A drive mechanism for an applicator for delivering multiple doses of medicament and a method of assembling said drive mechanism

Abstract

A drive mechanism for an applicator for delivering multiple doses of medicament, comprising an axially moveable piston rod (2) having a non-circular cross-section and an external thread, a mounting member (4) with one member of a pair of blocking means, said pair comprising a toothed rim (4a, 3b) and at least one ratchet arm (3a, 4b); a drive sleeve (3) having an internal thread coupled with the thread of the piston rod (2), the drive sleeve (3) provided on the distal end with the other member of said pair of blocking means. A method of assembling the drive mechanism of the invention, in which the drive sleeve (3) together with the piston rod (2) and the piston rod guide (5) into the mounting member (4) are inserted from the side of the distal end of the applicator.

Claims

1. A drive mechanism for an applicator for delivering multiple doses of medicament, the drive mechanism having a distal end facing the needle end of the applicator, the drive mechanism comprising: an axially moveable piston rod (2) having a non-circular cross-section and provided with an external thread (2b), a mounting member (4) provided with one member of a pair of blocking means, said pair comprising a toothed rim (4a, 3b) and at least one ratchet arm (3a, 4b); a drive sleeve (3) having an internal thread coupled with the external thread of the piston rod (2), the drive sleeve (3) being provided on the distal end with the other member of said pair of blocking means, wherein the blocking means of the mounting member (4a, 4b) and the blocking means of the drive sleeve (3a, 3b) cooperate radially during rotation of the drive sleeve (3), the rotation causing translation of the piston rod (2), characterized in that the drive mechanism further comprises a piston rod guide (5) provided with a central aperture (6), in which the piston rod (2) is axially movable and blocked in rotation, the piston rod guide (5) and the mounting member (4) being provided with coupling elements (5a, 5b, 4d) for preventing rotation of the piston rod guide (5) relative to the mounting member (4).

2. The drive mechanism according to the claim 1, characterized in that the mounting member (4) is provided with the member of said pair of blocking means constituted by the internal toothed rim (4a) and the drive sleeve (3) is provided with the member of said pair of blocking means constituted by the at least one ratchet arm (3a).

3. The drive mechanism according to the claim 1, characterized in that the mounting member (4) is provided with the member of said pair of blocking means constituted by the at least one ratchet arm (4b) and the drive sleeve (3) is provided with the member of said pair of blocking means constituted by the external toothed rim (3b).

4. The drive mechanism according to any of the preceding claims, characterized in that the coupling elements are constituted by a flange (5a) of the piston rod guide (5), the flange (5a) being provided at its circumference with at least one projection (5b, 5b′) and by at least one indentation (4d) of the mounting member (4).

5. The drive mechanism according to any of the preceding claims, characterized in that the mounting member (4) comprises an internal resilient projection (4e) allowing the piston rod guide (5) to be inserted into the mounting member (4) from the distal end and preventing the piston rod guide (5) from sliding back out of the mounting member (4).

6. The drive mechanism according to claim 5, characterized in that, the internal projection (4e) is a circumferential shoulder.

7. A method of assembling the drive mechanism of any of the preceding claims, the method comprising the following steps: a step of sliding the piston rod guide (5) onto the piston rod (2); a step of screwing the drive sleeve (3) onto the piston rod (2); a step of inserting the drive sleeve (3) together with the piston rod (2) and the piston rod guide (5) into the mounting member (4), characterized in that the step of the inserting the drive sleeve (3) together with the piston rod (2) and the piston rod guide (5) into the mounting member (4) is realized from the side of the distal end, and in that the drive sleeve (3) is coupled with the mounting member (4) by the pair of blocking means comprising a toothed rim (4a, 3b) and at least one ratchet arm (3a, 4b) while the coupling elements (5a, 5b, 4d) of the piston rod guide (5) are simultaneously engaged with the mounting member (4), wherein an axial position of the piston rod (2) in relation to the drive sleeve (3) is pre-set by rotation of the piston rod guide (5) relative to the mounting member (4) prior to the coupling of the blocking means (3a; 4a; 3b; 4b) and engaging the coupling elements (5a, 5b, 4d).

8. The method according to the claim 7, characterized in that the step of inserting the drive sleeve (3) with the piston rod (2) and the piston rod guide (5) into the mounting member (4) involves overcoming resistance of the internal resilient projection (4e) of the mounting member (4).

Description

[0036] Embodiments of the drive mechanism according to the invention are presented in the drawings, in which:

[0037] FIG. 1 shows a partially cross-sectional perspective view of the drive mechanism according to a first embodiment of the invention;

[0038] FIG. 2 shows a longitudinal section along a plane A-A indicated in FIG. 6 of a fragment of an applicator in which the drive mechanism is mounted;

[0039] FIG. 3 shows a longitudinal section along a plane B-B indicated in FIG. 6 of a fragment of an applicator in which the drive mechanism according to the invention is mounted;

[0040] FIG. 4 shows a detailed view of a connection of the drive mechanism of FIG. 1 with an applicator housing;

[0041] FIG. 5a shows a cross-section along a plane C-C indicated in FIG. 2 of the drive mechanism according to the invention placed in the housing:

[0042] FIG. 5b shows a cross-section along the plane C-C indicated in FIG. 2 of another embodiment of the drive mechanism according to the invention placed in the housing;

[0043] FIG. 6 shows a cross-section along a plane D-D indicated in FIG. 2 of the drive mechanism according to the invention placed in the housing;

[0044] FIG. 7 shows an isometric view of the components of the drive mechanism according to the invention;

[0045] FIG. 8 shows a cross-section along the plane D-D indicated in FIG. 2 of still another embodiment of the drive mechanism according to the invention placed in the housing;

[0046] FIG. 9 shows an isometric view of the components of the embodiment shown in FIG. 8;

[0047] FIG. 10 shows a sequence of steps of the method of assembling the drive mechanism according to the invention.

[0048] In the following description the term “distal” relates to the end of the drive mechanism facing the needle side of the applicator in which it is mounted and the term “proximal” relates to the opposite end thereof.

[0049] The drive mechanism 1 is presented in FIG. 3 as assembled. In FIG. 1 the drive mechanism is shown as seen from its distal end and it comprises the following components: a piston rod 2 with a piston foot 2a at its end, a drive sleeve 3, a mounting member 4 and a piston rod guide 5. The same components are shown in the longitudinal sections of FIGS. 2-3, which present a fragment of an applicator with the drive mechanism mounted in a housing 7.

[0050] The piston rod 2 has a non-circular cross-section and it is provided with an external thread. After the assembly of the drive mechanism in an applicator, the piston rod 2 may be displaced only along a longitudinal axis of the applicator in a distal direction.

[0051] The drive sleeve 3 is screwed onto the piston rod 2 and it has an internal thread coupled with the external thread of the piston rod 2. Furthermore, the drive sleeve 3 has two resilient ratchet arms 3a at its distal end (FIG. 1 shows one of them).

[0052] As can be seen in FIG. 5a, the mounting member 4 has an internal toothed rim 4a. The resilient ratchet arms 3a and the toothed rim 4a form a pair of blocking means of the drive sleeve 3 and the mounting member 4. Cooperation of this pair of blocking means, i.e. the ratchet arms 3a of the drive sleeve 3 and the toothed rim 4a of the mounting member 4, allows to rotate the drive sleeve 3 in one direction by subsequent incremental displacements, each corresponding to one tooth of the toothed rim 4a.

[0053] Said pair of blocking means may be implemented otherwise, for example the drive sleeve 3 may have different number of the resilient arms, in particular a single arm or more than two arms. Alternatively, as in the embodiment shown in FIG. 5b, a toothed rim—the toothed rim 3b—may be formed on the drive sleeve 3 and the mounting member 4 may have at least one ratchet arm—the ratchet arm 4b.

[0054] The drive sleeve 3 has also a flange 3c which, once the drive sleeve 3 has been inserted into the drive mechanism, abuts a ledge 4c formed on the mounting member 4. Consequently, the drive mechanism is stably fastened in the mounting member 4 and upon installation of the drive mechanism in the applicator housing any undesired axial movement of the drive sleeve 3 is prevented. The above described components are indicated in FIG. 3.

[0055] The mounting member 4 has also an internal resilient projection 4e allowing the piston rod guide 5 to be inserted into the mounting member 4 from the distal end, along the proximal direction and preventing the piston rod guide 5 from sliding out from the mounting member 4 in the opposite direction. Preferably, the projection 4e is made of a polymer. During assembly of the drive mechanism, a flange 5a formed on the piston rod guide 5 passes through the projection 4e due to its resilience. The projection 4e may have e.g. a triangular cross-section in order to make the insertion of the piston rod guide 5 into the mounting member 4 easier. Once the drive mechanism has been assembled, the piston rod guide 5 abuts the projection 4e, which may extend along the whole circumference of the mounting member 4 so as to form a circumferential shoulder. Alternatively, the projection 4e may only extend along a part of the internal circumference of the mounting member 4.

[0056] The housing 7 has an indentation 7a in which a radially outermost part 4g of the mounting member 4 is fitted during the assembly. This arrangement blocks axial movement of the mounting member 4 once installed in the housing 7. Other methods of blocking the axial movement of the mounting member 4 in the housing are also possible. For example, the housing may have projections (ledges) between which the radially outermost part 4g is fitted tightly. In such case, due to the resilience of the material, the mounting member may be pressed through said projection (ledge) during the assembly.

[0057] FIG. 3 presents a longitudinal section of a fragment of an applicator in which the described above drive mechanism is mounted. Due to the described design, the assembly of the drive sleeve 3, the piston rod 2, and the piston rod guide 5 is secure within the mounting member 4 and any undesired axial movement is prevented. After securing the assembled drive mechanism in the housing 7, the piston rod 2 is the only element which can move axially and it is displaced distally during medicament delivery, while both the piston rod guide 5 and the drive sleeve 3 are axially immovable.

[0058] As can be seen in FIGS. 5a and 5b, the mechanism, once mounted in the housing 7, is prevented from rotating by cooperation of at least one projection 7b, located radially on an internal surface of the housing 7, with at least one indentation 4f located on the circumference of the mounting member 4. In FIG. 4, showing the mechanism mounted in the housing 7 in an isometric view (a part of the housing 7 is removed for the sake of clarity), one indentation 4f engaged with one projection 7b may be seen. FIG. 5b presents the cooperation of the two mutually opposite projections 7b with the respective indentations 4f. As the mounting member 4 cannot rotate in the housing 7, the piston rod guide 5, which is coupled to the housing 7, is also blocked in rotation after the assembly and the piston rod 2 is guided to move axially.

[0059] FIG. 5a, presenting a cross-section of the drive mechanism according to the first embodiment, shows the toothed rim 4a cooperating with the ratchet arms 3a. In the presented embodiment, the toothed rim 4a is formed on the mounting member 4 and the two ratchet arms 3a are disposed on the drive sleeve. FIG. 5b shows another embodiment, in which the toothed rim 3b is located on the drive sleeve 3 and the cooperating ratchet arms 4b are disposed on the mounting member 4.

[0060] The piston rod guide 5 and the mounting member 4 are provided with cooperating coupling elements preventing the piston rod guide 5 from rotation relative to the mounting member 4 after assembly—see FIG. 6 and FIG. 3. In the embodiment shown in these figures said coupling elements are formed by a flange 5a (shown in FIG. 3) of the piston rod guide 5, two radial projections 5b and two indentations 4d (shown in FIG. 6). The projections 5b are formed on the circumference of the flange 5a and the two indentations 4d are formed in the mounting member 4. The projections 5b and the indentations 4d have mutually corresponding shapes so that they can be coupled during assembly by insertion of the piston rod guide 5 into the mounting member 4 in the proximal direction. After the final assembly of the mechanism, i.e. once the indentations 4d and the projections 5b have been coupled, the piston rod guide 5 cannot rotate relative to the mounting member 4. There may be at least one indentation 4d and any number of the projections 5b, provided that the number of the projections 5b is not larger than the number of the indentations 4d.

[0061] Therefore, when the drive mechanism is assembled in the applicator the piston rod guide 5 is immovable relative to the housing 7. The piston rod guide 5 has a central, non-circular aperture 6 with a shape matching the non-circular cross-section of the piston rod 2. This aperture can be seen for example in FIG. 7 presenting the components of the drive mechanism in an isometric view.

[0062] The piston rod 2, when coupled with the piston rod guide 5 through its aperture 6, can only move axially and cannot rotate as the piston rod guide 5 does not rotate. The shape matching of the piston rod 2 and the aperture 6 may be implemented for example as flattenings on the surface of the piston rod 2 engaging a planar internal surface of the aperture 6, indentations on the surface of the piston rod 2 engaging projections on the piston rod guide aperture 6 or other formations engaging a suitable shape of the aperture 6, preventing rotation of the piston rod 2 within the aperture 6. In FIG. 7 an exemplary projection 5d engaging the internal surface of the aperture 6 is shown. In FIG. 7 also ribs 5c are indicated (also to be seen in FIG. 1) enhancing the stiffness and stability of the piston rod guide 5, which may be made of a polymer by injection moulding.

[0063] The piston rod 2 has a thread 2b and projections for fixing the piston rod foot 2a. This connection may also be realised otherwise, by methods known in the art. The piston rod 2 may also be made integrally with the piston rod foot 2a.

[0064] FIGS. 8-9 show still another embodiment, where the piston rod guide 5 is coupled to the mounting member 4 by means of numerous projections 5b′ cooperating with indentations 4d′ and alternating projections 4e′ of the mounting member 4. The numerous projections enable a more precise positioning of the piston rod guide 5 with respect to the mounting member 4 and, as a result, a more precise adjusting of the initial axial position of the piston rod 2. The width of the projections 4e′ is selected so as to match the distance between the subsequent projections 5b′ of the piston rod guide. FIG. 8 shows a cross-section of this embodiment and FIG. 9 shows the components of the embodiment of the drive mechanism of FIG. 8 in an isometric view.

[0065] Subsequent steps of the method of assembling the drive mechanism according to the invention are presented in FIGS. 10a-10c.

[0066] The assembly of the drive mechanism according to the invention starts with sliding the piston rod guide 5 onto the piston rod 2 having the piston rod foot 2a fixed on its distal end. The piston rod guide 5 is being slid from the proximal side. This step is shown in FIG. 10a. Alternatively, the piston rod guide 5 can be slid onto the piston rod 2 before the piston rod foot 2a is fixed at its distal end. In this case the piston rod guide 5 may be slid from any side. Further (FIG. 10b), the drive sleeve 3 is being screwed onto the piston rod 2. The drive sleeve 3, with the piston rod 2 having the piston rod guide slid onto it, is then being inserted into the mounting member 4. Before this step (shown in FIG. 10c), the angular position of the piston rod guide 5 is being set. To that purpose, the piston rod guide 5 is being rotated which enables the setting of the initial axial position of the piston rod 2. The rotation of the piston rod 2 along with the piston rod guide 5 causes the axial displacement of the piston rod 2 due to its threaded engagement with the drive sleeve 3. When the assembly of the drive sleeve 3, the piston rod 2 and the piston rod guide 5 is engaged with the mounting member 4, the drive sleeve 3 is coupled with the mounting member 4 by the pair of the blocking means 3a and 4a (or alternatively 3b and 4b). In this step the coupling elements (5a, 5b, 5d) of the piston rod guide 5 and the mounting member 4 are also coupled fixing the position of the piston rod guide 5 in the mounting member 4 as well as the initial axial position of the piston rod 2. This axial position should be adjusted to the initial position of the piston in the cartridge with medicament to be delivered by means of the applicator. As the initial position of the piston rod foot 2a can be adjusted, the drive mechanism may be used with many different kinds of the medicament cartridges having the pistons located initially in the different axial positions. An important feature of the method according to the invention is that the drive sleeve 3 together with the piston rod guide 5 and the piston rod 2 are inserted into the mounting member 4 from the side of the distal end. Preferably, the drive sleeve 3 with the piston rod 2 and the piston rod guide 5 are inserted into the mounting member 4 by overcoming the resistance of the internal resilient projection 4e of the mounting member 4. Alternatively, in each step the assembly may be realised by movement of the other of the connected components in a direction opposite to the direction indicated in the respective figures. In FIG. 10c for example the drive sleeve 3, the piston rod 2 and the piston rod guide 5 are inserted into the mounting member 4 from the distal side. However, it is also possible to realise this step the way round, i.e. the drive sleeve 3, the piston rod 2 and the piston rod guide 5 may be motionless and the mounting member 4 may be mounted thereon in the direction opposite to the direction marked in FIG. 10.

[0067] After the above steps of the assembly have been completed, the drive mechanism is being located within the applicator housing, where it is being blocked axially by securing the mounting member 4 in the indentation 7a.