Medication delivery device with telescopic piston rod

DETAILED DESCRIPTION OF THE INVENTION Initially it may be convenient to define that, the term "distal end" of the housing 1 and of the cartridge 2 is meant to refer to the end carrying the conduit through which the medicine is expelled, whereas the term "proximal end" is meant to refer to the opposite end carrying the drive mechanism.
FIGS.
1 to 3 shows a medical injection device comprising a housing 1 accommodating a cartridge 2 containing the fluent medicine to be injected.
An elastomeric piston 3 is movable mounted inside the cartridge 2.
The fluent medicine will be expelled when the movable elastomeric piston 3 is moved towards the distal end of the medical injection device.
The elastomeric piston 3 is moved forward by a first telescopic piston rod 4 made up from three parts 5, 6, 7.
The first part 5 has an interior thread mating the exterior thread of the second intermediate part 6.
The second intermediate part 6 is in addition provided with an interior thread mating the exterior thread of the third part 7.
When the first part 5 is rotated, and the elastomeric piston 3 as well as the third part 7 of the first telescopic piston rod 4 is locked against rotation, the second intermediate part 6 and the third part 7 will be moved in the distal direction due to the mating threads.
This will cause the elastomeric piston 3 to move in the distal direction and expel the medicine contained in the cartridge 2.
Rotating the first part 5 of the first telescopic piston rod 4 is done by an electrical motor 8 which is coupled to the first part 5 of the first telescopic piston rod 4 through a number of gearing wheels 9, 10, 11.
The first part 5 of the telescopic piston rod is rotatably mounted in the housing 1 through a number of ball bearings 12.
Other types of bearings can off cause be used if so wanted.
Locking the elastomeric piston 3 and the first part 5 of the telescopic piston rod 4 against rotation can be done in many different ways.
In the embodiment shown in the figures the locking is realized by providing an additional telescopic piston rod 14