DRIVE MECHANISM FOR AN INJECTION DEVICE

摘要

A drive mechanism for an injection device is disclosed in which piston means are selectively driven to expel medicament from within a medicament cartridge. The drive mechanism comprises a drive means (170) associated with a firs ratchet means (178), a second ratchet means (174) associated with the piston means (180), a housing (176), the first ratchet means (178) and the second ratchet means (174) being disposed within the housing (176). The second ratchet means (174) are biassed by biassing means (182) towards the first ratchet means (178). The drive means (170) is actuable reciprocally to drive the first ratchet means (178) in a first angular direction such that the first ratchet means (178) drives the second ratchet means (174) along its longitudinal axis against the biassing means (182) along at least a part of its movement and subsequently drives the first ratchet means (178) and the second ratchet means (174) together in a second angular direction thereby to drive the piston means (180).