Patent ID: 7998117

Claim:
A drug delivery device comprising: (a) a housing containing a drug reservoir; (b) means for expelling drug from the drug reservoir; (c) a ratchet mechanism in communication with the expelling means, the ratchet mechanism being operable to undergo incremental advancement and thereby drive the drug from the reservoir in a series of fixed increments, wherein the ratchet mechanism comprises a helical spring having coils, and one or more fingers which make a ratcheting engagement with the coils of the spring; (d) a member operatively associated with the ratchet mechanism to cause the incremental advancement of said ratchet mechanism as the member moves in a first direction; and (e) a delivery mechanism located within the housing and operable to expand a chamber, the member being in transmission relation to the chamber, whereby the member is driven by the movement of the chamber to advance the delivery helical spring and thereby drive the drug from the reservoir in the series of fixed increments, each of the fixed increments corresponding to a respective advancement of the ratchet mechanism.