Patent Publication Number: US-2021187200-A1

Title: Electronic add-on module for injection devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to International Patent Application No. PCT/IB2019/057866, filed Sep. 18, 2019, entitled “ELECTRONIC ADD-ON MODULE FOR INJECTION DEVICES,” which in turn claims priority to European Patent Application No. 18195521.2, filed Sep. 19, 2018, entitled “ELECTRONIC ADD-ON MODULE FOR INJECTION DEVICES”, each of which is incorporated by reference herein, in the entirety and for all purposes. 
    
    
     TECHNICAL FIELD 
     The present disclosure is directed to the field of medical injection devices for administering liquid substances, in particular drugs or medicinal substances such as insulin and hormone preparations. The disclosure more particularly relates to a portable electronic add-on module to be mounted on a medical injection device. 
     BACKGROUND 
     The patent application EP 2781230 describes an injection device, also referred to as an autoinjector, for automatic dispensing of a medical substance by means of a preloaded injection spring which presses a stopper into a syringe via a plunger rod. The movement of the stopper brings about a dispensing or delivery of the substance through a needle on a distal end of the syringe. Optionally, the injection spring or an additional energy storage element can also automatically perform an injection movement of the syringe in the distal direction relative to a housing of the injection device. The injection device further comprises a needle protection sleeve which can be shifted in a longitudinal direction between a proximal position and a distal position. The needle protection sleeve is coupled with a needle protection sleeve spring as a separate drive element which shifts the needle protection sleeve, after the substance delivery has occurred, into the distal position in which it laterally surrounds or shields the needle. A movable stop element is accelerated toward a stop by the needle protection sleeve spring and acts as a feedback device for generating an acoustic signal after the delivery of a certain quantity of substance, e.g., an end signal. A second feedback device with a stop element accelerated by the dispensing spring signals the beginning of the substance delivery, e.g., a start signal. 
     The patent application WO 2018/064784 describes a portable, reusable electronic add-on module to be mounted on a proximal end of an injection device. The add-on module comprises an inductive sensor for detecting a movement of a magnetic or electrically conductive component of the injection device between an output position and an intermediate position, and between the intermediate position and an end position during a dispensing process. This allows a simple and reliable control and monitoring of injection device use. 
     Placing an add-on module on the injection device adds additional weight to the injection device and thus increases the inert mass of the device components carried by the add-on module. If the injection device with the add-on module mounted falls to the floor from the edge of a table before the injection, the injection device can be exposed to additional stress as a result. If the add-on device is mounted on the proximal end as a carrier component of the injection device and if a distal end strikes the floor as the impacting component of the injection device, the junctions between the carrier component and the impacting component are considerably stressed. If the impacting component is connected to the carrier component only via an interface or contact site of small dimension and therefore insufficiently connected by non-positive connection, this can result in damage at the interface. This can occur, for example, if the housing of the injection device functions only as a carrier component and if the needle protection cap remover, as an impacting component, can be shifted with respect to the housing, in the process moving the syringe holder along as an additional device component. Consequently, the syringe holder can hit a stop secured to the housing and be damaged in the process. In the case of an impact against a needle protection cap remover of the injection device, the needle protection sleeve can also be accelerated with respect to the injection device, and, as a result, a locking mechanism of the needle protection sleeve can be negatively affected, so that the needle protection device no longer functions as intended after the injection process. Since, as a result of such an impact, the injection device is not necessarily spontaneously triggered or does not necessarily suffer damage that can be visually recognized from the outside, a user may under some circumstances still wish to use the injection device without being aware of possible functional impairments from the impact. 
     In this context, the term “drug” or “medical substance” comprises any flowable medical formulation which is suitable for the controlled administration by means of a cannula or a hollow needle, for example, of a liquid, a gel, or a fine suspension containing one or more medically active substances. A drug can thus be a composition with a single active substance or a premixed or co-formulated composition with a plurality of active substances from a single container. In particular, the term covers medicines such as peptides (for example, insulins, insulin-containing drugs, GLP-1-containing drugs, as well as derived or analogous preparations), proteins and hormones, biologically prepared or active substances, active substances based on hormones or genes, nutrition formulations, enzymes and additional substances in solid (suspended) or liquid form. The term moreover also covers polysaccharides, vaccines, DNA or RNA or oligonucleotides, antibodies or parts of antibodies, as well as suitable base, adjuvant and carrier substances. 
     SUMMARY 
     Implementations are configured to minimize additional mechanical stressing of individual components of an injection device caused by an add-on module mounted on the injection device. This is achieved by providing an add-on module as disclosed herein and by a use of injection device with such an add-on module. 
     According to implementations, before the start of an injection, an electronic add-on module is releasably placed or mounted on an injection device with a longitudinal or main axis that connects an insertion-side distal end to an opposite proximal end. The add-on module includes a sensor element for detecting a state or process in the injection device, a processor element (or elements) for evaluating and/or processing a signal of the sensor element, an energy storage for the energy supply of the sensor and/or the processor elements, and optionally a communications unit for wireless communication of data of the processor elements. The add-on module comprises a first module part which, in the direction of the longitudinal axis, can be connected to the injection device in an axially fixed manner within the limits of manufacturing tolerances and which, in the mounted state, is connected by a holding mechanism to the injection device in an axially fixed manner. The add-on module, in addition, comprises a second module part which can be moved at least in a distal direction parallel to the longitudinal axis for a relative movement with respect to the first module part, for instance, for a damped deceleration or braking movement. During relative movement, the first module part remains connected to the injection device in an axially fixed manner, and the holding mechanism remains effective independently of the relative movement until a release unit is actuated; thus, for example, the relative movement does not lead to the release of the add-on module from the injection device. The holding mechanism for connecting the injection device and the first module part in an axially fixed manner is preferably a positive connection and, for this purpose, it comprises, for example, holding elements on the first module part, which are engaged with positive connection in recesses in the injection device, such that the holding mechanism in particular does not comprise a coil spring positioned proximally with respect to the first module part and coaxially with respect to the longitudinal axis, for a non-positive-connection, (merely) pressing of the first module part against the injection device. 
     According to implementations, by the relative movement between two module parts following an impact, the force and/or energy transmission between the add-on module and the injection device in the direction of the longitudinal axis is controlled, and, in particular, a maximum force surge onto the injection device is decelerated and preferably also limited. At the end of a relative movement with an amplitude between 0.2 and 10 millimeters, and preferably between 0.5 and 5 millimeters, the second module part can impact an end-stop on the first module part or on the injection device and/or it can be clamped to the first module part or the injection device via surfaces which are in an angled position with respect to the longitudinal axis. Thus, a maximum action of the inert mass of the first module part occurs only at the end of the relative movement and thereby with a delay with respect to the direct action of the inert mass of the first module part. The stressing of the carrier component of the injection device, which is connected to the first module part in an axially fixed manner, and the stress on the interfaces between the carrier component and additional components of the injection device are as a result distributed with lower intensity over the relative movement. 
     In some implementations, the add-on module comprises a damping element which is different from the module parts, in order to dampen the relative movement between the module parts. The damping element can be provided directly between the two module parts, or it can act between the second module part and the injection device. The damping element can be designed so that it can completely absorb the kinetic energy of the second module part. Alternatively, the damping element can reach its capacity, for example, by a maximum compression of a compression spring, wherein, subsequently, as in the case of an explicit end-stop, the deceleration force of the second module part is taken over by the carrier component of the injection device. Preferably, the damping element includes an elastic spring component for storing potential energy and/or a non-elastic dissipation component for dissipating the kinetic energy of the second module part and for a preferably aperiodic oscillation damping. The dissipation occurs, for example, by a frictional connection of the spring component with a wall or by an integrated or separate friction element. A completely non-elastic damping with a plastic deformation of the damping element can also be useful at least for a one-time damage prevention on the injection device. 
     For the purposes of the present disclosure, the term damping also includes an approximately elastic spring action, so that kinetic energy of the second module part is dissipated by the damping during the deceleration and/or converted by the spring action into potential energy. At the end of a damped deceleration stroke with an amplitude between one and ten millimeters, and preferably between two and four millimeters, the second module can impact a deceleration end-stop on the first module part or on the injection device, and/or it can be clamped to the first module part or the injection device via surfaces which are in an angled position with respect to the longitudinal axis. Thus, the deceleration force of the inert mass of the second module part can be temporally distributed over a duration of the deceleration movement and be transmitted with corresponding damping or moderation. The stressing of the carrier component of the injection device, which is connected to the first module part in an axially fixed manner, and the stressing of the interfaces between the carrier component and additional components of the injection device are decreased as a result. 
     In some alternatives, the inert mass of the second module part is greater than the inert mass of the first module part. In particular, the energy storage may be a component of the second module part. 
     In some implementations, the sensor element is arranged in the first module part. Thereby, it is ensured that the sensor element is positioned axially as intended and oriented toward the signal component of the injection device that is to be detected. During the dispensing process, an axial spacing in the longitudinal direction between the sensor element and the signal component thus does not depend, for example, on a holding force of the user who grips the add-on module by the second module part and presses it against the injection site. In addition, vibrations of components of the injection device are better transmitted to an acceleration sensor or a gyroscope as sensor element in the first module part, which is firmly connected to the injection device. The sensor element(s) may produce an analog electrical sensor signal which is transmitted via a flexible connection independently of said axial spacing to a sensor control unit of the processor elements independently of said axial spacing. The sensor elements ensure a contactless inductive, capacitive, optical, acoustic detection, or a contact-based detection of a position or of a state of components of the injection device. Alternatively, sensor elements which tolerate axial shifting can also be mounted on the second module part, in particular in a housing insert or in the electronics unit and connected via rigid conductor tracks to the processor unit. 
     In embodiments, the second module part comprises a stop or a stop surface, which, at the end of a deceleration or braking movement decelerated by a damping element or the damping element can strike or impact a deceleration end-stop or a counter-end-stop of the injection device or of the first module part. By means of this stop, the amplitude or the stroke of the deceleration movement is limited. Correspondingly, the damping element can have a lower damping constant and/or the deceleration stroke can have a smaller length than in an embodiment with a damping element designed for complete absorption of the kinetic energy of the second module part. This stop can at the same time also receive a holding force of the user who grips the add-on module by the second module part and presses it against the injection site. 
     The damping element may be a helicoidal or coil spring which is preloaded when the add-on module is mounted on the injection device and it thus also serves as a receiving or mounting spring. Here, the two module parts are shifted with respect to one another along a receiving path, wherein the damping element is compressed or expanded in the axial direction. The preloaded damping element is prevented from relaxation by latching or fixation of the first module part in the preloaded position; however, for damping according to implementations, the damping element can be tensioned further in the longitudinal direction. As a damping element, other springs such as, for example, a clip spring formed from a spring wire, a leaf spring, a spring element made of plastic, or a non-elastic damping element would also be conceivable. 
     In some implementations, the first module part comprises an internal space for an encapsulated reception of the second module part, and the second module part, or at least the energy storage, performs the deceleration movement within this internal space. The first module part thus protrudes or has a protrusion in the radial direction, which is adapted to the dimensions of the second module part. The first module part defines a receiving volume for the injection device and can include a holding element with elastic module wings for the lateral snapping on or axial slipping on of the add-on module onto the injection device. 
     In alternative implementations, the first module part comprises an internal sleeve as a receiving unit for the injection device, which surrounds the received injection device in the axial direction over a length of at least 2 cm and preferably 5 cm on all sides, and the second module part at least partially surrounds an external module housing which at least partially surrounds the internal sleeve. Here, the second module part may comprise a grip or a gripping region or position for gripping the add-on module and the injection device, extending in the direction of the longitudinal axis and corresponding to at least half of the width of the hand of a user. This gripping region covers and may replace a gripping region of the injection device, which would be chosen by the user when using the injection device without the add-on module. Alternatively, the second module part can be offset axially with respect to the first module part, and the grip can be provided on the first module part. The holding mechanism may include holding elements attached laterally on the internal sleeve for radial engagement in lateral recesses of the injection device. Correspondingly, the internal sleeve extends in the longitudinal direction along a length that corresponds at least to the distance between the proximal end of the injection device and the position of the recesses, and the recesses may be different from any viewing windows in the injection device and may be provided proximally thereto. 
     In addition, the add-on module in the coupled state may be positioned so that a distally directed stop surface or stop edge of the second module part is opposite a proximally directed deceleration end-stop surface or edge of a needle protection cap remover and strikes said needle protection cap remover at the end of the damped relative movement of the module parts. Thereby, the remaining kinetic energy of the second module part of the add-on module is deflected via the needle protection cap remover, and the carrier component of the injection device is unburdened. The deceleration path or the amplitude of the deceleration stroke and the damping of same may be reduced toward zero or at least to manufacturing tolerances or to a minimum necessary for radial movements of a holding element. Alternatively, and in particular in axially shorter add-on modules, a proximally oriented surface or edge of the injection device or of the first module part functions as a deceleration end-stop for the second module part. 
     In additional embodiments, the first module part comprises a holding element, in particular a holding arm with a projection for engaging in a recess of the injection device, and the second module part comprises a release unit for limiting a movement of the receiving unit in the distal direction with respect to the module housing. The release unit includes, in particular, a release button with an actuation surface which can be moved in the radial direction, perpendicularly to the longitudinal axis. In a holding configuration, the release unit prevents a release movement of the receiving unit, and the holding element holds the injection device in an axially fixed manner in the receiving unit. The holding element may be locked in the holding configuration by the module housing. In a release configuration, the add-on module releases the receiving unit from the release unit and the injection device from the holding element. The add-on module can be moved from the holding configuration into the release configuration by a release movement of the receiving unit, and from the release configuration back into the holding configuration by a receiving movement. 
     Moreover, the release unit includes a guiding cam (or projection) and the receiving unit includes a locking cam (or projection), wherein, in the holding configuration, the guiding cam cooperates in such a manner with the locking cam that the receiving unit is prevented from a movement in the distal direction with respect to the housing. However, the receiving unit can still be moved for a deceleration movement under continued compression of the receiving spring. The locking cam can also be provided on the injection device, at a site which can come into contact with the guiding cam, such as through a recess in the receiving unit. Furthermore, the guiding cam can be shifted along a securing path and from a holding position in which the guiding cam cooperates with the locking cam, into a release position in which the locking cam is released by the guiding cam. The guiding cam can be preloaded by a release button spring as an elastic securing element into its holding position and it is secured in said holding position. 
     In an additional embodiment, the add-on module includes a release assistance for the release movement in the form of an elastic spring element which, when a release unit or the release unit is actuated for removing the injection device, is first tensioned or loaded and subsequently relaxes as a result of the same actuation movement. Thereby, the previously received energy is released again for the release movement of the receiving unit in the distal direction for the release configuration. By this assisted release movement, the holding elements are released from their engagement into the injection device, so that the injection device can subsequently be removed from the add-on module without additional force expenditure by the user. Likewise, by this movement, an indicator edge for signaling the release configuration can become visible. 
     As described above, for the final detachment or removal of the injection device from the add-on module, a release assistance can also be helpful independently of the relative movement in the received or inserted state of the injection device. This is the case, in particular, if the injection device is surrounded at least essentially completely by a module housing of the add-on module and/or if it has less suitable gripping regions via which a user could apply forces for releasing holding elements from their engagement with the injection device. Otherwise, this is also the case if a damping element for damping the relative movement is provided, but not tensioned when the injection device is inserted or not available as release assistance for other reasons. 
     An electronic add-on module which has been extended or augmented in this manner is detachably mounted on or plugged to an injection device with a longitudinal or main axis which connects an insertion-side distal end to the facing proximal end of the injection device. The add-on module comprises a sensor element for detecting a state or process in the injection device, a processor element for evaluating and/or processing a signal of the sensor element, an energy storage for supplying energy to the sensor and/or the processor element, and optionally a communication unit for wireless communication of data of the processor element. The add-on module comprises a module housing which, in the direction of the longitudinal axis, can be connected in an axially fixed manner to the injection device by a holding mechanism in the context of manufacturing tolerances, and which, in the mounted state, is connected in an axially fixed manner to the injection device. The add-on module comprises a release unit for releasing the holding mechanism and for moving the injection device into a release position. According to implementations, a release assistance for the release movement is provided in the form of an elastic spring element which, when the release unit is actuated for removing the injection device, is first tensioned or loaded and which subsequently relaxes as a result of the same actuation movement. Thereby, the previously received energy is delivered again for the release movement of the injection device in the distal direction. 
     An add-on module according to implementations can also comprise a communication unit for wireless communication with a mobile device, for example, a cell phone or a smartphone, and/or for an optical, acoustic or tactile state display. A displayed state can include a device state of the injection device, a module state of the add-on module, or a process state of an ongoing or completed injection process. The state display of the add-on module can be kept simple and be limited to a few LEDs, for example, in traffic light colors, and/or an acoustic signal generator for generating voice-independent sounds or melodies. This is advantageous particularly in connection with the advanced graphic display possibilities and speech output possibilities of a smartphone, since the smartphone, coupled wirelessly to the add-on module, takes over the refined communication with a user, which goes beyond a status display. The state information can include an indication of the expiration of a holding time or a waiting time, during which the user must wait after the dispensing has been completed, before the injection device can reliably be removed from the injection site. A simple acquisition of the time that has expired since the detected end of dispensing and a comparison with a target duration makes it possible to display for the user the time when the injection device can be safely removed. This can occur both by means of an add-on module with a time acquisition function and also by means of a real-time event transmission to the mobile device coupled to the add-on module. 
     An add-on module may be used repeatedly for monitoring a use or actuation of automatic disposable injection devices or autoinjectors. In particular, the add-on module may be suitable for retrofitting existing injection devices which are not available for adaptation or modification. In this configuration, in the injection device, no sensors are provided for acquiring or processing sensor data on the operation of the device, and also there is no communication interface for transmitting this data to a receiver. Accordingly, the sensor elements in the add-on device may need to be configured and positioned in such a manner that they can detect the state changes or primary signals from within the injection device. 
     The person skilled in the art can directly and in an obvious manner recognize additional embodiments and designs which result from combinations of the described examples or from combinations of the described examples with the general expert knowledge of the person skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In connection with the appended figures, implementations of the present disclosure are described below. They are intended to show basic possibilities of the implementations and should not be interpreted as limiting. 
         FIGS. 1A-1C  show a perspective view of an injection device, an add-on module, and the add-on module connected to the injection device, respectively, according to certain implementations; 
         FIGS. 2A-2C  show various implementations of the add-on module of the present disclosure in a starting state, according to certain implementations; 
         FIG. 3  is an illustration of a force action curve in the case of an impact of the injection device, according to certain implementations (V 1 -V 3  in  FIGS. 2A-2C ); 
         FIG. 4  shows an exploded view of the individual components of the add-on module, according to certain implementations; 
         FIGS. 5A-5C  shows detailed views of certain components of the add-on module of  FIG. 4 , according to certain implementations; 
         FIG. 6  shows a first cross-section through the add-on module and the injection device in the region of the end surface  40   b , according to certain implementations; 
         FIG. 7  shows a second cross-section through the add-on module, according to certain implementations; 
         FIG. 8  shows a cross-sectional view of the add-on module in a release configuration, according to certain implementations; 
         FIG. 9  shows a middle region of the add-on module in the release configuration, according to certain implementations; 
         FIG. 10  shows a cross-sectional view of the add-on module in a holding configuration, according to certain implementations; 
         FIG. 11  shows a middle region of the add-on module in the holding configuration; 
         FIGS. 12A-C  show a first variant of a tensionable ejection aid (release assistance) and operation of the first variant of the tensionable ejection aid, according to certain implementations; and 
         FIGS. 13A-C  show a second variant of a tensionable ejection aid (release assistance) and operation of the second variant of the tensionable ejection aid, according to certain implementations. 
     
    
    
     DESCRIPTION OF THE FIGURES 
       FIGS. 1A-1C  show an injection system with an injection device  1  ( FIG. 1A ), an add-on module  2  ( FIG. 1B ) in their separated states ( FIGS. 1A and 1B , respectively), and in the mounted or coupled state ( FIG. 1C ). The injection device  1  comprises a longitudinal device housing  10 , which is symmetric about a longitudinal axis, including windows  10   a  enabling a syringe body to be viewed, recesses  10   b  configured for attachment to the add-on module, and a needle protection sleeve  11 , which can be shifted between a first position (e.g.,  FIG. 1A ) shielding a needle of the injection device and a second position releasing or exposing the needle. The injection device  1  inserted into the add-on module  2  is shown with a needle protection cap remover  12 , which, in the delivered state, is mounted on a distal end of the injection device and mechanically protects the needle. The needle protection cap remover  12  is removed or pulled off before the injection, together with a needle protection cap, e.g., mounted on an injection needle. 
     The add-on module  2  has an elongate sleeve-shaped module housing  20  with an internal volume configured for receipt of the injection device  1 , e.g., the module housing  20  is adapted to receive an outer shape of the device housing  10 . The add-on module  2  may thus serve as a carrier component of the injection device  1 , so that the injection device  1  can be inserted into the add-on module  2  for coupling the injection device  1  thereto. The add-on module  2  includes an actuation surface  51  for decoupling (or release) from the injection device  1 . The add-on module  2 , on a proximal end, includes an indicator light (e.g., via a light guide  65  and light sources of the electronics unit  60  described herein) for providing an optical state display for visual feedback to a user. As illustrated in  FIG. 1B , the module housing  20  includes a slightly concave gripping region  20   a  which may be limited distally by a slight elevation or a region with increased diameter to facilitate the absorption of a force exerted by the user. 
     In the distal direction, the add-on module  2  includes two links  20   b  or longitudinal arms which are slightly bent outward on their distal end and connected to one another by stabilizing stop ridges  20   c . Between the links and limited by the stop ridges  20   c , lateral longitudinal openings  20   d  are formed, which in the coupled state to the injection device  1 , are aligned with the windows  10   a  of the device housing  10  and allow a user to view a substance stored in the injection device  1 . In a state without the inserted injection device  1  ( FIG. 1B ), an indicator edge  40   a  of a longitudinal shiftable receiving unit  40  can be viewed in the longitudinal opening  20   d . By means of the inserted injection device  1 , this indicator edge  40   a  is shifted proximally into the module housing  20 . A distal end surface of the links  20   b  is located opposite a proximal edge of the needle protection cap remover  12  with a spacing of a few millimeters in the axial direction. 
     The device housing  10  and the module housing  20  may have an approximately square shape in cross section, wherein each side of the square is curved slightly outward. In the following description, for the sake of simplicity, a direction from the middle longitudinal axis of the housing  20  outward is referred to as radial direction. 
       FIGS. 2A-C  show three different implementations, V 1 , V 2 , V 3  of the add-on module  2 , according to the present disclosure, each in the starting state before the needle protection cap remover  12  is pulled off. For each implementation, a respective view of an injection device  1  with device housing  10  and needle protection cap remover  12  is shown, as well as a section through a mounted add-on module  2  with a first module part as receiving unit  40 , axially connected to the device housing  10  as carrier component, and with a second module part comprising a module housing  20 . The two module parts are connected or elastically coupled via a damping element  70 . 
       FIG. 3  is a diagram showing a temporal course of the force action on the carrier component (housing  10 ), starting with an initial loading at the time of an impact of the needle protection cap remover  12  and followed by a deceleration loading during a relative movement of the two module parts  10 ,  20 , and of a final loading. The force curve is represented for the injection device without a mounted add-on module (minimum initial loading—solid line), for a mounted single-part add-on module (maximum initial loading—short dashed line), as well as for each of the three variants V 1 , V 2 , V 3  according to the present disclosure (reduced initial loading followed by deceleration loading). 
     Variant one (V 1 ,  FIG. 2A , left) corresponds to the configuration shown in  FIG. 1B  in which the second module part has extended longitudinal links  20   b  and is arranged so that a distally directed stop surface  24  of the longitudinal link is located opposite a proximally directed deceleration end-stop surface of the needle protection cap remover  12  with a spacing D of a few millimeters. After a damped deceleration stroke with amplitude D ( FIG. 2A ), the stop surface  24  hits the needle protection cap remover  12 , and the deceleration stroke or the braking movement of the second module part is thus limited by an end surface of the needle protection cap remover  12  serving as an end stop surface. When the two stop surfaces are in contact, no additional loading of the carrier components occurs, and the final loading thus remains at the level of the deceleration loading, as represented in  FIG. 3 . 
     In variant two (V 2 ,  FIG. 2B , middle), the add-on module  2  is shorter than in variant one and is not provided with extended distal longitudinal links  20   b , or alternatively, the needle protection cap remover  12  has been removed from V 1  of  FIG. 2A  beforehand. In  FIG. 2B , a distally directed stop surface  24  in the interior of the module housing  20  is located opposite a proximally directed deceleration end-stop surface of the first module part, i.e., the receiving unit  40 , with a spacing D of a few millimeters. The damped relative movement of the module parts thus ends after a deceleration path D, after which the deceleration force of the second module part is taken over by the carrier component. This leads to a force action on the carrier component, represented in  FIG. 3 , which is elevated in comparison to the level of the deceleration load. In variant two, the stop surface  24  is also pressed for the absorption of a holding force of the user who grips the add-on module  2  by the second module part and presses on the injection site. 
     In variant three (V 3 ,  FIG. 2C , right), an elastic damping element with an increased damping or spring constant and/or with a long deceleration or spring path between the two module parts, e.g., module housing  20  and receiving unit  40 , is provided. Thereby, the kinetic energy of the second module part is completely absorbed in the elastic damping element, and a hard stop between the two module parts no longer occurs. The force transmission between the two module parts is distributed better over time, and the deceleration load onto the carrier component persists up to the maximum compression of the damping element  70  on a level which is increased with respect to variants one and two, as represented in  FIG. 3 . 
       FIG. 4  shows an exploded view of the individual components of an add-on module  2  according to implementations of the present disclosure, including variants one through three of  FIGS. 2A-2C . The add-on module  2  comprises a module housing  20  including multiple parts with an upper housing half  21   a , a lower housing half  21   b  connected thereto, a housing closure  22 , a housing insert  30 , a receiving unit  40 , a release button  50 , an electronics unit/elements  60 , a damping element  70 , and a release button spring  80 . 
     The upper and the lower housing halves  21   a ,  21   b  each have an approximately semi-circular shape, and they are nondetachably snapped on and/or connected to one another, e.g., by ultrasound welding, laser welding, gluing or bolting. Due to the shape of the housing halves, an internal space is formed between them. On a proximal end, the internal space is limited by the housing closure  22  or a closure wall between the housing halves. On the distal end, the housing halves form an opening toward the internal volume or space. In the internal space, the housing insert  30 , the release button  50  and the electronics unit  60  are arranged in an axially non-movable manner. In a middle region between the gripping region  20   a  and the links  20   b  ( FIG. 1B ), the upper housing half  21   a  comprises a radial opening  23  through which an actuation surface  51  of the release button  50  protrudes in the mounted state. 
     The receiving unit  40  is mounted in an axially movable manner in the module housing  20 , as described below, and furthermore comprises sensor elements, which may be in the form of two inductive sensor elements or sensor coils  41   a ,  41   b  which are arranged in corresponding circumferential grooves in an outer surface of the receiving unit  40 . The sensor coils  41   a ,  41   b  are contacted or electrically connected on a shapeable or flexible carrier via a circuit board  41   c , which may be in the form of a printed circuit board, including a flexible conductor  41   d  (also known as flexprint). Laterally between the two inductive sensor coils  41   a ,  41   b , the circuit board  41   c  can comprise a NFC (Near Field Communication) coil for reading information of an RFID (Radio Frequency Identification) label on the injection device. A flexible connection  41   d  in the form of a wire, a cable, or, as represented, as a continuation of the circuit board  41   c , e.g., printed conductor tracks of the mentioned flexible conductor  41   d  for the transmission of signals of the sensor coils  41   a ,  41   b  and of the NFC coil leads to circuit boards  64   a ,  64   b  (e.g., processor elements) of the electronics unit  60 . The flexibility of this signal connection allows compensation of the varying axial spacing between the receiving unit  40  and the electronics unit  60 . 
     The electronics unit  60  is arranged in a proximal region of the internal space in such a manner that it directly adjoins the housing closure  22  and comprises an electronics holder  61 , an energy storage with battery  62  and accumulator/rechargeable battery  63 , a first and a second circuit board  64   a ,  64   b  with light sources and processor elements for processing signals of the sensor coils  41   a ,  41   b , for actuating the light sources, and for communication with additional external devices. The electronics unit  60  moreover comprises a light guide  65  which guides the light of the light sources to the surface of the module housing  20 , and an antenna  66  for setting up a communication connection with a third device, in particular for out-of-band pairing for initiating a Bluetooth or other wireless connection. 
     Between a proximal end surface of the receiving unit  40  and a distal end surface of the electronics holder  61  (the end surfaces may be oriented at a right angle with respect to the longitudinal axis of the housing), is an elastic damping element  70  in the form of a compressed or compressible coil spring. The damping element  70  pretensions the receiving unit  40  in the distal direction via the end surface. The damping element  70  can also be provided between other components of the module housing  20  and of the receiving unit  40  or of the injection device  1  in such a manner that it acts axially to dampen relative movement between the add-on module  2  and the injection device  1 . 
       FIGS. 5A-5C  show perspective views and further details of components of the housing insert  30  ( FIG. 5A ), the receiving unit  40  ( FIG. 5C ), and the release button  50  ( FIG. 5B ). In  FIG. 5A , the housing insert  30  has a sleeve-shaped configuration and comprises an opening  31 . 1 ,  31 . 2  in each of two opposite first outer sides, which extends inward from an outer side in the proximal direction through the wall of the housing insert  30 . The housing insert  30  moreover comprises two additional second outer-side perforations  33  in the wall, which are offset by 90° with respect to the first outer sides in the direction of rotation of the longitudinal axis, through which guiding cams  52  of the release button  50  can cooperate with locking cams  42  of the receiving unit  40 . Moreover, the housing insert  30  mounts the release button  50  in an axially movable manner. For this purpose, the housing insert  30 , on the two second outer sides, comprises two respective guiding grooves  32 . 1 ,  32 . 2 . The housing insert  30  can be received in a radial recess or convexity in the module housing  20 , whereby the housing insert  30  is fixed in such a manner that it cannot be moved relative to the module housing  20 . In the circumferential direction, the housing insert  30  is held in such a manner that it cannot be moved relative to the module housing  20  via ribs which are attached on outer sides of the housing insert  30  and which engage in corresponding grooves in the inner wall of the module housing  20 . 
     In  FIG. 5B , the release button  50  has a U-shaped cross section and is mounted on the housing insert  30  such that the arms of the U-shape surround the housing insert  30  on both sides and engage in the guiding grooves  32 . 1 ,  32 . 2 . Between the arms, the release button  50  comprises, on an outer side, the actuation surface  51 , which the user can actuate manually, in order to move the release button  50  radially in a direction at a right angle with respect to the longitudinal axis of the module housing  20  along a linear securing path. Furthermore, the arms comprise, on their inner side, a respective triangular guiding cam  52 , which can cooperate with a respective triangular locking cam  42  of the receiving unit  40  or of the injection device, and thereby limits a distal movement of the receiving unit  40  with respect to the module housing  20 . Between the housing insert  30  and the release button  50 , the release button spring  80  is located, which pretensions the release button  50  radially outward in a securing direction. 
     As seen in  FIG. 5C , the receiving unit  40  is mounted so that it can be moved in the axial direction relative to the module housing  20  and thus relative to the housing insert  30 . The receiving unit  40  is also designed in the shape of a sleeve and has a square shape in cross section substantially matching the cross section of the injection device  1 , wherein the side walls of the square are each bent slightly outward. Moreover, for the proximal limit of the internal space, the receiving unit  40  has an end surface  40   b  which is oriented at a right angle with respect to the longitudinal axis of the receiving unit  40  and which extends over the entire cross section of the internal space of the receiving unit  40 . 
     On two mutually facing first sides of the essentially square shape of the receiving unit  40 , a respective holding element in the form of a holding arm  43 . 1 ,  43 . 2  is arranged, wherein the holding arms  43 . 1 ,  43 . 2  are located in a distal region of the receiving unit  40  with respect to the axial length of the receiving unit  40 . The holding arms  43 . 1 ,  43 . 2  are pivotably connected on a first end to the receiving unit  40 . In the region of the free end of an outer side of the holding arms  43 . 1 ,  43 . 2  facing away from the internal space, said holding arms each have a cam  44 . 1 ,  44 . 2 , each of which can be received in one of the openings  31 . 1 ,  31 . 2  of the housing insert  30 . However, in the region of the free end of the holding arms  43 . 1 ,  43 . 2 , on an inner side which faces the internal space of the receiving unit  40 , the holding arms  43 . 1 ,  43 . 2  each have a projection  45 . 1 ,  45 . 2  ( FIG. 8 ). On the other two sides of the square shape, a respective triangular locking cam  42  is arranged, which can cooperate in each case with a guiding cam  52  of the release button  50 . 
       FIG. 6  shows a longitudinal cross section in the region of the end surface  40   b  of the receiving unit  40  of the add-on  2  and injection device  1 . The distal side of the end surface  40   b  comprises, in the middle, a convexity  40   c  or an elevation with a flat plateau, on which a proximal front surface of the injection device housing  10  lies. However, the end surface  40   b  can also be provided with separate elements for non-surface contacting and force transmission onto the injection device  1 , for example, with a central convex curvature, with multiple pins or pegs distributed over the cross section or with one-dimensional links which are preferably arranged concentrically relative to the cross section of the injection device  1 . On the other hand, the shape of the end surface  40   b  can be matched to an uneven shape of the proximal front surface of the injection device  1 , in order to enable a large-surface contact. 
     In the perspective view of  FIG. 5C , a flange section  40   d  extending outward in the radial direction and an arm  40   e  pointing in the proximal direction, which is used for preliminary snapping onto the housing during the mounting of the receiving unit  40 , are also represented. An extension or tip on the arm  40   e  may act on a mechanical or optical switch, and may activate the processor units of the electronics unit  60  from a standby or rest state as soon as the receiving unit  40  is shifted proximally along a receiving path. The switch arranged on the circuit board  64   a ,  64   b  thus detects the end of the receiving movement of the arm  40   e  and thus of the receiving unit  40 , and any absence of the injection device  1  can then be detected via the activated sensor elements or sensor coils ( 41   a ,  41   b ), or another RF identification signal of the injection device  1  can be detected. Instead of the circuit board  64   a ,  64   b , a switch for the detection of the axial position of the receiving unit  40  can also be mounted on any site of the inner side of the module housing  20  and cooperate there with a projection, for example, the mentioned flange section  40   d  or with a groove of the receiving unit  40 . 
     Alternatively, a switch for detecting the axial position of the receiving unit  40  can be arranged on the receiving unit  40  itself and cooperate with an element secured on the module housing  20  or a projection. In this case, the switch can be fitted on the circuit board  41   c  (for example manufactured using a so-called flexprint printed circuit) which may be fastened permanently on the outer surface of the receiving unit  40 . In an embodiment with a release button  50  which, when the injection device  1  is inserted, is moved with respect to the module housing  20  and/or housing insert  30 , this relative movement can also be detected by a switch. In all these cases, a mechanical switch may be used primarily for activating the electronics and additional sensor elements of the electronics unit  60 , so that the axial positioning of the switch is not critical and the switch can trigger already before the holding configuration is reached. 
     If a switch is arranged on the circuit board  64   a ,  64   b  and provided with a suitably extended plunger or completed with a separately spring-mounted adapter, wherein the plunger and adapter preferably pass through the end surface  40   b  in the longitudinal direction, the presence of the injection device  1  in the holding configuration can also be detected. In this case, sensor elements for the additional identification of the injection device  1  can be omitted. 
       FIG. 7  shows a longitudinal cross section through an embodiment of the add-on module  2  with a switch  41   e  for the detection of the presence of the injection device  1  in the receiving unit  40 . The switch  41   e  is arranged laterally on the receiving unit  40 , e.g., on the circuit board  41   c  (see above) next to a lateral opening in the receiving unit  40 . In this case, the presence of the receiving unit  40  including the injection device  1  in the holding configuration must also be detected. 
       FIG. 8 , shows a longitudinal cross section view of the add-on module  2  in a release configuration. The receiving unit  40 , shiftably mounted in the module housing  20 , is in the release position on a distal end of a receiving or configuration adjustment path. The receiving unit  40  is pushed into this position by a receiving spring illustrated as the elastic damping element  70 , and in the process a flange section  40   d  (circled) or a radial pin impacts against a distal receiving path limit formed by the housing insert  30 . In the process, the indicator edge  40   a  protrudes into the viewing area of the longitudinal opening  20   d  of the module housing  20 ; and the indicator edge  40   a  is thus visible for a user and thereby indicates to the user the release position. If the receiving unit  40  is to be shifted in the proximal direction relative to the module housing  20 , it must be moved against the pretensioning force of the receiving spring, e.g., damping element  70 . The receiving unit  40  can be shifted in the proximal direction relative to the module housing  20 , until the damping element  70  is maximally compressed or until the flange section  40   d  impacts against a proximal receiving path limit formed by the housing. Said receiving path limit can simultaneously function as a stop and cooperate with the flange section  40   d  as a deceleration end-stop. 
     In  FIG. 8 , as shown, the two holding arms  43 . 1 ,  43 . 2  protrude outward from the body of the receiving unit  40 , in that the cams  44 . 1 ,  44 . 2  of the holding arms  43 . 1 ,  43 . 2  ( FIG. 5C ) are received in respective openings  31 . 1 ,  31 . 2  ( FIG. 5A ) in the housing insert  30  and guided by force in said openings. Since the holding arms  43 . 1 ,  43 . 2  as a result point outward, the projections  45 . 1 ,  45 . 2  (circled) on the respective inner sides of the holding arms  43 . 1 ,  43 . 2  do not protrude into the internal space of the receiving unit  40  but are instead substantially flush with the inner surface of the receiving unit  40 . In this position, the holding arms  43 . 1 ,  43 . 2  are thus in a release position. 
     In comparison to  FIG. 8 ,  FIG. 9  shows an enlarged middle region of the add-on module  2  in a release configuration, wherein the outer wall of the module housing  20  and of the housing insert  30  and an arm of the U-shape of the release button  50  are omitted in the representation. As mentioned above, the receiving unit  40  comprises on two outer sides a respective locking cam  42 , and the release button  50  comprises, on its inner side, two radially mutually facing guiding cams  52 , wherein one of the guiding cams  52  and one of the locking cams  42  as shown in  FIG. 9 . 
     In a release configuration, the locking cams  42  are located on the distal side of the guiding cams  52 . The locking cams  42  each include a contact surface  46  which forms an acute angle with the longitudinal axis of the module housing  20 . The guiding cams  52  comprise a respective guide surface  53 , each being also oriented at this angle with respect to the longitudinal axis. In the release configuration shown, the guiding cams  52  are in a release position in which the contact surfaces  46  of the locking cams  42  and the guide surfaces  53  of the guiding cams  52  are in contact with one another. The guide surface  53  is pretensioned in the direction of the contact surface  46  by the release button spring  80 . In a release configuration in which the receiving unit  40  is located on a distal end of its receiving path, which is determined by the relative arrangement of the flange section  40   d  and the distal receiving path limit, the guide surface  53  and the contact surface can also be axially separated. 
     In order to connect the injection device  1  to the add-on module  2 , the latter must be moved from the release configuration into a holding configuration. For this purpose, the receiving unit  40  must be shifted relative to the module housing  20  from a distal into a proximal end position. This shift occurs by means of positioning the injection device  1 , the proximal end of which can be inserted into the opening on the distal end of the module housing  20  and moved in the direction of the proximal end of the module housing  20 . In the process, the proximal end of the injection device  1  first impacts against the end surface  40   b  of the receiving unit  40 ; subsequently the injection device  1  and the receiving unit  40  are shifted against the receiving spring, e.g., damping element  70 , in the proximal direction. During this shift, the holding arms  43 . 1 ,  43 . 2  are moved along in the proximal direction, whereby the cams  44 . 1 ,  44 . 2  of the holding arms  43 . 1 ,  43 . 2  slide out of the respective angled openings  31 . 1 ,  31 . 2  in the housing insert  30  and move toward the internal space of the housing or the inserted injection device  1 . As a result, the respective projections  45 . 1 ,  45 . 2  on the inner sides of the holding arms  43 . 1 ,  43 . 2  also move toward the injection device  1  and with increasing shifting of the receiving unit  40  in the proximal direction they engage in the recesses  10   b  in the injection device  1  ( FIG. 1A ). By the continued shifting of the receiving unit  40 , the cams  44 . 1 ,  44 . 2  are guided further through the inner wall of the housing insert  30 , so that the holding arms  43 . 1 ,  43 . 2  can no longer be deflected outward in the radial direction. The holding arms  43 . 1 ,  43 . 2  are thus locked by the housing insert  30  in a holding position, and the projections  45 . 1 ,  45 . 2  cannot be released unintentionally from the recesses  10   b  in the injection device  1 . 
     When the receiving unit  40  is shifted from the distal end position into the proximal end position, the locking cams  42  of the receiving unit  40  cooperate with the guiding cams  52  of the release button  50 . Indeed, as soon as the receiving unit  40  has been shifted from its distal end position in the proximal direction, the respective angled contact surfaces  46  of the locking cams  42  of the receiving unit  40  are pressed against the angled guide surfaces  53  of the guiding cams  52  of the release button  50 . Since the release button  50  cannot move in the axial direction but is instead movably mounted in the radial direction against the securing direction, the guiding cams  52  shift due to the pressure of the locking cams  42  against the pretensioning force of the release button spring  80  in the radial direction until the locking cams  42  slide beyond the guide surfaces  53  and thereby release the guiding cams  52 . At this time, the release button  50  springs back in the securing direction due to the spring force of the release button spring  80 . The locking cams  42  are then located on the proximal side of the guiding cams  52 . The guiding cams  52  in this position are in their holding position in which they prevent the locking cams  42  from moving in the distal direction, by means of their locking surface  54  oriented at a right angle with respect to the longitudinal position. In this position, the receiving unit  40  is located on a proximal end of its receiving path, and the add-on module  2  is in the holding configuration. 
       FIG. 10  shows the add-on module  2  in a cross-sectional view in the holding configuration with an injection device  1  held in the module housing  20  in a top view. Said injection device  1  contacts, with its front surface, the end surface  40   b  of the receiving unit  40  which is located on the proximal end of the receiving path. In this position of the receiving unit  40 , the receiving spring is not yet maximally compressed, the flange section  40   d  (circled) is located between the distal receiving movement limit and a distally directed stop surface in the interior of the module housing. Due to the above-described cooperation of the locking cams  42  and the guiding cams  52 , the receiving unit  40  is held in this position, which is pretensioned by the receiving spring. The holding arms  43 . 1 ,  43 . 2  are in their holding position in which the respective projections  45 . 1 ,  45 . 2  engage in the recesses  10   b  in the injection device  1  (the position of the projections and recesses is circled, but hidden by the top view of the injection device) and in which the inner wall locks the cams  44 . 1 ,  44 . 2  of the holding arms  43 . 1 ,  43 . 2  against radial movement. 
       FIG. 11  shows a middle section of the add-on module in the holding configuration. Here, as in  FIG. 9 , an outer wall of the module housing  20  and of the housing insert  30 , and a portion of the arm of the release button  50  are omitted so that one of the guiding cams  52  of the release button  50  and one of the locking cams  42  of the receiving unit  40  can be viewed. In  FIG. 11 , the guiding cam  52  is shown in its holding position. In this holding position, the guiding cam  52  with its locking surface  54  and with the pretensioning force of the release button  50 , which is generated by the release button spring  80 , prevents the locking cam  42  and thus the receiving unit  40  from moving in a distal direction. Thus, an undesired shifting of the receiving unit  40  is not possible at least in the distal direction, and the injector  1  cannot be unintentionally released from the module housing  20  of the add-on module  2 . 
     In order to separate the injection device  1  from the add-on module  2 , the add-on module  2  must be moved from the holding configuration into the release configuration. This is achieved by pressing the actuation surface  51  of the release button  50  so that the release button is shifted along its securing path in the radial direction toward the module housing  20 . Thereby, the release button spring  80  is compressed, and the guiding cams  52  are shifted from their holding position into a release position, whereby the locking cams  42  of the receiving unit  40  can be released and moved in the distal direction. 
     By manual pressing of the release button  50  against the securing direction and transversely to the longitudinal direction, a short but nonetheless easily recognizable release or ejection movement of the receiving unit  40  in the distal direction of the receiving path is started, at the end of which the add-on module  2  is in the release configuration, and the removal of the injection device  1  from the add-on module can occur. The ejection movement of the receiving unit  40  can here occur exclusively due to the directly exerted force of the user, for example, by a careful deflection of the force transversely to the longitudinal direction via a cam control or a wedge into a force in the direction of the receiving pass, or by pressing an alternative release button or manual shifting of the receiving unit  40  in the longitudinal direction. However, the ejection movement can also occur completely automatically and be driven and assisted by a preloaded energy source, so that the release button is used exclusively as trigger and can thus also be implemented as an electronic contact sensor. Preloaded energy sources are maximally loaded when the add-on module is delivered and they release a smaller amount of energy with each ejection. In addition to a preloaded mechanical energy storage in the form of a spring or a pressurized gas reservoir, an electrical drive is also conceivable. 
     The release or ejection movement can also be assisted by the release of energy from a rechargeable energy source as release assistance, which is loaded into the add-on module at the time of the axial insertion of the injection device into the add-on module. For this purpose, a separate spring element, a compressible gas volume, or the receiving spring in the form of an elastic damping element  70  can be provided. At the time of the injection, the spring element compressed in the holding configuration can be relaxed and it can press against the end surface  40   b , whereby the receiving unit  40  is shifted in the distal direction. However, the loading or tensioning of the release assistance can also occur only when the ejection occurs by initial pressing of the release button  50  via a first partial stroke, wherein a subsequent final movement of the release button via a second partial stroke serves as trigger for the assistance. 
       FIGS. 12A-12C  show a first variant with a tensionable release assistance, including two elastic spring arms  55   a ,  55   b  or links, which are each fastened to an inner side of the two arms of the release button  50  and may be configured to form a single piece therewith. In the holding configuration represented in  FIG. 12B , a portion of an arm is omitted, so that a spring arm  55   a , a locking cam  42  of the receiving unit  40  and a guiding cam  52  of the release button  50  are visible. A proximal end of the locking cam  42  is located with a slight distal offset next to the non-tensioned spring arm  55   a . When the release button  50  with spring arm  55   a  and guiding cam  52  is moved opposite its securing path in the direction of the arrow ( FIG. 12C ), the spring arm  55   a  is clamped on the locking cam  42 . As illustrated in  FIG. 12C , toward the end of this movement, the guiding cam  52  releases the locking cam  42  for a movement in the distal direction, and the energy previously stored in the spring arm  55   a  drives the locking cam  42  and thus the receiving unit  40  in the distal direction. At the site of the locking cam  42 , the spring arm  55   a  can also act on another projection of the receiving unit  40 . 
       FIGS. 13A-13C  show a second variant with a separate tensionable release assistance made of spring wire in the form of a clip spring with a U-shaped clip  56  and two tensioning arms  57   a ,  57   b  angled at a right angle therefrom. At the transitions between the clip  56  and the tensioning arms  57   a ,  57   b , two pivot and contact points are located, at which the clip spring is clamped on the housing insert  30  ( FIGS. 13B and 13C ). In the holding configuration represented in  FIG. 13B , the tensioning arms  57   a ,  57   b  are oriented approximately parallel to the longitudinal axis, so that, as shown in  FIG. 13B , a distal end of the tensioning arms  57   b  is positioned in the securing direction beneath a nose  58 , an edge, or a projection of the release button. The clip  56  is arranged distally on a pin  40   f  of the receiving unit  40  or is guided in a recess of the receiving unit  40 . As represented in  FIG. 13C , by a movement of the release button  50  in the direction of the arrow, during a first partial stroke, the tensioning arms  57   a ,  57   b  are pressed downward and the clip  56  is clamped with an at least essentially rigid angle between the tensioning arms  57   a ,  57   b  and the clip  56 . A release of the receiving unit  40  occurs subsequently, as in the variant described herein. 
     Due to the movement of the receiving unit  40  in the distal direction, the holding arms  43 . 1 ,  43 . 2  are also shifted in the distal direction, and the cams  44 . 1 ,  44 . 2  of the holding arms  43 . 1 ,  43 . 2  run along the inner wall of the housing insert  30  and into the openings  31 . 1 ,  31 . 2  due to their shape, e.g., angle, and are force-guided by the openings  31 . 1 ,  31 . 2 . The holding arms  43 . 1 ,  43 . 2  are moved outward at an angle away from the internal space of the receiving unit  40 , e.g., radially away, whereby the projections  45 . 1 ,  45 . 2  (see, e.g.,  FIGS. 8 and 10 ) are also moved from the internal space or from the injection device  1  radially away and out of its recess  10   b . As a result of the force of the receiving spring, e.g., the damping element  70 , the receiving unit  40  is shifted distally to the distal end of its receiving path or up to a distal stop on the module housing  20 . During this movement of the receiving unit  40 , the free end of the holding arms  43 . 1 ,  43 . 2  is shifted further into the respective openings  31 . 1 ,  31 . 2  in the housing insert  30  until the holding arms  43 . 1 ,  43 . 2  are in their release position. When the receiving unit  40  has arrived on the distal end of its receiving path, the add-on module  2  is located in the release configuration, and the injector  1  can be removed from the module housing  20 . 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               1  Injection device 
               10  Device housing 
               10   a  Window 
               10   b  Recess 
               11  Needle protection sleeve 
               12  Needle protection cap remover 
               2  Add-on module 
               20  Module housing 
               20   a  Gripping region 
               20   b  Link 
               20   c  Stop ridge 
               20   d  Longitudinal opening 
               21   a ,  21   b  Housing halves 
               22  Housing closure 
               23  Radial opening 
               24  Stop surface 
               30  Housing insert 
               31 . 1 ,  31 . 2  Opening 
               32 . 1 ,  32 . 2  Guide grooves 
               33  Perforation 
               40  Receiving unit 
               40   a  Indicator edge 
               40   b  End surface 
               40   c  Convexity 
               40   d  Flange section 
               40   e  Arm 
               40   f  Pin 
               41   a ,  41   b  Sensor coils 
               41   c  Circuit board 
               41   d  Connection 
               41   e  Switch 
               42  Locking cam 
               43 . 1 ,  43 . 2  Holding arm 
               44 . 1 ,  44 . 2  Cam 
               45 . 1 ,  45 . 2  Projection 
               46  Contact surface 
               50  Release button 
               51  Actuation surface 
               52  Guiding cam 
               53  Guide surface 
               54  Locking surface 
               55   a ,  55   b  Spring arm 
               56  Clip 
               57   a ,  57   b  Tensioning arms 
               58  Nose 
               60  Electronics unit 
               61  Electronics holder 
               62  Battery 
               63  Accumulator/recharchable battery 
               64   a ,  64   b  Circuit board 
               65  Light guide 
               66  Antenna 
               70  Damping element 
               80  Release button spring