fig1 shows a cross - section of a drug delivery device in the shape of an injection pen . the drug delivery device can have another suitable shape instead , according to the shape of a body or housing . the term “ body ” encompasses any exterior housing , like a main housing or shell , as well as an interior housing , like an insert or inner body arranged within an exterior housing . in the embodiment shown in fig1 , the body 1 is of elongated shape . it has a proximal end 2 and a distal end 3 . the body 1 can be composed of at least two attachable and separable parts enabling a refill of the device . the body 1 comprises a receptacle 4 for a drug . the receptacle 4 can be designed to be filled by means of a cartridge 5 containing the drug and being inserted in the receptacle 4 . a full cartridge 5 preferably contains a plurality of doses of the drug . when the cartridge 5 is empty , it can be removed and substituted with a new cartridge . the drug is dispensed through an opening of the receptacle 4 by means of a piston 6 , which is advanced in the receptacle 4 , particularly within the cartridge 5 , towards the distal end 3 by means of a piston rod 7 . the distal end 3 can be provided with a needle , not shown in fig1 , or with a needle unit , for instance . if the piston rod 7 is to be moved relatively to the piston 6 , a bearing , which is schematically shown in fig1 , can be arranged at the connection of the piston 6 with the piston rod 7 to reduce damages that may be caused by friction . the drive mechanism shown in fig1 can be operated by means of a dose button 20 at the proximal end 2 . the dose button 20 is located outside the body 1 and can be gripped by a user . the drive mechanism comprises a drive sleeve 11 , which is partially surrounded by a cylindrical dose member 12 provided with the dose button 20 . the drive sleeve 11 and the dose member 12 are coupled by means of a thread 15 of the dose member 12 engaging a corresponding thread 16 of the drive sleeve 11 . because of the threads , the dose member 12 can be moved helically with respect to the drive sleeve 11 . the drive sleeve 11 can be rotated with respect to the body 1 , but a movement of the drive sleeve 11 in the distal direction or in the proximal direction is inhibited or at least restricted . to this purpose , the body 1 can be provided with stop means , which can be interfaces or webs 13 , 14 , for instance , which stop a shift of the drive sleeve 11 in the distal direction and in the proximal direction . the movement of the piston rod 7 with respect to the body 1 is guided by a suitable guide means 17 . the guide means 17 can be an integral part of the body 1 , or it may be an element which is permanently or temporarily fastened to the body 1 , like a nut , for example . the piston rod 7 passes through an opening of the guide means 17 , which engages a thread of the piston rod 7 to restrict the movement of the piston rod 7 with respect to the body 1 to a helical movement . a rotation of the piston rod 7 with respect to the body 1 thus comprises a simultaneous shift of the piston rod 7 with respect to the body 1 . a clutch sleeve 18 comprising a clutch 19 is arranged between the body 1 and the dose member 12 . the clutch 19 can be formed by a surface area of the clutch sleeve 18 and a corresponding surface area of the dose member 12 , the surface areas touching each other when the dose member 12 is moved towards the distal end 3 and rotationally coupling the clutch sleeve 18 and the dose member 12 by means of friction . instead , the clutch 19 can be formed by a structured surface area of the clutch sleeve 18 and a corresponding structured surface area of the dose member 12 . the surface structure may comprise teeth , for instance . when the dose member 12 is moved towards the distal end 3 , the structured surface areas engage with each other , thus coupling the clutch sleeve 18 and the dose member 12 rotationally . the clutch sleeve 18 is rotationally locked to the body 1 , which may be achieved by an axial groove or track and a corresponding element , like a track , pin , peg , hook , spike or lug , which is guided by the groove or track , for instance . the embodiment according to fig1 further comprises a spring 8 , a stop member 9 , and a drive member 10 , which can be substituted with other means to couple the piston rod 7 with the drive sleeve 11 . the drive member 10 and the drive sleeve 11 are rotationally coupled by a ratchet , and so are the drive member 10 and the stop member 9 . the stop member 9 is rotationally locked to the body 1 , but is allowed to perform a reciprocating motion enabling the ratchets to engage and disengage during a rotation in the permitted direction . the stop member 9 , the drive member 10 , and the drive sleeve 11 are held in contact by the action of the spring 8 , which is supported by the web 14 of the body 1 . the ratchets allow unidirectional rotations of the drive member 10 with respect to the stop member 9 and with respect to the drive sleeve 11 . in both of these relative movements , the drive member 10 rotates in the same sense of rotation with respect to the proximal direction . this means that , depending on the sense of rotation of the drive sleeve 11 with respect to the body 1 , either the drive sleeve 11 is rotationally locked to the drive member 10 , which rotates together with the drive sleeve 11 relatively to the body 1 and to the stop member 9 , or the drive sleeve 11 rotates relatively to the body 1 and to the drive member 10 , which is rotationally locked to the stop member 9 . the drive member 10 essentially stays at its position within the body 1 and is rotationally locked to the piston rod 7 , while the piston rod 7 is able to move axially with respect to the body 1 in the distal direction or in the proximal direction . because of the guide means 17 , a rotation of the piston rod 7 by means of the drive member 10 generates a helical movement of the piston rod 7 relatively to the body 1 . the guide means 17 is provided to convert a rotation of the drive member 10 that is permitted by the stop member 9 into a helical movement of the piston rod 7 shifting the piston rod 7 in the distal direction . an operation to set a dose is performed by a helical movement of the dose member 12 with respect to the body 1 in the proximal direction . the dose member 12 can be rotated by turning the dose button 20 , the helical movement being guided by the thread of the dose member 12 engaging the thread of the drive sleeve 11 . the drive sleeve 11 is stationary with respect to the body 1 , because the drive sleeve 11 is in contact with the web 13 or with another suitable stop means of the body 1 , which inhibits a shift of the drive sleeve 11 in the proximal direction . a premature rotation of the drive sleeve 11 according to the rotation of the dose member 12 is preferably inhibited in view of dose accuracy . this can be achieved , for example , by means of the friction between the surfaces of the drive sleeve 11 and the web 13 which touch one another ; instead , these surfaces may be provided with a structure engaging the drive sleeve 11 with the web 13 to inhibit a relative rotation . fig2 shows a cross - section of the drive mechanism after the setting of a dose . further to the dose button 20 , a portion of the dose member 12 now juts out of the body 1 . an axial coupling means highlighted at letter a in fig2 is provided to shift the clutch sleeve 18 in the proximal direction simultaneously with the dose member 12 to keep the clutch 19 ready for coupling the clutch sleeve 18 and the dose member 12 . the clutch 19 thus forms a rotational coupling means highlighted at letter b in fig2 . since the clutch sleeve 18 is rotationally locked to the body 1 , the dose member 12 rotates relatively to the clutch sleeve 18 during the set operation . this is made possible by the clutch 19 not being engaged during the movement of the dose member 12 in the proximal direction . a correction of the set dose is easily possible by a helical movement of the dose member 12 with respect to the body 1 in the distal direction . this is achieved by turning the dose button 20 in the opposite direction until the desired position of the dose member 12 is obtained . the correct value of the set dose may be indicated by a scale or a numbering applied to the dose member 12 or dose button 20 . audible and / or tactile means can also be provided to guide the user when setting a dose . when the dose member 12 is helically moved back in the distal direction , the helical movement of the dose member 12 with respect to the body 1 is again guided by the threads 15 , 16 of the dose member 12 and the drive sleeve 11 . a rotation of the drive sleeve 11 according to the rotation of the dose member 12 can be inhibited , in the described embodiment for example , by the coupling between the surfaces of the drive sleeve 11 and the web 13 . a rotation of the drive sleeve 11 according to the rotation of the dose member 12 during the correction of the set dose may be allowed in embodiments comprising the arrangement of the spring 8 , the stop member 9 , and the drive member 10 as described above , because the stop member 9 inhibits an undesired rotation of the drive member 10 during the correction operation , even if the drive sleeve 11 rotates in the same sense as the dose member 12 . if the dose button 20 is not turned but pressed in the distal direction , the clutch 19 engages , and the dose member 12 and the clutch sleeve 18 are rotationally locked . this means that the dose member 12 cannot rotate with respect to the body 1 , because the clutch sleeve 18 is rotationally locked to the body 1 . the drive sleeve 11 is decoupled from the web 13 or other stop means and is free to rotate relatively to the body 1 . a distal movement of the drive sleeve 11 is inhibited or restricted by a further stop means , which can be the web 14 or the stop member 9 under the load of the spring 8 , for example . the shift of the dose member 12 with respect to the body 1 therefore requires a corresponding relative movement of the dose member 12 with respect to the drive sleeve 11 . this movement can only be a helical relative movement because of the threads 15 , 16 coupling the dose member 12 and the drive sleeve 11 . the drive sleeve 11 is thus rotated with respect to the body 1 . if the device is provided with the arrangement of the stop member 9 and the drive member 10 , this rotation of the drive sleeve 11 locks the drive member 10 rotationally to the drive sleeve 11 , and the drive member 10 is permitted to rotate in this sense of rotation . the drive member 10 therefore rotates according to the drive sleeve 11 and rotates the piston rod 7 , which advances in the distal direction because of the guide means 17 . fig3 shows a cross - section of the drive mechanism after the delivery of several doses . apart from rotations , the dose member 12 is again in the position which it occupied when the device was in the initial state shown in fig1 . the position of the piston rod 7 is now changed , because the piston rod 7 was shifted several times in the distal direction in the course of delivery operations . the other components of the drive mechanism are arranged according to the state shown in fig1 , and a further set operation can be performed by turning the dose button 20 as described above . the drive mechanism is easily and reliably operated and is therefore especially appropriate for drug delivery devices that are designed for repeated setting of doses , particularly varying doses . the drive mechanism allows a correction of the set dose in an easy way by just reversing the setting operation . it is an advantage of the drive mechanism that the accuracy in setting the dose is not adversely affected by a correction of the set dose . the correct use of the device is therefore assured , thus helping the user to administer the medication correctly .
a drive sleeve is arranged within a body and coupled with a dose member by means of threads . stop means inhibit a shift of the drive sleeve while allowing a rotation of the drive sleeve . a clutch is provided to lock the dose member rotationally to the body in a releasable manner when a force is exerted on the dose member in the distal direction , the clutch permitting a movement of the dose member in the distal direction with respect to the body .