Patent ID: 7699815

Claim:
A drive mechanism for an injection device in which piston means are selectively driven to expel medicament from within a medicament cartridge, the drive mechanism comprising: a drive means associated with a first ratchet member; a second ratchet member associated with the piston means; and a housing, wherein the first ratchet member and the second ratchet member are disposed within the housing, the second ratchet member being biased by biasing means towards the first ratchet member, in which the drive means is actuable reciprocally to drive the first ratchet member in a first angular direction of rotary motion such that the first ratchet member drives the second ratchet member along its longitudinal axis against the biasing means along at least a part of its movement and subsequently to drive the first ratchet member and the second ratchet member together in a second angular direction thereby to drive the piston means, and the drive means comprises a rotary solenoid.