Medicament injection device

1. A medicament injection device comprising:

a housing arranged to receive a medicament container,

a needle cover movable relative to the housing, from a retracted position in which the needle cover engages the housing and enables medicament delivery, to an extended position,

a plunger rod, and

a plunger driver movable relative to the housing from an initial position to a final position, and arranged to actuate the plunger rod,

wherein the plunger rod has a first guide arrangement and the housing has a second guide arrangement, the first guide arrangement and the second guide arrangement being arranged to cooperate to guide movement of the plunger rod relative to the housing,

wherein the first guide arrangement and the second guide arrangement in a first stage provide a linear motion path for the plunger rod, enabling the plunger rod to initially move in an axial direction relative to the housing and in a second stage provide a rotational motion path for the plunger rod, enabling the plunger rod to rotate relative to the housing to release the plunger rod from the plunger driver,

whereby the plunger driver attains a released state enabling movement of the plunger driver to its final position, and wherein in the released state the plunger driver is arranged to move proximally to initiate contact between the needle cover and the plunger driver to thereby release the needle cover from the housing a to actuate the needle cover to its extended position.

2. The medicament injection device as claimed in claim 1 ,

wherein the plunger driver has a final position-maintaining arrangement arranged to engage the housing in the final position of the plunger driver to maintain the plunger driver in the final position.

3. The medicament injection device as claimed in claim 2 ,

wherein the final position-maintaining arrangement includes a snap-mechanism.

4. The medicament injection device as claimed in claim 3 ,

wherein the snap-mechanism is arranged to engage a shoulder on an inner surface of the housing.

5. The medicament injection device as claimed in claim 1 ,

wherein the plunger driver is arranged to release the needle cover by movement of the plunger driver towards the final position.

6. The medicament injection device as claimed in claim 1 ,

wherein in the initial position of the plunger driver engages with the plunger rod to enable actuation of the plunger rod.

7. The medicament injection device as claimed in claim 1 ,

wherein the needle cover has a first blocking arrangement and the housing has a second blocking arrangement.

8. The medicament injection device as claimed in claim 7 ,

wherein the first blocking arrangement is arranged to engage the second blocking arrangement in the extended position of the needle cover to prevent the needle cover from sliding out of the housing.

9. The medicament injection device as claimed in claim 1 ,

wherein the first guide arrangement is a groove.

10. The medicament injection device as claimed in claim 9 ,

wherein the second guide arrangement is a protrusion slidably arranged in the groove.

11. The medicament injection device as claimed in claim 1 ,

wherein the plunger driver has a central rod extending coaxially in a central opening of the plunger rod.

12. The medicament injection device as claimed in claim 11 ,

wherein an outer surface of the central rod has a plunger rod engagement arrangement and a surface of the central opening has a central rod engagement arrangement.

13. The medicament injection device as claimed in claim 12 ,

wherein the plunger rod engagement arrangement and the central rod engagement arrangement are arranged to be engaged along the linear motion path and arranged to disengage along the rotation motion path.

14. The medicament injection device as claimed in claim 1 ,

wherein the needle cover has a housing engagement arrangement arranged to engage the housing in the retracted position.

15. The medicament injection device as claimed in claim 14 ,

wherein the housing engagement arrangement comprises a flexible tongue and a heel arranged at a tip of the flexible tongue,

wherein an inner surface of the housing has a first cut-out arranged to receive the heel.

16. The medicament injection device as claimed in claim 15 ,

wherein the heel has a proximal end surface arranged to abut a proximal wall defining the first cut-out, thereby retaining the needle cover in the retracted position.

17. The medicament injection device as claimed in claim 15 ,

wherein the heel has a distal end and a proximal end,

wherein the heel has a thickness that gradually increases in a direction from the distal end towards the proximal end.

18. The medicament injection device as claimed in claim 15 ,

wherein the plunger driver has a proximal end arranged to slide onto the heel to bend the flexible tongue away from the housing to thereby release the needle cover from the housing.

19. The medicament injection device as claimed in claim 1 , comprising the medicament container and a needle, wherein in the extended position the needle cover is arranged to cover the needle.