3B. The dial coupling161,181disengages and the reset tube160decouples from the dial member and subsequently the clutch element140disengages the housing splines104. Now the dial mechanism returns to “zero” together with the drive element130, this leading to a dose of drug being expelled. It is possible to stop and start a dose at any time by releasing or pushing the push button at any time during drug delivery. A dose of less than 5 IU normally cannot be paused, since the rubber piston is compressed very quickly leading to a compression of the rubber piston and subsequently delivery of insulin when the piston returns to the original dimensions.

The EOC feature prevents the user from setting a larger dose than left in the cartridge. The EOC member128is rotationally locked to the reset tube, which makes the EOC member rotate during dose setting, resetting and dose delivery, during which it can be moved axially back and forth following the thread of the piston rod. When it reaches the proximal end of the piston rod a stop is provided, this preventing all the connected parts, including the dial member, from being rotated further in the dose setting direction, i.e. the now set dose corresponds to the remaining drug content in the cartridge.

The scale drum170is provided with a distal stop surface174adapted to engage a corresponding stop surface on the housing inner surface, this providing a maximum dose stop for the scale drum preventing all the connected parts, including the dial member, from being rotated further in the dose setting direction. In the shown embodiment the maximum dose is set to 80 IU. Correspondingly, the scale drum is provided with a proximal stop surface adapted to engage a corresponding stop surface on the spring base member, this preventing all the connected parts, including the dial member, from being rotated further in the dose expelling direction, thereby providing a “zero” stop for the entire expelling mechanism.

To prevent accidental over-dosage in case something should fail in the dialing mechanism allowing the scale drum to move beyond its zero-position, the EOC member serves to provide a security system. More specifically, in an initial state with a full cartridge the EOC member is positioned in a distal-most axial position in contact with the drive element. After a given dose has been expelled the EOC member will again be positioned in contact with the drive element. Correspondingly, the EOC member will lock against the drive element in case the mechanism tries to deliver a dose beyond the zero-position. Due to tolerances and flexibility of the different parts of the mechanism the EOC will travel a short distance allowing a small “over dose” of drug to be expelled, e.g. 3-5 IU of insulin.

The expelling mechanism further comprises an end-of-dose (EOD) click feature providing a distinct feedback at the end of an expelled dose informing the user that the full amount of drug has been expelled. More specifically, the EOD function is made by the interaction between the spring base and the scale drum. When the scale drum returns to zero, a small click arm106on the spring base is forced backwards by the progressing scale drum. Just before “zero” the arm is released and the arm hits a countersunk surface on the scale drum.

The shown mechanism is further provided with a torque limiter in order to protect the mechanism from overload applied by the user via the dial member. This feature is provided by the interface between the dial member and the reset tube which as described above are rotationally locked to each other. More specifically, the dial member is provided with circumferential inner teeth structure181engaging a number of corresponding outer teeth161, the latter being arranged on a flexible carrier portion of the reset tube. The reset tube teeth are designed to transmit a torque of a given specified maximum size, e.g. 150-300 Nmm, above which the flexible carrier portion and the teeth will bend inwards and make the dial member turn without rotating the rest of the dial mechanism. Thus, the mechanism inside the pen cannot be stressed at a higher load than the torque limiter transmits through the teeth.

Having described the working principles of a mechanical drug delivery device, embodiments of the present invention will be described.

FIGS.4A and4Bshow a schematic representation of a first assembly of a pre-filled pen-formed drug delivery device200and a therefor adapted add-on dose logging device300. The add-on device is adapted to be mounted on the proximal end portion of the pen device housing and is provided with dose setting and dose release means380covering the corresponding means on the pen device in a mounted state as shown inFIG.4B. In the shown embodiment the add-on device comprises a coupling portion385adapted to be mounted axially and rotationally locked on the drug delivery housing. The add-on device comprises a rotatable dose setting member380which during dose setting is directly or indirectly coupled to the pen dose setting member280such that rotational movement of the add-on dose setting member in either direction is transferred to the pen dose setting member. In order to reduce influences from the outside during dose expelling and dose size determination, the outer add-on dose setting member380may be rotationally decoupled from the pen dose setting member280during dose expelling as will be described in greater detail with reference to theFIG.5embodiment. The add-on device further comprises a dose release member390which can be moved distally to thereby actuate the pen release member290. As will be described in greater detail below with reference toFIG.5the add-on dose setting member gripped and rotated by the user may be attached directly to the pen housing in rotational engagement therewith.

Alternatively, the shown configuration may be adapted to serve primarily as an aid for people with impaired dexterity to set and release a dose of drug and thus dispense with any dose sensing and dose logging functionality. For such a configuration it is less important that the outer add-on dose setting member is rotationally decoupled from the pen dose setting member280during expelling of a dose. Correspondingly, the outer add-on dose setting member may be in permanent rotational engagement with the pen dose setting member280.

Turning toFIG.5a first exemplary embodiment of an add-on dose logging device400adapted to be mounted on a pen-formed drug delivery device100will be described in greater detail. The drug delivery device essentially corresponds to the drug delivery device described with reference toFIGS.1-3and thus comprises a housing101, a rotatable dose setting member180allowing a user to set a dose amount of drug to be expelled, a release member190actuatable between a proximal dose setting position and a distal dose release position, a scale drum170as well as a reset tube160. In order to cooperate with the add-on logging device the drug delivery device has been modified to comprise a generally ring-formed tracer magnet160M attached to or formed integrally with the reset tube proximal end, the magnet serving as an indicator rotating during expelling of a dose amount, the amount of rotational movement being indicative of the size of the expelled dose amount. Further, the housing has been provided with a circumferential groove101G just distally of the dose setting member serving as a coupling means for the add-on device.

The add-on device comprises an outer assembly410releasably attachable to the drug delivery device housing as well as an inner assembly480. The inner and outer assemblies are rotationally locked to each other during dose setting, but rotationally de-coupled from each other during dose expelling. The shown embodiment is based on an experimental prototype for which reason some of the structures are formed from a number of assembled parts.

The outer assembly410comprises a generally cylindrical housing member411defining a general axis for the add-on device and serving as an add-on dose setting member, distally arranged coupling means415adapted to engage the coupling groove101G of the pen housing, and a proximally arranged dose release member490coupled to the housing member411and axially moveable between an initial proximal position and an actuated distal position. In the shown embodiment the coupling means415is in the form of a number of spring-biased coupling members adapted to be releasable received in the housing groove101G by snap action when the add-on device is slid over the proximal end of the drug delivery device100, the coupling means thereby axially locking the add-on device to the pen device. The coupling means may be released by e.g. a pulling action or by actuation of a release mechanism. The housing comprises in the proximal portion an inner circumferential flange412and a number of axially oriented guide grooves413. The dose release member490comprises a number of peripherally arranged axially oriented flanges493received in the guide grooves413, the grooves providing a proximal stop against which the dose release member is biased by a first return spring418supported between the housing flange412and the dose release member490. The dose release member comprises an inner cylindrical skirt portion492with a distal inner flange portion494, the inner flange portion comprising a distal circumferential lip495and a proximal array of axially oriented locking splines496.

The inner assembly480comprises an inner housing481and a therein arranged axially moveable sensor system in the form of a sensor module460. The inner housing comprises a proximal wall portion482from which a hollow transmission tube483extends proximally, an inner circumferential flange portion484serving as support for a second biasing spring468, and a distally extending circumferential skirt portion487provided with a number of axially oriented inner projections adapted to be received in the pen dose setting member drive grooves182(seeFIG.1A) to thereby rotationally lock the two members to each other, the engagement allowing some axial play during mounting and operation of the add-on device. Alternatively, the skirt portion487may be provided with radially inwardly biased drive structures of the type described below. The hollow tube483comprises at the proximal end a disc-formed portion having a distally facing stop surface adapted to engage the circumferential lip495and a circumferential array of axially oriented splines486adapted to engage the locking splines496on the dose release member490to thereby rotationally lock the inner assembly to the dose release member and thus the outer assembly.

The sensor module460comprises a sensor portion and a proximally extending actuation rod portion462. The sensor portion comprises a generally cylindrical sensor housing461in which the electronic circuitry465is arranged (shown schematically inFIG.5). The sensor housing comprises a distal actuation surface adapted to engage the pen actuation member190. In the initial dose setting mode (i.e. with the dose release member490in the initial proximal position) the sensor housing is biased proximally by the second bias spring468into engagement with the inner housing proximal wall portion482and with the actuation rod462extending from the transmission tube483into the interior of the dose release member490, an axial gap being formed between the proximal end463of the actuation rod and an inner actuation surface of the dose release member.

The electronic circuitry465comprises electronic components including processors means, one or more sensors, one or more switches, wireless transmitter/receiver means and an energy source. The sensors comprise one or more magnetometers adapted to measure a magnetic field generated by the pen tracer magnet160M, this allowing rotational movement of the pen reset tube and thus the size of an expelled dose to be determined, see e.g. WO 2014/161952. Further sensor means may be provided allowing the type of the device to be recognized, e.g. a light emitter and a colour sensor adapted to determine the colour of the pen release member, the colour serving as an identifier for the drug type contained in the prefilled pen device. The processor means may be in the form of a generic microprocessor or an ASIC, non-volatile program memory such as a ROM providing storage for embedded program code, writable memory such as flash memory and/or RAM for data, and a controller for the transmitter/receiver.

In a situation of use with the add-on device400mounted on the pen drug delivery device100as shown inFIG.5, the user starts setting a desired dose by rotating the housing member411(i.e. the add-on dose setting member) and with that also the dose release member490. During dose setting the dose release member is biased towards its initial proximal position whereby it is rotationally locked to the inner assembly480via the locking splines486,496, this allowing the rotational movement of the add-on dose setting member to be transferred to the inner housing461and thus the pen dose setting member180.

When a dose has been set the user will actuate the dose release member490by moving it distally against the force of the first bias spring418. During the initial release movement the locking splines486,496will disengage, this rotationally de-coupling the inner assembly480from the dose release member and thus from the add-on dose setting housing member411. During the further release movement the dose release member490engages the actuation rod proximal end463whereby the sensor module460during the further release movement will be moved distally towards the pen dose release member190and subsequently into contact with the pen release member. The engaging surfaces of the actuation rod462and the add-on dose release member490are optimized for minimal transfer of rotational movement. Finally, further distal movement of the add-on release member490will result in actuation of the pen release member190and thereby expelling of the set dose, the sensor module460thereby serving as an actuator.

In order to determine the size of an expelled dose the amount of rotation of the tracer magnet160M and thus the reset tube160is determined. More specifically, initial movement of the sensor module will activate a sensor switch (not shown) which in turn will activate the sensor electronics465and start sampling of data from the magnetometers, this allowing a rotational start position of the tracer magnet160M to be determined prior to release of the expelling mechanism. During this period also the colour of the pen release member and thus the type of drug contained in the cartridge may be determined. As the reset tube may rotate more than 360 degrees during expelling of a dose of drug, rotational movement during expelling will be detected and the number of full rotations (if any) determined. When it is detected that rotation of the reset tube has stopped, e.g. when a set dose has been fully expelled or when out-dosing is paused by the user, a rotational end position will be determined, this allowing the size of an expelled dose to be determined. Alternatively, the rotational end position may be determined when the sensor switch detects that the sensor module460has returned to its initial position.

As appears, due to the rotational un-coupling of the inner assembly460from the outer assembly480during drug expelling, it is prevented to a high degree that movements of the outer parts of the add-on device will negatively influence the precise determination of rotational movement and rotational positions of the reset tube160.

The determined dose size (or data on basis of which a dose size can subsequently be calculated) will be stored together with a time stamp and, if detected, a drug type identifier in a log memory. The content of the log memory may then be transmitted by NFC, Bluetooth® or other wireless means to an external device, e.g. a smartphone, which has been paired with the add-on logging device. An example of a suitable pairing process is described in EP application 17178059.6 which is hereby incorporated by reference.

Turning toFIG.6a second exemplary embodiment of an add-on dose logging device700adapted to be mounted on a pen-formed drug delivery device600will be described in greater detail. The drug delivery device essentially corresponds to the drug delivery devices described with reference toFIGS.1-3and thus comprises a housing601, a rotatable dose setting member680allowing a user to set a dose amount of drug to be expelled, a release member690actuatable between a proximal dose setting position and a distal dose release position, a scale drum670as well as a reset tube660. In order to cooperate with the add-on logging device700the drug delivery device has been modified to comprise a generally ring-formed magnet660M attached to or formed integrally with the reset tube proximal end, the magnet serving as an indicator rotating during expelling of a dose amount, the amount of rotational movement being indicative of the size of the expelled dose amount. Further, the housing proximal portion602has been provided with a number of protuberances601P just distally of the dose setting member serving as a coupling means for the add-on device. In the shown embodiment three coupling protrusions are located equidistantly on the housing.

The add-on device700comprises an outer assembly710releasably attachable to the drug delivery device housing as well as an inner assembly (see below). The outer assembly710comprises a generally cylindrical distal coupling portion719(as in the embodiment ofFIG.4A) defining a general axis for the add-on device, the coupling portion having a generally cylindrical bore702adapted to receive a corresponding generally cylindrical coupling portion of the drug delivery pen and being adapted to be mounted axially and rotationally locked on the drug delivery housing by means of a number of bayonet coupling structures715adapted to engage the corresponding coupling protuberances601P on the pen housing and releasably snap into engagement. The add-on device further comprises a proximal dose setting member711mounted freely rotatable on the coupling portion and which like in the embodiment ofFIG.5is coupled to the pen dose setting member680such that rotational movement of the add-on dose setting member711in either direction is transferred to the pen dose setting member. The add-on device further comprises a dose release member790which during dose setting rotates with the dose setting member. A first biasing spring718supported on an inner circumferential flange712on the dose setting member provides a proximally directed biasing force on the dose release member. As in the embodiment ofFIG.5the inner and outer assemblies are rotationally locked to each other during dose setting, but rotationally de-coupled from each other during dose expelling.

The inner assembly780generally corresponds to the inner assembly480of theFIG.5embodiments and thus generally comprises the same structures providing the same functionality. Correspondingly, the inner assembly comprises (seeFIG.7A) an inner housing781and a therein arranged axially moveable sensor module760. The inner housing comprises a proximal wall portion782from which a hollow transmission tube structure783extends proximally, a distal inner circumferential flange portion784serving as support for a second biasing spring768, and a distally extending circumferential skirt portion787adapted to engage the pen dose setting member drive grooves682(seeFIG.6) to thereby rotationally lock the two members to each other, the engagement allowing some axial play during mounting and operation of the add-on device. In the shown embodiment the structures engaging the dose setting member drive grooves682are in the form of flexible fingers751allowing for ease of mounting as will be described in greater detail below. The fingers may as shown be mounted to the skirt portion787, e.g. formed as part of a sheet metal member, or they may be formed integrally with the skirt portion. The hollow tube783comprises at the proximal end a number of flange portions788having distally facing stop surfaces adapted to engage a circumferential inner flange795of the dose release member790, as well as a number of axially oriented splines adapted to engage the locking splines796on the dose release member790to thereby rotationally lock the inner assembly to the dose release member and thus the outer assembly.

The sensor module760comprises a sensor portion and a proximally extending actuation rod portion762. The sensor portion comprises a generally cylindrical sensor housing761in which the electronic circuitry765(see below) is arranged. The sensor housing comprises a distal spacer cap764covering the magnet sensors and being adapted to engage the pen actuation member690. In the initial dose setting mode (i.e. with the dose release member790in the initial proximal position) the sensor housing is biased proximally by the second bias spring768into engagement with the inner housing proximal wall portion782and with the actuation rod762extending from the transmission tube783into the interior of the dose release member790, an axial gap being formed between the proximal end763of the actuation rod and an inner actuation surface of the dose release member.

The electronic circuitry765comprises electronic components including processor means, sensors, an activation switch, e.g. a dome switch actuated by an axial force exerted on the actuation rod portion762, wireless transmitter/receiver means and an energy source. More specifically, in the shown embodiment the electronic circuitry765comprises a layered construction comprising, from the distal end, a first PCB766A on which a number of sensor components, e.g. magnetometers766M, are arranged, a pair of battery connector discs766B for a pair of coin cells, a second PCB766C on which the majority of the electronic components are mounted (e.g. processor, transmitter/receiver and memory), and an upper disc766D with a slot allowing the actuation rod portion762to contact and actuate a PCB mounted activation switch766S, the five members being interconnected by flexible ribbon connectors.

The sensors comprise a number of magnetometers adapted to measure a magnetic field generated by the pen magnet660M, this allowing rotational movement of the pen reset tube and thus the size of an expelled dose to be determined, see e.g. WO 2014/0161952. Further sensor means may be provided allowing the type of the device to be recognized, e.g. a light emitter and a colour sensor adapted to determine the colour of the pen release member, the colour serving as an identifier for the drug type contained in the prefilled pen device. The colour sensor and light emitter may operate with visible (to the human eye) light or light fully or partly outside the visible spectrum. The processor means may be in the form of a generic microprocessor or an ASIC, non-volatile program memory such as a ROM providing storage for embedded program code, writable memory such as flash memory and/or RAM for data, and a controller for the transmitter/receiver.

In a situation of use with the add-on device700mounted on the pen drug delivery device600, the user starts setting a desired dose by rotating the dose setting member711(i.e. the add-on dose setting member) and with that also the dose release member790. During dose setting the dose release member is biased towards its initial proximal position whereby it is rotationally locked to the inner assembly780via the locking splines786,796, this allowing the rotational movement of the add-on dose setting member to be transferred to the inner housing761and thus the pen dose setting member680.

When a dose has been set the user will actuate the dose release member790by moving it distally against the force of the first bias spring718. During the initial release movement the locking splines786,796will disengage, this rotationally de-coupling the inner assembly780with the electronics from the dose release member790and thus from the add-on dose setting member711. During the further release movement the dose release member790engages the actuation rod proximal end763(seeFIG.8A) whereby the sensor module760during the further release movement will be moved distally towards the pen release member690and subsequently into contact with the pen release member (seeFIG.8B). The engaging surfaces of the actuation rod762and the add-on dose release member790are optimized for minimal transfer of rotational movement. Finally, further distal movement of the add-on release member790will result in actuation of the pen release member690(seeFIG.8Cin which the reset tube outer teeth661has been moved distally) and thereby expelling of the set dose (seeFIG.8D), the sensor module760thereby serving as an actuator.

In order to determine the size of an expelled dose the amount of rotation of the magnet660M and thus the reset tube660is determined. More specifically, initial movement of the sensor module will activate a sensor switch which in turn will activate the sensor electronics765and start sampling of data from the magnetometers, this allowing a rotational start position of the magnet660M to be determined prior to release of the expelling mechanism. During this period also the colour of the pen release member and thus the type of drug contained in the cartridge may be determined. As the reset tube660may rotate more than 360 degrees during expelling of a dose of drug, rotational movement during expelling will be detected and the number of full rotations (if any) determined. When it is detected that rotation of the reset tube has stopped, e.g. when a set dose has been fully expelled or when out-dosing is paused by the user, a rotational end position will be determined, this allowing the size of an expelled dose to be determined. Alternatively, the rotational end position may be determined when the sensor switch detects that the sensor module760has returned to its initial position.

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As appears from the above description several events take place during axial movement of the sensor module and subsequently the combined axial movement of the sensor module and the reset tube. The sensor module is first moved away from its initial proximal position. After a relatively short travel the sensor switch will be activated and the sensor electronics turned on, this allowing the sensor system to start measuring values indicative of movement of the reset tube. Subsequently the sensor module is moved into contact with the pen release member from which point the sensor module and the reset tube move together axially. Further axial movement of the pen release member will release the spring-driven expelling mechanism and the reset tube will start rotating (which axial position may be termed an intermediate position). To ensure that the expelling mechanism is safely released the sensor module and reset tube will travel a further distance until the reset tube reaches a distal stop. Thus the reset tube will have started rotating as it travel towards the distal stop at which location the majority of rotational movement of the reset tube will take place. If the user allows the set dose to be fully expelled the reset tube will reach its rotational end position when in its distal-most position. When it has been detected that rotational movement has stopped a rotational end position of the reset tube can be determined. If the user desires to pause the expelling, the user will release pressure on the add-on release member and the reset tube will start moving proximally, however, until the reset tube reaches the intermediate axial position it will continue to rotate.

As initially disclosed, an aspect of the present invention provides that the sensor component (or as in the above-described embodiment the entire sensor module) moves axially together with the indicator (e.g. the reset tube provided with a magnet as in the above-described embodiment) during measuring of movement. Depending on the actual mechanical and electronic design of the system, the two structures may move axially together fully or partly during the measuring of movement. As appears from the above description of an exemplary embodiment, the sensor module moves together with the reset tube during rotation of the reset tube, this providing essentially constant measuring conditions for the sensor system during rotation. To provide corresponding essentially constant conditions for the sensor system when measuring the rotational start and end positions of the reset tube, these positions would have to be measured while the sensor module is in contact with the pen release member and thus moving together therewith. To ensure this the sensor module may be provided with switch or detection means allowing contact between the sensor module and the pen release member. Indeed, the initial rotational position of the reset tube would have to be determined before the expelling mechanism is released and the reset tube starts to rotate. Alternatively, the sensor module may be designed to measure the initial rotational position of the reset tube before the sensor module engages the pen release member. Although this would result in slightly different conditions for the sensor system when measuring the rotational start and end positions of the reset tube, such a set-up would provide more time for the rotational start position to be properly determined before the reset tube starts to rotate.

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As appears, due to the rotational un-coupling of the inner assembly760from the outer assembly780during drug expelling, it is prevented to a high degree that movements of the outer parts of the add-on device will negatively influence the precise determination of rotational movement and rotational positions of the reset tube660.

Turning toFIG.9a third exemplary embodiment of an add-on dose logging device900adapted to be mounted on a pen-formed drug delivery device800will be described in greater detail. The slightly modified drug delivery pen device800will be described with reference toFIGS.10A and10B.

The add-on dose logging device900essentially corresponds to the add-on dose logging device600described with reference toFIGS.6-8and thus comprises an outer assembly releasably attachable to the drug delivery device housing, an inner assembly with a sensor module as well as a release member assembly. In contrast to the above described embodiments, the exploded view ofFIG.9shows the individual components from which the assemblies are formed.

The outer assembly is formed by a distal housing coupling portion901, a thereto attachable proximal housing portion919, an add-on dose setting member911adapted to be mounted freely rotatable on the proximal housing portion, and a locking ring916adapted to be mounted in the dose setting member to enclose the release member assembly. A locking assembly comprises a release slider908, a catch member905, a bias spring906as well as a pair of return coil springs909for the slider, the locking assembly components being adapted to be mounted in the housing coupling portion901.

More specifically, the distal housing coupling portion901comprises a cylindrical bore902adapted to receive a corresponding cylindrical coupling portion of the drug delivery pen device in a snug fit (see below). The bore is provided with a distally facing and axially oriented groove adapted to receive a pen housing locking protuberance805when the add-on device is axially mounted on the pen device. The proximal portion of the distal housing coupling portion tapers outwardly to a larger diameter and comprises a plurality of longitudinal ribs907each having a proximally facing end surface, the end surfaces serving as a distal stop for the inner assembly. The coupling portion901is adapted to cover the pen device display window when mounted and thus comprises a window opening904allowing the display window and thus the scale drum to be observed. Opposite the window opening a second opening903is provided adapted to receive the locking assembly components. The catch member905is pivotably mounted in the second opening and biased inwards by bias spring906, this allowing the catch member to snap in place distally of the pen housing locking protuberance805when the add-on device is axially mounted on the pen device. As the locking means is arranged opposite the window opening904it is assured that the user can easily orient the add-on device rotationally during mounting. The release slider908is slidingly mounted in the second opening and biased in the distal direction by the return springs909. When the user moves the release slider proximally this lifts the catch member905out of engagement with the housing locking protuberance805allowing the add-on device to be moved proximally and thus to be removed from the pen device. The proximal housing portion919is fixedly attached to the coupling portion901by e.g. welding, adhesive or snap means, and comprises a circumferential ridge917allowing the dose setting member911to be mounted freely rotatable by snap action. The dose setting member comprises a circumferential inner flange912which in an assembled state serves as a proximal stop for the inner assembly and a distal stop for the release member return spring918, as well as a number of axially extending inner flanges forming a number of guide tracks913for the release member assembly. The locking ring916is adapted to be mounted axially fixed in the dose setting member by e.g. welding, adhesive or snap means as shown to thereby seal the gap between the dose setting member911and the cap member998.

The inner assembly comprises a generally cylindrical inner housing member981, a cylindrical locking member950adapted to be mounted on the inner housing member, and a proximal wall or lid member982adapted to be attached to the inner housing member to enclose the therein mounted sensor module. The wall member comprises a proximally extending tube portion983adapted to receive a proximal flange member988.

More specifically, the inner housing member981comprises a larger diameter distal skirt portion987with a number of openings989, a smaller diameter proximal portion with a number of axially extending wall sections985forming a number of guide tracks for the sensor module. The transition between the two portions forms an outer circumferential distal support984for a sensor spring968(see below). In the shown embodiment the cylindrical locking member950is formed from a single piece of sheet metal wherein is formed a first plurality of axially extending flexible dial locking arms951each having a proximal free end portion extending radially inwards, and a second plurality of axially extending flexible mounting arms955each having a proximal free end portion extending radially inwards. The mounting arms serve to snap into engagement with corresponding mounting openings989when the locking member is mounted on the inner housing member981, this axially and rotationally locking the two members. The dial locking arms951distal ends are inwardly rounded and adapted to engage the pen dose setting member drive grooves882(see below). The proximal wall member982is adapted to be fixedly attached to the inner housing flanges by e.g. welding, adhesive or snap means and serves in an assembled state as a proximal stop for the sensor module. The proximally extending tube portion983comprises at the proximal end a pair of opposed radial extensions each comprising a plurality of axially oriented locking splines986adapted to engage corresponding splines on the release member in an assembled state. The proximal flange member988is adapted to be fixedly attached to the tube portion983by e.g. welding, adhesive or snap means as shown. The flange member comprises a central bore with a diameter smaller than the distal larger diameter end of the actuation rod962(see below), this providing a proximal stop for the actuation rod.

The sensor module960comprises a generally cylindrical sensor housing961in which electronic circuitry965with distally facing sensor components966M (seeFIG.12B) is mounted, a spacer cap964adapted to be mounted on the sensor module housing distal end to cover and enclose the sensor components, as well as an actuation rod962adapted to be arranged in the wall member tube portion983. A sensor module return spring968is adapted to be arranged between the inner housing member981and the sensor housing961to provide a proximally directed biasing force on the sensor module.

More specifically, the spacer cap964is adapted to be fixedly attached to the sensor housing by e.g. welding, adhesive or snap means and serves in an assembled state to protect the sensor components and as a distally facing contact surface adapted to engage the pen device release member890(seeFIG.13A). The sensor housing comprises a number of radially protruding distal and proximal guide flanges967adapted to be received non-rotationally but axially free in the inner housing member guide tracks. The distal guide flanges also provide a proximal stop surface for the sensor spring968. A distal stop for the sensor module is provided by the inner housing corresponding to the distal end of the guide tracks and/or the compressed sensor spring. The actuation rod962comprises a larger diameter distal portion allowing the rod to be freely received in the tube portion983and a smaller diameter proximal portion adapted to protrude through the bore in the flange member988. The actuation rod comprises a rounded proximal end963, the engaging surfaces of the actuation rod and the cap member998being optimized for minimal transfer of rotational movement. The sensor module comprises a proximally facing centrally arranged actuation switch966, e.g. a dome switch, adapted to be actuated by the actuation rod.

The release member assembly comprises a body member990and a thereon mountable cap member998. A release member return spring918is adapted to be arranged between the dose setting member flange912and the release body member990to provide a proximally directed biasing force on the release body member.

More specifically, the release body member990comprises a distal ring portion994with an inner circumferential array of axially oriented splines996adapted to engage the locking splines986on the tube portion983in an assembled state, as well as a number of radially protruding guide flanges993adapted to be received non-rotationally but axially free in the dose setting member guide tracks913. The cap member998is adapted to be axially fixedly attached to the body member by e.g. welding, adhesive or snap means995as shown. In an assembled state flange member988serves as a proximal stop for the release body member990and the release member return spring918acts on the ring portion distal surface.

Turning toFIGS.10A and10Bthe proximal portion of a slightly modified pen drug delivery device800is shown in combination with the parts of the add-on device inner assembly providing rotational engagement between the add-on device and the pen dose setting member.

More specifically, the pen housing801generally corresponds to the embodiment ofFIG.6, however, instead of a slightly tapered housing the proximal coupling portion802of the housing including the window809has a “true” cylindrical form adapted to be received in the cylindrical bore of the add-on device. Alternatively, both structures may have a light taper. Further, the coupling means is in the form of a single locking protuberance805adapted to cooperate with the catch member905for easy axial mounting. Also shown is the dose setting member880having a generally cylindrical outer surface881(i.e. the dose setting member may be slightly tapered) which in the shown embodiment is textured by comprising a plurality of axially oriented fine grooves to improve finger grip during dose setting, as well as a number of axially oriented drive grooves882corresponding to the embodiment ofFIG.6.

As described above with reference toFIGS.9A and9Bthe inner assembly comprises a housing member981with a distal skirt portion987having a number of openings989, as well as a cylindrical locking member950mounted thereon, the locking member comprising a number of flexible dial locking arms951and a number of flexible mounting arms (the latter not being shown inFIGS.10A and10B).

InFIG.10Athe inner housing981is shown in its axially mounted position (as determined by non-shown parts of the add-on device). Whereas the outer add-on housing901is mounted in a rotationally pre-determined position, this is not the case for the inner housing assembly which in an un-mounted state is allowed to freely rotate relative to the outer housing, this providing that the inner housing and thus the locking arms951are mounted in a “random” rotational position such that the locking arms are not rotationally in register with the dose setting member drive grooves882. Additionally, although the dose setting member880has an initial “parked” rotational “zero” position corresponding to no dose having been set, it may have been set in a random position. Additionally, even when parked in the zero position slack in the dose setting mechanism may result in slight variations in the rotational position of the dose setting member drive grooves.

Thus, when the add-on device is mounted on the pen device the flexible dial locking arms951may be out of rotational register with the dose setting member drive grooves882. However, due to the dial locking arms being flexible they will be moved outwards by the dose setting member and axially slide on the outer circumference of the dose setting member in parallel with the drive grooves, this as shown inFIG.10A. As the resistance provided by the flexible locking arms is small the user will in most cases not notice what has happened during mounting of the add-on device and will not be aware of the fact that the add-on device has not yet rotationally engaged the pen device dose setting member. In the shown embodiment the free end of the locking arms951are oriented proximally, however, alternatively they may be oriented distally with the free end of the locking arms and the proximal edge of the pen device dose setting member880configured to move the locking arms outwards during mounting of the add-on device.

Subsequently, when the user desires to set a dose, the user will start rotate the add-on device dose setting member911and thereby the inner housing with the locking arms951which then will be rotated into register with the dose setting member drive grooves882and thus be allowed to flex inwardly to rotationally engage the drive grooves, this as shown inFIG.10B. To assure that the locking arms will easily engage the drive grooves they are formed slightly narrower than the drive grooves. Further movement of the add-on device dose setting member911will then cause the pen device dose setting member to rotate correspondingly, this allowing the user to set and adjust a dose as normally. Indeed, in a number of cases the locking arms will be moved directly into the drive grooves.

The number and the mechanical properties of the locking arms951should be dimensioned to allow for safe and robust operation of the add-on device. To assure this the combined assembly, i.e. the pen device and the add-on device may comprise an over-torque mechanism in case the user tries to dial below zero or above the maximum settable dose amount. For the add-on device an over-torque mechanism may be incorporated in the spline engagement between inner housing assembly and the add-on dose setting member, however, in most cases such a mechanism for the add-on device can be dispensed with, as pen devices in general will be provided with an over-torque protection mechanism, e.g. as know from the FlexTouch® drug delivery pen. Indeed, the locking arms951and the dose setting member drive grooves882should be designed and dimensioned to withstand torque above the limit for the pen device over-torque mechanism.

FIGS.11A and11Bshows in cross-sectional views when the locking arms951have engaged the outer circumference of the pen device dose setting member880respectively have engaged the pen device dose setting member drive grooves882.

Turning toFIGS.12A and12Bthe components ofFIG.9Aare shown in an assembled state corresponding to an initial non-mounted and non-actuated state.

More specifically,FIG.12Ashows the sensor module960arranged inside the inner assembly and being biased towards its proximal-most position by the sensor spring968acting between the inner housing spring support984and the sensor housing distal guide flanges967. A dial locking arm951can be seen protruding into the interior of the inner housing skirt portion987.

The release body member990is biased towards its proximal-most position by the release member return spring918acting between the dose setting member inner flange912and the ring portion994of the release body member. The actuation rod962is arranged inside the inner housing tube portion983and axially held in place by the flange member988, an axial gap being formed between the actuation rod proximal end963and the distal surface of the cap member998. The inner housing and the release member assembly are rotationally locked to each other via the splined engagement between the tube portion983and the release body member990(cannot be seen inFIG.12A).

With reference toFIGS.13A-13Fdifferent operational states of the third exemplary embodiment of an add-on dose logging device900in combination with a pen-formed drug delivery device800will be described. The shown pen device is in the form of a FlexTouch® prefilled drug delivery device from Novo Nordisk A/S.

FIG.13Ashows the add-on dose logging device900prior to being mounted on the pen-formed drug delivery device800. As described above the drug delivery device comprises a proximal coupling portion802having a “true” cylindrical form adapted to be received in the cylindrical bore of the add-on device, a window809, a locking protuberance805adapted to cooperate with the add-on device catch member905, a dose setting member880having a generally cylindrical outer surface881with a number of axially oriented drive grooves882, and a proximally arranged release member890. The add-on device900comprises a cylindrical bore902adapted to receive the cylindrical coupling portion802of the pen device, a catch member905adapted to engage locking protuberance805, and a window opening904arranged to be mounted in register with the pen device window809, a dose setting member911and a dose release member998. Projecting into the bore902a dial locking arm951can be seen. Corresponding toFIG.12Athe add-on device is in its initial non-mounted and non-actuated state.

InFIG.13Bthe add-on device900has been mounted on the pen device800, with the catch member905seated distally of the locking protuberance805and the two windows904,809in alignment. Corresponding to the situation shown inFIG.10Athe dial locking arms951have not yet engaged the drive grooves882.

InFIG.13Cthe add-on dose setting member911and thereby the inner assembly has been rotated, the dial locking arms951have engaged the drive grooves882, and a dose has been set.

InFIG.13Dthe add-on dose release member998has been partly actuated to just engage the actuation rod rounded proximal end963, in which state the inner circumferential array of axially oriented splines996on the release body member990has disengaged the locking splines986on the tube portion983, this rotationally decoupling the dose setting member911from the inner assembly and thus the sensor module960. Further distal movement of the add-on dose release member will998start move the actuation rod962distally which initially will result in the proximally facing centrally arranged actuation switch966(seeFIG.9) being actuated by the actuation rod, this turning the sensor module into its operational state.

InFIG.13Ethe add-on dose release member998has been further actuated to just move the sensor module spacer cap964into engagement with the pen device release member890.

InFIG.13Fthe add-on dose release member998has been fully actuated and the sensor module and thereby the pen device release member890have been moved to their distal-most operational positions, this releasing the expelling mechanism whereby the set dose of drug is expelled through a hollow needle mounted on the drug-filled cartridge. Determination of the expelled dose size may take place as described above with reference toFIGS.8A-8D. When the set dose has been expelled the user may release pressure on the add-on dose release member998and the components will return to their initial axial positions due to the return springs968,918.

As appears, the axial movements performed by the sensor module and the reset tube relative to each other are the same for the embodiment described with reference toFIGS.13A-13Fas the embodiment described with reference toFIGS.8A-8D, for which reason the same considerations apply in respect of the sensor module moving axially together, fully or partly, with the reset tube during measuring of movement.

Having described the mechanical concept and working principle of the add-on dose logging devices ofFIGS.5,7A and12A, the sensor and tracer system per se will be described in greater detail. Basically, the sensor and tracer system comprises a moving magnetic tracer component and a sensor system comprising one or more magnetometers, e.g. 3D compass sensors.

In an exemplary embodiment the magnetic tracer component is in the form of a multi-pole magnet having four poles, i.e. a quadrupole magnet. InFIG.14four dipole standard magnets661have been arranged equidistantly in a ring-formed tracer component660M, the four separate dipole magnets providing a combined quadrupole magnet with the four poles offset by 90 degrees. Indeed, each of the dipole magnets are formed by a very large number of individual magnetic particles oriented in the same direction. The individual magnets may be arranged in the same plane or may be axially offset from each other.

Alternatively, a multi-pole magnet660M can be created by magnetization of a magnetisable material either by use of individual powerful magnets as shown inFIG.15A, or through use of electromagnetic fields as shown inFIG.15B.

A given sensor system may be using e.g. 4, 5, 6 or 8 magnetometers766M arranged relative to a tracer component660M as illustrated inFIG.16. The sensors may be arranged in the same plane, e.g. as shown inFIG.7B, or they may be axially offset from each other. The more sensors, the smaller spacing between the sensors and thus more data with a better signal-to-noise ratio can be gathered. However, the more sensors, the more data processing is required and the more power is consumed.

In some cases, not only disturbances from external fields need to be handled. The torque-providing spring for driving the dose expelling motor in the disposable device as described above may be magnetized when subjected to an external magnetic field and thus provide an internal disturbing magnetic field.

Where external disturbances may be cancelled out to a large extent by signal processing algorithms, because they influence all the sensors more or less equally and in the same direction, a magnetized torque spring will influence the sensors much like the tracer magnet and therefore be more likely to offset the measurements and cause errors.

However, as it can be seen fromFIGS.17A and17Bthe use of a quadrupole tracer magnet instead of a dipole tracer magnet, significantly reduce the error in determining the position of the tracer magnet.

More specifically,FIGS.17A and17Bshow simulations of the influence of a magnetized torque spring at four different levels of magnetization (TS1-TS4) for both dose-setting (DS) and outdosing (D).FIG.17Aillustrates the calculated angle measuring error (i.e. the difference between the calculated angle and the true angle) for a dipole tracer magnet in combination with a 4 sensors set-up, andFIG.17Billustrates the calculated angle measuring error for a quadrupole tracer magnet in combination with an 8 sensors set-up. Due to the sensors being closer to the tracer magnet during out-dosing (see e.g.FIGS.8A and8C) the angle error is slightly smaller during out-dosing. This said, in the above-described embodiment sensor measurements take place only during out-dosing. For the quadrupole tracer magnet 8 sensors were used as the smaller circumferential spacing between the individual poles in the quadrupole tracer magnet provides a higher input rate to the sensor system which can be more precisely captured by 8 instead of 4 sensors, however, comparable results would be expected for a quadrupole tracer magnet in combination with a 4 sensors set-up. As appears, use of a quadrupole tracer magnet reduces the angle error from ca. 4-8 degrees to ca. 0.5-1 degrees, roughly a factor of 8.

In the shown FlexTouch® drug delivery device the reset tube660and thus the tracer magnet660M rotates 15 degrees for each unit of insulin expelled. Thus, a possible angle error in the 4-8 degrees range may result in an incorrect determination of the expelled dose amount.

The quadrupole tracer magnet is thus not only reducing the systems sensitivity to disturbances from external fields, but also from internal fields. This is an important aspect of using a multipole tracer magnet, since traditional magnetic shielding of external sources by use of an iron-containing metallic sheet may be used to reduce the influence of external fields, but may not be possible to fit between the tracer magnet and an internal disturbing magnetic field. Further, incorporating a magnetic shield would take up space and introduce additional costs.

Alternatively, this may be mitigated by using a spring of a non-magnetisable material, however, current spring-driven pens on the market today comprise a magnetisable torque spring and replacement may not be feasible due to other requirements of the spring.

Having described the structural set-up for a sensor assembly incorporating a rotating quadrupole tracer magnet, in the following an exemplary method of determining actual movements for such an assembly will be described.

The signal from the quadrupole magnet is periodic with a period two over one full revolution of the magnet. This can be seen fromFIG.18where the tangential, radial and axial field level is pictured.

Mapping the frequency components of the signal, it is seen that all most the entire signal from the magnet fits into the frequency two signal, seeFIG.19.

To determine a dose size utilizing at the quadrupole field, it is necessary to determine the static start and end angle of the quadrupole magnet. Since the magnet is static before and after the dose has been delivered, the field is sampled over space instead of sampled over time. In an exemplary embodiment a measurement system is configured with N=7 sensors with circular layout and equal spacing, seeFIG.20showing sensor766M placements relative to the quadrupole magnet660M.

In order to determine the orientation or the magnet, a discrete Fourier transform (DFT) is computed on the field measured in the sensors

B^j⁢n=2N⁢∑k=1N⁢Bj⁢k⁢exp⁡(-2⁢π⁢i⁢k⁢n/N).

Here Bjkis the field in the j′th channel of the k′th sensor, j=1 is tangential field, j=2 is radial, and j=3 is axial, i=√{square root over (−1)} is the imaginary unit, and {circumflex over (B)}jnis the n′th frequency component of the signal in the j′th channel.

As described above, the signal from the quadrupole magnet is a period n=2 signal, and therefore we can determine the orientation of the magnet relative to the sensor board by looking at the phase of {circumflex over (B)}j2,
φj=atan 2[Im({circumflex over (B)}j2), Re({circumflex over (B)}j2)]/2.

Because the samples of sines and cosines at different frequencies are orthogonal, any disturbance to the signal that is, e.g., period n=0, 1 or 3, will be filtered out by the Fourier transform.

This relates to both external as internal disturbances. An internal component in an auto-dose pen-injector is the metal torsion spring to drive the dosing mechanism. In the case of this being magnetized, the spring field will primarily look like a period 1 signal at the sensors position. External disturbances like a dipole magnet in the vicinity of the sensors will also tend to have a signal with period 0 or 1. Using the DFT, it is possible to filter out the disturbances from other frequencies and only determining the magnet orientation from the frequency 2 signal.

The combination of a quadrupole magnet and the DFT is therefore superior compared to a dipole magnet whose period 1 signal is similar to the frequency of common disturbances.

Using a DFT based algorithm gives a larger freedom to choose an arbitrary number of sensors, compared to a lookup based algorithm. The chosen number of sensors is preferably at least 5 due to the Nyquist sampling theorem. Besides that the number of sensors can be freely and actively used in order to filter out specific frequencies of the signal to prevent aliasing effects.

With reference to the above-described exemplary embodiments it has been described that initial movement of the sensor module will activate a sensor switch which in turn will activate the sensor electronics and start sampling of data from the magnetometers, this allowing a rotational start position of the magnet to be determined prior to release of the expelling mechanism. When it is detected that rotation of the reset tube has stopped, e.g. when a set dose has been fully expelled or when out-dosing is paused by the user, a rotational end position will be determined, this allowing the size of an expelled dose to be determined. Alternatively, the rotational end position may be determined when the sensor switch detects that the sensor module has returned to its initial position.

The sampling frequency should be chosen to reliably detect rotational movement and to be as power-efficient as possible. However, analysis of rotational speeds during out-dosing in a spring-driven device has shown that the rotational speed of the reset tube is not constant. Especially, it has been found that the rotational speed of the reset tube may be very high in the beginning of the expelling event. Two reasons for the high rotational speed have been identified. A first reason is that the cartridge rubber piston is in an uncompressed state before the out-dosing starts. When the energy in the drive spring is suddenly released, the rubber piston starts being compressed before it starts to move distally in the cartridge. When enough pressure is build up in the cartridge, the piston starts moving and the cartridge content starts to flow out of the needle. The compression of the plunger happens very fast, but is slowed down as it is being compressed.

A further reason is when there exists an air gap between the piston rod and the cartridge piston. This may occur e.g. if the user leaves a needle on the drug delivery device after use or it may be due to cycling temperatures. Since there is no reaction force from the rubber piston, the expelling mechanism rotates very fast until the piston rod hits the piston after which the above-described compression of the piston starts.

When detecting rotation of a component in order to estimate the expelled dose volume, it is important to accurately count all rotations. If not, this can lead to a smaller dose being estimated, which could cause the user to take another dose and have a severe overdose.

If one uses an active sensor to sample the position of the component, e.g. by measuring the change in magnetic field, the high rotational speed requires a high sampling frequency in order to see all rotations. However, using a high sampling frequency can be very power consuming and can collect large amounts of data that needs to be stored. This can lead to high power use and running out of memory issues. This is especially an issue for memory devices provided with a non-replaceable energy source. In contrast, if the frequency is too low, one or more cycles of the signal might go undetected. The two situations are illustrated inFIGS.23A and23Brespectively.

Addressing this issue, a dynamic sampling scheme may be used based on (i) knowledge of system behaviour, and (ii) sensing of actual rotational speed of the measured component. The system can be expected to behave as follows: Staring with a period of fast rotation of the expelling mechanism, followed by a period with normal/moderate rotation speed, and ending in a state with no rotation when a set dose has been fully expelled—or the expelling has been stopped by the user. Thus an adaptive sampling scheme can be implemented that adapts the mode as the rotational speed changes and starting at a high sampling frequency.

Corresponding to the above-described embodiments an exemplary use scenario is illustrated inFIG.24. More specifically, after having set a dose amount of drug to be expelled the user presses the add-on release button and the subsequent axial travel of the sensor module triggers the sensor switch and starts continuous sampling and evaluation of rotational speed with the sampling frequency initially being set to “high”. The sensor module subsequently engages the pen release button and releases the pen expelling mechanism. Due to plunger compression and/or an air gap between piston and the piston rod, the expelling mechanism may initially rotate at a high speed for a shorter or longer period. When the expelling mechanism subsequently slows down it can be detected that the rotational speed is lower than a first threshold (Threshold1), this allowing the sample frequency to be adjusted to “low”. Ultimately, when it is detected that rotation has stopped, i.e. rotational speed is lower than a second threshold (Threshold2), the sampling stops in order to save power. In other embodiments more than two thresholds may be used.

Indeed, other adaptive sampling schemes may be utilized. For example, the sampling frequency may vary continuously with the rotational speed for a predefined range of rotational speeds.

In the above disclosure the issue of both external disturbing magnet fields as well as an internal disturbing magnet field from the pen device torque spring have been addressed by the use of a quadrupole tracer magnet in combination with a sensor array comprising a number of magnetometers. In the following this issue is addressed by a different approach which may be used as an alternative or in addition to the above-described quadrupole design.

Using magnetic shields to shield magnetic systems from outside interference is commonly known and used. Normally shields are used as a barrier to either contain magnetic fields and prevent them from influencing other systems, or as a barrier to contain a system and shield it from being influenced by outside (unshielded) magnetic fields. Internal components of the system, that may introduce disturbing fields, are normally placed outside the shielded volume of the system. Indeed, it may be possible to incorporate a shield in a drug delivery device comprising a drive spring manufactured from a magnetisable material, however, as this may require a major redesign of the pen device this may not be a cost-effective option.

The technical problem to be solved, is thus to provide a magnetic shield preventing/reducing internal magnetic fields from disturbing the measurements of the magnetic sensors in a capturing device or assembly based on magnetometers. Additionally, such a shield may also serve to prevent/reduce the disturbances from “normal” external magnetic fields.

The suggested solution is to introduce a shield of mu-metal, to not only shield the sensor system from external magnetic fields, but also divert any unintended internal magnetic field introduced by the torque spring towards the shield and reduce the disturbance of the field of the tracer magnets. By reducing the strength of the disturbing field from the torque spring it may enable the use of fewer sensors and thus lower signal processing requirements to obtain required accuracy and redundancy, and thereby reduce both costs and power consumption.

Mu-metal is a nickel-iron soft magnetic alloy with very high permeability. It has several compositions, with approximately 80% nickel, 15% a few percent molybdenum and in some compositions a little copper and chromium. Mu-metal is very ductile and workable and can easily be formed into thin sheets needed for magnetic shields. However, mu-metal objects require heat treatment after they are worked into their final form.

Magnetic shields made with mu-metal works by providing a path for the magnetic lines around the shielded area instead of blocking them. The mu-metal sort of offers an “easier” path than thought the air with much lower relative permeability and thus diverts the magnetic field. However, mu-metal has a much lower saturation level and are thus not suitable for shielding against stronger magnetic fields.

FIG.21shows an assembly essentially corresponding to the assembly shown inFIG.8Aalbeit with the drug delivery device torque drive spring655shown, the add-on dose logging device1000being provided with a cylindrical shield1020made of mu-metal covering the axial length of the sensors and tracer magnet volume, as well as the proximal part of the torque drive spring655. The cylindrical mu-metal shield essentially absorbs the magnetic lines from a torque spring having been magnetized and guides them towards the circumferential shield and thereby limits the extent of the disturbing field of the torque spring in axial direction and thus towards the sensors. At the same time the cylindrical shield helps reduce the influence of external magnetic fields EMF on the sensor electronics arranged in the interior of the cylindrical volume.

Although the cylindrical mu-metal shield1020principally will also absorb magnetic lines from the tracer magnet660M, this will influence the measuring performance to a smaller degree as (i) the torque drive spring655is axially arranged farther away from the magnetic sensors1066M than the tracer magnet, and (ii) the torque spring is arranged radially closer to the shield than the tracer magnet. In this way the sensor system will be able to measure the magnetic field from the tracer magnet as only a smaller portion of the field is absorbed by the shield, whereas the above-described geometrical properties will allow a magnetic field from the torque spring to be absorbed by the shield to a high degree and thus influence the sensors to a smaller extent.

FIG.22shows an embodiment of an add-on dose logging device1100in which an outer shield of steel1121, able to handle stronger magnetic fields without saturation, is applied to provide a path for external magnetic fields. An inner shield1122in mu-metal is arranged to provide a path for a relative weak internal magnetic field introduced by the torque spring, without being saturated by a strong external field.

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.