Ratchet Systems for Drug Delivery Devices

A drug delivery device comprising:

• a system comprising:
• a first member, a second member, and a third member,
• wherein the first member and the second member are rotatable relative to the third member,
• wherein the first member and the second member are coupled to one another by a dead-angle follower coupling, wherein the dead-angle follower coupling is configured such that the first member and the second member are rotatable relative to one another but only within a limited angular range,
• wherein the second member and the third member are rotationally coupled to one another by a switchable coupling mechanism, wherein the switchable coupling mechanism is switchable between two different states, a locked state and a non-locked state, wherein the maximum torque transferable between the second member and the third member via the switchable coupling mechanism in the locked state is greater than in the non-locked state,
• wherein the switchable coupling mechanism is configured such that the switchable coupling mechanism is in the locked state when the first member is in a locking position relative to the second member, the locking position being within the limited angular range, and wherein the locking position is chosen such that, starting from the locking position, the first member is rotatable relative to the second member by a first dead-angle in a first rotational direction to switch the coupling mechanism to the non-locked state and by a second dead-angle in a second rotational direction opposite to the first rotational direction to switch the coupling mechanism to the non-locked state;
• and
• a reservoir comprising a drug.