Patent ID: 8167834

Claim:
An injection device configured for dispensing a substance from a dual or multi-chamber cartridge, said cartridge having a bung moveable in a first reconstitution phase of movement and a second, dosing phase of movement, said device comprising: a body portion ( 12 ); a plunger ( 24 ) mounted in said body portion for longitudinal movement with respect thereto in a forward dispensing direction to co-operate in use with said bung ( 18 ″ 18 ′); a plunger drive element ( 34 ) disposed adjacent said plunger for driving said plunger; said plunger having a drive portion ( 24 ″) adapted drivingly to engage a complementary drive portion ( 33 a ) on said drive element and adapted to impart dosing movement to said plunger ( 24 ), said drive portion extending only partly along said plunger to leave a forward non-drive portion; and a drive mechanism to apply a pre-selectable amount of angular movement to said plunger drive element on activation thereof, said drive mechanism comprising: a user suitable dose setting member rotatably mounted on said body portion to set a dose; a spring acting between said dose setting means and said body portion, said spring being strained to a variable extent depending on movement of said dose setting member; a ratchet arrangement disposed between said dose setting member and said plunger drive element for allowing one way relative movement therebetween as said dose setting member is rotated to set a dose; and a trigger member operable to prevent rotary movement of said drive element and releasable to allow said spring to rotate said dose setting member and said plunger drive element by an amount corresponding to the set dose, whereby, during a reconstitution phase, said plunger is moved longitudinally forward from a position with the non-drive portion adjacent said drive element but not in driving engagement therewith, to bring its drive portion into driving engagement with the drive portion on said drive element.