Patent Publication Number: US-2023158252-A1

Title: Method for assembling a cassette for use in an auto injector

Description:
The invention relates to a method for assembling a cassette for use in an auto injector. 
     BACKGROUND 
     Auto injectors for the delivery of medicament to a patient comes in many varieties depending on the type of medicament, which is to be delivered to the patient. Assembling of the auto injector and cassette to obtain a good fit between the two parts is often only ensured if the two parts are aligned in a specific manner. The same applies of the assembly of the individual parts in the cassette and the auto injector. 
     If the auto injector is a re-usable item into which a cassette is inserted, the user needs to ensure that all operational parts stay full functional in order to prolong the lifetime of the auto injector. 
     SUMMARY 
     Throughout this description, all references to the proximal direction or proximal surfaces refer to parts, surfaces and similar oriented in the direction of insertion, i.e. in the direction of the insertion needle and the outer part of the auto injector touching the skin during injection of the medicament. Movement of parts in a proximal direction and/or proximately refers to a movement in the direction of the insertion needle and the outer part of the auto injector touching the skin during injection of the medicament. 
     Likewise, all references to the distal direction or distal surfaces refer to parts, surfaces and similar oriented in the direction away from the direction of the insertion needle, i.e. in the direction of the user. Movement of parts in a distal direction and/or distally refers to a movement in the direction away from the insertion needle and the outer part of the auto injector touching the skin during injection of the medicament, i.e. in the direction of the user. 
     Disclosed herein in a first aspect is an auto injector adapted for receiving a cassette with medicament and for administering the medicament in the cassette to a patient, the auto injector extending from a proximal end to a distal end along a longitudinal axis, wherein the cassette is removable received in the auto injector along the longitudinal direction, wherein the auto injector further comprises one or more cassette interacting parts adapted for securing and locking the cassette inside the auto injector and for facilitating administering of the medicament, wherein the one or more cassette interacting parts are configured for moving in parallel with the longitudinal axis of the auto injector. 
     By removable received is meant is meant a disposable cassette, which may be received in a reusable auto injector. The disposable cassette may be a one-time use cassette, or a cassette comprising multiple doses. 
     By a movement in parallel with the longitudinal axis of the auto injector it is ensured that a minimum of stress is inflicted on the auto injector. This prolongs the lifetime of the auto injector. Further, a slimmer design is obtainable by the movement of the cassette interacting parts in parallel with the longitudinal axis of the auto injector. As the auto injector and the cassette may be constructed to be interfacing with the auto injector and the cassette sharing the same longitudinal axis, the risk of the cassette getting stuck inside in the injector is mitigated. This helps make the connection as slim as possible, and the auto injector as robust as possible. 
     Disclosed herein in a second aspect is an auto injector adapted for receiving a cassette with medicament and for administering the medicament, wherein the cassette is removable received in the auto injector, wherein the auto injector is consisting of a housing extending from a proximal end to a distal end and a multiple of internal injector parts positioned inside the housing, the housing consisting of:
         a cassette covering section extending to cover at least a part of the cassette when received inside the injector; and   a distal section extending to cover the internal injector parts inside the housing before the cassette is secured inside the injector.       

     By cover the internal injector parts is meant to cover the internal injector parts along the longitudinally extending direction of the internal injector parts. 
     By having two sections, the auto injector can be constructed such that the cassette is interfacing with the auto injector at the proximal end of the internal injector parts with the cassette sharing the same longitudinal axis as the auto injector. This mitigates risk of the cassette getting stuck inside in the injector and also help to make the connection as slim as possible. Also, by the two-sectional construction where there is only a need for the cassette to positioned in the cassette covering section, user access to the internal parts inside the auto injector may be blocked. This also reduces impurities/dust from penetrating into the auto injector internal parts, in turn keeping the auto injector easily clean due to avoidance of grooves to e.g. collect dirt and dust etc. A more robust auto injector is thereby obtained. This prolongs the lifetime of the auto injector. 
     Disclosed herein in a third aspect is an auto injector adapted for receiving a cassette with medicament and for administering the medicament, wherein the auto injector comprises a housing extending from a proximal end to a distal end along a longitudinal direction, the housing comprising:
         a cassette covering section extending to cover the cassette when received inside the injector; and   a distal section extending to cover all internal injector parts,
 
wherein the auto injector comprises a cassette abutting surface adapted for abutting a distal end of the cassette when secured inside the auto injector,
 
wherein the cassette abutting surface defines a proximal end plane from where substantially no internal injector parts extends proximally prior to assembling the cassette and the auto injector.
       

     By cover the internal injector parts is meant to cover the internal injector parts along the longitudinally extending direction of the internal injector parts. 
     By substantially is included a situation where only a minor part of the internal injector parts protrude a small amount, such as up to 2%, 5%, or 10%, proximally compared to the cassette abutting surface. In some examples no parts protrude proximately. 
     By having cassette abutting surface from where substantially no internal injector parts extends proximally prior to assembling the cassette and the auto injector provides a smooth interior and cassette interface, which mitigates risk of the cassette getting stuck inside in the injector. Also, by the cassette abutting surface, user access to the internal parts inside the auto injector may be blocked. This also reduces impurities/dust from penetrating into the auto injector internal parts, in turn keeping the auto injector easily clean due to avoidance of grooves to e.g. collect dirt and dust etc. A more robust auto injector is thereby obtained. In turn, the lifetime of the auto injector is prolonged. 
     In one or more examples, the cassette abutting surface defines a proximal end plane from where substantially no cavities extends distally into the distal section. 
     In one or more examples, the housing encloses internal injector parts, the internal injector parts including at least a piston, a drive module adapted for moving the piston proximately, and a chassis, wherein the internal injector parts are defined by a proximal end plane and a distal end plane, and wherein the auto injector comprises noise reducing material at both the proximal end plane and the distal end plane of the internal parts. 
     Disclosed herein in a fourth aspect is an auto injector adapted for receiving a cassette with medicament and for administering the medicament, wherein the cassette is removable received in the auto injector, wherein the auto injector comprises a housing enclosing internal injector parts, the internal injector parts including at least a piston, a drive module adapted for moving the piston proximately, and a chassis, wherein the internal injector parts are defined by a proximal end plane and a distal end plane, and wherein the auto injector comprises noise reducing material, at both the proximal end plane and the distal end plane of the internal parts. 
     By the noise reducing material, the user experience is improved, as the sounds during use, which may concern a user, is reduced if not eliminated. A first noise reducing material may be positioned between the cassette and the internal injector parts, i.e. the proximal end plane, to damper noise created when auto injector parts move and come in contact with and/or act on cassette parts. The auto injector housing may also comprise a distal housing end plate against which a second noise reducing material is positioned. Thus, the second noise reducing material may be positioned between the distal end plane of the distal housing end plate. This dampers noise may by primarily distally moving parts in the auto injector and/or the cassette transferring force to the auto injector. 
     In one or more examples, the drive module is further adapted for moving the piston distally. Thus, the drive module may move the piston distally after end delivery of medicament to reset the auto injector making it ready for delivery of a new medicament dose when a new cassette is mounted in the auto injector. 
     In one or more examples, the noise reducing material, is one or more O-rings. Alternatively or complementary, the noise reducing material, is a soft material, such as rubber. 
     In one or more examples, the proximal end plane is extending in a direction perpendicular to the longitudinal direction of the auto injector. 
     In one or more examples, auto injector comprises one or more cassette interacting parts adapted for securing and fixating the cassette inside the auto injector and for facilitating administration of the medicament, wherein the one or more cassette interacting parts does not extend proximally from the proximal end plane prior to securing the cassette inside the injector. 
     In one or more examples, the one or more cassette interacting parts are adapted for moving in a proximal direction after a cassette has been positioned in the auto injector, whereby at least a part of one or more of the cassette interacting parts are extending proximally from the proximal end plane inside the auto injector. 
     In one or more examples, each of the cassette interacting parts are adapted for moving through the proximal end plane independently of another one of the cassette interacting parts. 
     In one or more examples, one or more cassette interacting parts includes a piston configured for proximal movement of a stopper comprised within the cassette, and one or more injector pins including:
         a first cassette locking pin; and   a skin sensor pin.       

     In one or more examples, one or more cassette interacting parts includes a cassette detection pin. The cassette detection pin may be substituted by other detection means such as a magnetic detection system, e.g. with magnets on cassette and auto injector surfaces coming in contact with each other and a corresponding Hall sensor inside the chassis. Alternatively, the cassette may have a pin, which comes in contact with a surface on the injector, whereby detection of the cassette is registered in the auto injector. 
     In one or more examples, the one or more injector pins further include a second cassette locking pin. The term ‘first’ and ‘second’ cassette locking pin is only meant to symbolise the presence of two pins. The pins may perform the same operation depending on the orientation of the cassette when inserted into the auto injector. Thus, both pins may e.g. function to lock the cassette into the auto injector, and/or to release cassette parts enabling delivery of medicament and/or for locking cassette parts relative to each other after delivery of medicament e.g. to prevent assess to an injection needle after delivery of medicament. If the auto injector is designed to allow insertion of a cassette only if it is orientated in a specific manner, fewer pins are needed. If the auto injector is designed to allow insertion of a cassette when orientated in a multiple manners compared to the auto injector, additional pins are normally needed. The pins may be arranged in a mirror image configuration allowing for insertion of the cassette when turning it 180 degrees around. 
     In one or more examples, the auto injector comprises a chassis with a proximal chassis part at a proximal end of the chassis. The proximal chassis part is normally perpendicular to the longitudinal direction of the auto injector. The proximal chassis part may be a plate having a circular shape, an elliptical shape, a square shape, a square shape with round corners, or similar. The proximal chassis part may be symmetrical around at least one mirror-image plane. 
     In one or more examples, the proximal chassis part comprises one or more openings adapted for allowing passage of an injector pin or the piston through each opening after or during securing of the cassette inside the auto injector. The proximal chassis part may further comprises an opening having a U-shape adapted for limiting movement of any cassette parts distally past the proximal end plane. By U-shaped is also included a U with sharp corners. 
     In one or more examples, one or more openings comprises:
         a piston opening for allowing passage of the auto injector piston there through;   a first pin opening for allowing passage of the first cassette locking pin there through;   a third pin opening for allowing passage of the skin sensor pin of the auto injector there through.       

     In one or more examples, the one or more openings further comprises a second pin opening for allowing passage of a first cassette skin sensor pin comprised in the cassette. The second pin opening may be a U-shaped opening with an end surface limiting the distal movement of the first cassette sensor pin and thereby the cassette skin sensor inside the auto injector. 
     In one or more examples, the one or more openings further comprises a fourth pin opening for allowing passage of the second cassette locking pin there through. As described above, the definition of ‘first’ and ‘second’ locking pin may depend and be defined by the orientation of the cassette, when the cassette is inserted into the au injector. 
     In one or more examples, the one or more openings further comprises a fifth opening for allowing passage of the cassette detection pin there through. The cassette detection pin may be substituted by an alternative cassette detection system and the need for the fifth opening eliminated. 
     In one or more examples, the auto injector comprises a drive module adapted for moving the piston in a proximal direction along the longitudinal axis. The drive module may further be adapted for moving the piston in a distal direction along the longitudinal axis 
     In one or more examples, drive module is further configured for moving the first cassette locking pin, and/or the skin sensor pin, and/or the second cassette locking pin in the proximal direction along the longitudinal axis. Further, the first cassette locking pin and the second cassette locking pin may be locked to the piston such that the piston and the cassette locking pins move together along the longitudinal axis. 
     Disclosed herein in a sixth aspect is a system comprising a cassette with medicament and an auto injector for administering the medicament, wherein the cassette is removable received in the auto injector, 
     wherein the auto injector comprises a housing extending from a proximal end to a distal end along a longitudinal axis, the housing comprising a cassette covering section covering the cassette when received inside the injector, the cassette covering section comprising at least one opening extending in the longitudinal direction of the housing;
 
wherein the cassette extends from a proximal end to a distal end along a longitudinal axis and comprising a cassette housing enclosing at least:
         a syringe compartment containing the medicament and adapted to be in connection with a needle for delivery of the medicament;   a stopper movable from a distal position to a proximal position inside the syringe compartment for emptying the syringe compartment;
 
wherein the cassette housing comprises at least one opening extending along a longitudinal axis of the cassette housing;
 
wherein the opening in the cassette housing and the opening in the cassette covering section are aligned when the cassette is positioned inside auto injector to facilitate inspection of the medicament in the syringe compartment.
       

     By opening is also included an opening covered by a see-through material, i.e. a window type opening. The opening allows for easy inspection of the medicament. Further, the aligned openings allows for a user friendly assembly and guidance of the cassette into the auto injector. 
     In one or more examples, the cassette covering section and the cassette housing each comprise two openings, extending in the longitudinal direction on opposite sides of the housing and the cassette housing, respectively, wherein the openings, are aligned when the cassette is positioned inside auto injector to facilitate inspection of the medicament in the syringe compartment from two opposite directions. The openings may be formed as U-shaped openings extending into the housing. This allows a user to see through the entire device, thereby enabling more light to shine through the syringe compartment to provide a better view of possible miscolouring and possibly particulates in the drug contained within syringe compartment. 
     In one or more examples, the cassette covering section comprises interior guiding tracks in parallel with the longitudinal direction configured for guiding the cassette to a correct position when inserting the cassette into the cassette covering section. An easy guiding of the cassette inside the auto injector is ensuring correct positioning inside the injector. 
     In one or more examples, the cassette covering section comprises interior guiding tracks in parallel with the longitudinal direction. 
     In one or more examples, the interior guiding tracks forms part of the one or more openings inside the cassette covering section of auto injector housing. 
     The cassette receiving chassis, the piston, and the drive module are comprised inside the housing of the auto injector. The cassette is removable received in the auto injector. 
     Disclosed herein in a fifth aspect is a system comprising an auto injector according to any of the above aspects and a cassette comprising:
         a syringe compartment containing the medicament and extending from a proximal end to a distal end, wherein the proximal end is adapted for being in connection with a needle through which the medicament is allowed to exit the syringe compartment;   a stopper movable from a distal position to a proximal position inside the syringe compartment by means of a piston in the auto injector moving the stopper proximally for emptying the syringe compartment; and   a syringe holder extending around at least part of the syringe compartment.       

     The needle may be a hollow needle in fluid connection with the proximal end of the syringe compartment and connected to the syringe as part of the syringe. Alternatively, a luer lock needle may be connected to the syringe prior to injection of medicament. As yet a further alternative, a syringe system with a syringe terminated with a stopper at its distal end and a rubber septum at its proximal end, where a penetrating needle at a distal end pierces the septum when mounted onto the syringe while a proximal needle end penetrates into the patient skin. 
     In one or more examples, the cassette further comprises a hollow needle in fluid connection with the proximal end of the syringe compartment. Further, the cassette may comprise a rigid needle shield connected to the proximal end of the syringe compartment and adapted for covering a hollow needle. The hollow needle may be part of the cassette or be connected to the syringe in the cassette prior to medicament delivery. The latter may be the case if a luer lock or a needle system penetrating a septum in the syringe when connected to the cassette as described above. 
     In one or more examples, the cassette further comprises a cassette cap, and a cassette skin sensor. In one or more examples, the cassette cap comprises a first part positioned between the rigid needle shield and the proximal end of the syringe compartment. The first part could alternatively have a ‘hook’ with sharp edges, which carve into the side of the rigid needle shield instead of at the distal end of it. Other alternatives may also be possible. 
     The cassette may thus comprise:
         a syringe compartment containing the medicament and extending from a proximal end to a distal end;   a hollow needle in fluid connection with the proximal end of the syringe compartment;   a rigid needle shield connected to the proximal end of the syringe compartment and covering the hollow needle;   a stopper movable from a distal position to a proximal position inside the syringe compartment by means of the piston moving the stopper proximally for emptying the syringe compartment;   a syringe holder extending around at least part of the syringe compartment;   a cassette cap having a first part positioned between the rigid needle shield and the proximal end of the syringe compartment, and   a cassette skin sensor.       

     In one or more examples, the syringe compartment, the hollow needle and the stopper is part of a syringe. The syringe may be fixed inside the syringe holder, at a distal end of the syringe. 
     In one or more examples, the cassette is interfacing with the auto injector at the distal end of the cassette sharing the same longitudinal axis. This mitigates risk of the cassette getting stuck inside in the injector and also help to make the connection as slim as possible. 
     In one or more examples, the cassette is adapted for being received in the auto injector by movement of the cassette and the auto injector towards each other along a shared longitudinal axis without significant rotation of the cassette around the shared longitudinal axis. 
     In one or more examples, when the drive module moves the first cassette locking pin proximally, the cassette is locked in auto injector. The second cassette locking pin may in addition or alternatively lock the cassette in the auto injector by proximal movement of the second cassette locking pin. The cassette locking pins may move simultaneously or individually. The cassette locking pins may also move together with the piston by e.g. locking/connecting the three pins together. 
     In one or more examples, when the drive module moves the first cassette locking pin further in the proximal direction, the cassette skin sensor is adapted for being distally unlocked from the syringe holder allowing for distal movement of the cassette skin sensor. The second cassette locking pin may in addition or alternatively unlock the syringe holder by further proximal movement of the second cassette locking pin. The cassette locking pins may move simultaneously or individually. The cassette locking pins may also move together with the piston by e.g. locking/connecting the three pins together. Thus, when the drive module moves the second cassette locking pin further in the proximal direction, the cassette skin sensor may be adapted for being proximally unlocked from the syringe holder allowing for proximal movement of the cassette skin sensor relative to the syringe holder. 
     In one or more examples, when the drive module moves the piston proximally, the second cassette locking pin is adapted for also unlocking for movement of the cassette skin sensor. 
     In one or more examples, the system according further comprising a skin sensor spring system adapted for pushing the skin sensor pin of auto injector against a second cassette skin sensor pin at least after release of the cassette skin sensor from the syringe holder by movement of the first cassette locking pin and/or the second cassette locking pin in a proximal direction. 
     In one or more examples, the skin sensor spring system is adapted for pushing the cassette skin sensor in a proximal direction into a locked position preventing movement of the cassette skin sensor in a distal direction. This ensures that the needle is not exposed after end delivery of medicament. The cassette skin sensor may be pushed into a locked position preventing distal movement of the cassette skin sensor. The distal locking may be facilitated by a cassette skin sensor arm, where a locking surface of the cassette skin sensor arm locks into an inner opening in the cassette housing. Proximal movement of the cassette skin sensor may also be prevented, e.g. by an additional set of housing-skin sensor surfaces. 
     In one or more examples, the syringe holder comprises a syringe holder support tube, which supports the syringe compartment. 
     In one or more examples, the cassette skin sensor covers at least part of the syringe holder, such as the majority of the syringe holder. 
     In one or more examples, the cassette skin sensor comprises at least a first skin sensor pin and/or a second skin sensor pin extending from the distal end of the cassette skin sensor. 
     In one or more examples, the syringe holder comprises one or more openings selected from the group of:
         a first pin opening for allowing passage of a first cassette locking pin of the auto injector there through;   a second pin opening for allowing passage of the first cassette skin sensor pin;   a third pin opening for allowing passage of a skin sensor pin of the auto injector, and/or the second cassette skin sensor pin there through;   a fourth pin opening for allowing passage of a second cassette locking pin of the auto injector there through;   a piston opening for allowing passage of the auto injector piston there through.       

     In one or more examples, the syringe holder comprises a syringe holder plate, wherein the piston opening and/or one or more of the pin openings are positioned in the syringe holder plate. 
     In one or more examples, the syringe holder comprises a first syringe holder arm extending in a proximal direction from the syringe holder plate. 
     In one or more examples, the first syringe holder arm comprises a proximal surface, and wherein the cassette skin sensor comprises a first locking protrusion engaging with the proximal surface, wherein the engagement of the first locking protrusion and the proximal surface prevents movement of the cassette skin sensor towards the syringe holder. 
     In one or more examples, the first syringe holder arm is flexibly connected to the syringe holder plate. 
     In one or more examples, the first syringe holder arm is deflectable by proximal movement of the first cassette locking pin of the auto injector through the first pin opening in the syringe holder, wherein the deflection of the first syringe holder arm releases the cassette skin sensor allowing it to move towards the syringe holder. 
     In one or more examples, upon movement of the cassette skin sensor towards the syringe holder:
         the first cassette skin sensor pin is brought into/extends through the second pin opening in the syringe holder, and   the second cassette skin sensor pin is brought into/extends through the third pin opening in the syringe holder.       

     In one or more examples, the syringe holder comprises a second syringe holder arm extending in a proximal direction from the syringe holder plate. 
     In one or more examples, the second syringe holder arm comprises a distal surface, and wherein the cassette skin sensor comprises a second locking protrusion against which the distal surface is resting, wherein the engagement of the second locking protrusion and the distal surface prevents movement of the cassette skin sensor away from the syringe holder. 
     In one or more examples, the second syringe holder arm is flexibly connected to the syringe holder plate. 
     In one or more examples, the second syringe holder arm is deflectable by proximal movement of the second cassette locking pin of the auto injector through the fourth pin opening in the syringe holder, wherein the deflection of the second syringe holder arm allows the cassette skin sensor it to move away from the syringe holder. 
     In one or more examples, the syringe holder further comprises one or more syringe locking protrusions locking the syringe in the cassette. 
     In one or more examples, the syringe holder and thereby the cassette is locked to the auto injector housing when the cassette is positioned in the auto injector. 
     In one or more examples, the syringe holder and the skin sensor are longitudinally movable relative to each other upon release of the skin sensor from the syringe holder. 
     In one or more examples, the cassette further comprises a cassette housing extending from a proximal to a distal end, the cassette housing enclosing at least the syringe holder and the cassette skin sensor. 
     In one or more examples, the cassette housing comprises one or more locking openings at the distal end into which the one or more syringe holder locking protrusions on the syringe holder locks syringe holder to the cassette housing. 
     In one or more examples, the cassette housing comprises one or more internal protruding rails inside the cassette housing for guiding the skin sensor inside the cassette housing. 
     In one or more examples, the cassette housing comprises a distal end surface with a skin sensor housing opening through which the cassette skin sensor extends. 
     In one or more examples, the cassette housing is oval. 
     In one or more examples, the cassette cap comprises an inner rigid needle shield tube with the first part and an outer an outer rigid needle shield tube, wherein:
         the outer rigid needle shield tube surrounds the inner rigid needle shield tube, and   the inner rigid needle shield tube surrounds the rigid needle shield.       

     In one or more examples, the outer rigid needle shield tube abuts the distal end surface of the cassette housing, and wherein the proximal end of the cassette skin sensor is positioned between the inner rigid needle shield tube and the outer rigid needle shield tube. 
     In one or more examples, the cassette cap is removable from the syringe compartment, and wherein when the cassette cap is removed, the rigid needle shield follows with it, whereby the hollow needle is exposed. 
     In one or more examples, the cassette cap is an elongated tube positioned between the syringe and the cassette skin sensor. 
     In one or more examples, the cassette cap comprises at least one holder pin extending from a distal end of the cassette cap. 
     In one or more examples upon proximal movement of a cassette cap pin in the auto injector abutting the at least one holder pin, the cassette cap and thereby also the rigid needle shield is pushed proximally for release of the rigid needle shield. 
     In one or more examples, the cassette covering section comprises at least one opening extending in the longitudinal direction of the housing, wherein the cassette housing comprises at least one opening extending along a longitudinal axis of the cassette housing, wherein the at least one opening in the cassette housing and the at least one opening in the cassette covering section are aligned when the cassette is positioned inside auto injector to facilitate inspection of the medicament in the syringe compartment. By opening is also included an opening covered by a see-through material, i.e. a window type opening. 
     In one or more examples, the cassette covering section and the cassette housing each comprise two openings, extending in the longitudinal direction on opposite sides of the housing and the cassette housing, respectively, wherein the openings, are aligned when the cassette is positioned inside auto injector to facilitate inspection of the medicament in the syringe compartment from two opposite directions. The openings may be formed as U-shaped openings extending into the housing. This allows a user to see through the entire device, thereby enabling more light to shine through the syringe compartment to provide a better view of possible miscolouring and possibly particulates in the drug contained within syringe compartment. 
     In one or more examples, the cassette and auto injector housing have cross sectional planes perpendicular to the longitudinal axis of the cassette housing and the auto injector housing, wherein the cross sectional planes are non-circular in shape, such as oval or square in shape. By cross sectional planes are meant planes perpendicular to the longitudinal axis. The oval shape includes cross-sectional planes where two perpendicular radius differs by at least 10% such as 20% such as 30%. Max 50% 
     In one or more examples, the cassette covering section comprises interior guiding tracks in parallel with the longitudinal direction configured for guiding the cassette to a correct position when inserting the cassette into the cassette covering section. Easy guiding of the cassette inside auto injector ensuring correct positioning inside the injector. 
     In one or more examples, the interior guiding tracks forms part of the openings inside the cassette covering section of auto injector housing. 
     In one or more examples, the cassette receiving chassis is a cassette receiving chassis extending from a proximal end to a distal end, wherein the proximal end of the chassis comprises a proximal chassis part with one or more openings selected from the group of:
         a piston opening for allowing passage of the auto injector piston there through;   a first pin opening for allowing passage of the first cassette locking pin there through;   a second pin opening for allowing passage of the first cassette skin sensor pin;   a third pin opening for allowing passage of:
           the skin sensor pin of the auto injector, and/or   the second cassette skin sensor pin   
           there through;   a fourth pin opening for allowing passage of the second cassette locking pin there through;   a fifth opening for allowing passage of the cassette detection pin there through.       

     In one or more examples, the second pin opening is a well-shaped opening with an end surface limiting the distal movement of the first cassette sensor pin and thereby the cassette skin sensor inside the auto injector. 
     In one or more examples, drive module is further configured for moving the first cassette locking pin, the skin sensor pin, the second cassette locking pin, and the cassette detection pin proximally. 
     In one or more examples, when the drive module moves the first cassette locking pin proximally, the cassette skin sensor is distally unlocked from the syringe holder allowing for distal movement of the cassette skin sensor, wherein the unlocking of the cassette skin sensor locks the cassette in the auto injector. 
     In one or more examples, when the drive module moves the piston proximally for delivery of medicament, the second cassette locking pin is also unlocked for movement of the cassette skin sensor proximally after delivery of medicament and/or removal of the auto injector from the patient&#39;s skin. 
     In one or more examples, the auto injector further comprising a skin sensor spring system pushing the skin sensor pin of the auto injector against the second cassette skin sensor pin at least after release of the cassette skin sensor from the syringe holder by proximal movement of the first cassette locking pin and the second cassette locking pin. 
     In one or more examples, the skin sensor spring system pushes the cassette skin sensor proximally in a locked position preventing distal movement of the cassette skin sensor. 
     In one or more examples, the housing is in one piece with a proximal opening for receiving the cassette. 
     Disclosed herein in a seventh aspect is a method for assembling a cassette for use in an auto injector, the method comprising:
         assembling an outer cassette part comprising a cassette housing and a cassette cap by connecting a proximal end of the cassette housing to a distal end of the cassette cap;   inserting a proximal end of an inner cassette part into a distal end of the outer cassette part and pushing the inner cassette part into the outer cassette part such that the majority of the inner cassette part is covered by the outer cassette part.       

     The method allows for very easy assembly of the cassette, which may be unscaled and atomized. Also, the method allows for assembly of the cassette at one location from where the cassette can be shipped to a different location for a subsequent step of inserting a syringe into the cassette. This allows the cassette to be used with a variety of syringes containing different medicament. 
     Assembling the distal end of the cassette cap to the proximal end of the cassette housing ensures that a minimum of material is needed for the cassette cap. WO 2021/085033 discloses a front end for an auto-injector with “cassette cap and cassette housing” parts in the form of a syringe cover (item 9) and an outer sleeve (item 2), respectively. However, in WO 2021/085033 it is essential that the syringe cover is attached at the distal end of the outer sleeve, since the syringe cover has an additional security function, which requires it to be positioned on the outer sleeve after delivery of medicament. To ensure that the syringe cover cannot be removed again, barbs (items 9.1) on the inside of the syringe cover engages an outer diameter of a locking sleeve (10), which has an extended position after medicament delivery. The barbs requires an amount of space preventing an assembly of the syringe cover at the proximal end of the outer sleeve. 
     In one or more examples, the inner cassette part comprises a comprising a syringe holder. In one or more examples, the method is further comprising assembling the inner cassette part comprising the syringe holder and a cassette skin sensor by inserting a proximal end of the syringe holder into a distal end of the cassette skin sensor and pushing the syringe holder into the cassette skin sensor such that a part of the syringe holder is covered by the cassette skin sensor. Assembling of the outer cassette part and inner cassette part may be performed simultaneously or in random order. 
     In one or more examples, the part of the syringe holder covered by the cassette skin sensor constitutes at least 10%, such as at least 20%, such as at least 30%, such as at least 40%, such as at least 50%. 
     In one or more examples, the cassette cap is extending from the distal end to a proximal end along a longitudinal axis, wherein the method further comprises positioning the cassette cap in a first mount with the longitudinal axis positioned in an upwards direction such that the distal end is positioned above the proximal end prior to the assembling of the outer cassette part. 
     In one or more examples, the cassette cap is maintained positioned in the position in the first mount while assembling the outer cassette part. 
     In one or more examples, the cassette skin sensor is extending from the distal end to a proximal end along a longitudinal axis, wherein the method further comprises comprising positioning the cassette skin sensor in a second mount with the distal end in an upwards direction such that the distal end is positioned above the proximal end prior to the assembling of the inner cassette part. 
     In one or more examples, the cassette skin sensor is maintained positioned in the second mount while assembling the inner cassette part. 
     In one or more examples, the inner cassette part is inserted into the outer cassette part while the outer cassette part is positioned in the first mount. The first and second mount may be an integrate mount or separate mounts. The first mount may e.g. by a first part of a mount and the second mount a second part of the same mount. By using mounts, a large batch of parts can be assembled at once. 
     The cassette housing may be extending from a distal end to the proximal end along a longitudinal axis. The method may also include positioning the cassette housing in an upwards direction such that the proximal end is positioned above the distal end prior to the assembling of the outer cassette part, and flipping the cassette housing around to have the distal end point in the upwards for assembling of the cassette housing and the cassette cap. 
     In one or more examples, the syringe holder comprises one or more syringe locking protrusions, wherein the method further comprises fixating a syringe inside the inner cassette part by inserting a proximal end of the syringe into the distal end of the inner cassette part, pushing the syringe into the inner cassette part, and moving the one or more syringe locking protrusions to lock the syringe inside the inner cassette. If the cassette housing is without the cassette locking protrusions, the syringe may be fixed in the syringe holder be frictional force. 
     In one or more examples, syringe extends from a proximal end to a distal end and comprises:
         a syringe compartment containing medicament, and extending from a proximal end to a distal end, wherein the proximal end is adapted for being in connection with a needle through which the medicament is allowed to exit the syringe compartment;   a stopper adapted for being moved from a distal position to a proximal position inside the syringe compartment.       

     The needle may be a hollow needle in fluid connection with the proximal end of the syringe compartment and connected to the syringe as part of the syringe. Alternatively, a luer lock needle may be connected to the syringe prior to injection of medicament. As yet a further alternative, a syringe system with a cartridge terminated with a stopper at its distal end and a rubber septum at its proximal end, where a penetrating needle at a distal end pierces the septum when mounted onto the cartridge while a proximal needle end penetrates into the patient skin. 
     In one or more examples, the syringe further comprises a hollow needle in fluid connection with the proximal end of the syringe compartment. The syringe may also comprise a rigid needle shield connected to the proximal end of the syringe compartment and adapted for covering the hollow needle. The hollow needle may be part of the cassette or be connected to the syringe in the cassette prior to medicament delivery. The latter may be the case if a luer lock or a needle system penetrating a septum in the syringe when connected to the cassette as described above. 
     The syringe may in this example for example be a 2.25 ml syringe. 
     In one or more examples, the method further comprises inserting a proximal end of a cassette sleeve into the distal end of the syringe holder and pushing the cassette sleeve into the syringe holder such that the majority of the cassette sleeve is covered by the syringe holder prior to or directly after inserting the syringe holder into the cassette skin sensor, the cassette sleeve thereby constituting a part of the inner cassette part. 
     In one or more examples, the cassette sleeve comprises proximal extending deflectable sleeve arms. 
     In one or more examples, the syringe comprises the hollow needle, and a rigid needle shield, wherein the deflectable sleeve arms deflects into openings in the syringe holder and cassette skin sensor when the syringe is inserted into the inner cassette part allowing the rigid needle shield to pass the deflectable sleeve arms. 
     In one or more examples, the deflectable sleeve arms relax into a position between the rigid needle shield and the syringe compartment after the rigid needle shield has passed the deflectable sleeve arms. 
     In one or more examples, wherein when the syringe is inserted into the cassette sleeve and the deflectable sleeve arms have relaxed into a position between the rigid needle shield and the syringe compartment, a collar on a distal end of the syringe abuts a distal part of the cassette sleeve preventing further proximal movement of the syringe relative to the cassette sleeve. 
     In one or more examples, after the deflectable sleeve arms have relaxed into a position between the rigid needle shield and the syringe compartment, and the syringe is pushed further proximally before locking it to the cassette, the cassette sleeve rotates into a position from where the deflectable sleeve arms cannot deflect. The proximal end of the cassette sleeve thereby prohibits/prevents proximal and axial movement of the syringe relative to the cassette sleeve. The syringe is thereby further secured inside the cassette sleeve. 
     In one or more alternative examples, the syringe comprises the hollow needle, and a rigid needle shield, and the deflectable sleeve arms forms a sleeve opening at the proximal end of the cassette sleeve, the sleeve opening allowing the rigid needle shield to pass through without the axially outward deflection of the deflectable sleeve arms. When the syringe is inserted into the cassette sleeve and the deflectable sleeve arms is between the rigid needle shield and the syringe compartment, a collar on a distal end of the syringe may abut a distal part of the cassette sleeve preventing further proximal movement of the syringe relative to the cassette sleeve. 
     In one or more examples when the deflectable sleeve arms is at a position between the rigid needle shield and the syringe compartment, further proximal movement of the syringe and the cassette sleeve into the cassette forces the cassette sleeve to rotate from a position where the deflectable sleeve arms are aligned with openings in the syringe holder to a position where the deflectable sleeve arms are pushed radially inward by the syringe holder into a position from where the deflectable sleeve arms cannot deflect back to the original position. The radially inward movement of deflectable arms pushes the proximal end of the cassette sleeve into a position between the rigid needle shield and the syringe compartment such that the proximal end of the cassette sleeve prohibits/prevents proximal and axial movement of the syringe relative to the cassette sleeve. The syringe is thereby further secured inside the cassette sleeve. 
     The cassette sleeve may comprises at least one sleeve locking protrusion coming in contact with at least one inner helical surface part inside the syringe holder when the syringe is pushed proximally. The helical shape of the at least one inner helical surface part forces the cassette sleeve to rotate. The rotation may be between 70-110 degrees, such as 80-100 degrees, such as 85-95 degrees, such as approximately 90 degrees. 
     In one or more examples, the rotation of the cassette sleeve rotates it into a position allowing a viewer to view the medicament inside the syringe. 
     In one or more examples, the syringe is inserted in the inner cassette part while the outer cassette part assembled with the inner cassette part is positioned in the first mount. 
     The cassette cap may comprise a first part positioned between the rigid needle shield and the proximal end of the syringe compartment when the syringe is positioned inside the inner cassette part, and an inner rigid needle shield tube with the first part and an outer rigid needle shield tube, wherein the outer rigid needle shield tube surrounds the inner rigid needle shield tube, and the inner rigid needle shield tube surrounds the rigid needle shield. 
     The first part of the cassette cap may extend inside the cassette housing opening when the outer cassette part is assembled. 
     Any of the above features described in conjunction with a particular aspect/example is not limited to that aspect/example and can be practiced in any other examples even if not so illustrated, or if not so explicitly described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various examples are described hereinafter with reference to the figures. Like reference numerals refer to like elements throughout. Like elements will, thus, not be described in detail with respect to the description of each figure. It should also be noted that the figures are only intended to facilitate the description of the examples. They are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention. In addition, an illustrated example needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular example is not necessarily limited to that example and can be practiced in any other examples even if not so illustrated, or if not so explicitly described. 
         FIG.  1 A  shows an example of a cassette in an exploded view, and  FIGS.  1 B-C  show a close-up of a syringe holder in the cassette in  FIG.  1 A  seen from two different directions. 
         FIG.  2    shows a cut-through of the assembled cassette of  FIG.  1 A . 
         FIG.  3    shows an example of an auto injector for receiving a cassette as shown e.g. in  FIGS.  1 - 2   , where the auto injector is shown in an exploded view. 
         FIG.  4 A  shows a cut-through view and  FIG.  4 B  a side-view of the of the auto injector of  FIG.  3   . 
         FIG.  5    shows a close-up of the chassis shown in  FIG.  3   . 
         FIGS.  6 A-C  show cut-through views of the auto injector of  FIGS.  3 - 5    with a cassette as shown in  FIGS.  1 - 2    in different positions during loading and locking of the cassette in the auto injector, and  FIG.  6 D  show the auto injector with the cassette in a perspective view. 
         FIGS.  7 A-C  show the steps in releasing the cassette skin sensor from the syringe holder in the cassette of  FIGS.  1 - 2    by means of the auto injector of  FIGS.  3 - 5   ,  FIGS.  7 D-F  show the locking of the cassette skin sensor in a proximal position after delivery of medicament, and  FIG.  7 G  shows the cassette skin sensor seen from a different angle compared to  FIGS.  7 A-F . 
         FIG.  8 A-B  show an assembly of an outer cassette part. 
         FIG.  9 A-C  show an assembly of an inner cassette part, and  FIG.  9 D  shows a cut-through of the inner cassette part of  FIG.  9 C . 
         FIGS.  10 A-C  show the assembly of a cassette comprising the outer cassette part of  FIGS.  8 A-C  and the inner cassette part of  FIGS.  9 A-D . 
         FIGS.  11 A-D  show the assembly of the cassette of  FIGS.  10 B-C  with a syringe. 
         FIGS.  12 A-B  show a cassette sleeve. 
         FIG.  13 A-B  show a cassette sleeve and the inside of a syringe holder. 
         FIGS.  14 A-E  show the assembling of a syringe into a cassette having a cassette sleeve as shown in  FIGS.  12 A-B  included. 
         FIGS.  15 A-D  show the assembling of a syringe into a cassette having a cassette sleeve as shown in  FIGS.  12 A-B  included in a cut-through view as compared to  FIGS.  14 A-E . 
         FIG.  16    shows an example of an auto injector for receiving a cassette as shown e.g. in  FIGS.  1 - 2    or  FIGS.  8 - 15   , where the auto injector is shown in an exploded view. 
         FIG.  17    shows a view into an assembled auto injector as shown in  FIG.  16   . 
         FIGS.  18 A-B  show the assembling of a cassette and an auto injector. 
         FIG.  19    shows a cut-through of the internal parts in the auto injector of  FIGS.  16 - 18   . 
         FIGS.  20 A- 1    show the steps in releasing the cassette skin sensor from the syringe holder in the cassette, and locking of the cassette skin sensor in a proximal position after delivery of medicament. 
     
    
    
     DESCRIPTION OF DRAWINGS 
     Exemplary examples will now be described more fully hereinafter with reference to the accompanying drawings. In this regard, the present examples may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the examples are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     In the drawings, thicknesses of a plurality of layers and areas are illustrated in an enlarged manner for clarity and ease of description thereof. When a layer, area, element, or plate is referred to as being “on” another layer, area, element, or plate, it may be directly on the other layer, area, element, or plate, or intervening layers, areas, elements, or plates may be present therebetween. Conversely, when a layer, area, element, or plate is referred to as being “directly on” another layer, area, element, or plate, there are no intervening layers, areas, elements, or plates therebetween. Further when a layer, area, element, or plate is referred to as being “below” another layer, area, element, or plate, it may be directly below the other layer, area, element, or plate, or intervening layers, areas, elements, or plates may be present therebetween. Conversely, when a layer, area, element, or plate is referred to as being “directly below” another layer, area, element, or plate, there are no intervening layers, areas, elements, or plates therebetween. 
     The spatially relative terms “lower” or “bottom” and “upper” or “top”, “below”, “beneath”, “less”, “above”, and the like, may be used herein for ease of description to describe the relationship between one element or component and another element or component as illustrated in the drawings. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the drawings. For example, in the case where a device illustrated in the drawings is turned over, elements described as being on the “lower” side of other elements, or “below” or “beneath” another element would then be oriented on “upper” sides of the other elements, or “above” another element. Accordingly, the illustrative term “below” or “beneath” may include both the “lower” and “upper” orientation positions, depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below, and thus the spatially relative terms may be interpreted differently depending on the orientations described. 
     Throughout the specification, when an element is referred to as being “connected” to another element, the element is “directly connected” to the other element, or “electrically connected” to the other element with one or more intervening elements interposed therebetween. 
     The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms, including “at least one,” unless the content clearly indicates otherwise. “At least one” is not to be construed as limiting “a” or “an.” It will be further understood that the terms “comprises,” “comprising,” “includes” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that, although the terms “first,” “second,” “third,” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, “a first element” discussed below could be termed “a second element” or “a third element,” and “a second element” and “a third element” may be termed likewise without departing from the teachings herein. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” may mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value. 
     Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which this invention pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined in the present specification. 
     Exemplary examples are described herein with reference to cross section illustrations that are schematic illustrations of idealized examples, wherein like reference numerals refer to like elements throughout the specification. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, examples described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims. Some of the parts which are not associated with the description may not be provided in order to specifically describe exemplary examples of the present disclosure. 
     All references to the proximal direction or proximal surfaces refer to parts, surfaces and similar oriented in the direction of insertion, i.e. in the direction of the insertion needle and the outer part of the auto injector touching the skin during injection of the medicament. 
     Likewise, all references to the distal direction or distal surfaces refer to parts, surfaces and similar oriented in the direction away from the direction of the insertion needle, i.e. in the direction of the user. 
       FIG.  1 A  shows an example of a cassette  500  in an exploded view. An auto injector  1000  for receiving the cassette  500  is shown in  FIGS.  3 - 5   . The cassette comprises a syringe  200  with a syringe compartment  202  containing the medicament, a hollow needle  204  in fluid connection with the syringe compartment, a rigid needle shield  206  connected to the proximal end of the syringe compartment and covering the hollow needle, and a stopper  208  movable from a distal position to a proximal position inside the syringe compartment  202  by means of a piston in the auto injector. 
     The needle shield  206  shown in  FIG.  1 A  has both an outer part  206 , and an inner part  207 . The parts may normally be a connected or even produced as a one-piece item. 
     Positioned around the syringe  200  is a syringe holder  510  extending around at least part of the syringe compartment  202 . The syringe holder  510  (see further details in  FIGS.  1 B-C ) has a syringe holder support tube  511 , which supports the syringe compartment  202 . The tube  511  has an opening for inspection of the medicament in the syringe compartment  202 . The syringe  200  is fixed inside the syringe holder  510  at the distal end  205  of the syringe  200 , which has a collar-like shape. Syringe holder rings  507   a,    507   b  may be used for further securing the syringe  200  inside the syringe holder  510 . These may also be omitted. 
     The cassette  500  comprises a cassette housing  540  extending from a proximal  541  to a distal end  542 . The cassette housing  540  is oval, which helps ensure an accurate positioning of the cassette  500  inside the auto injector  1000 . The oval shape may also make the cassette more compact. Alternative shapes such as square shape may also be imagined. 
     The cassette housing  540  is enclosing a cassette skin sensor  550 . At the proximal end  541  of the cassette housing  540  is a housing shoulder  546  with an opening  545  through which the cassette skin sensor  540  can extend. The cassette housing  540  have internal protruding rails  548  (not shown in the figure) on its inside for guiding the skin sensor  550 . The two parts  540 ,  550  are movable in relation to each other in an unlocked configuration. The cassette skin sensor  550  is positioned such that it extends proximally from the cassette housing  540 . 
     The cassette housing  540  has a distal end surface  543  with a skin sensor housing opening  545  through which the cassette skin sensor  550  extends. This is most clearly seen in the cut-through images, e.g. in  FIG.  2   . The cassette housing  540  has an opening  547  in the longitudinal direction for inspection of the medicament in the cassette  500 . 
     The cassette skin sensor  550  has two pins; a first skin sensor pin  557  and a second skin sensor pin  558 , extending from the distal end  552  of the cassette skin sensor  550 . 
     The cassette skin sensor  550  covers at least part if not the majority of a syringe holder  510 , which is shown in more details in  FIGS.  1 B-C  in a front-end and a rear-end perspective view. The syringe holder  510  has an elongated tubular part  511  with an opening for inspection of the medicament. At the distal end  509  of the syringe holder  510  is a syringe holder plate  519 , which has a number of openings including: a first pin opening  526 , a second pin opening  527 , a third pin opening  528 , a fourth pin opening  529 , and a piston opening  525 . It is through the piston opening  525  that the auto injector piston  1168  extends when medicament is delivered to the patient. The openings are normally circular, but may also have different shapes mimicking the shape of the pins extending there through. The openings may be positioned at the peripheral edge of the syringe holder plate  519  such that only part of the circular opening extends into the syringe holder plate  519 . This is shown in the example in  FIGS.  11 C-D . 
     The syringe holder  510  also comprises a first syringe holder arm  512  extending in a proximal direction from the syringe holder plate  519 . The first syringe holder arm  512  has a proximal surface  514  at the proximal end of the arm  512 . When the cassette skin sensor  550  and the syringe holder  510  are in a first position, a first locking protrusion  553  on the cassette skin sensor  550  engages with the proximal surface  514 . This engagement of the first locking protrusion  553  and the proximal surface  514  prevents movement of the cassette skin sensor  550  towards the syringe holder  510 . The first syringe holder arm  512  is flexibly connected to the syringe holder plate  519 . 
     The syringe holder  510  may also comprise a syringe holder ring  507   a,  which locks the syringe  200  inside the syringe holder  510 . 
     When the cassette  500  is positioned in the auto injector  1000 , the first pin opening  526  allows for passage of a first cassette locking pin  1156  of the auto injector  1000  there through. This is seen and described in connection with e.g.  FIGS.  7 A-F . When the first cassette locking pin  1156  of the auto injector  1000  passes through the first pin opening  526  in the syringe holder  510 , it comes in contact with the first syringe holder arm  512  and deflects it. This causes a release of the cassette skin sensor  550  allowing it to move towards the syringe holder  510 , i.e. a distal direction movement of the cassette skin sensor  550 . Upon movement of the cassette skin sensor  550  towards the syringe holder  510 , the first cassette skin sensor pin  557  moves towards—and possibly through—the second pin opening  527  in the syringe holder  510 . Similarly, the second cassette skin sensor pin  558  moves towards—and possibly through—the third pin opening  528  in the syringe holder  510  when the cassette skin sensor  558  moves distally. 
     The syringe holder  510  and the skin sensor  550  are longitudinally movable relative to each other upon release of the skin sensor  550  from the syringe holder  510 . 
     The syringe holder  510  also has a second syringe holder arm  516  extending in a proximal direction from the syringe holder plate  519  (see  FIG.  7 G ). The second syringe holder arm  516  comprises a distal surface  518  at the proximal end of the arm. The distal surface  518  is resting against a second locking protrusion  554  on the cassette skin sensor  550 . This engagement prevents movement of the cassette skin sensor  550  away from the syringe holder  510 . Before unlocking the cassette skin sensor  550  and the syringe holder  510  by deflection of the first syringe holder arm  512 , the two parts are thus prevented from both moving towards and away from each other. 
     The second syringe holder arm  516  is also flexibly connected to the syringe holder plate  519 . When a second cassette locking pin  1159  of the auto injector  1000  is pushed through the fourth pin opening  529 , it comes in contact with the second syringe holder arm  516  (see  FIG.  7 G ). This results in a deflection of the second syringe holder arm  516 , which in turn releases the cassette skin sensor  550  again, this time allowing it to move away from the syringe holder  510  in the proximal direction. 
     The third pin opening  528  allows passage of a skin sensor pin  1158  of the auto injector  1000  (see  FIGS.  7 A-F ), which pushes on the second cassette skin sensor pin  558  of the cassette skin sensor  550 . The second cassette skin sensor pin  558  may also pass through the third pin opening  528  before coming in contact with the skin sensor pin  1158 . 
     The syringe holder  510  has two syringe holder locking protrusions  524  fitting into openings  544  at the distal end  541  of the cassette housing  540 . This locks the syringe holder  510  and the cassette housing  540  together. More locking protrusions/openings could also be imagined. 
     The syringe holder  510  further comprises one or more syringe locking protrusions  515  locking the syringe  200  to the cassette  500 . 
     The cassette  500  further has a cassette cap  530  having a first part  531  positioned between the rigid needle shield  206  and the proximal end of the syringe compartment  201 . The cassette cap  530  comprises an inner rigid needle shield tube  535  with the first part  531  and an outer rigid needle shield tube  536 . This is most clearly seen in  FIGS.  6 A-C . The outer rigid needle shield tube  536  surrounds the inner rigid needle shield tube  535 , and the inner rigid needle shield tube  535  surrounds the rigid needle shield  206 . 
     The outer rigid needle shield tube  536  abuts the housing shoulder  546  of the cassette housing  540  as shown in  FIG.  2   . The proximal end  560  of the cassette skin sensor  550  is positioned between the inner rigid needle shield tube  535  and the outer rigid needle shield tube  536  as shown in  FIG.  2   . The cassette cap  530  is removable from the syringe compartment  202 , and when the cassette cap  530  is removed, the rigid needle shield  206  follows with it, whereby the hollow needle  204  is exposed. 
       FIGS.  3 - 4    show an example of an auto injector  1000  for receiving the cassette of  FIGS.  1 - 2   . The auto injector  1000  is shown in an exploded view in  FIG.  3   , whereas  FIG.  4 A-B  show the assembled auto injector  1000 . For obtaining a clear view inside the auto injector, the outer housing  1102  has been omitted. The outer housing  1102  can be seen in  FIGS.  6 A-D . 
     The auto injector  1000  extends from a proximal end to a distal end and comprises the housing  1102  extending from a proximal end  1103  to a distal end  1104 . The housing is in one piece in this example of the auto injector. The cassette  500  is loaded into the auto injector  1000  in a front-loading configuration. 
     The auto injector  1000  comprises a cassette receiving chassis  1110  configured to receive the cassette  500 . The cassette  500  is interfacing with the auto injector  1000  at the distal end of the cassette  500 , whereby the two parts are sharing the same longitudinal axis. This mitigates the risk of the cassette getting stuck inside in the auto injector. Further, it makes the connection as slim as possible. The only auto injector element, which extends in parallel with the cassette  500  is normally the injector housing  1102 . The injector housing may therefore be seen as having two sections; a cassette covering section  1108  and a distal section  1106  covering internal injector parts inside the auto injector  1000  (see the auto injector example in  FIGS.  18 A-B ). The internal injector parts includes a drive module  1150 , which is adapted to move a piston  1168 . The piston  1168  is moved proximally pushing on the stopper  208  inside the syringe whereby medicament can be expelled from the syringe  200 . The piston  1168  has an inner threading (not shown in the figure), which engages with an outer threading on a led screw  1169 . When the lead screw  1169  is rotated by the drive element  1150 , the piston  1168  moves proximally. The drive module  1150  includes a motor  1151 , which through a gear assembly  1153 , rotates the led screw  1151 . The gear assembly  1153  is covered by a gear cover  1152 , some  0 -rings  1155  and a chassis cover  1154 . The O-ring may be seen as a noise reducing material, which dampers any noise may by the internal parts inside the auto injector during use. A similar noise reducing material is found at the proximal end of the internal parts shown here in the form of a larger O-ring  1109 . 
     The drive element  1150  also controls the movement of a number of pins comprised in the auto injector  1000 . As shown in  FIG.  3   , the number of pins include; a first cassette locking pin  1156 , a skin sensor pin  1158 , a second cassette locking pin  1159 , and a cassette detection pin  1160 . Thus, the drive module  1150  is further configured for moving the first cassette locking pin  1156 , the skin sensor pin  1158 , the second cassette locking pin  1159 , and the cassette detection pin  1160  proximally. The pins and the piston may also be referred to as cassette interacting parts adapted for securing and locking the cassette  500  inside the auto injector  1000  and for facilitating administering of the medicament. In common for the cassette interacting parts shown in  FIG.  3    is that they move in parallel with the longitudinal axis of the auto injector  1000 . 
     Acting on the skin sensor pin  1158 , which pushes the cassette skin sensor  550  proximally after delivery of medicament, is a spring system  1140 . The spring system  1140  includes a spring guidance pin  1141  around which a supporting chassis  1142  connected to the skin sensor pin  1158  is found. Extending around the guidance pin  1141  is also a spring  1143 . When the spring  1143  is allowed to relax, it pushes the supporting chassis  1142  forward, which in turn pushes the skin sensor pin  1158  proximally. Inside the skin sensor pin  1158  at the distal end thereof is a guide pin  1161  for the skin sensor pin  1158 . When the skin sensor spring system  1140  pushes the cassette skin sensor  550  proximally after delivery of medicament, it is pushed into a locked position preventing distal movement of the cassette skin sensor  550 . Proximal movement of the cassette skin sensor  550  may also be prevented in this locked position. 
     The auto injector  1000  also comprises a cassette receiving chassis  1110  configured to receive a cassette  500 . The cassette receiving chassis  1110  is in the shape of a chassis as seen in  FIGS.  3  and  5   , the latter showing an enlarged view of the cassette receiving chassis  1110 . The cassette receiving chassis  1110  is extending from a proximal end  1111  to a distal end  1112 . At the proximal end  1111  of the chassis  1110 , is a proximal chassis part  1114  with a number of openings including a piston opening  1115 , a first pin opening  1116 , a second pin opening  1117 , a third pin opening  1118 , a fourth pin opening  1119 , and a fifth opening  1120 . Depending on the number of pins in the auto injector, fewer openings could also be used. The openings are round circular openings in this shown example in  FIG.  5   , but may also have a different shape mimicking the shape of the pins if they are not round. 
     When the cassette  500  is positioned in the auto injector  1000 , the piston opening  1115  is aligned with piston opening  525  in the syringe holder  510  to allow the auto injector piston  1168  to extend there through. Likewise, the first pin opening  526  in the syringe holder  510  is aligned with the first pin opening  1116  such that the first cassette locking pin  1156  can pass through both openings to deflect the first syringe holder arm  512  thereby unlocking the cassette skin sensor  550  from the syringe holder  510 . 
     The second pin opening  1117  in the proximal chassis part  1114  is aligned with the second pin opening  527  in the syringe holder  510  for allowing passage of the first cassette skin sensor pin  557  of the cassette skin sensor  550  to pass there through. The second pin opening  1117  does not extend all the way through, but instead has an end surface  1121  (see  FIG.  7 G ), which stops the first cassette skin sensor pin  557  of the cassette skin sensor  550  in its distal movement towards the auto injector. Thus, the second pin opening  1117  is a well-shaped opening with an end surface  1121  limiting the distal movement of the first cassette sensor pin  557  and thereby the cassette skin sensor  550  inside the auto injector  1000 . 
     The third pin opening  1118  is aligned with the third pin opening  528  in the syringe holder  510  for allowing passage of the skin sensor pin  1158 , and/or the second cassette skin sensor pin  558  there through. This is shown in details in  FIGS.  7 A-F . The fourth pin opening  1119  is aligned with the fourth pin opening  529  in the syringe holder  510  for allowing passage of the second cassette locking pin  1159  there through. 
     The fifth opening  1120  does not have a corresponding opening in the syringe holder. Instead, through the fifth opening  1120  cassette detection pin  1160  extends. The cassette detection pin  1160  detects when a cassette  500  is connected to the auto injector  1000 . The release of the cassette skin sensor  550  will not occur if there is no detection of a cassette by the cassette detection pin  1160 . Instead of a cassette detection pin, a detection system based on e.g. magnets on cassette and auto injector surfaces coming in contact with each other and a corresponding Hall sensor inside the chassis may be used elimination the need for a detection pin and a corresponding opening in the proximal chassis part  1114 . Alternatively, the cassette may have a pin, which comes in contact with a surface on the injector, whereby detection of the cassette is registered in the auto injector. 
     The cassette receiving chassis  1110 , the piston  1168  and the drive module  1150  are comprised inside the housing  1102  of the auto injector  1000 , and the cassette  500  is removable received in the auto injector  1000 . By removable received is meant is meant that the cassette is a disposable cassette, which may be received in a reusable auto injector. The disposable cassette may be a one-time use cassette, or a cassette comprising multiple doses for multiple individual injections. 
       FIGS.  6 A-C  show cut-through views of the auto injector  1000  with the cassette  500  during the loading and locking of the cassette  500  in the auto injector  1000 . In  FIG.  6 A , the cassette  500  has been received inside the auto injector housing  1102 . As seen in  FIGS.  6 A-C , the injector housing  1102  has a protruding tab  1105  on its inside. When the cassette  500  is positioned in the auto injector  1000 , a cassette locking protrusion  539  is positioned near the protruding tab  1105 . The auto injector then moves the cassette locking pins  1156 ,  1159  forward along with the piston  1168  as seen when comparing  FIGS.  6 A and  6 B . The cassette locking protrusion  539  are now prevented from deflecting the protruding tab  1105 , thereby locking the cassette  500  to the auto injector  1000 . As the cassette  500  is now firmly locked inside the auto injector  1000 , the cassette cap  530  can now be manually removed from the cassette  500 . This also removes the rigid needle shield  206  exposing the needle  204 . 
     By further proximal movement of at least the first cassette locking pin  1156 , the cassette skin sensor  500  is released from the syringe holder  510 . This process is shown in  FIGS.  7 A-C  illustrating the steps in releasing the cassette skin sensor  550  from the syringe holder  510  by means of moving the first cassette locking pin  1156  proximally. As seen in  FIGS.  7 B , the first locking protrusion  553  and the proximal surface  514  of the arm  512  no longer engage. The auto injector is now ready for insertion of the needle  204  into a patient. This is done by pressing the cassette  500  towards the skin of the patient thereby pushing the cassette skin sensor  550  distally as shown in  FIGS.  7 C and  7 D . Thus, when the drive module  1150  moves the first cassette locking pin  1156  proximally, the cassette skin sensor  550  is distally unlocked from the syringe holder  510  allowing for distal movement of the cassette skin sensor  550 , wherein the unlocking of the cassette skin sensor  550  locks the cassette  500  in the auto injector  1000 . 
     When the drive module  1150  moves the piston  1168  proximally for delivery of medicament, the second cassette locking pin  1156  is also unlocked for movement of the cassette skin sensor  550  proximally after delivery of medicament and/or removal of the auto injector  1000  from the patient&#39;s skin. 
       FIGS.  7 D-E  show the locking of the cassette skin sensor  550  in a proximal position after delivery of medicament.  FIG.  7 D  illustrates delivery position. In this position, the skin sensor pin  1158  exerts a pressure on the second cassette skin sensor pin  558  by the spring system  1140 . In  FIG.  7 E , the auto injector has been lifted from the skin of the patient. By doing so, the spring system  1140  pushes the cassette skin sensor  550  forward in the proximal direction. As the cassette skin sensor  550  has been unlocked for movement in the proximal direction by second cassette locking pin  1159 , the cassette skin sensor  550  can be locked in a forward position where contact with the needle is prevented by e.g. a protrusion inside the cassette housing engaging with the cassette skin sensor protrusion. 
     After delivery of medicament, the drive module retracts the piston and the skin sensor release pins  1156 ,  1157 , which unlocks the cassette from the auto injector allowing the user to remove the cassette. The rigid needle shield and the cassette cap cannot be connected to the cassette after use, which ensures that the user will not mistake a used cassette for a non-used. 
     In  FIGS.  8 A-B  and  FIGS.  9 A-C  is shown the assembly of a cassette  500  comprising similar parts as shown and discussed in the previous figures.  FIG.  8 A  show a cassette housing  540  and a cassette cap  530 , which is assembled in  FIG.  8 B  to form an outer cassette part  504  by connecting a proximal end  541  of the cassette housing  540  to a distal end  534  of the cassette cap  530 . Compared to the corresponding cassette housing  540  in  FIGS.  1 A,  2 , and  6 A -D, the cassette housing in  FIGS.  8 A-B  is absent of a housing shoulder  546 . 
     The cassette cap  530  comprises a first part  531  at the distal end  534  of the cassette cap  530 . The first part  531  may be part of an inner rigid needle shield tube  535  surrounded by an outer rigid needle shield tube  536 . If a syringe comprising a rigid needle shield is positioned in the cassette  500 , the first part  531  will normally be positioned between the rigid needle shield  206  and the proximal end of the syringe compartment or around the rigid needle shield  206  as shown in  FIG.  15 D , where the first part  531  is positioned around the distal end of the rigid needle shield. The first part  531  of the cassette cap  530  extend inside the cassette housing opening  545  when the outer cassette part  504  is assembled as shown in  FIG.  8 B . 
       FIGS.  9 A-C  show the assembling of an inner cassette part  501  comprising a syringe holder  510  and a cassette skin sensor  550 . In  FIG.  9 A , the two parts are shown as separate parts before assembling by inserting a proximal end  508  of the syringe holder  510  into a distal end  552  of the cassette skin sensor  550 . In  FIG.  9 B , the syringe holder  510  has been pushed part of the way into a distal end  552  of the cassette skin sensor  550 , and in  FIGS.  9 C-D , the two parts have been assembled such that a part of the syringe holder  510  is covered by the cassette skin sensor  550 . The part of the syringe holder  510  covered by the cassette skin sensor  550  constitutes at least 10%, such as at least 20%, such as at least 30%, such as at least 40%, such as at least 50%. 
     The inner and outer cassette parts are assembled by inserting a proximal end  502  of the inner cassette part  501  into a distal end  506  of the outer cassette part  504  and pushing the inner cassette part  501  into the outer cassette part  504  such that the majority of the inner cassette part  501  is covered by the outer cassette part  504 . This is shown in  FIGS.  10 A-B , where  FIG.  10 A  shows the initial position of the cassette parts before they have been completely assembled in  FIGS.  10 B-C . 
       FIGS.  11 A-D  shows the insertion and fixation of a syringe  200  inside the cassette  500 . The cassette parts can be assembled on one location and the syringe inserted at a different location. In  FIG.  11 A , the syringe  200  is ready for insertion into the cassette  500  by inserting a proximal end of the syringe  200  into the distal end  503  of the inner cassette part  501 , and pushing the syringe  200  into the inner cassette part  501  as shown in  FIGS.  11 B-C . 
     The syringe holder  510  shown in  FIGS.  9 A- 11 D  comprises one or more syringe locking protrusions  515 . By moving the one or more syringe locking protrusions  515  centrally, the syringe  200  is locked inside the inner cassette  501 . This is seen by comparing  FIG.  11 C and  11 D . If the cassette housing is without the cassette locking protrusions, the syringe may be fixed in the syringe holder  510  be frictional force. 
     The syringe  200  extends from a proximal end  201  to a distal end  203  and comprises a syringe compartment  202  containing medicament where a proximal end is adapted for being in connection with a needle through which the medicament is allowed to exit the syringe compartment  202 . In  FIG.  11 A , the needle is shown as a hollow needle  204  in fluid connection with the proximal end of the syringe compartment, i.e. connected to the syringe as part of the syringe. Alternatively, a luer lock needle may be connected to the syringe prior to injection of medicament. As yet a further alternative, a syringe system with a cartridge terminated with a stopper at its distal end and a rubber septum at its proximal end, where a penetrating needle at a distal end pierces the septum when mounted onto the cartridge while a proximal needle end penetrates into the patient skin. Inside the syringe compartment  202  is a stopper  208  adapted for being moved from a distal position to a proximal position inside the syringe compartment  202 . This forces the medicament out of the syringe. 
     The syringe  200  shown in  FIG.  11 A  also comprises a rigid needle shield  206  connected to the proximal end of the syringe compartment and covering the hollow needle  204 . If the hollow needle is not part of the syringe, but instead connected thereto prior to medicament delivery, e.g. by a luer lock or a needle system penetrating a septum in the syringe when connected to the cassette, the rigid needle shield  206  may still be present as part of the cassette and used after medicament delivery for shielding the used needle for the user. 
     The syringe may contain different amounts of medicament such as e.g. 1.00 ml or 2.25 ml medicament. When using the cassette  500  for smaller syringes, a cassette sleeve  570  may be included inside the syringe holder  510  to ensure that a thin syringe  200  is kept inside the syringe holder  510 . An example of a cassette sleeve is shown in  FIGS.  12 A-B . Prior to inserting a syringe  200  into a cassette  500  comprising the cassette sleeve  570 , a proximal end  571  of the cassette sleeve  570  is inserted into the distal end  509  of the syringe holder  510  and pushed into the syringe holder  510  such that the majority of the cassette sleeve  570  is covered by the syringe holder  510  prior to or directly after inserting the syringe holder  510  into the cassette skin sensor  550 . The cassette sleeve  570  thereby constituting a part of the inner cassette part  501  is shown as an included part in the cassette  500  in  FIG.  14 A . The sleeve  570  is secured in the syringe holder  510  by a small tap inside the syringe holder, which fits into the small opening  576  in the cassette sleeve  570 . 
     The cassette sleeve  570  comprises proximal extending deflectable sleeve arms  573  (see  FIGS.  12 A-B ). The deflectable sleeve arms  573  can deflect through an opening  580  in the syringe holder  510 . 
     In  FIGS.  14 A-E  and  15 A-D, inserting a syringe  200  inside a cassette  500  comprising the cassette sleeve  570  is shown. When inserting a syringe  200  comprises the hollow needle  204  and a rigid needle shield  206 , the deflectable sleeve arms  573  deflects into openings in the syringe holder  510  and cassette skin sensor  550  allows the rigid needle shield  206  to pass the deflectable sleeve arms  573 . By this motion, the locking in the opening  576  in the cassette sleeve  570  is unlocked. Further, the deflectable sleeve arms  573  relax into a position between the rigid needle shield  206  and the syringe compartment  202  after the rigid needle shield  206  has passed the deflectable sleeve arms  573 . This is seen in  FIGS.  14 B and  15 B , where the rigid needle shield  206  is shown after having passed the deflectable sleeve arms  573 . 
     When the syringe  200  is inserted into the cassette sleeve  570  and the deflectable sleeve arms  573  have relaxed into a position between the rigid needle shield  206  and the syringe compartment  202  as shown in  FIG.  15 B , the collar on a distal end of the syringe  205  abuts a distal surface of the cassette sleeve  572  preventing further proximal movement of the syringe  200  relative to the cassette sleeve  570 . 
     After the deflectable sleeve arms  573  has relaxed into a position between the rigid needle shield  206  and the syringe compartment  202 , and the syringe  200  and the cassette sleeve  570  are pushed further proximally before locking the syringe  200  to the cassette  500 , the cassette sleeve  570  rotates into a position from where the deflectable sleeve arms  573  cannot deflect. The rotation of the cassette sleeve  570  is seen in  FIGS.  14 B- 14 D , with  FIG.  14 B  showing the sleeve  570  prior to rotation,  FIG.  14 C  showing the sleeve  570  halfway rotated and  FIG.  14 D  showing the sleeve  570  fully rotated. The rotation may also be seen in the cut-through illustrations in  FIGS.  15 B-D . The rotation of the cassette sleeve  570  rotates it into a position allowing a viewer to view the medicament inside the syringe  200 . 
     As an alternative to the deflectable sleeve arms ( 573 ) flexing outwardly when the rigid needle shield  206  passes by the deflectable sleeve arms  573 , the deflectable sleeve arms can form a sleeve opening at the proximal end of the cassette sleeve ( 571 ) being large enough to allow the rigid needle shield ( 206 ) to pass through without the axially outward deflection of the deflectable sleeve arms ( 573 ). When the deflectable sleeve arms ( 573 ) is at a position between the rigid needle shield ( 206 ) and the syringe compartment ( 202 ), but not squeeze into contact with the syringe compartment  202 , the further proximal movement of the syringe ( 200 ) and the cassette sleeve ( 570 ) into the cassette ( 500 ) forcing the cassette sleeve ( 570 ) to rotate also pushes the deflectable sleeve arms ( 573 ) radially inward into a position from where the deflectable sleeve arms ( 573 ) cannot deflect back to the original position. In this manner, the skin sensor  510  ensures that the cassette sleeve  570  provides a secure positioning of the syringe  200  inside the cassette sleeve, where proximal and axial movement of the syringe relative to the cassette sleeve is prohibits/prevents. 
     The cassette sleeve  570  comprises at least one sleeve locking protrusion  574  as shown in  FIGS.  12 A-B . When the sleeve locking protrusion(s)  574  comes in contact with an inner helical surface part  575  inside the syringe holder  510  as the syringe  200  is pushed proximally, the helical shape of the at least one inner helical surface part  575  forces the cassette sleeve  570  to rotate. The rotation is approximately  90  degrees. The inner helical surface part  575  is shown in  FIGS.  13 A-B . When the syringe  200  has been inserted in the cassette  500  and the syringe locking protrusions  515  locked around the syringe  200  preventing it and thereby the also the cassette sleeve  570  from moving in the distal direction, the cassette sleeve  570  cannot rotate backwards as this rotational motion would require that the cassette sleeve  570  moves in the distal direction due to the interaction of the inner helical surface part  575  and the sleeve locking protrusion  574 . Thus, backwards rotation of the cassette sleeve  570  is prevented by the locking of the syringe  200  in the cassette  500 . Further rotational movement of the sleeve  570  is also prevented as the inner helical surface part  575  has an end surface point  577  stopping the rotational motion in the first direction. The end surface point  577  may be a small opening into which the sleeve locking protrusion  574  enters without the option to move away again. 
       FIGS.  16 - 19    show an example of an auto injector  1000  for receiving the cassette of  FIGS.  8 - 15   . The auto injector  1000  is shown in an exploded view in  FIG.  16   , whereas  FIGS.  17 - 19    show different views of the assembled auto injector  1000 . For obtaining a clear view inside the auto injector, the outer housing  1102  has been omitted in  FIGS.  16  and  19   . The outer housing  1102  can be seen in  FIGS.  17  and  18 A -B. The housing  1102  is in one piece in this example of the auto injector. A two-part housing could also be imagined. 
     The cassette  500  is loaded into the auto injector  1000  in a front-loading configuration. Thus, the proximal end of the cassette  500  is inserted into the proximal end of the auto injector  1000  as illustrated in  FIGS.  18 A-B . As also seen in  FIGS.  18 A-B , the housing  1102  comprises an opening  1107 , which facilitating inspection of the medicament in the cassette  500 . The opening  1107  extends into the housing surface. Along a longitudinal axis of the injector housing  1102 , the housing  1102  may be divided into two sections; a cassette covering section  1108  covering at least part of the cassette  500  when received inside the injector  1000 , and a distal section  1106  covering internal injector parts. These internal injector parts are shown in  FIG.  16    in the exploded view. The opening  1107  is in the cassette covering section  1108  and is extending in the longitudinal direction of the housing  1102 . 
     The auto injector  1000  as shown in  FIG.  16    comprises a cassette receiving chassis  1110  configured to receive the cassette  500 . By receiving the cassette is meant to connect/couple with the cassette. The cassette  500  is interfacing with the auto injector  1000  at the distal end of the cassette  500 , whereby the two parts are sharing the same longitudinal axis. This mitigates the risk of the cassette getting stuck inside in the auto injector. Further, it makes the connection as slim as possible. The only auto injector element, which extends in parallel with the cassette  500  when the cassette is inserted into the auto injector is normally the injector housing  1102 , i.e. the cassette covering section  1108 . 
     The internal injector parts include a drive module  1150 , which is adapted to move a piston  1168 . The piston  1168  is moved proximally pushing on the stopper  208  inside the syringe  200  whereby medicament can be expelled from the syringe  200 . The piston  1168  has an inner threading (see  FIG.  19   ), which engages with an outer threading on a led screw  1169 . When the lead screw  1169  is rotated by the drive element  1150 , the piston  1168  moves proximally. Rotation of the lead screw  1169  in the opposite direction, moves the piston  1168  distally. At the proximal end of the piston  1168  is a piston end plate  1178 , which fits into an opening  1115  in the chassis  1110 . 
     The drive module  1150  includes a motor  1151 , which through a gear assembly rotates the led screw  1169 . The gear assembly comprising a set of gears  1148 ,  1149 , a led screw plate  1176 , and a connecting ring between a chassis cover  1154  and the led screw  1169 . Different versions of this gear set may also be imagined. 
     The chassis  1110  comprises a cassette abutting surface  1114   a  adapted for abutting a distal end  503 ,  506  of the cassette  500  when secured inside the auto injector  1000 . The cassette abutting surface  1114   a  defines a proximal end plane from where substantially no internal injector parts extends in the proximal direction prior to assembling the cassette  500  and the auto injector  1000 . By substantially is included that a minor tip, e.g. up to 2%, 5% or 10%, of the total length of one or more of the pins  1156 ,  1158 ,  1159  extends proximately outside the cassette abutting surface  1114   a.  Similarly, at the distal end of the internal injector parts, is a distal plane. At both the proximal plane and the distal plan of the internal injector parts, noise reducing material  1109 ,  1155  is positioned for dampening noise made by any internal injector parts during use. The noise reducing material  1109 ,  1155  may be a flexible material, such as rubber, and/or one or more O-ring(s), possibly in the form of square shaped O-rings as shown in  FIG.  16   . 
     The drive element  1150  also controls the movement of a number of pins comprised in the auto injector  1000 . As shown in  FIG.  16   , the number of pins may include; a first cassette locking pin  1156 , a skin sensor pin  1158 , and a second cassette locking pin  1159 . The first locking pin  1156  and second locking pin  1159  are connected to the piston  1168 . This is obtained by a first locking pin bridge connection  1162  and a second locking pin bridge connection  1163  on the piston  1168 . The distal end  1166  of the first cassette locking pin  1156  is fixed to the first cassette locking pin bridge connection  1162  and the distal end  1167  of the second cassette locking pin  1159  is fixed to the second cassette locking pin bridge connection  1163 . This enables the drive module  1150  to move the first cassette locking pin  1156 , and the second cassette locking pin  1159  when moving the piston  1168 . Alternatively, the movement of the two cassette locking pins  1156 ,  1159  can be decoupled from the movement of the piston  1168 . Thus, the movement of the cassette locking pins can be individual or in the form of multiple pens moving simultaneously. 
     The skin sensor pin  1158  also moves with the piston  1168  as it moves proximally. The skin sensor  1158  is coupled to a spring system, which includes a spring  1143  and a stopper  1144  against which the spring  1143  presses in the proximal direction. The stopper  1144  is positioned in at the stopper accommodating part  1164  being the skin sensor. When the cassette  500  is positioned in the auto injector  1000  and the skin sensor pin  1158  is moved proximately, the skin sensor  1158  comes in contact with the second cassette skin sensor pin  558 . As long as the cassette skin sensor  550  is pushed in the distal direction, it prevents the skin sensor pin  1158  from moving with the piston  1168  and two cassette locking pins  1156 ,  1158  is the proximal direction. This tensions the spring  1143 . Since the tensioned spring  1143  acts on the skin sensor pin  1158 , when releasing the cassette skin sensor  550 , the spring  1143  pushes the cassette skin sensor  550  proximally. This ensures that the needle is not exposed after end delivery of medicament. The cassette skin sensor  550  is pushed into a locked position preventing distal movement of the cassette skin sensor  550 . The distal locking is facilitated by the cassette skin sensor arm  566 , where the locking surface  567  of the cassette skin sensor arm  566  locks into an inner opening in the cassette housing  540 . Proximal movement of the cassette skin sensor  550  may also be prevented by an additional set of housing-skin sensor surfaces. 
     As the cassette locking pins  1156 ,  1159  move in parallel in a symmetric configuration in the auto injector shown in  FIG.  16   , the naming of ‘first’ and ‘second’ could be interchanged. Also, depending on the direction, which the cassette  500  is inserted into the auto injector  1000 , the naming may change. By combining the features of the first and second syringe holder arms  512 ,  516 , into one syringe holder arm, the second cassette locking pin  1159  and corresponding opening  1119  could be removed. This would require that the cassette  500  is inserted in a specific manner ensuring that the one cassette locking pin comes in contact with the one syringe holder arm. 
     The pins  1156 ,  1158 ,  1159  and the piston  1168  may also be referred to as cassette interacting parts adapted for securing and locking the cassette  500  inside the auto injector  1000  and for facilitating administering of the medicament. In common for the cassette interacting parts shown in  FIG.  16    is that they move in parallel with the longitudinal axis of the auto injector  1000 . The cassette interacting parts could possibly be configured for rotating around their own axis in addition to moving in parallel with the longitudinal axis of the auto injector. Also, the cassette interacting parts may be prevented from moving in directions different from parallel with the longitudinal axis of the auto injector. 
     The cassette receiving chassis  1110  configured to receive a cassette  500 . The cassette receiving chassis  1110  is extending from a proximal end  1111  to a distal end  1112 , where at the distal end, distally extending chassis arms  1113  are found. At the proximal end  1111  of the chassis  1110  is a proximal chassis part  1114  with a number of openings including a piston opening  1115 , a first pin opening  1116 , a second pin opening  1117 , a third pin opening  1118 , and a fourth pin opening  1119 . Depending on the number of pins in the auto injector, fewer openings could also be used. The openings are round circular openings, but may also have a different shape mimicking the shape of the pins if they are not round. 
     When the cassette  500  is positioned in the auto injector  1000 , the piston opening  1115  is aligned with piston opening  525  in the syringe holder  510  to allow the auto injector piston  1168  to extend there through. Likewise, the first pin opening  526  in the syringe holder  510  is aligned with the first pin opening  1116  such that the first cassette locking pin  1156  can pass through both openings to deflect the first syringe holder arm  512  thereby unlocking the cassette skin sensor  550  from the syringe holder  510  as explained earlier in connection with  FIGS.  7 A-G . 
     The second pin opening  1117  in the proximal chassis part  1114  is aligned with the second pin opening  527  in the syringe holder  510  for allowing passage of the first cassette skin sensor pin  557  of the cassette skin sensor  550  to pass there through. The second pin opening  1117  does not extend all the way through, but instead has an end surface  1121  (see  FIG.  7 G ), which stops the first cassette skin sensor pin  557  of the cassette skin sensor  550  in its distal movement towards the auto injector. If the first cassette skin sensor pin  557  is shortened, the second pin opening  1117  can be eliminated and the first cassette skin sensor pin  557  instead be stopped by the proximal chassis part  1114 . 
     The third pin opening  1118  is aligned with the third pin opening  528  in the syringe holder  510  for allowing passage of the skin sensor pin  1158 , and/or the second cassette skin sensor pin  558  there through. This was also shown and discussed in connection with the auto injector in  FIGS.  7 A-F . The fourth pin opening  1119  is aligned with the fourth pin opening  529  in the syringe holder  510  for allowing passage of the second cassette locking pin  1159  there through. 
     When the cassette  500  is positioned in the auto injector  1000 , the cassette locking pins  1156 ,  1159  pass into the pin openings  526 ,  529  in the cassette  500  and push cassette locking protrusions into the auto injector housing  1102 , where internal parts inside the injector housing  1102  prevent the proximal movement of the cassette housing  530 , thereby locking the cassette  500  to the auto injector  1000 . As the cassette locking pins  1156 ,  1159  moves further into the cassette  500 , the first cassette locking pin  1156  deflects the first syringe holder arm  512 . This causes a release of the cassette skin sensor  550  allowing it to move towards the syringe holder  510 , i.e. a distal direction movement of the cassette skin sensor  550 . The syringe holder  510  and the skin sensor  550  are longitudinally movable relative to each other upon release of the skin sensor  550  from the syringe holder  510 . By pressing the auto injector against the patient&#39;s skin will allow the needle to be inserted into the patient as movement of the cassette skin sensor  550  distally exposes the needle. 
     Upon movement of the cassette skin sensor  550  towards the syringe holder  510 , the first cassette skin sensor pin  557  moves towards—and possibly through—the second pin opening  527  in the syringe holder  510 . Similarly, the second cassette skin sensor pin  558  moves towards—and possibly through—the third pin opening  528  in the syringe holder  510  when the cassette skin sensor  558  moves distally. When the second cassette skin sensor pin  558  passes through the openings  528 ,  1118  it comes in contact with the skin sensor pin  1158  as described above. 
     The further movement of the cassette locking pins  1156 ,  1159  into the cassette  500 , causes the second cassette locking pin  1159  to deflect the second syringe holder arm  516 . This releases the cassette skin sensor  550  allowing it to move away from the syringe holder  510  in the proximal direction. Thus, when/if the user removes the auto injector from the patient&#39;s skin, the cassette skin sensor  550  is now allowed to move proximally to cover the needle after end medicament injection. The spring  1143  acting on the skin sensor pin  1158  ensures that the cassette skin sensor  550  is locked after use as described above. 
     The auto injector as shown in  FIG.  16    also comprises a printed circuit board (PCB)  1180 , a USB connection  1181 , USB PCB plate  1182 , and a battery  1184 . On the PCB board  1180  is also positioned a number of switches  1171   a,    1171  b,  1171   c  for detecting the position of the pins inside the auto injector. 
       FIG.  17    shows the assembled auto injector  1000  in a view as seen from the front where the cassette  500  is inserted. The cassette abutting surface  1114   a  defines a proximal end plane from where substantially no internal injector parts extends proximally prior to assembling the cassette  500  and the auto injector  1000 . By substantially is included a situation where only a minor part of the internal injector parts protrude a small amount, such as up 2%, 5%, or 10% proximally compared to the cassette abutting surface  1114   a.  This is shown in  FIG.  19   , where the tip of the second cassette locking pin  1159  protrudes outside the cassette abutting surface  1114   a.  The pins  1156 ,  1158 ,  1159  are also indicated in  FIG.  17   . 
     The cassette abutting surface  1114   a  may also define a proximal end plane from where substantially no cavities extends distally into the distal section  1106 . By substantially is here also included that a small closed well-type opening is present in the surface  1114   a  as illustrated in  FIG.  7 G , item  1121 . 
     The smooth cassette abutting surface  1114   a  and the supporting plate  1114   b  behind it, ensure that the auto injector can be kept clean in an easy manner due to avoidance of grooves to e.g. collect dirt and dust etc. Also, a user is prevented from accessing the internal parts of the auto injector. This prolongs the lifetime of the auto injector  1000 . 
       FIGS.  20 A-I  shows the interaction between the cassette  500  of  FIGS.  8 - 15    and the auto injector of  FIGS.  16 - 19   . Compared to  FIGS.  7 A-G , the cassette release pins  1156 ,  1159  has switched position such that the second cassette release pin  1159  is positioned next to the skin sensor pin  1158 . As the cassette release pins  1156 ,  1158  are working in an interchangeable manner and move together, this has no impact on the interaction between the auto injector  1000  and the cassette  500 . Also, compared to  FIGS.  7 A-G ,  FIGS.  20 A-I  show the cassette  500  turned 180 degrees, thereby showing the second syringe holder arm  516  and the second cassette locking pin  1159  in  FIGS.  20 A-H  instead of the first syringe holder arm  512  and the first cassette locking pin  1156  as in  FIGS.  7 A-F . 
     The cassettes  500  and auto injectors  1000  are shown and described in a configuration using manual insertion of the needle. An automatic needle insertion could also be envisioned by included a spring-motor system. 
     REFERENCE 
     
         
           200  syringe 
           201  proximal end of the syringe/syringe compartment 
           202  syringe compartment 
           203  distal end of the syringe/syringe compartment 
           204  hollow needle 
           205  distal end surface of the syringe 
           206  rigid needle shield 
           207  inner part of the rigid needle shield 
           208  stopper 
           210  plunger rod 
           500  cassette 
           501  inner cassette part 
           502  proximal end of the inner cassette part 
           503  distal end of the inner cassette part 
           504  outer cassette part 
           505  proximal end of the outer cassette part 
           506  distal end of the outer cassette part 
           507   a  syringe holder ring 
           507   b  syringe holder ring 
           508  proximal end of the syringe holder 
           509  distal end of the syringe holder 
           510  syringe holder 
           511  syringe holder support tube 
           512  first syringe holder arm 
           513  proximal end of the first syringe holder arm 
           514  proximal surface at the proximal end of the first syringe holder arm 
           515  syringe locking protrusion 
           516  second syringe holder arm 
           517  proximal end of the second syringe holder arm 
           518  distal surface at the proximal end of the second syringe holder arm 
           519  syringe holder plate 
           520  proximal support surface of the syringe holder plate 
           521  distal support surface of the syringe holder plate 
           522  first syringe holder locking arm 
           523  second syringe holder locking arm 
           524  syringe holder locking protrusions housing 
           525  piston opening in the syringe holder plate 
           526  first pin opening in the syringe holder plate 
           527  second pin opening in the syringe holder plate 
           528  third pin opening in the syringe holder plate 
           529  fourth pin opening in the syringe holder plate 
           530  cassette cap 
           531  first part positioned between the rigid needle shield and the proximal end of the syringe compartment 
           532  proximal end of the cassette cap 
           534  distal end of the cassette cap 
           535  inner rigid needle shield tube 
           536  outer rigid needle shield tube 
           537  distal end of the cassette cap 
           538  proximal end of the cassette cap 
           539  cassette locking protrusion 
           540  cassette housing 
           541  proximal end of the cassette housing 
           542  distal end of the cassette housing 
           543  distal end surface of the cassette housing 
           544  locking opening in the cassette housing 
           545  skin sensor housing opening 
           546  housing shoulder 
           547  opening in the housing for inspection of medicament 
           548  protruding rail on the inside of the cassette housing 
           549  syringe locking arms 
           550  cassette skin sensor 
           552  distal end of the cassette skin sensor 
           553  first locking protrusion 
           554  second locking protrusion 
           556  opening for inspection of the syringe 
           557  first cassette skin sensor pin 
           558  second cassette skin sensor pin 
           560  proximal end of the cassette skin sensor 
           562  skin touching surface of the cassette skin sensor 
           566  cassette skin sensor arm 
           567  locking surface of the cassette skin sensor arm 
           568  cassette skin sensor rail to fit into the rails inside the cassette housing 
           570  cassette sleeve 
           571  proximal part of the cassette sleeve 
           572  distal part of the cassette sleeve 
           573  sleeve arms on the cassette sleeve 
           574  sleeve locking protrusion 
           575  inner helical surface part 
           576  opening in the cassette sleeve 
           577  end surface point on the inner helical surface part 
           580  opening in the syringe holder 
           1000  auto injector 
           1102  housing 
           1103  proximal end of the housing 
           1104  distal end of the housing 
           1105  protruding tab on the inside of the housing 
           1106  distal section of the housing covering internal injector parts 
           1107  opening in the housing 
           1108  cassette covering section 
           1109  noise reducing material/O-ring 
           1110  cassette receiving chassis 
           1111  proximal end of the chassis 
           1112  distal end of the chassis 
           1113  distally extending chassis arm 
           1114  proximal chassis part 
           1114   a  proximal surface of the proximal chassis part/cassette abutting surface 
           1114   b  support plate 
           1115  piston opening in the proximal chassis part 
           1116  first pin opening in the proximal chassis part 
           1117  second pin opening in the proximal chassis part 
           1118  third pin opening in the proximal chassis part 
           1119  fourth pin opening in the proximal chassis part 
           1120  fifth opening in the proximal chassis part 
           1121  end surface of the second pin opening 
           1140  spring system acting on the skin sensor 
           1141  spring guidance pin 
           1142  supporting chassis for guiding the skin sensor pin 
           1143  spring in the spring system acting on the skin sensor 
           1144  stopper for stopping the spring in the spring system acting on the skin sensor 
           1148  gear 
           1149  gear 
           1150  drive module 
           1151  motor 
           1152  gear cover 
           1153  gear assembly 
           1154  chassis cover 
           1155  noise reducing material/O-ring 
           1156  first cassette locking pin 
           1158  skin sensor pin 
           1159  second cassette locking pin 
           1160  cassette detection pin 
           1161  guide pin for the skin sensor pin 
           1162  first locking pin bridge connection 
           1163  second locking pin bridge connection 
           1164  stopper accommodating part 
           1166  distal end of the first cassette locking pin connecting to the bridge connection 
           1167  distal end of the second cassette locking pin connecting to the bridge connection 
           1168  piston internally threaded to match the led screw 
           1169  led screw 
           1170  bridge 
           1171  switch 
           1171   a  switch 
           1171   b  switch 
           1171   c  switch 
           1172  opening in the chassis cover 
           1174  connecting ring between the chassis cover and led screw 
           1176  led screw plate 
           1178  piston end plate 
           1180  printed circuit board 
           1181  USB connection 
           1182  USB printed circuit board plate 
           1184  battery