Injection device with machine-readable coding

Abstract

The present invention provides an injection device comprising a housing and a dose expelling mechanism employing a threaded piston rod. The injection device is provided with a first position indicator and a second position indicator for indicating, respectively, a current axial position and a current angular position of the threaded piston rod relative to the housing, and further with an inspection window allowing for simultaneous optical readout of the first position indicator and the second position indicator.

Description

[0001] INJECTION DEVICE WITH MACHINE-READABLE CODING

[0002] FIELD OF THE INVENTION

[0003] The present invention relates generally to medical devices, and more particularly to electronic dose logging for injection devices having a rotatable piston rod.

[0004] BACKGROUND OF THE INVENTION

[0005] Injection devices, such as injection pens, are widely used for self-administration of liquid drugs by people in need of therapeutic treatment. Many injection devices are capable of repeatedly setting and injecting either a fixed or a variable dose of drug upon operation of respective dose setting and dose expelling mechanisms in the device. Some injection devices are adapted to be loaded with a prefilled drug reservoir containing a volume of drug which is sufficient to provide for a number of injectable doses. When the reservoir is empty, the user replaces it with a new one and the injection device can thus be used again and again. Other injection devices are prefilled when delivered to the user and can only be used until the drug reservoir has been emptied, after which the whole injection device is discarded. The various injection devices typically expel the drug by advancing a piston in the reservoir using a motion- controlled piston rod.

[0006] Within some therapy areas the tendency of a patient to adhere to the prescribed therapy is dependent on the simplicity of the specific treatment regimen. For example, many people with type 2 diabetes are diagnosed with the disease at a relatively high age where they are less prone to accept a treatment that intervenes too much with their normal way of living. Most of these people do not like to be constantly reminded of their disease and, as a consequence, they do not want to be entangled in complex treatment patterns or waste time on learning to operate cumbersome delivery systems. In essence, many are of the opinion that the less manual involvement the better.

[0007] For a person with diabetes, it is important to timely administer one or more glucose regulating agents to maximise the time spent in normoglycemia. In that connection, in order to establish an overview of one’s adherence to a particular treatment regimen, it is significant to keep track of both when such a regulating agent is administered and how much is administered. Accordingly, it is recommended that the person keeps a log of administered dose sizes and times of administration. Previously, the establishment and maintenance of such a log would require manually noting down the data, e.g. on paper or a pc. However, as this would entail frequent active involvement many people neglected the importance of establishing the overview. In recognition of this undesirable situation various solutions have been suggested for automatic capturing of the relevant information from the individual injection devices.

[0008] WO 2013 / 050535 (Novo Nordisk A / S) discloses a reusable add-on unit adapted to be attached to a prefilled injection pen having a rotatable piston rod. A small magnet mounted on the piston rod generates a magnetic field which varies corresponding to the axial and rotational movement of the piston rod. Magnetometers in the add-on unit measure the amplitude of the generated magnetic field in three perpendicular directions, thereby enabling a detection of the position of the piston rod before and after a dose expelling event, the difference therebetween reflecting the expelled dose.

[0009] WO 2018 / 141571 (Novo Nordisk A / S) discloses a prefilled injection pen with a fully integrated sensor unit in the form of a piston washer module arranged between the piston rod of the dose expelling mechanism and the cartridge piston. The sensor unit operates like a rotary encoder and comprises a first sensor part which is rotationally locked with respect to the piston rod and a second sensor part which is rotationally locked with respect to the cartridge piston. The relative angular displacement between the two sensor parts exhibited during a dose expelling event when the piston rod rotates relative to the drug delivery device housing and the cartridge is detected galvanically and translated to an estimate of the size of the administered dose.

[0010] WO 2018 / 078161 (Novo Nordisk A / S) discloses a system of a prefilled injection pen and an add-on module with a camera, adapted to determine the amount of drug expelled from the injection pen by capturing image data from the scale drum.

[0011] While these exemplary solutions provide for automatic logging of dose data, they either require an addition of cost-increasing electronic components to the injection pen or an addition of a size-increasing measurement device which does not naturally form part of the injection pen.

[0012] Avoiding any such additions, CH 717 022 (Ypsomed AG) suggests providing an injection pen with a machine-readable printed code area that is fixed relative to the housing and arranged in such a way that the piston or the piston rod will have a surface that overlaps and covers a portion of the code area at any time. The current axial position of the piston rod relative to the housing can then be determined from the non-covered portion of the code area via a smartphone, or other portable computer, with a code reader or a camera. The use of a smartphone, which many people carry around during the day anyway, instead of a dedicated add-on module, and a printed code area instead of sensor electronics in the injection pen seemingly provides for a simple and cost-efficient system.

[0013] However, for high precision injection systems with small incremental advancements of the piston rod, like for example in a typical insulin injection pen where the insulin is delivered from a 3 ml cartridge and the piston rod only moves the piston 0.15 mm axially for every dispensed dose unit, it would seem practically impossible to obtain a reliable dose capturing, in particular of the smallest expellable doses, because to be able to detect that kind of movement by comparing coverage of a coded area before and after dose dispensing, the user would have to hold the smartphone camera completely still relative to the injection device when taking the picture and in the exact same position relative to the code area as when the last picture was taken. That would entail significant requirements to the user’s dexterity and vision as well as to the processor power in the smartphone.

[0014] SUMMARY OF THE INVENTION

[0015] In the above description, the background art has been framed in a context of diabetes. However, it is noted that the present invention may be relevant to other medical specialties where people benefit from parenteral dose administration by means of injection devices and is thus not limited to administration of insulin or other anti-diabetic agents.

[0016] It is an object of the invention to eliminate or reduce at least one drawback of the prior art, or to provide a useful alternative to prior art solutions.

[0017] In particular, it is an object of the invention to provide an injection device which allows for a precise capturing of dose related data in a simple and cost-efficient manner.

[0018] It is a further object of the invention to provide an injection device or system which allows for a precise capturing of dose related data without requiring an integration of sensor electronics in the injection device or use of a dedicated add-on component that does not naturally form part of the injection device.

[0019] It is an even further object of the invention to provide an injection device or system which allows for a precise capturing of even the smallest dose increments without requiring excessive motor skills of the user. In the disclosure of the present invention, aspects and embodiments will be described which will address one or more of the above objects and / or which will address objects apparent from the following text.

[0020] In one aspect the invention provides a device according to claim 1.

[0021] Hence, an injection device is provided comprising a housing extending along an axis and having an interior nut member, and a dose expelling mechanism comprising a threaded piston rod cooperatively engaged with the interior nut member, the threaded piston rod being advanceable in a distal direction relative to the housing. The cooperative engagement between the threaded piston rod and the interior nut member results in a helical motion of the threaded piston rod relative to the housing.

[0022] The device further comprises cartridge holding means for retaining a drug cartridge in an axially fixed position distally of the interior nut member. The device may either be of the prefilled, disposable type, adapted to expel the contents of a non-replaceable drug cartridge pre-attached to, or pre-inserted in, the cartridge holding means, or of the reusable type adapted to expel the contents of multiple attachable / insertable and replaceable drug cartridges. Regardless of the type of device, a present drug cartridge is fixed axially relative to the housing. The cartridge holding means may form part of the housing, or may be a separate component which is attached, or attachable, to the housing. In case of the former, the cartridge holding means may comprise a sleeve portion of the housing adapted to accommodate the drug cartridge, or reception means in or on the housing adapted to engage with a proximal end portion of the drug cartridge or with a portion of an adaptor device supporting and / or accommodating the drug cartridge.

[0023] Even further, the device comprises a first position indicator adapted to indicate an axial, or translational, position of the threaded piston rod relative to the housing, a second position indicator rotationally fixed to the threaded piston rod and adapted to indicate an angular, or rotational, position of the threaded piston rod relative to the housing, and an inspection window allowing for simultaneous optical readout of the first position indicator and the second position indicator to thereby enable determination of a current angular progression of the threaded piston rod relative to the housing. Hence, the inspection window allows for optical readout therethrough of both the first position indicator and the second position indicator.

[0024] The simultaneous optical readout of the first position indicator and the second position indicator may be performed by a smartphone with a camera, or a code reader, or by another readout device having image capturing, and potentially also image processing, means. In particular, the simultaneous optical readout may be adapted to be performed by an image capturing device taking a single picture.

[0025] In this type of dose expelling mechanism the exact helical motion of the threaded piston rod is determined by the pitch of the thread in the interior nut member, and the current angular progression of the threaded piston rod relative to the housing, which designates the accumulated angular displacement of the threaded piston rod since its pre-use starting position, is accordingly directly convertible to an accumulated axial displacement of the threaded piston rod relative to the housing during use.

[0026] The current angular progression of the threaded piston rod relative to the housing can thus be used to determine the size of a last expelled dose, by comparing the most recent optical readout with the second most recent optical readout, as well as how much has been expelled in total since the very first handling of the device, e.g. by comparing the most recent optical readout with an optical readout of the pre-use starting position of the threaded piston rod.

[0027] Dose related data can thereby be captured without the need for integrated electronics in the injection device or use of an add-on component. The injection device may accordingly be a sensorless injection device, in the sense that it is free from carrying or comprising any type of sensor means adapted to detect or monitor an operation of the dose expelling mechanism.

[0028] The threaded piston rod may be advanceable according to a continuous dosing scale, as is known from infusion pumps, or according to a discrete dosing scale, as is known from variable dose injection pens. In particular, the threaded piston rod may be advanceable according to a discrete dosing scale, where it is only possible for the threaded piston rod to advance an integer number of fixed angular increments, each fixed angular increment corresponding to a predefined dose measure for a given drug in a present drug cartridge. For example, a device adapted to deliver apportioned doses of insulin may be configured to advance the threaded piston rod in angular increments corresponding to 3 III or 1 IU (International Unit).

[0029] The device may further comprise a dose setting mechanism for setting a dose to be delivered from a present drug cartridge by operation of the dose expelling mechanism. The dose setting mechanism may be configured to allow a user to set a dose in fixed increments, which then corresponds to the discrete dosing scale. The determination of the size of the last expelled dose, and how much has been expelled in total, based on simultaneous optical readouts of the first position indicator and the second position indicator, is extremely precise and reliable because of the relatively large incremental movements in the angular dimension, which are much easier to distinguish than those in the axial dimension.

[0030] In fact, the readout of the second position indicator which determines an exact angular position of the threaded piston rod relative to the housing is so precise that the requirements to the resolution of the first position indicator can be lowered. This is because, in practice, the first position indicator is only used to determine how many full revolutions the threaded piston rod has undergone, and since the axial displacement experienced by the piston rod during one full revolution is much higher than an incremental axial displacement, and even an incremental angular displacement, the first position indicator need not be that finely graded.

[0031] All in all, the incremental movement in the angular dimension being the decisive factor for precision also means that it does neither require excessive motor skills, nor sharp sight of the user to perform a useful optical readout.

[0032] The device may further comprise a drug cartridge retained by the cartridge holding means. The drug cartridge may comprise a cylindrical wall portion and may be filled, or substantially filled, with a liquid drug.

[0033] The simultaneous optical readout of the first position indicator and the second position indicator may be performed by a user manually reading two scales (in which case the optical readout is likely rather quasi-simultaneous), or, alternatively, by a camera device capturing an image in which the first position indicator and the second position indicator are both readable by optics.

[0034] The second position indicator may comprise a pattern having a unique visual appearance in the inspection window for each angular position of the threaded piston rod relative to the housing. In particular, the second position indicator may comprise a pattern having a unique visual appearance in the inspection window for each incremental angular position of the threaded piston rod relative to the housing.

[0035] Each possible visual appearance of the pattern in the inspection window can then be correlated with a particular angular position of the piston rod relative to the housing and consequently used as an angular input for the dose determination. The correlation between the possible visual appearances of the pattern in the inspection window and the angular positions of the piston rod relative to the housing may be pre-identified in a readout device, or in another processing device operatively coupled with the readout device.

[0036] In exemplary embodiments of the invention the pattern comprises a circumferentially extending numerical scale. Such will be decipherable by the readout device, but also by a person, allowing for an optical readout by the user also without use of the readout device. In practice, though, the user would then have to subsequently carry out a manual conversion of the readout, or manually enter the readout data into a computing device, to obtain a useful dose determination.

[0037] In other exemplary embodiments of the invention the pattern comprises a circumferentially extending microdot code, or a circumferentially extending matrix code. Such will only be decipherable by the readout device and will thus not risk confusing the user with regard to the dose determination.

[0038] The second position indicator may be arranged directly on the piston rod. Alternatively, the second position indicator may be arranged on a cuff member which is rotationally fixed to the threaded piston rod. This provides for a larger and more presentable surface from which to read the second position indicator in the inspection window.

[0039] The cuff member may comprise an annular exterior surface for carrying the second position indicator, the annular exterior surface having a diameter which is larger than 80% but smaller than 100% of an inner diameter of the cylindrical wall portion of the drug cartridge. The diameter of the annular exterior surface must be smaller than the inner diameter of the cylindrical wall portion of the drug cartridge to allow the cuff member to enter the interior of the drug cartridge during axial advancement of the piston rod without contacting the drug cartridge and thereby creating friction. On the other hand, the larger the diameter of the annular exterior surface, the larger the distance which the second position indicator moves relative to the inspection window during an incremental rotation of the piston rod.

[0040] The second position indicator may be printed or etched or otherwise fixedly arranged on the cuff member.

[0041] The cuff member may be axially fixed to a distal end portion of the threaded piston rod. Thereby, the cuff member carrying the second position indicator will follow both the rotational and the axial movement of the threaded piston rod as the threaded piston rod advances into the drug cartridge. This may be advantageous because a marker for reading the first position indicator will naturally be positioned on either the piston, in which case the first position indicator indicates the axial position of the threaded piston rod indirectly via the axial position of the piston, or the cuff member, and then it will be possible to perform the simultaneous readout of the first position indicator and the second position indicator by focusing on a small area with a single camera.

[0042] In exemplary embodiments of the invention the cuff member comprises a circumferential marker adapted to move with respect to the first position indicator during dose expelling. The circumferential marker enables a reading of the first position indicator regardless of the angular position of the cuff member relative to the inspection window.

[0043] The cuff member may alternatively be axially fixed with respect to the housing and adapted to undergo relative axial displacement with respect to the threaded piston rod, such that the second position indicator remains in the same axial position relative to the housing when the threaded piston rod advances into the drug cartridge. If, for example, the initial position of the cuff member is at the distal end portion of the threaded piston rod, the corresponding axial position of the cuff member relative to the inspection window will then be retained throughout the lifetime of the injection device.

[0044] The first position indicator may comprise an axially extending ruler. Such will be decipherable by the readout device, but also by a person, allowing for an optical readout by the user also without use of the readout device.

[0045] Alternatively, the first position indicator may comprise an axially extending bar code, or an axially extending matrix code. Such codes will only be decipherable by the readout device and will thus not risk confusing the user with regard to the dose determination.

[0046] In a further alternative, the first position indicator may comprise a reference mark and / or an axially extending line having a well-defined length. That would allow e.g. an image processor in a standard 4K digital camera to easily estimate an axial position of the marker for reading the first position indicator along the axially extending line, and / or an axial distance of said marker from the reference mark, using the horizontal or vertical lines in the picture.

[0047] The first position indicator may be arranged on and / or along a portion of the cartridge holding means, or on and / or along a portion of the drug cartridge, whereby it is axially fixed with respect to the housing. Alternatively, the first position indicator may be arranged along a measurement rod which is operatively coupled with the threaded piston rod and configured to extend axially from the housing in concert with the threaded piston rod.

[0048] The inspection window may e.g. be provided as an axially extending slot in the cartridge holding means, as an axially extending slot between edges of a label adhered to a surface portion of the drug cartridge, or as an axially extending slot in a separate longitudinal structure arranged in extension of the housing. Alternatively, the inspection window may e.g. simply comprise a transparent portion of the drug cartridge.

[0049] It is noted that the term "inspection window", in this context, encompasses a single window as well as two or more axially aligned windows, such as, for example, one in the cartridge holding means and one in the housing (e.g. in case the cuff member is axially fixed in the housing). The two or more axially aligned windows need not be perfectly axially aligned, as long as they are arranged so that it is possible to perform a simultaneous optical readout of the first position indicator and the second position indicator.

[0050] The first position indicator may be arranged along an edge, or border, or frame portion, of the inspection window to thereby obtain close proximity to the second position indicator, making it easier to perform the simultaneous optical readout of the two position indicators. In case the inspection window is provided as an axially extending slot between edges of a label adhered to a surface portion of the drug cartridge the first position indicator may be printed on the label. The first position indicator may alternatively be arranged in or on a transparent portion of the drug cartridge.

[0051] The injection device may further comprise a protective cap configured for removable attachment to the housing to cover the cartridge holding means, the protective cap comprising a camera arrangement for capturing one or more images of the inspection window. The camera arrangement may include a battery and one or more flash means or other means for momentarily, or constantly, emitting light onto the inspection window.

[0052] Injection devices are typically provided with a protective cap for attachment to the housing to cover the cartridge holder and / or a present drug cartridge. Such protective cap is primarily for protecting the drug cartridge and the drug therein from mechanical impacts and sunlight. Incorporating a camera arrangement in the hollow of the protective cap provides for an opportunity to perform the simultaneous optical readout of the first position indicator and the second position indicator without the need of a separate readout device like a smartphone or an add-on unit, and since the protective cap, as a typical member of an injection device, is customarily handled by the user, the solution may be implemented without changes to the normal pattern of use.

[0053] The housing and the protective cap may comprise respective guide structures configured for mutual interaction to ensure that the protective cap is attached to the housing in a predetermined attachment position in which the camera arrangement is aligned with the inspection window. This will prevent the user from inadvertently attaching the protective cap in an angular position where the camera arrangement is incapable of performing the simultaneous optical readout of the first position indicator and the second position indicator.

[0054] The device may further comprise a trigger mechanism, e.g. arranged in the protective cap, configured to trigger the camera arrangement to capture an image in response to the protective cap assuming the predetermined attachment position. Thereby, an automatic optical readout of the first position indicator and the second position indicator will be performed when the user re-attaches the protective pen to the housing following an injection action.

[0055] The protective cap may further comprise processor means for processing readout data, storage means for storing readout data, or processed readout data, and / or communication means for relaying readout data, or processed readout data. The communication means may comprise a digital display and / or a wireless communication interface, such as Bluetooth.

[0056] The simultaneous optical readout of the first position indicator and the second position indicator may be processed by image processing means in the readout device used to perform the optical readout, such as the smartphone or the protective cap, or in a separate device operatively coupled to the readout device.

[0057] The injection device may further comprise a machine-readable information tag carrying drug related information, such as e.g. drug type, batch number, expiry date, etc. The machine- readable information tag may be arranged next to the inspection window, i.e. at or along a frame portion of the inspection window, or next to the first position indicator, to allow for a simultaneous optical readout of the first position indicator, the second position indicator, and the information tag. This would enable the image processing means to couple the dose determination directly to the drug type at each simultaneous optical readout. Alternatively, the information tag may be arranged at a distance from the inspection window which requires a separate optical readout. In another aspect the invention provides an injection system comprising an injection device as described above in combination with a readout device comprising image capturing means capable of performing the simultaneous optical readout of the first position indicator and the second position indicator. The image capturing means may comprise a camera device for obtaining an image of the first position indicator and the second position indicator through the inspection window. The readout device may further comprise processing means adapted to process the image obtained and to determine the current angular progression of the threaded piston rod relative to the housing therefrom.

[0058] In particular embodiments of the invention, the readout device is or comprises a smartphone.

[0059] The processing means may comprise an app on the smartphone, configured to determine the current angular progression of the threaded piston rod relative to the housing based on the simultaneous optical readout of the first position indicator and the second position indicator.

[0060] In a further aspect the invention provides a method for capturing dose related data from an injection device as described above, the method comprising: (A) operating a readout device comprising image capturing means and image processing means to perform a simultaneous optical readout of the first position indicator and the second position indicator through the inspection window, and (B) prompting the image processing means to process the simultaneous optical readout of the first position indicator and the second position indicator and thereby determine the current angular progression of the threaded piston rod relative to the housing.

[0061] For the avoidance of any doubt, in the present context the term “injection device” designates an apparatus suitable for injecting fluid media into the body of a subject, e.g. with the aid of an attachable needle device, and the term “drug” designates a medium which is used in the treatment, prevention or diagnosis of a condition, i.e. including a medium having a therapeutic or metabolic effect in the body. Further, the terms "distal" and "proximal" denote positions at, or directions along, a drug delivery device, a drug reservoir, or a needle unit, where "distal" refers to the drug outlet end and "proximal" refers to the end opposite the drug outlet end.

[0062] The term “drug cartridge” is used for the variable volume reservoir containing the drug. A cartridge is usually made from glass but may alternatively be moulded from a suitable polymer. It customarily comprises a mainly cylindrical, hollow body which is sealed at one end by a pierceable membrane and at the opposite end by a slidable stopper or piston, e.g. made at least partially from rubber, and the drug is contained in the space between the pierceable membrane and the slidable stopper.

[0063] In the present specification, reference to a certain aspect or a certain embodiment (e.g. "an aspect", "a first aspect", "one embodiment", "an exemplary embodiment", or the like) signifies that a particular feature, structure, or characteristic described in connection with the respective aspect or embodiment is included in, or inherent of, at least that one aspect or embodiment of the invention, but not necessarily in / of all aspects or embodiments of the invention. It is emphasized, however, that any combination of the various features, structures and / or characteristics described in relation to the invention is encompassed by the invention unless expressly stated herein or clearly contradicted by context.

[0064] The use of any and all examples, or exemplary language (e.g., such as, etc.), in the text is intended to merely illuminate the invention and does not pose a limitation on the scope of the same, unless otherwise claimed. Further, no language or wording in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0065] BRIEF DESCRIPTION OF THE DRAWINGS

[0066] In the following the invention will be further described with references to the drawings, wherein

[0067] Fig. 1 is a side view of an injection device illustrating corresponding axial and rotational movements of a threaded piston rod,

[0068] Fig. 2 is a perspective view of a threaded piston rod with a distally arranged cuff member assembly,

[0069] Figs. 3a and 3b are, respectively, a longitudinal section view and a perspective view of a distal end portion of the threaded piston rod,

[0070] Figs. 4-6 are perspective views of a distal end portion of an injection device housing, showing engaged threaded piston rods with respective cuff member assemblies according to three different embodiments of the invention,

[0071] Fig. 7 is a side view of an injection device according to an embodiment of the invention, Fig. 8 is a perspective view of an injection device according to another embodiment of the invention,

[0072] Fig. 9 shows an exemplary way of capturing an image of the injection device of Fig. 8 after an injection, for determination of the injected dose,

[0073] Fig. 10 shows an exemplary way of presenting determined dose related data to a user, and

[0074] Fig. 11 is a partially longitudinally sectioned side view of an injection device according to another embodiment of the invention.

[0075] In the figures like structures are mainly identified by like reference numerals.

[0076] DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0077] When / lf relative expressions, such as "upper" and "lower", "left" and "right", "horizontal" and "vertical", "clockwise" and "counter-clockwise", etc., are used in the following, these refer to the appended figures and not necessarily to an actual situation of use. The shown figures are schematic representations for which reason the configuration of the different structures as well as their relative dimensions are intended to serve illustrative purposes only.

[0078] Fig. 1 is a side view of a conventional insulin injection device (with a slight modification in the form of an added cuff member, cf. below), illustrating an important aspect of the present invention in the context of diabetes management. It is clear, however, that this is merely one exemplary context of the invention.

[0079] The figure shows an automatic injection pen T having a housing 2’ accommodating a spring- powered piston rod advancement mechanism (not visible) and a dose setting mechanism (not visible), operable to set a dose to be injected by turning of a dose dial 3’ relative to the housing 2’. A cartridge holder 15’ accommodating a transparent drug cartridge 10’ is attached to a distal end of the housing 2’. The drug cartridge 10’ is sealed proximally by a slidable piston 12’ and distally by a self-sealing septum (not visible). A pen needle assembly 50’ is attached to the cartridge holder 15’, whereby a rear portion of an injection needle 55’ has penetrated the self-sealing septum and established fluid connection to an interior of the drug cartridge 10’. The cartridge holder 15’ is designed with an elongate inspection window 19’ to allow for inspection of the drug cartridge 10’ along its entire length. The housing 2’ is provided with an interior nut member (not visible) which engages a threaded piston rod 20’. The piston rod 20’ is operatively coupled with the piston 12’ and configured to advance the piston 12’ in the drug cartridge 10’ to expel drug from the drug cartridge 10’ through the injection needle 55’. In the figure, a distal end portion of the piston rod 20’ is covered by a radially enlarged cuff member 40’ having a diameter which is only slightly smaller than the diameter of the drug cartridge 10’. This means that an exterior surface of the cuff member 40’ lies just beneath an interior surface of the drug cartridge 10’ but without contacting said interior surface. The cuff member 40’ is fixed to the piston rod 12’ and thus follows the helical movements thereof.

[0080] The piston rod advancement mechanism is adapted to advance the piston rod 20’ helically with respect to the housing 2’, and the helical movement of the piston rod 20’ is converted to an axial displacement of the piston 12’ in the drug cartridge 10’, which causes drug to be expelled through the injection needle 55’.

[0081] The dose scale (not visible) from which a dose is set by the turning of the dose dial 3’ is discrete, and during dose delivery the piston rod 20’ is advanced according to the set dose. This means that the total movement of the piston rod 20’ during a dose expelling action corresponds to an integer number of increments of the smallest settable dose. An exemplary design of such dose setting and piston rod advancement mechanism is taught in WO 2018 / 078161 , of which the relevant sections are hereby incorporated by reference.

[0082] An injection device based on the principle of advancing a piston by rotating a threaded piston rod in a fixed threading exhibits a dispensing ratio of X° per dose unit, i.e. the piston rod rotates X° about its own axis to cause the injection of the smallest settable dose. In this case, X depends on the concentration of the drug, the inclination (pitch) of the threading, and the inner diameter of the drug cartridge.

[0083] In a conventional injection device with a standard 3 ml drug cartridge and a 11100 insulin, as the one depicted in Fig. 1 , the piston is displaced 0.15 mm axially to expel 1 III, corresponding, in this example, to a rotation of the piston rod 20’ of 15°. The effect of the piston rod rotation is illustrated in the enhanced segment of the drug cartridge 10’ in the inspection window 19’. The segment highlights the visible portions of the piston 12’ and the cuff member 40’ and shows by respective markings 12a’, 40a’ on the piston 12’ and the cuff member 40’ how much each of these components move axially and how much the exterior surface of the cuff member 40’ moves transversally during delivery of one dose unit. It is seen that when the piston marking 12a’ moves an axial distance of a=0.15 mm in the course of the expelling of 1 III, the cuff member marking 40a’ moves a transversal distance of b=1.15 mm, which is the distance the exterior surface of the cuff member 40’ rotates, due to the fixation of the cuff member 40’ to the piston rod 20’, projected onto the plane of vision. The capturable angular displacement of the cuff member 40’ is thus almost eight times larger than the capturable axial displacement of the piston 12’, which is an important factor for the present invention, and a utilisation of this will be exemplified in the below.

[0084] Fig. 2 is a perspective view of a piston rod 20 as used in an injection device according to an embodiment of the invention. The piston rod 20 has an elongate main body with a thread 21 , and an axial track 24 in the thread 21 , extending along its entire length, a proximal end portion 23, and a distal end portion comprising a spearhead 22 (Fig. 3a).

[0085] The distal end portion of the piston rod 20 is covered by a cuff member 40. The cuff member 40 has a proximal cuff body portion 41 , and a distal cuff body portion 42, of larger diameter than the proximal cuff body portion 41. The distal cuff portion 42 is adapted to display a machine-readable coding, which has, however, for the sake of clarity, been omitted from this view. A piston washer 30 is arranged at the distal end of the piston rod 20 for distributing the load from the piston rod 20 to the piston 12.

[0086] Fig. 3a is a side view of a distal portion of the piston rod 20, with a sectioned view of the cuff member 40 and the piston washer 30, showing the engagements between the cuff member 40 and the piston washer 30 and between the piston washer 30 and the piston rod 20. The piston washer 30 has a circular main washer body 31 , fitted in a seat 46 of the cuff member 40, with proximally extending protrusions 32 carrying respective rod hook portions 33 for engagement with the piston rod 20 behind the spearhead 22, and cuff hook portions 34 for engagement with interior flange portions 44 of the cuff member 40. These engagements ensure that both the piston washer 30 and the cuff member 40 are axially fixed to the distal end portion of the piston rod 20.

[0087] Fig. 3b is a perspective proximal view of the distal portion of the piston rod 20, showing a radial protrusion 43 in the proximal cuff portion 41 slidably received in the axial track 24, ensuring a rotational fixation of the cuff member 40 to the piston rod 20. The distal cuff body portion 42 is here provided with a circumferential microdot pattern 80, presenting a machine- readable coding of a first exemplary type, the purpose of which will be clear from the below. It is noted that while the cuff member 40 is rotationally fixed to the piston rod 20, the piston washer 30 is not so restricted. This ensures a minimum waste of energy in the translation of the movement of the piston rod 20 to the piston 12 during dose delivery, since the piston washer 30 is allowed to remain non-rotatable relative to the piston 12, and the only frictional interface is resultantly that between the main washer body 31 and the spearhead 22.

[0088] Fig. 4 is a perspective distal view of the distal portion of the piston rod 20 as arranged in an internal nut member 5 of an injection device housing 2. Fig. 5 is a similar view but showing an alternative exemplary cuff member 140 having a printed numerical scale 180 as coding, and Fig. 6 shows yet another alternative exemplary cuff member 240 provided with an etched-in circumferential matrix code 280.

[0089] Fig. 7 is a side view of an injection device 1 according to an exemplary embodiment of the invention, which in core build and function is similar to the injection device T. Hence, the injection device 1 has a housing 2 which accommodates a spring-powered piston rod advancement mechanism (not visible) and a dose setting mechanism (not visible), operable to set a dose to be injected by turning of a dose dial 3 about a longitudinal centre axis of the housing 2.

[0090] A cartridge holder 15 accommodating a transparent drug cartridge 10 holding a liquid drug is attached to a distal end of the housing 2. The drug cartridge 10 is sealed proximally by a slidable piston 12 and distally by a self-sealing septum (not visible). A pen needle assembly 50 is attached to the cartridge holder 15, whereby a rear portion of an injection needle 55 has penetrated the self-sealing septum and established fluid connection to an interior of the drug cartridge 10. The cartridge holder 15 is designed with an elongate inspection window 19 to allow for inspection of the drug cartridge 10 along its entire length.

[0091] The housing 2 comprises an internal nut member 5 (Fig. 4) threadedly engaged with the piston rod 20. The distal end portion of the piston rod 20 is covered by the cuff member 240, and the cuff member 240 is provided with the circumferential matrix code 280 along an exterior cylindrical surface portion which has a diameter that is only slightly smaller than the diameter of the drug cartridge 10’. This means that the exterior cylindrical surface portion with the circumferential matrix code 280 lies just beneath an interior surface of the drug cartridge 10’ but does not touch said interior surface.

[0092] The cartridge holder 15 is provided with an axial matrix code 70 adjacent to the inspection window 19. Consequently, the axial matrix code 70 and a portion of the circumferential matrix code 280 displayed in the inspection window 19 are simultaneously optically capturable at all times. The piston 12 is provided with a circumferential marker 13 which slides along the cartridge holder 15 when the piston 12 is advanced in the drug cartridge 10 and visibly marks a current position of the piston 12 relative to the axial matrix code 70.

[0093] Fig. 8 is a perspective view of an alternative version of the injection device 1 in which the cartridge holder 15 is provided with a straight axial line 170 instead of the axial matrix code 70. The axial line 170 is arranged adjacent to the inspection window 19 and extends between a proximal reference point 171 and a distal reference point 172. The axial line 170 has a well- defined length between said two reference points 171 , 172. The cuff member 240 is provided with a circumferential marker 245 which moves helically along the cartridge holder 15 when the piston rod 20 rotates in the internal nut member 5 and visibly marks a current position of the cuff member 240 relative to the axial line 170.

[0094] Close to the proximal reference point 171 and adjacent to the axial line 170, a QR-code 90 is applied to the cartridge holder 15. The QR-code 90 contains drug related information such as drug type, batch number, expiry date, etc. In this case, the axial line 170, the proximal reference point 171 , the distal reference point 172, the QR-code 90, and a portion of the circumferential matrix code 280 displayed in the inspection window 19 are simultaneously optically capturable at all times.

[0095] Fig. 9 shows yet another alternative version of the injection device 1 , which is a hybrid of the previous versions in the sense that the cartridge holder 15 comprises the axial line 170 and the two reference points 171 , 172, and the distal end portion of the piston rod 20 is covered by the cuff member 40 with the circumferential microdot pattern 80. Furthermore, instead of a QR-code, the cartridge holder 15 is provided with a barcode 190 adjacent to the inspection window 19. The barcode 190 contains drug related information such as drug type, batch number, expiry date, etc.

[0096] The injection device 1 is in this figure shown without an attached pen needle assembly, instead revealing a needle mount 18 at the distal end of the cartridge holder 15. The needle mount 18 comprises a screw thread and a superposed bayonet track for reception of different types of pen needle assemblies.

[0097] In the below, the invention will be explained primarily on the basis of the embodiment of the injection device 1 shown in Fig. 9. As previously mentioned, an injection device based on the principle of advancing a piston by rotating a threaded piston rod in a fixed threading exhibits a dispensing ratio of X° per dose unit. This means that the injection device is configured to deliver 360 / X dose units per revolution of the piston rod. The inclination of the threading is known for each specific injection device, so the axial component of the piston rod displacement corresponding to delivery of one dose unit is also known.

[0098] The inclination Z of the thread in the interior nut member 5 is 3.6 mm / rev, meaning that for each revolution of the piston rod 20, the axial component of the piston rod displacement is 3.6 mm. Furthermore, the dispensing ratio X is 15° / dose unit which corresponds to an expelling Y of 360 / 15 = 24 dose units / rev, which again corresponds to an axial displacement of the piston rod 20 of 0.15 mm per dose unit expelled.

[0099] There is thus a strict, known, correlation between the rotational progression of the piston rod 20 relative to the housing 2 from a pre-use starting position and the number of dose units that have been expelled from the drug cartridge 10 since the very first dose expelling action. This known correlation is utilized in the present invention to electronically capture the size of the last expelled dose and the accumulated number of units expelled since the first use of the injection device 1 , and to electronically determine the number of units remaining in the drug cartridge 10.

[0100] The way this is done is by performing one or more optical readouts of the inspection window 19, using an electronic device with a camera or code reader, and processing power. One example of such an electronic device is depicted in Fig. 9 in the form of a smartphone 300.

[0101] In Fig. 9 the piston rod 20 has already displaced the piston 12 a significant distance within the drug cartridge 10, so the injection device 1 has been used to deliver at least one dose of the contained drug. Following each dose delivery, the user uses the smartphone 300 to take a picture 301 of the cartridge holder 15, in an orientation in which the inspection window 19, the axial line 170 and the barcode 190 are simultaneously capturable.

[0102] An exemplary result of such an action is shown in fig. 9 in a display 302 of the smartphone 300. The smartphone 300 comprises a dose app, which is capable of reading and processing various pieces of information from the picture 301 . Among these are the current axial position of a circumferential marker 45 on the cuff member 40 relative to the axial line 170, the particular segment of the microdot pattern 80 that is currently visible in the inspection window 19, and the barcode 190.

[0103] Since the injection device 1 is configured to deliver 24 dose units per revolution of the piston rod 20, there are 24 possible positions of the cuff member 40 relative to the cartridge holder 15 per revolution of the piston rod 20, each position resulting in a unique segment of the microdot pattern 80 being visible in the inspection window 19. From the picture 301 the dose app is able to determine the exact angular orientation of the cuff member 40, and hence the piston rod 20, relative to the housing 2.

[0104] With knowledge of the pre-use starting position of the piston rod 20, e.g. obtained from a similar picture taken before the very first dose expelling action, either by the user or by the injection device manufacturer, the dose app then calculates the number of angular increments the piston rod 20 has moved since the first dose expelling. Since the unique segments of the microdot pattern 80 that are visible in the inspection window 19 repeat every time the cuff member 40 has undergone one full revolution, the rotational position determination alone provides no information beyond the first 24 dose units expelled. However, when combined with a reading of the axial position of the circumferential marker 45 relative to the axial line 170, which provides information on the accumulated axial movement of the cuff member 40 since the first dose expelling, and with the knowledge of the inclination Z, which decides how much the piston rod 20 and the cuff member 40 move axially when the piston rod undergoes one full revolution, the dose app can determine an exact accumulated angular progression of the piston rod 20 relative to the housing 2 by adding a rounded down integer number of 360° corresponding to the accumulated axial advancement of the cuff member 40 to the rotational position determination.

[0105] Notably, the axial “scale” does not need to be highly resolved since the axial position of the circumferential marker 45 relative to the axial line 170 is only used to determine how many full revolutions the piston rod 20 has undergone, and the piston rod does move 3.6 mm axially per one full revolution. It is the angular “scale” which provides the high resolution for the dose determination, and since the angular displacement of the cuff member 40 is almost eight times higher than the corresponding axial displacement of the piston rod 20 and the piston 12 when one dose unit is expelled, the requirements to the optical readout system as well as to the motor skills of a user when taking a picture of the cartridge holder 15 are considerably smaller than in a setup where a picture of a single, axial dose scale is used as basis for determining an expelled dose. The above-mentioned comparison of information from the picture 301 with information from a picture taken before the first use of the injection device 1 thus enables a determination of the accumulated number of dose units delivered from the drug cartridge 10. Because the movement of the piston rod 20 is well-known and well-defined, small variations in the fill level of the drug cartridge 10 may be identified immediately from the initial rotational position of the cuff member 40 relative to the housing 2. The dose app may accordingly provide the user with reliable information of the remaining liquid volume in the drug cartridge 10. Furthermore, from the user’s log file of expelled dose data a use pattern may be established and used to provide timely notifications to the user when a new injection device should be acquired.

[0106] The smartphone solution also enables the user to keep track of dose administrations from different injection devices and even from injection devices of different types, as the dose app identifies the specific injection device from the bar-code or QR-code on the device at each optical readout and assigns the individual readings accordingly.

[0107] To determine the size of a last expelled dose from the injection device 1 the dose app compares the last picture taken of the cartridge holder 15 with the second to last picture taken to thereby establish the differences in visual presentation of the microdot pattern 80 in the inspection window 19 and axial position of the circumferential marker 45 relative to the axial line 170, and then processes these differences in a similar manner as described above to obtain a corresponding dose value.

[0108] The dose value, D, is obtained as where R2is the rotational incremental position of the cuff member 40 as identified in the last picture taken, R is the rotational incremental position of the cuff member 40 as identified in the second to last picture taken, A2is the approximate axial position of the cuff member 40 as identified in the last picture taken, A1is the approximate axial position of the cuff member 40 as identified in the second to last picture taken, Z is the inclination, Y is the units expelled per revolution of the piston rod 20, and round -) rounds the obtained number down to the nearest integer. It is noted that the first term on the right-hand side of the above equation constitutes the contribution from the angular position indication, whereas the last term constitutes the contribution from the axial position indication. The following provides an example of the reliable dose determination. A user has taken a first picture which is processed by the dose app to find a presentation of the microdot pattern 80 in the inspection window which corresponds to an angular position of the cuff member 40 at increment 3, and a relative axial position of the circumferential marker 45 at 3 mm from the proximal reference point 171. The user then sets and expels 61 dose units, which causes the piston rod 20 to rotate 915° (61 times 15° / dose unit) to a position where the presentation of the microdot pattern 80 in the inspection window 19 indicates an angular position of the cuff member 40 at increment 16, and where the circumferential marker 45 is 12.15 mm from the proximal reference point 171. This corresponds to two full revolutions and an additional 13 increments of 15° rotation of the piston rod 20.

[0109] The user then takes a second picture which is processed by the dose app. Now, even if the axial positions are estimated a bit off by the image processing software in the smartphone 300 and found to be, for example, respectively, 2.5 mm and 12.5 mm, and the estimation of the axial displacement of the cuff member 40 thus is overshot by 0.85 mm, the dose app will determine the dose value as

[0110] / 12 5 — 2 5\

[0111] D = (16 - 3) + round — ' ' ■ 24 = 13 + round(2.78) ■ 24 = 13 + 2 ■ 24 = 61 U

[0112] \ 3.6 /

[0113] This example demonstrates the robustness of the present solution in determining an expelled dose from a combination of an exact estimation of the angular displacement and an approximate estimation of the axial displacement of the piston rod 20, based on a simultaneous optical readout of respective position indicators.

[0114] Regarding the axial position estimation, it is noted that the camera in the smartphone 300 may use its own digital resolution as an aid in providing a fine estimate of the position of the circumferential marker 45 relative to the axial line 170, for example by counting the number of horizontal lines in the picture between the circumferential marker 45 and the proximal reference point 171 and dividing this number with the line density.

[0115] In the alternative version of the injection device 1 shown in Fig. 7, which includes the axial matrix code 70 instead of the axial line 170, the axial position estimation may be based on the specific configuration of the axial matrix code 70 in the circumferential direction at the position of the circumferential marker 13. The axial matrix code 70 is thus merely required to change configuration for every 3.6 mm along the inspection window 19 to allow for optical detection of a full revolution of the piston rod 20. Fig. 10 shows an exemplary presentation of results from the dose app on the display of the smartphone 300. Based on the processing of a simultaneous optical readout of the angular and axial position indicators and on the continuously updated log file for the specific injection device the dose app informs the user in a first display section 310 that a dose of 24 units was recently taken, in a second display section 320 that a last previous dose of 31 units was taken nine hours and 23 minutes prior, and in a third display section 330 that 120 units remain in the drug cartridge 10.

[0116] The use of the smartphone 300 to carry out the simultaneous optical readout of the angular and axial position indicators and to capture the expelled dose therefrom is advantageous because it removes the need for cost increasing electronics in the injection device 1 and separate add-on units to be attached to the housing 2. Instead, a dose log can be established electronically by a device which many users carry about during the day anyway.

[0117] However, an alternative way of capturing expelled doses for establishment of an electronic dose log etc. is indicated in Fig. 11 , which shows the injection device 1 in combination with a detachable protective cap 60. The cap 60 and a distal portion of the injection device 1 are sectioned for the sake of clarity. This solution employs the same principle of dose determination as described in the above but carries out the simultaneous optical readout of the angular and axial position indicators differently.

[0118] In essence, the smartphone 300 in the above setup is substituted by the cap 60, which is a modified version of the cap that an injection device of this type conventionally is equipped with for protection of the drug cartridge 10 from mechanical impacts and sunlight between injections. The cap 60 comprises a hollow main cap body 61 , which defines a cap interior for reception of a distal portion of the injection device 1 , and an attachment portion 62 which is configured to engage with the housing 2.

[0119] The cap interior houses a printed circuit board (PCB) 63 which carries an array of five axially distributed camera lenses 65 with accompanying image chips 66, four light emitting diodes (LEDs) 64, distributed axially such that one LED 64 is placed between two consecutive camera lenses 65, a pair of microprocessors 67, a switch 68, a Bluetooth interface 69, and a battery 95.

[0120] The attachment portion 62 and the housing 2 are configured to only allow attachment of the cap 60 onto the injection device 1 in one specific angular orientation of the main cap body 61 relative to the housing 2 which ensures alignment of the array of camera lenses 65 with the centre axis of the inspection window 19. This allows the camera lenses 65 to capture images of the inspection window 19 and the adjacent portions of the cartridge holder 15 which include the axial line 170 and the barcode 190.

[0121] In an alternative version the injection device 1 may comprise the QR-code 90 instead of the barcode 190, in which case the first camera lens 65 and the first image chip 66 in the array, i.e. those to the far right in Fig. 11 , may be dedicated to read the QR-code, while the remaining four camera lens 65 and image chip 66 pairs may be dedicated to read respective sections of the inspection window 19.

[0122] In the present embodiment, though, all camera lens 65 and image chip 66 pairs are dedicated to providing a readout of respective sections of the inspection window 19. Hence, when the user has performed an injection and attaches the cap 60 to the injection device 1 new positions of the microdot code 80 and the circumferential marker 45 in the inspection window 19 allows for a determination of the expelled dose in accordance with the above-described. As the attachment portion 62 ensures proper positioning of the main cap body 61 relative to the inspection window 19, an end portion of the cartridge holder 15 contacts the switch 68 which causes the LEDs 64 to light up, and the camera lenses 65 to automatically capture individual images of the inspection window 19. The captured images are subsequently processed by the microprocessors 67 to i.a. obtain a dose value which corresponds to the registered angular and axial displacements of the cuff member 40.

[0123] The obtained dose value may be transmitted to an external device via the Bluetooth interface 69 along with a time stamp and other relevant dose- and drug-related data read or induced from the captured images. Alternatively, or additionally, the data may be stored in the cap 60 and / or presented on an electronic display (not shown) of the main cap body 61 , e.g. corresponding to how similar data was presented on the smartphone 300.

[0124] The cap 60 is adapted to be reused with a plurality of different injection devices, reducing production costs and waste handling as well as the carbon footprint compared to a solution where electronics are integrated in a disposable injection device.

Claims

CLAIMS1. An injection device (1) comprising:- a housing (2) extending along an axis and having an interior nut member (5),- a dose expelling mechanism comprising a threaded piston rod (20) cooperatively engaged with the interior nut member (5), the threaded piston rod (20) being advanceable in a distal direction relative to the housing (2),- cartridge holding means (15) for retaining a drug cartridge in an axially fixed position relative to the housing (2) distally of the interior nut member (5),- a first position indicator (70, 170) for indicating an axial position of the threaded piston rod (20) relative to the housing (2),- a second position indicator (80, 180, 280) for indicating an angular position of the threaded piston rod (20) relative to the housing (2), the second position indicator (80, 180, 280) being rotationally fixed with respect to the threaded piston rod (20), and- an inspection window (19) allowing for simultaneous optical readout of the first position indicator (70, 170) and the second position indicator (80, 180, 280) to thereby enable determination of a current angular progression of the threaded piston rod (20) relative to the housing (2).

2. An injection device according to claim 1 , further comprising a drug cartridge (10) retained by the cartridge holding means (15).

3. An injection device according to claim 1 or 2, wherein the second position indicator (80, 180, 280) comprises a pattern having a unique visual appearance in the inspection window (19) for each angular position of the threaded piston rod (20) relative to the housing (2).

4. An injection device according to claim 3, wherein the pattern comprises a circumferentially extending numerical scale, a circumferentially extending microdot code, or a circumferentially extending matrix code.

5. An injection device according to any of the preceding claims, wherein the second position indicator (80, 180, 280) is arranged on a cuff member (40, 140, 240) which is rotationally fixed to the threaded piston rod (20).

6. An injection device according to claim 5, wherein the cuff member (40, 140, 240) is axially fixed to a distal end portion of the threaded piston rod (20).

7. An injection device according to claim 6, wherein the cuff member (40, 140, 240) comprises a circumferential marker (45, 245) adapted to move with respect to the first position indicator (70, 170) during dose expelling.

8. An injection device according to any of the preceding claims, wherein the first position indicator (70, 170) is arranged on a portion of the cartridge holding means (15).

9. An injection device according to claim 2, wherein the first position indicator (70, 170) is arranged on a portion of the drug cartridge (10).

10. An injection device according to claim 8 or 9, wherein the first position indicator (70, 170) comprises an axially extending ruler, an axially extending bar code, an axially extending matrix code, an axially extending line having a well-defined length, or a reference mark.

11. An injection device according to any of the preceding claims, further comprising a machine-readable information tag (90, 190) carrying drug related information, the machine- readable information tag (90, 190) being arranged next to the inspection window (19) or the first position indicator (70, 170).

12. An injection device according to any of the preceding claims, wherein the simultaneous optical readout is adapted to be performed by an image capturing device (300) taking a single picture.

13. An injection device according to any of the preceding claims, further comprising a protective cap (60) configured for removable attachment to the housing (2) to cover the cartridge holding means (15), the protective cap (60) comprising a camera arrangement (65) for capturing one or more images of the inspection window (19).

14. An injection device according to claim 13, wherein the housing (2) and the protective cap (60) comprise respective guide structures configured for mutual interaction to ensure that theprotective cap (60) is attached to the housing (2) in a predetermined attachment position in which the camera arrangement (65) is aligned with the inspection window (19).

15. An injection device according to claim 14, further comprising a switch mechanism (68) configured to trigger the camera arrangement (65) to capture the one or more images in response to the protective cap (60) assuming the predetermined attachment position.

16. An injection device according to any of claims 1 - 12 in combination with a readout device (300) comprising image capturing means capable of performing the simultaneous optical readout of the first position indicator (70, 170) and the second position indicator (80, 180, 280).

17. An injection device according to claim 16, wherein the readout device (300) is a smartphone comprising a camera.

18. An injection device according to claim 17, wherein the smartphone further comprises an app configured to determine the current angular progression of the threaded piston rod (20) relative to the housing (2) based on the simultaneous optical readout of the first position indicator (70, 170) and the second position indicator (80, 180, 280).

19. A method for capturing dose related data from an injection device according to any of claims 1 - 12, comprising:- operating a readout device (300) comprising image capturing means and image processing means to perform a simultaneous optical readout of the first position indicator (70, 170) and the second position indicator (80, 180, 280) through the inspection window (19), and- prompting the image processing means to process the simultaneous optical readout of the first position indicator (70, 170) and the second position indicator (80, 180, 280) and thereby determine the current angular progression of the threaded piston rod (20) relative to the housing (2).

Images