WO2017141182A1

WO2017141182A1 - Indication mechanism for an injection device for delivering a pharmaceutical substance and an injection device comprising such an indication mechanism

Info

Publication number: WO2017141182A1
Application number: PCT/IB2017/050870
Authority: WO
Inventors: Alberto LOZANO PLATONOFF; Adam Stefanski
Original assignee: Copernicus Sp. Z O.O.
Priority date: 2016-02-19
Filing date: 2017-02-16
Publication date: 2017-08-24
Also published as: PL229073B1; PL416191A1

Abstract

Indication mechanism (1) for an injection device for delivering settable doses of a pharmaceutical substance, comprising a rotatable control sleeve (2) on which an indication sleeve (3) and a push-pull nut (4) are mounted, the indication sleeve (3) being provided with markings (5), which are visible to a user and being engaged in rotation with the control sleeve (2) and being translatable along the control sleeve (2), the push-pull nut (4) being non-rotatable and engaged in translation with the indication sleeve (3) and cooperating threadably with the control sleeve (2), in which the indication sleeve (3) comprises an external portion (3a) and an internal portion (3b), the internal surface of the internal portion (3b) being adapted to facilitate translation of the indication sleeve (3) along the control sleeve (2), and the external surface of the external portion (3a) being adapted to facilitate application of the markings (5) thereon.

Description

Indication mechanism for an injection device for delivering a pharmaceutical substance and an injection device comprising such an indication mechanism

The present invention relates to an indication mechanism for an injection device for delivering a pharmaceutical substance. The indication mechanism according to the invention is particularly useful in multi-use injection devices having a function of setting and correcting the dose to be delivered that are connected to a replaceable cartridge with a pharmaceutical substance. The present invention also relates to an injection device comprising such an indication mechanism.

Various mechanisms of the above described type are known. One of them is described e.g. in a Polish patent PL220720 (patent family of WO 2013/119132) of the same Applicant of the present invention.

The housing of the indication mechanism according to PL220720 contains among others a cylindrical indicating element 16 and a pulling nut 15 both cooperating with a driving barrel 14. The pulling nut 15 cooperates with an external thread of the driving barrel 14 and it is mounted in longitudinal grooves within the housing 1 by means of longitudinal projections. The cylindrical indicating element 16 is mounted on longitudinal projections of the driving barrel 14 by means of internal longitudinal grooves. Consequently, when the driving barrel 14 is rotated during setting or correcting of the dose, the pulling nut 15 is translated in a defined direction along the housing 1. The pulling nut 15 is also engaged with the cylindrical indicating element 16 so that when the pulling nut 15 is translated in one direction the indicating element 16 is pushed and when the pulling nut 15 is translated in the opposite direction the indicating element 16 is pulled. As a result, when the indicating element 16 rotates together with the driving barrel 14 and advances together with the pulling nut 15 it is moved along a screw line in relation to the housing 1. In order to fulfil its function, the indicating element 16 must be provided with scale markings (e.g. digits) on its external surface that are visible through a housing window, showing the set dose to a user.

However, it has turned out that the above described construction of the indication mechanism according to PL220720 has two disadvantages.

First, the substantial number of the elements cooperating slidingly in the mechanism results in important friction resistance being generated, which is detrimental to the functioning of the indication mechanism and the whole device. In view of the above the designers aim to lower the friction, in particular by the use of low friction materials i.e. extra smooth materials having the lowest possible friction coefficient in relation to each other. In this respect the cylindrical indicating element constitutes a specific problem because its internal surface slides on the driving barrel and its external surface is provided with the markings. The most advantageous marking techniques are pad printing or thermal transfer printing. However, the markings made by means of these techniques result short-lived if applied on too smooth surfaces. In the pad printing and the thermal transfer printing the plastics having good sliding properties e.g. POM or POM with teflon have a very poor paint absorption ability. On the other hand, they constitute an excellent material for the elements of the connections cooperating in a sliding relationship. Friction resistance between the elements made of these materials is very low indeed. The plastics like e.g. ABS have very good absorption ability towards all kinds of prints and paints. However, cooperation of the elements made of ABS plastics involves additional friction, which deteriorates operation of the device. In some cases the surfaces of the cooperating elements are rubbed off which leads to permanent damage. Additionally, pulverized debris may appear affecting the cooperation of other elements of the device.

Another problem arising during the manufacture of the indication mechanism according to PL220720 is the difficulty of forming it in the injection molding process. The indicating element must be connected with the pulling nut but these two elements may not be formed in a single integral mould because it would be too complicated in view of numerous guiding elements having a form of internal and external threads and splines. Therefore the indicating element is engaged with the pulling nut by means of mutually engaging flanges formed on their edges. However, forming of these flanges is technologically difficult.

It was the aim of the invention to redress the above described disadvantages.

In particular, the aim of the invention was to provide an indication mechanism and an injecting device equipped with such a mechanism, in which friction resistance generated within the mechanism was minimalized and in which durable markings could be printed on the indicating element.

Another aim of the invention was to provide an indication mechanism and an injecting device equipped with such a mechanism, in which the connection between the indicating element and the pulling nut would be facilitated. According to the invention an indication mechanism for an injection device for delivering settable doses of a pharmaceutical substance is provided, the mechanism comprising a rotatable control sleeve on which an indication sleeve and a push-pull nut are mounted, the indication sleeve being provided with markings, which are visible to a user and being engaged in rotation with the control sleeve and translatable along the control sleeve, the push-pull nut being non-rotatable and engaged in translation with the indication sleeve and cooperating threadably with the control sleeve.

The indication mechanism according to the invention is characterized in that the indication sleeve comprises an external portion and an internal portion, the internal surface of the internal portion being adapted to facilitate translation of the indication sleeve on the control sleeve, and the external surface of the external portion being adapted to facilitate application of the markings thereon.

Preferably, the internal surface of the internal portion of the indication sleeve has a lower coefficient of friction on the material of the control sleeve than the external surface of the external portion of the indication sleeve.

Also preferably, the internal portion and the external portion of the indication sleeve are made of different materials.

Optionally, the external portion is made of a plastic material, preferably ABS.

The internal portion may be made of a plastic material, preferably POM or POM with addition of teflon.

Preferably, the external surface of the external portion of the indication sleeve is adapted to be overprinted by means of pad printing or thermal transfer printing with durable dose indicating markings.

The external portion may consist of a coating applied on the internal portion, the coating being applied by means of a spraying technique upon activation of the external surface of the internal portion, by the IML technique or by means of two-component injection.

Preferably, the external portion, which is longer than the internal portion, is provided at its end engaging the push-pull nut with a collar extending inwardly, so that between the respective end of the internal portion and said collar an annular engaging groove is formed.

The control sleeve may comprise two sections, one being provided with an external thread cooperating with the push-pull nut having and internal thread, and the other being provided with longitudinal engaging elements cooperating with complementary longitudinal engaging elements located on the internal surface of the internal portion of the indication sleeve. Preferably, the longitudinal engaging elements located on the control sleeve consist of multi- projections and the engaging elements of the indication sleeve consist of grooves.

Optionally, the longitudinal engaging elements located on the control sleeve consist of grooves and the engaging elements of the indication sleeve consist of multi-projections.

According to the invention an injection device for delivering settable doses of a pharmaceutical substance is also provided, the injection device being characterized in that it comprises the indication mechanism according to the invention.

Short description of the drawing

Preferred embodiments of the invention are shown in the appended drawings in which:

Fig. 1 presents a perspective exploded view of the indication mechanism according to a first embodiment of the invention;

Fig. 2 presents a side view of the assembled mechanism of fig. 1, in which a portion of the housing has been removed in order to make the inside visible;

Fig. 3 presents a perspective view of the mechanism of fig. 1 in which a portion of the housing and the indication sleeve have been removed in order to make the inside visible;

Fig. 4 presents a perspective exploded view of the indication mechanism according to a second embodiment of the invention;

Fig. 5 presents a perspective exploded view of the injection device according to the invention comprising the indication mechanism according to the invention;

Fig. 6 presents a longitudinal cross-sectional view of the assembled device shown in fig.

5.

Detailed description of the drawing

Fig. 1 shows an indication mechanism 1 as oriented when mounted in an injection device according to the invention, the proximal end of which (the one held by a user) being on the right side of the figure, and the distal end (the one applied to the patient's body) being on the left side of the figure. The mechanism 1 comprises a control sleeve 2, an indication sleeve 3 and a push-pull nut 4. The indication sleeve comprises an external portion 3a and an internal portion 3b, the portions 3a and 3b being fixedly connected to each other in the assembled mechanism. Markings 5 are applied on the external portion 3a, which in the assembled injection device are visible to a user through a window 6 in the housing 7 of the device.

In fig. 2 the assembled mechanism of fig. 1 is shown. As may be seen, the indication sleeve 3 and the push-pull nut 4 are mounted on the control sleeve 2, and all of three sleeves are located within the housing 7. The proximal end of the control sleeve (to be engaged with a knob 11 of the injection device - see fig. 5) may be seen near the proximal end 7a of the housing 7 in fig. 2.

Fig. 3 shows the elements that enable mutual cooperation of the control sleeve 2, the indication sleeve 3, the push-pull nut 4 and the housing 7. The control sleeve 2 has an external thread 2.1 formed on one section of its length (here on its distal section) enabling cooperation of the control sleeve 2 with the push-pull nut 4. The push-pull nut 4 is provided with a cooperating spiral rib 4.1 on its internal surface. On the other section of the control sleeve 2 (here on its proximal section) there is at least one longitudinal projection, preferably multi-projections, cooperating with complementary longitudinal grooves formed on the internal surface of the internal portion 3b of the indication sleeve 3. Optionally, the control sleeve 2 may have longitudinal grooves on its external surface and the complementary cooperating multi- projections may be formed on the internal surface of the internal portion 3 b of the indication sleeve. The push-pull nut 4 is further provided with at least one projection 4.2 on its external side, preferably multi-projections, for engagement with corresponding longitudinal grooves formed on the internal surface of the housing 7. The proximal edge of the push-pull nut 4 is provided with a catch having a form of an externally extending annular flange 4.3 for engagement with the indication sleeve 3 so that the push-pull nut 4 and the indication sleeve 3 may be rotated relative to each other but they are mutually fixed in translation. Such an engagement is possible due to the fact that the external portion 3a of the indication sleeve 3 is longer than its internal portion 3b and it has a collar 3a.1 on its distal end, the collar 3a.1 extending inwardly. In such a way, an annular engaging groove is formed between said collar 3a.1 and the respective end of the internal portion 3b. Such a design of the indication sleeve 3 constitutes an important advantage of this embodiment of the indication mechanism 1 because formation of the above described elements designed for engagement of the indication sleeve 3 with the push-pull nut 4 is technologically easy. Further, the indication sleeve 3 may be easily connected with the push-pull nut 4 just by pushing the flange 4.3 through the collar 3a.1 and then mounting the indication sleeve 3 and the push-pull nut 4 on the control sleeve 2. Once the indication sleeve 3, already connected with the push-pull nut 4 have been mounted on the control sleeve 2, they may not be self-disassembled because the external surface of the control sleeve 2 makes it impossible to deform the flange 4.3 and the collar 3a.1.

The indication mechanism 1 according to the invention operates as follows. Upon rotation of the control sleeve 2 in a first direction (the rotation being realized due to engagement of the control sleeve 2 with the dose setting knob 11 of the injection device, as will be described below) the push- pull nut 4 is translated distally due to its engagement with the control sleeve 2 by means of the thread 2.1; the rotation of the push-pull nut 4 in relation to the housing 7 is blocked by the multi-projections 4.2 and the corresponding grooves in the housing 7. The push-pull nut 4 pulls the indication sleeve 3 so that the latter is also translated distally. At the same time the indication sleeve 3 is rotated by its engagement with the control sleeve 2 by means of the multi-projections 2.2 and the corresponding grooves in the indication sleeve 3. As a consequence, the indication sleeve 3 is moved along a spiral line. The markings (preferably digits, dots, etc.) are arranged along a spiral line on the indication sleeve 3 so that successive digits corresponding to successive doses that are being set are visible through the window 6 in the housing 7 during setting of the dose. Preferably, a marking point (e.g. a distinctive color point) indicating that a whole dose has been delivered, is also present on the indication sleeve 3, to be seen through a window 7.1 near the proximal end of the housing 7.

On the other hand, upon rotation of the control sleeve 2 in a second direction (during correction of a dose), the push-pull nut 4 is translated proximally simultaneously pushing the indication sleeve 3 in the same direction. Similarly to the setting of a dose, the indication sleeve 3 is moved along a spiral line but in the opposite direction.

The indication mechanism 1 is engaged with a driving spring 12, a clutch assembly and an operating assembly of the injection device as will be described in detail with reference to fig. 5. Consequently, the indication mechanism indicates to the user the current state of the device and what dose has been set.

As it results clearly from the above description, how important it is to minimalize the resistance arising from the relative movements of the elements of the mechanism 1. Therefore these elements should be as smooth as possible and should be made of the materials generating the lowest possible friction. However, in the case of the indication sleeve 3 this requirement is difficult to be met because the external surface of a smooth material is hard to be overprinted with the markings. In the case of the one-piece indication sleeve according to PL220720 all the attempts of producing it of a smooth material meeting the low friction requirement led to difficulties related to printing. The preferred techniques for application the markings are pad printing or thermal transfer printing, which however require a suitable backing so that the paint is not rubbed off. Laser marking of the external portion 3a is also possible but it requires that a suitable substance (e.g. Iriodin) is added to the plastic material the external portion is made of. However the markings applied by this technique have inferior contrast proprieties.

According to the invention a novel two-part indication sleeve 3 has been designed that enabled to meet both the requirements concerning its internal surface and the substantially contrary requirements concerning its external surface. It has turned out that the external portion 3a of the indication sleeve 3 is most preferably made of an ABS plastic material, which is adapted to facilitate the application of the markings thereon; on the other hand the internal portion 3b is most preferably made of a POM or POM with teflon plastic material, which is adapted to facilitate translation of the indication sleeve 3 on the control sleeve 2.

In fig. 4 a second embodiment of the mechanism 1 according to the invention is shown. In this embodiment the externa l portion 3a of the indication sleeve 3 is formed as a thin coating applied upon activation of the external surface of the internal portion 3b or as a second component of the plastic material in an injection moulding process. The external portion 3a may also be formed in the I ML technique (In Mould Labeling) with the thin coating consisting of a printed label introduced to the injection mould prior to the injection process.

In this embodiment the indication sleeve 3 is engaged with the collar 4.3 of the push-pull nut 4 by means of internal projections 3.1.

Fig. 5 shows an exploded perspective view of the injection device equipped with the above described indication mechanism 1 according to the invention. The device shown in fig. 5 is in this particular embodiment an applicator for a liquid pharmaceutical substance. The applicator comprises three main parts connected by a twist-type double-start thread:

• an operating part comprising an enclosure 8 for a disposable pharmaceutical substance cartridge into which a piston 9 is introduced, the operating portion having at its distal end an external thread for engagement of a double-sided injection needle (not shown). The engagement is such that the needle perforates the enclosure enabling injection. Upon injection, the operating portion together with the needle and the enclosure are shielded by a cap 10 provided with a clip 10.1 for fixing the applicator to the user's clothes;

• a dosing-driving mechanism for precise setting of a dose of a pharmaceutical substance and for automatic injection of the set dose by translation of the piston 9 located within the cartridge by a defined distance;

• a trigger assembly.

The dosing-driving mechanism comprises:

the indication mechanism according to the invention;

a driving spring 12;

a clutch assembly comprising a clutch 13, a clutch body 14, movable ratchet ring 15, fixed ratchet ring 16 and a blocking ring 17;

an operating assembly comprising a piston rod 18 and a nut 19 located in a bearing 20. The clutch assembly connects the knob 11 with the indication mechanism 1 and the operating assembly. The driving spring 12 is mounted on the clutch 13 and located within the control sleeve 2 of the indication mechanism 1. The driving spring 12 is hooked by its distal end to the distal end of the control sleeve 2; the proximal end of the driving spring 12 is fixed to the housing 7 by a dedicated spring lock (not shown) so that a spring force necessa ry for the injection may be generated.

A dose is set manually by rotating the knob 11 that is connected to the clutch 13 by means of multi-projections. During the setting of a dose the nut 19 and the blocking ring 17 are blocked against rotation by means of the triggering assembly, which is connected to the housing 7. At the same time, the control sleeve 2 is rotated relative to the operating assembly due to the rotation of the knob 11; the scope of rotation is limited by the indication mechanism 1.

The setting of a dose and its subsequent correction are possible thanks to the clutch assembly. The clutch assembly enables rotation of the control sleeve 2 together with the clutch body 14 relative to the immobilized nut 19. The operation of the clutch assembly will be described below in greater detail.

Once a chosen dose has been set, the operating assembly may be released by activating the triggering assembly in order to deliver the dose. The operation of the triggering assembly will be described below.

Upon activation of the triggering assembly, the nut 19 is unblocked and it rotates by the force of the tensioned spring 12 (the cooperation of the driving spring 12 with the nut 19 is ensured by the clutch assembly). The rotation of the nut 19 causes translation of the piston rod 18 and the piston 9, as well as rotation of the knob 11 together with the whole mechanism back to its starting position. The piston is translated distally by a predefined distance pushing the set dose of a pharmaceutical substance out of the cartridge through the needle fixed to the enclosure 8. Delivery of the whole volume from the cartridge is signaled by the marking point visible through the window 7.1 (described above) when the indication mechanism 1 returns to its initial position. When the marking point is visible through the window 7.1 the trigger may be released , which causes it to return to its starting position due to the action of the trigger spring 22 and to block the nut 19 again.

Operation of the clutch assembly Mutual configuration of the components of the clutch assembly enables the setting of a dose (e.g. by the clockwise rotation) and the correction of a dose (by rotation in the opposite direction). In the case of each of these rotations specific positions of the components exist in which the clutch assembly is stopped so that successive full doses of the substances are set. The rotations are accompanied by a characteristic click sound, which is different in the case of the setting rotation than in the correction rotation.

The clutch assembly comprises the clutch 13, the clutch body 14 and two ratchet rings - the movable ratchet ring 15 and the fixed ratchet ring 16. The movable ratchet ring 15 is located within the fixed ratchet ring 16. Both ratchet rings 15 and 16 are provided with teeth on the same (proximal) side. The teeth of the ratchet rings 15, 16 cooperate with an internal ratchet of the clutch body 14, which is located vis a vis the teeth of the ratchet rings 15 and 16. The clutch body 14 and the movable ratchet ring 15 are rotatable and the fixed ratchet ring 16 is blocked against rotation and it is only translatable axially. Another component of the clutch assembly is the blocking ring 17.

The clutch 13 is engaged with the movable ratchet ring 15 by means of multi-projections.

Due to such arrangement the movable ratchet ring 15 may be translated axially relative to the clutch 13. When the clutch 13 rotates during the setting of a dose, the teeth of the movable ratchet ring 15 cooperate with the internal ratchet of the clutch body 14. When the clutch 13 rotates in the first direction i.e. clockwise during the setting of a dose the teeth of the ring 15 are engaged with the ratchet of the clutch body 14 which results in simultaneous rotation of the clutch body 14 in the first direction. The ratchet of the clutch body 14 is also engaged with the teeth of the fixed ratchet ring 16, which is blocked against rotation during the setting of a dose by means of the multi-projections of the blocking ring 17. The blocking ring 17 is fixed within the nut 19 by multi-projections. On the other hand, the nut 19 is blocked during the setting of a dose by the triggering assembly (described above). Hence, the movable ratchet ring 15 rotates with the clutch body 14; the ratchet of the clutch body 14 slides on the teeth of the fixed ratchet ring 16 causing it to move axially in the distal direction. A spring 23 is located under the fixed ratchet ring 16. The spring 23 is compressed during the axial movement of the ring 16 until the tips of the ratchet of the clutch body 14 pass the tips of the teeth of the ratchet ring 16. Then the spring 23 expands and causes the ratchet of the clutch body 14 and the teeth of the ratchet ring 16 to be mutually engaged again in a new position. Due to the described arrangement the dose may be set incrementally. Rotation of the movable ratchet ring 15 in the second direction causes its teeth to slide on the ratchet of the clutch body 14 which results in axial translation of both ratchet rings 15 and 16 because the movable ratchet ring 15 abuts an inside step within the fixed ratchet ring 16. As the teeth of the movable ratchet ring 15 are higher than the teeth of the fixed ratchet ring 16, their axial movement causes the teeth of the fixed ratchet ring 16 to disengage from the ratchet of the clutch body 14. Then the clutch body 14 is not retained any more by the teeth of the movable ratchet ring 15 (which has been translated axially in the distal direction) and it may rotate freely. On the other hand, the clutch body 14 is engaged in rotation with the control sleeve 2 of the indication mechanism 1 on which the force of the driving spring 12 is imposed. Consequently, when the clutch body 14 is released by the teeth of the movable ratchet ring 15 and fixed ratchet ring 16, the driving spring 12 rotates the clutch body 14 in the direction of the dose correction releasing the energy accumulated during the setting of a dose. Hence, as a result of the rotation in the second direction, the clutch body 14 catches up with the movable ratchet ring 15 and the fixed ratchet ring 16, being pushed by the spring 23, makes the teeth of the ratchet rings re-engage in a position one tooth further in the second direction which corresponds to the correction of the dose by one unit.

The rotation in the correction direction is therefore additionally supported by the driving spring 12 accumulating energy during the setting of a dose and releasing it during the correction of the dose. For this reason the click sound accompanying the setting of a dose is different to the sound accompanying the correction. The mechanism is additionally protected against overloading after the starting point has been reached ("zero" shown on the scale). An attempt to further correct the dose is signaled by still another sound, a more subtle one, resembling the sound of a bicycle shifter, and the knob rotates more easily. Therefore, if the correction rotation goes under the scope of operation of the device, the knob 11 may still be rotated but it will not set a dose and the click sound is different than that accompanying the setting and correction of a dose.

As explained above, upon activation of the triggering assembly during delivery of a pharmaceutical substance, the nut 19 is unblocked and it rotates by the action of the tensioned driving spring 12. Simultaneously the whole mechanism rotates with the nut 19 and the relative positions of the components of the mechanism remain the same. Therefore, the clutch assembly operates only during the setting or correction of a dose. At least one ratchet teeth must be located within the clutch body 14; the maximum number of these teeth is the number of the teeth on the ratchet rings 15, 16. An important feature of the device is that the blocking ring 17 is fastened to the clutch body 14 by means of detents so that the force of the spring 23 is enclosed within the clutch assembly and is not transferred to the other components of the injection device.

Operation of the trigger assembly

The trigger assembly is composed of an internal trigger 21, a trigger spring 22, an external trigger 23 and a trigger cap 24. The internal trigger 21 has a tab 21.1 for engagement with the external trigger 23. Due to such arrangement both triggers may cooperate in order to activate the delivery of a dose (the injection) as well as after the delivery has been completed. The internal trigger 21 is pressed by the user via the external trigger 23.

The internal trigger 21 is located in a trigger body 25. The internal trigger 21 has two- part multi-projections on its internal surface. At the distal side, i.e. in the first part, the multi- projections have a form adapted for cooperation with internal teeth of the trigger body 25 so that the multi-projections slide axially on said teeth. At the proximal side, i.e. in the second part, the internal trigger 21 has a toothed flange for immobilizing the nut 19 by means of its internal peripheral teeth. When the external trigger 23 is pressed in order to deliver a dose (the injection), the internal trigger 21 is axially translated in the distal direction and its toothed flange becomes disengaged from the nut 19. Consequently, the nut 19 is released and it may rotate. The external trigger 23 should remain pressed during the whole delivery. The nut 19 is arranged in a bearing 20 with a play. The bearing 20 is fixedly connected to the blocking ring 19. The rotation of the nut 19 causes the operating assembly to rotate and the piston rod 18 to advance out distally. This is caused by the fact that the piston rod 18 has a double-start thread that unscrews during rotation of the nut 19, the piston rod 18 being blocked against rotation by a blocking ring 26. The blocking ring 26 is indirectly connected to the housing 7 via the trigger body 25 by means of the toothed flanges (in fig. 5 only the toothed flange of the trigger body 25 may be seen). The toothed flanges are located inside and outside the proximal end of the blocking ring 26.

As explained in the beginning of the description of fig. 5, the automatic applicator comprises three main assemblies connected by a nut 28 having a twist-type double-start thread: the operating part comprising an enclosure 8 for a disposable pharmaceutical substance cartridge into which a piston 9 is introduced, the dosing-driving mechanism and the trigger assembly.

In order to replace the pharmaceutical substance cartridge, the operating part of the applicator (i.e. the enclosure 8 connected to the housing 7 by the nut 28) should be unscrewed by anticlockwise rotation. Upon unscrewing of the enclosure 8 the blocking ring 26 becomes automatically disengaged from the trigger body 25 by the force of a spring 27. The disengagement is caused by the axial translation of the blocking ring 26 distally by a distance limited by an abutment ring located inside the nut 28 and disengagement of the above mentioned toothed flanges.

Once the operating part has been disconnected, the piston rod 18 may be manually retracted to its initial position (by pressing the piston 9) and screwed into the nut 19 in the clockwise direction until it projects just a bit from the housing 7 and enables a new cartridge to be mounted. The piston 9 may be freely rotated relative to the piston rod 18. This is advantageous because during this operation the piston rod is rotated together with the nut 19 cooperating therewith by means of a non-self-locking rectangular thread having a pitch adapted for delivering a defined dose.

Next, the needle fixed to the enclosure 8 should be unscrewed and removed and the empty cartridge should be removed from the enclosure 8. Then a new cartridge may be installed by placing it in the enclosure 8 and a new needle may be fixed.

Fig. 6 presents a longitudinal cross-sectional view of the assembled injection device according to the invention comprising the indication mechanism 1 according to the invention.

Claims

Patent claims

1. Indication mechanism (1) for an injection device for delivering settable doses of a pharmaceutical substance, comprising a rotatable control sleeve (2) on which an indication sleeve (3) and a push-pull nut (4) are mounted, the indication sleeve (3) being provided with markings (5), which are visible to a user and being engaged in rotation with the control sleeve (2) and translatable along the control sleeve (2), the push-pull nut (4) being non-rotatable and engaged in translation with the indication sleeve (3) and cooperating threadably with the control sleeve (2), characterized in that the indication sleeve (3) comprises an external portion (3a) and an internal portion (3b), the internal surface of the internal portion (3b) being adapted to facilitate translation of the indication sleeve (3) on the control sleeve (2), and the external surface of the external portion (3a) being adapted to facilitate application of the markings (5) thereon.

2. The indication mechanism according to claim 1, characterized in that the internal surface of the internal portion (3b) of the indication sleeve (3) has a lower coefficient of friction on the material of the control sleeve (2) than the external surface of the external portion (3a) of the indication sleeve (3).

3. The indication mechanism according to claim 1 or 2, characterized in that the internal portion (3b) and the external portion (3a) of the indication sleeve (3) are made of different materials.

4. The indication mechanism according to claim 3, characterized in that the external portion (3a) is made of a plastic material, preferably ABS.

5. The indication mechanism according to claim 3 or 4, characterized in that the internal portion (3b) is made of a plastic material, preferably POM or POM with addition of teflon.

6. The indication mechanism according to claim 1 or 2 or 3, characterized in that the external surface of the external portion (3a) of the indication sleeve (3) is adapted to be overprinted by means of pad printing or thermal transfer printing with durable dose indicating markings.

7. The indication mechanism according to claim 1 or 3, characterized in that the external portion (3a) consists of a coating applied on the internal portion (3b), the coating being applied by means of a spraying technique upon activation of the external surface of the internal portion (3b) by the IM L technique or by means of two-component injection.

8. The indication mechanism according to claim 1, characterized in that the external portion (3a), which is longer than the internal portion (3b), is provided at its end engaging the push- pull nut (4) with a collar (3a.1) extending inwardly, so that between the respective end of the internal portion (3b) and said collar an annular engaging groove is formed.

9. The indication mechanism according to claim 1 or 8, characterized in that the control sleeve (2) comprises two sections, one being provided with an external thread (2.1) cooperating with the push-pull nut (4) having and internal thread, and the other being provided with longitudinal engaging elements (2.2) cooperating with complementary longitudinal engaging elements located on the internal surface of the internal portion (3b) of the indication sleeve (3).

10. The indication mechanism according to claim 9, characterized in that the longitudinal engaging elements (2.2) located on the control sleeve (2) consist of multi-projections and the engaging elements of the indication sleeve (3) consist of grooves.

11. The indication mechanism according to claim 9, characterized in that the longitudinal engaging elements (2.2) located on the control sleeve (2) consist of grooves and the engaging elements of the indication sleeve (3) consist of multi-projections.

12. Injection device for delivering settable doses of a pharmaceutical substance, characterized in that it comprises the indication mechanism according to any of the preceding claims 1-11.