IMPROVED INJECTION DEVICE

摘要

An injection device comprising a main housing (4) defining a first screw thread (20) and a plunger comprising a leadscrew (19) and a cap (11) rotatably attached to the leadscrew such that, in use, the cap engages a bung of a cartridge containing medicament. A drive gear is mounted within the housing for rotating around the leadscrew to drive the plunger axially through the housing when the leadscrew is locked against rotation with respect to the housing. A cartridge housing (2) is also provided for holding a cartridge containing medicament. This housing defines a second screw thread (27) for engagement with said first screw thread in order to secure the cartridge housing to the main housing. The device further comprises a locking mechanism (26,28) which is actuated when the cartridge housing is secured to the main housing and which locks the leadscrew against rotation with respect to the housing. Cooperating features are provided for allowing the leadscrew to rotate relative to the cartridge housing during attachment of the cartridge housing to the main housing whilst allowing relative rotation of the engaged first and second screw threads to cause rotation of the leadscrew relative to the housing and hence axial movement of the leadscrew into the housing.