A MULTI-STATE RATCHET MECHANISM FOR DRUG INJECTION DEVICES

The present invention relates in a first aspect to a multi-state ratchet mechanism for a drug injection device. The multi-state ratchet mechanism comprises a ratchet gear member and a cooperating ratchet pawl member. An annular inner surface of the ratchet gear member comprises a first ring shaped surface portion with a first predetermined cross-sectional profile comprising a first asymmetrical toothing arranged at a first axial position of the inner annular surface. The annular inner surface of the ratchet gear member further comprises a second ring shaped surface portion arranged at a second axial position of the inner surface axially spaced apart from the first axial position. The second ring shaped surface portion comprises a second predetermined cross-sectional profile differing from the first predetermined cross-sectional profile. The ratchet pawl member is axially displaceable between the first ring shaped surface portion and the second ring shaped surface portion to provide first and second operating states, respectively, of the multi-state ratchet mechanism. The first operational state of the multi-state ratchet mechanism provides unidirectional rotation between the ratchet gear member and the ratchet pawl member in a first direction. The present multi-state ratchet mechanism is particularly suitable for drug injection devices such as user operated drug injection devices for administration of insulin for treating diabetes.