Relating in and relating to an injection device

Abstract

Injection devices are known for the self administration of a medicament by patients in which the medicament is contained within a cartridge located within the injection device. It is a problem that such injection devices should be small enough to fit into a jacket pocket or a hand bag without difficulty. Concurrently, the injection device must be of size that enables a piston or similar used to drive a cartridge bung within the cartridge to be moved both to a maximum dispense position within the cartridge and to be fully withdrawn from the cartridge to allow for replacement of the cartridge. A drive mechanism for an injection device is disclosed comprising a piston member, a semi rigid beltconnected to the piston member, a belt drive means to selectively engage with the semi rigid beltto drive the semi rigid belt, and a dose setting mechanism to control the selective engagement of the semi rigid belt in which the semi rigid beltincludes a track incorporated therein and the belt drive means comprises a toothfor selective engagement with the track to drive the beltonly when there is relative movement between the semi rigid beltand the toothin a first direction. An injection device comprising such a drive mechanism is also disclosed.